Neutron diffraction investigations of l- and d-alanine at different temperatures: the search for structural evidence for parity violation

Abstract

Single crystal neutron diffraction has been used in an investigation of the structures of the amino acids L- and D-alanine. The aim of the study was to look for proposed phase transitions around T_c ≈ 270 K. Measurements of both structures at 295 K and 60 K—the neutron structure of D-alanine being determined for the first time—show no significant structural basis for this phase transition in alanine. Further, confirmatory, investigation of the structure of D-alanine at temperatures of 240, 250, 260 and 300 K also showed no significant changes in bond lengths or angles. We can thus offer no structural support to other physical measurements, which are indicative of the observable effect of parity violation of the electroweak force in these phase transitions.