ABSORPTION AND CIRCULAR DICHROIC SPECTRAL STUDIES ON COMPLEXES OF NICKEL(II) WITH ALPHA-AMINO ACIDS

A characteristic circular dichroic spectrum is demonstrated for the 1:1 chelate of Ni(II) formed with the L-amino acids, alanine, serine, valine, arginine, ornithine, and glutamic acid. This chelate, which involves the carboxyl and the α-amino groups, becomes detectable between pH 3 and 4, as acidity is decreased. With higher ratios of amino acid to Ni(II), evidence is seen for formation of a bis chelate, starting at about pH 7. No sign is seen of a tris chelate. The 1:1 chelates of asparagine or aspartic acid with Ni(II) have a dichroic spectrum different from the one above, which is attributed to terdentate chelation. Solutions of asparagine and Ni(II) with ratios of ligand to metal ion 2:1 or greater apparently revert to α-amino chelates like the normal amino acids, above pH 8-9. © 1969, American Chemical Society. All rights reserved.