Conformations of Pyridoxal Schiff Bases of Amino Acids. A Circular Dichroism Study

Article abstract of DOI:10.1021/ja00342a026

The conformations of a series of peridoxal-L-amino acid Schiff bases in methanol solution were deduced from their circular dichroism spectra.The N-salicylidene analogues of the pyridoxal Schiff bases were used as appropriate reference compounds.The predominant conformation of the C_α-N bond was found to be approximately the same for all the Schiff bases and involves a pseudoequatorial disposition of the C_α-H bond with respect to the plane of the extended ? system.The sign of the Cotton effects near 420 and 340 nm varies with the nature (polar, nonpolar, aromatic) of the amino acid side chain, according to the chirality of the dominant interaction of the amino acid residue with the pyridoxylideneamino chromophore.The circular dichroism spectra of zinc(II) complexes of N-pyridoxylidene-L-amino acids were also discussed in relation to the metal-free systems.