Free energies of adsorption of amino acids, short linear peptides and 2,5-piperazinediones on silica from water as estimated from high-performance liquid-chromatographic retention data

Abstract

Equilibrium constants (K) and free energies (— ΔG) of adsorption of amino acids, short linear peptides and cyclic dipeptides (2,5-piperazinediones) on silica from neutral aqueous solutions were calculated from the retention values measured by means of high-performance liquid chromatography on a silica gel column. For most amino acids and linear peptides — ΔG values were negative and K 0 and K > 1) as compared to related dipeptides. Influence of the structure of a-substituent on the adsorbability is analyzed. A linear dependence of — ΔG on the number of aliphatic carbon atoms in a sorbate molecule was found for the series of aliphatic bifunctional amino acids, related dipeptides and 2,5-piperazinediones, as well as for the group from glycine to triglycyl glycine.