Imidazolate-bridged dicopper(II) and copper(II)–zinc(II) complexes of macrocyclic ligand with methylimidazol pendants: Model study of copper(II)–zinc(II) superoxide dismutase

Two new homo- and hetero-dinuclear complexes, [Cu₂L(im)](ClO₄)₃4H₂O (1) and [CuZnL(im)](ClO₄)₃4H₂O (2) (where Im=1H-1midazole and L = 3, 6, 9, 16, 19, 22-hexaaza-6, 19-bis(1H-imidazol-4-ylmethyl)tricycle[22, 2, 2, 2^11,14]triaconta-1, 11, 13, 24, 27, 29-hexaene) were synthesized and characterized as model compounds for the active site of copper(II)–zinc(II) superoxide dismutase (Cu₂Zn₂–SOD). X-ray crystal structure analysis revealed that the metal centers in both complexes exhibit distorted trigonal-bipyramid coordination geometry and the CuCu and CuZn distances are both 6.02 Å. Magnetic and ESR spectral measurements of 1 showed antiferromagnetic exchange interactions between the imidazolate-bridged Cu(II) ions. The ESR spectrum of 2 displays typical signals of mononuclear Cu(II) complex, demonstrating the formation of heterodinuclear complex 2 rather than a mixture of homodinuclear Cu(II)/Zn(II) complexes. pH-dependent ESR and UV–visible spectral measurements manifest that the imidazolate exists as a bridging ligand from pH 6 to 11 for both complexes. The IC₅₀ values of 1.96 and 1.57 μM [per Cu(II) ion] for 1 and 2 suggest that they are good models for the Cu₂Zn₂–SOD.     

Helicobacter pylori cadA encodes an essential Cd(II)–Zn(II)–Co(II) resistance factor influencing urease activity

Inactivation of Helicobacter pylori cadA, encoding a putative transition metal ATPase, was only possible in one of four natural competent H. pylori strains, designated 69A. All tested cadA mutants showed increased growth sensitivity to Cd(II) and Zn(II). In addition, some of them showed both reduced 63Ni accumulation during growth and no or impaired urease activity, which was not due to lack of urease enzyme subunits. Gene complementation experiments with plasmid (pY178)-derived H. pylori cadA failed to correct the deficiencies, whereas resistance to Cd(II) and Zn(II) was restored. Moreover, pY178 conferred increased Co(II) resistance to both the cadA mutants and the wild-type strain 69A. Heterologous expression of H. pylori cadA in an Escherichia coli zntA mutant resulted in an elevated resistance to Cd(II) and Zn(II). Expression of cadA in E. coli SE5000 harbouring H. pylori nixA, which encodes a divalent cation importer along with the H. pylori urease gene cluster, led to about a threefold increase in urease activity compared with E. coli control cells lacking the H. pylori cadA gene. These results suggest that H. pylori CadA is an essential resistance pump with ion specificity towards Cd(II), Zn(II) and Co(II). They also point to a possible role of H. pylori CadA in high-level activity of H. pylori urease, an enzyme sensitive to a variety of metal ions.     

One-dimensional helical coordination polymers of cobalt(II) and iron(II) ions with 2,2′-bipyridyl-3,3′-dicarboxylate (BPDC)

One-dimensional (1-D) helical coordination polymers, [M^II(H₂O)₃(BPDC)]_n · nH₂O (M = Co (1), Fe (2)), have been prepared by the self-assembly of cobalt(II) and iron(II) ions, respectively, with 2,2′-bipyridyl-3,3′-dicarboxylic acid (H₂BPDC) in an aqueous solution. X-ray crystal structures of compounds 1 and 2 show that each metal ion displays a distorted octahedral coordination geometry including three water oxygen atoms, one oxygen atom of the carboxylate of a BPDC²⁻ belonging to the adjacent metal ion and two nitrogen atoms from the BPDC²⁻ acting as a chelating ligand. In 1 and 2, one carboxylate oxygen atom of coordinated BPDC²⁻ binds to the neighboring metal ion, which give rise to 1-D helical coordination polymers. The helical chains of 1 and 2 are linked by the hydrogen bonding interactions between the carboxylate oxygen atom of the BPDC²⁻ ion belonging to a chain and the water molecule of the adjacent helical chain, which lead to 2-D networks extending along the ab plane. The supramolecules 1 and 2 show isomorphous structures regardless of the metal ions.     

Synthesis and properties of trinuclear polypyridyl complexes Ru(II)-Co(II)-Ru(II) and Ru(II)-Co(III)-Ru(II): Their photoinduced interconversion

The trinuclear [{Ru^II(bpy)₂(bpy-terpy)}₂Co^II]⁶⁺ complex (1⁶⁺) in which a Co(II)-bis-terpyridine-like centre is covalently linked to two Ru(II)-tris-bipyridine-like moieties by a bridging bipyridine-terpyridine ligand has been synthesised and characterised. Its electrochemical, photophysical and photochemical properties have been investigated in CH₃CN. The cyclic voltammetry exhibits two successive reversible oxidation processes, corresponding to the Co^III/Co^II and Ru^III/Ru^II redox couples at E_1/2 = −0.06 and 0.91 V vs Ag/Ag⁺ 10 mM, respectively. The one-electron oxidized form of the complex, [{Ru^II(bpy)₂(bpy-terpy)}₂Co^III]⁷⁺ (1⁷⁺) obtained after exhaustive electrolysis carried out at 0.2 V is fully stable. 1⁶⁺ and 1⁷⁺ are only poorly luminescent, indicating that the covalent linkage of the Ru(II)-tris-bipyridine centre to the cobalt subunit leads to a strong quenching of the Ru^II excited state by an intramolecular process. Luminescence lifetime experiments carried out at different temperatures indicate that the transfer is more efficient for 1⁷⁺ compare to 1⁶⁺ due to lower activation energy. Continuous irradiation of 1⁷⁺ performed at 405 nm in the presence of P(Ph)₃ acting as sacrificial electron donor leads to its quantitative reduction into 1⁶⁺, whereas similar experiment starting from 1⁶⁺ with a sulfonium salt as sacrificial electron acceptor converts 1⁶⁺ into 1⁷⁺ with a slower rate and a maximum yield of 80%. These photoinduced electron transfers were followed by UV-Visible spectroscopy and compared with those obtained with a simple mixture of both mononuclear parent complexes i.e. [Ru^II(bpy)₃]²⁺ and [Co^II(tolyl-terpy)₂]²⁺ or [Co^III(tolyl-terpy)₂]³⁺ (tolyl-terpy = 4′-(4-methylphenyl)-2,2′:6′,2′′-terpyridine).     

Antiplasmodial activity of iron(II) and ruthenium(II) organometallic complexes against Plasmodium falciparum blood parasites

This work reports the in vitro activity against Plasmodium falciparumblood forms (W2 clone, chloroquine-resistant) of tamoxifen-based compounds and their ferrocenyl (ferrocifens) and ruthenocenyl (ruthenocifens) derivatives, as well as their cytotoxicity against HepG2 human hepatoma cells. Surprisingly with these series, results indicate that the biological activity of ruthenocifens is better than that of ferrocifens and other tamoxifen-like compounds. The synthesis of a new metal-based compound is also described. It was shown, for the first time, that ruthenocifens are good antiplasmodial prototypes. Further studies will be conducted aiming at a better understanding of their mechanism of action and at obtaining new compounds with better therapeutic profile.     

Adriamycin Complexes of Pd(II) and Pt(II)

Perturbations of the ¹H NMR spectrum of the free base of Adriamycin in DMF solution were found when MCl₂(DMF)₂ (M = Pd or Pt) was added to the Adriamycin solutions. These perturbations were greatest for the 3' proton on the sugar ring and the effect decreased as the distance from this site increased. No changes were observed in the NMR spectrum of the rest of the molecule nor was there any color change when the metal solutions were added. This is interpreted as evidence that Adriamycin binds to these metals at the 3 ' amino group in DMF solution and that there is no reaction at the chromophore. The complexes were found to be in the fast exchange regime on the NMR time scale. As well, some products were isolated from reactions of Adriamycin with MCl₂(DMF)₂ in 20% MeOH/CH₂Cl₂ and MCl₂ in DMF solution. They were characterized by their elemental analyses, as well as by ¹H NMR and infrared spectroscopies.     

Synthesis, characterization and crystal structures of Cd(II) and Zn(II) complexes with 2,2′-biimidazole

The reactions of zinc and cadmium salts with 2,2′-biimidazole (H₂biim) yielded a series of compounds in which the ligand is coordinated in the chelating bidentate mode. ZnCl₂ and [Ag(H₂biim)](NO₃) in methanol in a 2:1 proportion produced Zn(H₂biim)Cl₂, in which the metal has a distorted tetrahedral coordination. A 1:2 ratio led to [Zn(H₂biim)₂(CH₃OH)₂](NO₃)₂, containing an octahedrally coordinated Zn(II) center with the O-bonded methanol ligands occupying trans positions. The corresponding [Cd(H₂biim)₂(CH₃OH)₂](NO₃)₂ compound was obtained from CdCl₂. By starting with Cd(NO₃)₂ and Cd(ClO₄)₂ in aqueous media, the related octahedral bis-chelate compounds [Cd(H₂biim)₂(NO₃)(H₂O)](NO₃) and Cd(H₂biim)₂(ClO₄)₂, respectively, were isolated, the apical positions being filled by perchlorate oxygens in the latter case. With Cd(BF₄)₂, the glass container participated in the reaction and a tris-chelate complex [Cd(H₂biim)₃]₂(SiF₆)(BF₄)₂ · 6EtOH was isolated. The [Cd(H₂biim)₃]²⁺ and ions define an extended hydrogen-bonded network, in which ions surrounded by disordered ethanol molecules occupy large cavities. The two free N-H groups provide H₂biim with a unique ability to form hydrogen bonds and their interactions with counter anions or other acceptors play a determining role in controlling molecular packing. The IR spectra of all compounds are discussed.     

Ratiometric and selective fluorescent chemodosimeter for Cu(II) by Cu(II)‐induced oxidation

A new rhodamine derivative, rhodamine B 4‐N,N‐dimethylaminobenzaldehyde hydrazone (1), was designed for ratiometric sensing of Cu(II) selectively. A red‐shift from 515 to 585 nm was observed in the fluorescence spectrum when Cu(II) was added to 1 in acetonitrile. Other metal ions of interest showed no ratiometric response. The interaction between Cu(II) and 1 was found to be the Cu(II)‐induced oxidation of 1. Copyright © 2008 John Wiley & Sons, Ltd.     

Squarate complexes of diamine palladium(II) and platinum(II)

Reactions of cis-diaminediaqua palladium and platinum dinitrates and of trans-diaminediaqua platinum dinitrate give complexes of the type Pd(tmeda)(OH)(C₄O₄)Pd(tmeda)(C₄O₄H) (tmeda = tetramethylethylenediamine) (1), (en)M(C₄O₄)₂M(en) (en = ethylenediamine (M = Pd, Pt) and trans-[Pt- (NH₃)₂C₄O₄]_n, respectively. The structures of these compounds are discussed on the basis of their spectroscopic data.     

New dinuclear copper(II) and zinc(II) complexes for the investigation of sugar–metal ion interactions

We have studied the binding interactions of biologically important carbohydrates (d-glucose, d-xylose and d-mannose) with the newly synthesized five-coordinate dinuclear copper(II) complex, [Cu₂(hpnbpda)(μ-OAc)] (1) and zinc(II) complex, [Zn₂(hpnbpda)(μ-OAc)] (2) [H₃hpnbpda = N,N′-bis(2-pyridylmethyl)-2-hydroxy-1,3-propanediamine-N,N′-diacetic acid] in aqueous alkaline solution. The complexes 1 and 2 are fully characterized both in solid and solution using different analytical techniques. A geometrical optimization was made of the ligand H₃hpnbpda and the complexes 1 and 2 by molecular mechanics (MM+) method in order to establish the stable conformations. All carbohydrates bind to the metal complexes in a 1:1 molar ratio. The binding events have been investigated by a combined approach of FTIR, UV–vis and ¹³C NMR spectroscopic techniques. UV–vis spectra indicate a significant blue shift of the absorption maximum of complex 1 during carbohydrate coordination highlighting the sugar binding ability of complex 1. The apparent binding constants of the substrate-bound copper(II) complexes have been determined from the UV–vis titration experiments. The binding ability and mode of binding of these sugar substrates with complex 2 are indicated by their characteristic coordination induced shift (CIS) values in ¹³C NMR spectra for carbon atoms C1, C2, and C3 of sugar substrates.     

真菌吸附铅锌的研究

正随着采矿业的迅速发展,越来越多的重金属通过多种途径进入土壤环境中,对生态环境造成了不可估量的破坏并严重威胁人类健康。铅锌在工业上具有非常重要的作用且其应用极为广泛,而他们具有的难去除、难迁移和生物累积等特性使得铅锌在环境中的污染尤为突出。通过微生物的生长代谢,有效降低土壤重金属毒性,是促进植物生长的重要步骤之一。同时也要求微生物自身具有抵抗重金属的功能,根际微生     

Nickel(II) and copper(II) complexes of mixed benzene-triazolehemiporphyrazines

The kinetics of substitution reactions of [η-CpFe(CO)₃]PF₆ with PPh₃ in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH)₄, 4-Ph, 3-Me, 2,3-(CH)₄, 2,6-Me₂, 2-Me), the reactions yeild the same product [η⁵-CpFe(CO)₂PPh₃]PF₆, according to a second-order rate law that is first order in concentrations of [η⁵-CpFe(CO)₃]PF₆ and of R-PyO but zero order in PPh₃ concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH^≠ = 13.4 ± 0.4 kcal mol⁻¹, ΔS^≠ = −19.1 ± 1.3 cal k⁻¹ mol⁻¹ for 4-PhPyO; ΔH^≠ = 12.3 ± 0.3 kcal mol⁻¹, ΔS^≠ = 24.7 ±1.0 cal K⁻¹ mol⁻¹ for 2-MePyO. For the various substituted pyridine N-oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N-oxide basicities, but decrease with increasing ¹⁷O chemical shifts of the N-oxides. Electronic and steric factors contributing to the reactivity of pyridine N-oxides have been quantitatively assessed.     

Photochemical reactions of bis(bistrimethylsilylamido)tin(II) with; Hexacarbonylmolybdenum and tungsten

Irradiation of M(CO)₆ (M = Mo. W) and Sn[N(SiMe₃)₂]₂ in hexane with UV light results in carbonyl substitution to form both M(CO)₅Sn[N(SiMe₃)₂]₂ and M(CO)₄Sn[N(SiMe₃)₂]₂)₂ complexes. The M(CO)₄L₂ species present the first examples in which both cis and trans isomers have been observed upon substitution of bulky divalent main group IV ligands. The highly air-sensitive W(CO)₅L and W(CO)₄L₂ complexes have been isolated.     

Studies on nitrosyl hemes in Ni(II)–Fe(II) hybrid hemoglobins

Subunit heterogeneity within a particular subunit in hemoglobin A have been explored with electron paramagnetic resonance spectroscopy using the nitrosyl hemes in Ni-Fe hybrid Hb under various solution conditions. Our previous studies on the crystal structure of NiHb demonstrated the presence of subunit heterogeneity within alpha-subunit. To further cross check this hypothesis, we made a hybrid Hb in which either the alpha- or beta-subunit contains iron, which alone can bind to NO. By this way dynamic exchange between penta- and hexa-coordinated forms within a subunit was confirmed. Upon the addition of inositol hexa phosphate (IHP) to these hybrids, R to T state transition is observed for [alpha(2)(Fe-NO)beta(2)(Ni)] but such a direct transformation is less marked in [alpha(2)(Ni)beta(2)(Fe-NO)]. Hence the bond between N(epsilon) and Fe is fundamental to the structure-function relation in Hb, as the motion of this nitrogen triggers the vast transformation, which occurs in the whole molecule on attachment of NO.     

The interaction of methylcobalamin with tetracyanoplatinate(II), tetrathiocyanoplatinate(II) and tetrachloroplatinate(II)

The interactions of methylcobalamin (CH₃-B₁₂) with Pt(CN)₄^2?, PtCl₄^2?, and Pt(SCN)₄^2? in aqueous solution were studied by UV-visible and ¹H NMR spectroscopy. Together with earlier results on the mechanism of the Pt(IV)-dependent methyl-transfer reaction from CH₃-B₁₂ to Pt(II), these studies suggest at least three Pt binding sites on CH₃-B₁₂. One site, which is occupied by all three complexes (K₁ = 4 X 10³ M^?1 for Pt(CN)₄^2? and 3 X 10³ M^?1 for PtCl₄^2?), is located on the CoCH₃ side of the corrin macrocycle, and is involved in the methyl-transfer process in the presence of a Pt(IV) complex. An additional site for Pt(SCN)₄^2? is the N-3 of the benzimidazole group, resulting in dissociation of this group from the cobalt. An additional site for Pt(CN)₄^2? has a binding constant of 16 M^1? and ¹H NMR changes indicate perturbation but not dissociation of the benzimidazole group. Only the first interaction is discerned for PtCl₄^2?.     

Complexes of chromium(II) and iron(II) with hexamethylphosphoramide

The chromium(II) complexes CrX₂(HMPA)₂, in which X = Cl or Br and HMPA is hexamethylphosphoramide, and Cr(HMPA)₄(BF₄)₂ have been prepared. The effective magnetic moments show little deviation from the value expected for high spin chromium(II) from room temperature to liquid nitrogen temperature. The diffuse reflectance spectra suggest that the chromium ions are in a strongly distorted six coordinate environment. The iron(II) complexes, FeX₂(HMPA)₂, X = Br or I, and [Fe(HMPA)_4](BF₄)₂, from their magnetic behaviour and Mössbauer and electronic spectra, contain tetrahedral iron(II). The isomer shift of the last complex is the most positive so far reported for a tetrahedral iron(II) complex.     

Triphenylbismuth seven-coordinate complexes of molybdenum(II) and tungsten(II)

The seven-coordinate complexes [MI₂(CO)₃(NCMe)₂] (M = Mo and W) react with one equivalent of BiPh₃ in CH₂Cl₂ at room temperature to give the monoacetonitrile complexes [MI₂(CO)₃(NCMe)(BiPh₃)]. The molybdenum complex [MoI₂(CO)₃(NCMe)(BiPh₃)] after stirring in CH₂Cl₂ at room temperature for 5 h affords the iodide-bridged dimer [Mo(μ-I)I(CO)₃(BiPh₃)]₂, whereas the tungsten complex [WI₂(CO)₃(NCMe)(BiPh₃)] does not appear to dimerise even after stirring for 48 h in CH₂Cl₂ at room temperature. Reaction of [MI₂(CO)₃(NCMe)₂] with two equivalents of BiPh₃ gives the bistriphenylbismuth compounds [MI₂(CO)₃(BiPh₃)₂] in good yield. The new mixed ligand complexes [MI₂(CO)₃L(BiPh₃)] were prepared either by reaction of [MI₂(CO)₃(NCMe)(BiPh₃)]in situ with one equivalent of L(L = P(OPh)₃), or an in situ reaction of [MI₂(CO)₃(NCMe)L] (L = PPh₃ and SbPh₃; and L = AsPh₃ and PPh₂Cy (for M = Mo only) with an equimolar quantity of BiPh₃. Reaction of [MoI₂(CO)₃(NCMe)(BiPh₃)] with one equivalent of 2,2′-bipyridyl (bipy) in CH₂Cl₂ at room temperature afforded the cationic complexes [MoI(CO)₃(bipy)(BiPh₃)]I in good yield. The complex [WI₂(CO)₃(NCMe)(BiPh₃)] (prepared in situ) reacts with two equivalents of NaS₂CNMe₂·2H₂O to eventually give the non-triphenylbismuth containing product [W(CO)₃(S₂CNMe₂)₂] in high yield.