Temperature Dependences And Enthalpic Discrimination Of Homochiral Pairwise Interactions Of Six Alpha-Amino Acid Enantiomers In Pure Water

Dilution enthalpies of six alpha-amino acid enantiomers (L-alanine vs d-alanine, l-serine vs d-serine, and l-proline vs d-proline) in pure water were determined at T = (288.15 to 323.15) K by isothermal titration calorimetry (ITC). Homochiral enthalpic pairwise interaction coefficients (h(xx)) at each temperature were evaluated according to the McMillan-Mayer theory. The h(xx) values of a-alanine and a-proline enantiomers are all positive (h(LL) > hDD > 0), while those of a-serine enantiomers are all negative (h(LL) < h(DD) < 0). In both cases, the h(xx) values increase uniformly and gradually with elevating temperatures. A slight but significant enthalpic discrimination effect is found in the homochiral pairwise interactions of these a-amino acid enantiomers. The positive growth of h(xx) values indicates that increasing temperature promotes the predominance of hydrophobic interactions in the binary aqueous solutions studied.