title: Unexpected differences between D- and L- tyrosine lead to chiral enhancement in racemic mixtures.
abstract: We report here an unexpected difference in the solubilities of D- and L-tyrosine in water, which could be discerned by their rate of crystallization and the resulting concentrations of their saturated solutions. A supersaturated solution of 10 mM L-tyrosine at 20 degrees C crystallized much more slowly than that of D-tyrosine under the same conditions, and the saturated solution of L-tyrosine was more concentrated than that of D-tyrosine. Supersaturated solutions of 10 mM DL-tyrosine in water formed precipitates of predominantly D-tyrosine and DL-tyrosine, resulting in an excess of L-tyrosine in the saturated solution. The experimental setups were monitored independently by UV-absorption, radioactivity tracing, optical rotation and X-ray diffraction. The process of nucleation and crystallization of D- and L-tyrosine is characterized by an exceptionally high cooperativity. It is possible that minute energy differences between D- and L-tyrosine, originating from parity violation or other non-conservative chiral discriminatory rules, could account for the observations. The physical process that initiated chiral selection in biological systems remains a challenging problem in understanding the origin of life, and it is possible that chiral compounds were concentrated from supersaturated racemic mixtures by preferential crystallization.
authors.affiliation: Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, Israel. meir.shinitzky@weizmann.ac.il
authors.forename: Meir
authors.initials: M
authors.lastname: Shinitzky
authors.forename: Fabio
authors.initials: F
authors.lastname: Nudelman
authors.forename: Yaniv
authors.initials: Y
authors.lastname: Barda
authors.forename: Rachel
authors.initials: R
authors.lastname: Haimovitz
authors.forename: Effie
authors.initials: E
authors.lastname: Chen
authors.forename: David W
authors.initials: DW
authors.lastname: Deamer
mesh_terms: D003460:Crystallization; D008968:Molecular Conformation; D012995:Solubility; D012996:Solutions; D013237:Stereoisomerism; D013696:Temperature; D013816:Thermodynamics; D014443:Tyrosine / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; D014867:Water; D014443:Tyrosine