Model Complexes for Non-Redox Active Metalloenzymes(Structural and Functional Model Complexes for Non-Redox Active Metalloenzymes Involving Dinuclear Metal Centers)

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1. Carboxylate-bridged dinuclear metal centers containing non-redox active ions such as Mg^<2+>, Ca^<2+>, Mn^<2+> and Zn^<2+> arc an important bioinorganic motif occurring at the active centers of phosphate ester-processing metalloenzymes. We have systematically studied non-redox active dimetallic complexes by utilizing a biscarboxylate ligand, m-xylylendiamine bis(Kemps triacid imide) (H^2XDK). Zinc-containing homo- and heterodimetallic complexes with diphenylphosphate, [ZnM(XDK){ mu-eta^<12>-(PhO)_2O_2}{eta^1-(PhO_2PO_2}(CH_3OH)_2(H20)]( M = Zn, Co), were prepared in the reactions of [ZnM(XDK)(acac)_2(CH_3OH)_2]with (PhO)_2PO_2H_2. Analogous Mg_2, Mn_2, and Ca_2 complexes. [M_2(XDK){mueta_2-(PhO)_2PO_2){mu_1-(PhO)_2PO_2}(CH_3OH)m(H_2O)n] ( M = Mg, m = 3, n = 1 ; M = Mn, m = n = 2 ; M = Ca, m = 3, n = 1), were obtained. Complexes were characterized by X-ray crystallography, consisting of an asymmetric dimetallic center bridged by XDK and (PhO)_2P0_2, . Variable-temperature ^<3l>p{^1H} … More NMR experiments demonstrated that the terminally coordinated phosphate ester ligand dissociates from the dimetallic center in solution and exchanges with the bridging one. The phosphate ester exchange rate increases in the order Ca^<2+> > Zn^<2+> > Mg^<2+>, providing useful information for understanding phosphate ester-processing metalloenzymes. New dinuclear complexes of Co(II), Cu(I), and Cu(II) were also prepared and their biorelevant reactions were examined.2. Interactions of carbohydrates with metal ions are vital in biological systems. We have studied the synthesis, characterization, and reactivities of various transition metal complexes with sugar ligands. The mononuclear Co(II) complexes with a heptadentate N-glycoside ligand, [Co(II)((L-Rha or D-Man)_3-tren)]^<2+> showed a molecular recognition property for SO^<2-> anton through chiral inversion of the metal center. Peroxo-bridged dinuclear cobalt (III) comp1ex, [((D-Glc, or Mal)_2-tren)Co(mu-02)Co((D-Glc, or Mal)_2-tren)]X3 (X = Cl, Br), were prepared and characterized by X-ray crystallography to consist of two octahedral Co(III) ions bridged by peroxide. The dinuclear structure is further supported by some hydrogen bonds between the sugar moieties. Interestingly, almost reversible dioxygen binding through the mu-peroxo dimer was monitored by electronic absorption spectral changes upon UV irradiation ; Novel Mn(II)Mn(III)Mn(II) trinuclear complexes with mannopyranose-bridging uri'rs were prepared and characterized by X-ray crystallography. Futhermore, many attempts were made to form biomimetic dimetal centers with tacn-anchored sugar moieties. Less