Página 1 dos resultados de 102 itens digitais encontrados em 0.001 segundos

Electrochemical and spectroelectrochemical characterization of meso-tetra-alkyl porphyrins

Paliteiro, Carlos; Sobral, Abílio
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
27.216855%
A series of three meso-tetra-alkyl porphyrins (H2TAPs) were synthesised and their electrochemical properties were studied in dichloromethane containing either tetra-butyl ammonium perclorate (TBAP) or tetra-butyl ammonium hexafluorophosphate TBA(PF6) as supporting electrolyte (SE) by cyclic voltammetry and in situ UV/vis spectroelectrochemistry. Values of E1/2 for the recorded four redox processes of these porphyrins and of the meso-tetra-phenyl porphyrin (H2TPP) on glassy carbon and platinum were measured and compared. The redox data collected on the first oxidation and the first reduction processes predict that the value of [Delta](LUMO - HOMO) for the H2TAPs is lower than for meso-tetra-phenyl porphyrin and, therefore, that the first Q band of the electronic spectra of the H2TAPs is red shifted relatively to the same band in the spectrum of H2TPP; this shift was indeed found. The second oxidation process of the H2TAPs is influenced by the supporting electrolyte used and the dication then formed is consumed by an irreversible chemical reaction. The species produced in this reaction is irreversibly reduced at a considerably lower potential. The electrochemical and spectroelectrochemical data collected are consistent with the occurrence of structural distortion in the macrocycle rings of the H2TAPs.; http://www.sciencedirect.com/science/article/B6TG0-4DWGWN2-4/1/2d901dbaf4ae85016a0364d6ba38f810

Electrochemical and photocatalytic reactions of polycyclic aromatic hydrocarbons investigated by raman spectroscopy

CORDEIRO, Denise S.; CORIO, Paola
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
16.612258%
This paper presents the study of photochemical behavior of polycyclic aromatic hydrocarbons (PAHs), potential pollutants in secondary reactions in aerosols, through Raman spectroscopy compared with its electrochemical behavior. The PAHs studied include pyrene, anthracene, phenanthrene and fluorene. These were adsorbed onto TiO2 and irradiated with ultraviolet light (254 nm). Their electrochemical oxidation was studied by in situ Surface-enhanced Raman Scattering (SERS) and led to the formation of carbonyl-containing products. Oxidized intermediates bearing the C=O group were also formed during photodegradation. The joint analysis of the photodegradation data with those produced by electrochemical means - using spectroscopic techniques for the identification and characterization of the products - revealed the formation of identical products for anthracene, but not for pyrene. A reasonable explanation for this difference in results is that photochemical and electrochemical oxidation reactions proceed via different mechanisms. While photocatalytic degradation over TiO2 is initiated by hydroxyl radicals, electrochemical oxidation is initiated by the direct electron transfer from adsorbed PAH to the electrode, generating PAH cation radicals that undergo subsequent reactions.; Este trabalho apresenta o estudo do comportamento fotoquímico de hidrocarbonetos policíclicos aromáticos (HPAs)...

Probing the electronic delocalization in a cyclic pyrazine ruthenium cluster hexamer

NIKOLAOU, Sofia; FORMIGA, Andre Luiz Barboza; TOMA, Henrique E.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
16.612258%
[Ru(3)O(CH(3)COO)(6)(pz)(CO)](6) is a cyclic hexamer species encompassing six triangular ruthenium cluster centers bridged by pyrazine ligands. The electronic communication among the cluster units strongly depends on their oxidation states, and has been successfully probed by means of cyclic voltammetry and UV-vis spectroelectrochemistry. (C) 2010 Elsevier B.V. All rights reserved.; FAPESP; CNPq

Spectroelectrochemistry and investigation of charge transport mechanisms of iron poly(pyridyl) redox polymers

CHIERICATO JR., Glaico; SILVA, Ana Paula Saldanha
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.216855%
In this work, we describe the characterization of the complex [Fe(tpy-NH2)(2)](PF6)(2) (tpy-NH2 = bis[4`-(3-aminophenyl)-2, 2`:6`,2 ``-terpyridine]. The complex was oxidatively electropolymerized on glassy.-carbon electrodes in CH3CN/0.1 M tetraethylammonium perchlorate (TEAP) to generate polymer films that exhibit reversible oxidative electrochemical behavior in a wide potential range (0.0-1.6 V), as well as high conductivity and stability/durability. In situ spectrocyclic voltammetry of this modified electrode was carried out on a photodiode array spectrophotometer attached to a potentiostat, which provided UV-Vis absorption spectra of the redox species during the potential sweep. We determined charge transport parameters as a function of time and thickness of the modified electrode, and the results showed that poly-[[Fe(tpy-NH2)(2)](2+)](n) can be made to exhibit three regimes of charge transport behavior by manipulation of the film thickness and the experimental time-scale. Morphological characterization of the film was provided by atomic force microscopy. (C) 2008 Elsevier Ltd. All rights reserved.

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

PFAFFEN, V.; ORTIZ, P. I.; TORRESI, S. I. Cordoba de; TORRESI, R. M.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
16.612258%
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.; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq (Brazil); CONICET (Argentina); CONICET (Argentine); CAPES (Brazil); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); SPU (Argentine)[025/05]; SPU (Argentine); CONICET; CONICET

Spectroscopic evidences of the presence of hydrogenated species on the surface of copper during CO(2) electroreduction at low cathodic potentials

BATISTA, Elisete A.; TEMPERINI, Marcia L. A.
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
16.612258%
Carbon dioxide electroreduction on copper electrode was studied by surface enhanced Raman scattering (SERS) in K(2)SO(4) aqueous solutions with different pH values. CO(2) was bubbled into the solution at 0 V vs. Ag/AgCl, i.e., on an oxidized copper surface. In acidic solutions (pH around 2.5), at -0.2 V, bands indicative of the presence of ethylene on the electrode surface were detected. Although ethylene is knowledgably a product of CO(2) electroreduction on copper, it was not experimentally identified on the electrode`s surface at such a low cathodic potential in prior works. In solutions with pH around 2.5, CO bands were not observed, suggesting that hydrocarbons could be formed by a pathway that does not occur via adsorbed CO. In solutions with higher pHs, a complex spectral pattern, between 800 and 1700 cm(-1), was observed at approximately -0.4 V. The observed spectrum closely resembles those reported in the literature for adsorption of monocarboxylic acids with small chains. The spectral features indicate the presence of a structure containing a double C=C bond. a carboxyl group, and C-H bonds on the electrode`s surface. SERS spectra obtained in CO-saturated solution are also presented. However, in this case, no SERS bands were observed in the region between 800 and 1700 cm(-1) at low cathodic potentials. (c) 2009 Elsevier B.V. All rights reserved.; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP; CNPq; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Surface-enhanced Raman study of electrochemical and photocatalytic degradation of the azo dye Janus Green B

BONANCEA, Carlos E.; NASCIMENTO, Gustavo M. do; SOUZA, Michele L. de; TEMPERINI, Marcia L. A.; CORIO, Paola
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
16.612258%
The photocatalytic degradation of Janus Green B azo dye over silver modified titanium dioxide films was investigated by surface-enhanced Raman spectroscopy (SERS). An optimized SERS-active substrate was employed to study the photodegradation reaction of Janus Green B. Considering that photocatalytic degradation processes of organic molecules adsorbed on TiO2 might involve either their oxidation or reduction reaction, the vibrational spectroelectrochemical study of the dye was also performed, in order to clarify the transformations involved in initial steps of its photochemical decomposition. In order to understand the changes in Raman spectra of Janus Green B after photodegradation and/or electrochemical processes, a vibrational assignment of the main Raman active modes of the dye was carried out, based on a detailed resonance Raman profile. Products formed by electrochemical and photochemical degradation processes were compared. The obtained results revealed that the first steps of the degradation process of Janus Green B involve a reductive mechanism. (C) 2007 Published by Elsevier B.V.

Electrochemical Control of the Time-Dependent Intensity Fluctuations in Surface-Enhanced Raman Scattering (SERS)

SANTOS, Diego P. dos; ANDRADE, Gustavo F. S.; TEMPERINI, Marcia L. A.; BROLO, Alexandre G.
Fonte: AMER CHEMICAL SOC Publicador: AMER CHEMICAL SOC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
16.612258%
Time-dependent fluctuations in surface-enhanced Raman scattering (SERS) intensities were recorded from a roughened silver electrode immersed in diluted solutions of rhodamine 6G (R6G) and congo red (CR). These fluctuations were attributed to a small number of SERS-active molecules probing regions of extremely high electromagnetic field (hot spots) at the nanostructured surface. The time-dependent distribution of SERS intensities followed a tailed statistics at certain applied potentials, which has been linked to single-molecule dynamics. The shape of the distribution was reversibly tuned by the applied voltage. Mixtures of both dyes, R6G and CR, at low concentrations were also investigated. Since R6G is a cationic dye and CR is an anionic dye, the statistics of the SERS intensity distribution of either dye in a mixture were independently controlled by adjusting the applied potential. The potential-controlled distribution of SERS intensities was interpreted by considering the modulation of the surface coverage of the adsorbed dye by the interfacial electric field. This interpretation was supported by a two-dimensional Monte Carlo simulation that took into account the time evolution of the surface configuration of the adsorbed species and their probability to populate a hypothetical hot spot. The potential-controlled SERS dynamics reported here is a first step toward the spectroelectrochemical investigation of redox processes at the single-molecule level by SERS.; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP[01/09497-8]; NSERC; NSERC; CNPq; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Canadian Bureau for International Education Department of Foreign Affairs; Canadian Bureau for International Education Department of Foreign Affairs; International Trade (CBIEDFAIT) of Canada; International Trade (CBIEDFAIT) of Canada

ESTUDO DAS PROPRIEDADES QUÍMICAS E ELETROQUÍMICAS DE trans-[RuCl(NO)(py)4](PF6)2½H2O e trans-[RuCl(NO)(py)4]Cl23H2O; Chemistry and Electrochemistry studies of trans-[RuCl(NO)(py)4](PF6)2½H2O e trans-[RuCl(NO)(py)4]Cl23H2O

Calandreli, Ivy
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 16/09/2005 PT
Relevância na Pesquisa
17.53355%
Neste trabalho foram realizados as sínteses, caracterização e o estudo da reatividade química dos complexos trans-[RuCl(NO)(py)4](PF6)2½H2O e trans-[RuCl(NO)(py)4]Cl23H2O. Os compostos foram isolados e caracterizados através de técnicas espectroscópicas (UV-vis, infravermelho e 1H RMN), eletroquímicas (voltametria cíclica e polarografia de pulso diferencial) e análise elementar. Os dados espectroscópicos, eletroquímicos e os resultados da análise elementar foram consistentes com as fórmulas dos complexos analisados. Foram utilizados como precursores os compostos [RuCl2(DMSO)4], trans-[RuCl2(py)4] e trans-[Ru(NO2)2(py)4]. O composto com NO foi obtido a partir do complexo trans-[Ru(NO2)2(py)4] em ácido clorídrico concentrado e precipitado como sal de PF6-, formando o complexo trans-[RuCl(NO)(py)4](PF6)2½H2O. O trans-[RuCl(NO)(py)4]Cl23H2O foi obtido a partir de uma solução do complexo trans-[RuCl(NO)(py)4](PF6)2.½H2O, adicionando-se uma solução de cloreto de tetrabutilamônio para precipitar o composto na forma de cloreto. Os espectros na região do UV-vis dos complexos trans-[RuCl(NO)(py)4](PF6)2½H2O e trans-[RuCl(NO)(py)4]Cl23H2O apresentaram três bandas nas regiões ao redor de 230 nm, 260nm e 450 nm. Os espectros de infravermelho apresentaram freqüência de estiramento NO entre 1900 e 1925 cm-1...

Synthesis and Characterization of Free-Base, Copper and Nickel Isocorroles

Pomarico, Giuseppe; Xiao, Xiao; Nardis, Sara; Paolesse, Roberto; Fronczek, Frank R.; Smith, Kevin M.; Fang, Yuanyuan; Ou, Zhongping; Kadish, Karl M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 21/06/2010 EN
Relevância na Pesquisa
17.216855%
A series of free-base and metalated isocorroles represented as (TT-n-iso-Cor)H2 and (TT-n-iso-Cor)MII, where n = 5 or 10 and M = Ni or Cu, were synthesized and characterized by electrochemistry and spectroelectrochemistry in CH2Cl2 containing 0.1 M TBAP. A metalation of the free-base macrocycles with CoII, MnIII or ZnII was also attempted but was unsuccessful. Five isocorroles were isolated and shown to undergo two stepwise oxidations to give π-cation radicals and dications in CH2Cl2, with the most stable products being obtained in the case of the 10-substituted derivatives. The same isocorroles could also be reduced by one or two electrons but the initial one-electron addition products are unstable and undergo a rapid chemical reaction giving a reduced corrole or corrole-like product, which could be reoxidized to the corresponding (TTCor)M at a controlled positive potential. This series of reactions effectively gives an isocorrole to corrole conversion upon reduction and reoxidation and was monitored by both electrochemistry and thin-layer spectroelectrochemistry.

In situ regeneration of NADH via lipoamide dehydrogenase-catalyzed electron transfer reaction evidenced by spectroelectrochemistry

Tam, Tsz Kin; Chen, Baowei; Lei, Chenghong; Liu, Jun
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.216855%
NAD/NADH is a coenzyme found in all living cells, carrying electrons from one reaction to another. We report on characterizations of in situ regeneration of NADH via lipoamide dehydrogenase (LD)-catalyzed electron transfer reaction to regenerate NADH using UV-vis spectroelectrochemistry. The Michaelis-Menten constant (Km) and maximum velocity (Vmax) of NADH regeneration were measured as 0.80 ± 0.15 mM and 1.91 ± 0.09 μM s-1 in a 1-mm thin-layer spectroelectrochemical cell using gold gauze as the working electrode at the applied potential -0.75 V (vs. Ag/AgCl). The electrocatalytic reduction of the NAD system was further coupled with the enzymatic conversion of pyruvate to lactate by lactate dehydrogenase to examine the coenzymatic activity of the regenerated NADH. Although the reproducible electrocatalytic reduction of NAD into NADH is known to be difficult compared to the electrocatalytic oxidation of NADH, our spectroelectrochemical results indicate that the in situ regeneration of NADH via LD-catalyzed electron transfer reaction is fast and sustainable and can be potentially applied to many NAD/NADH-dependent enzyme systems.

UV/Vis Spectroelectrochemistry as a Tool for Monitoring the Fabrication of Sensors Based on Silver Nanoparticle Modified Electrodes

Fernández-Blanco, Cristina; Colina, Álvaro; Heras, Aránzazu
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 02/05/2013 EN
Relevância na Pesquisa
27.53355%
A new controlled current multipulse methodology has been developed to modify the screen-printed electrode surface with silver nanoparticles (AgNPs). Spectroelectrochemistry has provided not only information about the type of nanoparticles (NPs) deposited on the electrode surface, but also about the electrosynthesis process. Small NPs without plasmon band are initially generated. Next, these nuclei grow to form bigger NPs in the reduction pulses with a characteristic plasmon band centered at 400 nm. Most of the NPs are generated during the first reduction pulses and a linear growth of the absorbance at a lower reaction rate was obtained in the subsequent pulses. Oxidation pulses do not redissolve completely silver NPs but only partially, meaning that very stable NPs are generated. AgNPs-modified electrodes have been successfully used to determine hydrogen peroxide. Spectroelectrochemistry has also yielded very useful information to understand the voltammetric signal obtained during the reduction of H2O2 on silver modified electrodes.

Sensitivity of activatable reactive oxygen species probes by fluorescence spectroelectrochemistry

Wang, Steven T.; Zhegalova, Natalia G.; Gustafson, Tiffany P.; Zhou, Andy; Sher, Joel; Achilefu, Samuel; Berezinand, Oleg Y.; Berezin, Mikhail Y.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.216855%
We have developed a new analytical method of evaluating activatable fluorescent probes for ROS detection using integrated fluorescence spectroelectrochemistry. Tafel formalism was applied to describe the process of the probes’ oxidation under electrochemical conditions and identify a novel parameter defined as the threshold oxidation potential. This potential can serve as an approximation to the equilibrium potential and can be utilized for determining the sensitivity of a probe to oxidation. Based upon the measured values of threshold potentials, the order of sensitivity towards oxidation among several mostly used probes was determined to be following (from highest to lowest): 2,7-dichlorodihydrofluorescein > dihydroethidium > dihydrorhodamine 123 > dihydrorhodamine 6G. The presented approach opens up a new direction in synthesizing and screening novel ROS probes with a well-defined sensitivity for in vitro and in vivo applications.

POCN-type Pincer Complexes of NiII and NiIII : synthesis, reactivities, catalytic activities and physical properties

Spasyuk, Denis M.
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
EN
Relevância na Pesquisa
27.216855%
Cette thèse décrit la synthèse, la caractérisation, les réactivités, et les propriétés physiques de complexes divalents et trivalents de Ni formés à partir de nouveaux ligands «pincer» de type POCN. Les ligands POCN de type amine sont préparés d’une façon simple et efficace via l’amination réductrice de 3-hydroxybenzaldéhyde avec NaBH4 et plusieurs amines, suivie par la phosphination de l’amino alcool résultant pour installer la fonction phosphinite (OPR2); le ligand POCN de type imine 1,3-(i-Pr)2PC6H4C(H)=N(CH2Ph) est préparé de façon similaire en faisant usage de PhCH2NH2 en l’absence de NaBH4. La réaction de ces ligands «pincer» de type POCN avec NiBr2(CH3CN)x en présence d’une base résulte en un bon rendement de la cyclométalation du lien C-H situé en ortho aux fonctions amine et phosphinite. Il fut découvert que la base est essentielle pour la propreté et le haut rendement de la formation des complexes «pincer» désirés. Nous avons préparé des complexes «pincer» plan- carrés de type POCN, (POCNRR΄)NiBr, possédant des fonctions amines secondaires et tertiaires qui démontrent des réactivités différentes selon les substituants R et R΄. Par exemple, les complexes possédant des fonctions amines tertiaires ArCH2NR2 (NR2= NMe2...

Synthesis, characterization, EPR spectroelectrochemistry studies and theoretical calculations of manganese(II) complexes with the ligands H3bpeten and H3bnbpeten

Romanowski,Stela Maris de M.; Machado,Sérgio P.; Friedermann,Geraldo R.; Mangrich,Antonio S.; Hermann,Monique de F.; Lima,Hugo Orofino; Nakagaki,Shirley
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
Relevância na Pesquisa
27.216855%
The synthesis and characterization of the manganese(II) complexes [MnII(Hbpeten)] and [MnII(Hbnbpeten)], where H3bpeten and H3bnbpeten are respectively [N,N'-bis-(2-hydroxybenzyl)-N-(2-pyridylmethyl)-N'-(2-hydroxyethyl)ethane-1,2-diamine] and [N,N'-bis-(5-nitro-2-hydroxybenzyl)-N'-(2-hydroxyethyl)ethane-1,2-diamine], are reported. The characterization was carried out by elemental analyses, cyclic voltammetry, spectroscopic methods (UV-Vis, FTIR, ¹H NMR), electronic paramagnetic resonance spectroelectrochemistry (EPR) and theoretical DFT calculations. The electrochemistry and EPR espectroelectrochemistry data were consistent with the reduction of one of the nitro groups in free H3bnbpeten and in the respective manganese(II) complex. These results were supported by DFT calculations, which showed that only one nitro group contributes to the LUMO. The theoretical data appear to be suitable to describe the electronic properties of the compounds.

Complejos de metales de transición con el ligando rédox activo NO: estructura electrónica, interconversión y reactividad; Transition metal complexes with the redox active ligand NO: electronic structure, interconversion and reactivity

Pellegrino, Juan
Fonte: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires Publicador: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
Tipo: info:eu-repo/semantics/doctoralThesis; tesis doctoral; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2012 SPA
Relevância na Pesquisa
17.216855%
El óxido nítrico (NO) puede unirse a los metales como NO+ (nitrosonio), NO● o NO¯ /HNO (nitroxilo), resultando ambiguos los estados de oxidación del metal y el ligando en los fragmentos M-NO. Por eso, Enemark y Feltham propusieron designar estos fragmentos como {MNO}n, donde "n" es la suma de los electrones d del metal y los electrones π* del NO. En esta tesis se trabajó con complejos {MNO}n con dos enfoques diferentes. El primero se enmarca en el área de química bioinorgánica y está relacionado con el estudio de complejos {MNO}n biológicamente relevantes (porfirinatos de hierro). El otro enfoque involucra complejos {MNO}n organometálicos y el objetivo específico es estudiar la estructura electrónica y reactividad de complejos {RhNO}n con ligandos pinza tridentados y complejos {ReNO}n con un ligando derivado de ciclopentadienilo. En la primera parte, nos enfocamos particularmente en complejos {FeNO}n (n= 6, 7, 8) con ligandos porfirinatos, dado que estas especies han sido postuladas como intermediarias en variedad de procesos catalíticos en sistemas biológicos. Nuestro modelo de nitrosilo hémico es el complejo {FeNO}7 Fe(TFPPBr8)NO (1●) (TFPPBr8 = meso-[tetrakis(pentafluorofenil)]-octabromoporfirina), cuyo voltagrama presenta dos ondas de reducción reversibles y una onda de oxidación. Se presentan resultados del estudio de los tres procesos de transferencia electrónica observados para 1● por métodos químicos...

Thermodynamic Investigations of Metalloproteins: Metal as Probe and Protein as Probe

Siburt, Claire Jarvis Parker
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação Formato: 21399473 bytes; application/pdf
Publicado em //2010 EN_US
Relevância na Pesquisa
27.53355%

In this dissertation several metalloproteins, both metal transport proteins and the classic metalloprotein hemoglobin, are investigated using a variety of biophysical and electrochemical techniques. In each case, thermodynamic measurements provide insight into the role and mode of action of the metalloprotein under investigation. In Chapters 2 and 3, we focus on the thermodynamic properties of the metal while bound by the protein. In Chapter 4, we focus on the thermodynamic properties of the protein with and without the metal. In Chapter 5, we utilize both the metal and the protein as our probe.

In Chapter 2, we probe the thermodynamic properties of the heme-bound iron to elucidate the structure-function relationships underlying two important physiological responses of hemoglobin (Hb): the Root Effect of hemoglobin from certain fish and the different nitrite reactivities of hemoglobins from clams. Hemoglobins of some fish exhibit significantly lowered oxygen affinity at low pH, allowing for proton-mediated release of O2. This phenomenon, known as the Root Effect, serves as a proton-driven pump delivering O2 to the swim bladders and eyes of the fish. The clam, ,L. pectinata...

Porphyrin dimers linked by conjugated butadiyne bridges: preparations, spectra, voltammetry and reductive spectroelectrochemistry of {[M(OEP)](m-C4)[M(OEP)]} (M2 � H4, Co2, Ni2, Cu2, Zn2, Pd2, Pt2, Co/Ni, Ni/Cu, Ni/Zn)

Arnold, Dennis; Heath, Graham; James, Dionne
Fonte: John Wiley & Sons Inc Publicador: John Wiley & Sons Inc
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.216855%
A series of derivatives M2P2 (M2 ≡ H4, Co2, Ni2, Cu2, Zn2, Pd2, Pt2, Co/Ni, Ni/Cu, Ni/Zn) of the ligand meso,meso′-bis(octaethylporphyrinyl)butadiyne has been prepared and characterized by 1H NMR, FT Raman and visible absorption spectroscopies as well

Mixed-metal cluster chemistry. 19. Crystallographic, spectroscopic, electrochemical, spectroelectrochemical, and theoretical studies of systematically varied tetrahedral group 6-iridium clusters

Lucas, Nigel; Blitz, Jonathan; Petrie, Simon; Stranger, Robert; Humphrey, Mark; Heath, Graham; Otieno-Alego, Vincent
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
17.216855%
A systematically varied series of tetrahedral clusters involving ligand and core metal variation has been examined using crystallography, Raman spectroscopy, cyclic voltammetry, UV - vis - NIR and IR spectroelectrochemistry, and approximate density functional theory, to assess cluster rearrangement to accommodate steric crowding, the utility of metal-metal stretching vibrations in mixed-metal cluster characterization, and the possibility of tuning cluster electronic structure by systematic modification of composition, and to identify cluster species resultant upon electrochemical oxidation or reduction. The 60-electron tetrahedral clusters MIr3(CO)11-x(PMe3)x (η5-Cp) [M = Mo, x = 0, Cp = C5H4Me (5), C5HMe4 (6), C5Me5 (7); M = W, Cp = C5H4Me x = 1 (13), x = 2 (14)] and M2Ir2(CO)10-x (PMe3)x(η5-Cp) [M = Mo, x = 0, Cp = C5H4Me (8), C5HMe4 (9), C5Me5 (10); M = W, Cp = C5H4Me, x = 1 (15), x = 2 (16)] have been prepared. Structural studies of 7, 10, and 13 have been undertaken; these clusters are among the most sterically encumbered, compensating by core bond lengthening and unsymmetrical carbonyl dispositions (semi-bridging, semi-face-capping). Raman spectra for 5, 8, WIr3(CO)11(η5- C5H4Me) (11), and W2Ir2(CO)10- (η5-C5H4Me)2 (12), together with the spectrum of Ir4(CO)12...

High-field NMR spectroelectrochemistry of spinning solutions: simultaneous in situ detection of electrogenerated species in a standard probe under potentiostatic control

Prenzler, Paul D; Bramley, Richard; Downing, Stephen; Heath, Graham
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.53355%
This report summarizes the design and performance of the first practicable in situ electrogenerative high-field solution-NMR cell, designed for simultaneous NMR spectroelectrochemistry in a conventional 10- or 16-mm 300 MHz probe. The axially symmetric three-electrode assembly is stationary and self-aligning. It dips into a standard spinning 10-mm sample tube and is adapted for convenient operation in any commercial high-field, multi-nuclear, variable-temperature FT NMR spectrometer. The tubular, rf-transparent working electrode (presently consisting of a gold film, coated on glass) completely spans the detection region; the recommended coating thickness is ≤ 0.01 δ where δ is the rf-absorbing conductor skin depth. With careful shimming, very narrow1H signals (~ 1 Hz) can be obtained. The performance of the in situ NMR-electrochemical cell is illustrated by monitoring the progressive reduction of 'p-quinone' (1,4-benzoquinone) to its dihydro-form by controlled-potential electrolysis in an acidic medium. (C) 2000 Elsevier Science S.A.