A theoretical study of N-nitrosamine metabolites: Possible alkylating species in carcinogenesis by N,N'-dimethyl nitrosamine

The results of ab initio calculations using a 4–21G basis set are reported for various possible metabolites of N,N'-dimethylnitrosamine. The relevance of these results to the nature of the alkylating agent is discussed. Although the calculations widen the range of possible alkylating agents that need to be considered, the diazonium ion appears to be the most likely candidate.     

Enantioselective synthesis of the excitatory amino acid (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid

An enantioselective synthesis of the alpha,alpha-dialkyl-alpha-amino acid (1S,3R)-ACPD has been achieved using an alkylidene carbene 1,5-CH insertion reaction as a key step. The ketone cyclization precursor was synthesized from Garner's aldehyde in high yield via a Wittig homologation and subsequent catalytic hydrogenation. Treatment of the ketone with 1.2 equiv of lithio(trimethylsilyl)diazomethane in THF resulted in the formation of the corresponding cyclopentene-containing CH-insertion product in 62-69% yield in high enantiomeric excess. Subsequent functional group manipulation allowed the synthesis of the amino acid (1S,3R)-ACPD to be completed.     

The structure and acid–base properties of methyl and silyl amines and phosphines: An ab-initio SCF study

The structures of the methyl and silyl amines and phosphines and their ions have been calculated using ab-initio SCF theory and the 3-21G basis set. The computed structures give excellent agreement with the available experiment data without the inclusion of d functions, with the exception of (SiH₃)₂N– and the isoelectronic molecules (SiH₃)₂O and (SiH₃)₂C^2? where d functions are essential. The observed trends in computed basicities and acidities are reproduced by the calculations.     

IMPACT OF ENHANCED SIMULATED SOLAR ULTRAVIOLET RADIATION UPON A MARINE COMMUNITY

Abstract—There is evidence to indicate that an increased exposure to solar radiation in the UV-B region (specifically, 290–320 nm) may occur as a result of anthropogenic degradation of stratospheric ozone. The fact that present levels of solar UV radiation can detrimentally affect marine organisms led to experiments to quantify the impact of increased UV radiation upon a marine community. Two 720–l seawater chambers (continuous flow-through design) were exposed to simulated solar UV radiation. Fluorescent sunlamps filtered by a 290 nm cutoff filter (a 0.13 mm thickness of cellulose triacetate film) were used as the radiation source. Utilization of three different weighting factors for the spectral irradiances at the surface of the chambers yielded differences of 18%, 35% and 40% in biologically effective fluence rate between the two chambers. Analysis of attached forms of algae at various depths demonstrated that a surface exposure of 1.4W/m² in the 290–315nm waveband as contrasted with the chamber receiving a surface exposure of 1.0W/m² resulted in depressed Chl a concentrations, reduced biomass, increased autotrophic indices, and decreased community diversity. These results indicate a potential for adverse effects of increased solar UV-8 radiation: decreased community diversity, community structure shifts, and decreased productivity.     

Koopmans' theorem ionization potentials of methyl and silyl halides,chalcogenides, amines,and phosphines: An ab InitioSCF study

Koopmans' theorem ionization potentials have been calculated for a series of hydrides, methyls, and silyls H_nX, (CH₃)_nX, and (SiH₃)_nX (X = F, Cl, n = 1; X = O, S, n = 2; X = N, P, n = 3), together with some mixed species (MH₃)_nXH_3-n (X = N, P; M = C, Si) using ab initio SCF methods. The calculated values give excellent agreement with experimental values without the inclusion of d functions. For the chlorides, HCl, CH₃Cl, and SiH₃Cl, the values vary rather little over a wide range of basis sets, and are unaffected by the inclusion of d functions.