Considerations about the chirality of the saturated six-membered rings with two or more heteroatoms

The chirality of the title heterocycles is discussed considering their genesis by desymmetrization of the corresponding adamantanes. Some rules for the specification of the absolute configurations of the enantiomers (R or S) for this type of compounds are proposed. © 1996 Wiley-Liss, Inc.     

Transformation of group A streptococci by electroporation

Abstract The introduction, via electroporation, of free plasmid DNA into three strains of Streptococcus pyogenes is described. The method is very simple and rapid and efficiencies vary from 1 × 10³ to 4 × 10⁴ per μg of DNA. The method was also used to introduce an integrative plasmid and transformants were obtained, albeit at a somewhat lower frequency (2 × 10²). Some of the plasmids used in this study are derivatives of the Lactococcus lactis subsp. cremoris Wg2 plasmid pWV01. These broad host range vectors replicate in Gram-positives as well as Gram-negatives (viz. Escherichia coli ). Here we show that they also replicate in S. pyogenes and S. sanguis .     

Attraction of Fish to Mercury Vapour Light and Its Application in a Generating Station Forebay

Laboratory and field tests were conducted to determine the effectiveness of filtered mercury vapour lights in attracting fish with possible utilization in a fish conserving scheme at an electrical generating station. In laboratory tests, alewife demonstrated an attraction to the mercury vapour light which was associated with an increase in swimming activity. This response was maintained over a 48-hour period. When the filtered mercury vapour lights were utilized in association with a fish pump in the Nanticoke Generating Station forebay, juvenile gizzard shad and smelt were attracted to the pump area. Although there was variation with time of day, tubidity and lighting array; the results suggested that the number of fish passing through the pump increased when the mercury vapour lights alone or when the mercury lights in association with a white strobe light were employed.     

GENETIC ANALYSIS OF MORNINGNESS AND EVENINGNESS

We studied the influence of genetic factors on individual differences in morningness-eveningness in a sample of Dutch twin families. Data were collected from adolescent twins (mean age 17.8 yr) and their parents (mean age of fathers 48.0 yr and of mothers 46.0 yr) and a sample of older twins (mean age 46.5 yr). Scores on morningness-eveningness were rated on a 5-point scale. Parents were more morning oriented than their children, and women were more morning oriented than men. With a twin-family study, separation of genetic and environmental influences on variation in morningness-eveningness is possible. Including parents and older twins in the study makes it possible to explore generation differences in these effects. The correlation between monozygotic twins was more than twice the correlation between dizygotic twins. This indicates that genetic effects may not operate in an additive manner. Therefore, a model that included genetic dominance was explored. Biometrical model fitting showed no sex differences for the magnitude of genetic and environmental factors. The total heritability—the sum of additive and nonadditive genetic influences—for morningness-eveningness was 44% for the younger generation and 47% for the older generation. However, the genetic correlation between the generations turned out to be lower than 0.5, suggesting that different genes for morningness-eveningness are expressed in both generations. (Chronobiology International, 18(5), 809-822, 2001)     

Immunological Monitoring of Fenton Fragmentation of Fibrinogen

Fibrinogen is transformed into insoluble “neofibe” by reaction with up to IOOpM Cu(II) and 1.5 mM ascorbate. The soluble peptides which are released during the reaction can be monitored by amino acid analysis and by measuring released keto-carbonyl (with DNPH). Immunologic characterization of the soluble peptides. with anibodies directed against fibrino-peptide A (FPA) clearly show the release of this epitope. optimally at 50 pM Cu(II). Anti-FPB gives no evidence for the release of that epitope. However, N-terminal amino acid analyses reveals the presence of 3 peptides terminating in ALA (alpha chain FPA). GLU (beta chain FPB) and SER/ASP (unknown). The release of fibrinopeptides is interpreted within the context of a general mechanism for OH'-induced peptide chain cleavage via intermediate Schiff-base hydrolysis.     

Signal peptidase I overproduction results in increased efficiencies of export and maturation of hybrid secretory proteins in Escherichia coli

Summary The effects of 25-fold overproduction ofEscherichia coli signal peptidase I (SPase I) on the processing kinetics of various (hybrid) secretory proteins, comprising fusions between signal sequence functions selected from theBacillus subtilis chromosome and the mature part of TEM-β-lactamase, were studied inE. coli. One precursor (pre[A2d]-β-lactamase) showed an enhanced processing rate, and consequently, a highly improved release of the mature enzyme into the periplasm. A minor fraction of a second hybrid precursor (pre[Al3i]-β-lactamase), which was not processed under standard conditions of SPase I synthesis, was shown to be processed under conditions of SPase I overproduction. However, this did not result in efficient release of the mature β-lactamase into the periplasm. In contrast, the processing rates of wild-type pre-β-lactamase and pre(A2)-β-lactamase, already high under standard conditions, were not detectably altered by SPase I overproduction. These results demonstrate that the availability of SPase I can be a limiting factor in protein export inE. coli, in particular with respect to (hybrid) precursor proteins showing low (SPase I) processing efficiencies.     

Syntheses and characterization of neutral complexes of Zn(II) with mono- and dianionic pyrrole-2-imine ligands [(pyrrole-2-CHN)nR]n− (n = 1, 2)

The reactions of the dianionic [(pyrrole-2-CHN)₂R]^2? ligands [(N′₂N₂)^2?] (R = (R)(S)-1,2-cyclohexane or 1,2-ethane) with Zn(II) yield neutral dimeric [Zn₂(N′₂N₂)₂] complexes. The dimeric nature of the complexes was established by field-desorption mass spectrometry. ¹H NMR studies show that these complexes have dimeric structures in solution in which the (N′₂N₂)^2? ligands act as di-bidentates.The metal centres have tetrahedral geometries and bot have Δ or Λ configurations. The complex with the (R)(S)-1,2-cyclohexanediyl bridges has a rigid structure in solution. Neither intermolecular nor intramolecular exchange processes are observed The ¹H NMR spectrum of the complex with the 1,2-ethanediyl bridging groups shows that at 213 K in CDCl₃ a fast conformational movement is already taking place between two identical structures of the complex. It is not possible to determine whether in this complex intermolecular exchange processes are also taking place.The reactions of the anionic [pyrrole-2-CHNR′]^? ligands [(N′N)^?] (R′ = t-Bu, i-Pr, (S)-CHMePh or 2,6-xylyl) with Zn(II) yield the neutral Zn(N′N)₂ complexes. These complexes were synthesized to study the coordination properties of the [pyrrole-2-CHNR′]^? moieties with Zn(II). A ¹H NMR study established that the zinc centres in the complexes containing the prochiral i-Pr or chiral (S)-CHMePh substituents have tetrahedral geometries with Δ or Λ configurations in CDCl₃ at 213 K. These complexes undergo an intramolecular exchange process at higher temperatures (above 260 K when R′ = i-Pr) which involves inversion of the configuration of the zinc centre. A mechanism for this exchange process is proposed.     

Reproductive success and clonal genetic structure of the rareArnica montana (Compositae) in The Netherlands

In a medium-sized population ofArnica montana, a threatened species in The Netherlands, the breeding system, reproductive success and genetic clonal structure were studied. Pollination experiments suggested thatA. montana is largely self-incompatible. Inbreeding depression was observed for seedling weight but not for fruit weight and germination rate. Although genetic variation is rather low in this population, the data suggest an outcrossing mating system. Analysis of the genotype of all mapped rosettes in a plot of 100 m² indicated that dense clusters often consist of identical genotypes, suggesting a clonal structure. Open clusters frequently contained several different genotypes. This may be caused by limited fruit dispersal, since seedlings were found mainly within or in the near surroundings of the clusters.