Intermediates in the metal catalysis of the transamination reaction: A study of some transition-metal complexes of pyridoxal phosphate, of pyridoxamine phosphate, and of their Schiff's bases

Abstract

Complexes of Cu(II), Zn(II), Ni(II) and Co(II) with pyridoxal-5-phosphate and pyridoxamine-5-phosphate were prepared. Some Schiff base-metal complex intermediates postulated to exist in the metal catalysed transamination reaction between pyridoxal-5-phosphate and a-glutamic acid, and pyridoxamine-5-phosphate with a-oxoglutamic acid were isolated.The possibility that the latter may exist as chelates was explored by means of infrared spectroscopy, by visible and ultra violet spectra of buffered solutions and of solid state samples. The magnetic properties of the compounds have been studied over a wide range of temperatures.The subsequent discussion includes e.s.r. studies on Cu(II) complexes. Infared spectra were studied for the phosphate group interms of group theory and the presence of infrared bands at 1200-900 cm region confirms the coordination of phosphate group in PLP and PamP complexes Infrared spectral studies confirmed that all complexes involve bonding through the phenolic oxygen. The formation of Schiff's base complexes through the aldehydic group has been confirmed. The visible electronic spectra of the copper, nickel and cobalt complexes indicated the probable stereochemical shapes of the metal ion. The diffuse reflectance spectra of copper(ll) Schiff's base complexes all exhibited an absorption bandin the 14000-14033 cm region and would suggest a square-planar structure or square planar bridging. However, the g-values from the e.s.r. results suggest a tetragonal-octahedral, square planar and square pyramidal environment of Copper(II).