Complexes of vitamin B 6—part XXII. The interaction of vitamin B 6 compounds with CU II-glycinehydroxamic acid binary system

Abstract

Binary complexes of the glycinehydroxamic acid (GX) with copper(II) (GX-Cu II), as well as their interaction with vitamin B 6 compounds [pyridoxol (P), pyridoxal (PL) and pyridoxamine (PM)] were studied by pH-metric, differential pulse polarography (DPP), and electron paramagnetic resonance techniques at the ionic strength of 0.15 M NaCl and at 25°C. The formation constants of the binary and ternary species were determined using the SUPERQUAD program. The three ternary systems do not show the same stoichiometries of the different species, in addition, PL interacts with GX to form Schiff bases at pH > 4.5. Comparative studies of the DPP of the binary and ternary systems of Cu II revealed that Cu II is more stabilized toward reduction in the presence of PM than in presence of GX at pH > 6.0; in addition the redox behaviour of Cu II in the presence of PM is similar to that of the GX-Pm-Cu II ternary system. On the other hand, the DPP of the ternary systems GX-P (or PL)-Cu II are similar to those of GX-Cu II binary system at different pH values. The nuclear spin-electron spin coupling of Cu II in these systems is discussed.