Non-heme iron(II/III) complexes that model the reactivity of lipoxygenase with a redox switch.

Three ferrous/ferric complexes of a N6 hexadentate ligand, N,N,N',N'-tetrakis(2-benzimidazolyl-methyl)ortho-diamine-trans-cyclohexane (ctb), [Fe(II)(ctb)](ClO(4))(2).EtOH (), [Fe(III)(OEt)(Hctb)](ClO(4))(3).EtOH (), and [Fe(III)(OMe)(Hctb)](ClO(4))(3).3MeOH.4.5H(2)O (), were synthesized and characterized as models of lipoxygenase. The lipoxygenase activities of the complexes were checked and the results indicate that ferrous complex is inactive while ferric alkoxide complexes and show catalytic activity via the hydrogen atom abstraction reaction mechanism.

Recognition of secondary structures in proteins by a diiron(III) complex via a hydrolytic pathway.

The diiron(III) complex Fe(2)(DTPB)(mu(2)-O)(mu(2)-OAc)Cl(BF(4))(2) [DTPB = 1,1,4,7,7-pentakis(2'-benzimidazol-2-yl-methyl)triazaheptane, OAc = acetate] exhibits a similar affinity for proteins belonging to different structural patterns. However, this diiron complex is sensitive to secondary structures in a protein when it is used to promote the protein hydrolysis, indicating that some metal complexes, such as artificial proteolytic agents, could become a new hydrolytic probe of protein structures.

Crystal structure and catecholase-like activity of a mononuclear complex [Cu(EDTB)]2+ (EDTB=N,N,N',N'-tetrakis(2'-benzimidazolyl methyl)-1,2-ethanediamine).

The crystal structure and catecholase-like activity of a mononuclear complex, Cu(EDTB)(NO3)2.C2H5OH (here EDTB stands N,N,N',N'-tetrakis(2'-benzimidazolyl methyl)-1,2-ethanediamine) has been studied in comparison with a binuclear complex Cu2(EDTB)(NO3)4.3H2O. The results show that the reactive rate constants increase with increases of reaction temperature and pH value of intermediate. Electrospray ionization mass spectrum (ESI-MS) shows that tautomerism isomers of catechol with the title complex exist in reaction solution, and catechol is oxidized to quinone, then it is further oxidized resulting in muconic acid and its derivatives via an intradiol mechanism, just like that catalyzed by a mononuclear non-heme iron-containing dioxygenase.

DNA hydrolytic cleavage by the diiron(III) complex Fe(2)(DTPB)(mu-O)(mu-Ac)Cl(BF(4))(2): comparison with other binuclear transition metal complexes.

The binuclear structure of Fe(2)(DTPB)(mu-O)(mu-Ac)Cl(BF(4))(2) (DTPB = 1,1,4,7,7-penta (2'-benzimidazol-2-ylmethyl)-triazaheptane, Ac = acetate) was characterized by UV-visible absorption and infrared spectra and NMR and ESR. The binding interaction of DNA with the diiron complex was examined spectroscopically. Supercoiled and linear DNA hydrolytic cleavage by the diiron complex is supported by the evidence from anaerobic reactions, free radical quenching, high performance liquid chromatography experiments, and enzymatic manipulation such as T4 ligase ligation, 5'-(32)P end-labeling, and footprinting analysis. The estimation of rate for the supercoiled DNA double strand cleavage shows one of the largest known rate enhancement factors, approximately 10(10) against DNA. Moreover, the DNA hydrolysis chemistry needs no coreactant such as hydrogen peroxide. The poor sequence-specific DNA cleavage indicated by the restriction analysis of the pBR322 DNA linearized by the diiron complex might be due to the diiron complex bound to DNA by a coordination of its two ferric ions to the DNA phosphate oxygens, as suggested by spectral characterizations. The hydrolysis chemistry for a variety of binuclear metal complexes including Fe(2)(DTPB)(mu-O)(mu-Ac)Cl(BF(4))(2) is compared. It is established that the dominant factors for the DNA hydrolysis activities of the binuclear metal complexes are the mu-oxo bridge, labile and anionic ligands, and open coordination site(s). Concerning the hydrolytic mechanisms, the diiron complex Fe(2)(DTPB)(mu-O)(mu-Ac)Cl(BF(4))(2) might share many points in common with the native purple acid phosphatases.