Heat Capacity and DC-Magnetic Susceptibility Evidence for the Asymmetry of Electron Spin-Flip Phase Transition of N + H…O - Bond in Chiral Alanine Crystal

With a view to understanding the argument of phase-transition mechanisms of D- and L-alanine at around 270 K, the temperature dependence of heat capacity measurements was investigated, for single crystals, ground powders, and polycrystalline products, using differential scanning calorimetry (DSC). The Cp (heat capacity under constant pressure) values of D- and L-alanine were calibrated with standard sapphire by the triple-curve method; these values coincide with the standard Cp values in the literature. Endothermic transition peaks were observed at Tc=272.02 K, ∆H=1.87 J·mol - 1 and Tc=271.85 K, ∆H=1.46 J·mol - 1 for D- and L- alanine, respectively, and Tc=273.59 K, ∆H=1.75 J·mol - 1 and Tc=273.76 K, ∆H=1.57 J·mol - 1 for the reference crystals D- and L-valine, respectively. The energy differences of 0.41 J·