Design, Synthesis And Characterization Of Oxovanadium Compounds Derived From Amino Acids And Derivatives

The bioinorganic chemistry of vanadium is a completely new field. Vanadium is a trace element, which may be beneficial and possibly essential in humans but certainly essential for some living organisms. Vanadium ions can play a role in biology as counterions for protein, DNA, RNA, and in various biological organelles. Vanadium ions have many structural roles reflected by its structural and electronic analogy to phosphorus.Vanadium has some significant biological functions in biological systems. Vanadium is present in the active sites of some metalloenzymes, such as haloperoxidases and nitrogenases, which catalyze the halogenaition of organic substrates and biological nitrogen fixation respectively. Vanadium can inhibit ribonaeases and Na, K, ATPase, thus has its role in signal transduction and bioenergetics. Vanadyl (IV) ion has only one unpaired electron (d1) and can be used as an EPR spin probe in biological systems. It can substitute for Mg (d0), Zn (d10) and other divalent metal ions and help elucidate the active sites of many enzymes. And more noticeable, many vanadyl (IV) complexes have insulin-mimetic effects, thus have the potential as medicines to cure diabetes. Thus, the studies of the vanadium coordination chemistry and bioinorganic chemistry have developed extensively in recent years.In order to understand the exact role of vanadium in biological system and search for more efficacious compounds for pharmacy, great efforts have been made to investigate the relationships between the chemical and biological properties of vanadium compounds.The most important oxidation states of vanadium are +3, +4, and +5. And the V (IV) compounds are the most commonly observed in the form of compounds of the vanadyl ion, VO²⁺. Therefore, we put the emphases on the design, synthesis and characterization of oxovanadium (IV) complexes.Ligands are important for these syntheses. Studies on interaction of vanadium with biologically important ligands aimed at finding structural and/or functional models of biological compounds are numerous and have been the subject of several reviews. Amino acids are biological material, so the knowledge of the interaction of VO2+ in the presence of amino acids is relevant in understanding its possible interaction with likely biological ligands. Amino acids have been considered to be candidates, which allow easy artificial linkage of various functional groups with N-terminal to generate a variety of multidentate ligands.Taking into consideration the international studies, we have focused our study on the investigation of vanadium compounds derived from amino acids and their derivatives. We discuss here the syntheses and structural features of these novel compounds and the structural relationships among them. The results of my work are as follow:1. Two N-pyridoxylideneamino acidato complexes of oxovanadium (IV), [VO(pyr-D,L-Met)(bipy)] 1 and [VO(pyr-D,L-Thr)(bipy)]·H₂O 2 with Schiff bases, made from amino acids (DL-methionine and DL-threonine) and pyridoxal, were prepared by an amine-diffusion reaction and characterized by single crystal X-ray diffraction. Both [VO(pyr-D,L-Met)(bipy)] and [VO(pyr-D,L-Thr)(bipy)]·H₂O crystallize in triclinic P-1. They contain two diastereomers, donating the chiral vanadium centers as A or C, e.g. [A(pyr-D-Met)(bipy)], [C(pyr-L-Met)(bipy)] and [A(pyr-D-Thr)(bipy)]·H₂O, [C(pyr-L-Thr)(bipy)]·H₂O. The complexes were also characterized by elemental analysis, IR and EPR spectroscopy. The EPR spectra illustrate well-resolved coupling of the unpaired electron with 51V nucleus (I = 7/2). Under hydrothermal condition, a unexpected dinuclear vanadium compound bridged by nitrogen atoms, [VO(L)(bipy)]·H₂O (L=C₁₂H₁₁N₂O₄) 3, was obtained from pyridoxal and amino acid. A reasonable mechanism of this reaction is also given here.2. Two dinuclear oxovanadium (IV) compounds [V(O)(N₂Met)(μ-OMe)]₂·MeOH 4 and [V(O)(N₂Thr)(μ-OMe)]₂·MeOH 5 were prepared by the reaction of VOSO₄ and ONN donor ligands, HN2Met and HN2Thr (HN2Met = N-(2-pyridylmethyl)-DL-methionine, HN₂Thr = N-(2-pyridylmethyl)-DL-threonine) derived from 2-pyridinecarbaldehyde and DL-methionine/DL-threonine. X-ray crystallography revealed that the two vanadium (IV) compounds are both dinuclear structures bridged by methanol groups. Each vanadium atom is six coordinated in a distorted octahedral environment. From the reaction of the same ligands and VO(acac)₂, two mononuclear products [VO(NMet)(acac)]·MeOH 6 and [VO(NThr)(acac)]·MeOH 7 were obtained and characterized by X-ray crystallography. They can probably be candidates for antidiabetic use due to their good lipophilicity and hydrophilicity.3. A dinuclear oxovanadium compound [V₂O₂(L-His)₂(2, 2'-bipy)₂]·[C₂H₆O₂·(2, 2'-bipy)] 8 was synthesized under hydrothermal condition and characterized by single-crystal X-ray diffraction. X-ray crystallography revealed that each vanadium center is six coordinated and adopts a distorted octahedral structure. The equatorial plane is coordinated by the N atom of the terminal amine group, one of the O atoms of the carboxylate group and the deprotonated imidazolyl nitrogen of a different histidine molecule. One of the nitrogen atoms from bipy occupies the fourth equatorial position. IR spectroscopy, ESR spectrum and magnetic susceptibility data for this compound are given. X-band ESR spectroscopy of the sample indicated the existence of vanadium (IV) ions in the compound. The temperature dependent magnetic susceptibility data showed the presence of a ferromagnetic coupling between the two V (IV) ions in the range 4-180 K.