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Deviation from Physical Identity Between D- and L-tyrosine-Chapter 27

Elsevier Ltd
DOI: 10.1016/b978-008044396-6/50029-0
  • Biology


Publisher Summary Symmetry under reflection—nature's indifference to the “right” and “left” directions (P symmetry)— is one of physics' most profound and well-established principles, and is unlikely to be violated by a biological process. Nevertheless, experimental studies and intensive survey of the literature have presented that such a violation may occur in natural amino acids. In one such case, tyrosine, significant deviations from macroscopic identity between the L- and D-enantiomers were detected. It was then reported that a supersaturated solution of L-tyrosine in water forms crystalline precipitates much more slowly than the analogous solution of D-tyrosine. Furthermore, supersaturated solutions of DL-tyrosine in water formed a precipitate of predominantly D- and DL-tyrosine, resulting in excess L-tyrosine in the aqueous layer. Again, it was suggested that the minute energy difference between these enantiomers, in combination with the highly cooperative process of crystallization of tyrosine, could account for this unexpected observation. The chapter summarizes a series of additional experiments that seem to support this unexpected phenomenon. It also discusses its possible origins and suggests a mechanism for the violation of chiral identity, which, in practice, can lead to chiral enhancement.

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