Copper(II) Complexes of Potentially Terdentate N2-[(R)-2-Hydroxypropyl]- and N2-[(S)-2-Hydroxypropyl]-(S)-phenylalaninamide for Chiral Recognition: Synthesis of the Ligands and Formation Constants

Copper(II) complexes of the ligands N2-[(R)-2-hydroxypropyl]- and N2-[(S)-2-hydroxypropyl]-(S)-phenylalaninamide performed chiral separation of N-dansyl-protected and unmodified amino acids in HPLC (reversed phase). With the aim of investigating which species are potentially involved in the discrimination mechanism, the two ligands were synthesized and their complexation equilibria with Cu2+ studied by potentiometry and spectrophotometry in aqueous solution up to pH 11.7. The formation constants of the species observed, [CuL]2+, [CuL2]2+, [CuLH–1]+, [CuL2H–1]+, [CuL2H–2], and [CuL2H–3]−, were quite similar for both compounds and were compared to those of (S)-phenylalaninamide. Most probably, in [CuL2H–3]− the ligands behave as terdentate, with the deprotonated OH group occupying an apical positio