Interactions between D,L dansyl amino acids and immobilized teicoplanin: Study of the dual effect of sodium citrate on chiral recognition

The binding of a series of D,L dansyl amino acids (used as test solutes) to immobilized teicoplanin has been investigated over a wide range of sodium citrate buffer concentrations, c (2.5 x 10(-3) to 10(-1) M). An approach ba sed on the use of both the Gibbs adsorption isotherm and a solute displacem ent model was used to describe solute behavior in this chromatographic syst em. Variation of thermodynamic quantities was calculated from Van't Hoff pl ots to enable understanding of the forces driving solute association with t he teicoplanin phase. An enthalpy-entropy compensation study was also perfo rmed for further exploration of the interaction mechanisms. The results sug gested that variations of solute retention when c changed were governed by both (i) the salting-out effect of the salt and (ii) competitive displaceme nt of the dansyl amino acids from their teicoplanin binding site by the cit rate anion. The study also shows that hydrophobic interactions and hydrogen -bond formation are important to chiral discrimination in this chromatograp hic system.