Studies of new phosphothreonine complexes formed in binary and ternary systems including biogenic amines and copper(II)

Abstract

Binary and ternary systems of copper(II) with O-phospho-L-threonine (Thr-P) and biogenic amines (putrescine or spermidine or spermine) have been investigated. The studies were performed in aqueous solution. Overall stability constants of the complexes were determined by pH-metric study and the coordination sites were identified by 31P NMR, visible and electron paramagnetic resonance spectroscopies. Results of the equilibrium and spectral studies have shown that in the phosphothreonine binary system Cu(HThr-P), Cu(Thr-P) and Cu(Thr-P)(OH) are formed. In the binary system at low pH, only the phosphate group is involved in coordination but at higher pH, the efficiency of −PO4 2− is low and the amine and carboxylate are the main sites of coordination. Formation of complexes was established in ternary systems with all bioamines studied. In these systems the reaction centers of phosphothreonine are the same as in the binary systems: phosphate, carboxylate and amine. Additionally, amine groups from the polyamines (PAs) are involved in the complex formation. Besides the heteroligand complexes with intermolecular interactions, also molecular complexes with the protonated bioamine in the outer coordination sphere appeared. In these molecular species, PA was involved in non-covalent interactions with the anchoring phospho-threonine complex.