Study on hydrophobic self-association of aliphatic α-amino acids by flow microcalorimetry

A chemical interaction model has been established for the hydrophobic self-association of aliphatic alpha-amino acids in aqueous solutions. In order to obtain the parameters of the model equation, dilution enthalpies of 5 aliphatic a-amino acids aqueous solutions have been measured at 298.15 K by flow rnicrocalorimetry. The equilibrium constants (K), enthalpy change (Delta H-m) and entropy change (Delta S-m) have been determined for the equal-step association. It was found that between enthalpy and entropy exists a good compensation relationship. In addition, partial molar excess entropies of water in solutions (S-l(E)) were calculated, and were discussed according to the hydration model for aliphatic a-amino acids. Noteworthily, the parameters in the model equation can be used to explain the homogeneous enthalpic interaction coefficients in McMillan-Mayer model to some extent.