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  • 1991  (9,623)
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  • Insulin
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  • 2020-2022
  • 1990-1994  (9,623)
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  • 1
    Electronic Resource
    Electronic Resource
    Effect of hyperkalemia on insulin secretion (1991)
    Springer
    Cellular and molecular life sciences 47 (1991), S. 270-272 
    Details
    ISSN: 1420-9071
    Keywords: Insulin ; potassium ; hyperkalemia ; portal vein ; glucose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effect of hyperkalemia on insulin secretion remains undefined. We evaluated portal and peripheral insulin levels in anesthetized dogs after infusions of KCl. The mean maximal increase in peripheral plasma potassium at infusion rates of 0.2 mEq/kg/h was 0.68±0.20 mEq/l. There were no significant increases in either portal or peripheral insulin levels. In contrast, in six dogs whose plasma potassium concentration increased in each case by more than 2.0 mEq/l (infusion rate of 0.5 mEq/kg/h), portal insulin levels increased fivefold (p〈0.05). We conclude that only marked increases in plasma potassium concentration stimulate pancreatic insulin secretion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01958157
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  • 2
    Electronic Resource
    Electronic Resource
    Serum levels of glucose, insulin, and C-peptide during long-term D-ribose administration in man (1991)
    Springer
    Journal of molecular medicine 69 (1991), S. 31-36 
    Details
    ISSN: 1432-1440
    Keywords: (D-)ribose ; Glucose ; Insulin ; C-peptide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary D-ribose was given orally and/or intravenously to nine healthy subjects at doses ranging from 83.3 to 222.2 mg/kg per hour for at least four hours. The serum ribose level increased in a dose-dependent manner to maximum concentrations of 75 to 85 mg/dl. The serum glucose level decreased after the beginning of continuous ribose administration and was reduced as long as ribose was being administered. The oral or intravenous administration of 166.7 mg/kg per hour of ribose resulted in a 25% decrease in serum glucose. Higher intravenous doses of ribose did not provoke a further decrease in serum glucose concentration. Oral administration of 166.7 mg/kg per hour led to an increase in serum insulin concentrations from a mean of 8.4 (range 6.4–11.5) to 10.4 (range 6.3–15.4) μU/ml (p〈0.05). In contrast, intravenous administration did not change serum insulin concentrations significantly. The serum c-peptide concentration remained unchanged regardless of treatment. We conclude that the variations in plasma insulin concentrations do not account for the observed decrease in mean serum glucose concentrations accompanying D-ribose administration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01649054
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  • 3
    Electronic Resource
    Electronic Resource
    Different aetiologies of Type 2 (non-insulin-dependent) diabetes mellitus in obese and non-obese subjects (1991)
    Springer
    Diabetologia 34 (1991), S. 483-487 
    Details
    ISSN: 1432-0428
    Keywords: Insulin ; glucose ; obesity ; glucose disposal ; insulin secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Insulin responses to intravenous glucose infusion and glucose utilization during hyperinsulinaemic euglycaemic clamp were determined in a large homogeneous group of 65-year-old male subjects. Twenty-eight had untreated Type 2 (non-insulin-dependent) diabetes mellitus and the remaining 44 control subjects had a normal glucose tolerance. Diabetic patients with abdominal obesity displayed peripheral insulin resistance in combination with defective insulin secretion, whereas non-obese diabetic patients showed only a secretory defect. Thus, Type 2 diabetes in obese and non-obese elderly male subjects may take two forms where the cause of hyperglycaemia differs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00403284
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  • 4
    Electronic Resource
    Electronic Resource
    No glucotoxicity after 53 hours of 6.0 mmol/l hyperglycaemia in normal man (1991)
    Springer
    Diabetologia 34 (1991), S. 570-575 
    Details
    ISSN: 1432-0428
    Keywords: Insulin ; glucose ; insulin resistance ; man ; glucotoxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In vitro and in vivo studies have suggested that metabolic deterioration can be induced by hyperglycaemia per se. The effect of 53 h of 2.2 mg glucose · kg ideal body weight−1· min−1 was examined in four normal male subjects. This produced overnight hyperglycaemia of 6.0 mmol/l on the two nights of the study compared with 4.7 mmol/l on the control night (p〈0.05). In response there was a sustained, two-fold increase in basal plasma insulin (p〈0.005) and C-peptide (p〈0.05) levels. After two days of hyperglycaemia an increased Beta-cell response was demonstrated in response to an additional glucose infusion stimulus (estimated Beta-cell function median of 84% on the control day to 100% after two days glucose infusion). Plasma insulin and C-peptide responses to a 10.0 mmol/l hyperglycaemic clamp increased over the two days of the study (insulin from median 48 mU/l to 73 mU/l and C-peptide from median 2.0 pmol/ml to 2.6 pmol/ml). Glucose tolerance to the additional glucose infusion stimulus improved, suggesting that the increased insulin response during hyperglycaemia was enhancing peripheral glucose uptake. The calculated peripheral insulin sensitivity was unchanged during the hyperglycaemic clamp. Thus, in response to the two days of basal hyperglycaemia, both the basal and stimulated Beta-cell responses were enhanced and there was no evidence for ‘glucose toxicity’ to the Beta-cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00400275
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  • 5
    Electronic Resource
    Electronic Resource
    Receptor-recycling model of clearance and distribution of insulin in the perfused mouse liver (1991)
    Springer
    Diabetologia 34 (1991), S. 613-621 
    Details
    ISSN: 1432-0428
    Keywords: Insulin ; hepatic clearance ; receptor recycling ; receptor-mediated endocytosis ; physiological model ; mouse liver perfusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary After perfusion of mouse livers with A14-125I-insulin for designated intervals, an acid-wash technique was employed to separately measure the surface-bound (Xs) and intracellular (Xi) A14-125I-insulin, as well as intracellular degradation products (Xdeg) of labelled insulin. From the perfusate concentrations (Cp) of A14-125I-insulin, the apparent intrinsic hepatic clearance of labelled insulin at a high dose (0.2 nmol/l) was shown to be 60% smaller than that at a low dose (0.018 nmol/l), indicating that the cellular uptake of insulin is remarkably nonlinear at the concentration range examined. From the time courses of Cp, Xs, Xi and Xdeg, the hepatic insulin disposition was shown to be largely accounted for by the receptor-mediated endocytosis. The observed data at the low dose were analysed to estimate biochemical parameters, (i.e., total receptor number, endocytotic rate constant and intracellular degradation rate constant) according to “receptor-recycling” and “non-receptor-recycling” models, using a computer-aided optimization procedure. The “receptor-recycling” model could not only adequately explain the Cp, Xs, Xi and Xdeg at the low dose, but also predict the Cp at the high dose. On the other hand, a “non-receptor-recycling” model, in which recycling of receptors was not assumed, could also explain the observed data at the low dose, but failed to predict the Cp at the high dose, indicating that the receptor recycling process is necessary to explain the hepatic insulin clearance at high insulin concentrations, at which hepatic insulin clearance should be limited by the rate of receptor recycling. However, the applicability of our model might be limited within the physiologic insulin concentrations, because of the negative co-operativity of insulin-receptor interaction and a high-capacity, non-degradative and more rapidly recycling pathway for receptors that may occur at high concentrations of insulin. In conclusion, we have developed a mathematical model of hepatic insulin clearance and distribution under physiological conditions, including receptor binding, receptor-mediated endocytosis and receptor recycling, which has been so far demonstrated using isolated hepatocytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00400989
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  • 6
    Electronic Resource
    Electronic Resource
    Time-related, cross-sectional and prospective follow-up of pancreatic endocrine function after pancreas allograft transplantation in Type 1 (insulin-dependent) diabetic patients (1991)
    Springer
    Diabetologia 34 (1991), S. S57 
    Details
    ISSN: 1432-0428
    Keywords: Insulin ; C-peptide ; Glucagon ; Pancreas ; Transplantation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary It has been established that successful pancreas transplantation in Type 1 (insulin-dependent) diabetic patients results in normal but exaggerated phasic glucose-induced insulin secretion, normal intravenous glucose disappearance rates, improved glucose recovery from insulin-induced hypoglycaemia, improved glucagon secretion during insulin-induced hypoglycaemia, but no alterations in pancreatic polypeptide responses to hypoglycaemia. However, previous reports have not segregated the data in terms of the length of time following successful transplantation and very little prospective data collected over time in individual patients has been published. This article reports that in general there are no significant differences in the level of improvement when comparing responses as early as three months post-operatively up to as long as two years post-operatively when examining the data cross-sectionally in patients who have successfully maintained their allografts. Moreover, this remarkable constancy in pancreatic islet function is also seen in a smaller group of patients who have been examined prospectively at various intervals post-operatively. It is concluded that successful pancreas transplantation results in remarkable improvements in Alpha and Beta cell but not PP cell function that are maintained for at least one to two years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587621
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  • 7
    Electronic Resource
    Electronic Resource
    In vivo metabolic action of insulin-like growth factor I in adult rats (1991)
    Springer
    Diabetologia 34 (1991), S. 144-149 
    Details
    ISSN: 1432-0428
    Keywords: Insulin ; insulin-like growth factor I ; euglycaemic clamping ; glucose metabolism ; lipogenesis ; glycogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The acute metabolic actions of insulin-like growth factor I were studied in anaesthetized adult rats and its potency was compared to that of insulin. Following an i. v. bolus injection of insulin-like growth factor I a dose-dependent decrease of blood glucose and serum non-esterified fatty acid concentrations was noted with a potency of about 2% that of insulin. Stimulation of total body glucose disposal during euglycaemic clamping required ∼ 50times higher insulin-like growth factor I serum concentrations to achieve an identical half-maximal response. A similar difference in potency was observed for the stimulatory action on 2-de-oxyglucose uptake and on glycogen formation in skeletal muscle. Lipogenesis in epididymal fat pads was increased dose-dependently by both hormones requiring approximately 30 times higher half-maximally effective serum concentrations of insulin-like growth factor I. These data demonstrate that insulin-like growth factor I exerted acute insulin-like metabolic actions in vivo with low potency. These effects were probably mediated via insulin receptors. A preferential stimulation of glucose metabolism in skeletal muscle was not observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00418267
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  • 8
    Electronic Resource
    Electronic Resource
    Ontogenesis of insulin processing in fetal rat hepatocytes (1991)
    Springer
    Diabetologia 34 (1991), S. 868-876 
    Details
    ISSN: 1432-0428
    Keywords: Insulin ; fetal rat hepatocytes ; glycogen ; endocytosis ; degradation ; retroendocytosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We studied insulin processing and hepatic glycogenesis in cultured hepatocytes isolated from rat fetuses of 17, 19, and 21 days of gestation. Steady-state insulin binding increased by 250% between days 17 and 19, from 145±8 to 361±52 fmol/mg protein, and by an additional 40% (405±69 fmol/mg protein) by 21 days of gestation. At 37°C, 125I-insulin was rapidly (t1/2〈5 min) internalized by hepatocytes at all three ages, reaching maximal levels (63–76% of the total cell-associated radioactivity) by 15 min. 125I-labelled degradation products appeared rapidly (t1/2〈15 min) within the cells. Yet, the majority (68–77%) of the intracellular radioactivity consisted of intact 125I-insulin, even after 4 h at 37°C. Hepatocytes pre-loaded with 125I-insulin and then acid-stripped of surface-bound radioactivity, rapidly released both intact 125I-insulin (retroendocytosis) and its radiolabelled degradation products. While intact insulin was initially released more rapidly (t1/2〈6 min), and reached a plateau after 15–30 min, the degradation products continued to accumulate in the medium for at least 4 h. Methylamine inhibited intracellular 125I-insulin degradation at all three gestational ages and also blocked insulin-stimulated glycogenesis in 19- and 21-day hepatocytes, without altering basal glycogen synthesis. Insulin-stimulated glycogenesis was not induced in 17-day fetal rat hepatocytes in control or methylamine-treated cultures. We conclude that both degradative and retroendocytotic pathways for processing insulin are present in fetal rat hepatocytes by 17 days of gestation. Further, insulin-receptor processing was functionally related to the glycogenic action of insulin in responsive 19- and 21-day fetal rat hepatocytes
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00400194
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  • 9
    Electronic Resource
    Electronic Resource
    Binding and biological effects of insulin, insulin analogues and insulin-like growth factors in rat aortic smooth muscle cells. Comparison of maximal growth promoting activities (1991)
    Springer
    Diabetologia 34 (1991), S. 307-313 
    Details
    ISSN: 1432-0428
    Keywords: Insulin ; insulin analogues ; insulin-like growth factors ; proliferation ; vascular smooth muscle cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Binding and growth promoting effects of insulin, insulin analogues modified in the B chain, proinsulin, insulin-like growth factor-I and -II were studied in cultured rat aortic smooth muscle cells. Specific binding of125I-insulin was 0.9±0.2% of total 125I-insulin added, and the IC50-value was estimated to 8.9 pmol/1. The insulin analogue B10 Asp tended to be more potent than insulin in displacing 125I-insulin, B28 Asp was equipotent, B9 Asp/B27 Glu was approximately 100 times less potent and insulin-like growth factor-I more than 1000 times less potent than insulin. Specific binding of 125I-insulin-like growth factor-I after 4 h incubation at 10 °C was five times higher than the specific binding of insulin (4.4±0.4% of total 125I-insulin-like growth factor-I added), and the IC50-value was 0.3 nmol/l. Insulin was approximately 500 times less potent than insulin-like growth factor-I in displacing 125I-insulin-like growth factor-I. The insulin analogue B10 Asp was slightly more potent and analogue B28 Asp was equipotent with insulin. Analogue B9 Asp/B27 Glu was ten times less potent and proinsulin was more than ten times less potent than insulin. The order of potency was similar for 3H-thymidine incorporation into DNA: insulin-like growth factor-I 〉 B10 Asp 〉 insulin-like growth factor-II 〉 insulin 〉 B28 Asp 〉 B9 Asp/B27 Glu 〉 proinsulin. The maximal effect of insulin-like growth factor-I on 3H-thymidine incorporation was 71±16% higher than the maximal effect of insulin. The maximal effect of insulin-like growth factor-II was at least as high as the effect of insulin-like growth factor-I. Furthermore, the maximal effect of B10 Asp was 62±10% higher than the maximal effect of insulin. Insulin-like growth factor-I and B10 Asp tended to increase cell number more than insulin. In conclusion, this study shows that insulin analogues interact with different potencies with receptors for insulin and insulin-like growth factor-I in vascular smooth muscle cells and that insulin-like growth factors and the insulin analogue B10 Asp have more pronounced growth effects than insulin. Substitution of the amino acid Asp for His at position B10 in insulin makes the molecule more similar to insulin-like growth factor-I, chemically and probably also biologically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00405001
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  • 10
    Electronic Resource
    Electronic Resource
    Reduced secretion of gastric inhibitory polypeptide in turner patients with impaired glucose tolerance (1991)
    Springer
    European journal of pediatrics 150 (1991), S. 339-342 
    Details
    ISSN: 1432-1076
    Keywords: Glucose tolerance ; Turner syndrome ; Insulin ; GIP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract There is a well documented increase in the incidence of abnormal glucose tolerance in patients with Turner syndrome. To elucidate the pathophysiology of this phenomenon, we studied the serum concentrations of gastric inhibitory polypeptide (GIP) — as probably the most important hormonal factor of the entero-insular axis — in relation to impaired glucose tolerance in this syndrome. Oral glucose tolerance tests were performed in 12 Turner patients with simultaneous determination of plasma glucose, insulin and GIP. An impaired glucose tolerance (iGT) was found in four patients with a chronological age between 12.3 and 14.9 years. These patients were compared with found Turner patients of similar age and weight and a normal glucose tolerance (nGT). The highest insulin level occurred 90 min after stimulation in the patients with iGT compared to 30 min in the nGT group. Interestingly, the total areas under the insulin curves were not different. Stimulated plasma GIP concentrations and the areas under the GIP curves wer significantly lower in iGT compared to nGT patients. A disturbed entero-insular axis might contribute to the delayed — rather than diminished — release of insulin in patients with Turner syndrome and impaired glucose tolerance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01955936
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  • 11
    Electronic Resource
    Electronic Resource
    Extrapancreatic insulin effect of glibenclamide (1991)
    Springer
    European journal of clinical pharmacology 40 (1991), S. 379-381 
    Details
    ISSN: 1432-1041
    Keywords: Insulin ; glibenclamide ; C-peptide ; insulin catabolism ; diabetes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary In eight patients with uncomplicated non insulin dependent diabetes mellitus, serum insulin levels, serum C-peptide levels and blood glucose levels were measured before and after oral administration of glibenclamide 0.1 mg/kg body weight and a test meal, or after a test meal alone. The rise in serum insulin levels persisted longer after glibenclamide. The initial rise in serum insulin was of the same magnitude in both situations, as was the rise in serum C-peptide levels during the entire 5 h study. It is concluded that glibenclamide is able to maintain a more protonged increase in serum insulin levels by inhibiting the degradation of insulin in the vascular endothelial cells of the liver. The inhibition contributes to the blood glucose lowering effect of glibenclamide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00265847
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  • 12
    Electronic Resource
    Electronic Resource
    Risks of jet injection of insulin in children (1991)
    Springer
    European journal of pediatrics 150 (1991), S. 554-556 
    Details
    ISSN: 1432-1076
    Keywords: Diabetes ; Insulin ; Therapy ; Child
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of our study was to assess whether a non-invasive insulin injector could improve the metabolic control of ten diabetic children complaining of painful injections with syringe and needle. The cumulative study period amounted to 1347 days. Whereas a non-significant rise in insulin needs was observed (from 0.98±0.03 to 1.03±0.06 units/kg per day, mean ± sem), mean HbA1c value remained unchanged (8.9%±0.4% vs 9.0%±0.5%). Jet injections were felt as less painful than those using syringe and needle (nine out of ten cases). This advantage was hampered by side-effects in eight out of ten cases such as episodes of glycoketonuria (six out of ten cases) leading to hospitalization in three patients. Other side-effects included inability to adjust injection pressure (four out of ten cases) and technical failure requiring an exchange of injector in five cases. The four children with most serious problems were significantly younger (P=0.009) than other subjects. In conclusion, this type of injector should be discouraged in young diabetic children. For older children and adolescents, it may be an alternative to syringe and needle provided repeated detailed information and tight medical supervision is available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02072205
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  • 13
    Electronic Resource
    Electronic Resource
    Effects of insulin and somatostatin on the growth and the colony formation of two human pancreatic cancer cell lines (1991)
    Springer
    Journal of cancer research and clinical oncology 117 (1991), S. 416-420 
    Details
    ISSN: 1432-1335
    Keywords: Pancreas cancer ; Insulin ; Somatostatin ; Growth ; Colony formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of insulin and somatostatin on the growth and the colony formation of two human pancreatic cancer cell lines, BxPC-3 and SOJ-6, were studied. The BxPC-3 cell line (American Type Culture Collection no. CRL 1687) was derived from a moderately differentiated pancreatic adenocarcinoma. The SOJ-6 cell line is a subclone of SOJ that was initiated from ascites of a well-differentiated pancreatic adenocarcinoma. Both cell lines express fetoacinar pancreatic antigen, an antigen that might be associated with early transformation stages. However, these lines have different proliferation and tumoral powers. SOJ-6 cells showed an almost twofold higher division rate over BxPC-3 cells when cultured in RPMI-1640 medium containing 10% fetal bovine serum. The tumorigenic degree of SOJ-6 cells, as assessed by tumor growth in nude mice, was about three times greater than that of BxPC-3. The in vitro growth of BxPC-3 cells was significantly promoted by insulin, and was slightly inhibited by somatostatin, whereas the growth of SOJ-6 cells was not influenced by these hormones. Using a clonogenic assay in soft agar, the average ratio of colony numbers formed by SOJ-6 and BxPC-3 was about 10/1, indicating a good correlation between the colony formation and tumorigenic degree in vivo. In this test, the number of colonies formed by BxPC-3 cells was increased about twofold in insulin-supplemented medium. On the other hand, somatostatin inhibited the colony formation by a factor of four to six. However, no hormonal modulation of the colony formation of SOJ-6 cells was observed. Our data show that pancreatic cancer cell lines respond differently to pancreatic hormones, and suggest that this may be correlated to a tumour stage or a tumour type.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01612760
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  • 14
    Electronic Resource
    Electronic Resource
    Linear prediction enhancement of 2D heteronuclear correlated spectra of proteins (1991)
    Springer
    Journal of biomolecular NMR 1 (1991), S. 237-246 
    Details
    ISSN: 1573-5001
    Keywords: Linear prediction ; Heteronuclear correlation ; 2D NMR spectra ; Protein ; Insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Linear prediction has been used to extrapolate the t1 domain of natural abundance1H−13C correlated two-dimensional (2D) FIDs of insulin. The FIDs were obtained by two different heteronuclear correlation experiments, one that utilizes heteronuclear multiple-quantum coherence during t1, and one that utilizes13C single-quantum coherence. It is shown that the enhancement of the resolution and sensitivity in the F1 dimension of the Fourier transform spectrum that results from the linear prediction extrapolation allows the t1 domain to be confined to a relatively short time period where the signal intensity is at maximum. In particular, it is found that the enhancement thus obtained is sufficiently good to allow an observation of the difference between the F1 line widths in the single-quantum and double-quantum coherence spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01875517
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  • 15
    Electronic Resource
    Electronic Resource
    Effect of sulphonylurea on glucose-stimulated insulin secretion in healthy and non-insulin dependent diabetic subjects: a dose-response study (1991)
    Springer
    Acta diabetologica 28 (1991), S. 162-168 
    Details
    ISSN: 1432-5233
    Keywords: Insulin ; C-peptide ; Glucose ; Glipizide ; Non-insulin-dependent diabetes mellitus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of a rapid-acting sulphonylurea, glipizide, on the dose-response relationship between the β-cell response (insulin and C-peptide secretion) and the ambient plasma glucose concentration was examined in 12 healthy and 6 non-insulin-dependent diabetic subjects. The subjects participated in two sets of experiments which were performed in random order: (A) four hyperglycaemic clamp studies, during which the plasma glucose concentration was raised for 120 min by 1 (only in healthy subjects), 3, 7, and 17 mmol/l; and (B) the same four hyperglycaemic clamp studies preceded by ingestion of 5 mg glipizide. All subjects participated in a further study, in which glipizide was ingested and the plasma glucose concentration was maintained at the basal level. In control subjects in the absence of glipizide, the firstphase plasma insulin response (0–10 min) increased progressively with increasing plasma glucose concentration up to 10 mmol/l, above which it tended to plateau. Glipizide augmented the first-phase insulin response without changing the slope of the regression line relating plasma insulin to glucose concentrations. The second-phase plasma insulin response (20–120 min) increased linearly with increasing hyperglycaemia (r=0.997). Glipizide alone increased the plasma insulin response by 180 pmol/l. A similar increase in plasma insulin response following glipizide was observed at each hyperglycaemic step, indicating that glipizide did not affect the sensitivity of the β-cell to glucose. First-phase insulin secretion was reduced in the type 2 (non-insulin-dependent) diabetic patients, and was not influenced by glipizide. The dose-response curve relating second-phase insulin secretion to the ambient plasma glucose concentration was significantly (P〈0.001) flatter in the diabetic patients than in the control subjects. Glipizide alone increased the plasma insulin response by 60 pmol/l without changing the slope of the dose-response curve. It is concluded that, in both type 2 diabetic patients and healthy subjects: (A) sulphonylurea augments glucose-stimulated second-phase insulin secretion without changing the sensitivity of the β-cell to glucose; (B) first-phase insulin secretion is reduced in non-insulin-dependent diabetic patients with fasting hyperglycaemia and is not influenced by sulphonylurea.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00579720
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  • 16
    Electronic Resource
    Electronic Resource
    Immunohistochemical colocalization of insulin, aromatic L-amino acid decarboxylase and dopamine beta-hydroxylase in islet B cells of chicken pancreas (1991)
    Springer
    Cell & tissue research 263 (1991), S. 131-136 
    Details
    ISSN: 1432-0878
    Keywords: B cells ; Insulin ; Catecholamine ; synthesizing enzymes ; Immunohistochemistry ; Chicken
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The identity of the monoamine which produces a very weak formaldehyde-induced fluorescence in some pancreatic islet cells was studied by fluorescence microscopy and immunohistochemistry either on the same tissue section or on serial tissue sections of tissue from male chickens. Pancreatic islet cells showing this very weak formaldehyde-induced fluorescence react immunohistochemically with antisera directed against insulin, aromatic L-amino acid decarboxylase and dopamine beta-hydroxylase and therefore appear to be islet B cells producing insulin and noradrenaline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318408
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  • 17
    Electronic Resource
    Electronic Resource
    The endocrine pancreas of glucagon-and somatostatin-immunized rabbits (1991)
    Springer
    Cell & tissue research 265 (1991), S. 261-273 
    Details
    ISSN: 1432-0878
    Keywords: Endocrine pancreas ; Immunization ; Insulin ; Glucagon ; Somatostatin ; Electron microscopy ; Rabbit (Chinchilla, Ch: b Ch)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary An active or passive immunization against hormones and the subsequent neutralization of hormones by circulating antibodies is a valuable tool for the identification of hormonal action. To recognize presumed local (autocrine, paracrine) effects exerted by pancreatic hormones, the endocrine pancreas of rabbits was investigated electron-microscopically after long-term immunization against glucagon or somatostatin. Glucagon immunization resulted in hyperplasia and hypertrophy of glucagon- (A-) cells and in their increased metabolic activities: They showed prominent nucleoli, increased amounts of endoplasmic reticulum, Golgi areas, and mitochondria. These changes were paralleled by alterations in secretion granules (increased size, decreased hormonal content), increased numbers of lysosomes (crinophagic bodies), and an increment of the filamentous system. Basically, these findings point to an autocrine regulation of A-cells. Following somatostatin immunization, somatostatin- (D-) cells were hyperplastic but unchanged in their metabolic state. Instead, insulin-(B-) cells and A-cells exhibited equivalents of increased cellular activities (parameters, see above). This stimulation most probably is caused by cancelled paracrine (inhibitory) effects of somatostatin. The changes observed after both immunizations were differently expressed in morphologically heterogeneous islet types (size, angioarchitecture, cellular composition, microtopology of the various cell types). It is concluded, therefore, that the regulation of islets is not uniform. Autocrine and paracrine effects exerted by islet hormones are of different significance in individual islets, or they interfere differently with other regulatory signals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00398074
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  • 18
    Electronic Resource
    Electronic Resource
    Effects of carbohydrate type on postprandial blood pressure, neuroendocrine and gastrointestinal hormone changes in the elderly (1991)
    Springer
    Clinical autonomic research 1 (1991), S. 219-224 
    Details
    ISSN: 1619-1560
    Keywords: Postprandial hypotension ; Elderly ; Carbohydrate ; Neurotensin ; Catecholamines ; Insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previous studies have demonstrated that blood pressure falls postprandially in fit elderly subjects, the greatest changes occurring after meals with a high carbohydrate content. To evaluate the influence of the type of carbohydrate on postprandial blood pressure, the effects of equivalent energy content (2.4 MJ) high complex (starch) and high simple (monosaccharide) carbohydrate meals were studied in seven healthy elderly subjects. Blood pressure, heart rate, autonomic function, plasma catecholamines, insulin and neurotensin levels were measured pre- and postprandially. Greater falls in supine and erect systolic blood pressure occurred after the high simple than the high complex carbohydrate meal (p 〈 0.05). No differences were found in supine or erect diastolic blood pressure, heart rate or in any of the biochemical parameters measured between the meal types. It is concluded that a simple carbohydrate meal results in a greater postprandial fall in blood pressure than an equivalent energy complex carbohydrate meal in the elderly, although the mechanisms for these changes are unknown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01824990
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  • 19
    Electronic Resource
    Electronic Resource
    Glucoregulatory hormones in man at high altitude (1991)
    Springer
    European journal of applied physiology 62 (1991), S. 286-291 
    Details
    ISSN: 1439-6327
    Keywords: High altitude ; Cortisol ; Insulin ; Growth hormone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Concentrations of glucose, lactic acid, free fatty acid (FFA), insulin, cortisol and growth hormone (GH) in the blood were monitored in 15 euglycaemic men (sojourners, SJ) at sea level (SL) and while at altitudes of 3500 m and 5080 m, in acclimatised low landers (ALL) and in high altitude natives (HAN). In SJ, blood glucose and insulin concentrations showed a significant increase on the 3rd and 7th day after arrival at high altitude (HA), thereafter returning to sea level values and remaining the same during the entire period of their stay at 3500 m. Subsequently, on arrival at higher altitude (5080 m) the glucose concentrations again showed an increase over the preceding values and returned to SL values on day 41 while at 5080 m. A significant increase in cortisol concentrations was seen on day 3 after arrival at HA and the increased levels were maintained until day 21 at 3500 m. The cortisol concentrations on day 30 after arrival at 5080 m came down to SL values and remained unchanged thereafter. No appreciable change in GH and FFA was seen during the sojourn at HA. On the other hand, blood lactic acid concentration decreased significantly. There was no difference between the fasting glucose concentrations in ALL at 3500 m and in HAN at 3500 m and 4200 m compared to values of SJ at SL, whereas ALL at 4200 m had higher glucose values. Concentrations of plasma insulin and GH in ALL and HAN were higher than the values of SJ at SL, whereas cortisol values did not show any difference. These observations indicated that at HA the glucose values were high for the insulin concentration observed and might have been due to increased secretion of GH by the pituitary gland.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00571554
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  • 20
    Electronic Resource
    Electronic Resource
    Training effects of cross-country skiing and running on maximal aerobic cycle performance and on blood lipids (1991)
    Springer
    European journal of applied physiology 62 (1991), S. 400-404 
    Details
    ISSN: 1439-6327
    Keywords: Endurance conditioning ; Aerobic fitness ; Lipoproteins ; Insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Two experiments were carried out to compare the cardiorespiratory and metabolic effects of cross-country skiing and running training during two successive winters. Forty-year-old men were randomly assigned into skiing (n = 15 in study 1,n = 16 in study 2), running (n = 16 in study 1 andn = 16 in study 2) and control (n = 17 in study 1 andn = 16 in study 2) groups. Three subjects dropped out of the programme. The training lasted 9–10 weeks with 40-min exercise sessions three times each week. The training intensity was controlled at 75%–85% of the maximal oxygen consumption (VO2max) using portable heart rate metres and the mean heart rate was 156–157 beats·min−1 in the training groups. In the pooled data of the two studies the mean increase in theVO2max (in ml·min−1·kg−1) on a cycle ergometer was 17% for the skiing group, 13% for the running group and 2% for the control group. The increase inVO2max was highly significant in the combined exercise group compared to the control group but did not differ significantly between the skiing and running groups. The fasting serum concentrations of lipoproteins and insulin did not change significantly in any of the groups. These results suggested that training by cross-country skiing and running of the same duration and intensity at each session for 9–10 weeks improved equally the cardiorespiratory fitness of untrained middle-aged men.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00626610
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  • 21
    Electronic Resource
    Electronic Resource
    Effects of supramaximal exercise on blood glucose levels during a subsequent exercise (1991)
    Springer
    European journal of applied physiology 63 (1991), S. 48-51 
    Details
    ISSN: 1439-6327
    Keywords: Insulin ; Hyperglycemia ; Hyperinsulinemia ; Human subjects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The purpose of the present investigation was to examine the effects of hyperglycoemia induced by supramaximal exercise on blood glucose homeostasis during submaximal exercise following immediately after. Six men were subjected to three experimental situations; in two of these situations, 3 min of high-intensity exercise (corresponding to 112, SD 1%VO2 max) was immediately followed by either a 60-min period of submaximal exercise (68, SD 2%VO2 max) or a 60-min resting period. In the third situation, subjects performed a 63-min period of submaximal exercise only. There were no significant differences between the heurt rates, oxygen uptakes, and respiratory exchange ratios during the two submaximal exercise bouts (〉 15 min) whether or not preceded by supramaximal exercise. The supramaximal exercise was associated within 10 min of the start increases (P〈0.05) in blood glucose, insulin, and lactate concentrations. This hyperglycemia was more pronounced when subjects continued to exercise submaximally than when they rested (at 7.5 min;P〈0.05). There was a more rapid return to normal exercise blood glucose and insulin values during submaximal exercise compared with rest. The data show that the hyperinsulinemia following supramaximal exercise is corrected in between 10–30 min during submaximal exercise following immediately, suggesting that this exercise combination does not lead to premature hypoglycemia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00760800
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  • 22
    Electronic Resource
    Electronic Resource
    Thermogenic effect of adrenaline: interaction with insulin (1991)
    Springer
    European journal of applied physiology 63 (1991), S. 417-423 
    Details
    ISSN: 1439-6327
    Keywords: Energy expenditure ; Thermogenesis ; Epinephrine ; Insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The contribution of insulin (3.6 pmol sd kg body mass−1·min−1 to adrenaline-induced (0.164 nmol · kg fat free mass−1·min−1) thermogenesis was studied in ten postabsorptive healthy volunteers using two sequential protocols. Variables considered were oxygen consumption as well as carbon dioxide production, heart rate, blood pressure, plasma concentrations of glucose, insulin, glycerol, free fatty acids,β-HO-butyrate and lactate. Adrenaline increased plasma concentrations of glucose, glycerol, free fatty acids, andβ-HO-butyrate, and heart rate and metabolic rate during normo-insulinaemia [61.3 (SEM 6.6) pmol·−1]. Similar effects were observed during hyperinsulinaemia [167.9 (SEM 18.7) pmol·−1], but the effect of adrenaline on oxygen consumption was reduced. On average, metabolic rate increased by 12.9% during normo-insulinaemia and by 8.9% during hyperinsulinaemia. We concluded that relative hyperinsulinaemia resulted in decreased adrenaline-induced thermogenesis and therefore increased whole body anabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00868072
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  • 23
    Electronic Resource
    Electronic Resource
    Effects of muscarinic blockade on the thermic effect of oral or intravenous carbohydrate (1991)
    Springer
    European journal of applied physiology 63 (1991), S. 242-249 
    Details
    ISSN: 1439-6327
    Keywords: Atropine ; Glucose ; Fructose ; Dietary thermogenesis ; Insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Muscarinic blockade by atropine has been shown to decrease the thermic effect of a mixed meal, but not of intravenous glucose. To further delineate the mechanisms involved in the atropine-induced inhibition of thermogenesis after a meal, plasma substrate and hormone concentrations, energy expenditure (EE) and substrate oxidation rates were measured before and during a continuous glucose infusion (44.4 μmol·kg−1·min−1) with or without atropine. After 2 h of glucose infusion, a 20-g oral fructose load was administered while the glucose infusion was continued. Plasma insulin concentrations attained a plateau at 596 (SEM 100) pmol·l−1 after 120 min of glucose infusion and were not affected by muscarinic blockade; plasma glucose concentrations peaked at 13.3 (SEM 0.5) mmol·l−1 at 90 min and decreased progressively thereafter; no difference was observed with or without atropine. Plasma free fatty acid and glucagon concentrations, with or without atropine, were both decreased to 201 (SEM 18) μmol·l−1 and 74 (SEM 4) ng·l−1, respectively, after 2 h of glucose infusion, and were not further suppressed after oral fructose. Carbohydrate oxidation rates (CHOox) increased to 20.8 (SEM 1.4) μmol·kg−1·min−1 and lipid oxidation rates (Lox) decreased to 1.5 (SEM 0.3) μmol·kg−1·min−1 between 90 and 120 min after the beginning of glucose infusion and were not affected by atropine. Glucose-induced thermogenesis was similar with [6.5% (SEM 1.4%) of basal EE] or without [6.0% (SEM 1.0%), NS) muscarinic blockade during the 30 min preceding fructose ingestion. During the second half-hour after fructose ingestion, atropine infusion inhibited markedly the stimulation of CHOox [+2.8 (SEM 1.0) μmol·kg−1·min−1 vs +6.9 (SEM 1.0) μmol·kg−1·min−1, saline, P〈0.02] and the suppression of Lox [−0.8 (SEM 0.2) μmol·kg−1·min−1 vs −1.4 (SEM 0.2) μmol·kg−1·min−1, saline, P〈0.05]. Carbohydrate-induced thermogenesis during the second half-hour after fructose ingestion, increased to 13.0% (SEM 2.0%) without atropine and was suppressed to 7.7% (SEM 1.9%) (P〈 0.05, vs saline) with atropine. It was concluded that muscarinic blockade suppressed the increase of thermogenesis observed after oral fructose, but not during intravenous glucose infusion and that this suppression occurred independently of alterations of plasma insulin concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00233855
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  • 24
    Electronic Resource
    Electronic Resource
    PVC as pharmaceutical packaging material (1991)
    Springer
    Pharmacy world & science 13 (1991), S. 109-118 
    Details
    ISSN: 1573-739X
    Keywords: Chemistry ; Consumer product safety ; Drug packaging ; Environmental pollution ; Plasticizers ; Polyvinyls
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In this report the state of the art with respect to PVC as pharmaceutical packaging material is described. A general introduction into the applications of PVC is followed by a description of its production process. The metabolic effects of the monomer of PVC, vinyl chloride and of the most commonly used plasticizer diethylhexylphthalate are mentioned. Special attention is given to the pharmaceutical properties of plasticized PVC bags in comparison to other plastics and the environmental aspects of waste PVC disposal. Although there are emotional and political queries regarding the future use of PVC as a (pharmaceutical) packaging material, we conclude that there is no scientific justification for a total or partial ban of PVC. PVC will remain a fact of life as a cheap, versatile, high-performance and well-investigated plastic material for medical and pharmaceutical applications, to be replaced by newer plastics only for certain well-defined indications where the requirements of the plastic to be used are so specific that it will economically and technically be justified to use another polymer. Community and hospital pharmacists have to be prepared for a role in intake of waste plastic disposables, probably against deposit money, in order to fulfil the logistics needed for recycling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01981526
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  • 25
    Electronic Resource
    Electronic Resource
    Properties of a single chain embedded into a polymer matrix of varied thermodynamic quality and densityDedicated to Prof. Dr. D. Braun on the occasion of his 60th birthday (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 189-202 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The properties (squared dimensions, anisotropy, numbers of intra- and intermolecular contacts) of a single five-way cubic lattice chain embedded into an environment (matrix) of chains of the same length n = 50 were evaluated as a function of matrix volume fraction (matrix density) v and intermolecular interaction between the matrix polymer and the minority chain segments, characterized by a parameter φ. No convincing evidence was found for the occurrence of a coil-globule transition in the range of matrix densities (v ≤ 0.7) and repulsive interactions between matrix and minority chain (φ ≤ 0.2) investigated. For moderate attractive interaction (φ ≈ -0.17) a compensation of the chaincompressing action of the matrix and the chain-expanding interaction with the matrix was observed resulting in a zero-dependence of the size and shape of the minority chain on matrix density. It further turned out that there are fixed relations among the various size and shape data irrespective of the specific combination of matrix density and thermodynamic interaction by which a particular polymer dimension is produced. These interrelations are fairly the same as those evaluated for isolated chains the size of which is varied by an intramolecular energy parameter φi.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850118
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  • 26
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    Electronic Resource
    MATERIAUX TRIPHASIQUES ALVEOLAIRES POLYMERE / CHARGE / LIQUIDE OU GAZ. Préparation de Matériaux triphasiques Polystyrène / billes de Verre / Eau ou AirDédié au Prof. Dr. D. Braun à l'occasion de son 60ème anniversaire (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 227-237 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: New three phases composite materials made of glassbeads as filler, water as liquid dispersed phase and polystyrene as matrix were obtained by polymerization of a water in oil emulsion formed by water dispersed in styrene in which glass beads are added. For this purpose glass beads have to be modified by silanization by a coupling agent 3-(Trimethoxysilyl)propylmethacrylate (TPM) or a silane Octadecyltrichlorosilane (ODMS), in order to prevent the wetting of the glass by water. Only low coverage of the glass surface by the coupling agent (0,05% of TPM) are convenient for the preparation cellular materials having good mechanical properties. At higher coverage ratio, strong hydrophobic glass beads are obtained which destabilize the water / styrene emulsion and lead to macroporous products. Study of the rheology of the filled emulsion appears to be the more simple and more sensitive method to determine the level of wettability of the glass bead by the emulsion which is the most significant parameter for the preparation of such three phases composite materials. Composite materials made of glass beads, air and polystyrene are simply obtained by evaporation of water under vacuum.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850121
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  • 27
    Electronic Resource
    Electronic Resource
    Gas sorption in poly(butylene terephthalate). A critical test of the influence of molecular gas dataDedicated to Prof. Dr. D. Braun on the occasion of his 60th birthday (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 265-274 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: To test the molecular parameters concerning gas sorption in polymers, the concentration of CO2, N2O, CO, N2, CH4 and the noble gases Ne, He in glassy poly(butylene terephthalate) films (PBTP) has been studied gravimetrically with a recording microbalance at 25°C. The sorption isotherms exhibit downward curvature to the pressure axis. As neither solubility nor adsorption can explain the experimental results, analysis was carried out based on the dual-sorption model: gas dissolution and microvoid filling are considered as independent sorption mechanisms. The parameters of the dual-sorption model for the mentioned penetrants are determined. The results indicate that for parameter correlation the Lennard-Jones potential parameters give a rough idea, but size exclusion of gases in small diameter microvoids is proposed and special chemical interactions must be considered.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850125
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  • 28
    Electronic Resource
    Electronic Resource
    RINGÖFFNENDE METATHETISCHE POLYMERISATION (ROMP) VON 5-CYANO-2-NORBORNENHerrn Prof. Dr. D. Braun zum 60. Geburtstag gewidmet (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 283-292 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The ring opening metathesis polymerisation (ROMP) of 5-cyano-2-norbornene with tungsten hexachloride, tungesten oxytetrachloride, bis(dichloralkoxo)tungsten tetrachloride and bis(dichloralkoxo)tungsten oxydichloride as transition metal component was studied. Methylaluminoxan, diethylaluminium ethoxide, tetraisobutyldialuminoxan and tetrabutyltin served as cocatalyst. Toluene, Chlorobenzene and dichloromethane were used as solvents. The concentration of the tungsten components was in the range from 5 × 10-4 to 5 × 10-3 mol/l. Among the catalyst studied, tungsten hexachloride with diethylaluminium ethoxide proved to be the best. The polymerisation was highly selective with this system even at high monomer/tungsten ratios (e.q. 10200:1) and let to high conversions (≥82%).
    Notes: Die ringöffnende metathetische Polymerisation (ROMP) von 5-Cyano-2-norbornen wurde unter Einsatz von Wolframhexachlorid, Wolframoxidterachlorid, Bis(dichloralkoxo)wolframtetrachlorid und Bis(dichloralkoxo)wolframoxiddichlorid als Übergangsmetallkomponente untersucht. Als Cokatalysatoren dienten Methylaluminoxan, Diethylaluminiumethoxid, Tetraisobutyldialuminoxan und Tetrabutylzinn. Als Lösungsmittel wurden Toluol, Chlorbenzol und Dichlormethan verwendet. Die Konzentration der Wolframkomponente lag im Bereich 5 × 10-4 - 5 × 10-3 mol/l. Unter den geprüften Katalysatoren erwies sich Wolframhexachlorid in Verbindung mit Diethylalumiumethoxid als der geeignetste. Mit diesem System verlief die Polymerisation auch bei großen Monomer/Wolfram-Verhältnissen (10200 :1) hochselektiv und führte zu großen Umsätzen (≥82%).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850127
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  • 29
    Electronic Resource
    Electronic Resource
    Kinetics of radical polymerization, LIII. The absolute rate constants in the radical polymerization of ethyl acrylateDedicated to Prof. Dr. D. Braun on the occasion on his 60th birthday (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 303-310 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dependence of dilution on the chain propagation and termination rate constants was investigated in the polymerization of ethyl acrylate in benzene solution at 50°C, with the rotating sector method. The errors of the above rate constants were determined and, by our method applied to decrease these errors, the errors of the propagation rate constant was reduced to its half value. By the application of our earlier results in polymerization kinetics, we found that in this system the chain propagation step is exclusively responsible for the solvent effects observed. Our experimental results can be quantitatively described in terms of the hot redical theory.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850129
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  • 30
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    Electronic Resource
    Organische Gläser mit hohen Glasumwandlungstemperaturen auf Basis niedermolekularer Verbindungen.Herrn Prof. Dr. D. Braun zum 60. Geburtstag Gewidmet (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 329-334 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850132
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    Soluble maleimide prepolymers containing 1,3,5-triazine groups as composite resin matrices. Synthesis, characterization, and evaluation (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 190 (1991), S. 1-14 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch gemeinsame Reaktion von Benzophenontetracarbonsäuredianhydrid, Maleinsäureanhydrid und Diaminen mit 1,3,5-Triazingruppen wurden niedermolekulare Prepolymere mit Amin-Endgruppen erhalten, die sowohl 1,3,5-Triazingruppen als auch Etherbindungen enthalten. Diese reaktiven Prepolymeren sind in niedrigsiedenden Lösemitteln wie z. B. Chloroform und Tetrahydrofuran löslich. Sie wurden durch Elementaranalyse, IR- und NMR-Spektroskopie, Dampfdruckosmometrie und Viskosimetrie charakterisiert. Beim Erhitzen der Prepolymeren auf Temperaturen zwischen 180 und 190°C tritt Kettenverlängerung durch Michael-Addition auf; gleichzeitig vernetzen sie durch Reaktion der Amin- mit den Maleimid-Endgruppen. Die vernetzten Polymeren sind thermisch stabil; ihr thermisches Verhalten wurde durch TGA, DTA und isotherme Alterung untersucht. Die Biegefestigkeit und interlaminare Scherfestigkeit von aus den Prepolymeren und Carbonfasergeweben hergestellten Laminaten wurden gemessen.
    Notes: Low molecular weight amine-terminated monomaleimide prepolymers containing 1,3,5-triazine groups as well as ether linkages were synthesized by reacting benzophenone tetracarboxylic dianhydride, diamines having 1,3,5-triazine group and maleic anhydride. These reactive prepolymers are soluble in low boiling solvents such as chloroform, tetrahydrofuran etc. They were characterized by elemental analyses, IR and NMR spectroscopy, vapour pressure osmometry, and viscosity. On heating at 180-190°C these prepolymers undergo simultaneous chain extension by Michael addition reaction and crosslinking by mutual reaction between their amine-terminated and maleimide-terminated ends. The cured polymers are thermostable and the thermal behaviour was studied by TGA, DTA, and isothermal aging. Laminates fabricated using these prepolymers and carbon fiber as reinforcing agent were evaluated by their flexural strength and interlaminar shear strength.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051900101
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  • 32
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    Synthesis and properties of cationic resins derived from aniline/benzylamine-modified epoxy resins and diethylamines (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 190 (1991), S. 15-32 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Ein Epoxidharz wurde durch Reaktion mit Anilin bzw. Benzylamin in unterschiedlichen molaren Verhältnissen modifiziert. Die modifizierten Harze wurden dann mit Diethylamin und anschließend mit teilblockiertem Toluylendiisocyanat umgesetzt, wobei thermisch vernetzbare Harze mit tertiären Aminen in und am Ende der Polymerkette erhalten wurden. Die partielle Ansäuerung mit Essigsäure lieferte thermisch vernetzbare kationische Harze, aus denen durch Lösen in geeigneten Lösungsmitteln und Zugabe von entionisiertem Wasser Emulsionen hergestellt wurden. Diese wurden hinsichtlich ihrer Eignung zur elektrolytischen Abscheidung untersucht und verglichen. Die Ergebnisse zeigen, daß die Abscheidungsausbeute und das Streuvermögen der Emulsionen aus Benzylamin-modifizierten Epoxidharzen besser sind als die der Anilin-modifizierten Epoxidemulsionen. Ein hohes, vom pH-Wert der Emulsion abhängiges Streuvermögen ist für diese kationischen Harze charakteristisch.
    Notes: Aniline/benzylamine-modified epoxy resins with different molecular weights, which contain tertiary amines in the middle of the polymer chain, were synthesized by the reaction of aniline/benzylamine with epoxy resin at various molar ratios. The resulting aniline/benzylamine-modified epoxy resins were reacted with diethylamine and subsequently reacted with 2-ethylhexanol-blocked toluene diisocyanate to obtain thermally crosslinkable resins which contain tertiary amines at the end and in the middle of the polymer chain. These resins were partially neutralixed with acetic acid to give thermally crosslinkable cationic resins. The resulting cationic resins were dissolved in suitable solvents and mixed with deionized water to form various emulsions. The emulsion and electrodeposition properties of these resins were studied in some detail to compare the properties of these cationic resins. The results show that the deposition yields and throwing power of the emulsions prepared from benzylaminemodified epoxy resins are higher than those of the emulsions prepared from anilinemodified epoxy resins. The emulsion having proper pH values can give a high throwing power. High throwing power is the characteristic property of these modified cationic resins. Factors determining the throwing power and deposition yield of the emulsions were also investigated.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051900102
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    Studies on new non-shrinking, thermally stable araldite-type photopolymers with pendent arylacryloyl-groups. I. Photoreaction of some aryl acrylic-acid methyl esters in solution (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 190 (1991), S. 33-52 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Arylacrylsäuren, wie Furylacrylsäure und Thienylacrylsäure können durch Knoevenagel-Reaktion der Arylcarbaldehyde mit Malonsäure in Pyridin dargestellt werden. Durch einfache Veresterung der Arylacrylsäuren in Methanol/Schwefelsäure werden die entsprechenden Arylacrylsäuremethylester mit guten Ausbeuten erhalten. Diese isomerisieren bei Bestrahlung mit UV-Licht (λ ≥ 280 nm) in methanolischer Lösung. Bei der Photoreaktion in Lösung wurde keine Photodimerisierung beobachtet. Die Reaktionskinetik der Photoreaktionen wurde untersucht.
    Notes: Aryl acrylic acids, e. g. furyl acrylic acid or thienyl acrylic acid are readily formed by the Knoevenagel condensation reaction of arylcarbaldehydes and malonic acid in pyridine. Esterification of these acids with methanol/sulfuric acid gives the corresponding aryl acrylic acid methyl esters in good yields. In methanolic solution these methyl esters isomerize upon irradiation (λ 280 nm). No photodimerization was observed. Kinetic data are given.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051900103
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    Matériaux composites à base de bois rétifié, IIIPartie 2 cf. lit.7.. Etude de l'influence de la granulométrie des charges lignocellulosiques (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 190 (1991), S. 67-80 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Different composite materials, with retified or natural poplar and polyester resin were prepared by molding. The influence of the filler granulometry on certain physicochemical (density, humidity, hardness) or mechanical properties of the materials was studied. The density and the increase of mass in humid atmosphere were always found to be less when the wood was thermally treated. On the other hand, the hardness of the composites made from natural poplar was much higher. The mechanical properties were found to be weak when the wood was retified.When the wood was thermally treated, it was possible to optimise the three parameters, namely, density, water retention capacity and mechanical properties. The optimal granulometry of poplar was determined between 0.75 and 1.5 mm.The results obtained are discussed considering the physico-chemical properties of the different varieties of wood studied and the interactions which exist between the polar resin and the wood.
    Notes: Divers matériaux composites à base de peuplier rétifié ou naturel et de résine polyester insaturée ont été préparés par moulage. L'influence de la granulométrie de la charge a été étudiée sur quelques propriétés physico-chimiques (densité, reprise d'humidité, dureté) ou mécaniques des matériaux obtenus. La densité et la reprise de masse en milieu humide sont toujours plus faibles si la charge est traitée thermiquement sous atmosphère inerte. Par contre, la dureté des composites issus du peuplier naturel est plus importante. Les propriétés mécaniques sont inférieures si la charge est rétifitée.Si la charge lignocellulosique est traitée thermiquement, il est possible d'optimiser les trois paramètres: densité, reprise d'eau et propriétés mécaniques; la granulométrie optimale du peuplier est ainsi comprise entre 0,75 et 1,5 mm.Les résultats obtenus sont expliqués en tenant compte des propriétés physico-chimiques des charges et des interactions existant entre la résine polaire et le bois.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051900105
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    Pervaporation separation of water-ethanol through modified chitosan membranes, IIPart I: cf.1.. Carboxymethyl, carboxyethyl, cyanoethyl, and amidoxime chitosan membranesPresented at The 1990 International Congress on Membranes and Membrane Processes (ICOM ′90), Chicago 20 to 24 August 1990. (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 169-181 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die vorliegende Arbeit untersucht das Wasserdurchlässigkeitsverhalten von vier Arten verschieden modifizierter Chitosanmembranen zur Abtrennung von Wasser aus wäßrigen Ethanolmischungen. Chitosan wurde aus Chitin von Krebstierschalen durch Verseifung (Deacetylierung) gewonnen. Die in dieser Arbeit untersuchten modifizierten Chitosanmembranen enthielten Carboxymethyl-, Carboxyethyl-, Cyanethyl- und Amidoxim-Chitosan. Die Einführung hydrophiler funktioneller Gruppen in der 6-O Position des Chitosans erhöht die Selektivität der modifizierten Membranen im Vergleich zu den mit Essigsäure komplexierten Chitosanmembranen. Die Untersuchungen zeigen, daß Chitosanmembranen, die Carboxygruppen enthalten, die höchste Wasserdampfdurchlässigkeit aufweisen. Carboxymethyl-Chitosanmembranen zeigen eine maximale Quellung und den höchsten Ethanoldurchfluß bei einer Ethanolkonzentration von ca. 15 Gew.-% im Zulauf aufgrund von Bindungs- und Weichmachereffekten.
    Notes: The present study investigates the pervaporation performance of four kinds of modified chitosan membranes to separate water from aqueous ethanol solution. Chitosan was prepared from chitin abstracted from the crab shell and subsequently deacetylated with aqueous NaOH solution. Modified chitosan membranes examined in this study include carboxymethyl chitosan, carboxyethyl chitosan, cyanoethyl chitosan, and amidoxime chitosan. The incorporation of hydrophilic functional groups into the 6-O position of chitosan enhances the selectivity of modified chitosan membrane compared to the previously reported chitosan-acetic acid complex membrane. Among the modified chitosan membranes, membranes containing carboxy groups show the best pervaporation performance. Carboxymethyl chitosan membranes show the maximum swelling and ethanol flux at approx. 15 wt.-% feed ethanol concentration due to the coupling and plasticizing effect.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920114
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    Zusammenhänge zwischen mechanischem Verhalten und Morphologie von eigenfaserverstärkten Poly(propylen)/Poly(1-buten)-Blends, kristallisiert aus der hochorientierten Schmelze (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 183-197 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The tensile properties of self reinforced poly(propylene)/poly(1-butene) composites, obtained by rapid extension of the melt, have been measured and correlated to morphological parameters derived from x-ray experiments. Critical fiber lengths as a function of sample composition and the elastic modulus and yield stress of the fibers could be determined. It is shown, that, applying a load to the system, the forces are fully taken up by the fibers and the system breaks by fail of the fibers. The longitudinal structure of the fibers is found to be independent of sample composition.
    Notes: Mechanische Parameter wie Elastizitätsmodul, Fliß- und Bruchspannung von aus der hochorientierten Schmelze hergestellten nadelkristallinen Mischungen aus Poly(propylen) und Poly(1-bute) wurden mit morphologischen Parametern, die aus Röntgenmessungen abgeleitet wurden, korreliert. Es wird gezeigt, daß der Elastizitätsmodul des Verbundes aus den E-Moduln der Fasern und der Matrix berechnet werden kann (Mischungsregel). Die an der Probe angreifenden Kräfte werden voll auf die Fasern übertragen; der Verbund kann daher als eigenfaserverstärktes System angesehen werden. Die Abschätzung der kritischen Faserlänge ergibt, daß die Festigkeit der FAsern voll ausgenutzt wird; der Bruch des Systems bei Belastung ist daher auf das Versagen der Fasern zurückzuführen. Das mechanische Verhalten des Verbundes wird stark beeinflußt durch die Komponentenzusammensetzung. Die longitudinale Struktur der Nadeln beider Komponenten bleibt unbeeinflußt von der jeweiligen Co-Komponente.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920115
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    Cationic polyelectrolytes, XIPart X cf.7.. Polymers with quaternary N-atoms in the main chain obtained by condensation polymerization of epichlorohydrin with amines (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 199-211 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Lösliche kationische Polyelektrolyte mit quartären Stickstoffatomen in der Hauptkette wurden durch Polykondensation von Epichlorhydrin (ECH) mit Dimethylamin (DMA) und N,N-Dialkylaminoakylaminen erhalten. Die Reaktionsparameter, die die Polymereigenschaften hauptsächlich beeinflussen, sind: Molverhältnis DMA/asymmetrische Diamine, Ausgangskonzentration der Aminlösung, Molverhältnis ECH/Amine und die Struktur der asymmetrischen Diamine. Das viskosimetrische Verhalten verdünnter wäßriger Lösungen mit oder ohne Zugabe neutraler Salze veranschaulicht die flexible Natur der Polyelektrolyten.
    Notes: Water soluble cationic polyelectrolytes containing quaternary nitrogen atoms within the main chain were prepared via condensation polymerization of epichlorohydrin (ECH) with dimethylamine (DMA) and N,N-dialkylaminoalkylamines. The main parameters of the reaction that influence the polymer properties are: DMA/asymmetrical diamine molar ratio, the initial concentration of amine solution, NaOH/amine molar ratio, ECH/amine molar ratio, and asymmetrical diamine structure. The feature of flexible polyelectrolyte own to the investigated polymers was emphasized by the viscosimetric behaviour in dilute aqueous solutions with and without salt presence.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920116
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    MITTEILUNGEN (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 213-213 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051920117
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    Studies on rubber bound antioxidants (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 193 (1991), S. 1-11 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Antioxidantien wurden in einer modifizierten Friedel-Crafts-Reaktion mit wasserfreiem Zinkchlorid als Katalysator an Flüssig-Naturkautschuk mit Hydroxy-Endgruppen gebunden. Die immobilisierten Antioxidantien waren weniger flüchtig und extrahierbar als konventionelle Antioxidantien. Sie wurden sowohl einem Latex als auch trockenem Kautschuk zugesetzt; die daraus hergestellten Vulkanisate zeigten eine bessere Alterungsbeständigkeit als Vulkanisate mit konventionellen Antioxidantien.
    Notes: Antioxidants were attached to hydroxy-terminated liquid natural rubber by modified Friedel-Crafts alkylation reaction using anhydrous zinc chloride as catalyst. The rubber bound antioxidants were found to be less volatile and less extractable compared to conventional antioxidants. The bound antioxidants were tried both in latex compounds and dry rubber compounds. The vulcanizates showed improved ageing resistance compared to vulcanizates based on conventional antioxidants.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051930101
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    Study of the conduction mechanisms in polycarbonate (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 193 (1991), S. 13-20 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Strom-Spannungs-Charakteristik eines Bisphenol-A-Polycarbonats im Span-nungsbereich 50-1000 V und der Einfluß von UV-Bestrahlung (λ = 225 und 300 nm) und Tempern auf die elektrische Leitfähigkeit (σ) des Polycarbonats wurden untersucht. Die Abhängigkeit von σ gegen 1/T deutet auf zwei verschiedene Leitfähigkeits-mechanismen hin. Aus den Ergebnissen wurden die Aktivierungsenergien der Leitfähigkeit und die Sprungdistanzen berechnet.
    Notes: Current-voltage characteristics of polycarbonate samples (PC) have been studied in the voltage range 50-1000 V. The effect of UV-irradiation at λ = 225 and 300 nm, and thermal annealing on the electrical conductivity (σ) of PC was studied. The σ vs. 1/T relationship shows two slopes, i.e. two possible conduction mechanisms. The obtained results made it possible to determine a complete set of conduction parameters including activation energy and jump distance.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051930102
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    Porous terpolymers: Poly(acrylonitrile-co-vinyl acetate-co-divinylbenzene) (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 193 (1991), S. 21-28 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch Suspensionspolymerisation wurden Terpolymere aus Acrylnitril (AN), Vinylacetat (VA) (7,5-30 mol-%, bezogen auf AN) und Divinylbenzol (DVB) (10 Gew.-%) hergestellt. Als Verdünner wurden Mischungen von Toluol oder Cyclohexanol (90 Vo1.-%) mit Hexadecan, Octan, Dodecan, 2-Ethylhexanol oder Benzylalkohol (jeweils 10 Vo1.-%) verwendet.Die Porosität der AN-VA-DVB-Terpolymeren ist mit 0,61-0,68 größer als die der entsprechenden AN-DVB-Copolymeren. Die übermolekulare Struktur der Terpolymeren hängt vom verwendeten Verdünner ab, obwohl sich die Porositäten nicht sehr voneinander unterscheiden. Die beim Erhitzen der Terpolymeren auf Temperaturen über 200°C auftretenden thermischen Effekte sind signifikant größer als die bei der Cyclisierung von AN-Polymeren gemessenen.
    Notes: Terpolymers of acrylonitrile (AN), vinyl acetate (VA) (7.5-30 mol-%, related to AN), and divinylbenzene (DVB) (10 wt.-%) were prepared by suspension polymerization. The diluents used were mixtures of toluene or cyclohexanol (90 vol.-%) with solvents (10 vol.-%) such as hexadecane (HD), octane (O), dodecane (D), 2-ethylhexanol (E) or benzyl alcohol (B).It has been found that AN-VA-DVB terpolymers have a higher porosity, about 0.61-0.68, than corresponding AN-DVB copolymers. The terpolymers obtained with mixtures of various diluents differ in their supermolecular structure although they had similar porosity characteristics.The thermal effects accompanying heating of the terpolymers above 200°C significantly exceed that of nitrile groups cyclization observed of the other AN polymers.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051930103
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    Studies on PE-HD/PE-LLD blends (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 193 (1991), S. 39-49 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die rheologischen und mechanischen Eigenschaften von Blends aus PE-HD und zwei verschiedenen PE-LLD-Typen wurden im gesamten Mischungsbereich gemessen. Die Polymeren sind im festen Zustand und in der Schmelze ausreichend verträglich, so daß ihre vorteilhaften Eigenschaften genutzt werden können.
    Notes: A high density polyethylene grade is blended with two selected grades of linear low density polyethylene and the mechanical and rheological properties of the blends are evaluated over the entire composition range. The blends show sufficient compatibility in the solid phase and in the melt and hence they can be advantageously used to capitalize on their useful properties.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051930105
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    Copolymerization reactivity ratios of N,N-dimethyl acrylamide and isopropyl methacrylate determined by 1H-NMR spectroscopy (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 51-55 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: N,N-Dimethylacrylamid (DMA) und Isopropylmethacrylat (IPM) wurden in Dimethylformamid mit Azoisobutyronitril als Initiator copolymerisiert. Die Copolymerzusammensetzung wurde 1H-NMR-spektroskopisch ermittelt. Die Copolymerisationsparameter (rDMA = 0,58, rIPM = 2,76) wurden nach Kelen-Tüdős berechnet.
    Notes: Copolymers of N,N-dimethyl acrylamide (DMA) and isopropylmethacrylate (IPM) were prepared in dimethyl formamide using azoisobutyronitrile as initiator. The composition of copolymers was determined by 1H-NMR analysis. Reactivity ratios (rDMA = 0.58, rIPM = 2.76) were calculated from these values by using the Kelen-Tüdős differential linear equation.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920104
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    Polymer molecular properties and hydrodynamic lubrication (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 69-79 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wird ein allgemeines numerisches Verfahren vorgestellt, um die Modifikation der Grundgleichung für hydrodynamische Schmierung, die von mit Polymeren versetzten Schmierölen mit scherabhängiger Viskosität erbracht wird, zu berechnen.Das Verfahren basiert auf dem verallgemeinerten Newtonschen Fileßmodell und erlaubt, alle Fileßregionen zwischen dem rein Newtonschen und dem Exponentialgesetzverhalten kontinuierlich zu behandeln. Die Ergebnisse zeigen, daß der Einfluß der scherspannungsabhängigen Viskosität durch eine dimensionslose Zahl vollkommen charakterisiert wird, nämlich U · τ*/h*, wobei U die relative Gleitgeschwindigkeit, h* die charakteristische Filmdicke und τ* die Relaxationszeit des Schmieröles darstellen.Als praktisches Beispiel wird die Anwendung des Verfahrens aufgezeigt, um den Einfluß des Molekulargewichts und der Konzentration der Polymerkomponente des Schmieröls auf die hydrodynamische Schmierung zu bestimmen. Dieser Einfluß ist durch die starke Beziehung zwischen Polymereigenschaften und τ* verursacht.
    Notes: A general numerical procedure is presented to calculate the modification of the basic equation for hydrodynamic lubrication brought about by the use of polymeric fluids with shear depending viscosity. The procedure is based on the generalized Newtonian fluid model and allows to treat continuously all the flow regions between the pure Newtonian and the power law behavior. The results show that the influence of the viscosity depending on shear stress is completely characterized by one dimensionless number, namely U.·τ*/h*, where U is the relative sliding velocity, h* is the characteristic film thickness, and τ* is a characteristic time of the lubricant. The procedure is exemplified by applying it for the determination of the influence of the molecular weight and concentration of the polymeric component of the lubricant on the hydrodynamic lubrication. This influence is brought about by the strong relation between the polymer properties and τ*.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920106
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    Tensile properties and morphology of injection-molded poly(1-butene) (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 57-67 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Morphologien von spritzgegossenem und formgepreßtem Poly(1-buten) (PB-1) wurden im Polarisationsmikroskop und im Transmissionselektronenmikroskop untersucht. Eine dünne Oberflächenhaut und bis in den Kern der Probekörper reichende abgeplattet-sphärolithische Strukturen werden bei spritzgegossenem PB-1 beobachtet, während in formgepreßtem PB-1 typische Sphärolithe vorliegen. Das Bruchbild des spritzgegossenen PB-1 zeigt unter der Oberflächenhaut viele aufgereihte streifenartige Hohlräume, die senkrecht zur Spritzrichtung zur Mitte des Probekörpers wachsen. Aus diesen Beobachtungen kann geschlossen werden, daß eine beim Spritzgießen durch den Schmelzefluß induzierte Scherspannung nicht nur die Entstehung der Oberflächenhaut verursacht, sondern auch bis in die Mitte des Probekörpers hinein die Bildung abgeplatteter Sphärolithe bewirkt. Diese abgeplattet-sphärolithischen Strukturen sind für die beim Dehnen des spritzgegossenen PB-1 entstehenden, streifenartigen Hohlräume verantwortlich, während die Oberflächenhaut und die abgeplatteten Sphärolithe im Kern die Sprödigkeit und die im Vergleich zu formgepreßtem PB-1 geringere Bruchdehnung bewirken. Diese kann durch Tempern oberhalb des Schmelzpunktes erhöht werden.
    Notes: The injection-molded poly(1-butene) (PB-1) is found to be more brittle than the compression-molded PB-1. The morphologies of these specimens are examined by use of polarized optical microscopy and scanning electron microscopy (SEM). A skin layer and an oblate spherulitic structure extended to the core region are observed in the injection-molded PB-1, while typical spherulites exist in the compression-molded PB-1. Below the skin layer of the injection-molded PB-1, the fracture surface is found to consist of many aligned strip-like voids with ribbon edges propagating to the center of the specimen and perpendicular to the flow direction of injection-molding. Based on these observations, it can be inferred that shear stress induced by the melt flow during the injection-molding does not only cause the formation of skin layer, but also penetrates deeply into the central region of the injection-molded specimen causing the formation of oblate spherulites. The oblate spherulitic structure is responsible for the aligned voids during elongation of PB-1, while the existence of the skin layer and the oblate spherulites in core region is responsible for the brittleness of the injection-molded PB-1. The elongation of the injection-molded PB-1 is found to be lower than that of the compression-molded. This can be attributed not only to the presence of the skin layer but also to the oblate spherulites in the core region. The elongation can be improved by annealing at a temperature above the melting point of PB-1.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920105
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    Electronic Resource
    Synthesis and biological activity of chlorinated polyketone resins (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 103-111 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch Kondensation von p-Xylol mit Chloracetylchloride, 1,2-Dichlorethan und Dichlormethan mit Aluminiumtrichlorid in Schwefelkohlenstoff wurden Polyketone hergestellt und IR-spektroskopisch sowie bezuglich des Molekulargewichtes charakterisiert. Die thermischen Eigenschaften wurden thermogravimetrisch und mittels DSC untersucht. Die Prüfung der Harze auf ihre biologische Aktivität gegen Pseudomonas fluorescens, Bacillus subtilis and Aspergillus niger ergab, daß deren Wachstum durch die Polyketonharze kontrolliert werden kann.
    Notes: Some polyketones were prepared from p-xylene, chloroacetylchloride, 1,2-dichloroethane and dichloromethane using anhydrous aluminiumtrichloride and carbon disulfide as solvent. The resins thus obtained have been characterized by IR spectra and number average molecular weight. The thermal properties have been studied by thermogravimetry and differential scanning calorimetry. All the resins were tested for their biological activity against Pseudomonas fluorescens, Bacillus subtilis and Aspergillus niger. The results show that the growth of the tested organisms can be controlled by the polyketone resins.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051920109
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  • 47
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    The reaction of pyromellitic dianhydride with 4,4′-diaminodiphenylmethane (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 145-153 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: In der Arbeit wurde die homogene Polyaddition von Pyromellitsäuredianhydrid und 4,4′-Diaminodiphenylmethan untersucht. Die Abhängigkeit des zahlenmittleren Molekulargewichts (M̄n) von der Zeit weist ein Maximum auf. Die Ursache der niedrigen Gleichgewichtswerte von M̄n beruht auf einer durch Wasserspuren im Lösungsmittel verursachten Dianhydridhydrolyse und damit einer gestörten Äquimolarität der funktionellen Gruppen. Im Laufe der Stabilisierung des M̄n-Gleichgewichtswertes entsteht auch die wahrscheinlichste Molmassenverteilung.
    Notes: The homogeneous polyaddition reaction of pyromellitic dianhydride with 4,4′-diaminodiphenylmethane was investigated. The dependence of the number average molecular weights on time has a maximum; low equilibrium values of M̄n are caused by a disturbed equimolarity of functional groups due to the hydrolysis of dianhydride with water present in the solvent. In the course of establishment of the equilibrium M̄n value, the molecular weight distribution changes to the most probable value.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051920112
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  • 48
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    Miscibility of polyarylate/phenoxy/poly(butyleneterephthalate) ternary blends (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 133-144 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Das Phasen- und Mischbarkeitsverhalten der binären und ternären Polymermischungen von Polyarylat (PAR), Phenoxid und Poly(butylenterephthalat) (PBT) wurde untersucht. Die Mischungen wurden durch Ausfällen aus gemeinsamen Lösungen hergestellt, und die Mischbarkeit wurde durch DSC-Messungen und Transparenz der Schmelze beurteilt. Im Falle der binären Blends zeigten PAR/PBT und Phenoxid/PBT Mischbarkeit, während sich PAR/Phenoxid nicht mischen ließ. Die Mischbarkeitstendenz der unmischbaren PAR/Phenoxid-Mischungen konnte jedoch durch Zugabe von PBT erhöht werden; eine ausreichende Menge PBT machte die ternären Mischungen mischbar, so daß diese eine einzige Tg in der DSC-Kurve zeigten. Im ternären Phasendiagramm war das Maximum der Mischbarkeitsgrenze in Richtung auf die Phenoxidseite hin verschoben, was auf die bessere Mischbarkeit von PAR/PBT im Vergleich zu Phenoxid/PBT zurückgeführt wird.
    Notes: The phase and miscibility behavior of binary and ternary blends containing polyarylate (PAR), polyhydroxyether of bisphenol AIUPAC: poly[oxy(2-hydroxytrimethylene)oxy-1,4-phenylene-isopropylidene-1,4-phenylene]. (Phenoxy), and poly(butylene terephthalate) (PBT) were studied. The blends were prepared by solution-precipitation method and miscibility was examined by DSC and melt transparency. In binary blends, PAR/PBT and Phenoxy/PBT blends show miscibility, while PAR/Phenoxy appeared to be immiscible. However, the miscibility of incompatible PAR/Phenoxy blend was enhanced by addition of PBT. The addition of sufficient amount of PBT caused the ternary blend to have a single glass transition temperature. The shape of miscibility boundary of ternary blend was skewed to the apex of Phenoxy, which was attributed to the better miscibility of PAR/PBT than that of Phenoxy/PBT.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051920111
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  • 49
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    Solid-state polycondensation of poly(ethylene terephthalate) films (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 155-168 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Festphasen-Polykondensation von amorphen, unorientierten Poly(ethylenterephthalat)-Folien (PET) (Vorstufe der Du Pont Mylar® -Polyesterfilme), die mit einem speziellen Katalysator-und Monomer-System hergestellt wurden, war Gegenstand dieser Arbeit. Der Einfluß verschiedener Reaktionsparameter, wie Reaktionstemperatur und -zeit, auf die inhärente Viskosität (ηinh) und auf die Anzahl der Carboxy-und Hydroxy-Endgruppen wurde untersucht. Aus den Messungen von ηinh wurde eine empirische Gleichung erstellt, die die Berechnung von M̄n der PET-Folien nach der Festphasen-Polykondensation bei gegebener Zeit und Temperatur erlaubt. Das Schmelzverhalten verschiedener Festphasen-Polykondensate wurde ebenfalls untersucht.
    Notes: The solid-state polycondensation of poly(ethylene terephthalate) (PET) amorphous and unoriented films from Du Pont (precursor for their Mylar® Du Pont's registered trade mark for the polyester film. polyester film) prepared from a specified catalyst and monomer system has been studied. The effect of various reaction parameters such as reaction temperature and time on inherent viscosity (ηinh) and number of carboxy and hydroxy end-groups has been investigated. From ηinh measurements an empirical equation was taken which allows the calculation of (M̄n) of PET film after solid-state polycondensation at a certain temperature and time. The melting behaviour of the solid-state polycondensated samples was also studied.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051920113
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  • 50
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    Preparation and properties of porous particles from trimethylolpropane trimethacrylateSystematic UIPAC name: 2,2-bis(methacryloyloxymethyl)butyl methacrylate. (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 113-132 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Sphärische makroporöse Partikel, die als Trägermaterialen für verschiedene Säulen-Operationen eingesetzt werden sollen, wurden mittels Suspensions- und Mikrosuspensionspolymerisation von Trimethylolpropan-trimethacrylat (TRIM) in Gegenwart verschiedener Mengen porogener Reagenzien (Toluol bzw. Mischungen von Toluol und Isooktan) hergestellt. Textur und Eigenschaften der Partikel variierten deutlich mit dem Anteil und der Zusammensetzung des porogenen Reagens und wurden zusätzlich durch die Wahl des Suspensionstabilisators beeinflußt. Die makroporösen Partikel wiesen ein Gesamtporenvolumen von 0,4 bis 3,6 cm3/g und eine spezifische Oberfläche von 7 bis 〉 450 m2/g auf. Alle Partikel enthielten Makroporen und, außer den Teilchen mit sehr niedriger spezifischer Oberfläche, einen gewissen Anteil an Mikroporen (Durchmesser 〈 60 Å). Durch Erniedrigung der Monomerkonzentration und Erhöhung des Isooktan-Gehaltes im porogenen Reagens auf 50 Gew.-% konnte das Auftreten von Mikroporen vollständig unterdrückt werden. Das Erhöhen des Isooktan-Gehaltes führte zu einem vergrößerten Gesamtporenvolumen und zu einem verringerten Quellvermögen der Polymermatrix in Toluol. Der Einfluß einer Hitzebehandlung bei 130°C und eines Aufpfropfens von Polymethylmethacrylat auf die Partikeleigenschaften wurde ebenfalls untersucht.Die Menge an nicht umgesetzten Doppelbindungen in den Partikeln konnte durch Variation der Polymerisationstemperatur verändert werden. Das Vorhandensein leicht zugänglicher Doppelbindungen ist wichtig, da sie zur Funktionalisierung der festen makroporösen Partikel verwendet werden können.
    Notes: Spherical macroporous particles, intended for use as carrier particles in various types of column operations, were prepared by suspension and microsuspension polymerization of trimethylolpropane trimethacrylate (TRIM), in the presence of various amounts of porogenic agents (toluene or mixtures of toluene and isooctane). The texture and properties of the particles varied markedly with the amount and composition of the porogenic agent, and were also affected by the choice of suspension stabilizer. Macroporous particles were prepared, ranging in total pore volume from 0.4 to 3.6 cm3/g, and in specific surface area from 7 to 〉450 m2/g. All of the particles contained macropores, and except for those with very low specific surface area, contained a certain fraction of micropores (diameter 〈60 Å). The presence of micropores could be eliminated completely by decreasing the monomer concentration and increasing the isooctane content of the porogenic agent to 50 wt.-%. Increasing the isooctane content also resulted in an increase in the total pore volume and a decrease in the tendency of the polymer matrix to swell in toluene. The effect on properties of particles by heat treatment at 130°C and by grafting poly(methyl methacrylate) onto the particles was also studied.The amount of unreacted double bonds of the particles could be varied by varying the polymerization temperature. The presence of easily accessible double bonds is important as they can be utilized for functionalization of the rigid macroporous particles.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051920110
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    Interfacial adhesion in short-fibre composites (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 31-38 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Eine einfache Methode für die Bestimmung der Grenzflächenhaftung in kurzfaserverstärkten Polymeren, beruhend auf der Längenverteilung von aus der Bruchfläche herausgezogenen Faserteilen, wurde entwickelt. Die Messungen mit Faserverbundwerkstoffen von isotaktischem Polypropylen mit 32 Gew.-% Kurzglasfasern bestätigen die Brauchbarkeit dieser Methode für eine empfindliche Beurteilung von Unterschieden in der Grenzflächenhaftung. Die Einflüsse von Temperatur, Polymer- und Glasfasermodifizierung sowie Faserorientierung auf die Grenzflächenhaftung wurden untersucht.
    Notes: For the evaluation of the interfacial adhesion in short-fibre composites, a simple method based on fibre pull-out length distribution was proposed. The experiments with three composites of isotactic polypropylene with 32 wt.-% of short-glass fibres confirm the potentials of the method for a sensitive determination of differences in the interfacial adhesion. The effects of temperature, crystallinity and fibre orientation angle on the interfacial adhesion were investigated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051910103
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  • 52
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    Functionalization of polyethylene and ethylene propylene diene terpolymer in the bulk through dibutyl maleate grafting (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 15-30 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: PE und EPDM-Kautschuk wurden durch Aufpfropfen von Dibutylmaleat (DBM) mit Dicumylperoxid (DCP) als Initiator in Substanz im Temperaturbereich von 140-220°C funktionalisiert. Der Pfropfungsgrad wurde IR-spektroskopisch und durch DSC-Messungen ermittelt. Die für die Pfropfung optimalen DBM- und DCP-Konzentrationen betragen 0,5 bzw. 0,2 Gew.-%. Die Kinetik der Pfropfreaktion ist für PE und EPDM vergleichbar; die Aktivierungsenergien betragen ca. 145 bzw. 130 kJ/mol. Die Pfropfungsgrade sind für PE höher als für EPDM; bei PE/EPDM-Blends steigt der Pfropfungsgrad mit zunehmendem PE-Anteil. Ein Pfropfungsmechanismus, der Nebenreaktionen berucksichtigt, wird vorgeschlagen.
    Notes: Functionalization of polyethylene (PE) and ethylene propylene diene terpolymer (EPDM) in the bulk through dicumyl peroxide (DCP) initiated grafting of dibutyl maleate (DBM) has been studied in the temperature range from 140 to 200°C. The degree of grafting has been determined by infrared spectrophotometry and DSC. The concentration of DBM and DCP has been optimized. 0.5 wt.-% and 0.2 wt.-% DCP for PE and EPDM, respectively, and 10% DBM for both have been found to be the optimum. The kinetics of the grafting reaction is comparable for PE and EPDM. The activation energy of grafting is ca. 145 kJ/mol for PE and ca. 130 kJ/mol for EPDM. The influence of structure of polyolefins on the degree of grafting has also been studied. A higher degree of grafting is obtained for PE than for EPDM. For PE/EPDM blends, the degree of grafting increases with increasing PE content in the blends. A through discussion and proposed mechanism for grafting and other competitive secondary reactions has been provided.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051910102
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  • 53
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    Effect of surface structure of porous silica microballoons on dynamic mechanical properties of amine cured epoxy resin composites (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 71-80 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die dynamisch-mechanischen Eigenschaften von gehärteten Epoxidharzen, gefüllt mit porösen Siliciumdioxid-Mikrokugeln mit unterschiedlichen spezifischen Oberflächen, Porenradien, Porenvolumina und adsorbierter Wassermenge, wurde untersucht. Die Glasubergangstemperaturten (Tg) der Composite sind 12-14°C niedriger als die des ungefullten Harzes, was auf die bevorzugte Adsorption von Härter an den porösen Mikrokugeln zurückgeführt wird. Mit zunehmender adsorbierter Wassermenge steigt die Tg der Composite an. Der Speichermodul ist mit der mit Quecksilber bestimmten spezifischen Oberfläche (Hg-Oberfläche) der Mikrokugeln, die der Summe der Oberfläche von Poren mit einem Durchmesser größer als 4 nm entspricht, korreliert.Das Verbältnis tan δc/tan δm nimmt mit zunehmender Hg-Oberfläche ab.
    Notes: Dynamic mechanical properties were studied for epoxy resin filled with porous silica microballoons with varying surface area, pore radius, pore volume and adsorbed water. The glass transition temperature (Tg) of the composites is 12-14°C lower than the Tg of the unfilled epoxy resin. This Tg depression is attributed to the preferential adsorption of curing agents on the porous silica microballoons. Tg of the composite increases with increase in the adsorbed water on fillers. The storage modulus has a distinct correlation with the Hg-surface area of silica microballoons, which corresponds to the sum of the surface area of pores with radii larger than about 4 nm.Tan δc tan δm decreases with increasing Hg-surface area.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051910105
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  • 54
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    Pervaporation separation of pentane-alcohol mixtures through ionically crosslinked blended membranes. I. Thermal measurements, electron microscopy and tensile studies (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 39-69 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Membranen aus Blends von Nylon 6 mit Poly(acrylsäure) (PAA) mit PAA-Gehalten zwischen 25 und 45 Gew.-% wurden durch Filmgießen hergestellt und anschließend durch Eintauchen in eine Aluminiumsalzlösung ionisch vernetzt. Die Glasübergangstemperaturen (Tg) der Membranen wurden mit der DSC-Methode bestimmt. Alle Proben zeigen eine einzige Tg oberhalb der Tg der Homopolymeren, die sich mit zunehmender Scanzeit verschiebt; dies wird auf die Eliminierung von Wasser und die Bildung von Anhydriden im nicht vernetzten PAA-Anteil zurückgeführt.Die Morphologie wurde rasterelektronenmikroskopisch untersucht; die Membranen zeigen eine dichte, porenfreie Struktur ohne Phasenseparation, was auf eine völlige Mischbarkeit der beiden Homopolymeren im untersuchten Zusammensensetzungsbereich schließen läßt. Die Festigkeit der Membranen liegt je nach PAA-Gehalt zwischen 5 und 26 MPa; Membranen mit hohem PAA-Anteil zeigen trotz höherer Vernetzungsdichte eine geringere Zugfestigkeit, was mit der geringen Festigkeit von PAA und der mit größerem PAA-Anteil zunehmenden Quellung zusammenhängt. Letztere wurde durch Messen der Wasseraufnahme trockener Membranen bestimmt; sie steigt von 23,6 Gew.-% bei einem PAA-Gehalt von 25 auf 76,3 Gew.-% bei einem PAA-Gehalt von 45 Gew.-%.
    Notes: Ionically crosslinked blended membranes were prepared from blends of nylon 6 and poly(acrylic acid) (PAA) with the proportion of PAA ranging from 25 to 45 wt.-%. The technique consists of casting a film of the blend, followed by drying and immersion in an aluminum salt crosslinking solution for a predetermined time. The glass transition temperature (Tg) of the membranes was determined by differential scanning calorimetry (DSC). All the samples exhibited a single Tg, which is higher than that of either polymer. There is also a shift in the Tg with increasing scanning time. This phenomenon is attributed to the elimination of water molecules and the formation of anhydrides in the non-crosslinked PAA portion of the membrane. The membrane morphology was studied using scanning electron microscopy (SEM) and shows a dense structure without any pores. No phase separation is observed by scanning cross-sections of the samples, indicating that nylon 6 and PAA are completely miscible in the ranges studied. The membrane material strength lies in the range of 5 to 26 MPa and varies with the amount of PAA in the membrane. Samples with higher PAA content show lower tensile strength in spite of increased crosslinking density. This is due to the inherent low strength of PAA, coupled with increasing swelling of the membrane with increasing PAA content. The latter is confirmed by the measurement of water uptake into a dry membrane which increases from 23.6% to 76.3% with the membrane PAA content increasing from 25 to 45 wt.%.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051910104
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    Mehrphasensysteme auf basis von fluorpolymeren, 1. Modifizierung von füllstoffoberflächen (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 81-107 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Practically no adhesion is observed at the interface poly(tetrafluoroethylene)/glass fiber. We have investigated methods to improve adhesion between these interfaces. We have also discussed the question of possible reinforcement, i.e. increase of tensile strength and a simultaneous decrease of elongation.In this first part we present some calculations demonstrating the prerequisites for reinforcement using existing theoretical models. We describe the influence of modification of the glass fiber surface by dispersion coating or by plasma polymerization.In a second part the influence of polymer surface modification and of additives will be dealt with.
    Notes: In Mehrphasensystemen aus Poly(tetrafluorethylen) (PTFE) und Glasfasern besteht praktisch keine Haftung zwischen Matrix und Füllstoff. Es wurde der Frage nachgegangen, ob es Wege zur Verbesserung der Grenzflächenhaftfestigkeit gibt und ob diese Verbesserungen ausreichen, eine Verstärkung, d. h. Anhebung der Reißfestigkeit bei gleichzeitigem Rückgang der Dehnung des Gesamtsystems zu erzielen.In diesem ersten Teil wird den theoretischen Voraussetzungen und der Modifizierung der Füllstoffoberflächen mittels Dispersionsbeschichtungen sowie Plasmaätzen und Plasmapolymerisation nachgegangen.In einem zweiten Teil werden Möglichkeiten zur Verbesserung der Grenzflächenhaftung durch Modifizierung der Polymer-Oberfläche und durch Additive untersucht.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051910106
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  • 56
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    Mehrphasensysteme auf basis von fluorpolymeren, 2Teil 1 siehe1.. Modifizierung der polymermatrix (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 109-126 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Practically no adhesion is observed at the interphase of poly(tetrafluoroethylene)/glass fiber. We have investigated methods to improve this adhesion and discuss the influence of this improved adhesion on the mechancial properties of the multiphase system.In this paper the influence of a modified polymer surface and of additives is described.
    Notes: In Mehrphasensystemen aus Poly(tetrafluorethylen) (PTFE) und Glasfasern besteht praktisch keine Haftung zwischen Matrix und Füllstoff.Es wurde die Frage untersucht, ob es Methoden gibt, diese Grenzflächenhaftung zu erhöhen und welchen Einfluß diese Erhöhung auf die Eigenschaften des Verbundsystems hat.In dem hier vorliegenden Teil 2 wird speziell auf den Einfluß der Modifizierung der Polymeroberfläche und des Zusatzes von Additiven eingegangen.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051910107
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    Zur reaktionstechnischen und fluiddynamischen stabilität von multirohrreaktoren für die massepolymerisation (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 127-144 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Due to the very strong variation of the viscosity of the reaction mass with increasing monomer conversion, three stationary states for the tubes of a multitubular system with cooling vessel can be found. As a consequence, a maldistribution of the fluid arises, so that the reactor stability and the polymer quality are negatively influenced. The recycling of the reaction mass is a helpful method to increase the reactor stability. In this paper some fundamental aspects of the use of multitubular reactors for the polymerization of styrene are studied.
    Notes: Infolge der sich mit steigendem Monomerumsatz stark verändernden Viskosität der Reaktionsmasse existieren im Multirohrreaktor mit Kühlung mindestens drei stationaäre Punkte bezüglich des Einzelrohrmassenstromes gleichzeitig. Als Konsequenz ergibt sich eine Ungleichverteilung der Rohrbelastung, die sowohl die Reaktorstabilität als auch die Polymerqualität negativ beeinflußt. Das Betreiben einer Rückführung kann das Reaktorverhalten stabilisieren. In der vorgelegten Arbeit werden einige fundamentale Aspekte der Anwendung von Multirohrreaktoren für die Massepolymerisation von Styrol untersucht.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051910108
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    Nucleophilic substitution reaction of ethanolamine onto poly(phenyl acrylate) and substituted poly(phenyl acrylate)s (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 171-176 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die nucleophile Substitution von verschieden substituierten Phenoxygruppen in Polyphenylacrylaten durch Ethanolamin in Dioxan wurde bei 60, 80 und 100°C untersucht. Der Umsatz wurde IR- und 1H-NMR-spektroskopisch und elementaranalytisch bestimmt; er hängt sowohl von der Temperatur als auch von der Art der Substituenten am Phenylring ab.
    Notes: The nucleophilic substitution reaction of differently substituted phenoxy groups with ethanolamine in various poly(phenyl acrylate)s was investigated in dioxane at 60, 80, and 100°C. The conversion, as determined from IR- and 1H-NMR spectroscopy and elemental analysis, depends on the temperature and the kind of substituents at the phenyl ring.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051910111
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    Masthead (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360310101
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    Heteronuclear two-dimensional 15N- and 13C-nmr studies of DNA oligomers and their netropsin complexes using indirect proton detection (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 45-55 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heteronuclear multispin coherence proton-detected two-dimensional nmr spectroscopic experiments were used to obtain information on protonated carbons and nitrogens of the self-complementary d (G-G-T-A-T-A-C-C) and d (G-G-A-A-T-T-C-C) duplexes, with and without the drug netropsin dissolved in aqueous solution. Many correlations of protons coupled to 13C nuclei on the base and sugar rings of the octanucleotides were detected, allowing the carbon resonances to be assigned based on previous homonuclear proton two-dimensional nmr studies. Imino nitrogen assignments can also be made using the proton assignments from previous one-dimensional nuclear overhauser effect experiments. Imino nitrogen shifts may be useful indicators of changes in local hydrogen-bonding interactions to base-pair edges.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310105
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    Polyelectrolyte properties of biopolymers: Conductivity and secondary structure of polyriboadenylic acid and its salts in solutions (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 65-76 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polyriboadenylates of alkali metals were obtained from (1) K+-poly(A) (salts I) and (2) H+-poly( A) (salts II) by the ion-exchange method. The conductivity of these salts as well as of H+-poly(A) were studied. Salts I and II of the same counterion were shown to have significantly different conductivity coefficients (f) and polyion conductances (λp0). The charge density parameter (ζ) was 1.3 and 2.5, respectively, with λp0 equal to 44 and 83 ohm-1 cm2 mole-1 for poly(A)-I and poly (A)-II salts, respectively. This is credited to the difference in the conformations of corresponding polyions. The linear dependence of equivalent conductivity on the square root of polymer concentration (Kohlrausch coordinates), earlier obtained for DNA, is also satisfied for the studied polynucleotides. A comparison of the slopes of straight lines in Kohlrausch coordinates for poly(A), simple electrolytes, and for earlier studied polyribouridylic acid salts lends credence to the concepts, developed by a number of authors, that DNA can act as a “buffer” against the ion-ion interaction in concentrated electrolyte solutions. Using the approximation that the polyion conductance is independent of the counterion nature, parameter f (agreeing in this case with Eisenberg parameter φ) has been shown to decrease as the polynucleotide concentration is increased; the decrease is caused by the relaxation effect. The transference numbers of counterions, which have negative values in poly (A)-II solutions, grow with the increase in polymer concentration; the higher the ζ, the more apparent is this increase. This is explained by the increase in the fraction of conductivity along the polyion chains (“surface” conductivity) with the growth of polyelectrolyte concentration.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310107
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    Study of the “molten globule” intermediate state in protein folding by a hydrophobic fluorescent probe (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 119-128 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Binding of the hydrophobia fluorescent probe, 1-anilino-naphthalene-8-sulfonate (ANS), to synthetic polypeptides and proteins with a different structural organization has been studied. It has been shown that ANS has a much stronger affinity to the protein “molten globule” state, with a pronounced secondary structure and compactness, but without a tightly packed tertiary structure as compared with its affinity to the native and coil-like proteins, or to coil-like, α-helical, or β-structural hydrophilic homopolypeptides.The possibility of using ANS for the study of equilibrium and kinetic molten globule intermediates is demonstrated, with carbonic anhydrase, β-lactamase, and α-lactalbumin as examples.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310111
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    Premelting thermal fluctuational base pair opening probability of poly(dA) · poly(dT) as predicted by the modified self-consistent phonon theory (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 139-148 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We employ a mean field, modified, self-consistent phonon theory to evaluate the single base-pair opening rate and the probability of a base pair in the amino proton exchangeable state for the homopolymer poly(dA) · poly(dT) at temperatures below the helix-coil transition region. Our calculated premelting single base-pair opening probabilities are in general agreement with several available experimental estimates from imino proton exchange and formaldehyde-induced DNA melting measurements. These calculated opening probabilities, however, are in disagreement with the prediction of the helix-coil transition theory. Possible reasons for the differences are discussed, especially the possible different definition of a meaningful open state in the premelting region. The premelting open state of the modified self-consistent phonon approximation theory seems to be appropriate to describe a solvent-accessible open configuration that is sufficient to facilitate important chemical reactions such as imino proton exchange and formaldehyde reaction with the bases. This can be compared with the completely unstacked open state of the helix-coil transition theory originally defined in the helix-coil transition region. We propose that the amino proton exchangeable state is different from the open state associated with melting and only involves the breaking of the amino interbase H bond. The agreement between the calculated and experimentally estimated probability of a base pair in the amino proton exchangeable state seems to support this hypothesis.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310202
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    Shielding effects of small ions in gel electrophoresis of DNA (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 169-176 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Results of free electrophoresis and free sedimentation of charged rods are introduced to allow for electrical double-layer effects in the gel electrophoresis of DNA, modeled as a Random flight sequence of rodlike Kuhn chain elements. The kinetics of DNA is shown to depend strongly on the orientation of the chain elements with respect to the external field and with respect to the direction of their velocity. The new theory gives approximate agreement between the DNA charge derived from electrophoresis of free and tethered DNA (close to 1.0e per DNA phosphate in both cases), compared with the earlier discrepancy of a factor 10 or 20 for the theory without shielding by salt. As part of a realistic force field for macromolecular dynamics simulation, the small ion effects are included in an expression for the gel forces restraining the DNA in gel electrophoresis from moving as in free electrophoresis.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310205
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    A molecular dynamics study of the effect of G · T mispairs on the conformation of DNA in solution (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 211-232 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of G · T mispair incorporation into a double-helical environment was examined by molecular dynamics simulation. The 60-ps simulations performed on the two hexanucleotide duplexes d (G3C3)2 and d (G3TC2)2 included 10 Na+ counterions and first hydration shell waters. The resulting backbone torsional angle trajectories were analyzed to select time spans representative of conformational domains. The average backbone angles and helical parameters of the last time span for both duplexes are reported. During the simulation the hexamers retained B-type DNA structures that differed from typical A- or B-DNA forms. The overall helical structures for the two duplexes are vary similar. The presence of G · T mispairs did not alter the overall helical structure of the oligonucleotide duplex. Large propeller twist and buckle angles were obtained for both duplexes. The purine/pyrimidine crossover step showed a large decrease in propeller twist in the normal duplex but not in the mismatch duplex. Upon the formation of wobble mispairs in the mismatched duplex, the guanines moved into the minor groove and the thymines moved into the major groove. This helped prevent purine/purine clash and created a deformation in the relative orientation of the glycosidic bonds. It also exposed the free O4 of the thymines in the major groove and N2 of the guanines in the minor groove to interactions with solvent and counterions. These factors seemed to contribute to the apparently higher rigidity of the mismatched duplex during the simulation.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310209
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    Biased sinusoidal field gel electrophoresis for size-dependent DNA separation (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 253-254 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360310212
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    Evidential study of correlated events in biochemistry: Physicochemical mechanisms of nucleic acid hydration as revealed by factor analysis (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 255-273 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using a factor analysis technique, the experimental physicochemical data on the hydration of mononucleotides, several polynucleotides, their double-helical complexes and natural DNAs were studied. The information about the factors determining the changes in physicochemical parameters vs the hydration was obtained. This work discusses a possible physical sense of the factors obtained and the expedience of using factor analysis to interpret the molecular-biophysical experiments.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310302
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    The Electrostatically Driven Monte Carlo method: Application to conformational analysis of decaglycine (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 319-330 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Electrostatically Driven Monte Carlo (EDMC)method was applied in a study of a decamer of glycine whose conformational behavior is described by the Empirical Conformational Energy Program for Peptides (ECEPP/2) potential energy model. When free neutral end groups were used, it was found that conformations that were not α-helical had significantly lower potential energies than fully α-helical ones. However, when the N- and C-termini were blocked by acetyl and methyl amide groups, respectively, the number of unsatisfied hydrogen-bond donors and acceptors at the helix termini was diminished from 8 to 6; in this case, the possibility of forming two additional α-helical hydrogen bonds was an important enough factor in making the α-helical conformation the one with the lowest energy. The EDMC method was used as a global energy optimizer since it does not often become trapped in high-energy local minima.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310306
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    1H- and 31P-nmr studies of ditercalinium binding to a d(GCGC)2 and d(CCTATAGG)2 minihelices: A sequence specificity study (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 331-353 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structures of the complexes formed in aqueous solution between ditercalinium, a bisintercalating drug, and both the self-complementary tetranucleotide d(GCGC)2 and octanucleotided(CCTATAGG)2, have been investigated by 400-MHz 1H-nmr and 162-MHz 31P-nmr. All the nonexchangeable protons, as well as the exchangeable imino protons and the phosphorus signals, have been assigned. Both oligonucleotides have been shown to adopt a right-handed B-DNA type structure. The addition of ditercalinium to the oligo-nucleotides lead to the formation of complexes in slow exchange at the nmr time scale with the free helices. At all drug-to-helix ratios studied, the ditercalinium was found in the bound form, whereas free and complexed oligonucleotides were in slow exchange, allowing resonance assignments through two-dimensional chemical exchange experiments.For d(GCGC)2 the strong upfield shifts induced on all aromatic protons of both the bases and the drug by complexation with ditercalinium suggest an interaction by intercalation of the two rings. However, the loss of twofold symmetry upon binding, as well as the chemical shift variation of the drug proton signals of one of the chromophores with temperature and concentration, favor a model in which the drug-nucleotide complexes have one ring of the drug intercalated and the other stacked on top of the external base pair. The intermolecular contacts between drug protons and nucleotide protons give a defined geometry for complexation that is consistent with the proposed model.In contrast, with d(CCTATAGG)2 several drug-nucleotide complexes were formed and a large increase in line broadening was observed at high drug-to-DNA ratios, precluding a detailed analysis of these complexes. However, the large upfield shift in the imino proton resonances together with the shielding of the ditercalinium ring protons favor a model with bis-intercalation of ditercalinium. This model is supported by the downfield shift of at least 4 out of 14 phosphorus signals. The results are compared with those obtained on ditercalinium binding to the homologous sequences d(CGCG)2 and d(TTCGCGAA)2, and discussed in terms of sequence specificity.
    Additional Material: 24 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310307
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    A sequence preference for nucleation of α-helix - crystal structure of Gly-L-Ala-L-Val and Gly-L-Ala-L-Leu: Some comments on the geometry of leucine zippers (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 397-407 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthetic peptide Gly-L-Ala-L-Val (C10H19N3O4·3H2O; GAV) crystallizes in the monoclinic space group P21, with a = 8.052(2), b = 6.032(2), c = 15.779(7) Å, β = 98.520(1)°, V = 757.8 Å3, Dx = 1.312 g cm-3, and Z = 2. The peptide Gly-L-Ala-L-Leu (C11H21N3O4·3H2O; GAL) crystallizes in the orthorhombic space group P212121, with a = 6.024(1), b = 8.171(1), c = 32.791(1) Å, V = 1614 Å3, Dx = 1.289 g cm-3, and Z = 4. Their crystal structures were solved by direct methods using the program SHELXS-86, and refined to an R index of 0.05 for 1489 reflections for GAV and to an R index of 0.05 for 1563 reflections for GAL. The tripeptides exist as a zwitterion in the crystal and assume a near α-helical backbone conformation with the following torsion angles: ψ1 = -150.7°; φ2, ψ2 = -68.7°, -38.1°; φ3, ψ31, ψ32, = -74.8°, -44.9°, 135.9° for GAV; ψ1 = -150.3°; φ2, ψ2 = -67.7°, -38.9°; φ3, ψ31, ψ32 = -72.2°, -45.3°, 137.5°, for GAL. Both the peptide units in both of the tripeptides show significant deviation from planarity [ω1 = -171.3(6)° and ω2 = -172.0(6)° for GAV; ω1 = -171.9(5)° and ω2 = -173.2(6)° for GAL]. The sidechain conformational angles χ21 and χ22 are -61.7(5)° and 175.7(5)°, respectively, for valine, and the side-chain conformations χ12 and χ23's are -68.5(5)° and (-78.4(6)°, 159.1(5)°) respectively, for leucine. Each of the tripeptide molecule is held in a near helical conformation by a water molecule that bridges the NH3+ and COO- groups, and acts as the fourth residue needed to complete the turn by forming two hydrogen bonds. Two other water molecules form intermolecular hydrogen bonds in stabilizing the helical structure so that the end result is a column of molecules that looks like an α-helix.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310405
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    Mobility models for stiff and flexible macromolecules in dilute gels (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 435-447 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effective sphere approximation for modeling electrophoretic transport of macromolecules in highly porous gels (the “Ogston model”) is examined, and contrasted with similar mobility models for stiff and flexible solutes. Calculation of segmental depletion near gel obstacles of various shapes demonstrates the limited applicability of the effective sphere approach. For highly flexible chains, both theory and experiment reveal a nonunique mapping between mobility and molecular size when the molecular radius is comparable to that of gel fibers. Turning to mobility behavior in more concentrated gels, neither flexible or stiff macromolecules behave as spheres; for the particular case of flexible chains, the presence of entropic barriers in concentrated gels can be understood in terms of a simple random planes model for the gel structure.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310409
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    Differential scanning calorimetry studies of NaCl effect on the inverse temperature transition of some elastin-based polytetra-, polypenta-, and polynonapeptides (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 465-475 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Differential scanning calorimetry studies of the effect of NaCl on protein-based polymer self-assembly has been carried out on six elastin-based synthetic sequential polypeptides- i.e., the polypentapeptide (L-Val1-L-Pro2-Gly3-L-Val4-Gly5)n and its more hydrophobic analogues (L-Leu1-L-Pro2-Gly3-L-Val4-Gly5)n and (L-Val1-L-Pro2-L-Ala3-L-Val4-Gly5)n; the polytetrapeptide (L-Val1-L-Pro2-Gly3-Gly4)n and its more hydrophobic analogue (L-IIe1-L-Pro2-Gly3-Gly4)n; and the polynonapeptide (a pentatetra hybrid), (L-Val1-L-Pro2-Gly3-L-Val4-Gly5-L-Val6-L-Pro7-Gly8-Gly9)n.Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order of the polypentapeptide, as the temperature is raised from below to above that of the transition, has been repeatedly observed using different physical characterizations.In the present experiments, it is observed that the transition temperatures of the polypeptides studied are linearly dependent on NaCl concentration. The molar effectiveness of NaCl in shifting the transition temperature ΔTm/[N], is about 14°C/[N], with the dependence on peptide hydrophobicity being fairly small. Interestingly, however, the δΔQ/ [N] does depend on the hydrophobicity of a polypeptide.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310502
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    Masthead (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360310801
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    A molecular dynamics study of thermodynamic and structural aspects of the hydration of cavities in proteins (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 919-931 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and activity of a protein molecule are strongly influenced by the extent of hydration of its cavities. This is, in turn, related to the free energy change on transfer of a water molecule from bulk solvent into a cavity. Such free energy changes have been calculated for two cavities in a sulfate-binding protein. One of these cavities contains a crystallo graphically observed water molecule while the other does not. Thermodynamic integration and perturbation methods were used to calculate free energies of hydration for each of the cavities from molecular dynamics simulations of two separate events: the removal of a water molecule from pure water, and the introduction of a water molecule into each protein cavity. From the simulations for the pure water system, the excess chemical potential of water was computed to be -6.4 ± 0.4 kcal/mol, in accord with experiment and with other recent theoretical calculations. For the protein cavity containing an experimentally observed water molecule, the free energy change on hydrating it with one water molecule was calculated as -10.0 ± 1.3 kcal/mol, indicating the high probability that this cavity is occupied by a water molecule. By contrast, for the cavity in which no water molecules were experimentally observed, the free energy change on hydrating it with one water molecule was calculated as 0.2 ± 1.5 kcal/mol, indicating its low occupancy by water. The agreement of these results with experiment suggests that thermodynamic simulation methods may become useful for the prediction and analysis of internal hydration in proteins.
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    URL: http://dx.doi.org/10.1002/bip.360310802
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    Topographical requirements for δ-selective opioid peptidesAbbreviations: All amino acids are of the L variety unless otherwise stated. Abbreviations for amino acid residues follow those recommended by the IUPAC. Other abbreviations include the following: DPDPE. enkephalin, H-Tyr-D- Pen, penicillamine or β,β-dimethylcysteine; DCFPE, DRE, dermen kephalin, H-Tyr-D-Met-Phe-His-Leu-Met-Asp-NHg; DPLPE, DSLET, H-Tyr-D-Ser-Gly-Phe-Leu-Thr-OH; DSTBULET, H-Tyr-D-Ser(OtBu)-Gly-Phe-Leu-Thr-OH; BUBU, H-Tyr-D-Ser(OtBu)-Gly-Phe-Leu-Thr(OtBu)-OH; DAGO, [D -ala2, N-MePhe4, Gly5]enkephalin-OL. (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 941-955 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational possibilities of three different δ-selective opioid peptides, which are DPDPE , and DRE (Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2, dermenkephalin), were explored using energy calculations. Sets of low-energy conformers were obtained for each of these peptides. The sets consisted of 61 structures for DPDPE, 32 for DCFPE, and 38 for DRE, including various types of rotamers of the Tyr and Phe side-chain groups. Comparison of the geometrical shapes of the conformers was performed for these sets using topographical considerations, i.e., examination of the mutual spatial arrangement of the N-terminal α-amino group, and of the Tyr and Phe side-chain groups. The results obtained suggest a model for the δ-receptor-bound conformer(s) for opioid peptides. The model suggests the placement of the Phe side chain in a definite position in space corresponding to the g- rotamer of Phe for peptides containing Phe4 and to the t rotamer for peptides containing Phe.3 The position of the Tyr1 side chain cannot be specified so precisely. The proposed model is in a good agreement with the results of biological testing of β-Me-Phe4-substituted DPDPE analogues that were not considered in the process of model construction.
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    Conformational analysis of two cyclic disulfide peptides (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 835-843 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complete nmr and CD studies of two cyclic tetrapeptides with disulfide bonds, 1 and 2 bonds have been carried out in different solvents to investigate the formation and stabilization of β-turn structures and to determine the stereochemistry of the disulfide linkage. Both peptides have three-dimensional structures with a type II β-turn, as derived from quantitative nuclear Overhauser effect data. The combined use of CD and nmr indicates that the dihedral angle of the disulfide bridge is different in the two peptides, although the chirality is maintained.
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    URL: http://dx.doi.org/10.1002/bip.360310704
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    Time-Resolved study of network self-organization from a biopolymeric solution (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 859-868 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Time-resolved studies of network self-organization from homogeneous solutions of the representative biostructural polymer agarose are presented. Solutions are temperature quenched and observed by several techniques. Consistent with previous suggestions by the authors, experiments at concentrations up to about 1.75% w/v provide direct kinetic evidence for the occurrence of at least two distinct processes, leading, in sequence, to self-assembly. These are as follows: (a) a liquid-liquid phase separation of the solution occurring via spinodal demixing and resulting in two sets of regions that have, respectively, higher and lower than average concentrations of random-coiled polymers; and (b) the subsequent 2 coils → double helix transition and accompanying cross-linking and gelation (due to branching of double helices), occurring in the high-concentration regions. The size of the high-concentration regions depends upon agarose concentration and quenching temperature, and is in the range from a fraction of micrometers to a few micrometers, in agreement with earlier experiments. Bundling of the double-helical segments is known to follow self-assembly and can be considered as a third step (gel curing). This follows from the thermo-dynamic instability of the helical segments in the solvent, behaving as a system of rod-like particles connected by more or less flexible joints.The two processes leading in succession to self-assembly are discussed in terms of a phase diagram consistent with available data. Their time scales differ remarkably. At the end of the first process, all polymers remain random coiled and freely drifting. Much later coil-helix transition is observed, always in coincidence with polymer cross-linking and gelation. The enhancement of concentration of random-coiled polymers in specific regions of the sol caused by spinodal demixing is thus a prerequisite for self-assembly of these biostructural gels in the concentration interval studied. Conceptually, concentration enhancements of this type can provide a new pathway for promotion of functional biomolecular interactions even at very low average concentrations. The mechanism will work identically if the region of instability is reached by varying the polymer concentration (e.g., by biosynthesis), rather than by temperature quenching.
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    URL: http://dx.doi.org/10.1002/bip.360310706
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    Molecular and crystal structures of Aib-containing oligopeptides Boc-Leu4-Aib-Leu4-OBzl and Boc-(Leu4-Aib)2-OBzl (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 975-985 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sample peptides Boc-Leu4-Aib-Leu4-OBzl and Boc-(Leu4-Aib)2-OBzl, were crystallized by the solvent-evaporation method. Both crystals are monoclinic, with space group of P21 and Z = 2. The cell parameters are a = 16.580(7), b = 21.105(7), c = 11.583(4) Å, and β = 104.90(3)° (Boc-Leu4-Aib-Leu4-OBzl), and a = 15.247(9), b = 19.04(l), c = 16.311(9) Å, and β = 117.10(1)° [Boc-(Leu4-Aib)2-OBzl]. Crystal structures were solved by the direct method and refined to R values of 0.096 (the former peptide) and 0.112 (the latter). Peptide backbones fold into a right-handed α-helix, except for the C-terminal Aib residue in Boc-(Leu4-Aib)2-OBzl. Both peptide molecules are stabilized by six (the former) or seven (the latter) intramolecular (5 → 1) hydrogen bonds, and arranged in the head-to-tail fashion, which makes an infinite column. In this column, one (the former) or two (the latter) intermolecular hydrogen bonds link the neighboring molecules. In the case of Boc-Leu4-Aib-Leu4-OBzl, the solvent molecule N, N-dimethylformamide was found in the difference Fourier map. There was a hydrogen bond between peptide and solvent molecule. Along the lateral direction, only hydrophobic contacts were observed between adjacent peptide molecules.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360310807
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    Masthead (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360310901
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  • 80
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    Ionization of clusters. IV. Cooperativity and allosterism derived from shared clusters in macromolecules (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1037-1047 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Clusters of ionizable groups are examined for conditions that develop cooperativity (1) on the binding of protons, and (2) on the binding of an associated ligand when the clusters are shared between domains or subunits in macromolecules. Cooperative binding isotherms for protons have long been observed (but not emphasized as cooperative binding) when studies have been done on clusters for the evaluation of metal ion complexation [A. E. Martell & M. Calvin (1952) Chemistry of the Metal Chelate Compounds, Prentice-Hall, Englewood Cliffs, New Jersey]. Reactions are formulated in this paper to show that anions, chelating to positively charged clusters, are also capable of developing the cooperative binding of protons. Extension of these simple reactions to those where clusters of ionizable groups are shared between domains of macromolecules provides models for cooperative binding, which include the allosteric, Bohr, anion, and cation effects in proteins.
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    URL: http://dx.doi.org/10.1002/bip.360310904
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    Mass-weighted molecular dynamics simulation of cyclic polypeptides (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1077-1086 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A modified molecular dynamics (MD) method in which atomic masses are weighted was developed previously for studying the conformational flexibility of neuroregulating tetra-peptide Phe-Met-Arg-Phe-amide (FMRF-amide). The method has now been applied to longer and constrained molecules, namely a disulfide-linked cyclic hexapeptide, c [CYFQNC], and its linear and [pseudo-cyclic] analogues. The sampling of dihedral conformational space of the linear hexapeptide in mass-weighted MD simulations was found to be improved significantly over conventional MD simulations, as in the case of the shorter FMRF-amide molecule studied previously. In the cyclic hexapeptide, the internal constraint of the molecule due to the intramolecular disulfide bond (hence the absence of free terminals in the molecule) does not adversely affect the significant improvement of conformational sampling in mass-weighted MD simulations over normal MD simulations. The pseudo-cyclic polypeptide is identical to the linear CYFQNC molecule in amino acid sequence (i.e., side chains of the cysteine residues are reduced), but the positions of its two terminal heavy atoms were held fixed in space such that the molecule has a nearly cyclic conformation. For this molecule, the mass-weighted MD simulation generated a wide range of polypeptide backbone conformations covering the internal dihedral degrees of freedom; moreover, the physical space of the pseudo-cyclic structure was also sampled in a complete revolution of the entire molecular fragment about the two fixed termini during the simulation. These characteristics suggest that mass-weighted MD can also be an extremely useful method for conformational analyses of constrained molecules and, in particular, for modeling loops on protein surfaces.
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    URL: http://dx.doi.org/10.1002/bip.360310907
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    Intercalation binding of 6-substituted naphthothiopheneamides to DNA: Enthalpy and entropy components (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1105-1114 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-(3-dimethylaminopropyl) naphtho [2, 1-b] thiophene-4-carboxamide and the 6-substituted methoxy, methyl, fluoro, chloro, bromo, trifluoromethyl, and cyano derivatives have been shown to bind to DNA via intercalation with binding constants in the 35-900 × 103 range at 25°C, pH 7, and [Na+] = 0.019M . Both electron-donating and -withdrawing substituents enhance intercalation binding, but the binding affinity is most enhanced by the cyano substituent. Calorimetric titrations for calf thymus DNA differ dramatically from those reported for ethidium [Hopkins et al. (1990) Biopolymers Vol. 29, pp. 449-459]. Apparent enthalpy parameters (ΔHB) for intercalation are constant only at low coverage of sites and become much more positive as saturation is approached. In the plateau region, ΔHB values for the parent and the cyano-, fluoro-, chloro-, and bromo-substituted compounds are nearly the same (∼ -5.9 kcal/mol). For the methyl- (-6.8 kcal/mol) and methoxy- (-7.5 kcal/mol) substituted compounds, the ΔHB values are more exothermic than that for the un-substituted compound, whereas ΔHB for the trifluoromethyl compound is approximately 1 kcal/mol less exothermic. The corresponding ΔSB values, corrected for mixing effects, are in the 7-15-cal/deg/mol range and are approximately linearly related to ΔHB if the cyano derivative is excluded.
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    URL: http://dx.doi.org/10.1002/bip.360310910
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    Differential behavior of the two free sulfhydryl groups of human plasma fibronectin: Effects of environmental factors (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1159-1170 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report here a novel approach to label specifically one of the two cryptic, free sulfhydryl groups per subunit of human plasma fibronectin with either an 15N, 2H-maleimide spin label or a coumarinylphenyl maleimide fluorescent label. This permits the use of electron spin resonance (ESR) or fluorescence techniques to study molecular dynamics of fibronectin with the label attached to a single site per chain on the protein molecule. The method is based on our observation that upon adsorption of fibronectin to a gelatin-coated surface, the SH1 site, located between the DNA-binding and the cell-binding domains, is partially exposed, while the SH2 site, located within the carboxyl-terminal fibrin-binding domain, remains buried and unreactive. The procedures for the preparation of the selectively labeled fibronectins are described in detail. The physicochemical properties of these single-site labeled fibronectins, particularly as affected by high salt, heparin, surface binding, and temperature, were characterized by ESR spin-label and steady-state fluorescence techniques. The steady-state fluorescence measurement indicates that both local environments of SH1 and SH2 sites are relatively hydrophobic, and that the SH2 site is more hydrophobic than the SH1 site. The ESR results show that heparin or high salt induces an increase in the domainal flexibility in both SH1 and SH2 regions, perhaps through the disruption of domain-domain interactions in the fibronectin molecule, and that the former is more effective than the latter in producing such an effect. The observed heparin effect is reversible by addition of calcium ions in the SH2 regions but not in the SH1 regions. In addition, at temperatures above 44°C, both type III homologous regions containing the free sulfhydryl groups are shown to undergo denaturation and aggregation processes. The data presented here suggest that the newly developed method for differential labeling of the free sulfhydryl groups in fibronectin should be useful for mapping the spatial arrangement of structural domains in the protein molecule using spin-label-spin-probe and fluorescence energy transfer techniques.
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    URL: http://dx.doi.org/10.1002/bip.360311004
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    Experimental and theoretical studies of DNA separations by capillary electrophoresis in entangled polymer solutions (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1221-1228 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Studies of electrophoretic separations of DNA restriction fragments by capillary electrophoresis in solutions of (hydroxyethyl) cellulose (HEC) were performed. Rheological studies were used to confirm that the entanglement threshold (Φ*) for the HEC solutions used is approximately 0.004 g/mL, in good agreement with theoretical predictions. A mesh size an order of magnitude smaller than that found in agarose gels (on a per weight basis) was calculated using polymer-entanglement theory and was confirmed by electrophoretic measurements. Electrophoretic migration was shown to follow the Ogston regime under most conditions. An approach for obtaining smaller mesh sizes is presented.
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    URL: http://dx.doi.org/10.1002/bip.360311010
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  • 85
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    Masthead (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311101
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  • 86
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    Probe diffusion in solutions of filamentous actin formed in the presence of gelsolin (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1265-1271 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dynamic light scattering was used to characterize the diffusion of monodisperse polystyrene latex spheres (PLS) of different sizes (55-, 105-, and 265-nm radii) in column-purified 0.65 mg/mL actin solutions polymerized with 100 mM KCl in the absence and presence of various amounts of the actin-binding protein gelsolin. The gelsolin and its interaction with actin was initially studied to ensure that the gelsolin could be used to produce filament populations with well-defined mean lengths. Measurements with PLS diffusion probes present showed, in the absence of gelsolin, that the effective local microviscosity in the actin solutions was 5-20 times that of water and that a large fraction of the PLS are trapped within the pores of the actin filament network, as found previously [J. Newman, K. L. Schick, & K. S. Zaner, (1989) Biopolymers 28, 1969-1980]. As the molar ratio of gelsolin to actin was increased, the diffusion coefficients of the PLS approached those in pure water while the degree of PLS trapping went to zero. Measurements of the dependence of the PLS diffusion coefficients on the ratio of actin concentration to the semidilute overlap concentration showed, for the smaller PLS, a transition occurring near the mean global overlap concentration. These results reflect the dissolution of the actin network as the gelsolin concentration is increased and illustrate the role of gelsolin/actin interactions in the control of macromolecular transport within the periphery of cells.
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    URL: http://dx.doi.org/10.1002/bip.360311104
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    A reexamination of 25Mg2+ nmr in DNA solution: Site heterogeneity and cation competition effects (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1343-1346 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360311111
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    Drug-DNA interactions: Spectroscopic and footprinting studies of site and sequence specificity of elliptinium (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1325-1341 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The binding of the antitumoral ellipticine derivative 2-methyl-9-hydroxyellipticinium acetate (elliptinium; NMHE) to DNA was analyzed by the combined use of DNase I foot-printing and spectroscopic methods. Using two fragments of pBR322 DNA, five discrete NMHE binding sites of 5-7 protected base pairs (bp) were detected by footprinting at 4°C on the analyzed regions. These corresponded to alternating pyrimidines and purines. The inactive derivative 2-methyl ellipticinium acetate L(NME) lacking a hydroxy group failed to demonstrate DNA protection even at low temperature. Ultraviolet-absorption and 1H-nmr analysis was performed using two autocomplementary octanucleotides d(TGACGTCA) (I) and d(ACTGCAGT) (II). The uv-absorption titrations resulted in an intercalative binding mode for NMHE in the oligomers. Analysis of the derived biphasic Scatchard plots yielded two binding sites corresponding to ∼6-bp and 2-bp sizes and characterized by apparent association constants K1 ∼ 108M-1 and K2 ∼ 106M-1, respectively. The 1H-nmr analysis of exchangeable (imino) protons and nonexchangeable protons performed in the one- and two-dimensional modes confirmed the intercalation of NMHE, and further revealed the existence of multiple sites on DNA. Assuming that imino resonance line width concerned the sole kinetic effects, 10-ms order lifetimes were estimated for the drug-oligonucleotide complexes at 7°C, pH 7, and 0.1 ionic strength. Finally examination of every drug-DNA spectra in the light of the footprinting results indicated that there was a preference for binding of NMHE to the CpG (octamer I) and TpG (octamers I and II) steps.
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    Resolution of end-to-end diffusion coefficients and distance distributions of flexible molecules using fluorescent donor-acceptor and donor-quencher pairsDedicated to Professor Robert F. Steiner on the occasion of his 65th birthday. (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1363-1378 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We used time-dependent fluorescence energy transfer, time-dependent collisional quenching, and global analysis of the data resulting from these through-space and contact interactions to recover the end-to-end distance distributions and diffusion coefficients of flexible fluorescent molecules. The fluorescence decays of covalently linked tryptamine-acceptor and tryptamine-quencher pairs were measured by the frequency-domain method. These data were fit using numerical solutions of the differential equation, which predicts the time-and distance-dependent population of the excited state donors in the presence of energy transfer or collisional quenching, followed by transformation to the frequency domain for nonlinear least-squares comparison with the experimental data. We found that the energy transfer data for the donor-acceptor pair alone were adequate to recover the starting distribution and the end-to-end diffusion coefficient; however, the resolution is dramatically improved by the use of both the through-space and contact interactions.
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    URL: http://dx.doi.org/10.1002/bip.360311203
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    Photodegradation of hyaluronic acid: EPR and size exclusion chromatography study (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1429-1435 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photochemically induced radical reactions involving the lateral sequences and the end macromolecular chain groups of hyaluronic acid in aqueous solutions at 293K were studied by EPR spin trapping technique with DMPO (5,5-dimethylpyrroline-1-oxide). In the first 1-10 minutes of irradiation EPR indicates spin adducts of two carbon centered radicals with the splitting constants of aN = 1.60 mT, aH = 2.51 mT and aN = 1.56 mT, aH = 2.28 mT. After longer irradiation time (over 10 minutes) dominate two further DMPO adducts of radicals centered on hetero-atoms with splitting constants of aN = 1.44 mT, an = 1.60 mT and of aN = 1-49 mT, aH = 1.49 mT. Simultaneously, molecular weight followed by SEC decreases, suggesting that UV irradiation leads to the breaking of interglycosidic bonds of hyaluronic acid main macromolecular chain.
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    Photograph of Bruno Zimm (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1459-1459 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311302
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    The Hodgkin-Huxley Na+ channel model versus the five-state Markovian model (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1483-1502 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In describing the Na+ channel-gating kinetics, it is generally believed the Hodgkin-Huxley model is inadequate and other types of Markovian models are more appropriate. In this paper, we perform detailed kinetic analyses to find out whether the Hodgkin-Huxley model is really unacceptable. Specifically, we consider two models for the analyses: A five-state Markovian model that allows inactivation to take place before opening and a Hodgkin-Huxley eight-state model. The criteria used to check the goodness of the two models are (a) Akaike's information criterion; (b) χ2 tests on the waiting-time, open-time, and closed-time distributions, and the number of openings per record; and (c) comparison between all latency distributions and the probability of the open state predicted from the two models. In order to do this, we first develop a method of constructing probability density histograms of a specified event (e.g., waiting time, closed time, open time, number of openings per patch) from the multichannel patch-clamp recordings. The goodness of our method is checked by simulating multichannel patch recordings using a multinomial random number generator. Our kinetic analysis on the single Na+ channel recordings from the cardiac cells revealed that (a) on the basis of Akaike's information criterion, the Hodgkin-Huxley model is definitely a better model than the five-state model, but (b) on the basis of χ2 tests on the probability density functions, the latter model is slightly better than the former. We find no evidence that the Hodgkin-Huxley model is inferior to the five-state model for this cell type.
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    URL: http://dx.doi.org/10.1002/bip.360311306
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    The elastic resilience of DNA can induce all-or-none structural transitions in the nucleosome core particle (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1543-1557 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: DNA on the surface of the histone octamer in the native nucleosome core particle is modeled as a circumferentially wound elastic line on the surface of a cylinder. In a model for the radial transition, the line is allowed to straighten, and thus lose energy, by swinging off the surface, but it is impeded in such an excursion by a radial force field representing the attractive interaction between DNA and histone octamer. In a model for the axial transition, the line may straighten by becoming more parallel to a generator of the cylinder while remaining on the surface. In this mode of straightening, dimer-tetramer or tetramer-tetramer interfaces are disrupted, and the resulting energy gain impedes the transition. Both radial and axial transitions are predicted to occur in all-or-none fashion. We propose that these models are related to the abrupt transitions actually observed in the nucleosome core particle.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311310
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  • 94
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    A probabilistic model for genetic recombination of nonreplicating λ-phage DNA, stimulated by “mismatch repair” of UV photoproducts (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1565-1579 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Genetic recombination of nonreplicating phage λ-DNA, during infection of homoimmune lysogenic bacteria, was previously observed to be dramatically stimulated by prior uv irradiation of the phages, even when the Escherichia coli hosts lacked the major uv-photo-product excision-repair system (UvrABC). UvrABC-independent recombination of circular phage molecules depends on host MutHLS functions and on undermethylation of adenines at GATC sites in the phage DNA, and thus appears to be the result of “mismatch repair” of uv photoproducts. Recombinant frequencies pass through a relatively sharp maximum at 20 J/m2 and decrease at higher doses, whereas most plausible models for the process predict monotonic increases with dose, or a plateau at high uv doses. A uv-dose-dependent loss of biological activity (restriction) of all intracellular phage DNA was also observed previously. In order to provide a framework for testing possible explanations for the unusual recombinant-frequency vs uv-dose curve, a statistical model was constructed. This model includes probability terms for all possible one-exchange and two-exchange recombination processes, and incorporates the assumption that dimer recombinants are more susceptible to restriction than monomer parents (or recombinants), because of their larger target size. By adjustment of model parameters, particularly ∊, the efficiency per photoproduct of initiation of a recombinational exchange, a theoretical dose-response curve that agreed well with experiment was obtained. The best fit corresponded to ∊ = 0.035, close to the previously observed restriction efficiency of 0.053. In the calculations, the value for h0, the average length of heteroduplex DNA, was taken to be 0.5 λ units, i.e., about 25 kilobase pairs. This estimate for h0 was obtained here by analysis of the density distributions of the progeny of crosses between nonreplicating density-labeled λ-phage chromosomes, published by others [M. S. Fox, C. S. Dudney and E. J. Sodergren (1979) Cold Spring Harbor Symposium on Quantitative Biology, Vol. 43, pp. 999-1007].
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311312
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    Importance of oligoelectrolyte end effects for the thermodynamics of conformational transitions of nucleic acid oligomers: A grand canonical Monte Carlo analysisDedicated to Emeritus Professor Bruno H. Zimm, in whose laboratory one of us (MTR) began his study of the thermodynamic behavior of nucleic acid polyelectrolytes. (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1593-1604 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Effects of salt concentration on the stabilities of oligonucleotide helices are analyzed directly in terms of ΔΓN→yN ≡ ΓyNden - ΓNnat, the difference in the salt-nucleotide phosphate preferential interaction coefficients for the denatured state, having yN phosphate charges, and for the native state, having N phosphate charges (y = 1 for hairpin denaturation and y = 0.5 for dimer denaturation). Previous experimental studies of the denaturation of hairpin oligo-nucleotides (having 18 〈 N 〈 44) indicate significant differences between ΔΓN→N and ΔΓ∞, the value determined for the denaturation of the corresponding polynucleotide. These differences are thermodynamic manifestations of the oligoelectrolyte end effect. In contrast, the available data on the denaturation of oligonucleotide dimer helices (N ≤ 22) imply that differences between ΔΓ∞ and ΔΓN→0.5N, and hence oligoelectrolyte end effects, are small or negligible. To determine the origin of these apparently conflicting implications concerning the importance of oligoelectrolyte end effects, we have calculated the N dependence of ΓN from grand canonical Monte Carlo simulations for an idealized model of the structure and charge distribution of each oligomer conformation. Our calculations are in quantitative agreement with the experimental finding for d(TA) hairpin oligomers that - ΔΓN→N decreases linearly as N-1 increases, and with the extant experimental determinations of ΔΓN→0.5N. These results provide an illustration of how the large electrostatic end effects exhibited by the hairpin denaturation data are masked when ΔΓ∞ is compared with values of ΔΓN→0.5N for short dimer helices (N ≤ 22). For 0.5N 〉 24, - ΔΓN→0.5N is predicted to be a linear function of N-1 whose slope has the opposite sign from, and is more salt-concentration dependent than, the corresponding slope of - ΔΓN→N as a function of N-1. Our calculations also yield predictions about the N dependences of the individual values of ΓN that can be tested by determining Donnan coefficients from membrane dialysis equilibrium experiments. For long enough hairpin and dimer oligonucleotides (yN ≥ 24), in either native or denatured forms, we predict that the (positive) difference Γ∞ - ΓN increases linearly with increasing N-1. For smaller values of N the difference Γ∞ - ΓN continues to increase with increasing N-1.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360311314
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  • 96
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    Transient electric birefringence of two small DNA restriction fragments of the same molecular weight (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1651-1667 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transient electric birefringence of two small DNA restriction fragments of the same molecular weight, one of which migrates anomalously slowly on polyacrylamide gels, has been investigated. Both fragments exhibit negative birefringence. The decay of the birefringence of the anomalously slowly migrating fragment is 8-9% faster than that of the normally migrating fragment. The faster birefringence decay of the anomalous fragment 12A persists under a variety of buffer conditions, suggesting that it is due primarily to static bending and/or curvature of fragment 12A. In reversing electric fields the absolute amplitude of the birefringence of fragments 12A and 12B decreased about 26% before returning to the steady state value. The minimum in the birefringence occurred faster than expected from the birefringence decay times and decreased with increasing electric field strength, suggesting that the minimum is due to a slow polarization of the ion atmosphere. For both fragments, the rise of the birefringence in the Kerr region is about 10% slower than the field-free decay. The buildup of the negative birefringence is preceded either by an interval when no birefringence is observed or by a small positively birefringent transient, suggesting that a small transverse ionic polarizability is also present. Both DNA fragments exhibit Kerr law behavior over most of the range of electric field strengths investigated. Analysis of the shapes of the saturation curves suggests that differences may exist in the polarization mechanisms of the two fragments.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311318
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  • 97
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    On the flexibility of myosin in solution (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1677-1687 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rabbit skeletal muscle myosin from the same rabbit was prepared by two different methods, and then purified by either Sephadex or hydroxylapatite chromatography. The resulting myosin samples were analyzed in 2-10 mM sodium pyrophosphate solutions at pH 9 using transient electric birefringence. The birefringence decay signals were fitted using a Fortran program called DISCRETE and two relaxation times, 49.7 ± 5.6 and 11.2 ± 2.5 μs, were determined. These relaxation times were independent of the method of myosin preparation, the method of myosin purification, the concentration of sodium pyrophosphate between 2 and 10 mM, the concentration of myosin between 0.08 and 1.59 mg/mL, and the temperature between 4.0 and 20.0°C, after correction to 20.0°C. The longer relaxation time is consistent with a rigid, linear myosin molecule. The shorter relaxation time is consistent with myosin that has a completely flexible hinge region in the myosin tail. Both relaxation times are inconsistent with the previously reported single relaxation time of myosin obtained by fitting the birefringence decay data to only 90% of the decay signal. By forcing some of the birefringence decay data in the present work to fit 90% of the decay signal with a single relaxation time, approximately the same relaxation time as previously reported was obtained.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311403
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    Heterogeneous molecular aggregation and fractal structure in chitosan/acetic acid systems (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1721-1726 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of deacetylation degree on heterogeneous molecular aggregation has been investigated for chitosan solution in 2 wt % acetic acid aqueous solution using rheological and small-angle x-ray scattering (SAXS) methods. Three samples of chitosan, which were designated CS62, CS79, and CS96, were used, and the deacetylation degrees of these samples were 0.62, 0.79 and 0.96, respectively.Rheological properties show that the systems of CS62 and CS96 are homogeneous, and the system of CS79 has a certain heterogeneous structure with a long-time relaxation mechanism. According to the SAXS measurement, the heterogeneous system has a fractal structure and the fractal dimension is about 1.3.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311406
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  • 99
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    Salt dependence and ion specificity of the coil-helix transition of furcellaran (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1727-1736 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational transition and the cation-binding properties of aqueous furcellaran (a gel-forming, low-sulfated polysaccharide of the carrageenan family) in various salts and salt mixtures was studied by optical rotation and by 133Cs-nmr. The results were compared with theoretical predictions based on the Poisson-Boltzmann cell model (PBCM). The conformational transition of furcellaran occurs in a single step, which implies a nonblocklike distribution of sulfate groups along the polymer chain. The chloride salts of sodium, lithium, and tetramethylammonium are equally potent in inducing helix formation of furcellaran, indicating that these ions act by nonspecific electrostatic interactions. In contrast, the potassium and cesium ions specifically promote helix formation and aggregation (gelation) of furcellaran. The divalent calcium and magnesium ions are nonspecific, but more potent than the nonspecific monovalent ions in inducing helices. Anions differ in their capacity to stabilize the furcellaran helix in the sequence Cl- 〈 NO3- 〈 Br- 〈 SCN- 〈 I-. The iodide and thiocyanate anions impede aggregation and gel formation. 133Cs-nmr chemical shifts indicate specific binding of cesium ions to the furcellaran helix. Thus, with respect to its ion specificity and ion-binding properties, furcellaran, with 0.6 sulfate group per repeating disaccharide, resembles κ-carrageenan (1 sulfate/disaccharide) but differs from ι-carrageenan (2 sulfates/disaccharide). The conformational transition temperatures of furcellaran are, however, generally higher than those of κ-carrageenan under comparable conditions, and in mixtures of the two polysaccharides, separate transitions still occur, indicating that no mixed helices are formed. The observed ion sensitivity and cation-binding properties of furcellaran agree with predictions, by the PBCM, for a K-carrageenan with a reduced charge density.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311407
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  • 100
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    Conformational preferences of oligopeptides rich in α-aminoisobutyric acid. I. Observation of a 310/α-helical transition upon sequence permutation (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1763-1774 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solution conformation of peptides rich in the α,α-dialkylated amino acid Aib has proven to be a subtle problem, not because of helix/coil transitions, but rather because of α-helical/310-helical competition. A special series of peptides containing 75% Aib has been synthesized that feature identical amino acid composition but differing sequences; they are sequence permutation isomers. Nuclear magnetic resonance hydrogen-bonding studies reveal that there is a sequence permutation induced transition between the two alternative helical forms within this set. The implications for the design and conformational prediction of helical Aib-rich peptides are discussed.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360311410
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