Complexes of dioxouranium(VI) with pyridoxal and glycine

Abstract

The catalytic effect of metal ions upon transamination reactions of aminoacids by pyridoxal and its derivatives has been demonstrated through formation of intermediate metal complexes of Schiff bases [1–5]. In our laboratory the role of dioxouranium(VI) ions in biochemical processes is under investigation and several complexes between UO 2+ 2 and biomolecules have been hitherto prepared and studied. Recently, the interaction of dioxouranium(VI) acetate with the ligand pyridoxal has been studied and the bonding of dioxouranium(VI) to phenolic and aldehydic oxygen atoms of pyridoxal has been proved [6,7]. The influence of uranyl ions on aminoacid-pyridoxal complexes has been investigated as well. The pyridoxal-glycine-uranyl acetate system has been studied both in solution and in solid state by electronic spectra and i.r. measurements respectively. The electronic spectra of an equimolar mixture of methanolic pyridoxal and glycine show peaks near 360 nm and 320 nm. The peaks markedly increase, when uranyl is added in equimolar amount, as a function of time with a red shift to 390 nm and 343 nm respectively. The band at 278 nm, due to the phenolic group of pyridoxal, appears also slightly shifted to 275 nm and two isosbestic points are present at 290 nm and 275 nm. The resulting spectrum of methanolic pyridoxal-glycine-uranyl complex is identical to that of a pyridoxylidene-glycine-dioxouraniuim(VI) mixture. The results obtained in the solid state indicate that ternary complexes 1:1:1 are formed and the elemental analysis is in agreement with the formulation: UO 2(C 8H 8NO 2)(C 2H 3NO 3)(CH 3COO)2H 2O. The i.r. spectrum of the uranyl solid complex was compared with the spectra of the free components. Changes in the i.r. absorptions are observed in particular in the regions where the azomethine CN stretching, the phenolic carbon–oxygen stretching and the asymmetric carboxyl stretching respectively occur. In fact, the azomethine stretch , v CN, is assignable to the strong band near 1610 cm −1 and the v COO and v CO to the absorption peaks near 1570 cm −1 and 1510 cm −1 respectively.