Demonstration of the parity-violating energy difference between enantiomers

Abstract

Racemic mixtures of (؉) and (؊) sodium potassium tartrate, tris(1,2-ethanediamine)cobalt(III), and tris(1,2-ethanediamine)iridium(III) molecules were crystallized, and the optical activities of the resulting crystalline materials, dissolved in water, were carefully measured to study the inf luence of the parity-violating energy difference in the crystallization process. Although no effect was found in the case of tartrate, enantiomeric excess appeared in the crystallization of the cobalt and iridium complexes. These investigations, performed in our laboratory, demonstrated the contribution of the parity-violating neutral weak current to the forces acting in molecules.The electromagnetic and weak interactions were unified by Weinberg, Salam, and Glashow in the concept of the electroweak interaction. This work is reviewed in simplified form in ref.1. An important consequence of the unified theory of the electromagnetic and weak interaction is the existence of the weak neutral current that generates parity-violating interactions between electrons and electrons and between electrons and neutrons. Experiments involving elementary particles and atoms confirmed the theory. In enantiomeric molecules, the interaction induces a small difference between the energies of the different enantiomers. The theory was extended to calculations of the parity-violating energy difference (PVED) between the L-and D-amino acids, for example. The main impetus behind these calculations was the hope of explaining the origin of the homochirality of biomolecules, i.e., the phenomenon that living systems contain nearly completely L-amino acids and D-sugars (2). The asymmetry found in the weak neutral current incited the idea of the universal unity of the effects of parity violation in the inanimate and living world (for reviews see refs. 3-5). Other asymmetric forces also were considered as possible causes of homochirality. On the other hand, strong arguments exist that homochirality might have originated by spontaneous processes that appeared in the evolving system of molecules before life existed (6). The questions now are: was homochirality a result of spontaneous processes or of the action of a certain asymmetric physical agent and if the latter, was it the parity-violating weak interaction?In the first approach to estimating PVED, Rein (7) calculated a difference of the order of 10 Ϫ13 eV between the binding energies of L-and D-alanine. According to Gajzágó and Marx (8) an estimate of 10 Ϫ13 eV is rather optimistic for the energy splitting between the mirror molecules. The same order of magnitude was found by Zel'dovich et al. (9). Later, in the calculations of Rein et al. (10) PVED Ϸ10 Ϫ17 kT (kT ϭ 0.025 eV at room temperature) was found for a model molecule (twisted ethylene), but the sign of the effect could not be determined. From the works of Mason, Tranter, and MacDermott (11-15), we know that the value of PVED is Ϸ1 ϫ 10 Ϫ17 kT for the amino acids, the L-amino acids having the lower energy. New calculations demonstrated th...

Intrinsic asymmetries of amino acid enantiomers and their peptides: A possible role in the origin of biochirality

“…5 Szabo-Nagy and Keszthelyi 59 claimed to detect a parity-violating difference in the CD spectra of cobalt(III) and iridium (III) salts of tris(ethanediamine). Wang and coworkers [60][61][62] have attempted to test Salam's conjecture that a phase transition should appear at a temperature T c $250 K, at which certain physical properties will become substantially different for D and L enantiomers.…”

Supramolecular Chirality: Solvent Chirality Transfer in Molecular Chemistry and Polymer Chemistry

“…This non-mirror-image relation may be ascribed to some impurities, as claimed in several papers [68,71,73,117]. It may also infer other unknown reasons, such as an inherent mirror symmetry breaking at a global level upward, our universe scale [123,124] and macroscopic MPV effects [21,37,43,46,51,67,72,74]. The commercially available chiral alcohols shown above are very expensive compared to common chemicals.…”

Efficient Asymmetry Generation in the Synthesis of Oxo‐Rhenium(V) Complex cis‐[ReOCl2{OCMe2CMe2OP(OCMe2CMe2O)}py]

“…[8] Keszthelyi and Szabó-Nagy have described a small enantiomeric excess found in polycrystalline material upon crystallization from racemic solutions of (þ)-and (À)-tartrate(2À) with either (þ)-and (À)-[Co(en) 3 ] 3+ or [Ir(en) 3 ] 3+ ions. [9] The authors of the latter two works have claimed that the observed partial deracemization is because of electroweak forces. Clearly, these preparations could only be successful under nonequilibrium conditions involving physical fields and/or autocatalytic chirality-amplification mechanisms.…”