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Polynuclear copper complexes with two or three Cu(BPA) (BPA, bis(2-pyridylmethyl)amine) motifs, [Cu2(mTPXA)Cl4]3 H2O (1), [Cu2(pTPXA)Cl4]3 H2O (2), [Cu3(HPTAB)Cl5]Cl3 H2O (3) (mTPXA = N,N,N',N'-tetra-(2-pyridylmethyl)-m-xylylene diamine; pTPXA = N,N, N',N'-tetra-(2-pyridylmethyl)-p-xylylenediamine; HPTAB = N,N,N',N',N'',N''-hexakis(2-pyridylmethyl)-1,3,5-tris-(aminomethyl)benzene) have been synthesized and characterized. The crystal structures of compounds 2 and 3 showed each Cu(BPA) motif had a 4+1 square-pyramidal coordination environment with one chloride occupying the apical position and three N atoms from the same BPA moiety together with another Cl atom forming the basal plane. Fluorescence and circular dichroism (CD) spectroscopy studies indicated that the DNA binding followed an order of 3>2>1 in the compounds. These complexes cleave plasmid pUC19 DNA by using an oxidative mechanism with mercaptopropionic acid (MPA) as the reductant under aerobic conditions. Dinuclear Cu2+ complexes 1 and 2 showed much higher cleavage efficiency than their mononuclear analogue [Cu(bpa)Cl2] at the same [Cu2+] concentration, suggesting a synergistic effect of the Cu2+ centers. Moreover, the meta-dicopper centers in complex 1 facilitated the formation of linear DNA. Interestingly, the additional copper center to the meta-dicopper motif in complex 3 decreased the cleavage efficacy of meta-dicopper motif in complex 1, although it is able to cleave DNA to the linear form at higher [Cu2+] concentrations. Therefore, the higher DNA binding ability of complex 3 did not lead to higher cleavage efficiency. These findings have been correlated to the DNA binding mode and the ability of the Cu2+ complexes to activate oxygen (O2). This work is a good example of the rational design of multinuclear Cu2+ artificial nuclease and the activity of which can be manipulated by the geometry and the number of metal centers.

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A highly water soluble 3:2 complex of copper(II) and 2,4,6-tris(di-2-pyridylamine)-1,3,5-triazine (TDAT) has been synthesized and structurally characterized. The complex crystallized in a triclinic P1 space group with a molecular formula of [Cu3(TDAT)2Cl3]Cl3.2H2O (1), where each copper ion is coordinated by four pyridine nitrogen atoms and an apical chloride. The trinuclear complex is stable at physiological relevant conditions. It can bind to DNA through electrostatic attraction and cleave efficiently the supercoiled pBR322 DNA into its nicked and linear forms at micromolar concentrations. Active oxygen intermediates such as hydroxyl radicals and singlet oxygen generated in the presence of 1 may act as active species for the DNA scission.

A phosphodiesterase model with two zinc centers has been synthesized and characterized. The compound, [Zn(2)(L(-)(2H))(AcO)(H(2)O)](PF(6)).2H(2)O (Zn(2)L'), was formed using an "end-off" type compartmental ligand, 2,6-bis{[(2-pyridylmethyl)(2-hydroxyethyl)amino]methyl}-4-methylphenol (L), and zinc acetate dihydrate. The X-ray crystallographic analysis shows that Zn(2)L' contains a mu-acetato-mu-cresolato-dizinc(II) core comprised of a quasi-trigonal bipyramidal Zn and a distorted octahedral Zn, and the distance between them is 3.421 Angstroms which is close to the dizinc distance in related natural metalloenzymes. Phosphodiesterase activity of Zn(2)L' was investigated using bis(4-nitrophenyl) phosphate (BNPP) as the substrate. The pH dependence of the BNPP cleavage in aqueous buffer media shows a sigmoid-shaped pH-k(obs) profile with an inflection point around pH 7.13 which is close to the first pK(a) value of 7.20 for Zn(2)L' obtained from the potentiometric titration. The catalytic rate constant (k(cat)) is 4.60 x 10(-6) s(-1) at pH 7.20 and 50 degrees C which is ca. 10(5)-fold higher than that of the uncatalyzed reaction. The deprotonated alcoholic group appended on Zn(2)L' is responsible for the cleavage reaction. The possible mechanism for the BNPP cleavage promoted by Zn(2)L' is proposed on the basis of kinetic and spectral analysis. The dizinc complex formed in situ in anhydrous DMSO exhibits a similar ability to cleave BNPP. This study provides a less common example for the phosphodiesterase model in which the metal-bound alkoxide is the nucleophile.

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