Collect. Czech. Chem. Commun. 1994, 59, 1721-1728

Free Energies of Adsorption of Dipeptides and 2,5-Piperazinediones on Silica from Neutral Aqueous Solutions as Estimated from High-Performance Liquid-Chromatographic Retention Data

Vladimir A. Basiuk and Taras Yu. Gromovoy

Institute of Surface Chemistry, Academy of Sciences of the Ukraine, Prospekt Nauki 31, Kiev 252022, Ukraine


The equilibrium constants (K) and free energies (-∆G) of adsorption of dipeptides and their cyclic derivatives, 2,5-piperazinediones, on silica from neutral aqueous solutions were calculated from their HPLC retention data on a silica gel column. For the majority of the dipeptides -∆G values were negative, ranging from -1 170 to 430 J mol-1, and K < 1, thus indicating a very weak adsorption. The 2,5-piperazinediones under study exhibited higher adsorbabilities (-∆G -1 070 + 3 030 J mol-1, K > 1) as compared to the respective dipeptides. The effect of the α-substituent structure on the adsorbability is analyzed. A linear dependence of -∆G on the number of aliphatic carbon atoms in a sorbate molecule was observed for the series of dipeptides and 2,5-piperazinediones derived from bifunctional aliphatic amino acids.