Electron paramagnetic resonance parameters and equilibria of manganese(II)–amino-acid complexes in aqueous solution

Abstract

Manganese(II) binding to amino-acids is studied, bearing in mind the role that this paramagnetic ion plays in the action of certain enzymes, in order to contribute to a clarification of its interactions with protein molecules. Information on the equilibria of Mn–amino acid complexes is derived from e.p.r. and n.m.r. spectra. Particularly, the following parameters are taken into consideration: the e.p.r. intensity, the Mn^II electron spin relaxation time, and the nuclear relaxation time T₂ of the water protons involved in complex formation. Attention is focused on four complexes: Mn–glycine, Mn–valine, Mn–proline, and Mn–α-alanine. Outer sphere co-ordination is taken into account and the dynamic aspects in the solvation shell of the manganese(II) ion are discussed.