Synthesis, X-ray structure and properties of (eta(6)-p-cymene)ruthenium(II) Schiff-base complexes of vinylpyridine and vinylimidazole ligands

Complexes of the formulation [(eta(6)-p-cymene)Ru(O-2-C6H4-CH=NC6H4-4-CH3)(L)](ClO4), where L is gamma-picoline, 4-vinylpyridine, 1-methylimidazole and 1-vinylimidazole have been prepared and characterised. The molecular structure of the vinylpyridine adduct has been determined by X-ray crystallography. The crystal belongs to the monoclinic space group P2(1) with the following cell dimensions for the C31H33CIN2O5Ru(M = 650.11): a = 10.890(2)Angstrom, b = 22.295(9)Angstrom, c = 12.930(2)Angstrom, beta = 109.30(2)degrees(3), V = 2964(l)Angstrom 3, Z = 4; D-c = 1.457g cm(-3), lambda(Mo-K alpha) = 0.7107 Angstrom; mu(Mo-K alpha)= 6.61 cm(-1); T = 293 K; R = 0.0359 (wR(2) = 0.0981) for 4819 reflections with I > 2 sigma(I). The structure shows the non-bonding nature of the double bond of the 4-vinylpyridine ligand in the complex in which the metal is bonded to the eta(6)-p-cymene, the N, O-bidentate chelating schiff-base and the unidentate N-donor pyridine ligands.

Synthesis and characterization of novel charge transfer complexes formed by N,N%-bis(ferrocenylmethylidene)-p-phenylenediamine and N-(ferrocenylmethylidene)aniline

N,N'-Bis(ferrocenylmethylidene)-p-phenylenediamine 1 and N-(ferrocenylmethylidene) aniline 2 are readily synthesized by Schiff base condensation of appropriate units. Iodine (I-2), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetrachloro-1,4-benzoquinone (CA), tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) form charge transfer complexes with 1 and 2. IR spectroscopy suggests an increase in the amount of charge transferred from the ferrocenyl ring to the oxidant in the order, I-2 < CA < TCNQ < TCNE approximate to DDQ. EPR spectra of the oxidized binuclear complexes are indicative of localized species containing iron- and carbon-centered radicals. The Mossbauer spectrum of the iodine oxidized complex of 1 reveals the presence of both Fe(III) and Fe(II) centers. Variable temperature magnetic and Mossbauer studies show that the ratio of Fe(III)/Fe(II) centers varies as a function of temperature. The larger Fe(II)/Fe(III) ratio at lower temperatures is best explained by a retro charge transfer from the iodide to the iron(III) metal center. There is negligible solvent effect on the formation of the iodine oxidized charge transfer complex of 1. (C) 1999 Elsevier Science S.A. All rights reserved.

Molecular self-assembly of cadmium-triazolate complexes via hydrogen bonding: Synthesis, structures and photoluminescent properties

Two new cadmium coordination polymers namely Cd(HAmTrz-COO)(4)(NH4+)(2)] 1; and Cd(HAmTrz)(2)I-2](n) 2; (HAmTrz-COOH = 3-amino-1,2,4-triazole-5-carboxylic acid), have been prepared based on HAmTrz-COOH as ligand. The crystal structures of 1 and 2 have been determined by single-crystal X-ray diffraction technique. In coordination-complex 1 four triazole ligands coordinate via N1 nitrogen leading to a tetrahedral geometry around cadmium ion, while in 2 the ligand prefers to coordinate to the metal in a bidentate bridging mode. The structures of both the coordination polymers can be envisaged as 3D hydrogen bonded networks. Thermogravimetric analysis shows that 2 is more stable than 1 owing to different coordination numbers of cadmium atoms. Photoluminescence properties of both the compounds have been investigated in the solid state. (C) 2011 Elsevier B.V. All rights reserved.

Dendritic encapsulation of amino acid-metal complexes. Synthesis and studies of dendron-functionalized L-tyrosine-metal (Zn-II, Co-II) complexes

This paper describes the synthesis, characterization and studies of dendrimers possessing an amino acid-metal complex as the core. Using Frechet-type polyaryl ether dendrons, L-tyrosine-metal (Zn-II and Co-II) complex cored dendrimers of 0-4 generations were synthesized. The metal complexation of the tyrosine unit at the focal point of these dendrons took place smoothly, in excellent yields, even though the sizes of the dendrons increase as the generations advance. Spectrophotometric titrations with CoII metal ion confirmed the formation of a 2 : 1 dendritic ligand to metal complex and the existence of a pseudotetrahedral geometry at the metal centre is also inferred. Cyclic voltammetric studies of dendrimer-Co-II complexes showed that while the electron transfer of Co-II to Co-I was facile for generations 0-2, such a process was difficult with generations 3 and 4, indicating a rigid encapsulation of the metal ion centre by proximal dendron groups. Further reduction of Co-I to Co-0 and the corresponding oxidation processes appear to be limited by adsorption at the surfaces of the electrodes.

Self-assembled molecular films of tetraamino metal (Co, Cu, Fe) phthalocyanines on gold and silver. Electrochemical and spectroscopic characterization

The formation of molecular films of 2,9,16,23-tetraamino metal phthalocyanines [TAM(II)Pc; M (II) = Co, Cu, and TAM(III)Pc; M = Fe] by spontaneous adsorption on gold and silver surfaces is described. The properties of these films have been investigated by cyclic voltammetry, impedance, and FT-Raman spectroscopy. The charge associated with Co(II) and Co(I) redox couple in voltammetric data leads to a coverage of (0.35+/-0.05) x 10(-10) mol cm(-2), suggesting that the tetraamino cobalt phthalocyanine is adsorbed as a monolayer with an almost complete coverage. The blocking behavior of the films toward oxygen and Fe(CN)(6)(3-/4-) redox couple have been followed by cyclic voltammetry and impedance measurements. This leads to an estimate of the coverage of about 85 % in the case of copper and the iron analogs. FT-Raman studies show characteristic bands around 236 cm(-1) revealing the interaction between the metal substrate and the nitrogen of the -NH2 group on the phthalocyanine molecules.

Solid state structural and solution studies on the formation of a flexible cavity for anions by copper(I) and 1,2-bis(diphenylphosphino)ethane

Copper(l) complexes of 1,2-bis(diphenylphosphino)ethane (dppe) with a stoichiometry Cu-2(dppe)(3)(X)(2) [X- = CN- (1), SCN- (2), NO3- (3)] are obtained from direct reactions of CuX and dppe. The complexes are structurally and spectroscopically (NMR and IR) characterized. The structure of the [Cu-2(dPPe)(3)](2+) dication is similar to the structural motif observed in many other complexes with a chelating dppe and a bridging dppe connecting two copper centers. In complexes 1 -3, the anions are confined to the cavity formed by the phosphines which force a monodentate coordination mode despite the predominant bidentate/bridging character of the anions. The coordination angles rather than the thermochemical radii dictate the steric requirement of anions. While the solution behavior of 3, with nitrate, is similar to complexes studied earlier, complexes with pseudohalides exhibit new solution behavior. (C) 2002 Elsevier Science Ltd. All rights reserved.

Tailoring of Structural Morphology of Silver Nanowires in Electrochemical Growth

Noble metal such as Ag normally exists in an fcc crystal structure. However as the size of the material is decreased to nanometer lengthscales, a structural transformation from that of its bulk state can be expected with new atomic arrangements due to competition between internal packing and minimization of surface energy. In many previous studies, it has been shown that silver nanowires (AGNWs) grown inside anodic alumina (AAO) templates by ac or dc electrochemical deposition from silver salts or complexes, adopt fcc structure and below some critical diameter ∼ 20 nm they may acquire hcp structure at low temperature. This is, however, critically dependant on the nature of confinement, as AgNWs grown inside nanotube confinement with subnanometer diameter have been reported to have fcc structure. Hence the question of the crystal structure of metal nanowires under combined influence of confinement, temperature and deposition condition remains open. In this abstract we show that the alternative crystal structures of AGNWs at room temperature can be achieved with electrochemical growth processes under specific conditions determined by the deposition parameters and nature of confinement. We fabricated AgNWs of 4H hexagonal structure with diameters 30 – 80 nm inside polycarbonate (PC) templates with a modified dc electrodeposition technique, where the nanowires were grown at deposition potentials as low as 10 mV in 2 M silver nitrate solution[1]. We call this low-potential electrodeposition (LPED) since the electrodeposition process occurs at potential much less than the standard Nernst potential (770 mV) of silver. Two types of electrodes were used – stainless steel and sputtered thin Pt film, neither of which had any influence on the crystal structure of the nanowires. EDS elemental analysis showed the nanowires to consist only of silver. Although the precise atomic dynamics during the LPED process is unclear at present, we investigated this with HRTEM (high-resolution transmission electron microscopy) characterization of nanowires grown over various deposition times, as well as electrical conductivity measurements. These experiments indicate that nanowire growth does not occur through a three-dimensional diffusion controlled process, as proposed for conventional over-potential deposition, but follow a novel instantaneous linear growth mechanism. Further experiments showed that, (a) conventional electrochemical growth at a small over-potential in a 2 mM AgNO3 solution yields nanowires with expected fcc structure inside the same PC templates, and (2) no nanowire was observed under the LPED conditions inside hard AAO templates, indicating that LPED-growth process, and hcp structure of the corresponding nanowires depend on deposition parameters, as well as nature of confinement.

Ternary copper(II) complexes of thiosemicarbazones and heterocyclic bases showing N3OS coordination as models for the type-2 centers of copper monooxygenases

Six ternary copper(II) complexes of general formulation [CuLB] (1-6), where L is dianionic ONS-donor thiosemicarbazones derived from the condensation of salicylaldehyde with thiosemicarbazides and B is NN-donor heterocyclic bases like 2,2'-bipyridine, 1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline, are prepared from a reaction of copper(II) acetate hydrate with the heterocyclic base (B) and the thiosemicarbazone (H2L) in MeOH, and structurally characterized by X-ray diffraction technique. Crystal structures of the complexes display a distorted square-pyramidal (4 + 1) coordination geometry having the ONS-donor thiosemicarbazone bonded at the basal plane. The chelating heterocyclic bases exhibit axial-equatorial mode of bonding. The complexes are one-electron paramagnetic and they show axial X-band EPR spectra in DMF-toluene glass at 77 K giving g(parallel to)(A(parallel to)) and g(perpendicular to) values of similar to2.2 (175 x 10(-4) cm(-1)) and similar to2.0 indicating a {d(x2-y2)}(1) ground state. The complexes show a d-d band near 570 nm and a charge transfer band near 400 nm in DMF. The complexes are redox active and exhibit a quasireversible Cu(II)-Cu(I) couple in DMF-0.1 M tetrabutylammonium perchlorate near 0.1 V vs. SCE. They are catalytically active in the oxidation of ascorbic acid in presence of dioxygen. The complexes with a CuN3OS coordination model the ascorbate oxidation property of dopamine beta-hydroxylase and peptidylglycine a-hydroxylating monooxygeanase. (C) 2003 Elsevier Science B.V. All rights reserved.

Trans -> Cis isomerization of trans-[(dPPM)(2)Ru(H)(L)][BF4] (L = P(OR)(3)) Complexes: Preparation of cis-[(dppm)(2)Ru(eta(2)-H-2)(L)][BF4](2)

A series of new dicationic dihydrogen complexes of ruthenium of the type cis-[(dppm)(2)Ru(eta(2)-H-2)(L)][BF4](2) (dppm = Ph2PCH2PPh2; L = P(OMe)(3), P(OEt)(3), PF((OPr)-Pr-i)(2)) have been prepared by protonating the precursor hydride complexes cis-[(dppm)(2)Ru(H)(L)][BF4] (L = P(OMe)(3), P(OEt)(3), P((OPr)-Pr-i)(3)) using HBF4.Et2O. The cis-[(dppm)(2)Ru(H)(L)][BF4] complexes were obtained from the trans hydrides via an isomerization reaction that is acid-accelerated. This isomerization reaction gives mixtures of cis and trans hydride complexes, the ratios of which depend on the cone angles of the phosphite ligands: the greater the cone angle, the greater is the amount of the cis isomer. The eta(2)-H-2 ligand in the dihydrogen complexes is labile, and the loss of H-2 was found to be reversible. The protonation reactions of the starting hydrides with trans PMe3 or PMe2Ph yield mixtures of the cis and the trans hydride complexes; further addition of the acid, however, give trans-[(dPPM)(2)Ru(BF4)Cl]. The roles of the bite angles of the dppm ligand as well as the steric and the electronic properties of the monodentate phosphorus ligands in this series of complexes are discussed. X-ray crystal structures of trans-[(dppm)(2)Ru(H)(P(OMe)(3))][BF4], cis-[(dppm)(2)Ru-(H)(P(OMe)(3))][BF4], and cis-[(dppm)(2)Ru(H)(P((OPr)-Pr-i)(3))][BF4] complexes have been determined.

Ferrocene-Conjugated L-Tryptophan Copper(II) Complexes of Phenanthroline Bases Showing DNA Photocleavage Activity and Cytotoxicity

Ferrocene-conjugated L-tryptophan (L-Trp) reduced Schiff base (Fc-TrpH) copper(II) complexes [Cu(Fc-Trp)(L)](ClO(4)) of phenanthroline bases (L), viz. 2,2'-bipyridine (bpy in 1), 1,10-phenanthroline (phen in 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 3), and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 4), were prepared and characterized and their photocytotoxicity studied. Cationic reduced Schiff base (Ph-TrpH) complexes [Cu(Ph-Trp)(L)(H(2)O)] (ClO(4)) (L = phen in 5; dppz in 6) having the ferrocenyl moiety replaced by a phenyl group and the Zn(II) analogue (7) of complex 4 were prepared and used as control species. The crystal structures of 1 and 5 with respective square-planar CuN(3)O and square-pyramidal CuN(3)O(2) coordination geometry show significantly different core structures. Complexes 1-4 exhibit a Cu(II)-Cu(I) redox couple near -0.1 V and the Fc(+)-Fc couple at similar to 0.5 V vs SCE in DMF-0.1 M [Bu(4)(n)N] (ClO(4)) (Fc = ferrocenyl moiety). The complexes display a copper(II)-based d-d band near 600 nm and a Fc-centered band at similar to 450 nm in DMF-Tris-HCl buffer. The complexes are efficient binders to calf thymus DNA. They are synthetic chemical nucleases in the presence of thiol or H(2)O(2), forming hydroxyl radicals. The photoactive complexes are cleavers of pUC19 DNA in visible light, forming hydroxyl radicals. Complexes 2-6 show photocytotoxicity in HeLa cancer cells, giving IC(50) values of 4.7, 10.2, 1.3, 4.8, and 4.3 mu M, respectively, in visible light with the appearance of apoptotic bodies. The complexes also show photocytotoxicity in MCF-7 cancer cells. Nuclear chromatin cleavage has been observed with acridine orange/ethidium bromide (AO/EB) dual staining with complex 4 in visible light. The complexes induce caspase-independent apoptosis in the HeLa cells.

Structural characterization of angiotensin I-converting enzyme in complex with a selenium analogue of captopril

Human somatic angiotensin I-converting enzyme (ACE), a zinc-dependent dipeptidyl carboxypeptidase, is central to the regulation of the renin-angiotensin aldosterone system. It is a well-known target for combating hypertension and related cardiovascular diseases. In a recent study by Bhuyan and Mugesh [Org. Biomol. Chem. (2011) 9, 1356-1365], it was shown that the selenium analogues of captopril (a well-known clinical inhibitor of ACE) not only inhibit ACE, but also protect against peroxynitrite-mediated nitration of peptides and proteins. Here, we report the crystal structures of human testis ACE (tACE) and a homologue of ACE, known as AnCE, from Drosophila melanogaster in complex with the most promising selenium analogue of captopril (SeCap) determined at 2.4 and 2.35 angstrom resolution, respectively. The inhibitor binds at the active site of tACE and AnCE in an analogous fashion to that observed for captopril and provide the first examples of a protein-selenolate interaction. These new structures of tACE-SeCap and AnCE-SeCap inhibitor complexes presented here provide important information for further exploration of zinc coordinating selenium-based ACE inhibitor pharmacophores with significant antioxidant activity.

Ferrocene-Conjugated Copper(II) Complexes of L-Methionine and Phenanthroline Bases: Synthesis, Structure, and Photocytotoxic Activity

Ferrocene-conjugated reduced Schiff base (Fc-metH) copper(II) complexes of L-methionine and phenanthroline bases, namely, Cu(Fc-met)(B)](NO3), where B is 1,10-phenanthroline (phen in 1), dipyrido3,2-d:2',3'-f]quinoxaline (dpq in 2), dipyrido3,2-a:2',3'-c]phenazine (dppz in 3), and 2-(naphthalen-1-yl)-1H-imidazo4,5-f]1,10]phenanthroline (nip in 4), were prepared and characterized and their photocytotoxicity studied (Fc = ferrocenyl moiety). Complexes Cu(Ph-met)(B)](NO3) of the reduced Schiff base from benzaldehyde and L-methionine (Ph-metH) and B (phen in 5, dppz in 6) were prepared and used as control species. Complexes 1 and 5 were structurally characterized by X-ray crystallography. Complex 1 as a discrete monomer has a CuN3OS core with the thiomethyl group as the axial ligand. Complex 5 has a polymeric structure with a CuN3O2 core in the solid state. Complexes 5 and 6 are formulated as Cu(Ph-met)(B)(H2O)] (NO3) in an aqueous phase based on the mass spectral data. Complexes 1-4 showed the Cu(II)-Cu(I) and Fc(+)-Fc redox couples at similar to 0.0 and similar to 0.5 V vs SCE, respectively, in DMF-0.1 M (Bu4N)-N-n](ClO4). A Cu(II)-based weak d-d band near 600 nm and a relatively strong ferrocenyl band at similar to 450 nm were observed in DMF-Tris-HCl buffer (1:4 v/v). The complexes bind to calf thymus DNA, exhibit moderate chemical nuclease activity forming (OH)-O-center dot radical species, and are efficient photocleavers of pUC19 DNA in visible light of 454, 568, and 647 rim, forming (OH)-O-center dot radical as the reactive oxygen species. They are cytotoxic in HeLa (human cervical cancer) and MCF-7 (human breast cancer) cells, showing an enhancement of cytotoxicity upon visible light irradiation. Significant change in the nuclear morphology of the HeLa cells was observed with 3 in visible light compared to the nonirradiated sample. Confocal imaging using 4 showed its nuclear localization within the HeLa cells.

Two Novel Heterometallic Chains Featuring Mn-II and Na-I Ions in Trigonal-Prismatic Geometries Alternately Linked to Octahedral Mn-IV Ions: Synthesis, Structures, and Magnetic Behavior

Two new one-dimensional heterometallic complexes, Mn3Na(L)(4)(CH3CO2)(MeOH)(2)]-(ClO4)(2)center dot 3H(2)O (1), Mn3Na(L)(4)(CH3CH2CO2)-(MeOH)(2)](ClO4)(2)center dot 2MeOH center dot H2O (2) LH2 = 2-methyl-2-(2-pyridyl)propane-1,3-diol], have been synthesized and characterized by X-ray crystallography. Both complexes feature Mn-II and Na-I ions in trigonal-prismatic geometries that are linked to octahedral Mn-IV ions by alkoxy bridges. Variable-temperature direct- and alternating-current magnetic susceptibility data indicated a spin ground state of S = 11/2 for both complexes. Density functional theory calculations performed on 1 supported this conclusion.

Reactions of Titanocene Bis(trimethylsilyl)acetylene Complexes with Carbodiimides: An Experimental and Theoretical Study of Complexation versus C-N Bond Activation

The reaction of the low valent metallocene(II) sources Cp'Ti-2(eta(2)-Me3SiC2SiMe3) (Cp' = eta(5)-cyclopentadienyl, 1a or eta(5)-pentamethylcyclopentadienyl, 1b) with different carbodiimide substrates RN=C=NR' 2-R-R' (R = t-Bu; R' = Et; R = R' = i-Pr; t-Bu; SiMe3; 2,4,6-Me-C6H2 and 2,6-i-Pr-C6H3) was investigated to explore the frontiers of ring strained, unusual four-membered heterometallacycles 5-R. The product complexes show dismantlement, isomerization, or C-C coupling of the applied carbodiimide substrates, respectively, to form unusual mono-, di-, and tetranuclear titanium(III) complexes. A detailed theoretical study revealed that the formation of the unusual complexes can be attributed to the biradicaloid nature of the unusual four-membered heterometallacycles 5-R, which presents an intriguing situation of M-C bonding. The combined experimental and theoretical study highlights the delicate interplay of electronic and steric effects in the stabilization of strained four-membered heterometallacycles, accounting for the isolation of the obtained complexes.

Cellular uptake and remarkable photocytotoxicity of pyrenylter pyridine oxovanadium(IV) complexes of dipyridophenazine bases

Pyrenylterpyridine (pytpy) oxovanadium(IV) complexes VO(pytpy)(L)]Cl-2 (1-6) of the dipyridophenazine bases (L), viz., dipyrido-6,7,8,9-tetrahydrophenazine (dpqC in 1), dipyrido3,2-a:2',3'-c]phenazine-2-carboxylic acid (dppzc in 2), dipyrido3,2-a:2',3'-c]phenazine-11-sulfonic acid (dppzs in 3), 7-aminodipyrido3,2-a:2',3'-c]phenazine (dppza in 4), benzo-i]dipyrido3,2-a:2',3'-c]phenazine (dppn in 5) and dipyrido3,2-a:2',3'-c]phenazine (dppz in 6) were prepared, characterized and their DNA binding, photocleavage activity and photocytotoxicity studied. The complexes which showed a d-d band near 750 nm in DMF are efficient binders to calf thymus DNA (K-b: 3.2 x 10(5)-2.9 x 10(6) M-1). The complexes showed significant pUC19 DNA cleavage in near-IR light of 785 nm forming center dot OH radicals and photocytotoxicity in HeLa cells in visible light with the benzo-i] dipyrido3,2-a:2',3'-c]phenazine complex 5 showing a remarkably low IC50 value of 0.036 mu M. Flow-cytometric analysis shows a high sub-G1 phase cell cycle arrest in HeLa cells by the complexes on photo-irradiation. The photocytotoxicity correlates well with the hydrophobicity, photosensitizing ability and DNA binding propensity of the complexes. (C) 2012 Elsevier B.V. All rights reserved.