Complex formation equilibria of L-amino-acid amides with copper(II) in aqueous solution

Protonation and Cu(II) complexation equil. of L-phenylalaninamide, N2-methyl-L-phenylalaninamide, N2,N2-dimethyl-L-phenylalaninamide, L-valinamide, and L-prolinamide have been studied by potentiometry in aq. soln. The formation consts. of the species obsd., CuL2+, CuL22+, CuLH-1+, CuL2H-1+, and CuL2H-2, are discussed in relation to the structures of the ligands. Possible structures of bisamidato complexes are proposed from visible and CD spectra. Since Cu(II) complexes of the present ligands (pH range 6-8) perform chiral resoln. of dansyl- and unmodified amino acids in reversed-phase HPLC, it is relevant for the investigation of the resoln. mechanism to know which are the species potentially involved in the recognition process.