Pyrimidine dimers kinetics

Katiyar, S.K., Matsui, M.S., and Mukhtar, H., Kinetics of UV light-induced cyclobutane pyrimidine dimers in human skin in vivo an immunohistochemical analysis of both epidermis and dermis, Photochem. Photobiol., 72(6), 788-793, 2000. 

However, although photolysis of dimethyluracil64 and of other pyrimidines may be genuinely oxygen independent, early observations of an oxygen effect on the rate of uracil photolyses have been confirmed (Sect. V) the kinetic evidence has been supplemented by the observation84 that dimer formation is almost entirely suppressed in oxygenated uracil solutions, and uracil hydrate is the whole product. This clear-cut... 

Scheme 6 Minimal kinetic model for the Soai reaction. A = pyrimidine carbaldehyde, Z = diisopropylzinc, R or S = enantiomeric zinc alkoxide, RR or SS = homochiral zinc alkoxide dimers, and RS = heterochiral zinc alkoxide dimer...

Pyrazine is exceptional, by comparison with pyridine, pyrimidine, and pyridazine, in forming a relatively stable anion (592) the ion pair association of pyrazine radical anions with alkali metals has been studied using e.s.r. techniques (593-595) and a study has been made of the kinetics of their dimerization (596). 

Direct asymmetric autocatalysis amplified the slight excess of one enantiomer, leading to the enantiopure compound by reaction with diisopropylzinc. It is widely accepted that enantiomerically enriched products must form from achiral precursors merely because of statistical fluctuations. Usually, however, enantiomeric enrichment by fluctuations is very low. Thus, an amplification process of enantiomeric enrichment is required. Detailed kinetic analysis revealed that autocatalysis and inhibition are the major players in asymmetric autocatalytic synthesis. It turned out that tetramers serve as catalyst in the Soai reaction. The transition state for the Soai reaction implicates two molecules of pyrimidine alcohols or alcoxides as the dimeric catalysts and one molecule of prochiral aldehyde substrate (Buono and Blackmond 2003). Further kinetic studies using different ratios of substrate and reagent showed that a tetramer template is used. 

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