Unexpected differences between D- and L- tyrosine lead to chiral enhancement in racemic mixtures.
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.
Shinitzky
Meir
M
Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, Israel. meir.shinitzky@weizmann.ac.il
Nudelman
Fabio
F
Barda
Yaniv
Y
Haimovitz
Rachel
R
Chen
Effie
E
Deamer
David W
DW
D003460:Crystallization; D008968:Molecular Conformation; D012995:Solubility; D012996:Solutions; D013237:Stereoisomerism; D013696:Temperature; D013816:Thermodynamics; D014443:Tyrosine / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D012996:Solutions; D014867:Water; D014443:Tyrosine