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  • 1995-1999  (259)
  • 1980-1984
  • 1998  (259)
  • Genetics  (153)
  • Nuclear reactions
  • Physical Chemistry
  • 1
    Digitale Medien
    Digitale Medien
    Crosses between diabetic BB/OK and wild rats confirm that a third gene is essential for diabetes development (1998)
    Springer
    Acta diabetologica 35 (1998), S. 109-111 
    Details
    ISSN: 1432-5233
    Schlagwort(e): Key words BB rat ; Diabetes ; Genetics ; Crossing study
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Several crossing studies with diabetic BB rats have shown that in addition to the lymphopenia (Iddm1) and the MHC class II genes of the RT1u haplotype (Iddm2) there are further non-MHC genes essential for diabetes development. Because diabetes-resistant inbred rat strains may be homozygous for one of the diabetogenic non-MHC genes, masking the expression of diabetogenic genes and leading to an underestimation of the number of diabetogenic genes, we crossed wild and diabetic BB/OK rats. The F1 hybrids were backcrossed onto diabetic female (BC1W-F, n=97) and male BB/OK rats (BC1W-M, n=98) transferred to a specified-pathogen-free environment and studied for the frequency and age at onset of diabetes up to an age of 30 weeks. Comparing the results of these BC1 W hybrids with similarly derived hybrids using diabetes-resistant DA rats (BC1DA-F, n=113; BC1DA-M, n=216), the diabetes frequency in total was comparable indicating the action of three recessive genes. The percentage of diabetics in Iddm1 and Iddm2 homozygotes confirmed the existence of the third gene, Iddm3, but there were some sex differences; significantly more male than female BC1W-F and significantly more BC1DA-M than BC1DA-F males were diabetic. Regarding the age at onset, the BC1W-F hybrids manifested not only significantly earlier, but also more uniformly than BC1DA-F and BC1-M hybrids.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005920050114
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  • 2
    Digitale Medien
    Digitale Medien
    Hepatocyte nuclear factor-1a gene and non-insulin-dependent diabetes mellitus in the Japanese population (1998)
    Springer
    Acta diabetologica 35 (1998), S. 150-153 
    Details
    ISSN: 1432-5233
    Schlagwort(e): Key words Non-insulin-dependent diabetes mellitus ; MODY ; Hepatocyte nuclear factor-1α ; Genetics ; Microsatellite polymorphism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Recently, hepatocyte nuclear factor-1α (HNF-1α, which is encoded by the TCF1 gene) mutations were reported in a subset of patients with maturity onset diabetes of the young (MODY3). We studied the contribution of TCF1 to genetic susceptibility to common non-insulin-dependent diabetes mellitus (type 2) in Japanese subjects by investigating allelic association with type 2 diabetes use of three markers. We also studied the frequency of the G191D mutation, the only mutation of TCF1 reported so far in late-onset type 2 diabetes. A total of 356 subjects were studied. There were no significant differences in allele frequency of the three markers between patients with type 2 diabetes and control subjects. A G191D mutation was not found in the subjects studied, giving a frequency of less than 0.4% in common type 2 diabetes. The lack of association of type 2 diabetes with three markers in and near TCF1 suggests that mutations in TCF1 derived from a limited number of founders are not a major cause of common type 2 diabetes even in the genetically homogeneous Japanese population. The data also indicate that the G191D mutation in TCF1 plays little, if any, role in susceptibility to common type 2 diabetes in the Japanese.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005920050120
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  • 3
    Digitale Medien
    Digitale Medien
    The effect of genotype on response thresholds to sucrose and foraging behavior of honey bees (Apis mellifera L.) (1998)
    Springer
    Journal of comparative physiology 182 (1998), S. 489-500 
    Details
    ISSN: 1432-1351
    Schlagwort(e): Key words Honey bee ; Behavior ; Genetics ; Neurobiology ; Foraging
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Honey bee foragers were tested for their proboscis extension response (PER) to water and varying solutions of sucrose. Returning pollen and nectar foragers were collected at the entrance of a colony and were assayed in the laboratory. Pollen foragers had a significantly higher probability of responding to water and to lower concentrations of sucrose. Bees derived from artificially selected high- and low-pollen-hoarding strains were also tested using the proboscis extension assay. Returning foragers were captured and tested for PERs to 30% sucrose. Results demonstrated a genotypic effect on PERs of returning foragers. The PERs of departing high- and low-strain foragers were consistent with those of returning foragers. The PERs were related to nectar and water reward perception of foragers. High strain bees were more likely to return with loads of water and lower concentrations of sucrose than foragers from the low pollen strain. Low-strain bees were more likely to return empty. We identified a previously mapped genomic region that contains a variable quantitative trait locus that appears to influence sucrose response thresholds. These studies demonstrate a gene-brain-behavior pathway that can be altered as a consequence of colony-level selection for quantities of stored food.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003590050196
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  • 4
    Digitale Medien
    Digitale Medien
    Genetics of psoriasis (1998)
    Springer
    Archives of dermatological research 290 (1998), S. 463-476 
    Details
    ISSN: 1432-069X
    Schlagwort(e): Key words Psoriasis ; Genetics ; HLA ; Linkage ; Epidemiology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Non-pustular psoriasis consists of two disease subtypes, type I and type II, which demonstrate distinct characteristics. Firstly the disease presents in different decades of life, in type I before the age of 40 years and later in type II. Secondly, contrasting frequencies of HLA alleles are found: type I patients express predominantly HLA-Cw6, -B57, and -DR7, whereas in type II patients HLA-Cw2 is overrepresented. Finally, familial inheritance is found in type I but not in type II psoriasis. The study of concomitant diseases in psoriasis contributes to deciphering the distinct patterns of the disease. Defence against invading microorganisms seems better developed in psoriatics than in controls. This evolutionary benefit may have caused the overall high incidence of psoriasis of 2%. Psoriasis is a multifactorial and heterogenetically inherited disease. The heterogeneity is evident by the diversity of genetically linked markers. The multifactorial component results from the observation of external trigger mechanisms, such as the Koebner phenomenon, stress and the intake of certain drugs. Twin studies have shown that environmental factors contribute to the onset of the disease. In type I psoriasis, special extended haplotypes such as EH57.1 (HLA-Cw6-B57-DRB1*0701-DQA1*0201-DQBl*0303) and EH65.1 (HLA-Cw8-B65-DRB1*0102-DQB1*0501) have been found to be increased. The application of microsatellite techniques has identified distinct positions on several chromosomes at which putative psoriasis genes may be located. Disease susceptibility genes are thought to be present on chromosomes 4q, 6p, 16q, 17q and 20p. Moreover, on chromosome 1q, genes regulating epidermal differentiation have been identified. Linkage to this area has been proposed. Furthermore, psoriasis gene loci on chromosomes 2, 8 and 20 have been suggested.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004030050338
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  • 5
    Digitale Medien
    Digitale Medien
    Recent advances in genetic research on schizophrenia (1998)
    Springer
    Journal of biomedical science 5 (1998), S. 28-30 
    Details
    ISSN: 1423-0127
    Schlagwort(e): Genetics ; Schizophrenia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Evidence for genetic factors in schizophrenia is reviewed with regard to family, twin and adoption studies, and recent advances in molecular genetic technology are applied to explore possible gene loci susceptible to schizophrenia. Application of neuropsychological and neuroimaging methodologies are also reviewed with an aim to develop criteria for defining phenotypes for genetic studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02253353
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  • 6
    Digitale Medien
    Digitale Medien
    Prediction of febrile seizures in siblings: a practical approach (1998)
    Springer
    European journal of pediatrics 157 (1998), S. 340-344 
    Details
    ISSN: 1432-1076
    Schlagwort(e): Key words Febrile seizures ; Genetics ; Family ; Risk factors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract To quantify the risk of febrile seizures (FS) in relatives of children with FS and to predict the risk of FS in siblings, we calculated cumulative risks of FS in first degree relatives of 129 children with FS. The study was conducted as a prospective follow up study of FS recurrences at the outpatient clinic of the Sophia Children's Hospital in Rotterdam. Thirteen parents and 12 siblings had experienced FS, accounting for a 6-year cumulative risk of 7%. The risk of FS was increased in relatives of children with recurrent FS (12%). The risk of FS in siblings (10%) in our study was more than twice the average risk in a similar population (4%). A positive FS history in a parent, young age at onset in the proband, and recurrences in the proband were selected in a multivariable prediction model. If two or more of these risk factors were present, the risk of West European siblings to develop FS was 46% (hazard ratio 5.4). Conclusion The cumulative risk of FS in siblings of children with FS is increased. The age attained risk of FS can be estimated using a practical model incorporating three readily available risk factors.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004310050824
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  • 7
    Digitale Medien
    Digitale Medien
    Paternal age is a risk factor for Alzheimer disease in the absence of a major gene (1998)
    Springer
    Neurogenetics 1 (1998), S. 277-280 
    Details
    ISSN: 1364-6753
    Schlagwort(e): Key words Alzheimer disease ; Risk factors ; Parental age ; Genetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: ABSTRACT We compared the parental age at birth of patients with Alzheimer disease (AD) with that of cognitively healthy control subjects. Within 206 carefully diagnosed AD patients, two groups were distinguished according to the likelihood of carrying a major gene for AD (MGAD). This likelihood was calculated by applying a Bayesian approach which incorporates data on aggregation of the disease, age at onset, and "censoring" ages within the family. All AD patients were ranked by MGAD probability. According to the sample's quartiles, two subgroups were defined representing the 52 individuals with the lowest and the 52 with the highest MGAD probability. Age at onset of dementia, education, and apolipoprotein E ε  4 allele frequencies were not statistically different between the two groups. Fathers of patients with a low MGAD probability were significantly older (35.7±8.1 years) than fathers of both other groups (high MGAD probability 31.3±6.9 years, P =0.004; controls 32.6±6.8 years, P =0.04, n=50). The differences for mothers were less pronounced and not statistically significant. These findings suggest that increased paternal age is a risk factor for AD in the absence of a major gene, whereas increased maternal age and AD are associated only weakly and independently of genetic disposition.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100480050041
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  • 8
    Digitale Medien
    Digitale Medien
    Recent progress in the genetics of human epilepsies (1998)
    Springer
    Neurogenetics 1 (1998), S. 153-163 
    Details
    ISSN: 1364-6753
    Schlagwort(e): Key words Epilepsy ; Genetics ; Linkage
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: ABSTRACT Despite several lines of evidence indicating a strong genetic influence in the etiology of idiopathic epilepsies, progress in the mapping and identification of human epilepsy genes has been limited until recently. In addition to the localisation and/or isolation of several genes causing progressive epilepsies associated with cerebral degeneration, at least seven human genomic regions (6p, 8q, 10q, 15q, 16p, 19q, 20q) are now known to harbour genes implicated in idiopathic epilepsies. In the case of nocturnal frontal lobe epilepsy, mutations in a nicotinic acetylcholine receptor subunit gene have been identified. Systematic studies of rare epileptic disorders inherited as monogenic Mendelian traits, as well as studies on more complex polygenic idiopathic epilepsies, are still needed in order to identify all the epilepsy genes. This will allow better diagnosis and genetic counseling in families of affected individuals, a better understanding of both the pathophysiology of epilepsies and normal brain functioning, and the design of new pharmacological and genetic therapies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100480050024
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  • 9
    Digitale Medien
    Digitale Medien
    Microsatellite DNA in Actinidia chinensis: isolation, characterisation, and homology in related species (1998)
    Springer
    Theoretical and applied genetics 97 (1998), S. 1269-1278 
    Details
    ISSN: 1432-2242
    Schlagwort(e): Key words Simple sequence repeat (SSR) ; Microsatellites ; Molecular markers ; Genetics ; Kiwifruit
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  We have isolated and sequenced 263 microsatellite-containing clones from two small insert libraries of Actinidia chinensis enriched for (AC/GT) and (AG/CT) repeats, respectively. Primer pairs were designed for 203 microsatellite loci and successfully amplified from both plasmid and A. chinensis genomic DNA. In this paper we report the sequences of 40 primer pairs for which we have demonstrated Mendelian segregation in the progeny from controlled crosses. The polymorphism of ten microsatellites of each type was evaluated in four diploid and six tetraploid genotypes of A. chinensis. All microsatellites proved to be polymorphic, the number of alleles per locus detected in polyacrylamide sequencing gels ranging from 9 to 17. The high degree of polymorphism in Actinidia renders these markers useful either for mapping in A. chinensis or for fingerprinting cultivars of both domesticated kiwifruit species (A. chinensis and A. deliciosa). While most primer pairs produced single amplification products, about 20% generated banding patterns consistent with the amplification of two different loci. This supports the hypothesis that diploid species of Actinidia (2n=2x=58) are polyploid in origin with a basic chromosome number x=14/15 and that chromosome duplication may have occurred during the evolution of the genus. Finally, we have assayed the cross-species transportability of primer pairs designed from A. chinensis sequences and have found extensive cross-species amplification within the genus Actinidia; 75% of primer pairs gave successful amplification in the eight species assayed (A. arguta, A. rufa, A. polygama, A. chrysantha, A. callosa, A. hemsleyana, A. eriantha, and A. deliciosa), which are representative of the four sections into which the genus is currently split.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001220051019
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  • 10
    Digitale Medien
    Digitale Medien
    Fruit tree genetics at a turning point: the almond example (1998)
    Springer
    Theoretical and applied genetics 96 (1998), S. 588-601 
    Details
    ISSN: 1432-2242
    Schlagwort(e): Key words Fruit trees ; Genetics ; Almond ; Prunus amygdalus ; Breeding
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  The large size and the long generation time of fruit trees generally reduce the possibilities of obtaining genetic information on the transmission and heritability of useful agronomic traits in these species. However, from breeding work carried out with fruit trees, an important amount of data is now available, although large differences are apparent among the different species. There is not much information known about almond compared to what is available on other Prunus fruit species, but more data have been accumulated on it than on most of the other nut trees, thus making almond special among all the temperate fruit and nut species. Only five qualitative traits have been described in almond, with an additional two also possibly qualitative. Heritabilities have been estimated for an important number of quantitative traits, mainly phenological times and fruit characters. Important information is available on molecular markers, including enzymes, RFLPs, RAPDs and other recently developed markers. Linkages, however, have only been established among molecular markers, allowing accurate genetic maps to be built but not yet enabling agronomical characters to be located in these maps, probably because the latter have not been sufficiently studied. The effectiveness of the application of genetic maps in plant breeding will depend on the accuracy of the study of different agronomic traits and their expression, implying more field work and recognition of this work. Ultimately, any new fruit cultivar has to be grown in the field and has to allow the grower to make a profit.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001220050777
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  • 11
    Digitale Medien
    Digitale Medien
    Cytological basis for a tetraspory in Cupressus sempervirens L. megagametogenesis and its implications in genetic studies (1998)
    Springer
    Theoretical and applied genetics 96 (1998), S. 776-779 
    Details
    ISSN: 1432-2242
    Schlagwort(e): Key words Cupressus sempervirens ; Cytology ; Megasporogenesis ; Megagametogenesis ; Genetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  The processes of megasporogenesis and early megagametogenesis were cytologically investigated in Cupressus sempervirens L. in order to elucidate, at the cellular level, the origin of the megagametophyte. After pollination, sporogenous tissue developed in the chalazal region of the nucellus, but only one megaspore mother cell differentiated and divided meiotically without cell-wall formation. This led to the development of a cell with four nuclei which directly functioned as a megaspore. The C. sempervirens megagametophyte is thus tetrasporic, in contrast to the majority of conifers where the megagametophyte is monosporic. The consequenses of this observation are discussed from a genetics point of view.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001220050801
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  • 12
    Digitale Medien
    Digitale Medien
    Patient regrets after bilateral prophylactic mastectomy (1998)
    Springer
    Annals of surgical oncology 5 (1998), S. 603-606 
    Details
    ISSN: 1534-4681
    Schlagwort(e): Breast cancer ; Genetics ; Prophylactic mastectomy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Background: The discovery of a cadre of breast cancer susceptibility genes has resulted in an increase in the number of women seeking information about prophylactic breast surgery, but virtually no large-scale prospective databases exist to assist women considering prophylactic mastectomy. Methods: The authors constructed a National Prophylactic Mastectomy Registry comprised of a volunteer population of 817 women from 43 states who have undergone prophylactic mastectomy. Results: In the registry, 370 women had undergone bilateral prophylactic mastectomy. Twenty-one (5%) women expressed regrets about the procedure. The median follow-up was 14.6 years (mean 14.8 years; range 0.2–51 years). Those with regrets were subsetted into those with major (n=10) or minor (n=7) regrets. Regrets were more common in those women with whom discussion about prophylactic mastectomy was initiated by a physician (19/255), compared with patients who initiated the discussion themselves (2/108;P〈.05). Conclusions: The overall satisfaction rate of 95% reported here may be explained by the voluntary nature of this registry. The most important factor that predicts an unfavorable outcome following bilateral prophylactic mastectomy is a physician-initiated discussion.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02303829
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  • 13
    Digitale Medien
    Digitale Medien
    Autosomal recessive polycystic kidney disease (1998)
    Springer
    Journal of molecular medicine 76 (1998), S. 303-309 
    Details
    ISSN: 1432-1440
    Schlagwort(e): Key words Autosomal recessive polycystic kidney disease ; Linkage study ; Genetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Autosomal recessive polycystic kidney disease (ARPKD) is a rare inherited disorder which usually becomes clinically manifest in early childhood, although the spectrum of ARPKD is much more variable than generally known. Presentation of ARPKD at later ages and survival into adulthood have been observed in many cases. The responsible gene has been mapped to chromosome 6p. Thus there is no evidence of genetic heterogeneity. The most important indication for DNA diagnosis is the prenatal diagnosis in families with at least one affected child. The critical region has been narrowed with the use of recombinant families of about 4 cM. Several possible candidate genes have been excluded.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001090050221
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  • 14
    Digitale Medien
    Digitale Medien
    Mixing in Stars and the Evolution of the 3He Abundance (1998)
    Springer
    Space science reviews 84 (1998), S. 199-206 
    Details
    ISSN: 1572-9672
    Schlagwort(e): Nuclear reactions ; Nucleosynthesis ; Abundances ; Stars:Evolution ; Interior ; Rotation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We first recall the observational and theoretical facts that constitute the so-called 3He problem. We then review the chemical anomalies that could be related to the destruction of 3He in red giants stars. We show how a simple consistent mechanism can lead to the destruction of 3He in low mass stars and simultaneously account for the low 12C/13C ratios and low lithium abundances observed in giant stars of different populations. This process should both naturally account for the recent measurements of 3He/H in galactic HII regions and allow for high values of 3He observed in some planetary nebulae. We propose a simple statistical estimation of the fraction of stars that may be affected by this process.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1005027519798
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  • 15
    Digitale Medien
    Digitale Medien
    The possibilities of modeling neural networks in the framework of the thermodynamics of genetically disordered systems (glasses) (1998)
    Springer
    Journal of biological physics 24 (1998), S. 41-58 
    Details
    ISSN: 1573-0689
    Schlagwort(e): Neural networks ; Associative memory ; Brain functions ; Disordered systems ; Genetics ; Synergetics ; Self-organization ; Vitreous state
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract Non-spin glasses possess a number of specific features which, in structural and dynamic aspects, are close to conditions necessary for neural networks to function. In a disordered network there exists a plurality of structural parameters and a number of two-level states defined by double-well potentials. Their characteristics are specified by the conditions of glass formation, i.e. by genesis. The thermodynamic description of glass as a self-organizing system (that does not require introducing an interacting potential model) leads to an unambiguous conclusion that its frequency spectrum is predetermined by the structure, which is characterized by zero-point entropy. Glass is a natural system of oscillators which form a disordered network. In this sense, glass conforms to a known model of a disordered neural network formed by interconnected oscillators. If one assumes that in living organisms the structure of a neural network (the brain) is inherited according to a genetic mechanism, the quickness of learning and recognition of patterns, the stability of associative memory and other capabilities have to be inherited genetically. The more ordered a neural network formed by distinguishable neurons, the better its capabilities.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1005071706864
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  • 16
    Digitale Medien
    Digitale Medien
    Genetic and Shared Environmental Influences on Adolescent BMI: Interactions with Race and Sex (1998)
    Springer
    Behavior genetics 28 (1998), S. 265-278 
    Details
    ISSN: 1573-3297
    Schlagwort(e): Genetics ; body mass index ; adolescents ; race ; sex
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Psychologie
    Notizen: Abstract The present study uses a behavioral genetic design to investigate the genetic and environmental influences on variation in adolescent body mass index (BMI) and to determine whether the relative influences of genetic and environmental factors on variation in BMI are similar across racial groups and sexes. Data for the present study come from the National Longitudinal Study on Adolescent Health (Add Health), a large, nationally representative study of adolescent health and health-related behaviors. The Add Health sample contains a subset of sibling pairs that differs in levels of genetic relatedness, making it well suited for behavioral genetics analyses. The present study examines whether genetic and environmental influences on adolescent BMI are the same for males and females and for Black and White adolescents. Results indicate that genetic factors contribute substantially to individual differences in adolescent BMI, explaining between 45 and 85% of the variance in BMI. Furthermore, based on an analysis of opposite-sex sibling pairs, the genes that influence variation in adolescent BMI are similar for males and females. However, the relative importance of genetic and environmental influences on variation in BMI differs for males and females and for Blacks and Whites. Although parameter estimates could be constrained to be equal for Black and White males, they could not be constrained to be equal for Black and White females. Moreover, the best-fitting model for Black females was an ADE model, for White females it was an ACE model, and for males it was an AE model. Thus, shared environmental influences are significant for White female adolescents, but not for Black females or males. Likewise, nonadditive genetic influences are indicated for Black females, but not for White females or males. Implications of these results are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1021619329904
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  • 17
    Digitale Medien
    Digitale Medien
    Neuronal ceroid lipofuscinoses: a review (1998)
    Springer
    Neurological sciences 19 (1998), S. 271-276 
    Details
    ISSN: 1590-3478
    Schlagwort(e): Neuronal ceroid lipofuscinosis ; Clinical features ; Classification ; Diagnosis ; Genetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Sommario Le ceroido lipofuscinosi neuronali (NCL) sono tra le encefalopatie progressive più freguenti nell'infanzia ed interessano, seppure più raramente, l'adulto. Clinicamente sono caratterizzate da demenza, deficit visivo, epilessia e disturbi motori. Gli aspetti patologici specifici sono rappresentati da degenerazione neuronale ed accumulo lisosomiale di lipopigmento in differenti tipi cellulari. Il difetto biochimico della malattia non e noto. La classificazione delle NCL, basata su criteri clinici, distingue sei forme classiche ed altre forme atipiche. L'elettrofisiologia e la neuroradiologia sono di importante ausilio diagnostico, ma la diagnosi si fonda sull'identificazione dell'accumulo di lipopigmento the presenta pattern ultrastrutturali specifici. Differenti difetti genetici sono stati dimostrati in diverse forme cliniche, ma il meccanismo patogenetico molecolare rimane ancora da chiarire.
    Notizen: Abstract Neuronal ceroid lipofuscinoses (NCLs) are among the most common neurodegenerative diseases in childhood but rarely present in adulthood. The main symptoms are psychomotor deterioration, visual failure, epilepsy and motor disturbances. The NCLs are morphologically characterized by the accumulation of lipopigments within numerous cell types and loss of neurons. Pathogenesis is unknown. The current clinical classification recognizes six classic types of NCL and several atypical forms. Electrophysiological and neuroradiological findings may be of diagnostic significance, but disease recognition rests on the demonstration of a typical ultrastructural pattern. Genetic studies have demonstrated that several different genetic loci are involved in the pathogenesis of NCL, but the molecular mechanisms underlying neuronal death and lipopigment accumulation are not understood.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00713852
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  • 18
    Digitale Medien
    Digitale Medien
    Molecular Genetic Investigations of Autism (1998)
    Springer
    Journal of autism and developmental disorders 28 (1998), S. 427-437 
    Details
    ISSN: 1573-3432
    Schlagwort(e): Genetics ; autism ; genotyping
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Psychologie
    Notizen: Abstract Genetic factors are likely to play a major role in the etiology of autism. The genetics of the disorder is however complex, probably involving the action of several genes. In an attempt to identify autism susceptibility loci we are currently undertaking a systematic screening of the whole human genome using multiplex families. We describe the resources and the methods needed to achieve such a task, including extensive collection of family data, semiautomated genotyping technology, and specialized statistical approaches for linkage analysis of complex traits.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026056522602
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  • 19
    Digitale Medien
    Digitale Medien
    Division of labor between scouts and recruits: genetic influence and mechanisms (1998)
    Springer
    Behavioral ecology and sociobiology 43 (1998), S. 191-196 
    Details
    ISSN: 1432-0762
    Schlagwort(e): Key words Honeybees ; Scouting ; Division of labor ; Genetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Every recruitment system in social insects requires some individuals that serve as scouts, foragers that search independently for food sources. It is not well understood which factors influence whether an individual becomes a scout or a recruit, nor how the division of labor between the two forager groups is regulated. It is shown here for honeybees (Apis mellifera), using two different molecular techniques, that there is a genetically based difference in the probability that individuals will scout independently for food. In contrast to earlier suggestions, experimental tests showed that the age of a bee does not seem to influence its probability of becoming a scout or a recruit. Furthermore, scout bees do not search opportunistically for either pollen or nectar but, rather, individuals have preferences that are genetically based. These findings are discussed in the framework of foraging regulation by specialization in honeybees and the adaptive significance of polyandry.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002650050480
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  • 20
    Digitale Medien
    Digitale Medien
    Vom Genotyp zum Phänotyp Molekulargenetische Diagnostik bei Intersexualität (1998)
    Springer
    Monatsschrift Kinderheilkunde 146 (1998), S. 86-91 
    Details
    ISSN: 1433-0474
    Schlagwort(e): Schlüsselwörter Geschlechtliche Differenzierung ; Androgenrezeptor ; Genetik ; Genotyp-Phänotyp-Korrelation ; Key words Sexual differentiation ; Androgen receptor ; Genetics ; Genotype-phenotype-correlation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Summary The determination of the genetic background of sexual development has not only assisted in the explanation of intersex disorders, but also in the diagnosis and clinical management of affected individuals. The possibilities and limitations of molecular genetic studies can be illustrated by the example of androgen insensitivity syndromes. The search for the underlying mutations within the androgen receptor gene is technically possible even for large numbers of patients. The characterization of mutations can be performed with high specificity and sensitivity. While large gene defects are associated with complete loss of function of the receptor, point mutations with subsequent amino acid changes are responsible for the phenotypic variability of the disease. Type and location of the amino acid substitution may influence the clinical appearance of the individual patient, but the phenotype can be highly variable even with the same underlying mutation. This is probably due to regulation mechanisms within the cell of which the androgen receptor is only one, although important, part. Therefore, results of molecular genetic testing have to be interpreted only in connection with clinical and laboratory findings. Further research will focus on the elucidation of the cellular mechanisms of androgen action in order to introduce the results into the clinical management of patients with androgen insensitivity.
    Notizen: Zusammenfassung Die Aufdeckung der genetischen Grundlagen von Störungen der Geschlechtsentwicklung hat neue Möglichkeiten nicht nur in der Erklärung dieser Erkrankungen, sondern auch für die Diagnostik und den klinischen Umgang mit betroffenen Individuen eröffnet. Am Beispiel der Androgenresistenz können die Erfolge, aber auch die Grenzen molekulargenetischer Untersuchungen aufgezeigt werden. Die Suche nach den zugrundeliegenden genetischen Veränderungen im Androgenrezeptorgen ist heute technisch auch zur Analyse größerer Patientenzahlen anwendbar. Der Nachweis von Mutationen kann mit hoher Sensitivität und Spezifität in großen Genabschnitten durchgeführt werden. Während größere Gendefekte mit einem völligen Funktionsverlust des Rezeptors einhergehen, sind Punktmutationen, die zu Veränderungen der Aminosäuresequenz führen, für das große phänotypische Spektrum der Androgenresistenz verantwortlich. Zwar wird das klinische Erscheinungsbild durch Art und Ort der Aminosäuresubstitution mitbestimmt, dennoch kann der Phänotyp auch bei gleicher Mutation sehr variabel sein. Dies ist mit großer Wahrscheinlichkeit auf zelluläre Regulationsmechanismen zurückzuführen, in deren Wirkungskette der Androgenrezeptor nur ein Glied, wenn auch ein wichtiges, darstellt. Daher müssen molekulargenetische Befunde immer in Zusammenhang mit den anamnestischen, klinischen und laborchemischen Parametern gesehen werden. Ziel wissenschaftlicher Untersuchungen ist es, die zellulären Mechanismen der Androgenwirkung weiter aufzuklären, um diese Erkenntnisse dann möglicherweise in die therapeutischen Entscheidungen bei Patienten mit Androgenresistenz einfließen zu lassen.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s001120050248
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  • 21
    Digitale Medien
    Digitale Medien
    Schiff bases of pyridoxal and polyallylamine. The formation rate determining step (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 1-6 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The apparent rate constants of formation (k1) and hydrolysis (k2) of the Schiff bases formed between pyridoxal and polyallylamine has been fitted to a kinetic scheme that involve the different protonated species in the reaction medium and the individual rate constants of formation (k1i) and hydrolysis (k2i). The (k1i) values precludes an acid catalyzed intramolecular process. The effects of hydrophobic medium due to the presence of the macromolecule on the reaction is also discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 1-6, 1998.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    Rate constants for the gas-phase reaction of ozone with unsaturated oxygenates (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 21-29 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The gas-phase reaction of ozone with a series of unsaturated oxygenates and with 1-pentene has been studied at ambient T (287-296 K) and p=1 atm. of air. Reaction rate constants, in units of 10-18 cm3 molecule-1 s-1, are 0.22±0.05 for 2 (5H)-furanone, 1.08±0.20 for methacrolein, 1.74±0.20 for crotonaldehyde, 5.84±0.39 for methylvinyl ketone, 1.05±0.15 for methyl acrylate, 3.20±0.47 for vinyl acetate, 59.0±8.7 for cis-3-hexenyl acetate, 154±30 for ethylvinyl ether, ≥(315±23) for linalool, and 10.9±1.4 for 1-pentene. The results are compared to literature data for the compounds studied and for other unsaturated oxygenates, and are discussed in terms of reactivity toward ozone as a function of the nature, number, and position of the oxygen-containing substituents (SINGLEBOND)CHO, (SINGLEBOND)C(O)R, (SINGLEBOND)C(O)OR, and (SINGLEBOND)OC(O)R. Atmospheric implications are briefly examined. © 1998 John Wiley & Sons, Inc. Int. J Chem Kinet: 30: 21-29, 1998.
    Zusätzliches Material: 3 Tab.
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  • 23
    Digitale Medien
    Digitale Medien
    Kinetic and mechanistic aspects for the tartaric acid oxidation by vanadium(V) in sulfuric acid medium (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 55-61 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Tartaric acid oxidation by vanadium(V) in sulfuric acid medium was investigated spectrophotometrically at 760 nm and 30°C by appearance of the vanadium(IV), as vanadyl. The reaction rate was determined under pseudo-first-order conditions with an excess of hydroxyacid over the oxidant concentration. The oxidation showed a first-order dependence with respect to vanadium(V) concentration and fractional orders with respect to tartaric acid and sulfuric acid concentrations, with no control and with constant ionic strength. The reaction rate is enhanced by an increase of ionic strength, and slightly reduced by a decrease of the dielectric constant of the medium. The activation parameters were calculated based on the rate constants determined in the 293 to 313 K interval. The proposed oxidation mechanisms and the derived rate laws are consistent with the experimental rate laws. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 55-61, 1998.
    Zusätzliches Material: 2 Ill.
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  • 24
    Digitale Medien
    Digitale Medien
    Studying of silane thermal decomposition mechanism (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 99-110 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The mechanism of silane thermal decomposition is investigated in a flow reactor. The time dependencies of silane consumption and disilane formation were compared with those parameters of solid product (aerosol particles) such as concentration, total hydrogen content in solid product, and fraction of hydrogen contained in solid product as polyhydride groups (SiH2)n. Silane loss and gaseous product formation were analyzed using a mass spectrometer. The hydrogen content in solid product was analyzed by the methods of IR-spectroscopy and hydrogen evolution. Based on a simple kinetic scheme we qualitatively explained the experimental dependencies of silane conversion and disilane formation, the effective activation energy of the decomposition process, and the amount of polyhydride groups in the solid product on reaction time and initial silane concentration. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 99-110, 1998.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 25
    Digitale Medien
    Digitale Medien
    Kinetics of liquid phase synthesis of tert-amyl methyl ether from tert-amyl alcohol and methanol catalyzed by ion exchange resin (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 137-143 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis of tert-amyl methyl ether (TAME) from methanol (MeOH) and tert-amyl alcohol (TAA) in the liquid phase was studied by using an ion exchange resin, Amberlyst15 (A15) in the H+ form. Experiments were carried out in a stirred batch reactor under atmospheric pressure. The effects of catalyst size, agitation speed, temperatures, feed ratio and water on the reaction rate were investigated. Both of intraparticle and external diffusion effects could be neglected in this system. The dehydration of TAA could be decreased by increasing the ratio of MeOH/TAA and the reaction rates were greatly inhibited by water.A kinetic model which considered the inhibition of water was proposed. The experimental results agreed well with the model. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 137-143, 1998.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 26
    Digitale Medien
    Digitale Medien
    Proton transfer involving nucleic acids: A temperature-jump study of the systems sulphonephthaleins-double stranded poly(A) and sulphonephthaleins-double stranded poly(C) (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 161-169 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of proton transfer between poly(A - AH) (partially protonated double-stranded polyadenylic acid) and CPR (chlorophenol red), and between poly(C - H - C) (partially protonated double-stranded polycytidylic acid) and the indicators CPR, BCP (bromocresol purple), and BCG (bromocresol green) have been investigated at 25°C and ionic strength 0.1 M (NaClO4) by the temperature-jump method. The acidic proton of poly(C - H - C) is engaged in a hydrogen bond (N3H+----N3) which is believed to contribute to stabilizing the double-strand conformation, whereas the acidic proton of poly(A - A - H) does not form hydrogen bonds. The analysis of the dependence of the relaxation times on the concentrations of the reactants has enabled the evaluation of the rate constants for the direct proton transfer and for the protolysis paths. The rate constants for proton recombination with the deprotonated forms of the polynucleotides and the indicators are of the order of magnitude expected for diffusion controlled processes involving oppositely charged ions (k2=(0.2-1.6)×1010 M-1s-1). The direct proton transfer from poly(C - H - C) to BCG is thermodynamically disfavored and its rate constant, k1, is lower than k2 by about three orders of magnitude. The (thermodynamically favored) proton transfers from poly(A - A - H) to CPR and from poly(C - H - C) to CPR and BCP are characterized by similar values of k1. This result indicates that the hydrogen bonds in poly(C - H - C) are very weak and suggests that the stabilization of the double-stranded conformation of this polynucleotide could be ascribed to the large number of hydrogen bonds rather than to their specific strength. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 161-169, 1998.
    Zusätzliches Material: 6 Ill.
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  • 27
    Digitale Medien
    Digitale Medien
    A dual-phase oscillatory behavior in Belousov-Zhabotinsky system with vanillin as the substrate (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 201-206 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Dual-phase oscillations are observed in Belousov-Zhabotinsky system with 4-hydroxy-3-methoxybenzaldehyde (vanillin) as the substrate and manganous sulphate or ammonium Ce(IV) sulphate as the catalyst. The nonoscillatory period of time between the two phases decreases with increase in the concentration of the catalyst and the substrate. Under uncatalyzed and ferroin catalyzed conditions the system exhibits single-phase oscillations. The first-phase oscillations are due to vanillin whereas the second-phase oscillations are brought about by 4-hydroxy-3-methoxybenzoic acid (vanillic acid) formed during the course of the first-phase reactions. The reactions are explained with relevant steps of the FKN mechanism. © 1998 John Wiley & Sons, Inc. Int J. Chem. Kinet 30: 201-206, 1998.
    Zusätzliches Material: 5 Ill.
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  • 28
    Digitale Medien
    Digitale Medien
    Reactions of the ferryl ion with some compounds found in cloud water (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 215-221 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The lifetime of the ferryl ion FeO2+, (minutes at pH below 1) is reduced by a factor of 50 at pH above 3. This is rationalized in terms of an acid-base equilibrium between two different hydrolytic forms of this species (Fe(OH)++2 and Fe(OH)+3) with a pKa=2.0. The rate constants for reactions between FeO2+ and selected compounds found in cloud water were measured in acid solutions by stopped-flow technique. For inorganic reactants: kHNO2=1.1×104 M-1 s-1, kNO2-≤105 M-1 s-1, kCl-=1.0×102 M-1 s-1, kHSO3-=2.5×105 M-1 s-1, kSO2=4.5×105 M-1 s-1, and kMn(II)=1.0×104 M-1 s-1 were obtained and for the organic reactants: kHCOOH=160 M-1 s-1, kHCOO-=3×105 M-1, kCH3COOH=3.1 M-1 s-1, kCH2(OH)2=400 M-1 s-1, kCH3COCH3=16 M-1 s-1, kCH3CH20H=2.5×103 M-1 s-1, kC6H5OH=4.0×103 M-1 s-1, and kC6H5COOH=80 M-1 s-1 were obtained. A good correlation between log(k) and the standard one electron reduction potential (E°) indicates that the reactions of inorganic compounds proceed by electron transfer. The reaction mechanisms in case of organic compounds are very similar to the reactions of the OH radical, i.e., H-abstraction, and a fairly good correlation between log(k) and the bond dissociation energy BDE was obtained. Activation parameters were measured for the reaction of FeO2+ with HNO2 (Ea=34.5 kJ/mol); Mn2+ (Ea=21.3 kJ/mol); HCOOH (Ea=22.3 kJ/mol); CH2(OH)2 (Ea=44.5 kJ/mol); and C6H5OH (Ea=28.1 kJ/mol). © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 215-221, 1998.
    Zusätzliches Material: 6 Ill.
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  • 29
    Digitale Medien
    Digitale Medien
    Kinetics of the reactions of CH3O with Br and BrO at 298 K (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 249-255 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A discharge flow reactor coupled to a laser-induced fluorescence (LIF) detector and a mass spectrometer was used to study the kinetics of the reactions CH3O+Br→products (1) and CH3O+BrO→products (2). From the kinetic analysis of CH3O by LIF in the presence of an excess of Br or BrO, the following rate constants were obtained at 298 K: k1=(7.0±0.4)×10-11 cm3 molecule-1 s-1 and k2=(3.8±0.4)×10-11 cm3 molecule-1 s-1. The data obtained are useful for the interpretation of other laboratory studies of the reactions of CH3O2 with Br and BrO. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 249-255, 1998.
    Zusätzliches Material: 5 Ill.
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  • 30
    Digitale Medien
    Digitale Medien
    Rate constants for the gas-phase reactions of selected dibasic esters with the OH radical (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 471-474 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Using a relative rate method, rate constants have been measured for the gas-phase reactions of the OH radical with the dibasic esters dimethyl succinate [CH3OC(O)CH2CH2C(O)OCH3], dimethyl glutarate [CH3OC(O)CH2CH2CH2C(O)OCH3], and dimethyl adipate [CH3OC(O)CH2CH2CH2CH2C(O)OCH3] at 298±3 K. The rate constants obtained were (in units of 10-12 cm3 molecule-1 s-1): dimethyl succinate, 1.4±0.6; dimethyl glutarate, 3.3±1.1; and dimethyl adipate, 8.4±2.5, where the indicated errors include the estimated overall uncertainty of ±25% in the rate constant for cyclohexane, the reference compound. The calculated tropospheric lifetimes of these dibasic esters due to gas-phase reaction with the OH radical range from 1.4 days for dimethyl adipate to 8.3 days for dimethyl succinate for a 24 h average OH radical concentration of 1.0×106 molecule cm-3. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 471-474, 1998
    Zusätzliches Material: 1 Ill.
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  • 31
    Digitale Medien
    Digitale Medien
    Effects of mixed CH3CN(SINGLEBOND)H2O solvents on rate of intramolecular general base-catalyzed cleavage of ionized phenyl salicylate in the presence of 3-aminopropan-1-ol, 1,2-diaminoethane, and glycine (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 301-307 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The effects of mixed CH3CN(SINGLEBOND)H2O solvents on rates of aminolysis of ionized phenyl salicylate, PS-, reveal a nonlinear decrease in the nucleophilic second-order rate constants, knms, (for aminolysis) with increase in the content of CH3CN until it becomes ∼50%, v/v. The values of knms remain almost unchanged with change in the CH3CN content within 50 to 70 or 80%, v/v. The effects of mixed CH3CN(SINGLEBOND)H2O solvents on pKa of leaving group, phenol, and protonated amine nucleophile have been concluded to be the major source for the observed mixed solvent effects on knms. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 301-307, 1998.
    Zusätzliches Material: 4 Ill.
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  • 32
    Digitale Medien
    Digitale Medien
    Experimental and modeling study of the oxidation of isobutene (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 629-640 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: This article describes an experimental and modeling study of the oxidation of isobutene. The low-temperature oxidation was studied in a continuous-flow stirred-tank reactor operated at constant temperature (from 833 to 913 K) and pressure (1 atm), with fuel equivalence ratios from 3 to 6 and space times ranging from 1 to 10 s corresponding to isobutene conversion yields from 1 to 50%. The main carbon containing products were analyzed by gas chromatography. The ignition delays of isobutene-oxygen-argon mixtures with fuel equivalence ratios from 1 to 3 were measured behind shock waves. Reflected shock waves permitted to obtain temperatures from 1230 to 1930 K and pressures from 9.5 to 10.5 atm.A mechanism has been proposed to reproduce the profiles obtained for the reactants consumption and the products formation during the slow oxidation and to compute the ignition delays in the shock tube. Simulations were performed using CHEMKIN II. A correct agreement between the simulated values and the experimental data has been obtained in both apparatuses. The main reaction paths have been determined for both series of measurements by a sensitivity and rate of production analysis. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 629-640, 1998
    Zusätzliches Material: 6 Ill.
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  • 33
    Digitale Medien
    Digitale Medien
    Determination of the rate constants for the gas-phase reactions of methyl butenol with OH radicals, ozone, NO3 radicals, and Cl atoms (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 589-594 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Using a relative rate method, rate constants for the gas-phase reactions of 2-methyl-3-buten-2-ol (MBO) with OH radicals, ozone, NO3 radicals, and Cl atoms have been investigated using FTIR. The measured values for MBO at 298±2 K and 740±5 torr total pressure are: kOH=(3.9±1.2)×10-11 cm3 molecule-1 s-1, kO3=(8.6±2.9)×10-18 cm3 molecule-1 s-1, kNO3=(8.6±2.9)×10-15 cm3 molecule-1 s-1, and kCl=(4.7±1.0)×10-10 cm3 molecule-1 s-1. Atmospheric lifetimes have been estimated with respect to the reactions with OH, O3, NO3, and Cl. The atmospheric relevance of this compound as a precursor for acetone is, also, briefly discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 589-594, 1998
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  • 34
    Digitale Medien
    Digitale Medien
    Kinetic stability of 1,1,1-Trifluoroethane (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 621-628 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1,1,1-Trifluoroethane has been decomposed in comparative rate single-pulse shock-tube experiments. The rate expression for elimination at ca. 2.5 bar and in the temperature range of 1050 to 1200 K has been found to be\documentclass{article}\pagestyle{empty}\begin{document}$ \it k\rm (CF_{3}\joinrel{\relbar\!\!\relbar}CH_{3}\relbar\!\!\rightarrow HF+CF_{2}=CH_{2})=7.0\times 10^{14}\ exp(-37260/T)s^{-1} $\end{document}The experimental conditions appear to be such that the unimolecular reaction is at the beginning of the fall-off region and we find that for step sizes down between 500 and 1000 cm-1 the high-pressure rate expression is in the range\documentclass{article}\pagestyle{empty}\begin{document}$ \it k\rm (CF_{3}\joinrel{\relbar\!\!\relbar}CH_{3}\relbar\!\!\rightarrow HF+CF_{2}=CH_{2})=2.0\times 10^{15}\ exp(-38300/T)\ to\ 4\ \times\ 10^{15}\ exp(-39000/T)s^{-1} $\end{document}where the smaller rate parameters refer to the larger step size down. The results are compared with those from an earlier study and the anomalously high A-factor is noted. It is suggested that the existing rate expressions for the fluorinated ethanes may need to be reevaluated. © 1998 John Wiley & Sons, Inc., Int J Chem Kinet: 30: 621-628, 1998
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  • 35
    Digitale Medien
    Digitale Medien
    On the apparent compensation effect found for two parallel reactions (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 673-681 
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    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The authors present a critical analysis of the use of an overall single reaction rate equation instead of the true rate equations corresponding to the decomposition of a substance according to two parallel reactions. Isothermal as well as nonisothermal decomposition are considered. An apparent compensation effect has been evidenced in both cases. It has been assigned to the dependence of the kinetic parameters on temperature (for the isothermal case), conversion, and heating rate (for nonisothermal one). © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 673-681, 1998
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  • 36
    Digitale Medien
    Digitale Medien
    Reduction of iodine by hydroxylamine within the pH range 0.7-3.5 (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 785-797 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reduction of iodine by hydroxylamine within the [H+] range 3×10-1-3×10-4 mol.L-1 was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH3OH+]0/[I2]0 ratio below 15, [H+] around 0.1 mol.L-1, and ionic strength around 0.1 mol.L-1), the [I2] and [I3-] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I2+I-⇔I3-, 2 I2+NH3OH++H2O→HNO2+4 I-+5 H+, NH3OH++HNO2→N2O+2 H2O+H+, and 2 HNO2+2 I-+2 H+→2 NO+I2+2 H2O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h).The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H+] is above 4×10-2 mol.L-1 at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH2OH and NH3OH+ as the reducing reactive species. The additional rate suppression by H+ at low pH would be connected to the existence of H2OI+ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785-797, 1998
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  • 37
    Digitale Medien
    Digitale Medien
    Kinetics of the reactions of OH radicals with some oxygenated volatile organic compounds under simulated atmospheric conditions (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 839-847 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Some relative rate experiments have been carried out at room temperature and at atmospheric pressure. This concerns the OH-oxidation of some oxygenated volatile organic compounds including methanol (k1), ethanol (k2), MTBE (k3), ethyl acetate (k4), n-propyl acetate (k5), isopropyl acetate (k6), n-butyl acetate (k7), isobutyl acetate (k8), and t-butyl acetate (k9). The experiments were performed in a Teflon-film bag smog chamber. The rate constants obtained are (in cm3 molecule-1 s-1): k1=(0.90±0.08)×10-12; k2=(3.88±0.11)×10-12; k3=(2.98±0.06)×10-12; k4=(1.73±0.20)×10-12; k5=(3.56±0.15)×10-12; k6=(3.97±0.18)×10-12; k7=(5.78±0.15)×10-12; k8=(6.77±0.30)×10-12; and k9=(0.56±0.11)×10-12. The agreement between the obtained rate constants and some previously published data has allowed for most of the studied compounds to point out a coherent group of values and to suggest recommended values. Atmospheric implications are also discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 839-847, 1998
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  • 38
    Digitale Medien
    Digitale Medien
    Reactivity of the bis[1-Hydroxy-2-(Salicylideneamino)Ethane]Manganese(II) complex toward hydrogen peroxide: Kinetics and intermediates of reaction (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 889-897 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Kinetic studies of the oxidation of the bis[1-hydroxy-2-(salicylideneamino)ethane]manganese(II) complex by hydrogen peroxide in acetonitrile solutions, at (30.0±0.2)°C, are described. A first-order dependence on the total manganese and the peroxide concentrations was verified, leading to the rapid formation of a Mn(III) intermediate, monitored by stopped-flow measurements, at 394 nm, with a rate constant kf=(1.15±0.03)×105 mol-1 dm3 s-1. The participation of hydroxyl radicals in the process was detected by spin-trapping EPR spectra. The final product was monitored both by EPR spectra, and spectrophotometrically by the slow decay of the intermediary Mn(III) species, with a rate constant kd=(2.60±0.09) s-1. It was identified as the corresponding mononuclear Mn(IV) complex, and characterized by different spectroscopic techniques. Comparative results of the reactivity of the starting complex versus molecular oxygen, leading to the same final product, were also discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 889-897, 1998
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  • 39
    Digitale Medien
    Digitale Medien
    Pressure dependence of the reaction of 1-butanethiol with hydrogen atoms (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 923-932 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of 1-butanethiol with hydrogen atoms was investigated at room temperature under pressures of 133, 266, 532, 2660, and 5320 Pa, using two types of fast-flow discharge reactors; the main products were n-butane and 1-butene with total yields of more than 90%. In the reaction of 1-butanethiol and deuterium atoms, monodeuterated 1-butanethiol was observed by a photo-ionizing mass spectrometer. The relative rate of the two initial reactions of 1-butanethiol with hydrogen atoms was 0.272 (k1/k2). The n-butane and 1-butene are considered to be produced via chemically activated 1-butanethiol on the basis of the pressure dependence of the two main products.\scriptfont4=\seveni \scriptscriptfont4=\fivei \halign{\hfill $#$&$#$\hfill &$#$\hfill &\hfill\qquad\qquad #\cr\rm 1\hbox{-}C_{4}H_{9}S&\rm H&\rm +H\longrightarrow 1\hbox{-}C_{4}H_{9}\cdot +H_{2}S& (1)\cr \rm 1\hbox{-}C_{4}H_{9}S&\rm H&\rm +H\longrightarrow 1\hbox{-}C_{4}H_{9}S\cdot +H_{2}& (2)\cr\rm 1\hbox{-}C_{4}H_{9}S&\rm \cdot &\rm +H\longrightarrow 1\hbox{-}C_{4}H_{9}SH\ast & (3)\cr } \bigskip\rm{}Relative rates of molecular elimination of hydrogen sulfide and C—S bond fission for the chemically activated 1-butanethiol, k5/k4 and k6/k4, were 0.114 and 0.0552 under 532 Pa of pressure at room temperature. Activation energies of the two reactions were calculated to be 228 [kJ/mol] and 297 [kJ/mol], respectively, by use of RRKM on the base of estimated A factors.\scriptfont4=\seveni \scriptscriptfont4=\fivei \halign{\hfill $#$&$#$\hfill &$#$\hfill &\hfill\qquad\qquad #\cr\rm 1\hbox{-}C_{4}H_{9}SH\ast +M&\rm \longrightarrow &\rm 1\hbox{-}C_{4}H_{9}SH& (4)\cr \rm 1\hbox{-}C_{4}H_{9}SH\ast &\rm \longrightarrow &\rm 1\hbox{-}C_{4}H_{8}+H_{2}S& (5)\cr\rm 1\hbox{-}C_{4}H_{9}SH\ast &\rm \longrightarrow &\rm 1\hbox{-}C_{4}H_{9}\cdot +HS\cdot & (6)\cr } \bigskip\rm{}© 1998 John Wiley & Sons, Inc. Int. J. Chem Kinet 30: 923-932, 1998
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  • 40
    Digitale Medien
    Digitale Medien
    Aminolysis of aryl dithio-2-thiophenates and dithio-2-furoates in acetonitrile (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 849-857 
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    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The aminolyses of the title substrates with anilines and benzylamines are investigated in acetonitrile. A clean second-order kinetics is obtained with a first-order rate law in the amine concentration, which is uncomplicated by the fast proton transfer step. The large magnitude of ρZ (ρ1g) as well as ρX (ρnuc) together with relatively large positive ρXZ values is consistent with a stepwise mechanism in which thiophenolate ion expulsion from the intermediate is rate limiting. For the reactions of aryl dithio-2-thiophenates with benzylamines the magnitude of ρX and ρZ values is relatively smaller suggesting that both the addition and expulsion of thiophenolate are partially rate determining. Relatively large secondary kinetic isotope effects, kH/kD≥1.7, with deuterated nucleophiles, support involvement a concurrent proton transfer to the departing thiophenolate ion in the transition state. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 849-857, 1998
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  • 41
    Digitale Medien
    Digitale Medien
    Carbon dioxide production in the oxidation of organic acids by Cerium(IV) under aerobic and anaerobic conditions (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 899-902 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The stoichiometry of CO2 production during the ceric oxidation of various organic acids is measured under conditions with organic acid excess. Measurements utilize a photometric methodology. For anaerobic conditions stoichiometries [CO2]produced:[Ce(IV)]reduced of about 0 (malonic acid), 0.5 (e.g., glyoxylic acid), and 1.0 (oxalic acid) are found. Oxalic acid showed an oxygen-induced decrease of CO2 production, while other compounds such as malonic acid increased the amount of produced CO2 or showed no changes (e.g., tartronic acid). In the case of mesoxalic acid the stoichiometry is increased from about 0.5 to 2.0 due to the presence of molecular oxygen. The results are discussed on the basis of simple reaction mechanisms demonstrating that useful information on reaction pathways and intermediates can be extracted from these simple measurements. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 899-902, 1998
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  • 42
    Digitale Medien
    Digitale Medien
    Oxidation of L-glutamine by manganese(iii) in aqueous sulfuric acid, acetic acid, and pyrophosphate media: A kinetic and mechanistic study (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 7-19 
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    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Manganese(III) solutions were prepared by known electrochemical methods in sulfuric acid, acetic acid, and pyrophosphate media. The nature of the oxidizing species present in manganese(III) solutions was characterized by spectrophotometric and redox potential measurements. Kinetics of oxidation of L-glutamine by manganese(III) in sulfuric acid (1.5 M), acetic acid (60% v/v), and pyrophosphate (pH=1.3) media at 313 K, 323 K, and 328 K, respectively, have been studied. Three different rate laws have been obtained for the three media. Effects of varying ionic strength, solvent composition, and added anions, such as fluoride, chloride, perchlorate, pyrophosphate, and bisulfate, have been investigated. There is evidence for the existence of free radicals as transient species. Activation parameters have been evaluated using Arrhenius and Eyring plots. Mechanisms consistent with the observed kinetic data have been proposed and discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 7-19, 1998.
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  • 43
    Digitale Medien
    Digitale Medien
    Study of the effects of concentration and pH on the dissociation kinetics of Fe(II)-fulvic acid complexes (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 63-67 
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    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The effects of reagent concentration and the pH in the kinetic behavior of the dissociation of Fe(II)-fulvic acid complexes were studied using a spectrophotometric technique. The results show that this behavior is not strongly affected by the concentration of fulvic acid, the concentration of the metal cation on the ratio of these concentrations and that variations in pH are more important in the dissociation process. A possible explanation based in the relative influence of proton concentration on the stability of the complexes is proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 63-67,1998.
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  • 44
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of reaction of toluidine blue with acidic bromate (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 111-120 
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    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The detailed kinetics of the reaction of toluidine blue {phenothiazine-5-ium, 3-amino-7(dimethylamino)-2-methyl chloride, tolonium chloride, TB+Cl-} with potassium bromate and with aqueous bromine reaction were studied. In most of the experiments, the kinetics were monitored by following the rate of consumption of TB+ at 590 nm with excess acid and bromate. The reaction exhibited complex kinetic behavior. Initial reaction was slow and after an induction time, the TB+ concentration decreased fast. It had first-order dependence on both TB+ and bromate, and second-order dependence on H+. Under excess bromate conditions, the stoichiometric ratio of TB+ to bromate was 1:1. Demethylated sulfoxides were found at the reaction products. Sharp increase in the overall potential synchronized with the increase in bromine levels and the fast depletion of [TB+]. The role of bromide ion and bromine in the reaction was established. A multi-step reaction mechanism is proposed consistent with the experimental results. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 111-120, 1998.
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  • 45
    Digitale Medien
    Digitale Medien
    Kinetic study of the nitrosation of N-alkylureas in dioxane-acetic acid mixtures (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 145-150 
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    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The rate constants were determined for the nitrosation reactions of the following substrates: Methyl (MU), Ethyl (EU),Propyl (PU)Butyl (BU), and Allylurea (AU). The rate equation found at a constant pH was: v=k[HNO2] [Urea]. The reactions were carried out in predominantly organic media(dioxane-acetic acid-water) with differing polarities. The proposed reaction mechanism involves the proton transfer from the protonated N-alkyl-N-nitrosourea to the acetate anion. As the polarity of the medium decreased, an approximation of the rate constants of the nitrosation of the different substrates was observed. This approximation can be interpreted as a function of the impediment generated by the R alkyl radical in the rate controlling step. Accordingly, the substrate reactivity will be associated with the ease in which the protonated N-alkyl-N nitrosurea can transfer the proton to the acetate anion. The results achieved in this study are in accordance with there activities observed in the nitrosation of these substrates in aqueous media MU≫(EU≈PU≈BU)〉AU. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 145-150, 1998.
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  • 46
    Digitale Medien
    Digitale Medien
    The pyrolysis of azetidine: Shock-tube kinetics similarities and contrasts with two analogs (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 185-191 
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    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of decomposition of azetidine {(CH2)3N(SINGLEBOND)H)} was measured using single-pulse shock-tube techniques, over the temperature range 855-1100 K, in high argon dilution. These data confirm and extend an earlier investigation that utilized the very low-pressure pyrolysis method. A brief survey of many reports regarding the interesting features of azetidine is presented. In two appendices the thermodynamic and kinetic data on trimethylene sulfide, oxide, and immine are intercompared. New ab-initio calculations are cited for the parent species and their fragmentation products. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 185-191, 1998.
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  • 47
    Digitale Medien
    Digitale Medien
    Oxidation of manganese(II) by ozone and reduction of manganese(III) by hydrogen peroxide in acidic solution (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 207-214 
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    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Manganese(II) is oxidized by ozone in acid solution, k=(1.5±0.2)×103 M-1 s-1 in HClO4 and k=(1.8±0.2)×103M-1 s-1 in H2SO4. The plausible mechanism is an oxygen atom transfer from O3 to Mn2+ producing the manganyl ion MnO2+, which subsequently reacts rapidly with Mn2+ to form Mn(III). No free OH radicals are involved in the mechanism. The spectrum of Mn(III) was obtained in the wave length range 200-310 nm. The activation energy for the initial reaction is 39.5 kJ/mol. Manganese(III) is reduced by hydrogen peroxide to Mn(II) with k(Mn(III)+H2O2)=2.8×103M-1 s-1 at pH 0-2. The mechanism of the reaction involving formation of the manganese(II)-superoxide complex and reaction of H2O2 with Mn(IV) species formed due to reversible disproportionation of Mn(III), is suggested. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 207-214, 1998.
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  • 48
    Digitale Medien
    Digitale Medien
    Belousov-Zhabotinskii type oscillations with amino acids or peptides as organic substrates in the presence of Mn2+ and Fe(phen)32+ as coupled catalysts (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 243-247 
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    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Nine amino acids, aspartic acid, glycine, serine, tyrosine, alanine, glutamic acid, threonine, cystine, phenylalanine, and two peptides, and two peptides, glycine-glycine peptide, glutamic acid-cystine-glycine peptide, give rise to damped oscillations of the Belousov-Zhabotinskii(BZ) type in a batch reactor. Both Mn2+ and Fe(phen)32 are essential for most of those oscillations; and the oscillations in [Mn3+] and [Fe(phen)33+] are also observed. The role of two metallic ions played in the oscillations are analyzed, showing that Mn2+ catalyzes the oxidation of the amino acids or peptides by BrO3- to produce some intermediates which effectively reduce Br2 to Br- catalyzed by Fe(phen)32+. © 1998 John Wiley & Sons, Inc. Int. J. Chem Kinet 30: 243-247, 1998.
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  • 49
    Digitale Medien
    Digitale Medien
    Concerted mechanism of the reactions of 2,4-dinitrophenyl 4-cyanobenzoate with secondary alicyclic amines in aqueous ethanol (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 267-272 
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    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The title reactions are subjected to a kinetic analysis in 44 wt% ethanol-water, at 25.0°C, ionic strength 0.2 (KCl). With a large excess of amine over the substrate, pseudo-first-order rate coefficients (kobs) are obtained, which are linearly dependent on the amine concentration. The nucleophilic rate constants (kN) are determined from plots of kobs vs. amine concentration. The Brönsted-type plot obtained with the kN values is linear, with slope β=0.63. The magnitude of this slope suggests that the mechanism is concerted, as opposed to a stepwise process with rate-determining breakdown of a zwitterionic tetrahedral intermediate (T±), in which the value of β is usually 0.8-1.0. The pyridinolysis of the same substrate in the same solvent is stepwise with the breakdown of T± as the rate-determining step. The change to a concerted mechanism for the title reactions is attributed to the superior nucleofugality of the alicyclic amines, compared to the isobasic pyridines, which destabilizes kinetically the “intermediate” T± in such a way that it does not exist, and the mechanism becomes enforced concerted. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 267-272, 1998.
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  • 50
    Digitale Medien
    Digitale Medien
    Comment: A kinetic study of chlorine radical reactions with ketones by laser-photolysis technique by Olsson et al. (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 309-310 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Zusätzliches Material: 1 Ill.
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  • 51
    Digitale Medien
    Digitale Medien
    Critical considerations on the methods for evaluating kinetic parameters from nonisothermal experiments (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 313-327 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: By surveying the most used methods for evaluating the kinetic parameters from nonisothermal experiments, a new classification scheme of the methods is proposed. For each method the number of principles and theoretical approximations required to derive the equation which grounds it, is considered as a comparison criterion. The methods are, finally, classified into classes of equivalence.As a result of the analysis it is also suggested that the activation energy, as calculated from nonisothermal data, should be given as a range of values instead of a unique value. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 313-327, 1998.
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  • 52
    Digitale Medien
    Digitale Medien
    Temperature dependence of the gas-phase reactions F+CHFO, CFO+F, and CFO+CFO (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 329-333 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The rate coefficients for the reactions CHFO+F, CFO+F and the self-reaction of CFO were determined over the temperature range of 222-298 K. A computer controlled discharge-flow system with mass spectrometric detection was used. The results are expressed in the Arrhenius form (with energies in J):CHFO+F→CFO+HF:k1(T)=(9.7±0.7)·10-12 exp[-(5940±150)/RT] cm3 molecule-1 s-1CFO+F+M→CF2O+M:FORMULA DISC=“MATH”〉k2(T)=(2.60±1.17)·10-10 exp[-(10110±1250)/RT cm3 molecule-1 s-1FORMULACFO+CFO→CF2O+CO:k3(T)=(3.77±2.7)·10-10 exp[-(8350±2800)/RT] cm3 molecule-1 s-1© 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 329-333, 1998
    Zusätzliches Material: 2 Ill.
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  • 53
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of the pyrolysis of 1-chloro-1,1-difluoroethane in the presence of additives (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 359-366 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The thermal dehydrochlorination CF2ClCH3→CF2(DOUBLEBOND)CH2+HCl has been studied in a static system between 597 and 664 K in the presence of CCl4, C2Cl6, CF2(DOUBLEBOND)CH2, HCl, and CF3CH3. A kinetic radical and molecular reaction model has been developed. In addition to describing earlier results on the acceleration of the pyrolysis by CCl4 and the further acceleration by HCl, this model describes quantitatively up to conversions of 20% (i) the dependence of the catalytic effect of CCl4 at low concentrations, (ii) the stronger catalytic effect of C2Cl6, and (iii) the inhibitory effect of added CF2CH2 and CF3CH3 when CCl4 is used as a catalyst. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 359-366, 1998
    Zusätzliches Material: 6 Ill.
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  • 54
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of oxidation of aspirin by bromamine-T, N-bromosuccinimide, and N-bromophthalimide (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 407-414 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the oxidation of aspirin (ASP) by bromamine-T (BAT), N-bromosuccinimide (NBS), and N-bromophthalimide (NBP) has been studied in aqueous perchloric acid at 303 K. The oxidation reaction follows identical kinetics with first-order in [oxidant], fractional-order in [ASP], and inverse fractional-order in [H+]. Under identical experimental conditions the extent of oxidation with different oxidizing agents is in the order: NBS 〉 BAT 〉 NBP. The rate decreased with decreasing dielectric constant of the medium. The variation of ionic strength and the addition of the reaction products and halide ions had no significant effect on the reaction rate. The solvent isotope effect was studied using D2O. Kinetic parameters were evaluated by studying the reaction at different temperatures. The reaction products were identified by GC-MS. The proposed reaction mechanism and the derived rate law are consistent with the observed kinetic data. Formation and decomposition constants for ASP-oxidant complexes have been evaluated. Decarboxylation, bromination, and loss of acetic acid gave 2,4,6-tribromophenol. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 407-414, 1998
    Zusätzliches Material: 8 Ill.
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  • 55
    Digitale Medien
    Digitale Medien
    Kinetic study and modeling of the hetero-homogeneous pyrolysis and oxidation of isobutane around 800 K. Part I. Pyrolysis in an unpacked pyrex reactor (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 425-437 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Isobutane pyrolysis is studied in an unpacked Pyrex reactor at 20-100 torr initial pressures and 750-793 K. Results are interpreted in terms of a long chain radical mechanism and the reaction is modeled. The reaction selectivity or ratio of the initial production rate of isobutene (or hydrogen) to that of propene (or methane) is practically given by the ratio of the rate constant of abstraction of a tertiary hydrogen atom of isobutane to that of a primary one. A sensitivity analysis clearly shows that self-inhibition is essentially due to methylallyl radicals produced by hydrogen abstraction from isobutene. The model has been manually adjusted to experimental results and most of the adjusted rate constants are in agreement with literature data. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 425-437, 1998
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  • 56
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of isatin ring opening in aqueous binary mixtures of methanol and acetonitrile cosolvents (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 463-469 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Solvent effects on the kinetics of hydrolysis of isatin by sodium hydroxide have been investigated within the temperature range (30-55°C) in methanol-water and acetonitrile-water media of varying solvent compositions up to 70% (v/v) of the organic solvent component. The thermodynamic activation parameters were calculated and discussed in terms of solvation effects. The determined isokinetic temperatures, in both systems, revealed the existence of compensation effect arising from strong solute-solvent interactions; log k was correlated with both log [H2O] and the reciprocal of the dielectric constant. The first correlation was observed to be linear while the second was nonlinear. Finally a mechanism for the isatin ring opening was proposed, which accounts for the role and the effect of the solvent on the reaction rate. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 463-469, 1998
    Zusätzliches Material: 4 Ill.
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  • 57
    Digitale Medien
    Digitale Medien
    Reaction of 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) derived radicals with hydroperoxides. Kinetics and mechanism (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 565-570 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Tert-Butyl hydroperoxide and hydrogen peroxide readily react with the radical cation derived from 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The reaction is inhibited by ABTS and protons, and can be interpreted in terms of a mechanism comprising a partially reversible electron transferROOH+ABTS•+↔ ROO · + ABTS + H+ (1)followed by the self-reactions of the hydroperoxide derived radicals and reactions between them and another ABTS derived radical. A complete kinetic analysis allows an evaluation of the rate constant for reaction (1). A value of 0.2 M-1 s-1 was obtained for both compounds. The back reaction of process (1) is more relevant when tert-butyl hydroperoxide is employed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 565-570, 1998
    Zusätzliches Material: 5 Ill.
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  • 58
    Digitale Medien
    Digitale Medien
    Kinetic study of the Ce(iii)- or Mn(ii)-catalyzed Belousov-Zhabotinsky reactions with mixed organic acid/ketone substrates (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 595-604 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In a stirred batch reactor, the Ce(III)- or Mn(II)-catalyzed Belousov-Zhabotinsky reaction with mixed organic acid/ketone substrates exhibits oscillatory behavior. The organic acids studied here are: dl-mandelic acid (MDA), dl-4-bromomandelic acid (BMDA), and dl-4-hydroxymandelic acid (HMDA), and the ketones are: acetone (Me2CO), methyl ethyl ketone (MeCOEt), diethyl ketone (Et2CO), acetophenone (MeCOPh), and cyclohexanone ((CH2)5CO). The effects of bromate ion, organic acid, ketone, metal-ion catalyst, and sulfuric acid concentrations on the oscillatory patterns are investigated. Both conventional and stopped-flow methods are applied to study the kinetics of the oxidation reactions of the above organic acids by Ce(IV) or Mn(III) ion. The order of relative reactivities of the oxidation reactions of organic acids in 1 M H2SO4 is Mn(III)(SINGLEBOND)HMDA reaction 〉 Ce(IV)(SINGLEBOND)HMDA reaction 〉 Mn(III)(SINGLEBOND)BMDA, reaction 〉 Mn(III)(SINGLEBOND)MDA reaction 〉 Ce(IV)(SINGLEBOND)BMDA reaction 〉 Ce(IV)(SINGLEBOND)MDA reaction. Spectrophotometric study of the bromination reactions of the above ketones shows that these reactions are zero-order with respect to bromine and first-order with respect to ketone and that ketone enolization is the rate-determining step. The order of relative rates of bromination or enolization reactions of ketones in 1 M H2SO4 is (CH2)5CO≫(MeCOEt, Et2CO, Me2CO)〉MeCOPh. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet:30: 595-604, 1998
    Zusätzliches Material: 10 Ill.
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  • 59
    Digitale Medien
    Digitale Medien
    Inhibition of chemical oscillations by bromide ion in the Briggs-Rauscher reaction (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 641-646 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The addition of bromide ions to the component solutions of the Briggs- Rauscher oscillating system produces a variety of phenomena, depending on the sequence of the addition and on the initial bromide concentration. If the addition is made some minutes after the mixing of H2O2 and acidic IO3- and before adding malonic acid and Mn2+ ions, the oscillations last for five or six cycles, then suddenly ceases. If the addition is made immediately after the mixing of H2O2 and acidic IO3- and before adding malonic acid and Mn2+ ions, the oscillations do not start at all. The addition of bromide ions to an actively oscillating BR reaction causes a rapid suppression of the oscillations. Our observations may be accounted for by a mechanism involving the IBr species. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 641-646, 1998
    Zusätzliches Material: 4 Ill.
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  • 60
    Digitale Medien
    Digitale Medien
    Parabenzoquinone pyrolysis and oxidation in a flow reactor (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 683-697 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An experimental and theoretical study of the pyrolysis and oxidation of parabenzoquinone has been performed. The experiments were conducted in an isothermal quartz flow reactor at atmospheric pressure in the temperature range 600-1500 K. The main variables considered are temperature, oxygen concentration, and presence of CO. A detailed reaction mechanism for the pyrolysis and oxidation chemistry of parabenzoquinone is proposed, which provides a good description of the experimental results. Both the experimental work and the kinetic mechanism proposed for the pyrolysis and oxidation of parabenzoquinone represent the first systematic study carried out for this important aromatic compound.Our pyrolysis results confirm that the primary dissociation channel for p-benzoquinone leads to CO and a C5H4O isomer, presumably cyclopentadienone. However, significant formation of CO2 during the pyrolysis may indicate the existence of a secondary dissociation channel leading to CO2 and a C5H4 isomer. Under oxidizing conditions, consumption of p-benzoquinone occurs mainly by dissociation at lower temperatures. As the temperature increases interaction of OC6H4O with the radical pool becomes more significant, occurring primarily through hydrogen abstraction reactions followed by ring opening reactions of the OC6H3O radical. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 683-697, 1998
    Zusätzliches Material: 9 Ill.
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  • 61
    Digitale Medien
    Digitale Medien
    Rate coefficients for the reactions of hydrogen atoms with 1-bromopropane, 2-bromopropane, 1-bromobutane, and 2-bromobutane (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 721-727 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The rate coefficients for the reactions of hydrogen atoms with n-C3H7Br, s-C3H7Br, n-C4H9Br, and s-C4H9Br were determined in a discharge flow-reactor at 298 K and a pressure of 4 mbar. Molecular-beam sampling and subsequent mass-spectrometric detection with electron-impact ionisation was used for the measurement of the bromo-hydrocarbon concentration. The rate coefficients obtained are (in 1010 cm3 mol-1 s-1): 2.3±1.2 for n-C3H7Br, 2.3±1.2 for s-C3H7Br, 2.4±1.2 for n-C4H9Br, and 2.8±1.4 for s-C4H9Br. The results are compared with predictions from bond-energy bond-order (BEBO) calculations, where a reasonable agreement is found. Furthermore, also by BEBO calculations, the relative importance of bromine abstraction as compared to hydrogen abstraction is estimated. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 721-727, 1998
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  • 62
    Digitale Medien
    Digitale Medien
    Rate constants for the reactions of methylvinyl ketone, methacrolein, methacrylic acid, and acrylic acid with ozone (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 769-776 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Rate constants for the reaction of ozone with methylvinyl ketone (H2C(DOUBLEBOND)CHC(O)CH3), methacrolein (H2C(DOUBLEBOND)C(CH3)CHO), methacrylic acid (H2C(DOUBLEBOND)C(CH3)C(O)OH), and acrylic acid (H2C(DOUBLEBOND)CHC(O)OH) were measured at room temperature (296±2 K) in the presence of a sufficient amount of cyclohexane to scavenge OH-radicals. Results from pseudo-first-order experiments in the presence of excess ozone were found not to be consistent with relative rate measurements. It appeared that the formation of the so-called Criegee-intermediates leads to an enhanced decrease in the concentration of the two organic acids investigated. It is shown that the presence of formic acid, which is known to react efficiently with Criegee-intermediates, diminishes the observed removal rate of the organic acids. The rate constant for the reaction of ozone with the unsaturated carbonyl compounds methylvinyl ketone and methacrolein was found not to be influenced by the addition of formic acid. Rate constants for the reaction of ozone determined in the presence of excess formic acid are (in cm3 molecule-1 s-1): methylvinyl ketone (5.4±0.6)×10-18; methacrolein (1.3±0.14)×10-18; methacrylic acid (4.1±0.4)×10-18; and acrylic acid (0.65±0.13)×10-18. Results are found to be consistent with the Criegee mechanism of the gas-phase ozonolysis. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 769-776, 1998
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  • 63
    Digitale Medien
    Digitale Medien
    Determination of propagation and termination rate constants by using an extension to the rotating-sector method: Application to PLPC and DLPC bilayers (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 753-767 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An extension to the rotating-sector method, which is usually applied to determine propagation and termination rate constants, is presented. The analytical treatment developed accounts for the simultaneous presence of a thermal initiation and of a first-order termination process. The applicability of the rotating-sector method is thus extended to situations where the rate in dark is higher than 5% of the rate in the presence of light, and more accurate estimates of the rate constants are obtained than before for any values of the “dark” rate. A previously published experiment on the application of the rotating-sector method to the autoxidation of styrene was reanalyzed. The estimates obtained for the propagation and the termination rate constants were 11% and 19% higher than the previous estimates, respectively. Finally, the improved rotating-sector method was also applied to the experimental determination of propagation (kp) and termination rate constants (2×kt) for both 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine (PLPC) and 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPC) liposomes. The following results were obtained at 37°C: for PLPC kp =16.6 M-1s-1, and 2×kt=1.27×105 M-1s-1; for DLPC kp(intermolecular)=(13.3-13.9) M-1s-1, kp(intramolecular)=(4.7-5.4) s-1, and 2×kt=(0.99-1.05)×105 M-1s-1. The separation of the intermolecular and intramolecular propagation rate constants for DLPC was made possible both by a special adaptation of the rotating-sector equations to substrates with two oxidizable moieties, and by the experimental determination of the ratio between partially oxidized DLPC molecules (only one acyl is oxidized) and fully oxidized DLPC molecules (both acyls are oxidized). © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 753-767, 1998
    Zusätzliches Material: 6 Ill.
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  • 64
    Digitale Medien
    Digitale Medien
    A comprehensive mechanism for methanol oxidation (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 805-830 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A comprehensive detailed chemical kinetic mechanism for methanol oxidation has been developed and validated against multiple experimental data sets. The data are from static-reactor, flow-reactor, shock-tube, and laminar-flame experiments, and cover conditions of temperature from 633-2050 K, pressure from 0.26-20 atm, and equivalence ratio from 0.05-2.6. Methanol oxidation is found to be highly sensitive to the kinetics of the hydroperoxyl radical through a chain-branching reaction sequence involving hydrogen peroxide at low temperatures, and a chain-terminating path at high temperatures. The sensitivity persists at unusually high temperatures due to the fast reaction of CH2OH+O2=CH2O+HO2 compared to CH2OH+M=CH2O+H+M. The branching ratio of CH3OH+OH=CH2OH/CH3O+H2O was found to be a more important parameter under the higher temperature conditions, due to the rate-controlling nature of the branching reaction of the H-atom formed through CH3O thermal decomposition. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 805-830, 1998
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  • 65
    Digitale Medien
    Digitale Medien
    The kinetics of the bromate-sulfite reaction system (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 869-874 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the reaction between BrO3- and sulfite was studied by measuring the concentrations of [Br-] and [H+] both in buffered and in unbuffered solutions. A mechanism was applied for simulation of the experimental observations. Rate constants k1=(0.027±0.004) M-1s-1 and k2=(85±5) M-1s-1 were determined for the following reactions:\halign{\hfill $#$\hfill &\hfill\qquad\qquad #\cr 3\ \rm HSO_{3}\!^{-}+BrO_{3}\!^{-}\longrightarrow 3\ SO_{4}\!^{2-}+Br^{-}+3\ H^{+}& (1)\cr 3\ \rm H_{2}SO_{3}(\hbox{or}\ SO_{2.}\hbox{aq})+BrO_{3}\!^{-}\longrightarrow 3\ SO_{4}\!^{2-}+Br^{-}+6\ H^{+}& (2)\cr }Rate constant k1 was obtained directly from the experimental results on unbuffered reactions, where Reaction (1) was predominant. Rate constant k2 was obtained by computer fitting of [Br-] to the experimental values for buffered reactions, where the rate of Reaction (2) was about four times higher than that of Reaction (1). © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 869-874, 1998
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  • 66
    Digitale Medien
    Digitale Medien
    Thermal decomposition of CF3Br using Br-atom absorption (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 859-867 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Br-atom atomic resonance absorption spectrometry (ARAS) has been developed and applied to measure thermal decomposition rate constants for CF3Br (+ Kr)→CF3+Br (+ Kr) over the temperature range, 1222-1624 K. The Br-atom curve-of-growth (145〈λ〈163 nm) was determined using this reaction. For [Br]≤1×1012 molecules cm-3, absorbance, (ABS)=1.410×10-13 [Br], yielding σ=1.419×10-14 cm2. The curve-of-growth was then used to convert (ABS) to Br-atom profiles which were then analyzed to give measured rate constants. These can be expressed in second-order by k1=8.147×10-9 exp(-24488 K/T) cm3 molecule-1 s-1 (±33%, 1222≤T≤1624 K). A unimolecular theoretical approach was used to rationalize the data. Theory indicates that the dissociation rates are closer to second- than to first-order, i.e., the magnitudes are 30-53% of the low-pressure-limit rate constants over 1222-1624 K and 123-757 torr. With the known, E0=ΔH00=70.1 kcal mole-1, the optimized theoretical fit to the ARAS data requires 〈ΔE〉down=550 cm-1. These conclusions are consistent with recently published data and theory from Kiefer and Sathyanarayana. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 859-867, 1998
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  • 67
    Digitale Medien
    Digitale Medien
    Application of a new method to the determination of rate constants: Examination of the effect of noise on the data (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 47-54 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new linear regression method is applied to determine the rate constants from time-dependent profiles. The method is effective for obtaining the rate constants of such consecutive processes as vibrational relaxation. The ambiguity of ordinary nonlinear analysis is eliminated by the linearization of regression equations. Because the new method also determines relative detectivity, the nascent vibrational distributions immediately following reactions or photolysis can be obtained simultaneously. In order to demonstrate the reliability of the new method under practical conditions, several examples of analysis of the data with noise are shown in detail. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 47-54, 1998.
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  • 68
    Digitale Medien
    Digitale Medien
    A new method for monitoring dediazoniation reactions: Simultaneous monitoring of concentration and rates of product formation and loss of starting material for the dediazoniation of p-methylbenzenediazonium tetrafluoroborate (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 31-39 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We have examined the kinetics and mechanism of the dediazoniation reaction of p-methylbenzenediazonium tetrafluoroborate in the presence and absence of CuCl2 using a methodology developed by us that allows, simultaneously, and within the same experiment to identify, to quantify, and to obtain the rate constants for the formation of all dediazoniation products, and, indirectly, the rate constant for the diazonium salt decomposition. The methodology developed combines the use of coupling reactions, to form a stable azo dye, followed by analysis by HPLC. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 31-39, 1998.
    Zusätzliches Material: 9 Ill.
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  • 69
    Digitale Medien
    Digitale Medien
    Thermochemical kinetics of bromine nitrate, bromine nitrite, halogen hydroperoxides, dichlorine pentoxide, peroxycarboxylic acids, and diacyl peroxides (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 41-45 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Heats of formation of BrONO2, BrONO, BrOOH, FOOH, FOOCl, CF3C(O)OOH, HC(O)OOH, CH3C(O)OOH, and [CH3C(O)O]2 are estimated from bond contributions taken from J. Phys. Chem.,100, 10150 (1996). They agree within ±2 kcal/mol with recent experimental or ab initio data. The resulting BDE(O(SINGLEBOND)O)=36 kcal/mol value in diacetyl peroxide requires the concerted assistance of exothermic C(SINGLEBOND)C(O) weakening in the transition state of its decomposition into free radicals. It also implies the existence of a previously unrecognized 12 kcal/mol nonbonded repulsion in acyl anhydrides. The formation of chloryl chlorate with ΔHf(O2ClOClO2)=50 kcal/mol, a marginally stable species toward dissociation into (ClO3+OClO), may account for observations made in the [O(3P+OClO] system at low temperatures. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 41-45, 1998.
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  • 70
    Digitale Medien
    Digitale Medien
    Kinetics of dichlorosilylene trapping by methane and mechanism and kinetics of the methyldichlorosilane decomposition (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 89-97 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Data relative to methane trapping of SiCl2 and a rate constant for the SiCl2 into C(SINGLEBOND)H bond insertion process of k-1=13.4 M-1s-1 at 921 K are reported. Results on the decomposition of the trapping product, methyldichlorosilane, are also reported. This decomposition follows first-order kinetics with a rate constant of k=1.5±0.2×10-3 s-1 at 905 K and produces methane, trichlorosilane, methyltrichlorosilane, and tetrachlorosilane. It is argued that the decomposition involves silylene intermediates, is nonchain, and is initiated primarily by the molecular methane elimination process MeSiHCl2(SINGLEBOND)1→ CH4+SiCl2. Free radicals and Si(SINGLEBOND)C bond fission may also contribute to the decomposition but are not dominant. The kinetics of MeSiHCl2 decomposition are shown to be consistent with the kinetics of the reverse SiCl2/CH4 trapping reaction and with the overall reaction thermochemistry. Reaction modeling gives product yields, reactant conversions, and rates in reasonable agreement with the data. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 89-97, 1998.
    Zusätzliches Material: 1 Ill.
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  • 71
    Digitale Medien
    Digitale Medien
    Thermodynamic analysis of 1,3-dicarbonylic monochelates of iron(III) from equilibrium and kinetic measurements (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 121-127 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: From a study of the complexation of FeIII with 2,6-dimethyl-3,5-heptanedione in aqueous solution, thermodynamic and kinetic parameters have been obtained. Results obtained for this system and a series of structurally similar iron(III) diketonates at different temperatures, establishes isokinetic behaviors of these kinds of reactions.Analytical correlations obtained may be useful to predict, for analogous ligands in similar experimental conditions, an essential mechanism, that pathways involving reaction of metal-hydrolyzed species with the enol tautomer are faster than pathways involving hexa-aqua species. Additionally, thermodynamic parameters associated with the monochelated complexations may be predicted. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 121-127, 1998.
    Zusätzliches Material: 1 Ill.
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  • 72
    Digitale Medien
    Digitale Medien
    Evaluation of the rate constants in chemical reactions (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 151-159 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: This article is concerned with the application of a new method to recover the rate constants in chemical reactions. The method is based on treating the unknown parameters as time dependent. With appropriate experimental data the unknown rate constants are guided from an arbitrary initial condition to their true value at a final time. An explicit equation describing the time evolution of the parameters is obtained by minimizing the error along the trajectory. The method leads to an iterative algorithm which is described in detail. Numerical results with the method indicate that accurate estimates of the rate constants can be obtained directly from experimental data. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 151-159, 1998.
    Zusätzliches Material: 5 Ill.
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  • 73
    Digitale Medien
    Digitale Medien
    A computational study of the reaction kinetics of methyl radicals with trifluorohalomethanes (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 179-184 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ab initio calculations have been used to characterize the transition states for halogen abstraction by CH3 in reactions with CF4, CF3Cl, CF3Br, and CF3I (1-4). Geometries and frequencies were obtained at the HF/6-31G(d) and MP2=full/6-31G(d) levels of theory. Energy barriers were computed via the Gaussian-2 methodology, and the results were employed in transition state theory analyses to obtain the rate constants over 298-2500 K. There is good accord with literature measurements in the approximate temperature range 360-500 K for reactions (2-4), and the computed activation energies are accurate to within ±6 kJ mol-1. Recommended rate constant expressions for use in combustion modeling are k;1=1.6×10-19 (T/K)2.41 exp(-13150 K/T), k2=8.4×10-20(T/K)2.34 exp(-5000 K/T), k3=4.6×10-19 (T/K)2.05 exp(-3990 K/T), and k4=8.3×10-19 (T/K)2.18 exp(-1870 K/T) cm3 molecule-1 s-1. The results are discussed in the context of flame suppression chemistry. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 179-184, 1998.
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  • 74
    Digitale Medien
    Digitale Medien
    Upper limits for the gas-phase reaction of H2O2 with O3 and NO. Atmospheric implications (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 707-709 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Upper limits of 4×10-20 and 7×10-20 cm3 molecule-1 s-1 were established for the gas-phase reactions of H2O2 with O3 and NO, respectively. These reactions are too slow to explain features observed in the atmospheric vertical profile of H2O2. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 707-709, 1998
    Zusätzliches Material: 2 Ill.
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  • 75
    Digitale Medien
    Digitale Medien
    The influence of mass transfer phenomena on the kinetic analysis for the thermal decomposition of calcium carbonate by constant rate thermal analysis (CRTA) under vacuum (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 737-744 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The influence of the mass transfer phenomena on the thermal decomposition of calcium carbonate powders under vacuum was investigated through a detailed kinetic analysis by the constant transformation rate thermal analysis (CRTA). Reliable kinetic curves, free from the mass transfer problems, can be obtained by CRTA under vacuum, but within a restricted range of small sample sizes, 〈10 mg. The influence of mass transfer phenomena on the apparent kinetic parameters is discussed in relation to the distribution of fractional reaction α of the individual particles in a sample assemblage. Only when the distribution of α is maintained constant among a series of experimental kinetic curves, can a reliable activation energy, E, be obtained by one of the isoconversion methods. In this respect, a single cyclic CRTA permits the α distribution to be maintained constant between the two adjacent data points with different decomposition rates. In the present study, an apparent E value of about 223 kJ mol-1 was obtained by the Friedman method from a series of CRTA curves with sample sizes less than 10 mg and by the rate jump method from a single cyclic CRTA curve with sample size of about 40 mg. The first-order (F1) law was determined to be the most appropriate kinetic model function, from a series of CRTA curves, instead of the ideal contracting geometry (R3) law formalized for the three-dimensional shrinkage of the reaction interface in the respective particles. The particle size distribution of the sample particles is suggested to be one possible reason for the apparent agreement with the F1 law. A kinetic exponent n of the nth-order law that deviated from unity was obtained from the CRTA curves with sample sizes larger than 10 mg, due to an additional distribution of α produced by mass transfer phenomena. Because the α distribution due to the mass and heat transfer phenomena cannot be expressed practically in an analytical function, a meaningful kinetic model and preexponential factor are difficult to estimate from kinetic data that are influenced by the transfer phenomena. © 1998 John Wiley & Sons, Inc. Int. J Chem Kinet: 30: 737-744, 1998
    Zusätzliches Material: 9 Ill.
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  • 76
    Digitale Medien
    Digitale Medien
    Alkaline hydrolysis of 2-phenoxyquinoxaline in reactive counter-ion micelles: Effects of head group size (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 777-783 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of 2-phenoxyquinoxaline (1) with hydroxide ion is accelerated by reactive counter-ion micelles of cetyltrialkylammonium hydroxides (alkyl=Me, Et, n-Pr, and n-Bu), cetylmethylpiperidinium hydroxide, and cetylquinuclidinium hydroxide containing bulky head groups. First-order rate constants for reaction of (1) with OH- increase with increasing bulk of the head group and are associated with an increase in nucleophile reactivity as water is squeezed away from the micelle surface. Micellar effects upon the alkaline hydrolysis of compound (1) were analyzed by using a model that describes micelle-ion interactions in terms of Langmuir isotherms. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 777-783, 1998
    Zusätzliches Material: 6 Ill.
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  • 77
    Digitale Medien
    Digitale Medien
    Kinetic studies on state-state coupling and collisional quenching of excited sulfur dioxide (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 831-837 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The time-resolved total emission of SO2 (B1B1→X1A1) at 354.9 nm were monitored following the direct excitation by a 266 nm laser pulse. A three-level model was proposed to deal with SO2 (X1A1, A1A2, B1B1) system. From a kinetic treatment of these measurements, the coupling coefficient, ξ, and the relaxation time, τ, relating to the high vibronic levels of A1A2 and B1B1 states were first obtained. It is found that ξ and τ values keep basically constant, reflecting the characteristics of the studied system. In addition, the quenching rate constants of SO2 (A1A2, B1B1) by some alkane and chloromethane molecules were measured at room temperature. The formation cross sections of complexes of SO2 (A1A2, B1B1) and quenchers were calculated by means of a collision complex model. It is shown that the dependence of the formation cross section of complex on the number of C(SINGLEBOND)H or C(SINGLEBOND)Cl bonds is generally in agreement with that of the measured quenching cross section. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 831-837, 1998
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  • 78
    Digitale Medien
    Digitale Medien
    Products of the gas-phase reaction of the OH radical with 3-methyl-1-butene in the presence of NO (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 577-587 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The products of the gas-phase reaction of the OH radical with 3-methyl-1-butene in the presence of NO have been investigated at room temperature and 740 torr total pressure of air by gas chromatography with flame ionization detection, in situ Fourier transform infrared absorption spectroscopy, and direct air sampling atmospheric pressure ionization tandem mass spectrometry. The products identified and quantified by GC-FID and in situ FT-IR absorption spectroscopy were HCHO, 2-methylpropanal, acetone, glycolaldehyde, and methacrolein, with formation yields of 0.70±0.06, 0.58±0.08, 0.17±0.02, 0.18±0.03, and 0.033±0.007, respectively. In addition, IR absorption bands due to organic nitrates were observed, consistent with API-MS observations of product ion peaks attributed to the β-hydroxynitrates (CH3)2CHCH(ONO2)CH2OH and/or (CH3)2CHCH(OH)CH2ONO2 formed from the reactions of the corresponding β-hydroxyalkyl peroxy radicals with NO. A formation yield of ca. 0.15 for these nitrates was estimated using IR absorption band intensities for known organic nitrates. These products account for essentially all of the reacted 3-methyl-1-butene. Analysis of the potential reaction pathways involved shows that H-atom abstraction from the allylic C(SINGLEBOND)H bond in 3-methyl-1-butene is a minor pathway which accounts for 5-10% of the overall OH radical reaction. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 577-587, 1998
    Zusätzliches Material: 9 Ill.
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  • 79
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of the oxidation of glycolaldehyde by tetrachloroaurate(III) (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 613-619 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the reaction between glycolaldehyde (GA) and tetrachloroaurate(III) in acetic acid-sodium acetate buffer has been studied. The reaction is first-order with respect to [AuIII] as well as [GA]. Both H+ and Cl- ions retard the rate of reaction. AuCl4-, AuCl3(OH2), and AuCl3(OH)- are the reactive species of gold(III) with gradually increasing reactivity. A reaction mechanism involving two-electron transfer rate determining steps has been proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 613-619, 1998
    Zusätzliches Material: 3 Ill.
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  • 80
    Digitale Medien
    Digitale Medien
    Modeling of the oxidation of n-octane and n-decane using an automatic generation of mechanisms (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 949-959 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Detailed modeling of the oxidation of n-octane and n-decane in the gas phase was performed by using mechanisms written by means of a software recently developed in our laboratory. This computer-aided design of mechanisms permits the automatic generation of detailed oxidation and combustion kinetic models in the case of paraffins and isoparaffins [1]. For n-octane, the predictions of the model were compared with experimental results obtained by Dryer and Brezinsky by means of a turbulent plug flow reactor (1080 K, 1 atm) [2]. The experimental study of Balès-Guéret et al., performed in a perfectly stirred reactor (922-1033 K, 1 atm) [3], was used as a basis of comparison for the modeling of the oxidation of n-decane. Considering that no fitting of any kinetic parameter was done, the agreement between the computed and the experimental values is satisfactory both for conversions and for the distribution of the products formed. This modeling has required improvement in the generation of the secondary reactions of alkenes, which are the main primary products obtained during the oxidation of these two alkanes in the range of temperature studied and for which reaction paths are detailed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 949-959, 1998
    Zusätzliches Material: 6 Ill.
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  • 81
    Digitale Medien
    Digitale Medien
    Flow cytometry and cell sorting for yeast viability assessment and cell selection (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 147-160 
    Details
    ISSN: 0749-503X
    Schlagwort(e): yeast physiology ; yeast viability ; flow cytometry ; bakers yeast ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Yeast suspensions were analysed by flow cytometry after dye staining for determination of total and viable cell densities. Results were comparable to traditional colony counting and, in addition, provided further information on the percentage of total cells that were viable. The flow cytometric methods provided results within 20 min whereas colony counts were not available until 36 h. We evaluated a number of fluorescent dyes: ChemChrome Y (CY), oxonol (Ox), propidium iodide (PI), Fungolight and rhodamine 123, for accurate determination of viability of industrial yeast cultures and freshly re-hydrated high activity dried yeast (HADY). PI, Ox and CY gave the most conclusive live/dead discrimination and were the simplest to use. Culturing after dye staining and cell sorting demonstrated that the yeast remained viable after cell sorting and incubation with PI, CY or Ox. The methods, therefore, permit physical selection of individual yeast cells from populations of mixed viability. Sorting demonstrated that PI stained non-culturable cells whilst CY stained culturable cells. Analysis of yeast stained simultaneously with CY and PI or with Ox and PI demonstrated that PI and CY assays were in mutual agreement with respect to viability assessments. The Ox assay was in agreement with CY and PI for live/heat-killed mixtures. However, for re-hydrated HADY, Ox stained a significantly (P≤0·05) higher proportion of cells than did PI. © 1998 John Wiley & Sons, Ltd.
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  • 82
    Digitale Medien
    Digitale Medien
    Investigation of two yeast genes encoding putative isoenzymes of phosphoglycerate mutase (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 203-213 
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    ISSN: 0749-503X
    Schlagwort(e): GPM2 ; GPM3 ; phosphoglycerate mutase ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Our previous data indicated that GPM1 encodes the only functional phosphoglycerate mutase in yeast. However, in the course of the yeast genome sequencing project, two homologous sequences, designated GPM2 and GPM3, were detected. They have been further investigated in this work. Key residues in the deduced amino acid sequence, shown to be involved in catalysis for Gpm1 (i.e. His8, Arg59, His181) are conserved in both enzymes. Overexpression of the genes under control of their own promoters in a gpm1 deletion mutant did not complement for any of the phenotypes. This could in part be attributed to a lack of expression due to their weak promoters. Higher level expression under the control of the yeast PFK2 promoter partially complemented the gpm1 defects, without restoring detectable enzymatic activity. Nevertheless, deletion of either GPM2 or GPM3, or the two deletions in concert, did not produce any obvious lesions for growth on a variety of different carbon sources, nor did they change the levels of key intermediary metabolites. We conclude that both genes evolved from duplication events and that they probably constitute non-functional homologues in yeast.
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  • 83
    Digitale Medien
    Digitale Medien
    The SPL1 tRNA splicing gene of Candida maltosa and Candida albicans (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 287-295 
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    ISSN: 0749-503X
    Schlagwort(e): Candida maltosa ; Candida albicans ; tRNA splicing gene ; silent genes ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: The tRNA splicing gene SPL1-1 has been cloned and sequenced in Saccharomyces cerevisiae (Kolman and Soll, 1993). Sequence adjacent to the LEU2 gene in Candida maltosa showed some homology to the SPL1-1 gene of S. cerevisiae. This work describes the sequencing of the SPL1 tRNA splicing genes from C. maltosa and C. albicans and the analysis of these genes. Comparison of these sequences and the relationship observed between the LEU2 and SPL1 genes in these yeasts suggests that there may be some synteny amongst various species of yeasts. The coding region of the C. maltosa SPL1 region described in this work differs from previously described partial sequences in that it is a complete uninterrupted open reading frame. Two strains of C. maltosa were each shown to contain different alleles, one uninterrupted open reading frame and one disrupted open reading frame. The sequences have been deposited in the GenBank/EMBL data libraries under Accession Numbers X72940, AF000115, AF000116, AF000117, AF000118, AF000119 and AF000120. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 4 Ill.
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  • 84
    Digitale Medien
    Digitale Medien
    Isolation and characteristics of yeasts able to grow at low concentrations of nutrients (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 233-238 
    Details
    ISSN: 0749-503X
    Schlagwort(e): Oligotrophic yeasts ; low-nutrient conditions ; starvation ; Cryptococcaceae ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Seven oligotrophic yeasts, which can grow in a 104-fold dilution of malt-yeast-glucose-peptone medium (10-4 YM), were mainly isolated from soil. These yeasts belong to the Cryptococcaceae. When inoculated at about 102 cells/ml in 10-4 YM, the isolates grew to 1·4×103-2·4×105 cells/ml after 3 days. Some culture collection yeasts fell into three groups according to their growth characteristics in 10-4 YM, one group showing characteristics of the oligotrophic yeasts. The half-saturation values of uptake by the five isolated oligotrophic yeasts for D-glucose, L-leucine and L-amino acids were 6·0-25·0, 1·7-43·3 and 3·5-21·6 μM, respectively. The oligotrophic yeasts suspended in 10 mM-phosphate buffer (pH 6·0) had high tolerances for starvation, and remained more than 15% viable after 90 days of starvation. © 1998 John Wiley & Sons, Ltd.
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  • 85
    Digitale Medien
    Digitale Medien
    Mam33p, an oligomeric, acidic protein in the mitochondrial matrix of Saccharomyces cerevisiae is related to the human complement receptor gC1q-R (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 303-310 
    Details
    ISSN: 0749-503X
    Schlagwort(e): Saccharomyces cerevisiae ; mitochondria ; mitochondrial matrix ; homo-oligomeric protein ; Mam33p ; gene disruption ; gC1q-R ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Mam33p (mitochondrial acidic matrix protein) is a soluble protein, located in mitochondria of Saccharomyces cerevisiae. It is synthesized as a precursor with an N-terminal mitochondrial targeting sequence that is processed on import. Mam33p assembles to a homo-oligomeric complex in the mitochondrial matrix. It can bind to the sorting signal of cytochrome b2 that directs this protein into the intermembrane space. Mam33p is encoded by an 801 bp open reading frame. Gene disruption did not result in a significant growth defect. Mam33p exhibits sequence similarity to gC1q-R, a human protein that has been implicated in the binding of complement factor C1q and kininogen. © 1998 John Wiley & Sons, Ltd.
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  • 86
    Digitale Medien
    Digitale Medien
    Assembly of phosphofructokinase-1 from Saccharomyces cerevisiae in extracts of single-deletion mutants (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 323-334 
    Details
    ISSN: 0749-503X
    Schlagwort(e): phosphofructokinase-1 ; Saccharomyces cerevisiae ; deletion mutants ; reactivation ; assembly ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Phosphofructokinase-1 from Saccharomyces cerevisiae is an octameric enzyme comprising two non-identical subunits, α and β, which are encoded by the unlinked genes PFK1 and PFK2. In this paper, assembly and reactivation of the enzyme have been studied in cell-free extracts of single-deletion mutants. In contrast to the previously described lack of phosphofructokinase-1 activity in cell-free extracts of these mutants, we could measure a temporary enzyme activity immediately after lysis of protoplasts. This result supports the assumption that each of the subunits forms an enzyme structure which is active in vivo but not stable after cell disruption.Upon mixing of separately prepared cell-free extracts of both deletion mutants very low activity could be measured. About 40% of the wild-type activity was regained when both mutants were mixed prior to disruption. The reactivation rate could be slightly increased by addition of ATP and fructose 6-phosphate and was found to be a function of the growth state, particularly of the β-subunit-carrying cells. The individual subunits did not interact with Cibacron Blue F3G-A, a biomimetic ligand of phosphofructokinase-1. After reassembly of both subunits in vitro a strong affinity of the reconstituted phosphofructokinase-1 to the dye-ligand was observed.The inability of the subunits to reconstitute under certain conditions seems to result from alterations of the intracellular environment following disruption. These changes give rise to induce an unproductive side reaction like self-aggregation of the subunits.Because reconstitution of phosphofructokinase-1 from S. cerevisiae behaves in a similar way to that of hemoglobin and luciferase, we would speculate a general mechanism for assembly of oligomeric proteins in vivo. © 1998 John Wiley & Sons, Ltd.
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  • 87
    Digitale Medien
    Digitale Medien
    The importance of the glycerol 3-phosphate shuttle during aerobic growth of Saccharomyces cerevisiae (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 347-357 
    Details
    ISSN: 0749-503X
    Schlagwort(e): Saccharomyces ; redox ; glycerol ; NADH ; shuttle ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Maintenance of a cytoplasmic redox balance is a necessity for sustained cellular metabolism. Glycerol formation is the only way by which Saccharomyces cerevisiae can maintain this balance under anaerobic conditions. Aerobically, on the other hand, several different redox adjustment mechanisms exist, one of these being the glycerol 3-phosphate (G3P) shuttle. We have studied the importance of this shuttle under aerobic conditions by comparing growth properties and glycerol formation of a wild-type strain with that of gut2Δ mutants, lacking the FAD-dependent glycerol 3-phosphate dehydrogenase, assuming that the consequent blocking of G3P oxidation is forcing the cells to produce glycerol from G3P. To impose different demands on the redox adjustment capability we used various carbon sources having different degrees of reduction.The results showed that the shuttle was used extensively with reduced substrate such as ethanol, whereas the more oxidized substrates lactate and pyruvate, did not provoke any activity of the shuttle. However, the absence of a functional G3P shuttle did not affect the growth rate or growth yield of the cells, not even during growth on ethanol. Presumably, there must be alternative systems for maintaining a cytoplasmic redox balance, e.g. the so-called external NADH dehydrogenase, located on the outer side of the inner mitochondrial membrane. By comparing the performance of the external NADH dehydrogenase and the G3P shuttle in isolated mitochondria, it was found that the former resulted in high respiratory rates but a comparably low P/O ratio of 1·2, whereas the shuttle gave low rates but a high P/O ratio of 1·7.Our results also demonstrated that of the two isoforms of NAD-dependent glycerol 3-phosphate dehydrogenase, only the enzyme encoded by GPD1 appeared important for the shuttle, since the enhanced glycerol production that occurs in a gut2Δ strain proved dependent on GPD1 but not on GPD2. © 1998 John Wiley & Sons, Ltd.
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  • 88
    Digitale Medien
    Digitale Medien
    Construction of PCR-ligated long flanking homology cassettes for use in the functional analysis of six unknown open reading frames from the left and right arms of Saccharomyces cerevisiae chromosome XV (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 391-399 
    Details
    ISSN: 0749-503X
    Schlagwort(e): modified LFH cassette ; EUROFAN 6-pack analysis ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Six open reading frames (ORFs) of unknown function from Saccharomyces cerevisiae chromosome XV, three from the left and three from the right arm, were deleted in two diploid strains by the short flanking homology method (Wach et al., 1994). Transformants were selected as Geneticin (G418)-resistant colonies and correct integration of the kanMX4 cassette was checked by colony PCR. Following sporulation of the diploids, tetrads were dissected and scored for the segregation of the G418-resistant marker. We have developed a widely applicable method for the construction of gap repair plasmids to obtain the cognate clones for each of the disrupted ORFs. The 5′- and 3′-flanks of the ORF in question are linked by a unique restriction endonuclease. When the plasmid is cut at this site it can be used to obtain, by selection for the appropriate antibiotic resistance, long flanking homology (LFH) cassettes containing the cognate clone or the disrupted allele. The LFH cassette containing the cognate clone or the disrupted allele can be released from the gap-repaired plasmid by cutting at the inserted flanking restriction sites. One of the six ORFs (YOR319w) corresponds to an essential gene whose product is part of the spliceosome complex. Haploid as well as homozygous and heterozygous diploid disruptant strains for each of the five non-essential ORFs were subjected to growth test on different media at 15°C, 30°C and 37°C. Disruption of YOR322c causes osmotically sensitive growth on YEPD at 37°C and the product of YOL091w appears to play a role in sporulation since the homozygous diploid disruptant has lost the ability to sporulate. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 4 Ill.
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  • 89
    Digitale Medien
    Digitale Medien
    Homolog of a-factor receptor gene in Saccharomyces exiguus (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 583-586 
    Details
    ISSN: 0749-503X
    Schlagwort(e): Saccharomyces exiguus ; STE3 ; homolog ; sequence analysis ; differentiation of species ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Homologs of Saccharomyces cerevisiae STE3, a-factor receptor gene were detected from S. exiguus NFRI 3539 by low stringency Southern hybridization. This strain might have at least two types of homolog. One of these homologs, designated as e-STE3 was cloned. Its nucleotide sequence revealed 60% identity to STE3. The putative protein coding region consisted of 453 amino acid residues. The amino acid sequence identity between STE3 and e-STE3 was 62%, and that of the N-terminal 303 amino acid residues considered to be the pheromone binding domain was 79%. The e-STE3 sequence submitted to the DDBJ/EMBL/GenBank data libraries is available under Accession Number AB003086. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 1 Ill.
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  • 90
    Digitale Medien
    Digitale Medien
    An improved protocol for the preparation of yeast cells for transformation by electroporation (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 565-571 
    Details
    ISSN: 0749-503X
    Schlagwort(e): Saccharomyces cerevisiae ; electroporation ; transformation ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Pretreatment of yeast cells with lithium acetate (LiAc) and dithiothreitol (DTT) enhances the frequency of transformation by electroporation. The method shows improvements of 6-67-fold in wild-type strains derived from commonly used Saccharomyces cerevisiae genetic backgrounds. In addition, 15-300-fold improvement in transformation frequency was achieved with several mutant strains of S. cerevisiae that transformed poorly by conventional procedures. Both DTT and lithium acetate were necessary for maximal transformation frequencies. Pretreatment with lithium and DTT also resulted in an ∼3·5-fold increase in the electroporation transformation frequency of the pathogenic fungus Candida albicans. © 1998 John Wiley & Sons, Ltd.
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  • 91
    Digitale Medien
    Digitale Medien
    Deletion of transmembrane domain 12 of CDR1, a multidrug transporter from Candida albicans, leads to altered drug specificity: Expression of a yeast multidrug transporter in baculovirus expression system (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 535-550 
    Details
    ISSN: 0749-503X
    Schlagwort(e): multidrug resistance ; CDR1 ; ABC transporter ; baculovirus expression ; C. albicans ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Cdr1p, an ATP-binding cassette transporter from the pathogenic yeast Candida albicans, confers resistance to several unrelated drugs including anti-Candida drugs (Prasad et al., 1995b). We demonstrate that the deletion of 237 bp (79 aa) from the 3′ end of CDR1 (which encompasses the transmembrane domain (TM) 12 of the putative transporter) did not result in the total loss of its ability to efflux cytotoxic agents. While the expression of ΔCDR1 in yeast resulted in impaired sensitivity to drugs like cycloheximide, anisomycin, sulfomethuron methyl and antifungal nystatin, its ability to confer resistance remained unaltered to drugs such as o-phenanthroline, 4-nitroquinoline-N-oxide, cerulenin, azoles, oligomycin, erythromycin, and benomyl. Similar to human MDR1p, Cdr1p might also have localized drug binding sites in TM 12, but that might not be the case for all the drugs. The TM 12 deletion also did not lead to any significant impairment in NTPase activities. Both ATPase and UTPase activities of complete Cdr1p and ΔCdr1p were not significantly altered, as was the case with respect to their ability to efflux Rh123 and steroid hormone like [3H]-β-estradiol. To further dissect the functionality of Cdr1p, its truncated version was overexpressed in a baculovirus-insect cell expression system. The synthesis of ΔCdr1p in Sf9 cells was temporally regulated as a function of the baculovirus polyhedrin gene promoter. The Sf9 derived ΔCdr1p was ∼130 kDa, which was lower than the expected size, probably due to the differences in glycosylation. This, however, did not affect the functionality of ΔCdr1p. The deletion of TM 12 did not affect the targeting of the protein and ΔCdr1p was exclusively localized in plasma membrane of Sf9 cells as detected by immunofluorescence. The expression of ΔCdr1p in the baculovirus-insect expression system generated a high drug-stimulated plasma membrane-bound ATPase activity which was not demonstrable when ΔCdr1p was expressed in yeast. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 6 Ill.
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  • 92
    Digitale Medien
    Digitale Medien
    Nucleotide sequence of the Schizosaccharomyces pombe lys1 + Gene and Similarities of the lys1+ protein to peptide antibiotic synthetases (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 479-484 
    Details
    ISSN: 0749-503X
    Schlagwort(e): lys1+ gene ; Schizosaccharomyces pombe ; α-aminoadipate reductase ; peptide synthetase ; lysine biosynthesis ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: The 4·2 kbp lys1+ gene of Schizosaccharomyces pombe encoding the large subunit of α-aminoadipate reductase (EC1.2.1.31), an enzyme specific to lysine synthesis in higher fungi, was completely sequenced at the nucleotide level from pLYS1H. The S. pombe lys1+ gene product consists of 1415 amino acid residues and has a putative molecular weight of 155·8 kDa. The encoded protein converts α-aminoadipic acid to α-aminoadipate-δ-semialdehyde by an ATP-mediated adenylation. Analysis of the sequence showed that the putative protein encoded by lys1+ shares strong homology with the peptide antibiotic synthetases which also use an adenylation step. The sequence data reported in this paper have been submitted to GenBank database (Washington DC, USA) under the Accession Number U15923. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 2 Ill.
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  • 93
    Digitale Medien
    Digitale Medien
    Heat shock transiently enhances the synthesis rate of Sis1p, a ribosome-associated DnaJ protein in the oleagenous yeast Apiotrichum curvatum (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 419-430 
    Details
    ISSN: 0749-503X
    Schlagwort(e): Apiotrichum curvatum ; cDNA sequence ; DnaJ protein ; cytosolic Hsp70s ; ribosome association ; Sis1 protein ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: DnaJ proteins have been localized in different intracellular compartments of eukaryotes. In Apiotrichum curvatum, a fat-storing yeast, we found a DnaJ homolog associated with ribosomes and large cytosolic complexes as well. Using a plant DnaJ probe and a cDNA library constructed from poly(A)+ -RNA of A. curvatum grown on oleate we isolated a SIS1 cDNA coding for a 39·5 kDa protein. The putative protein contains neither a zinc finger motif nor a CAAX motif but is characterized by a J-domain at the N-terminal region and a large G-rich region in the middle part of the molecule. Heat shock applied for 1 h resulted in a pronounced but transient increase of the SIS1 mRNA. An antiserum was raised against the bacterially expressed protein. Cell fractions from A. curvatum were further separated by sedimentation centrifugation on sucrose gradients. Analysing the sub-fractions, we detected Sis1p mainly associated with ribosomes, and with particles sedimenting at approximately 200S. Hsp70 was found to be associated with the 200S fraction. The respective cytosolic A. curvatum Hsp70 cDNA was cloned and sequenced. High salt conditions caused the removal of Hsp70 and Sis1p from the 200S complexes. Mild RNase treatment of the 200S fraction afforded monosomes and 200S complexes unaffected by RNase. Heat shock led to a pronounced increase in the rate of de novo synthesis. However, due to the large pools of Sis1p on ribosomes and large cytosolic complexes, the increase in gene activation did not lead to a significant change of the total amount of Sis1p. Accession numbers are: Y12079 for ACHSP70 and Y12080 for ACSIS1. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 7 Ill.
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  • 94
    Digitale Medien
    Digitale Medien
    Evolution of gene order and chromosome number in Saccharomyces, Kluyveromyces and related fungi (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 443-457 
    Details
    ISSN: 0749-503X
    Schlagwort(e): evolution ; polyploidy ; gene duplication ; gene order ; LEU2 ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: The extent to which the order of genes along chromosomes is conserved between Saccharomyces cerevisiae and related species was studied by analysing data from DNA sequence databases. As expected, the extent of gene order conservation decreases with increasing evolutionary distance. About 59% of adjacent gene pairs in Kluyveromyces lactis or K. marxianus are also adjacent in S. cerevisiae, and a further 16% of Kluyveromyces neighbours can be explained in terms of the inferred ancestral gene order in Saccharomyces prior to the occurrence of an ancient whole-genome duplication. Only 13% of Candida albicans linkages, and no Schizosaccharomyces pombe linkages, are conserved. Analysis of gene order arrangements, chromosome numbers, and ribosomal RNA sequences suggests that genome duplication occurred before the divergence of the four species in Saccharomyces sensu stricto (all of which have 16 chromosomes), but after this lineage had diverged from Saccharomyces kluyveri and the Kluyveromyces lactis/marxianus species assemblage. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 4 Ill.
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  • 95
    Digitale Medien
    Digitale Medien
    Regulation of alcoholic fermentation in batch and chemostat cultures of Kluyveromyces lactis CBS 2359 (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 459-469 
    Details
    ISSN: 0749-503X
    Schlagwort(e): Crabtree effect ; yeast ; biomass ; Kluyveromyces lactis ; oxygen ; pyruvate decarboxylase ; regulation ; fermentation ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Kluyveromyces lactis is an important industrial yeast, as well as a popular laboratory model. There is currently no consensus in the literature on the physiology of this yeast, in particular with respect to aerobic alcoholic fermentation (‘Crabtree effect’). This study deals with regulation of alcoholic fermentation in K. lactis CBS 2359, a proposed reference strain for molecular studies. In aerobic, glucose-limited chemostat cultures (D=0·05-0·40 h-1) growth was entirely respiratory, without significant accumulation of ethanol or other metabolites. Alcoholic fermentation occurred in glucose-grown shake-flask cultures, but was absent during batch cultivation on glucose in fermenters under strictly aerobic conditions. This indicated that ethanol formation in the shake-flask cultures resulted from oxygen limitation. Indeed, when the oxygen feed to steady-state chemostat cultures (D=0·10 h-1) was lowered, a mixed respirofermentative metabolism only occurred at very low dissolved oxygen concentrations (less than 1% of air saturation). The onset of respirofermentative metabolism as a result of oxygen limitation was accompanied by an increase of the levels of pyruvate decarboxylase and alcohol dehydrogenase. When aerobic, glucose-limited chemostat cultures (D=0·10 h-1) were pulsed with excess glucose, ethanol production did not occur during the first 40 min after the pulse. However, a slow aerobic ethanol formation was invariably observed after this period. Since alcoholic fermentation did not occur in aerobic batch cultures this is probably a transient response, caused by an imbalanced adjustment of enzyme levels during the transition from steady-state growth at μ=0·10 h-1 to growth at μmax. It is concluded that in K. lactis, as in other Crabtree-negative yeasts, the primary environmental trigger for occurrence of alcoholic fermentation is oxygen limitation. © 1998 John Wiley & Sons, Ltd.
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  • 96
    Digitale Medien
    Digitale Medien
    Influence of monovalent cations on yeast cytoplasmic and vacuolar pH (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 501-515 
    Details
    ISSN: 0749-503X
    Schlagwort(e): Saccharomyces cerevisiae ; bakers' yeast ; pH homeostasis ; cytoplasmic pH ; vacuolar pH ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: The effects of monovalent cations on the internal pH of yeast were studied. Our former procedure was modified, inducing maximal alkalinization of the cells with 100 mM-NH4OH instead of Tris base. The pH values were lower than reported before (Peña et al., J. Bacteriol. 1995 177, 1017-1022). With glucose as substrate, the internal cytoplasmic pH reached higher values when incubating at an external pH of 6·0, as compared to pH 4·0. Monovalent cations added approximately 5 min after glucose produced a further increase in the internal pH, which was higher at a previous incubation pH of 4·0 than that observed at pH 6·0. The selectivity of the changes followed a similar order to that of the transport system for monovalent cations.When incubating cells with glucose for more than 30 min, the initial changes of the internal pH appeared to be regulated by the cell. However, under the fluorescence microscope, it was observed that pyranine, which was confined to the cytoplasm during the first 15 min, was progressively concentrated in the vacuole. By studying the fluorescence changes of cells electroporated and then incubated with glucose or glucose plus potassium, we could follow the internal pH of this organelle, obtaining values within the range reported by other authors. Also, in cells preincubated with glucose for 60 min, and electroporated afterwards, the fluorescence of pyranine, which only entered the cytoplasm, allowed us to measure the pH of this compartment, showing that it was more alkaline than the vacuole. Moreover, the cytoplasmic pH increased upon addition of glucose or potassium. The vacuolar pH, on the other hand, increased upon addition of potassium after glucose, but decreased upon addition of glucose. In addition, incubation of the cells with glucose with or without pyranine produced vesiculation of the vacuole. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 10 Ill.
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  • 97
    Digitale Medien
    Digitale Medien
    A family of laboratory strains of Saccharomyces cerevisiae carry rearrangements involving chromosomes I and III (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 551-564 
    Details
    ISSN: 0749-503X
    Schlagwort(e): yeast ; S. cerevisiae ; genetics ; karyotypes ; chromosomal rearrangements ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: In order to study meiotic segregation of chromosome length polymorphism in yeast, we analysed the progeny of a cross involving two laboratory strains FL100trp and YNN295. Analysis of the parental strains led us to detect an important length polymorphism of chromosomes I and III in FL100trp. A reciprocal translocation involving 80 kb of the left arm of chromosome III and 45 kb of the right arm of chromosome I was shown to be the cause for the observed polymorphism in this strain. The characterization of the translocation breakpoints revealed the existence of a transposition hot-spot on chromosome I: the sequence of the translocation joints on chromosomes I and III suggests that the mechanism very likely involved homologous recombination between Ty2 transposable elements on each chromosome. Analysis of FL100, FL200 and FL100trp ura, which are related to FL100trp, shows that this reciprocal translocation is present in some of the strains of the FL series, whereas the parental strain FL100 does not carry the same rearrangement. We evidenced instead the duplication of 80 kb of chromosome III on chromosome I and a deletion of 45 kb of the right arm of chromosome I in this strain, indicating that secondary events might have taken place and that the strain currently named FL100 is not the common ancestor of the FL series. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 7 Ill.
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  • 98
    Digitale Medien
    Digitale Medien
    Identification of a putative histidine kinase two-component phosphorelay gene (CaHK1) in Candida albicans (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 665-674 
    Details
    ISSN: 0749-503X
    Schlagwort(e): histidine kinase ; phosphorylation ; signal transduction ; gene ; two-component ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: We have cloned and analysed the sequence of a putative histidine kinase, two-component gene (CaHK1) from Candida albicans. This gene encodes a 2471 amino acid protein (Cahk1p) with an estimated molecular mass of 281·8 kDa. A homology search of Cahk1p with other proteins in the databases showed that Cahk1p exhibits the greatest homology at its C-terminus with both the sensor and regulator components of prokaryotic and eukaryotic two-component histidine kinases. A further analysis of this homology showed that the Cahk1p possessed both sensor and regulator domains in the same polypeptide. Also, Cahk1p is likely to be a soluble protein. The sensor kinase domain of Cahk1p contains conserved motifs that are characteristic of all histidine kinase proteins, including the putative histidine which is believed to be autophosphorylated during activation, ATP binding motifs and others (F- and N-motifs), with unknown function. The Cahk1p regulator domain also contains conserved aspartate and lysine residues and the putative aspartate, which is secondarily phosphorylated by the autophosphorylated histidine. Finally, according to the codon usage frequency of the CaHK1 gene in comparison with other genes from C. albicans, there would appear to be a low level of expression of the gene. The accession number for the described sequence is AF013273, as filed in the EMBL/GenBank/DDBJ database. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 5 Ill.
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  • 99
    Digitale Medien
    Digitale Medien
    Genomic disruption of six budding yeast genes gives one drastic example of phenotype strain-dependence (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 655-664 
    Details
    ISSN: 0749-503X
    Schlagwort(e): Saccharomyces cerevisiae ; PCR-based disruption ; YOL113w ; YOL100w ; YOL107w ; YOR267c ; YGL196w ; YGL194c ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Using PCR to construct disruption cassettes, null alleles of six genes have been created in Saccharomyces cerevisiae. In a FY1679 background, no defects were detected in any of the haploid deletion mutants with respect to growth, gross morphology, or mating. A diploid FY1679-derived Δygl194c/Δygl194c homozygous disruptant displayed reduced sporulation. In contrast to the lack of phenotypic consequences of Δyol100w disruptions in the FY1679 background, in the CEN.PK2 strain even a heterozygous disruption of the same gene caused striking effects, very slow vegetative growth and highly impaired sporulation. Tetrad analysis showed YOL100w to be an essential gene in this strain. A copy of the YGL194c or the YOL100w wild-type gene borne on a centromeric episomal plasmid was introduced into a corresponding disruption mutant strain, and in both cases was found to partially complement the defects. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 3 Ill.
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  • 100
    Digitale Medien
    Digitale Medien
    Secretion and pH-dependent self-processing of the pro-form of the Yarrowia lipolytica acid extracellular protease (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 1115-1125 
    Details
    ISSN: 0749-503X
    Schlagwort(e): Yarrowia lipolytica ; secretion ; pH ; extracellular protease ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: The secretion and maturation of the acid extracellular protease (AXP) of the yeast Yarrowia lipolytica have been characterized using antiserum raised against this enzyme. A 42 kDa pro-enzyme form of AXP was identified from lysates of radiolabelled Y. lipolytica cells and found to contain no N-linked carbohydrate moieties. Using pulse-chase immune precipitation it was demonstrated that the AXP precursor was secreted into the extracellular medium where, under conditions of low pH, it underwent autocatalytic activation forming the mature enzyme. Conversion of the AXP pro-form in the presence of the protease inhibitor pepstatin indicated that an intramolecularly-catalysed reaction mechanism was involved in AXP maturation. Further evidence supporting the role of autocatalytic processing came from the side-chain specificity of mature AXP towards the oxidized B-chain of insulin. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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