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Photoreaction of rac ‐Leucine in Ice by Circularly Polarized Synchrotron Radiation: Temperature‐Induced Mechanism Switching from Norrish Type II to Deamination
Author(s) -
Nishino Hideo,
Hosaka Masahito,
Katoh Masahiro,
Inoue Yoshihisa
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201301831
Subject(s) - deamination , chemistry , photodissociation , enantiomer , meteorite , photochemistry , amino acid , decarboxylation , enantioselective synthesis , deuterium , enantiomeric excess , stereochemistry , astrobiology , organic chemistry , catalysis , biochemistry , physics , enzyme , atomic physics
The delivery of extraterrestrial organics to primitive Earth is considered to have triggered the origin and subsequent evolution of life. Indeed, enantiomerically enriched amino acids of nonterrestrial origin have been found in carbonaceous meteorites, and enantioselective photodecomposition by circularly polarized light (CPL) in outer space has been proposed to have played some role in the initial enantiomeric bias. To experimentally examine this possibility and elucidate the photoreaction mechanisms, we have studied the photolysis of racemic leucine ( rac ‐Leu) in acidic and neutral ice/water media at 21–298 K with left‐ and right‐CPL in an attempt to detect enantiomerically enriched D ‐ and L ‐Leu, respectively. Comprehensive product analyses revealed that the CPL‐induced deracemization of Leu proceeds in both acidic and neutral ice matrices even at 21 K, and that the main mechanism switches from Norrish‐type II γ‐hydrogen abstraction to S N i deamination on lowering the temperature. The potential role of the CPL‐induced photodecomposition of amino acids as a source of the enantiomer imbalance in meteorites is discussed.