Oscillatory Symmetry Breaking in the Soai Reaction

Abstract

A kinetic model of spontaneous amplification of enantiomeric excess in the autocatalytic addition of diisopropylzinc to prochiral pyrimidine carbaldehydes is extended by a negative feedback process. Simulations based on the extended model result in large-amplitude oscillations both in a continuous-flow stirred tank reactor (CSTR) and in a semibatch configuration under optimized initial conditions. When sustained oscillations are maintained in a CSTR, no enantiomeric product distribution could be observed in the calculated series; the system keeps its initial enantiomeric ratio endlessly. During damped oscillations, or steady-state conditions, however, chiral amplification from a very small initial enantiomeric excess to more than 99% occurs in a semibatch configuration. Calculations indicated spontaneous enantiomeric product enrichment (i.e., accumulation of one of the enantiomers at the cost of the other one) from strictly achiral starting conditions in a semibatch configuration due to the inherent numerical error of the integrator method, which can be regarded as a model of the statistical fluctuation in the numbers of enantiomeric molecules.

Condensation oscillations in the peptidization of phenylglycine

“…Mickskei et al [22] subsequently extended this idea to a detailed model and showed in numerical simulations that enantiomeric enrichment and oscillation can occur under appropriate conditions.…”

The Role of Stochastic Models in Interpreting the Origins of Biological Chirality

“…This effect primarily depended on the details of the numerical integrator used and was a consequence of the dynamic instability of the studied kinetic scheme. Micskei et al made very similar observations [66] while studying an oscillatory model of the Soai reaction in a semibatch reactor. They proposed that the inherent numerical error of the integrator method might be a model of the statistical fluctuations.…”

Natural Abundance Isotopic Chirality in the Reagents of the Soai Reaction

“…The quantity of these structures in the usual range of micropreparative laboratory practice, from millimol to femtomol sample sizes, could reach such levels, which are higher than the sensitivity threshold of the asymmetric autocatalysis towards chiral induction, demonstrated experimentally [16][17][18][19][20] and evaluated theoretically [21][22][23][24]. In the relevant literature, however, no experimental or theoretical effort has been published earlier that deals with this problem.…”

“…These data show that even if the expectable e.e. values are very low, according to experimental evidence [16][17][18][19][20] and theoretical considerations [21][22][23][24], the isotope chirality in the tert.-butyl group in compounds 1 and/or 3 could influence the outcome of the most sensitive variant of the Soai reaction, however, taking into regard that it is separated from the pyrimidyl unit by the rigid C 2 moiety, and thus from the decisive molecular events around the new stereocenter, this option appears as scarcely probable, but cannot be excluded.…”

“…The Soai reaction shows extreme sensitivity towards the chiral induction exerted by even very low quantities both of the autocatalyst [16][17][18][19][20][21][22][23][24] and of added (enantiomerically pure or enriched) "foreign" chiral molecules [25][26][27][28][29][30][31]. It has also been proved experimentally that such inductor molecules may include enantiomers of simple chiral organic compounds with chirality due only to stable isotopic substitution [32][33][34][35][36][37][38][39].…”