Use of the Na+ ion as an RPLC retention marker to investigate the association of dansyl amino acid ids with permethylated beta-CD

The mechanism of binding of D, L dansyl amino acids to permethylated beta - cyclodextrin (pM-beta CD) has been investigated. Sodium phosphate was used as an indicator of interactions between the solutes and pM-beta CD. The num ber (n) of sodium ions, Na+, excluded from the solute pM-beta CD cavity int erface when analyte transfer occurred was determined. These n values could be linearly correlated with the steric bulkiness of the solute. Thermodynam ic data for solute transfer are discussed in relation to the extent of incl usion of the dansyl amino acids. Enthalpy-entropy compensation showed that the retention mechanism was independent of the molecular structure of the e nantiomer, the configuration of the asymmetric carbon, or the concentration of salt in the mobile phase.