Stereoselectivity in the ternary complexes copper(II)–N-benzyl-L-proline–D- or L-α-amino-acids

Abstract

Chromatographic elutions of D,L-phenylalanine, D,L-proline, and D,L-histidine have been made on a copper-loaded polystyrene resin containing L-proline groups. The isomers of D,L-phenylalanine were not separated while D,L-proline and D,L-histidine could be completely resolved, the order of elution of the enantiomers being reversed.Ternary complexes, models of the associations occurring in the chromatographic process on the active sites of the resin, have been studied in aqueous solution. Formation constants of the ternary species copper(II)-N-benzyl-L-proline-D- or L-amino-acid have been calculated from potentiometric curves with the aid of the MINIQUAD program. The values allow us to explain the chromatographic results since stereoselectivity is significant only in the mixed systems containing proline and histidine. Suggestions are given for the structures of all the ternary complexes.