Synthesis, structure and magnetism of the oxalato-bridged chromium(III) complex [NBu4n](4)[Cr-2(ox)(5)]center dot 2CHCl(3)

The binuclear complex [NBu4n](4)[Cr-2(ox)(5)]. 2CHCl(3) has been prepared by an ion-exchange procedure employing Dowex 50WX2 cation-exchange resin in the n-butylammonium form and potassium tris(oxalato)chromate(III). The dimeric complex was characterised by a crystal structure determination: monoclinic, space group C2/c, a = 29.241(7), b = 15.192(2), c = 22.026(5) Angstrom, beta = 94.07(1)degrees, Z = 4. The magnetic susceptibility (300-4.2 K) indicated that the chromium(III) sites were antiferromagnetically coupled (J = -3.1 cm(-1)).

Crystal and molecular structure of 2-hydroxy-1-naphthaldehyde isonicotinoyl hydrazone (NIH) and its iron(III) complex: an iron chelator with anti-tumour activity

Previous studies have demonstrated that 2-hydroxy-1-naphthaldehyde isonicotinoyl hydrazone (NIH) and several other aroylhydrazone chelators possess anti-neoplastic activity due to their ability to bind intracellular iron. In this study we have examined the structure and properties of NIH and its Fe-III complex in order to obtain further insight into its anti-tumour activity. Two tridentate NIH ligands deprotonate upon coordination to Fe-III in a meridional fashion to form a distorted octahedral, high-spin complex. Solution electrochemistry of [Fe(NIH-H)(2)](+) shows that the trivalent oxidation state is dominant over a wide potential range and that the Fe-II analogue is not a stable form of this complex. The fact that [Fe(NIH-H)(2)](+) cannot-cycle between the Fe-II and Fe-III states suggests that the production of toxic free- radical species, e.g. OH. or O2(.-),is not part of this ligand's cytotoxic action. This suggestion is supported by cell culture experiments demonstrating that the addition of Fe-III to NIH prevents its anti-proliferative effect. The chemistry of this chelator and its Fe-III complex are discussed in the context of understanding its anti-tumour activity.

Can metal complexes serve as hypoxia activated prodrugs? Investigations of a Co(III) complex of the MMP inhibitor marimastat

For many years proof that the hypoxic nature of malignant tumours can be used to selectively target anticancer drugs has been sought. Several classes of potential redox activated anticancer drugs have been developed to take advantage of the reducing environment resulting from the hypoxia. Drug complexes with redox active metal centres as carriers have been investigated, but have largely been employed with cytotoxic drugs that require release of the drug intracellularly, complicating the design of such complexes. MMP inhibitors, a new class of anticancer drug, conversely act in the extracellular environment and we have investigated inhibitor complexes with several redox active transition metals. Marimastat is an MMP inhibitor with potent in-vitro antimetastatic activity and was recently in Phase III clinical trials for a variety of cancer types. We have synthesised a Co(II1) complex of marimastat incorporating the tetradentate ligand tpa (tris(2-methylpyridyl)amine) as a carrier ligand. The complex was structurally characterised in the solid state by single crystal X-ray diffraction, the first example of a crystal structure containing marimastat. 2D COSY and NOESY NMR spectra showed that the complex exists in two isomeric forms in solution, corresponding to the cis and trans isomers yet only crystallises in one of these forms. Biological testing of the complex in mice with 4T1.2 tumours showed interesting and unexpected outcomes. Initial results of the tumour growth inhibition study showed that a significant inhibition of growth was exhibited by the complex over the free inhibitor and the control. However, the metastatic potential of both free marimastat and the complex were higher than the control indicating likely problems with the experimental protocol. Further experiments are needed to determine the potential of such complexes as hypoxia activated prodrugs but there appears at least to be some promise.

Study of spectroscopic properties of Europium (III) Tris(beta-diketonate) complex and alpha-Cyclodextrin in aqueous medium

The solubilization of an europium (III) beta-diketonate chelate in aqueous medium and the changes in its photophysical properties upon its inclusion into an alpha-cyclodextrin hydrophobic cavity are described. The complex [Eu(tta)(3)center dot(H(2)O)(2)] (tta = 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dione) was synthesized, characterized, and incorporated into the hydrophobic cavity by stirring in an alpha-cyclodextrin aqueous solution. The inclusion was confirmed by (1)H NMR, and the stoichiometry of association was obtained by the Job method. The maximum in the excitation spectrum of the alpha-CD inclusion compound in aqueous solution was shifted 28 nm compared with the maximum of non alpha-CD complex. The emission spectrum of the association is similar to that of the free solid complex and displays the characteristic (5)D(0) -> (7)F(0-4) Eu(3+) transitions.

Ligand-field analysis of an Er(III) complex with a heptadentate tripodal N4O3 ligand

Polarized absorption and emission spectra of trigonal single crystals of an Er(III) complex coordinated to a heptadentate tripodal ligand are reported at temperatures between 8 and 298 K. The assigned energy levels below the onset of ligand absorption (< 25 000 cm(-1)) are fitted to a parametrized electronic Hamiltonian. The C-3 site symmetry of the Er(HI) ion requires eight parameters for a full description of the ligand field within a one-electron operator description. This compound shows unusually large splittings of the multiplets, and the fitted parameters imply that this heptadentate ligand imparts the largest ligand field reported for an Er(III) complex. The ligand field was also interpreted within the angular overlap model (AOM). We derive the AOM matrix to include both sigma and anisotropic pi bonding and show that a useful description of the C-3 ligand field can be made using only five parameters. The success of the AOM description is encouraging for applications on isomorphous complexes within the lanthanide series and in describing the ligand field of low-symmetry complexes with less parameters than in the usual spherical harmonic expansion.

Preparation and immobilization of diNOsarcobalt(III) complex in zeolite y for the catalyzed production of hydrogen peroxide

A complex cation, diNOsarcobalt(III), [Co(diNOsar)]3+, (diNOsar = 1,8-dinitro-3,6,10,13,16,19-hexaazabicyclo-[6.6.6]eicosane), was synthesized and immobilized in the cavities of a Y zeolite by the reaction of precursor species in the pores of the zeolite. The encapsulated material was compared to the compound diNOsarcobalt(III) chloride, [Co(diNOsar)]Cl3. Both diNOsarcobalt(III) chloride and the zeolite-encapsulated complex, [Co(diNOsar)]3+/zeolite, were obtained in high yield and characterized by ultraviolet-visible and infrared spectroscopy. X-ray diffraction demonstrated the incorporation of the complex cation into the pores of the zeolite. The catalytic production of hydrogen peroxide from oxygenated water confirmed the successful synthesis of the complex diNOsarcobalt(III) immobilized in the zeolite.

Synthesis and crystal structure of cobalt(III) complex with a Schiff base and azide

The cobalt(III) complex, [Co(L)2(N3)2]2(ClO4)2, L being a Schiff base N-[phenyl(pyridin-2-yl)methylene]aniline has been synthesized and the crystal structure determined using X-ray crystallography. The complex crystallizes in triclinic system, space group P-1 with unit cell parameters a=10.9367(9) , b=18.0817(17) , c=20.1629(16) , α=111.341(2), β=91.622(2), γ=107.5030(10), V=3499.1(5) 3 and Z=2. It crystallizes with two independent molecules in the asymmetric unit. The two cobalt atoms are hexa-coordinate and have a distorted octahedral geometry, satisfied by four nitrogen atoms from two molecules of the Schiff base and two nitrogen atoms from the monodentate azide group. The perchlorate ions are non-coordinating.

Dynamic behavior of Arabidopsis eif4a-iii, putative core protein of exon junction complex: fast relocation to nucleolus and splicing speckles under hypoxia

Here, we identify the Arabidopsis thaliana ortholog of the mammalian DEAD box helicase, eIF4A-III, the putative anchor protein of exon junction complex (EJC) on mRNA. Arabidopsis eIF4A-III interacts with an ortholog of the core EJC component, ALY/Ref, and colocalizes with other EJC components, such as Mago, Y14, and RNPS1, suggesting a similar function in EJC assembly to animal eIF4A-III. A green fluorescent protein (GFP)-eIF4A-III fusion protein showed localization to several subnuclear domains: to the nucleoplasm during normal growth and to the nucleolus and splicing speckles in response to hypoxia. Treatment with the respiratory inhibitor sodium azide produced an identical response to the hypoxia stress. Treatment with the proteasome inhibitor MG132 led to accumulation of GFP-eIF4A-III mainly in the nucleolus, suggesting that transition of eIF4A-III between subnuclear domains and/or accumulation in nuclear speckles is controlled by proteolysis-labile factors. As revealed by fluorescence recovery after photobleaching analysis, the nucleoplasmic fraction was highly mobile, while the speckles were the least mobile fractions, and the nucleolar fraction had an intermediate mobility. Sequestration of eIF4A-III into nuclear pools with different mobility is likely to reflect the transcriptional and mRNA processing state of the cell.

A deliberate synthesis of a mononuclear trans-dimethoxide complex of ruthenium(III). X-ray crystal structure, electrochemistry and electron paramagnetic resonance

Using bis(3,5-dimethylpyrazol-1-yl) methane as the bidentate N donor ligand L, the yellow compound trans-[(RuL2)-L-III(OMe)(2)]ClO4 center dot CH2Cl2 is synthesized. It is a rare example of a mononuclear dialkoxo complex of Ru(III). It shows a quasireversible Ru(II/III) couple at -0.65 V versus NHE in acetonitrile at a Pt electrode. Its magnetic moment at room temperature corresponds to one unpaired electron. It displays a rhombic EPR spectrum in acetone at 77 K with g = 2.219, 2.062 and 1.855. (C) 2009 Elsevier B. V. All rights reserved.

Synthesis, structure and properties of cobalt(II/III) seleno-bisphenolate complexes containing NN bidentate co-ligands: kinetic studies on the reduction of a cobalt(III) complex by ascorbic acid in 80% MeCN-20% water

Two cobalt complexes, [Co(L-Se)(phen)]center dot CH2Cl2 (1) and [Co(L-Se)(N,N-Me(2)en)(CH3COO-)] (2) have been synthesized and characterized by elemental analyses, magnetic measurements, i.r. studies etc. Single crystal X- ray studies reveal that in complex (1) cobalt atom is in +2 oxidation state with trigonal bipyramidal geometry, while in complex (2) it is in +3 oxidation state and surrounded octahedrally. The asymmetric unit of complex (2) contains two crystallographically independent discrete molecules. Complex (1) was found to be paramagnetic with mu(eff) = 2.19 BM indicating a low spin cobalt(II) d(7) system, whereas complex (2) is found to be diamagnetic with cobalt(III) in low spin d(6) state. The kinetic studies on the reduction of (2) by ascorbic acid in 80% MeCN-20% H2O (v/v) at 25 degrees C reveal that the reaction proceeds through the rapid formation of inner-sphere adduct, probably by replacing the loosely coordinated AcO- group, followed by electron transfer in a slow step and is supported by a large Q (formation constant) value.

Light-assisted synthesis of a Ru(VI) nitrido complex by the reaction of azide with a Ru(III) complex

Reaction of Ru(III)(L)(dmf)Cl-3 (1) (L = 4,4,4',4'-tetramethyl-2,2'- bisoxazoline, dmf = N,N-dimethylformamide) with an excess of sodium azide in a methanol-water mixture leads to the isolation of the sodium salt of a Ru( VI) nitrido complex of the tetraanion of N,N'-bis-(2,2-dimethyl-1-hydroxyethyl)-1,2-ethanediamide ( L'H-4; H a dissociable proton) of the formulation Na[Ru(L')(N)(H2O)].1.4H(2)O (2). Complex 2 is not generated in the absence of light. A tentative mechanism for the reaction is proposed and a Ru(IV) intermediate, Na[Ru(L')(N-3)(H2O)] . 2CH(3)OH.2H(2)O (3), isolated.

Supramolecular assemblies of metal ions in complex bimetallic and trimetallic salts based on hexacyanoferrate(III) ion

Two complex heterometallic salts with formulae Tl-6[Fe(CN)(6)](1) (33)(NO3)(OH) (1) and [Co(bpy)(2)(CN)(2)](2){[Ag(CN)(2)](0) (5)[Fe(CN)(6)](0) (5)} 8H(2)O (2) have been synthesized and fully characterized Single crystal X-ray analyses reveal that compound 1 is comprised of discrete Tl+ cations and [Fe(CN)(6)](3-) anions together with OH- and NO3- anions Compound 2 contains [Co(bpy)(2)(CN)(2)](+) cations and {[Ag(CN)(2)][Fe(CN)(6)]}(-) anions together with eight molecules of water of crystallization Both structures form unprecedented three-dimensional supramolecular networks via non covalent interactions Another important observation is that the stereochemically active inert (lone) pair present on Tl+ plays little role in controlling the structure of 1 The water molecules in 2 play important roles in providing stability organizing a supramolecular network through hydrogen bonding In the syntheses of 1 and 2 Fe(II) is oxidized to Fe(III) and Co(II) to Co(III) respectively facilitating the formation of the salts that are obtained Both compounds exhibit photoluminescence emission in solution near the visible region.

[Pr(NO3)3L]: a mononuclear ten-coordinate lanthanide(III) complex with a tetradentate di-Schiff base

The novel praseodymium(III) complex [Pr(NO3)3L] (1), where L=N,N′-bis[1-(pyridin-2-yl)ethylidene]ethane-1,2-diamine, has been obtained by direct reaction of the Schiff base and the metal salt; the gadolinium(III) homologue has also been prepared and so far characterized only spectroscopically. The crystal structure resembles those reported for hexadentate macrocyclic Schiff bases.

Synthesis and spectroscopic properties of cobalt(III) complexes of some aroyl hydrazones: x-ray crystal structures of one cobalt(III) complex and two aroyl hydrazone ligands

Cobalt(III) complexes of diacetyl monooxime benzoyl hydrazone (dmoBH(2)) and diacetyl monooxime isonicotinoyl hydrazone (dmoInH(2)) have been synthesized and characterized by elemental analyses and spectroscopic methods. The X-ray crystal structures of the two hydrazone ligands, as well as that of the cobalt(III) complex [Co(III)(dmoInH)(2)]Cl center dot 2H(2)O, are also reported. It is found that in the cobalt(III) complexes the Co(III) ion is hexa-coordinated, the hydrazone ligands behaving as mono-anionic tridentate O,N,N donors. In the [Co(III)(dmoInH) (2)]Cl center dot 2H(2)O complex, the amide and the oxime hydrogens are deprotonated for both the ligands, while the isonicotine nitrogens are protonated. In the [Co(III)(d-moBH)(2)] Cl complex, only the amide nitrogens are deprotonated. It is shown that the additional hydrogen bonding capability of the isonicotine nitrogen results in different conformation and supramolecular structure for dmoInH(2), compared to dmoBH(2), in the solid state. Comparing the structure of the [CoIII(dmoInH)(2)]Cl center dot 2H(2)O with that of the Zn(II) complex of the same ligand, reported earlier, it is seen that the metal ion has a profound influence on the supramolecular structure, due to change in geometrical dispositions of the chelate rings.

Structure and magnetic properties of an unprecedented syn-antiμ-nitrito-1κO:2κO′ bridged Mn(iii)-salen complex and its isoelectronic and isostructural formate analogue

The preparation, crystal structures and magnetic properties of two new isoelectronic and isomorphous formate-and nitrite-bridged 1D chains of Mn(III)-salen complexes, [Mn(salen)(HCOO)](n) (1) and [Mn(salen)(NO2)](n) (2), where salen is the dianion of N,N'-bis(salicylidene)-1,2-diaminoethane, are presented. The structures show that the salen ligand coordinates to the four equatorial sites of the metal ion and the formate or nitrite ions coordinate to the axial positions to bridge the Mn(III)-salen units through a syn-anti mu-1 kappa O:2 kappa O' coordination mode. Such a bridging mode is unprecedented in Mn(III) for formate and in any transition metal ion for nitrite. Variable-temperature magnetic susceptibility measurements of complexes 1 and 2 indicate the presence of ferromagnetic exchange interactions with J values of 0.0607 cm(-1) (for 1) and 0.0883 cm(-1) (for 2). The ac measurements indicate negligible frequency dependence for 1 whereas compound 2 exhibits a decrease of chi(ac)' and a concomitant increase of chi(ac)'' on elevating frequency around 2 K. This finding is an indication of slow magnetization reversal characteristic of single-chain magnets or spin-glasses. The mu-nitrito-1 kappa O:2 kappa O' bridge seems to be a potentially superior magnetic coupler to the formate bridge for the construction of single-molecule/-chain magnets as its coupling constant is greater and the chi(ac)' and chi(ac)'' show frequency dependence.