Tungsten Biomimetic Synthesis And Characterization Of The Activity Structure Factor

Tungstoenzymes play intimate roles in the global cycles of nitrate, carbon and sulfur. Structurally characterized synthetic analogs of the active sites of W-containing enzymes are essential for the interpretation of biochemical properties and catalytic activity of tungstoenzymes. So biomimetic synthesis and biochemical mechanism study of active cofactor of tungstoenzymes attracted considerable attention.X-ray structure analyses for tungstoenzymes indicated the metal W was coordinated to the cofactor through the dithiolene sulfers and formed the active site. Polyphenols are antioxidants, which are known to influence bioavailability of metals in the body. In addition, metal-catechol complexes can exhibit interesting electronic effects associated with the variable metal and ligand charge distribution, due to the delicate balance in energy between the frontier quinine and metal orbitals and they are believed to be a model for the biological transport of iron and catechol/quinine related enzymes and biomolecules. In this thesis, a series of biomimetic complexes with catechol ligand of tungstoenzyme cofactor have been synthesized and characterized by means of spectrum, X-ray analyses. The main points are as follows:1 Three different complexes (NH₃CH₂CH₂CH₂NH₂)₂[WO₂(C₆H₄O₂)₂] (1), [(NH₃CH₂CH(NH₂)CH₃)₂[WO₂(C₆H₄O₂)₂] (2) and (NH₃CH₂CH₂NH₂)₃[W^VO₂(C₆H₄O₂)₂] (3) were synthesized by the reaction of (n-Bu₄N)₄[W₁₀O₃₂] with catechol in the mixed solvent of CH₃OH, CH₃CN, with NH₂CH₂CH₂CH₂NH₂, NH₂CH₂CHNH₂CH₃, and NH₂CH₂CH₂NH₂ added.(a) Structural characterization by x-ray diffraction. The crystal structure results show that the mononuclear anionic unit of the three complexes displayed the same cis-dioxo fashion with pseudo-octahedral [WO₆] coordination geometry. But the three complexes have different crystal figure, stability and anti-cancer activity. The complex 3 shows the similar EPR signal with xanthenes oxidase in milk.(b) NMR results. The NMR studies on the interaction of the complex 2 with ATP reveal that ¹H chemical shifts of 1,2-propanediamine and catechol with and without ATP exhibit distinct difference, the reduction of W(VI) to W(V) occurs when the complex 2 is dissolved in D₂O and the W(V) is oxidized again when ATP solution is mixed with original solution and the hydrolysis of the catecholato ligand take places atmean time being monitored by ¹H NMR.2 Replace (n-Bu₄N)₄[W₁₀O₃₂] with NaWO₄·2H₂O, carry out the same reaction with catechol,and (NH₃CH₂CH₂CH₂NH₃)₂{Na₂[(C₆H₄O₂)₂](C₆H₄O₂H)₂}(4),[NH₃CH₂CH(NH₂)CH₃] {WO₂(C₆H₄O₂)₂Na[NH₂CH₂CH(NH₂)CH₃]}_n(5), (NH₂CH₂CH₂NH₂)₂ {Na₂[μ₂-(C₆H₆O₂)₂](C₆H₄OOH)₂} (6) will be formed.(a) Structural characterization by x-ray diffraction. The crystal structure results show that complex ₆ consists of two NH₂CH₂CH₂NH₂ and a discrete molecular {Na₂[μ₂-(C₆H₆O₂)₂](C₆H₄OOH)₂} cluster, while in complex 5 W atoms are bridged by O-Na-O units to constitute one-dimensional (1D) infinite chain along the α-axis, and the neighboring chains are linked by van der vaals force and H-bonds.(b) The comparison of ¹³C NMR spectrum of the complex 6 in solid state with that in solution indicates that the rapid exchange between the bridging μ2-(C₆H₆O₂) and terminal (C₆H₄OOH)^- ligands is presented in solution.