ESR SPECTROSCOPIC STUDIES OF HOMO- AND HETEROLIGAND COMPLEXES OF COPPER(II) AND OXOVANADIUM(IV) WITH GLUTAMINE

This article presents the results of studying and analyzing the electron-structural and coordination properties of various forms (protonated (cationic), zwitter-ionic (betaine), neutral and deprotonated (anionic)) glutamine using quantum chemical calculations. Taking into account this feature, to clarify the reactivity of glutamine in the above forms, the values of the distribution of atomic charges by Mulliken and the polarity of bonds in the amide and α-aminocarboxylate groups were used. Electronic parameters such as HOMO, LUMO energies and the molecular electrostatic potential (MEP) of the glutamine molecule are calculated. Quantum chemical calculations were carried out using the Gaussian 09 program using the density functional theory (DFT) method with the B3LYP hybrid functional and using the 6-311G++(d,p) basis set. Experimental IR spectra were obtained in the region of 4000-400 cm-1. The composition and structures of copper(II) and oxovanadium(IV) complexes in solutions were studied by ESR spectroscopy. Comparison of the ESR parameters of aqueous solutions of heteroligand copper(II) complexes with glutamine and amides (A = 55.44 Э, g = 2.1212; A = 56.24 Э, g = 2.1210; A = 57.35 Э, g = 2.1208) established dimeric, and in the glutamine-acetate complex (A = 90 Э, g = 2.0495) mononuclear composition. In DMSO solutions of molecular and intra-complex compounds of oxovanadium(IV), the same methods of coordination through the atoms of the N,O α-aminocarboxylate group of glutamine were established on the basis of the identity of the EPR parameters (A=97 Э, g = 1,971; A=96 Э, g = 1,971, A=97 Э, g = 1.971).