Cobalt complexes with pyrazole ligands as catalyst precursors for the peroxidative oxidation of cyclohexane: Z-ray absorption spectroscopy studies and biological applications

[CoCl(-Cl)(Hpz(Ph))(3)](2) (1) and [CoCl2(Hpz(Ph))(4)] (2) were obtained by reaction of CoCl2 with HC(pz(Ph))(3) and Hpz(Ph), respectively (Hpz(Ph)=3-phenylpyrazole). The compounds were isolated as air-stable solids and fully characterized by IR and far-IR spectroscopy, MS(ESI+/-), elemental analysis, cyclic voltammetry (CV), controlled potential electrolysis, and single-crystal X-ray diffraction. Electrochemical studies showed that 1 and 2 undergo single-electron irreversible (CoCoIII)-Co-II oxidations and (CoCoI)-Co-II reductions at potentials measured by CV, which also allowed, in the case of dinuclear complex 1, the detection of electronic communication between the Co centers through the chloride bridging ligands. The electrochemical behavior of models of 1 and 2 were also investigated by density functional theory (DFT) methods, which indicated that the vertical oxidation of 1 and 2 (that before structural relaxation) affects mostly the chloride and pyrazolyl ligands, whereas adiabatic oxidation (that after the geometry relaxation) and reduction are mostly metal centered. Compounds 1 and 2 and, for comparative purposes, other related scorpionate and pyrazole cobalt complexes, exhibit catalytic activity for the peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone under mild conditions (room temperature, aqueous H2O2). Insitu X-ray absorption spectroscopy studies indicated that the species derived from complexes 1 and 2 during the oxidation of cyclohexane (i.e., Ox-1 and Ox-2, respectively) are analogous and contain a Co-III site. Complex 2 showed low invitro cytotoxicity toward the HCT116 colorectal carcinoma and MCF7 breast adenocarcinoma cell lines.

Homo-and heteropolymetallic 3-(2-pyridyl)pyrazolate manganese and rhenium complexes

fac-[MBr(CO)(3)(pypzH)] (M = Mn, Re; pypzH = (3-(2-pyridyl) pyrazole) complexes are prepared from fac[ MBr(CO)(3)(NCMe)(2)] and pypzH. The result of their deprotonation depends on the metallic substrate: the rhenium complex affords cleanly the bimetallic compound [fac-{Re(CO)(3)(mu(2)-pypz)}] 2 (mu(2)-pypz = mu(2)-3-(2pyridyl-. 1N) pyrazolate-2. 1N), which was crystallographically characterized, whereas a similar manganese complex was not detected. When two equivalents of pyridylpyrazolate are used, polymetallic species [fac-M(CO) 3(mu(2)-pypz)(mu(3)-pypz) M'] (mu(3)-pypz = mu(3)-3-(2-pyridyl-kappa N-1) pyrazolate-1 kappa 2N, N: 2. 1N:; M = Mn, M' = Li, Na, K; M = Re, M' = Na) are obtained. The crystal structures of the manganese carbonylate complexes were determined. The lithium complex is a monomer containing one manganese and one lithium atom, whereas the sodium and potassium complexes are dimers and reveal an unprecedented coordination mode for the bridging 3-(2-pyridyl) pyrazolate ligand, where the nitrogen of the pyridyl fragment and the nitrogen-1 of pyrazolate are chelated to manganese atoms, and each nitrogen-2 of pyrazolate is coordinated to two alkaline atoms. The polymetallic carbonylate complexes are unstable in solution and evolve spontaneously to [fac-{Re(CO) 3(mu(2)-pypz)}](2) or to the trimetallic paramagnetic species [MnII(mu(2)-pypz) 2{fac-{MnI(CO) 3(mu(2)-pypz)}(2)}]. The related complex cis-[MnCl2(pypzH)(2)] was also synthesized and structurally characterized. The electrochemical behavior of the new homo-and heteropolymetallic 3-(2-pyridyl) pyrazolate complexes has been studied and details of their redox properties are reported.

Elétrodo de pasta de carbono molecularmente impresso para deteção voltamétrica de Furazolidona

A furazolidona é uma substância ativa do medicamento Giarlam que contém um espetro anti-bacteriano relativamente amplo e que é frequentemente usado para tratar certas doenças bacterianas e protozoárias no homem. A maioria dos fármacos exige uma dosagem que garanta os níveis de segurança e eficácia de atuação. A necessidade de dosear os medicamentos e os seus metabólitos exige o desenvolvimento constante de métodos analíticos eficientes. Neste trabalho desenvolveu-se um novo sensor eletroquímico para a deteção da furazolidona, baseado num elétrodo de pasta de carbono modificado com um polímero molecularmente impresso. A procura de novos materiais que permitam uma melhor seletividade e sensibilidade aos sistemas de deteção é especialmente importante no desenvolvimento de métodos analíticos. Os polímeros molecularmente impressos enquadram-se nesse perfil e o seu uso tem vindo a ser cada vez mais frequente como ferramenta importante em química analítica. Assim, sintetizou-se um polímero com cavidades seletivas para a Furazolidona. Este polímero foi, misturado com grafite e perafina de modo a produzir uma pasta de carbono. Uma seringa de plástico foi usada como suporte da pasta de carbono. O comportamento eletroquímico do sensor foi avaliado e diversas condições de utilização foram estudadas e otimizadas. O sensor apresenta um comportamento linear entre a intensidade do pico e a concentração numa gama de concentrações entre 1 e 100 μM, um limite de deteção de 1 μM e uma precisão (repetibilidade) inferior a 7%. A aplicabilidade do sensor fabricado em amostras complexas foi avaliada pela deteção do fármaco em amostras de urina.

Développement de nouveaux matériaux organométalliques pour des applications dans le domaine de la conversion d’énergie solaire

Dans un contexte où l’approvisionnement énergétique mondial du 21e siècle est un enjeu majeur, le développement de sources d’énergie renouvelables suscite l’attention croissante de la communauté scientifique et industrielle. L’énergie solaire est définitivement l’une des meilleures alternatives aux combustibles fossiles en tant que source d’énergie du monde de demain. Ce mémoire traite donc du développement de nouveaux matériaux organométalliques pour des applications de photorécoltage d’énergie en photovoltaïque et en production d’hydrogène. Le premier chapitre présente la synthèse assistée par microondes de quatre nouveaux complexes de Co(II), Ni(II), Cu(II) et Zn(II) basés sur le ligand tétra-p-méthoxyphényl-azadipyrrométhène (ADPM) avec des rendements variant de 89% à quantitatif. Ces complexes sont mis en relation avec d’autres complexes homoleptiques connus portant le tétraphényl-ADPM comme ligand ainsi qu’avec leurs chélates de BF2+ pour une meilleure compréhension des tendances engendrées par la substitution de l’agent coordonnant et/ou des substituants p-méthoxy. Pour ce faire, le comportement électrochimique et photophysique est présenté. De façon générale, la présence des quatre groupements p-méthoxy semble rendre les dérivés de cet ADPM plus susceptibles à la dégradation électrochimique en conditions d’oxydation et induire un déplacement bathochromique des propriétés optiques d’absorption et d’émission. Les structures rayons X du ligand tétra-p-méthoxyphényl-ADPM et de son complexe homoleptique de Co(II) sont aussi discutées. Cette étude a été effectuée dans l’espoir de fournir des informations utiles sur la stabilité des ADPM aux chercheurs du domaine photovoltaïque en quête de nouveaux chromophores dans le proche infrarouge (NIR). Le deuxième chapitre présente quant à lui les propriétés de senseur envers les anions F-, OAc- et H2PO4- de deux nouveaux complexes neutres de Re(I) de type mono- et dinucléaire basés sur une phénanthroline substituée en position 5 contenant un récepteur thio-urée. Ces composés ont été obtenus dans des rendements de 81% et 60%, respectivement. L’effet de la formation de ponts hydrogène lors de l’ajout d’anions versus la déprotonation du récepteur a été évalué par des titrations UV/Vis et RMN 1H et semble indiquer que la formation de la base conjuguée du récepteur est favorisée pour ce type de système. De plus, la structure rayons X d’un des précurseurs est présentée et permet une discussion sur la chiralité des complexes mono- et dinucléaire obtenus. L’obtention d’un complexe bimétallique par autoassemblage ouvre la voie à la préparation d’antennes moléculaires pour des systèmes de photosynthèse artificielle.

A novel heteroditopic terpyridine-pincer ligand as building block for mono- and heterometallic Pd(II) and Ru(II) complexes

A palladium-catalyzed Stille coupling reaction was employed as a versatile method for the synthesis of a novel terpyridine-pincer (3, TPBr) bridging ligand, 4'-{4-BrC6H2(CH2NMe2)(2)-3,5}-2,2':6',2 ''-terpyridine. Mononuclear species [PdX(TP)] (X = Br, Cl), [Ru(TPBr)(tpy)](PF6)(2), and [Ru(TPBr)(2)](PF6)(2), synthesized by selective metalation of the NCNBr-pincer moiety or complexation of the terpyridine of the bifunctional ligand TPBr, were used as building blocks for the preparation of heterodi- and trimetallic complexes [Ru(TPPdCl)(tpy)](PF6)(2) (7) and [Ru(TPPdCl)(2)]-(PF6)(2) (8). The molecular structures in the solid state of [PdBr(TP)] (4a) and [Ru(TPBr)(2)](PF6)(2) (6) have been determined by single-crystal X-ray analysis. Electrochemical behavior and photophysical properties of the mono-and heterometallic complexes are described. All the above di- and trimetallic Ru complexes exhibit absorption bands attributable to (MLCT)-M-1 (Ru -> tpy) transitions. For the heteroleptic complexes, the transitions involving the unsubstituted tpy ligand are at a lower energy than the tpy moiety of the TPBr ligand. The absorption bands observed in the electronic spectra for TPBr and [PdCl(TP)] have been assigned with the aid of TD-DFT calculations. All complexes display weak emission both at room temperature and in a butyronitrile glass at 77 K. The considerable red shift of the emission maxima relative to the signal of the reference compound [Ru(tpy)(2)](2+) indicates stabilization of the luminescent (MLCT)-M-3 state. For the mono- and heterometallic complexes, electrochemical and spectroscopic studies (electronic absorption and emission spectra and luminescence lifetimes recorded at room temperature and 77 K in nitrile solvents), together with the information gained from IR spectroelectrochemical studies of the dimetallic complex [Ru(TPPdSCN)(tpy)](PF6)(2), are indicative of charge redistribution through the bridging ligand TPBr. The results are in line with a weak coupling between the {Ru(tpy)(2)} chromophoric unit and the (non)metalated NCN-pincer moiety.

Synthesis, characterization, crystal structure, and DNA-binding of ruthenium(II) complexes of heterocyclic nitrogen ligands resulting from a benzimidazole-based quinazoline derivative

The reaction of cis-[RuCl2(dmso)(4)] with [6-(2-pyridinyl)-5,6-dihydrobenzimidazo[1,2-c] quinazoline] (L) afforded in pure form a blue ruthenium(II) complex, [Ru(L-1)(2)] (1), where the original L changed to [2-(1H-benzoimidazol-2-yl)-phenyl]-pyridin-2-ylmethylene-amine (HL1). Treatment of RuCl3 center dot 3H(2)O with L in dry tetrahydrofuran in inert atmosphere led to a green ruthenium(II) complex, trans-[RuCl2(L-2)(2)] (2), where L was oxidized in situ to the neutral species 6-pyridin-yl-benzo[4,5]imidazo[1,2-c] quinazoline (L-2). Complex 2 was also obtained from the reaction of RuCl3 center dot 3H(2)O with L-2 in dry ethanol. Complexes 1 and 2 have been characterized by physico-chemical and spectroscopic tools, and 1 has been structurally characterized by single-crystal X-ray crystallography. The electrochemical behavior of the complexes shows the Ru(III)/Ru(II) couple at different potentials with quasi-reversible voltammograms. The interaction of these complexes with calf thymus DNA by using absorption and emission spectral studies allowed determination of the binding constant K-b and the linear Stern-Volmer quenching constant K-SV

Synthesis and properties of new Mo(II) complexes with N-heterocyclic and ferrocenyl ligands

New Mo(II) complexes with 2,2'-dipyridylamine (L1), [Mo(CH(3)CN)(eta(3)-C(3)H(5))(CO)(2)(L1)]OTf (C1a) and [{MoBr(eta(3)-C(3)H(5))(CO)(2)(L1)}(2)(4,4'-bipy)](PF(6))(2) (C1b), with {[bis(2-pyridyl)amino]carbonyl}ferrocene (L2), [MoBr(eta(3)-C(3)H(5))(CO)(2)(L2)] (C2), and with the new ligand N,N-bis(ferrocenecarbonyl)-2-aminopyridine (L3), [MoBr(eta(3)-C(3)H(5))(CO)(2)(L3)] (C3), were prepared and characterized by FTIR and (1)H and (13)C NMR spectroscopy. C1a, C1b, L3, and C2 were also structurally characterized by single crystal X-ray diffraction. The Mo(II) coordination sphere in all complexes features the facial arrangement of allyl and carbonyl ligands, with the axial isomer present in C1a and C2, and the equatorial in the binuclear C1b. In both C1a and C1b complexes, the L1 ligand is bonded to Mo(II) through the nitrogen atoms and the NH group is involved in hydrogen bonds. The X-ray single crystal structure of C2 shows that L2 is coordinated in a kappa(2)-N,N-bidentate chelating fashion. Complex C3 was characterized as [MoBr(eta(3)-C(3)H(5))(CO)(2)(L3)] with L3 acting as a kappa(2)-N,O-bidentate ligand, based on the spectroscopic data, complemented by DFT calculations. The electrochemical behavior of the monoferrocenyl and diferrocenyl ligands L2 and L3 has been studied together with that of their Mo(II) complexes C2 and C3. As much as possible, the nature of the different redox changes has been confirmed by spectrophotometric measurements. The nature of the frontier orbitals, namely the localization of the HOMO in Mo for both in C2 and C3, was determined by DFT studies.

Dependence of the product on the P-P ligand in reactions of [RuCl(3)(NO)(P-P)] complexes (P-P = aromatic diphosphines) with 2-mercaptopyridine

This study presents the syntheses and characterization of 2-mercaptopyridine (pyS(-)) complexes containing ruthenium(II) with the following general formula [Ru(pyS)(2)(P-P)], P-P = (c-dppen) = cis-1,2-bis(diphenylphosphino)ethylene) (1); (dppe)=1,2-bis(diphenylphosphino)ethane (2); (dppp)=1,3-bis(diphenylphosphino)propane (3) and (dppb) = 1,4-bis(diphenylphosphino)butane (4). The complexes were synthesized from the mer- or fac-[RuCl(3)(NO)(P-P)] precursors in the presence of triethylamine in methanol solution with dependence of the product on the P-P ligand. The reaction of pyS- with a ruthenium complex containing a bulky aromatic diphosphine dppb disclosed a major product with a dangling coordinated dppbO-P, the [Ru(pyS)(2)(NO)(eta(1)-dppbO-P)]PF(6) (5). In addition, this work also presents and discusses the spectroscopic and electrochemical behavior of 1-5. and report the X-ray structures for I and S. (C) 2009 Elsevier Ltd. All rights reserved.

Ether-Bond-Containing Ionic Liquids and the Relevance of the Ether Bond Position to Transport Properties

The ionic liquids (ILs) 1-ethoxyethyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, [EtO-(CH(2))(2)MMI][Tf(2)N], and N-(ethoxyethyl)-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide, [EtO(CH(2))(2)MMor][Tf(2)N] were synthesized, and relevant properties, such as thermal stability, density, viscosity, electrochemical behavior, ionic conductivity, and self-diffusion coefficients for both ionic species, were measured and compared with those of their alkyl counterparts, 1-n-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, [BMMI][Tf(2)N], and N-n-butyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide,[BMP][Tf(2)N] and N-n-butyl-N-methylmorpholinium bis(trilfuoromethanesulfonyl)imide [BMMor][Tf(2)N][. This comparison was done to evaluate the effects caused by the presence of the ether bond in either the side chain or in the organic cation ring. The salt, LiTf(2)N, was added to the systems to estimate IL behavior with regard to lithium cation transport. Pure [EtO(CH(2))(2)MMI][Tf(2)N] and their LiTf(2)N solutions showed low viscosity and the highest conductivity among the ILs studied. The H(R) (AC conductivity/NMR calculated conductivity ratio) values showed that, after addition of LiTf(2)N, ILs containing the ether bond seemed to have a greater number of charged species. Structural reasons could explain these high observed HR values for [EtO(CH(2))(2)MMor][Tf(2)N].

Development of a sequential injection-square wave voltammetry method for determination of paraquat in water samples employing the hanging mercury drop electrode

This work describes the development and optimization of a sequential injection method to automate the determination of paraquat by square-wave voltammetry employing a hanging mercury drop electrode. Automation by sequential injection enhanced the sampling throughput, improving the sensitivity and precision of the measurements as a consequence of the highly reproducible and efficient conditions of mass transport of the analyte toward the electrode surface. For instance, 212 analyses can be made per hour if the sample/standard solution is prepared off-line and the sequential injection system is used just to inject the solution towards the flow cell. In-line sample conditioning reduces the sampling frequency to 44 h(-1). Experiments were performed in 0.10 M NaCl, which was the carrier solution, using a frequency of 200 Hz, a pulse height of 25 mV, a potential step of 2 mV, and a flow rate of 100 mu L s(-1). For a concentration range between 0.010 and 0.25 mg L(-1), the current (i(p), mu A) read at the potential corresponding to the peak maximum fitted the following linear equation with the paraquat concentration (mg L(-1)): ip = (-20.5 +/- 0.3) Cparaquat -(0.02 +/- 0.03). The limits of detection and quantification were 2.0 and 7.0 mu g L(-1), respectively. The accuracy of the method was evaluated by recovery studies using spiked water samples that were also analyzed by molecular absorption spectrophotometry after reduction of paraquat with sodium dithionite in an alkaline medium. No evidence of statistically significant differences between the two methods was observed at the 95% confidence level.

On the pH dependence of electroactivity of poly(methylene blue) films

The electrochemical behavior of poly(methylene blue) on different electrodes has been investigated by electrochemical quartz crystal microbalance and in situ spectrophotometric measurements coupled to cyclic voltammetry. Polymeric films were obtained potentiodynamically and the charge transport mechanism was analyzed. The electrochemical results show that polymer electroactivity depends not only on pH but also on the substrate. Charge compensation changes with both pH and the size of the anions showing a transition in the pH range of polymer pKa. It was demonstrated by spectroelectrochemical experiments that the electroactivity of the film depends on the radical/radical cation equilibrium. The potentials where the most electroactive species are formed have been determined. (C) 2009 Elsevier Ltd. All rights reserved.

Measurement of the anodic potential in solid state: A tool for determination of the antioxidant potential of phytomedicine

The electroanalytical techniques are very promissing to perform the quality control of crude vegetable. Solid State Differential Pulse Voltammetry in the supporting electrolyte is able to detect the oxidation signals of the active material, which can be used as a parameter to identify the type of crude vegetable and its antioxidant activity. The working electrode consisted in a carbon paste electrode modified with the powder of vegetable raw material (EMF). The electrochemical measurements were performed in a cell containing the working (EMF), reference (Ag/AgCl, KClsat) and auxiliary (Pt) electrodes.

Electroanalytical determination of promethazine hydrochloride in pharmaceutical formulations on highly boron-doped diamond electrodes using square-wave adsorptive voltammetry

The electrochemical oxidation of promethazine hydrochloride was made on highly boron-doped diamond electrodes. Cyclic voltammetry experiments showed that the oxidation mechanisms involved the formation of an adsorbed product that is more readily oxidized, producing a new peak with lower potential values whose intensity can be increased by applying the accumulation potential for given times. The parameters were optimized and the highest current intensities were obtained by applying +0.78 V for 30 seconds. The square-wave adsorptive voltammetry results obtained in BR buffer showed two well-defined peaks, dependent on the pH and on the voltammetric parameters. The best responses were obtained at pH 4.0, frequency of 50 s(-1), step of 2 mV, and amplitude of 50 mV. Under these conditions, linear responses were obtained for concentrations from 5.96 x 10(-7) to 4.76 x 10(-6) mol L-1, and calculated detection limits of 2.66 x 10(-8) mol L-1 (8.51 mu g L-1) for peak 1 and of 4.61 x 10(-8) mol L-1 (14.77 mu g L-1) for peak 2. The precision and accuracy were evaluated by repeatability and reproducibility experiments, which yielded values of less than 5.00% for both voltammetric peaks. ne applicability of this procedure was tested on commercial formulations of promethazine hydrochloride by observing the stability, specificity, recovery and precision of the procedure in complex samples. All results obtained were compared to recommended procedure by British Pharmacopeia. The voltammetric results indicate that the proposed procedure is stable and sensitive, with good reproducibility even when the accumulation steps involve short times. It is therefore very suitable for the development of the electroanalytical procedure, providing adequate sensitivity and a reliable method.

Ethanol oxidation reactions using SnO(2)@Pt/C as an electrocatalyst

This paper presents a study on the ethanol oxidation reaction using SnO(2)@Pt/C core-shell structures as electrocatalysts. All the materials used, including Pt/C and PtSn/C E-tek, were 20% (w/w) metal on carbon. The formation of core-shell nanoparticles (SnO(2)@Pt/C) was measured by UV-vis spectrophotometry. X-ray diffraction measurements showed Pt (shell) diffraction patterns without influence from the SnO(2) core and without any shift in 2 theta values for Pt. The diameters of the core-shell particle structures, measured using high-resolution transmission electron microscopy images, were in the range of 3-16 nm. The electrochemical profile for SnO(2)@Pt/C in an acidic medium (H(2)SO(4) at a concentration of 0.5 mol L(-1)) was almost the same as the typical electrochemical behavior for Pt in an acidic medium. Furthermore, the onset potential for the ethanol oxidation reaction using SnO(2)@Pt/C was almost the same as that for PtSn/C E-tek (0.23 V versus the reversible hydrogen electrode). However, the mass current peak densities for ethanol oxidation were 50% higher on SnO(2)@Pt/C than on PtSn/C E-tek. In the polarization curve, the mass current density for ethanol oxidation was higher at all potentials for SnO(2)@Pt/C when compared to Pt/C and PtSn/C E-tek. At 0.5 V, the current mass density for ethanol oxidation on SnO(2)@Pt was 2.3 times of that for the same process on the commercial material. The electrocatalytic activity of SnO(2)@Pt/C for ethanol oxidation was associated with an increase in the electrochemically active surface area. However, an electronic effect should also be considered because the Pt shell changes its electronic structure in the presence of the foreign core. (C) 2010 Elsevier B.V. All rights reserved.

On the activation and physical degradation of boron-doped diamond surfaces brought on by cathodic pretreatments

The electrochemical activation and physical degradation of boron-doped diamond (BDD) electrodes with different boron doping levels after repeated cathodic pretreatments are reported. Galvanostatic cathodic pretreatment passing up to -14000 C cm(-2) in steps of -600 C cm(-2) using -1 A cm(-2) caused significant physical degradation of the BDD surface, with film detachment in some areas. Because of this degradation, a great increase in the electrochemically active area was observed in Tafel plots for the hydrogen evolution reaction (HER) in acid media. The minimum cathodic pretreatment needed for the electrochemical activation of the BDD electrodes without producing any observable physical degradation on the BDD surfaces was determined using electrochemical impedance spectroscopy (EIS) measurements and cyclic voltammetry: -9 C cm(-2), passed at -1 A cm(-2). This optimized cathodic pretreatment can be safely used when electrochemical experiments are carried out on BDD electrodes with doping levels in the range between 800 and 8000 ppm.