Parity-violating energy effect

These experimental results could not be confirmed by Lahav and co-workers they suggest that impurities in the starting materials have a much greater effect on the crystallisation process than the PVED (Parity Violating Energy Difference). Extensive experimental studies indicate the importance of small quantities of impurities, particularly in early phases of crystallisation nucleus formation. Amino acids from various sources were used, and the analyses were carried out using the enan-tioselective gas chromatography technique (M. Lahav et al 2006). 

As has been discussed in the introduction, the possibility of a relation between parity violating energy differences and the biochemical homochirality observed on earth has been noted by Yamagata [11] a decade after the discovery of parity violation in nuclear physics. Various different kinetic mechanisms have been proposed which could possibly amplify the tiny energy difference between enantiomeric structures to result in an almost exclusive chiral bias on a time scale relevant for the biochemical evolution. This aspect as well as other hypotheses regarding the origin of the biochemical homochirality have been discussed and reviewed multiple times (see for instance [33,37-39,190-193] and literature cited therein) so that we can concentrate here on the computational aspects of molecular parity violating effects in biochemical systems. 

L. Wiesenfeld, Effect of atomic number on parity-violating energy differences between enantiomers. Mol. Phys. 64 (1988) 739-745. 

The influence of the weak interaction on chemical reactions can be calculated since it favours left-handedness, it has an effect on the energy content of molecules and thus on their stability. In the case of the amino acids, the L-form would be more stable than the corresponding D-form to a very small extent. Theoretical calculations (using ab initio methods), in particular by Mason and Tranter (1983), indicated that the energy difference between two enantiomers due to the parity violation is close to 10 14J/mol (Buschmann et al., 2000). More recent evidence suggests that the... 

Since the historical PV weak force origin /3-decay experiment of 60Co [ 106], theoreticians presumed that the tiny parity violating WNC at molecular and subatomic levels may also allow a distinction between mirror image molecules at the macroscopic level as well. This is because PV-WNC at the molecular level may be a candidate for the homochiral scenario under terrestrial and extraterrestrial conditions [1,2,104,109-118]. The WNC, however, did not induce any observable PV effects between enantiomers in their ground states because of the minuscule PV energy difference (PVED) of 10 19 eV and/or negligibly small 10 - % ee in racemates. Theoreticians also proposed several possible amplification mechanisms at reproducible detection levels within laboratory time scales and at terrestrial locations [113,117,118]. 

If we consider, instead of a two-level system, the multiple levels of ordinary chiral molecules, the states of well defined parity will in the low-energy region still come in almost degenerate pairs which are energetically separated from other states. Therefore the main contribution to parity violating effects will still be due to interpair coupling. In this limit A py can essentially be identified with 2 x fpvl-... 

The potentials (94) and (95) are already quite similar to the leading effective Hamiltonians that have been used so far in one- and four-component calculations of molecular parity violating eflFects. We have assumed above that the fermions are elementary particles. The effective potentials may, however, also be applied for the description of low energy weak neutral scattering events, in which heavy non-elementary fermions like the proton and the neutron or even entire atomic nuclei are involved, provided that properly adjusted vector and axial coupling coefficients py and for non-elementary fermions are used. 

The parity violating potentials in alanine in gas phase and solution have been studied in [106] within the framework of the multi-configuration linear response approach. Several low-energy conformers of neutral alanine as well as the zwitterionic form have been studied therein and solvent effects on structures and, for the first time, also on parity violating potentials have been accounted for within a multi-configuration self-consistent reaction field approach on the RPA and the CASSCF level of theory. The main result of these higher level calculations was, that they provided no... 

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