Development of open chemical systems constantly producing one of the enantiomers of chiral products

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Homochirality in biomolecules in nature can be regarded as a chiral symmetiy breaking, a dissipative structure, that is a self-orgnization in nonequilibrium open system as a result of growth of fluctuation by irreversible dissipative processes. The kinetic model for chiral symmetry breaking was proposed about 20 years ago (D.K.Kondepudi, G.W.Nelson. Nature, 1985, 314, 438). The real chemcal system in which spontaneous generation of homochirality by following the model, hewever, has not been realized.Crystallization of 1,1'-binaphthyl from its racemic melt was studied. Chiral crystal of 1,1'-binaphthyl is crystallized when the temperature is in the range from 145 to 158℃, and the crystallization process is chirally autocatalytic (D.K.Kondepudi, J.Laudadio, K.Asakura, J.Am.Chem.Soc., 1999, 121, 1448). Temperature distribution in crystallization system was monitored and the structure of the crystal phase thus generated was characterized by X-ray diffraction. Enantiomeric excess of the cry … More stal phase generated when the temperature of the growth front was in the range from 145 to 158℃ was bimodal and its average was about 60%. The spontaneous generation of chiral asymmetry was identified as the chiral symmetry breaking in the growth front. A kinetic model to explain the mechanism was developed to investigate the condition at which racemic state becomes unstable to lead to generate homochiral state.A mechanism of asymmetric amplification, chemical reaction in which enantiomeric excess of a product is higher than that of chiral auxiliary for catalyst, was also investigated. The ultimate goal of this research is to achieve chiral symmetry breaking by following Kondepudi & Nelson's model in organic chemical reaction system. The chirally autocatalytic reaction found by Soai et al. is one of the candidate reaction (K.Soai, et al., Nature, 1995, 378, 767) Similar compounds are used for the asymmetric amplification and the chirally autocatalytic reaction. Michaelis-Menten type intemediate was found to be generated in the asymmetric amplification. Less