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  • 1975-1979  (830)
  • 1965-1969  (281)
  • 1890-1899
  • 1820-1829
  • Atomic, Molecular and Optical Physics  (991)
  • Bone
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Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Skeletal radiology 4 (1979), S. 72-78 
    ISSN: 1432-2161
    Keywords: Sarcomas ; Bone ; Neoplasms ; Radiation induced
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Historically, the literature reveals that the incidence of radiation induced bone sarcomas is very low. Details related to epidemiology cannot be identified, however, because of the difficulty of identifying precisely the patient population at risk for development of the radiation induced sarcoma. The change in character of practice in cancer management with ever increasing numbers of patients receiving both radiation therapy and chemotherapy should alert physicians to the potential for increased incidence of this rare and unusual tumor.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 27 (1979), S. 33-40 
    ISSN: 1432-0827
    Keywords: Chick embryo ; Bone ; Organ culture ; Scanning electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The study describes the ultrastructure of the mineralized portion of chick tibiae from 10 days in ovo to 2 days post-hatch. At 10 days a single mineralized cylinder surrounds the diaphysis. On its outer surface columnar trabeculae join to form ridges parallel to the long axis of the bone. These ridges are covered by another cylinder and form the haversian canals. At 11 days vascular invasion of the marrow cavity occurs and resorption of the endosteal surface begins. This type of periosteal deposition and endosteal resorption is repeated during and subsequent to embryonic development. The mineralized portion of 10-day chick tibiae cultured for 2 days in modified BGJ medium was compared with 10-, 11-, and 12-day tibiae in ovo. Cultured tibiae were similar in length and calcium content to 11-day tibiae in ovo. The form of mineral deposited in ovo and in culture was the same, namely, aggregates of spherical mineral clusters. Differences in culture included the following: (a) few concentric cylinders were deposited as compared with tibiae in ovo; (b) trabeculae were not arranged in rows and ridges in culture; (c) osteocytic lacunae were restricted to bases of trabeculae rather than uniformly distributed as in ovo; and (d) the endosteal surface of tibiae in culture appeared etched.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 27 (1979), S. 57-64 
    ISSN: 1432-0827
    Keywords: Bone ; Bone formation ; Calcification ; Calcification nodule ; EM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Osteolathyrism has been used as an experimental model for the study of calcification nodules during the mineralization process. Periosteal exostoses developing in osteolathyrism characteristically have spherical basophilic structures (calcification nodules) in the vicinity of developing bone spicules. In thin sections, the nodules were seen scattered between collagen fibers in the intercellular matrix. Collagen fibers did not appear to be present within the nodules but sometimes were packed just outside them. Matrix vesicles were also present in areas of early mineralization. After EDTA decalcification, the majority of the nodules consisted of a fine granular material surrounded by an electron-dense peripheral zone. The peripheral dense zone was occasionally incomplete in small nodules in areas of early mineralization. An electron-dense central area could be observed in the center of the nodules. Evidence has been presented indicating that the calcification nodules arise from smaller mineralization foci, presumably matrix vesicles. The calcification nodules enlarge to approximately 1.0 µm in size, at which point development is slowed or halted allowing the formation of the peripheral dense zone. Although coalescence of nodules was observed, this was more a random event. The further mineralization of the trabeculae was achieved by the calcification of the collagen fibers. The mineralized trabeculae reflected this pattern of nodular and collagenous calcification. It is suggested that this pattern of calcification is characteristic of rapidly developing woven bone.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 28 (1979), S. 37-42 
    ISSN: 1432-0827
    Keywords: X-ray diffraction ; Hydroxyapatite ; Whitlockite ; Fish (Pisces) ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Pyrolyzed scales, fin spines, and bone from the ray-finned bony fishPolypterus (Actinopterygii) showed two mineral phases on X-ray diffraction: hydroxyapatite (HA), Ca5(PO4)3OH, and whitlockite, Ca3(PO4)2. The ratio of HA/whitlockite varied with the structure (scale, spine, bone) within each individual fish. The relative proportions of HA to whitlockite in pyrolyzed samples reflected the Ca/P ratio of the sample. Whitlockite appears after pyrolysis when the Ca/P is lower than 1.67. Among the five fish investigated, for each structure a general trend was noted. The proportion of HA relative to whitlockite increased with size (age) of the fish. Thus the smallest fish, a juvenile, exhibited a low Ca/P mineral in its calcified tissues, whereas the larger fish had progressively more HA and less whitlockite.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 28 (1979), S. 17-22 
    ISSN: 1432-0827
    Keywords: Anticonvulsant ; Ketogenic diet ; Calcium ; Vitamin D ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Vitamin D and mineral metabolism status was examined in five children maintained chronically on combined ketogenic diet-anticonvulsant drug therapy (KG), and the results compared to those obtained in 18 patients treated with anticonvulsant drugs alone (AD) and 15 normal controls. KG patients exhibited biochemical findings of vitamin D deficiency osteomalacia: decreased serum 25-hydroxyvitamin D (25OHD) and calcium concentrations, elevated serum alkaline phosphatase and parathyroid hormone concentrations, decreased urinary calcium and increased urinary hydroxyproline excretion, and decreased bone mass. Although the KG and AD groups demonstrated similar reductions in serum 25OHD concentration, the KG patients exhibited a significantly greater reduction in bone mass. In response to vitamin D supplementation (5000 IU/day), mean bone mass in the KG group increased by 8.1±0.9% (P〈0.001) over a 12-month period. These results suggest that ketogenic diet and anticonvulsant drug therapy have additive deleterious effects on bone mass and that these effects are partially reversible by vitamin D treatment.
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  • 6
    ISSN: 1432-0827
    Keywords: Bone ; Bone cells ; Cyclic AMP ; Osteoclast activating factor ; Lymphokine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Osteoclast activating factor (OAF) is a lymphokine which may participate in the pathologic destruction of bone observed in a number of disorders. In the current studies, we investigated the action of OAF on cAMP accumulation by bones and isolated bone cells in culture. OAF was shown to stimulate accumulation of cAMP in mouse cranial bones at doses between 1 and 1000 ng/ml. Stimulation of bone resorption was observed in bones treated with the same doses of OAF. In order to investigate the cell types responsible for cAMP responses to OAF, we isolated bone cells and grew them in monolayer culture. The cells were isolated by a variety of techniques which separate bone cells into two types of parathyroid hormone (PTH)-responsive populations: (a) cells derived from the periosteal regions of the bone, which also respond to calcitonin with increases in cAMP; and (b) cells derived from the matrix, which do not respond to calcitonin. OAF caused elevation of cAMP levels in both the periosteum-derived cells and the matrix-derived cells. The magnitudes and time courses of OAF effects in these populations resembled the effects previously reported for PTH in the same populations. OAF stimulated adenyl cyclase in both types of cell populations, but did not produce significant changes in cAMP phosphodiesterase activity. OAF differed from PTH in that its effects on cAMP accumulation decreased sharply at supramaximal doses in both bone and isolated cells, especially in the matrix-derived populations. Bone resorption did not decrease as markedly as did cAMP accumulation at high doses of OAF, suggesting that cAMP accumulation and resorption could be dissociated under some conditions. These results indicate that OAF has effects on cAMP production in the same cell populations as PTH, and suggest that OAF could modify not only resorption but also formation of bone in vivo. OAF may exert its effects on bone by means of cAMP-dependent mechanisms, but more data will be necessary to establish this unequivocally. The observed differences between OAF and PTH may be of relevance in the mechanism and treatment of pathologic bone destruction in vivo.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 27 (1979), S. 199-204 
    ISSN: 1432-0827
    Keywords: Bone ; Parathyroid hormone ; Calcitonin ; Osteoporosis ; Paraplegia ; Hydroxyproline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary In paraplegia, osteoporosis below the neurological lesion occurs early after the spinal cord affection. The serum levels of parathyroid hormone (PTH) and calcitonin (CT), using a radioimmunoassay for the measurement of immunoreactivity, were studied in 12 paraplegic patients for 9 months following onset. Serum Ca and P levels, urinary hydroxyproline excretion, and the kinetic metabolic clearance of45Ca have also been measured. P and immunoreactive (i) CT levels were found the highest at the beginning of the observation and progressively decreased with time. Ca and iPTH serum levels varied inversely with time, the highest level of Ca and the lowest level of iPTH being recorded at the third month following the paraplegia. Mean values of Ca, iPTH, and iCT were in the normal range throughout the study. P levels were increased during the first 3 months. Hydroxyprolinuria was also high and45Ca kinetics showed increased values of Vt, Vo+, and Vu. These parameters indicate a high degree of bone turnover. The results were consistent with the assumption that PTH is not responsible for the increased resorption of bone in paraplegia. Likewise, a deficiency of CT does not seem to be responsible for this bone resorption. These endocrine modifications could be secondary to an increase in the calcium flux from bone to blood and resulting from bone destruction as attested by the increase of urinary calcium and urinary hydroxyproline excretion.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 27 (1979), S. 233-237 
    ISSN: 1432-0827
    Keywords: Bone ; Vitamin D ; Acidosis ; Phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Vitamin D and phosphate deficiency were produced in rats in order (a) to evaluate the degree of bone mineral and matrix maturation using a bromoform/toluene density gradient technique; and (b) to compare the aforementioned bone maturational changes due to vitamin D and phosphate deprivation to those produced with superimposed severe acidosis. Rats were fed a diet deficient in vitamin D and phosphorus (0.2%) from 3 weeks through 7 weeks of age. To examine the additional contribution of dietary calcium, we gave one-half of the animals either a low (0.06%) or high (1.3%) calcium diet. Following the 4 weeks of vitamin D deficiency, one-half of each group was given 1.8% NH4Cl in the drinking water for 4 succeeding days to induce an acute, severe acidosis. The degree of bone maturation was quantitated via bromoformtoulene density gradient fractionation; total mineral and hydroxyproline (collagen) levels were quantitated as well. The vitamin D-deficient rats deprived of adequate dietary phosphate responded by conserving phosphorus, and as a consequence total bone phosphorus levels were maintained within that level for control rats. This conservation was independent of calcium intake but was extremely sensitive to acute acid loading, where a significant reduction in total bone phosphorus was noted. The bone maturational profile obtained from the vitamin D-phosphate deficient rats, however, revealed a significant accumulation of less mature or dense bone collagen and mineral with a corresponding decrease in the most mature or dense moieties. In contrast to the reduction of the total bone phosphorus content by acute acidosis, the skeletal collagen-mineral maturational profile was not significantly affected by the short-term systemic acidosis. The observed retardations in the bone collagen and mineral maturation of the vitamin D-deficient, phosphate-deprived state provide an additional observation which may well relate to the progressive osteopenia documented in states of chronic, mild acidosis.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 27 (1979), S. 275-279 
    ISSN: 1432-0827
    Keywords: Proline ; Cartilage ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Proline biosynthetic and degradative enzymes are unevenly distributed in differentiated mammalian tissues. Activities of the synthetic enzymes are relatively high in collagenous tissues, whereas activities of the degradative enzymes are high in noncollagenous tissues. In order to further characterize tissue-specific proline biosynthesis and degradation, we have determined proline enzyme activities during cartilage and bone formation induced by demineralized bone matrix. We can thus follow temporal changes in enzyme activity in a single tissue as different cell types develop. Ornithine aminotransferase and pyrroline-5-carboxylate reductase have peaks of activity which correlate with maximal type II collagen synthesis by chondrocytes. Both enzymes also are active during bone formation. In contrast, proline oxidase and pyrroline-5-carboxylate dehydrogenase are present at low levels and do not change as new cell types appear. Arginase activity peaks during the first 3 days and then rapidly decreases by the time cartilage and bone formation begin. These observations further substantiate the importance of proline biosynthesis in collagenous tissues. The close correlation between ornithine aminotransferase activity and type II collagen synthesis suggests that the pathway from ornithine to proline may be especially important during formation of type II collagen.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 29 (1979), S. 169-171 
    ISSN: 1432-0827
    Keywords: Glycosaminoglycans ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Compact bone tissue chondroitin sulphate, previously considered to be pure chondroitin-4-sulphate, was isolated from three adult human femoral diaphyses and digested with chondroitinase ABC. Assaying these digests by means of high performance liquid chromatography we could demonstrate that 12 to 14% of the disaccharide residues were 6-sulphated. The 4/6-ratios were also studied in chondroitin sulphate fractions of different molecular size. Slightly increasing amounts of 6-sulphated disaccharides were found with increasing size of the chondroitin sulphates.
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 27 (1979), S. 177-185 
    ISSN: 1432-0827
    Keywords: Calcification ; Bone ; Glycoprotein ; Golgi ; Osteoblasts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The elaboration of bone matrix glycoprotein by osteoblasts of alveolar bone was investigated by radioautography after the intravenous injection of3H-fucose into young rats. At selected times after injection, animals were sacrificed by intracardiac perfusion and demineralized specimens were prepared for light and electron microscope radioautography. At 5 and 10 min after injection, when the blood fucose level was high, silver grains were restricted to the spheroidal and cylindrical saccules of the Golgi apparatus. At 20 min membrane-limited secretory granules were also labeled. By 35 min, the blood fucose level had dropped and silver grains were detected over the apical cortical cytoplasm, in association with secretory granules located therein. Some grains were present over osteoblast processes and the adjacent prebone matrix. By 4 h most of the silver grains had left the cell. At that time they were observed over prebone, adjacent to osteoblast processes, as well as over the prebone-bone junction where a distinct band of label was noted. In demineralized preparations an electron-dense granular material was present at the prebone-bone junction in association with collagen fibrils. These findings provide evidence that osteoblasts in alveolar bone synthesize fucose-containing glycoprotein and indicate that the addition of3H-fucose occurs in the Golgi apparatus. The glycoprotein passes to the apical cortical cytoplasm by way of membrane-limited secretory granules, is exteriorized, and accumulates at the site where prebone transforms into bone (the prebone-bone junction). Since this is also the site of the calcification front, the deposition of labeled glycoprotein may be related to the deposition of bone mineral.
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 27 (1979), S. 95-99 
    ISSN: 1432-0827
    Keywords: Bone ; Fluoride ; Analysis ; Food ; Age
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Recently published bone fluoride values from Iowa are very high compared to earlier reports, suggesting an increase in fluoride intake. Reanalysis of the Iowa specimens shows levels one-fourth those reported by the Iowa laboratory indicating an error in the original report. Seventeen bone specimens, collected from long-term residents of Rochester, New York, drinking 1 ppm F− water, had a mean value of 2085±270 ppm F− on an ashed-weight basis. This value is not significantly different from that predicted by the data of Zipkin et al. in 1958. These data, therefore, do not support the contention that there has been an increase in fluoride intake.
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 27 (1979), S. 109-115 
    ISSN: 1432-0827
    Keywords: Bone ; Bending rigidity ; Disuse atrophy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The in vivo bending rigidity and bone mineral content of monkey ulnae and tibiae were measured. Bending rigidity in the anteroposterior plane was measured by an impedance probe technique. Forced vibrations of the bones were induced with an electromechanical shaker, and force and velocity at the driving point were determined. The responses over the range of 100–250 Hz were utilized to compute the bending rigidity. Bone mineral content in the cross section was determined by a photon absorption technique. Seventeen male monkeys (Macaca nemestrina) weighing 6–14 kg were evaluated. Repeatability of the rigidity measures was 4%. Bone mineral content was measured with a precision of 3.5%. Bending rigidity was correlated with the mineral content of the cross section,r=0.899. Two monkeys were evaluated during prolonged hypodynamic restraint. Restraint produced regional losses of bone most obviously in the proximal tibia. Local bone mineral content declines 17 to 24% and the average bending rigidity declines 12 to 22%. Changes in bones leading to a reduction in mineral content and stiffness are discussed.
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  • 14
    ISSN: 1432-0827
    Keywords: Calcium ; PTH ; 1,25(OH)2D ; Acid ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary We measured mineral and acid balances, serum iPTH, urinary cAMP/creatinine, and plasma concentrations of 25OHD and 1,25(OH)2D in 7 healthy adults during control conditions and during increased fixed acid production achieved either by the administration of NH4Cl (N=3) or by increased dietary protein intake (N=4). When acid production was increased, the subjects were in positive acid balance and negative Ca balance because of increased urinary Ca excretion. Serum iPTH fell slightly but urinary cAMP and the plasma levels of vitamin D metabolites did not change. We conclude that the accelerated skeletal and urinary losses of Ca that occur when fixed acid production is increased are not contributed to nor compensated for by the parathyroid-vitamin D endocrine systems.
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 29 (1979), S. 7-13 
    ISSN: 1432-0827
    Keywords: Bone ; Culture ; Resorption ; Acidosis ; Alkalosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary We have examined the effects of H+, CO2, and HCO3 − concentrations during metabolic and respiratory acidosis and alkalosis on bone resorption in vitro. Rat fetal bones prelabeled with45CaCl2 were cultured at 2%, 5%, and 10% CO2 for up to 120 h, and the release of45Ca was measured in devitalized bones (non-cell-mediated45Ca release) and in live bones (cell-mediated45Ca release) cultured with or without PTH and 1,25(OH)2D3. Non-cell-mediated mineral loss was linearly related to H+ concentration but not to CO2 or HCO3 − concentration. This effect was observed on both labeled and stable calcium. Over a wide pH range (6.9–7.5) H+, CO2, or HCO3 − concentrations did not influence cell-mediated bone resorption in control or in PTH-and 1,25(OH)2D3-stimulated cultures. However, inhibition of cell-mediated bone resorption was observed at higher or lower pH irrespective of CO2 or HCO3 − concentrations. These observations demonstrate that the bone mineral mobilizing effect of acidosis in vitro is mainly due to the effect of changing H+ concentration on devitalized bone. Effects on cell-mediated bone resorption and hormonal response were observed only at extremes of pH. The effects of H+ were independent of changes in CO2 or HCO3 − concentration and could be responsible for the negative calcium balance and increased urinary loss observed in metabolic acidosis in vivo, but do not explain the reported differences in effects on calcium metabolism between respiratory and metabolic acidosis.
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Calcified tissue international 27 (1979), S. 105-108 
    ISSN: 1432-0827
    Keywords: Bone ; Femur ; Strength ; Density ; Age
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary In order to ascertain whether the intrinsic strength of human bone changes with age or not, we have determined the ultimate tensile strength and density of strips of femoral cortical bone. These femora were collected from cadavers varying in age from 13 to 97 years. The results show that both density and intrinsic strength of bone increase up to about the fourth decade of life and then decrease with age. However, the rate of decrease of strength is greater than that of density. This indicates that the density of bone is not the sole determining factor of its strength, and that some other factors play an important part.
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  • 17
    ISSN: 1432-0827
    Keywords: Bone ; Rickets ; Hypophosphatemia ; Microradiography ; D-resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The perilacunar areas of low mineral density in microradiographs from cortical bone of patients with hypophosphatemic (vitamin D-resistant) rickets are not evenly distributed throughout the bone tissue. Their frequency and distribution were determined in bone from 9 patients with this disease. It was found that the lesion was more frequent in haversian bone than in interstitial bone, and along the inner circumference of growing haversian systems as compared with the outer circumference. These findings indicate that the lesion is the result of retarded mineralization, and that mineralization slowly proceeds in these areas as the bone becomes older. A relatively high frequency of the lesion was also found in osteons with an elliptical cross section along the long axis of the ellipse. The cause of the abundance of the lesion at these sites is not clear, but it is possible to explain the uneven distribution in elliptical osteons by assuming an unequal rate of bone formation in these structures.
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  • 18
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    Springer
    Calcified tissue international 27 (1979), S. 165-169 
    ISSN: 1432-0827
    Keywords: Oxygen uptake ; Bone ; Oxygen tension ; Carbon dioxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The present study was carried out to determine the influence of carbon dioxide and oxygen tension on the respiratory activity of bone cells in mouse calvaria in vitro. Five-day-old mouse calvaria were removed aseptically and incubated individually for 1 h at 37° C in a closed reaction chamber containing 1.5 ml of tissue culture medium made up of 60% horse serum in Gey's solution containing 100 unit/ml penicillin and 100µg/ml streptomycin. Before the calvaria were added, the medium in the incubation chamber was equilibrated with 10%, 20%, 30%, or 50% oxygen balanced with nitrogen. The effect of CO2 on oxygen utilization by the calvaria was determined by incubating the calvaria in a medium previously equilibrated with either 50% O2 balanced with N2 or 50% O2 and 5% CO2 balanced with N2. At each oxygen tension, the rate of oxygen utilization by the calvaria was measured polarographically by a Clark oxygen electrode. The results showed that the rate of oxygen uptake of bone increased as the oxygen tension increased and carbon dioxide stimulated significantly the rate of oxygen utilization by the bone cells. In view of the previous reports that both carbon dioxide and oxygen tension are implicated in the process of bone resorption, it is suggested that these two factors may affect bone resorption by influencing the oxygen utilization by bone cells and ultimately controlling their energy metabolism.
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  • 19
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    Calcified tissue international 28 (1979), S. 103-105 
    ISSN: 1432-0827
    Keywords: Bone ; Photodensitometry, X-ray ; Radiography ; Spectrophotometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A conventional spectrophotometer was used to do radiographic photodensitometry of bone mass. An experiment to produce osteoporosis in guinea pigs required quantification of changes in bone mass. Lack of a densitometer necessitated finding another method for quantification. The method developed involved using industrial film in a closed X-ray system. Optical density of X-rays was then read in a spectrophotometer at nine femur locations. Highly significant correlations between optical density and femur calcium content and femur dry weight per millimeter were obtained. Histological sections from an animal with low optical density measurements confirmed bone loss by showing decreased cortical width and loss of trabecular bone. In addition to using readily available equipment, this method offers the advantage of being able to detect bone loss in specific areas of the bones. In addition, bones are left intact and can be used for other purposes.
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  • 20
    ISSN: 1432-0827
    Keywords: ESR ; Bone ; Enamel ; CO3-Apatite ; Paramagnetism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Carbonate-containing hydroxyapatite, enamel, and bone were irradiated by an X-ray and investigated between 77° and 350°K by means of electron spin resonance (ESR) spectroscopy. The ESR spectrum of enamel irradiated at 77°K in vacuum and observed at the same temperature was almost the same as that of the carbonate-containing hydroxyapatite. The temperature dependence of signal intensities confirms a spin-energy exchange between the mineral and organic constituents in bone, but in enamel no or very little spinenergy exchange between the mineral and organic constituents. Considerable similarity among the ESR spectra of enamel, bone, and carbonate-containing apatite was obtained after X-ray irradiation in air at 300°K with both an X-band and a Q-band ESR spectrometer. The Q-band spectrum can be interpreted in terms of two paramagnetic species. One is identified as a CO 3 3− anion radical which has an axial symmetry withg factors of 2.0029 and 1.9972. The other species is found to be centered atg=2.0019.
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  • 21
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    Calcified tissue international 27 (1979), S. 13-18 
    ISSN: 1432-0827
    Keywords: Anticonvulsants ; Calcium ; Vitamin D ; Parathyroid hormone ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Parameters of mineral metabolism were examined in 6 patients with moderately severe anticonvulsant drug-induced osteomalacia. Compared to 15 matched controls, the patients exhibited significantly reduced serum calcium, inorganic phosphate, and 25-hydroxyvitamin D concentration, elevated serum alkaline phosphatase and immunoreactive parathyroid hormone (iPTH) concentration, reduced intestinal47Ca absorption, reduced urinary calcium and increased urinary hydroxyproline excretion, and reduced forearm bone mass. Intestinal absorption of vitamin D3 was normal. Following 4 months of treatment with vitamin D3 (4000 units/day), serum 25-OHD concentration was increased to 3 times mean normal values and all parameters except serum iPTH, urinary calcium excretion, and forearm bone mass were returned to levels not significantly different from normal. Serum iPTH concentration was reduced by 39% (P〈0.05); 24-h urinary calcium excretion rose by 98% (P〈0.001), and forearm bone mass increased by 5.6% (P〈0.05). It is concluded that moderate-dose vitamin D3 supplementation is effective in normalizing parameters of mineral metabolism in this disorder, despite evidence of resistance to the biologic effects of vitamin D.
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  • 22
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    Calcified tissue international 28 (1979), S. 33-36 
    ISSN: 1432-0827
    Keywords: Infrared, visible light ; Bone ; Collagen ; Apatite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Photovoltaic effect (infrared and visible light) is observed in bone and its two major components, collagen and apatite, at room temperature. A dimunition in the magnitude of photovoltage is observed after exposure to ultraviolet light in all the cases. The drift mobility of the charge carriers is obtained by measuring I versus V relationships in sandwich samples and relating them to the permitivity of the medium. Lifetime of the injected carriers is measured in the usual way. The data are consistent with the hypothesis that the effects are due to protonic conduction phenomena.
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  • 23
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    Medical & biological engineering & computing 17 (1979), S. 471-475 
    ISSN: 1741-0444
    Keywords: Bone ; Strain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Specimens of dry human cortical bone of a disc form were subjected to sinusoidal loading under controlled conditions. The results show a nonlinear increase of the measured peak potential with frequency which reaches a limiting value at about 200 Hz. The analysis, which is based on the circuit representation proposed previously by Shamos, indicates that such a behaviour can be attributed to the measuring circuit parameters. It was found that some relevant results can be interpreted qualitatively by similar analysis.
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  • 24
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    International Journal of Quantum Chemistry 15 (1979), S. 449-462 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New techniques have been developed for atomic self-consistent-field calculations by numerical integration. For the origin and tail regions we present analytical expansions which can represent the solutions to high accuracy. For the numerical integration in the central region a five-point generalization of the Numerov formula is used; the error term is of the order h10. While this formula is unstable if used in the customary way, stability is achieved by using a Gaussian elimination technique. The new procedures are tested on the ground state of the helium isoelectronic series; with 251 integration points all quantities are calculated with an inherent accuracy of better than 10-11.
    Additional Material: 2 Ill.
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  • 25
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    International Journal of Quantum Chemistry 15 (1979), S. 463-479 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coupled-cluster variational-like direct approach to the calculation of ionization and electron attachment energies and of excitation energies is applied to several π-electron model systems, using the PPP Hamiltonian with various parametrizations. A simple approximation, which represents the triexcited clusters in terms of disconnected W1T2 terms, is employed. All the necessary diagrams for both excitation energy and ionization potential (electron affinity) calculations are given in the compact Hugenholtz nonoriented form. The results of the calculations for benzene, trans-butadiene, all-trans-hexatriene, and fulvene are compared with the corresponding full CI results, and the conclusions about the validity and efficiency of this approach are drawn.
    Additional Material: 6 Ill.
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  • 26
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    International Journal of Quantum Chemistry 15 (1979), S. 481-489 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The paper reports the study of a possible mechanism of Ca+2 activation of prostaglandin PGF2α on the basis of molecular-orbital and conformation-energy calculations. The electronic charges on various atoms of the molecule have been evaluated from the available crystallographic data by the extended Hückel theory (EHT). Conformation energies were calculated for intrinsic torsional rotations around the C11—C12, C7—C8, and C14—C15 bonds. The minimum energy conformation was found to differ from the crystallographic conformation by 9.3 kcal/mol. Some additional local energy minima are also reported within this range. The calculation of the long-range interchain interaction energy between the α and ω chains shows variation with conformation. The binding site for the Ca+2 ion has been estimated on the basis of the molecular electrostatic potentials. Such a binding site was found near the carboxyl group, which agrees with the current chemical thinking. Changes in the electronic charge distribution due to Ca+2 complexation were studied by EHT method using the supramolecular approach. Calcium complexation decreases the conformation energy by 2-3 kcal/mol and has a small effect on the interchain interaction energy.
    Additional Material: 4 Ill.
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  • 27
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    International Journal of Quantum Chemistry 15 (1979), S. 491-497 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several analogs of valinomycin have been simulated. These are analogs obtained by changing the configuration of the amino acid and hydroxy acid residues one at a time. Nonbonded interactions have been calculated for three conformations of each analog. The electrostatic and polarization contributions to the energy are conformation selective, whereas the Pauli repulsion is the only component which is isomer selective. For the ring chirality considered here the analog of valinomycin having all the three L-valyl residues replaced by D-valyl residues is predicted to be frozen in a “top open” conformation.
    Additional Material: 3 Ill.
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  • 28
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    International Journal of Quantum Chemistry 15 (1979), S. 499-510 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ab initio SCF LCAO-MO method is used to compute the main electronic properties of a purine nucleoside, adenosine, in two specific conformational arrangements (3′-endo conformation of the ribose, gt orientation of the extracyclic CH2OH group, anti orientation of the base with respect to the sugar and 3′-endo conformation of the ribose, gg orientation of the extra-cyclic CH2OH group, syn orientation of the base with respect to the sugar). The results are compared with those performed for the isolated component fragments, adenine and 3′-endo riboses.
    Additional Material: 7 Ill.
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  • 29
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    International Journal of Quantum Chemistry 15 (1979), S. 745-750 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different kinds of improved uncoupled Hartree-Fock methods are proposed for the calculation of second-order perturbation energies. Using these methods inequalities are derived for the error of the uncoupled procedure with geometric approximation.
    Additional Material: 1 Tab.
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  • 30
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    International Journal of Quantum Chemistry 15 (1979), S. 731-744 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of multiple scattering techniques combined with a statistical exchange potential for the description of the electronic structure of atoms, molecules, and solids depends strongly on the geometry (muffin tin, overlapping spheres, or cellular potentials) and on the form of the electron gas exchange. In this work we compare only the effects of using different geometries. For that purpose we have done calculations on the hydrogen molecular ion and Hartree-type calculations on the hydrogen molecule so that no exchange effects are involved. To avoid arbitrariness in the choice of the sphere sizes we propose a nonempirical criterion that consists of using the set of radii that will minimize the charge in the interstitial region of the molecule or cluster. Some arguments are given to justify this criterion, and to clarify the differences between cellular, overlapping spheres, and muffin-tin geometries. It is found that the cellular geometry gives a very good description around the equilibrium internuclear distance. However, for most systems of interest, exchange will be present. Thus, we have done, for comparison, the calculation on H2 using Xαβ statistical exchange. It is shown through this calculation that some of the correlation energy may be obtained by redefining the molecular orbitals in terms of non-paired-spins spatial orbitals, this formulation being required to obtain the correct free-atom limit.
    Additional Material: 6 Ill.
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  • 31
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    International Journal of Quantum Chemistry 15 (1979), S. 751-767 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The theory of the open-and closed-shell restricted Hartree-Fock method is given a unitary group formulation. Both extremum and stability conditions are employed, the former leading to a generalized Brillouin theorem.
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  • 32
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    International Journal of Quantum Chemistry 15 (1979), S. 769-782 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved interaction potential has been devised for diatomic alkali halide molecules. This potential, in addition to similar attraction terms as in the Rittner potential, includes a new exponential for the short-range repulsion. The constant m in the exponential is seen to be well expressible in terms of the parameters of the Rittner potential. The new potential is also correlated with different properties, as for example, effective charges, effective radii, effective principal quantum numbers, etc., of the combining ions. Various spectroscopic constants, viz., the ionic dissociation energy Di, the vibrational-rotational coupling constant αe, the vibrational anharmonicity constant ωexe, as well as two second-order spectroscopic constants γe and βe have been calculated for this and for the Rittner potential. From comparisons between these two potentials, the new one has been observed better than the other.
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  • 33
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    International Journal of Quantum Chemistry 16 (1979) 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 34
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    International Journal of Quantum Chemistry 16 (1979), S. 87-110 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of a series of 25 chlorinated dibenzo-p-dioxins and dibenzofurans has been characterized by means of the ab initio molecular fragment technique. This information has been employed to investigate some of the factors affecting the affinity of the molecules for the hepatic cytosol binding species described by Poland, Glover, and Kende. A quantitative structure-activity relationship involving electronic and steric parameters could be established from the data. It appears that the toxins act as electron acceptors in a charge-transfer complex with the receptor.
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  • 35
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    International Journal of Quantum Chemistry 16 (1979), S. 111-117 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The circular dichroism of molecules, which are large compared to the wavelength of light, is considered. Explicit expressions are obtained for the circular dichroism and absorption of an exciton dimer and of a free particle on a helix. The dimensions are described for which the dipole approximation for the optical properties fails.
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  • 36
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    International Journal of Quantum Chemistry 16 (1979), S. 133-152 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The analysis of modern physical mechanisms of electron transfer in proteins is given. The tunnel electron transfer and donor-acceptor electron transfer through conducting states of a protein chain are discussed in detail. The expressions for the values of the electron resonance interaction and the formulas for probabilities of electron transfer between vibronic levels of donor and acceptor states in the presence of “transverse” and “longitudinal” relaxation are given.
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  • 37
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    International Journal of Quantum Chemistry 16 (1979), S. 119-132 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The expressions for the polymer absorption band hypochromism and oscillator strength are studied in frames of the first-order perturbation theory. The physically justified approximations for a polymer hypochromism calculation are indicated. The uniform interpretation of the effect origin is given independently on the approximation used. In frames of the perturbation theory the DNA hypochromism formula is obtained, from which the known experimental dependences of hypochromism on chain length and polymer helicity degree follows directly. The analytic expression of the DNA hypochromism dependence on AT pairs content is obtained. It is established that in most cases for natural DNA the nucleotide sequence does not influence in practice the value of the hypochromic effect.
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  • 38
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    International Journal of Quantum Chemistry 16 (1979), S. 153-157 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The intramolecular interaction energy of the regular double-helical polynucleotide as a function of variables that determine the mutual position of base pairs and sugar pucker was calculated using atom-atom potentials. The calculations showed the existence of two valley-like regions with minimal values on the energetic surface. One of them corresponds to the A family of nucleic acids, the other to the B family. The points that correspond to the models constructed by means of x-ray data are placed in a conformational space near the lines that describe the position of the bottom of the valleys.
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  • 39
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    International Journal of Quantum Chemistry 16 (1979), S. 243-256 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute rate theory (ART) was applied to a series of reactions of the type A+BC → AB+C containing H, F, HF, H2, and F2, trans-cis isomerization of dideuteroethylene, and processes H + CH4 → H2 + CH3 and H′+CH4 → H′CH3 + H. Geometries and energies of activated complexes were taken from the best ab initio studies reported in the literature in which at least a DZ + P basis set was used and a large portion of the correlation energy was included. Vibrational frequencies needed for the zero-point energies and vibrational partition functions were estimated from the reported potential surfaces (HHF and HFF) or evaluated from SCF 4-31G calculations (HFH, FHF, twisted C2H4, and CH5 complexes). Compatability of calculated rate constants with the experimental data was examined.
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  • 40
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    International Journal of Quantum Chemistry 16 (1979), S. 257-260 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The TΔS0 term has been estimated for various types of van der Waals molecules and its importance for the stability predictions has been demonstrated. With hydrogen-bonded complexes the absolute values of ΔH0 and TΔS0 are comparable at 289°K. With true van der Waals molecules the TΔS0 term even represents a dominant contribution to ΔG0.
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  • 41
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    International Journal of Quantum Chemistry 16 (1979), S. 261-264 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The geometrical parameters of the ammonia molecule in the lowest-lying triplet state have been estimated by means of the SCF method and by making an extrapolation to take into account electron correlation effects. The planar configuration has been obtained as the most probable geometrical arrangement (3 A2″).
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  • 42
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    International Journal of Quantum Chemistry 16 (1979), S. 265-272 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method for the calculation of electrostatic isopotential maps, based on completely transferable bond orbitals, is proposed. According to the simple form of the potential term the amount of computational work is proportional to the first power of the number of valence electrons. Slater-type atomic orbitals are used to construct the bond orbitals, thus all integrals can be calculated explicitly. The subtilisin charge-relay system is studied as an example. It is found, in agreement with the results of Beppu and Yomosa, that the two protons transfer in a stepwise manner.
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  • 43
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    International Journal of Quantum Chemistry 16 (1979), S. 273-275 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report here a summary of a limited CI calculation carried out on the C∞v and D∞h electronically excited states of bifluoride ion. This species is interesting as the prototype of a hydrogen-bonded system. It is determined that the lowest-lying excited states of the system are dissociative and/or autoionizing.
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  • 44
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    International Journal of Quantum Chemistry 16 (1979), S. 293-298 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The role of some amino acids and metal ions in the catalytic activity of carbonic anhydrase (carbonate dehydratase EC 4.2.1.1) has been investigated. The additional stabilization of the transition state complex was used as the qualitative measure of the effect of molecular surrounding on CO2 hydration reaction calculated within the approximate CNDO/2 approach. The effect of the molecular environment has been simulated by inclusion into the SCF LCAO MO Hamiltonian, a term representing the interaction with a set of point charges and atomic dipoles centered on experimentally determined position of Zn2+ ion and all atoms of histidine 94, 96, 119 and threonine 199, 200 (or histidine 200 in the case of carbonic anhydrase B). The possible molecular mechanism of CO2 hydration inside the active site has been also discussed.
    Additional Material: 1 Ill.
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  • 45
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    International Journal of Quantum Chemistry 16 (1979), S. 277-292 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations on the SCF level and with the inclusion of valence shell electron correlation in the IEPA-PNO (independent electron pair approximation with pair natural orbitals), the PNO-CI (pair-natural-orbital configuration interaction) and the CEPA-PNO (coupled electron pair approximation with pair natural orbitals) schemes with Gaussian lobe functions of “double zeta quality” have been performed for the minimum energy path of the insertion of singlet (1A1) methylene to the (1Σg+)H2 molecule to yield methane. The energy was minimized on the SCF level to all geometrical parameters for various values of the “approximate” reaction coordinate. The energy along the reaction path decreases monotonically without a barrier and the curves representing the total energy of the system as a function of approximate reaction coordinates obtained at different levels of approximations have the same shape. From the physical point of view three phases of the reaction can be distinguished (chemically two steps) with different geometrical arrangements and different internal geometries of the partners.
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  • 46
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    International Journal of Quantum Chemistry 16 (1979), S. 299-309 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of the model hydrogen-bonded systems has been studied at the all-valence level in relation to the charge transfer mechanism. It is concluded that together with the intermolecular proton transfer an electronic charge transport occurs for hydrogen bonds of 2.70-3.00 Å in length, i.e., when the proton motion within the bond is anticipated. For elucidation of transport properties of one-dimensional hydrogen-bonded systems the tunneling-hopping model is preferred instead of the band theory. The importance of the proposed mechanism of the charge transfer for biological processes has been emphasized.
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  • 47
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    International Journal of Quantum Chemistry 16 (1979), S. 311-329 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metalloporphyrins perform a variety of functions in nature from the storage and transport of electrons and molecular oxygen to the decomposition of hydrogen peroxide and the activation of oxygen. The chemistry of both the centrally coordinated metal and the porphyrin macrocycle play important roles in these reactions. The use of model systems and metalloporphyrins, other than iron porphyrins, is described for the elucidation of the mechanism of action of the natural systems.
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  • 48
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    International Journal of Quantum Chemistry 16 (1979), S. 353-366 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The general aspects of a theory of dense-phase reactions, based on an accurate quantum-mechanical formulation of the rate equation, are considered. Using an adiabatic one-frequency oscillator model, the theory is applied to several important biological processes at low temperatures: the photinduced oxidation of cytochrome C by bacteriochlorophyll, the electron transfer from primary to secondary acceptors in bacterial photosynthesis, and the ligand rebinding of carbon oxide and β-chain of hemoglobin. A very good agreement between theory and experiment is found making use of no more than one or two (or even without any) adjustable parameters.
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  • 49
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    International Journal of Quantum Chemistry 16 (1979), S. 331-352 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A discussion of the experimental evidence for the existence of special-pair chlorophyll in the reaction centers of plants and photosynthetic bacteria is presented, and an assessment of the adequacy of various in vitro chemical model systems designed to mimic the properties of these reaction centers is given. For plant systems it appears that the in vitro models successfully mimic almost all measured in vivo properties, whereas in bacterial systems a similar situation does not obtain. Possible structural models of special-pair chlorophyll derived primarily from in vitro model studies are described. Their suitability as models of the photooxidizable pigment in plant and bacterial reaction centers is analyzed, and alternative structures for the bacterial case, which is the least well characterized structurally, are considered.
    Additional Material: 7 Ill.
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  • 50
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methods for determining the thermal measurements of biological objects have found ever increasing application in biology. This paper analyzes the temperature dependence of the heat capacity of biopolymer solutions between 4-400°K. Four distinct temperature regions were discovered, and experiments on these temperature intervals are given.
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  • 51
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    International Journal of Quantum Chemistry 16 (1979), S. 379-386 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational structure of some biologically important compounds (formamide, 1-methyl-1,4-dihydronicotinamide, and chlorocholine) was examined using quantum-chemical methods. For each of the systems studied a theoretical model (supermolecule approximation, classical continuum model, or hydration shell model) was selected to estimate the influence of solvents on the conformational structure.
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  • 52
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    International Journal of Quantum Chemistry 16 (1979) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 53
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    International Journal of Quantum Chemistry 16 (1979), S. 395-403 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrostatic molecular potential minima around the guanine-cytosine base pair within a B-DNA minihelix are computed, taking into account the contributions of the sugar-phosphate backbone and of the adjacent base-pairs. The calculations are based on ab initio SCF wave functions of the different constituents of the nucleic acid. The results point to significant differences in the potential between the isolated nucleic acid bases or base-pairs and those within the DNA. Altogether the minima in the G-C regions are strongly enhanced in the minihelix. They benefit from the field created by the neighboring phosphates. From the purely electrostatic viewpoint an ambiguity remains as concerns the relative affinity of N7 and N3 of guanine for electrophiles. On the other hand, guanine should altogether be more susceptible than cytosine to such reagents, this ordering concerning also its NH2 group compared to that of cytosine.
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  • 54
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    International Journal of Quantum Chemistry 16 (1979), S. 387-394 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regularities of the donor-acceptor interaction of nucleic acid bases and some of their derivatives with the strong acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) in thin amorphous films at 77 K were studied using UV and visible spectroscopy. Purine and pyrimidine bases are shown to form charge transfer TCNQ complexes whose band energies hνct = Ip - EA - (H* - H0) are linearly dependent of the donor ionization potential Ip. Calculated differences between the interaction energies of uncharged molecules and ion radicals, ΔE ≈ 3.0 eV, are in good agreement with experimental variations of the complex dissociation energies in the ground and excited states, (H* - H0) = 2.73 eV. Annealing of the films of complexes containing cytosine, 1-methylcytosine, uracil, and caffeine leads to ordering of their structure and the formation of ion radical salts.
    Additional Material: 5 Ill.
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  • 55
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    International Journal of Quantum Chemistry 16 (1979), S. 407-418 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first stage of protein self-organization - the formation of a fluctuating secondary structure in the unfolded protein chain - is considered. The stereochemical theory is presented enabling one to calculate helix-coil and β-structure-coil equilibrium constants. It is shown that the most probable localization of fluctuating α- and β-structure in the unfolded protein chain corresponds to the native localization of these structures. The formation of large α- and β-structural blocks is observed, each of them including several native α-helices or β-strands.
    Additional Material: 6 Ill.
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  • 56
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    International Journal of Quantum Chemistry 16 (1979), S. 445-465 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The concept of potential surfaces and classification of various types of intermolecular forces are given. The possibilities and the criteria of applicability of modern methods for potential surface calculation at short, intermediate, and long distances are discussed. Special attention is paid to the methods for calculating interactions between large molecules.
    Additional Material: 3 Ill.
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  • 57
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    International Journal of Quantum Chemistry 16 (1979), S. 419-435 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new properties of clusters - the polynuclear Fe, Cu, Mo - containing metal-protein complexes have been discussed. The properties arose as a result of strong electron interaction and of the multiorbitals system existence in which the orbitals energetically fall close together. The clusters are characterized by (i) a high electronic capacity, (ii) an ability to multielectronic transfer without essential rearrangement of nuclei configuration, (iii) a high degree of donor-acceptor energetical levels fitting at tunnel transfer, (iv) high possibilities for avoiding of reaction pathways being quantum mechanically forbidded, and (v) an ability to provide smooth reaction energetic relief in coordinated sphere. The analysis of data on spin exchange between paramagnetic centers (binuclear transition-metal complexes, nitroxile biradicals, triplet exited chromophores) showed that in the range of spinexchanged constants Kex = 1014-1 sec -1 of the distances between the centers r = 3-17 Å the approximate relation Kex =1017 exp (-2.3r)sec-1 takes place. This relation may be considered as a criterion of nonspecific electron density transfer through nonconducting medium. The quantitation of exchange triplet-triplet energy migration permits one to estimate the degree of quantum-mechanical electron density penetration through biological matrix. By means of measurement of spin-lattice relaxation rate for oxidized primary donor in bacterial photosynthetic system - bacteriochlorophyll cation (BChl+ ) - it is shown that the distance between BChl+ and primary acceptor (complex FeQ) is about 34 Å. The proposed two-step photoelectron transfer model explains the effective charge separation by relatively slow tunnel recombination of the charges BChl+ FeQ-. As spin and Mössbauer labeling experiments showed the conformation mobility of surrounding protein and membrane matrix with frequency more than 107 sec-1 is required for photoelectron output from primary photosynthetic cell in chromotophores and reaction center to secondary acceptor.
    Additional Material: 9 Ill.
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  • 58
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    International Journal of Quantum Chemistry 16 (1979), S. 877-882 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The physical aspects of the primary charge separation processes in bacterial photosynthesis are discussed. The donor-acceptor model of electron transfer due to participation of protein current states is used. The kinetics of photosynthetic reaction center (PRC) processes is investigated and the PRC energetic scheme is constructed using the nonequilibrium density matrix method. It is shown that with allowance for the effect of vibrational sublevels of states participating in transitions the theory describes well experimental data.
    Additional Material: 3 Ill.
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  • 59
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    International Journal of Quantum Chemistry 16 (1979), S. 931-935 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rates of variations of the relative yield (αη) and decay time (ατ) with the acceptor concentration (CA) have been calculated in the vicinity of CA = 0. On the basis of the equations obtained, the ratio αη/ατ has been found and a simple scheme of experimental data analysis proposed.
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  • 60
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction energy between water and B-DNA in the single and double helix is computed at a number of planar cross sections perpendicular to the helix long axis and for a few cylindrical surfaces enclosing the helix. In addition, Monte Carlo simulations are presented for a small cluster of water around regions of energy minima. On the base of these simulations the structure of water for B-DNA in solution, the quaternary structure of B-DNA, is proposed and discussed. The intermolecular interaction used in the Monte Carlo computation has been derived from ab initio computations of complexes between water and the DNA bases, diethylphosphate, a ribose derivative, and other model compounds.
    Additional Material: 11 Ill.
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  • 61
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    International Journal of Quantum Chemistry 16 (1979), S. 1161-1194 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Quelques relations essentielles pour la théorie de la représentation et l'algèbre de Wigner et Racah d'un groupe fini ou compact sont discutées et transcrites en termes de diagrammes. Une attention toute particulière est réservée au cas d'un groupe simplement réductible et tous les diagrammes donnés ici sont applicables à SU2 sans aucun changement.
    Abstract: Einige grundlegende Beziehungen für die Darstellungstheorie und die Wigner-Racah-Algebra einer endlichen oder kompakten Gruppe werden diskutiert und mit Diagrammen beschrieben. Besonders betont wird der Fall einer einfach reduziblen Gruppe. Alle Diagramme können ohne Modifizierung auf SU2 angewandt werden.
    Notes: Some basic relations for the representation theory and the Wigner-Racah algebra of a finite or compact continuous group are discussed and transcribed in terms of diagrams. Special emphasis is placed on the case of a simply reducible group and all the diagrams are applicable to SU2 without any change.
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  • 62
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    International Journal of Quantum Chemistry 16 (1979), S. 1195-1207 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: La détermination des coefficients de sousduction pour les états du groupe unitaire U(n) avec les restrictions U(n) ↓ U(n1) ⊗ U(n2) a été considérée pour les états sans spin d'un système à plusieurs électrons. Un procédé simple et adapté à la programmation pour déterminer ces coefficients a été développé en utilisant les propriétés de transformation de la base tensorielle correspondant à la représentation irréductible 〈2N/2-S, 12S〉 de U(n). Ce procédé est illustré par un simple exemple.
    Abstract: Die Bestimmung der Subduzierungskoeffiziente für Zustären Gruppe U(n) mit den Einschränkungen U(n) ↓ U(n1) ⊗ U(n2) ist für die spinfreien Zustände von Vielelektronensystemen untersucht worden. Ein einfaches programmierbares Verfahren für die Bestimmung dieser Koeffiziente ist entwickelt worden, das die Transformationseigenschaften des der irreduziblen Darstellung 〈2N/2-S, 12S〉 von U(n) gehörenden Tensorbasissatzes benutzt. Dieses Verfahren ist mit einem einfachen Beispiel illustriert worden.
    Notes: The determination of the subduction coefficients for states of the unitary group U(n) under the restrictions U(n) ↓ U(n1) ⊗ U(n2) have been considered for the spin free states of many electron systems. Using the transformation properties of the tensor basis spanning the irreducible representation 〈2N/2-S, 12S〉 of U(n) under the permutations of electron coordinates, a simple programmable procedure has been developed for the determination of these coefficients. The procedure has been illustrated using a simple example.
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  • 63
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    International Journal of Quantum Chemistry 16 (1979), S. 1265-1277 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Dans la méthode ab initio ordinaire pour calculer des orbitales molćulaires le nombre d'intégrales à évaluer augmente comme M4, où M est le nombre de fonctions de base. Dans le présent article une méthode alternative est discutée où le temps de calcul augmente beaucoup moins rapidement. Les éléments de matrice du potentiel de déformation sont calculés par des méthodes utilisant des transformées de Fourier, tandis que les éléments de matrice du potentiel des atomes neutres sont calculés par des intégrales transmissibles. Ces intégrales transmissibles (moments des potentiels des atomes neutres) peuvent ětre évaluées une fois pour toutes et incorporées comme input dans des programmes d'ordinateur. Dans un appendice on discute un théorème de développement général. Ce théorème permet un développement d'une fonction radiale arbitraire autour d'un autre centre.
    Abstract: In der üblichen ab-initio-Methode für Molekülorbitalberechnungen wächst die Anzahl von Integralen, die berechnet werden müssen, wie M4, wo M die Anzahl von Basisfunktionen ist. In diesem Artikel wird ein alternatives Verfahren diskutiert, wo die Rechnungszeit viel weniger schnell mit M wächst. Matrixelemente des Deformationspotentials werden mit Fourier-transformmethoden berechnet, während Matrixelemente des Potentials der neutralen Atome mit Hilfe von übertragbaren Integralen berechnet werden. Diese übertragbaren Integrale (Momente der Potentiale für neutrale Atome) können ein für allemal berechnet und als Inputdaten in Computerprogramme eingegliedert werden. In einem Appendix wird ein allgemeiner Entwicklungssatz diskutiert, der eine Entwicklung einer wilkürlichen kugelsymmetrischen Funktion um ein anderes Zentrum erlaubt.
    Notes: In the usual ab initio method of calculating molecular orbitals, the number of integrals to be evaluated increases as M4, where M is the number of basis functions. In this paper, an alternative method is discussed, where the computation time increases much less violently with the number of basis functions. Matrix elements of the deformation potential are evaluated by Fourier transform methods, while matrix elements of the neutral-atom potential are evaluated by means of transferable integrals. The transferable integrals (moments of the neutral-atom potentials) can be evaluated once and for all and incorporated as input data in computer programs. In an appendix to the paper, a general expansion theorem is discussed. This theorem allows an arbitrary spherically symmetric function to be expanded about another center.
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  • 64
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    International Journal of Quantum Chemistry 16 (1979), S. 1347-1356 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: La méthode de relaxation optimale pour la recherche des valeurs propres d'une matrice symétrique, proposée par Shavitt, est adaptée pour résoudre le problème des équations de mouvement. Les matrices Z et Y sont obtenues en une seule diagonalisation; les matrices A et B ne sont pas modifiées par le calcul. La méthode est particulièrement utile quand la base est de grande dimension ou quand elle n'est pas orthogonale, si l'on ne recnerche que les énergies de transition le plus basses.
    Abstract: Die von Shavitt vorgeschlagene Methode mit Optimalrelaxierung für die Bestimmung der Eigenwerte von symmetrischen Matrizen, ist zur Lösung des Bewegungsgleichungsproblems angepasst worden. Die Matrizen Z und Y werden durch eine einzige Diagonalisierung erhalten, wobei die Matrizen A und B unverändert bleiben. Dieses Verfahren ist besonders anwendbar, wenn die Basis hochdimensional oder nicht orthogonal ist, und nur die tiefsten Übergangsenergien gebraucht werden.
    Notes: The method of optimal relaxation to determine the eigenvalues of symmetric matrices, as proposed by Shavitt, has been adapted to solve the equation-of-motion problem. Matrices Z and Y are obtained by one diagonalization, while matrices A and B remain unchanged. This procedure is particularly useful for high-dimensional or nonorthogonal bases, if one needs only the lowest transition energies.
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  • 65
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    International Journal of Quantum Chemistry 16 (1979), S. 1321-1335 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Les expressions explicites des éléments de matrice des générateurs du groupe unitaire entre des configurations à N électrons, antisymétriques géminalement et adaptées au spin, données comme des éléments de matrice par rapport aux fonctions de spin de certaines permutations orbitalaires, sont obtenues à l'aide des techniques diagrammatiques de la théorie à N corps indépendante du temps. Il est démontré aussi comment ce procédé peut ětre combiné avec les méthodes graphiques des algèbres de spin pour obtenir des expressions explicites des facteurs de spin, quand un schéma de couplage a été choisi. Cette méthode-ci fournit des expressions explicites pour les permutations orbitalaires qui définissent les facteurs de spin. Si préférable la détermination explicite des permutations “line-up” peut ětre évitée, parce qu'elles sont contenues implicitement dans les diagrammes orbitalaires. Ceci explique aussi la raison de choisir des fonctions de spin géminalement antisymétriques, si on demande un formalisme simple.
    Abstract: Die expliziten Ausdrücke für die Matrixelemente der Generatoren der unitären Gruppe ziwschen geminal-antisymmetrischen spinanggepassten N-Elektronenkonfigurationen, gegeben als Spinfunktionenmatrixelemente gewisser Orbitalpermutationen, werden mittels der Diagrammverfahren der zeitunabhängigen Vielteilchentheorie abgeleitet. Es wird auch gezeigt, wie dieses Verfahren mit der in den Spinalgebren benutzten graphischen Methoden kombiniert werden kann, um explizite Ausdrücke der Spinfaktoren zu erhalten, wenn ein bestimmtes Kopplungsschema gewählt worden ist. Diese Methode gibt explizite Ausdrücke für die Orbitalpermutationen, die die Spinfaktoren definieren. Wenn gewünscht kann die explizite Bestimmung der “line-up”-Permutationen in diesem Verfahren vermieden werden, da diese implizit in den Orbitaldiagrammen enthalten sind. Dieses erklärt auch warum die geminal-antisymmetrischen Spinfunktionen benutzt werden müssen, wenn einen einfachen Formalismus gewünscht wird.
    Notes: The explicit expressions for the matrix elements of unitary group generators between geminally antisymmetric spin-adapted N-electron configurations in terms of the orbital occupancies and spin factors, given as spin function matrix elements of appropriate orbital permutations, are derived using the many-body time-independent diagrammatic techniques. It is also shown how this approach can be conveniently combined with graphical methods of spin algebras to obtain explicit expressions for the spin factors, once a definite coupling scheme is chosen. This method yields explicit expressions for the orbital permutations defining the spin factors. However, if desired, the explicit determination of line-up permutations can be avoided in this approach, since they are implicitly contained in the orbital diagrams. It also clearly indicates why the geminally antisymmetric spin functions have to be used when a simple formalism is desired.
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  • 66
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    International Journal of Quantum Chemistry 16 (1979), S. 1337-1346 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: La position et l'intensité des bandes d'absorption d'un nombre de colorants chalcone ont été calculées par la méthode FEMO. Les trois à quatre maximums d'absorption de ces molécules ont été calculés en admettant que la molécule consiste de deux parties, avec le clivage hypothétique au site de la liaison C=O de façon à fournir six et huit électrons π à ces parties, respectivement. Puis chaque partie est traitée comme une entité indépendante. Les maximums d'absorption obtenus par l'application des conditions de Kuhn sont en accord avec les valeurs expérimentales. Ces maximums ont été corrigés par rapport aux perturbations dues aux groupes fonctionnels substitués avec une électronégativité plus importante que celle du carbone. Les forces d'oscillateurs correspondant aux maximums d'absorption ont aussi été calculés.
    Abstract: Die Lage und Intensität der Absorptionsbanden einer Reihe von Chalconfarben sind mit der FEMO-Methode berechnet worden. Die drei bis vier Absorptionsmaxima dieser Moleküle wurden unter der Annahme berechnet, dass das Molekül aus zwei Teilen besteht. Die hypothetische Spaltung befindet sich in der C=O-Bindung, so dass die zwei Teilen 6 und 8 π-Elektronen, bzw., enthalten. Jeder Teil wird dann als eine unabhängige Einheit behandelt. Die mit den Kuhn'schen Bedingungen erhaltenen Absorptionsmaxima stimmen mit den Experimentalwerten überein. Die von den substituierten Funktionalgruppen mit höherer Elektronegativität als Kohlenstoff herrührenden Störungsenergiekorrektionen zu den Absorptionsmaxima sind auch berechnet worden. Die diesen maxima entsprechenden Oszillatorstärken sind weiter berechnet worden.
    Notes: The position and intensity of the absorption bands of a number of chalcone dyes have been calculated on the basis of the free-electron molecular-orbital (FEMO) theory. The three to four absorption maxima of the chalcones are calculated by assuming the molecule to consist of two parts. The hypothetical cleavage is affected at the site of C=O bond such that first and second part of the molecule contains six and eight π electrons, respectively. Each part is then treated as an independent entity and the absorption maxima obtained by the application of joint and continuity condition of Kuhn are in agreement with the experimental values. The perturbation energy correction due to the substituted functional groups with higher electronegativity than carbon have also been made in the absorption maxima. The oscillator strengths corresponding to the values of the absorption maxima have been obtained as well.
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  • 67
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    International Journal of Quantum Chemistry 15 (1979), S. 389-401 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is found that ordinary STOs fall off too fast in the atomic region in many cases. A new type of basis set, which is more adaptable to the rather different requirements of the various atomic orbitals in an atom, is developed. The suggested functional form χ(r) = Nrn-1 exp{-α[(βr + 1)1/2 - 1]} contains the STOs as a limiting case. Calculations on a series of atoms from H to Zn show that the new basis gives better results than STOs for equal basis set size. The necessary integrals do not present any problem to evaluate.
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  • 68
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    International Journal of Quantum Chemistry 15 (1979), S. 403-410 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The valence spectrum of CoO has been calculated using the CoO610- cluster, stabilized by an electrostatic field, as a model of bulk CoO. The wave functions were generated using basis sets of better than double-zeta quality. SCF wave functions were obtained for the ground state and for the first ionized state of the cluster. Limited CI calculations were performed using these orbital sets. The lowest states of the ion correspond to the main lines in the spectrum, while higher states can give rise to high-energy satellites to the main lines. The relative intensities of these satellites were estimated in the case of high-energy incident photons.
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  • 69
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    International Journal of Quantum Chemistry 15 (1979), S. 445-445 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 70
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    International Journal of Quantum Chemistry 15 (1979), S. 411-421 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pseudospectra from Gaussian basis set calculations within a frozen-core approximation have been used in a moment analysis to obtain Tchebychev profiles for the photoabsorption process in the valence shell of Ne. The profiles show good agreement with cross sections obtained in equivalent calculations using numerical atomic wave functions and continuum orbitals, particularly when the dipole-velocity form is employed. Variation of the basis sets shows that it is possible to obtain meaningful photoabsorption profiles using 13-15 virtual orbitals to describe the outgoing electron.
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  • 71
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    International Journal of Quantum Chemistry 15 (1979), S. 579-588 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A procedure is outlined for a programmable spin-free configuration-interaction (CI) study in molecules using single-parameter alternant molecular orbitals for generating various configurations. The configurations were chosen to form bases for the irreducible representation {2N/2-2, 12S} of the general linear group GL(n). Using a transformation to biorthogonal space the CI matrix elements of a spin-free Hamiltonian were generated. The procedure has been used to obtain the π-electron energies for the 3,1Ag and 3,1Bu states of cis- and trans-butadiene.
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  • 72
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    International Journal of Quantum Chemistry 15 (1979), S. 713-715 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Longuet-Higgins group is used to obtain an alternative formulation of a criterion for optical activity of nonrigid molecules recently given by Frei and Günthard.
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  • 73
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The physical interpretation of intermolecular interactions is usually based on the well-known multipole expansion of the inverse of the interparticle distance. The interaction energy is then interpreted as a sum of terms arising from the interaction of various multipole moments of both systems. It is supposed that the interaction energy calculated via the truncated multipole expansion generally depends on the choice of local coordinate systems through the coordinate dependence of the multipole moments. In this paper we prove that each term of the multipole expansion given in the form ∑k = 1 Ck/Rk is invariant with respect to identical translations and arbitrary rotations of the local coordinate systems. The invariant form of the convergence criterion of the multipole expansion is given and discussed.
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  • 74
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    International Journal of Quantum Chemistry 15 (1979), S. 717-729 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Power moments for all of the reduced hydrogenic Green's functions have been computed. These moments have the same form as the corresponding moments of the free-particle Green's functions. Green's functions of the second kind are defined, and uses for these objects in model potential theory and the theory of many-body Green's functions are pointed out. In the case of the ground state of the hydrogenic atom, the Green's function of the second kind has been given.
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  • 75
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    International Journal of Quantum Chemistry 16 (1979), S. 79-86 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is described for processing the enthalpy, entropy, and Gibbs free energy terms of formation of the individual isomers of n-particle clusters obtained by means of quantum-chemical calculations, to enable a comparison of these partial theoretical characteristics with the overall experimental ones. The general scheme of weighting treatment is illustrated by examples based on recent quantum-chemical results of studies of isomeric forms of (NO)2, (H2O)5 and (D2O)5, and CH3OH · 3H2O and CH3OH · 6H2O clusters.
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    International Journal of Quantum Chemistry 16 (1979), S. 437-444 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present work is devoted to investigation of thermal transitions in the crystals of seven proteins to compare the protein globule stability in crystal and solution. Calorimetry methods, electron and optical microscopy, as well as x-ray diffraction studies are used. It is found that protein crystals do not melt and that the destruction of the crystal lattice is a result of protein globule denaturation within the crystal. It is demonstrated that during the heating of pepsin and DF-trypsin crystals it is possible to observe phase transition of the first order. Equilibrium temperatures of protein denaturation in crystals and in solution coincide. The peculiarities of the crystal state are revealed in the increasing thermal transition cooperativity and the system relaxation period.
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  • 77
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    International Journal of Quantum Chemistry 16 (1979), S. 509-515 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The steric constants Es and ν have the greatest chance of being independent of lipophilic substituent constants. There is a high probability among hydrocarbon substituents that the steric constants correlate with the lipophilic ones, while in the case of polar substituents the probability is low.
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  • 78
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    International Journal of Quantum Chemistry 16 (1979), S. 485-500 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The model systems of molecular nitrogen fixation [N2 + H]⋅, [N2 + H]+, [N2 + H]-, [N2 + H2], [N2 + H2]+, and [N2 + H2]- were studied by the semiempirical INDO method. The study was based on the formal analogy between the catalytic reactions and the photochemical, radical, and ionic reactions on the other side. Symmetrical and donor-acceptor properties of necessary catalytic systems were proposed using the dependence of energy characteristics and electron structure on reaction coordinate. On the basis of this MO study we have proposed the appropriate symmetry types of catalysts for each of acceptable models of nitrogen fixation. For one of the proposed systems there was realised a model MO computation with explicit inclusion of atoms of transition metals (Fe, V).
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  • 79
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    International Journal of Quantum Chemistry 16 (1979), S. 517-525 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: All equilibrium conformations of a series of N-alkyl-α-alkyl derivatives of noradrenaline and their synthetic precursors - phenylaminoketones - have been calculated. It has been shown that spasmodic changes in bronchodilating activity of the catecholamines, observed with the increase in α-alkyl substituent size, may arise from the difference in the ratio of diastereoisomers produced by reduction of aminoketones.
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  • 80
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    International Journal of Quantum Chemistry 16 (1979), S. 669-689 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper presents a critical discussion of recent discoveries on the metabolic transformations of polycyclic aromatic hydrocarbons and their interactions with nucleic acids in the light of quantum-mechanical theories of chemical carcinogenesis.
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  • 81
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    International Journal of Quantum Chemistry 16 (1979), S. 641-653 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In view of building a workable molecular model of tetraliganded zinc at the active site of carbonic anhydrase, an ab initio SCF study using pseudopotentials is performed on Zn2+(OH2)n from n = 2 to 6, Zn2+(NH3)n-1 (OH2) for n = 2 and 4, Zn2+(NH3)2 (imidazole) (OH2), and their ionized species involving OH- or imidazolate, considering in particular the evolution of the properties of the ligands and of the bound cation upon increasing n and upon replacement of one ligand by another. (Comparison of NH3 and imidazole binding was made in a full SCF calculation.) The results obtained in the tetraliganded complex confirm that zinc binding facilitates water deprotonation more than imidazole deprotonation, so as to reverse the order of their intrinsic ease of ionization. A study of the approach of CO2 toward the active site is made in an electrostatic approximation using as models the most representative of the computed four-ligand complexes.
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  • 82
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    International Journal of Quantum Chemistry 16 (1979), S. 655-668 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Of the two known families of double-stranded DNA conformations, A is stable in less-polar, and B in more-polar solutions. In some water-nonelectrolyte solutions, B to A transition occurs when water activity in the system is near 0.8. In such systems, however, as water-methanol, water-ethylene glycol, etc., B conformation is stable at very low water activity. Hyperfine splitting constant of a spin label (A), a widely used criterion of the solvent polarity, was measured by EPR method in the solutions, in which B to A transition takes place at 25°C. A values in solutions of different compositions are close to each other. A method for quantitative estimation of Van der Waals and hydrogen-bond contributions to A values is proposed. A values in water-methanol solutions show that their polarity is too high for the A form to be stable. Decreasing temperature shifts the B-A equilibrium to the B form, which correlates with increasing polarity of the water-alcohol solutions, as measured by the EPR method. Thus B to A transition is mainly determined by the polarity of the environment, which, in turn, is determined by the ability of the solvent molecules to participate in Van der Waals interactions and hydrogen bonding.
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  • 83
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    International Journal of Quantum Chemistry 16 (1979) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 84
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    International Journal of Quantum Chemistry 16 (1979), S. 691-706 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The problems connected with the transformations of energy in the living systems are reviewed. Possibility of Bose-Einstein condensation by input of radiant energy over a critical level is considered as a route for overcoming the barriers of activation energy under the conditions of a pump and a thermalizing environment. Molecular force fields constitute the pump. Under our scheme excitons constitute the major fraction of bosons to so condense. Instantaneous dipoles of London theory are then examined as excitons. Lastly an energy packet from a quantized dipolar field is suggested rather than the concept of “conformons.” Questions of charge and of other modes of energy transfer are briefly discussed.
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  • 85
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    International Journal of Quantum Chemistry 16 (1979), S. 833-837 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Excited π-electronic states of cytosine and uracil are calculated by the CI method. The effects of a transition from the single-excited configuration set to the set involving all double-excited configurations are considered. The set expansion is shown to affect essentially the transition energies and oscillator strengths, in particular, an additional electron transition related to the first absorption band occurs in the singlet uracil spectrum. When doubly excitations are taken into account the triplet transition energies considerably increase and become practically insensitive to repulsion integral parametrization.
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  • 86
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    International Journal of Quantum Chemistry 16 (1979), S. 839-845 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rotational isomerization of bipyridines C5H4N—C5H4N was studied by CNDO/2, PPP/CI, and CNDO/CI methods. It is shown that CNDO/2 overestimates the angle of rotation φ between the pyridine rings ca. two times. The angle φ was determined for 2,2′-bipyridine by means of correlation of the theoretical (CNDO/2) and experimental dipole moment. It was also found from the correlation between the theoretical and experimental UV spectra. It is shown that there is an explicit dependence of the results upon the distance between heteroatoms (PPP/CI). It has been found that the CNDO/CI method correctly predicts the value of the rotational angles and their sequence in bipyridines.
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  • 87
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    International Journal of Quantum Chemistry 16 (1979), S. 857-862 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the representation of a completely stiff macromolecule as a long rigid rod and the representation of a semiflexible macromolecule as a chain of freely rotating connected effective rigid rods, the conditions of formation of the liquid-crystalline phase in the solutions of such macromolecules are obtained and the diagram of states for the corresponding phase transitions in the variables temperature-volume fraction of polymer in the solution is constructed.
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  • 88
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    International Journal of Quantum Chemistry 16 (1979), S. 939-954 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quadrupole moments, dipole quadrupole polarizability A, and quadrupole polarizability C values have been obtained for a set of organic molecules, in both the ground and first singlet excited states, by means of Rayleigh-Schrödinger perturbation theory. Computations for π systems have been carried out using the PPP-SCF procedure. Results are discussed through the paper and compared with available experimental and theoretical information. Quadrupole moments are shown to be very sensitive to the quality of the wave functions, and the A and C polarizabilities are highly dependent on geometries.
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  • 89
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    International Journal of Quantum Chemistry 16 (1979), S. 955-972 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is proved that the values of various types of physical observables issued from a truncated CI are not size consistent. These observables include electronic transitions, ionization potential, and all the quantities depending on the one-electron density matrix γ. Numerical examples are given. It is found that the error due to this size inconsistency can be important for systems of moderate size (e.g., 16% on a matrix element of γ for a 20-electron system).
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  • 90
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    International Journal of Quantum Chemistry 16 (1979), S. 973-983 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is introduced which simplifies the derivation of equations for the calculation of statistical sums for vibronic systems. Within the “independent ordering approximation” analytical expressions are found for thermodynamic functions for molecules with degenerate electronic ground state (E-β and E - e types of degeneracies). Vibronic interactions are shown to yield an additional thermodynamic stabilization. The computations were carried out for VCl4 and VBr4 with doubly degenerate electronic ground states. For these molecules the effect is shown to be small.
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  • 91
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    International Journal of Quantum Chemistry 16 (1979), S. 985-991 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The role of the continuum, so important in ground-state properties, is known to be less important and may even be negligible in the computation of polarizabilities and other higher negative moments of the oscillator strength distribution. This can be rationalized in terms of the solutions of the inhomogeneous equation generating the moments as an alternative to the dominating first term in an eigenfunction expansion. This leads in a natural form to the approximation Fφ0(1 + w(r)) for the perturbed wave function where 1 + w(r) represents a nonuniform scaling of the unperturbed function φ0.
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  • 92
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    International Journal of Quantum Chemistry 16 (1979), S. 993-1007 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper attempts to apply the results of analytic perturbation theory to systems exhibiting some degree of randomness in their state variables. In particular, we focus on the localization problem in the Anderson model. It is shown that this approach proves the existence of bound states as a result of the statistical treatment of the Weinberg-van Winter-Hunziker irreducible N-particle kernel. The analysis is extended beyond the one-particle cluster approach and the occurrence of higher-order clusters is discussed in relation to the diluteness criterion and the conditions set on the interaction potential V.
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  • 93
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    International Journal of Quantum Chemistry 16 (1979), S. 1141-1148 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The semiempirical MINDO/3 method is employed to calculate the energies of various tautomers of model tautomeric compounds -  2-oxo- and 4-oxopyridines and pyrimidines. The results are compared with experimental data in the gas phase, where the solute-solvent interactions not included in theoretical calculations are absent. Although the relative energies obtained by the MINDO/3 method appear to be superior to other semiempirical and ab initio calculations, the accuracy of the method was determined to be as low as 3-4 kcal/mol. It indicates that it is exceedingly difficult to account theoretically for intrinsic stabilities of the tautomers. The importance of various factors influencing calculated free-energy differences is discussed. Particular attention is paid to the problem of geometry optimization.
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    International Journal of Quantum Chemistry 16 (1979), S. 1157-1157 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 95
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 96
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    International Journal of Quantum Chemistry 16 (1979), S. 1357-1368 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: L'utilisation effective des relations hypervirielles a été examinée en détail pour améliorer les approximations des fonctions d'onde représentant des états excités pour l'oscillateur harmonique. Une nouvelle méthode est présentée, qui utilise simultanément les relations hypervirielles nondiagonales et la relation diagonale. Afin d'employer plus effectivement ces relations les aspects suivants sont mis en évidence: (i) la méthode présentée est utile pour obtenier de meilleurs résultats raisonnables pour les énergies d'excitation et les fonctions d'onde; (ii) il faut que l'état fondamental donné satisfasse au théorème du viriel; (iii) dans l'opérateur hyperviriel utilisé ici comme xm, les valeurs les plus petities de m donnent les meilleurs résultats; (iv) l'utilisation d'un nombre relativement restreint de fonctions de base de type exp (-γ|x|) suffit pour reproduire l'état excité exact. Surtout la seconde condition est importante. Tenant compte de ces points-ci on a obtenu pour les deux premiers états excités des résultats sensiblement améliorés pour l'énergie d'excitation, la fonction d'onde et d'autres quantités physiques comme les moments de transition et les forces d'oscillateur. On trouve aussi que la méthode présentée ici est plus efficace que l'emploi des relations hypervirielles non-diagonales seules ou la méthode de Gopinathan.
    Abstract: Die effektive Anwendung der Hypervirialrelationen wird detailliert untersucht, um angenäherte Wellenfunktionen für angeregte Zustände des harmonischen Oszillators zu verbesseren. Eine neue Methode wird vorgelegt, die gleichzeitig die nicht-diagonalen und die diagonale Hypervirialrelationen verwenden. Um diese Relationen effektiver anzuwenden werden folgende Punkte unterstrichen: (i) die neue Methode gibt bessere Resultate für die Anregungsenergien und die Zustandsfunktionen; (ii) der gegebene Grundzustand muss den Virialsatz erfüllen; (iii) in dem hier benutzten Hypervirialoperator xm geben kleinere Werte von m bessere Resultate; (iv) die Verwendung einer relativ kleinen Anzahl von Basisfunktionen von Typ exp (-γ|x|) genugt um den exakten angeregten Zustand zu reproduzieren. Besonders die zweite Bedingung ist wichtig. Unter Berucksichtigung dieser Observationen sind fur die zwei ersten angeregten Zustande betrachtlich verbesserte Ergebnisse fur die Anregungsenergie, Wellenfunktion und andere physikalische Grosse wie z.B. Ubergangsrnomente und Oszillatorenstarke erhalten worden. Die vorgelegte Methode ist auch effektiver als die Anwen-dung der nicht-diagonalen Hypervirialrelationen allein oder der Methode von Gopinathan.
    Notes: The effective utilization of hypervirial relations is scrutinized to improve the approximate excited-state functions in the harmonic oscillator system. A new method is presented which simultaneously employs the off-diagonal hypervirial relations with the diagonal hypervirial relation. In order to use these relations effectively, the following points are pointed out: (i) the presented method is useful to get better reasonable results for the excitation energies and the state functions; (ii) the ground state given must satisfy the virial theorem; (iii) in the hypervirial operator used here as xm, the smaller integers of m's present better results; and (iv) the employment of the comparatively small number of trial basis functions of the type exp (-γ|x|) is sufficient for reproducing the exact excited state. Especially among them, condition (ii) plays an important role. Applying all the proposals to the first and the second excited states, one gets a highly improved excitation energy, state function, and other physical quantities (e.g., transition moment and oscillator strength). The presented method is also found to be more effective than the employment of only the off-diagonal hypervirial relations or the method of the scaling operation.
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    International Journal of Quantum Chemistry 15 (1979), S. 379-387 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new theoretical approach to the cooperativity of an enzyme has been proposed. When we applied the present theory to the allosteric effect of hemoglobin, we obtained a so-called Koshland-Nemethy-Filmer formula. Our theory suggested that the sigmoid curve becomes sharper when the affinity of the first oxygen molecule of the hemoglobin is smaller.
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The atomic dipole approximation has been employed to calculate the energies of electrostatic interaction between adenine and various pyrimidine derivatives. Minima of the interaction energy for various planar configurations were determined. Inclusion of the “monopole-dipole” and “dipole-dipole” terms in the multipole expansion improves considerably the agreement with experimental data. The effect of sulfur substitution has been investigated in detail. Formation of N—H…S hydrogen bonds is less favorable than of N—H…O bonds, due largely to the lower atomic dipole of the sulfur atom resulting from the shift of the π-electron charge toward the neighboring carbon. The results are relevant to the interactions of thiouracils in nucleic acids.
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 100
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    International Journal of Quantum Chemistry 15 (1979), S. 423-443 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The expectation energy values EK, Vee, Vnn, Ven, and ET have been calculated for H2 and the C1, C2, and C3 hydrocarbons using a (9,5) basis set and the experimental geometries. Treating the theoretical reaction heat, ΔET, as the resultant of the nuclear repulsion term, ΔVnn, and the net electron energy term, ΔEelec = ΔEK + ΔVee + ΔVen, the contribution of inner and outer shell electron energies to ΔEelec, and hence to ΔET, has been calculated for a large number of hydrocarbon reactions by evaluating the Coulson-Neilson energies ηi, where Σηi = Eelec. For the vast majority of reactions, 67/84, the change in inner shell electron energy, (Σηi)inner, accounts for more than 10% of ΔEelec, in many cases being as high as 20-35%. Furthermore, in addition to these cases in which the change in inner shell electron energy serves to augment (significantly) the change in outer shell electron energy, there are other cases in which the change in inner shell electron energy either exceeds in magnitude the change in outer shell energy, or is even opposite in sign, indicative of inner and outer shell electrons acting contrariwise. Inner shell electron energies contribute to the reaction heats because they are structure dependent, like the more familiar orbital energies ε, but the dependence is of a different kind.
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