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Redox Behavior (redox + behavior)
Selected AbstractsMulti-Input/Multi-Output Molecular Response System Based on the Dynamic Redox Behavior of 3,3,4,4-Tetraaryldihydro[5]helicene Derivatives: Reversible Formation/Destruction of Chiral Fluorophore and Modulation of Chiroptical Properties by Solvent PolarityCHEMISTRY - A EUROPEAN JOURNAL, Issue 37 2009Takanori Suzuki Prof. Abstract 3,3,4,4-Tetaaryldihydro[5]helicenes (1) and 1,1,-binaphthyl-2,2,-diylbis(diarylcarbenium)s (22+) can be reversibly interconverted upon electron transfer, which is accompanied by a vivid color change (electrochromism) as well as by the formation/cleavage of a CC bond ("dynamic redox behavior"). Because only the neutral donor 1 exhibits strong fluorescence, electrochemical input can further modify the fluorescent properties of the pair. Due to the configurational stability of the helicity in 1 and axial chirality in 22+, the redox reaction of optically pure material proceeds stereospecifically, which induces a chiroptical change such as circular dichroism (CD) as an additional output. The CD spectra of dications 22+ exhibit solvent dependency (chiro-solvatochromism), which is accompanied by solvatochromic behavior based on the ,,, interaction of the two cationic chromophores as well as coordinative interaction of the Lewis basic solvent to the Lewis acidic triarylcarbenium moieties. Thus, the present system is endowed with multi-input functionality for modifying multiple output signals. [source] Zinc Oxide/Zinc Hexacyanoferrate Hybrid Film-Modified Electrodes for Guanine DetectionELECTROANALYSIS, Issue 18 2007Hung-Wei Chu Abstract An electroactive polynuclear hybrid films of zinc oxide and zinc hexacyanoferrate (ZnO/ZnHCF) have been deposited on electrode surfaces from H2SO4 solution containing Zn(NO3)2 and K3[Fe(CN)6] by repetitive potential cycling method. Simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) measurements demonstrate the steady growth of hybrid film. There are two redox couples present in the voltammograms of hybrid film and it is obvious in the case of pH,2. Surface morphology of hybrid film was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Energy dispersive spectrometer (EDS) data confirm existence of zinc oxide in the hybrid film. The effect of type of monovalent cations on the redox behavior of resulting film was investigated. In pure supporting electrolyte, electrochemical responses of modified electrode resemble with that of a surface immobilized redox couple. The electrocatalytic activity of ZnO/ZnHCF hybrid film was investigated towards guanine using cyclic voltammetry and rotating disc electrode (RDE) techniques. Finally, feasibility of using ZnO/ZnHCF hybrid film-coated electrodes for guanine estimation in flow injection analysis (FIA) was also investigated. [source] Study of the Complexation, Adsorption and Electrode Reaction Mechanisms of Chromium(VI) and (III) with DTPA Under Adsorptive Stripping Voltammetric ConditionsELECTROANALYSIS, Issue 19 2003Sylvia Sander Abstract The complexation of Cr(III) and Cr(VI) with diethylenetriaminepentaacetic acid (DTPA), the redox behavior of these complexes and their adsorption on the mercury electrode surface were investigated by a combination of electrochemical techniques and UV/vis spectroscopy. A homogenous two-step reaction was observed when mixing Cr(III), present as hexaquo complex, with DTPA. The first reaction product, the electroactive 1,:,1 complex, turns into an electroinactive form in the second step. The results indicate that the second reaction product is presumably a 1,:,2 Cr(III)/DTPA complex. The electroreduction of the DTPA-Cr(III) complex to Cr(II) was found to be diffusion rather than adsorption controlled. The Cr(III) ion, generated in-situ from Cr(VI) at the mercury electrode at about ,50,mV (vs. Ag|AgCl) (3,mol,L,1 KCl), was found to form instantly an electroactive and adsorbable complex with DTPA. By means of electrocapillary measurements its surface activity was shown to be 30 times higher than that of the complex built by homogenous reaction of DTPA with the hydrated Cr(III). Both components, DTPA and the in-situ built complex Cr(III) ion were found to adsorb on the mercury electrode. The effect of nitrate, used as catalytic oxidant in the voltammetric determination method, on the complexation reaction and on the adsorption processes was found to be negligible. The proposed complex structures and an overall reaction scheme are shown. [source] Synthesis, Characterization, and Properties of Some Copper(II) Complexes of 2-Pyridineformamide Thiosemicarbazone (HAm4DH)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2006María del Carmen Aguirre Abstract Reactions between different copper(II) salts and 2-pyridineformamide thiosemicarbazone (HAm4DH) in neutral ethanolic media led to the formation of complexes with the formulae [Cu(HAm4DH)X2] (X = Cl or Br) (1, 2) and [Cu(HAm4DH)2]X2 (X = NO3 or ClO4) (3, 4). The same reactions carried out in the presence of triethylamine gave rise to new complexes with the general formulae [Cu(Am4DH)X] (X = Cl, Br, AcO, or NO3) (5,8), [Cu(H2O)(Am4DH)](ClO4) (9), and [Cu(Am4DH)2] (10), many of which were isolated with different molecules of crystallization and contain a deprotonated thiosemicarbazone (Am4DH). These complexes were characterized by elemental analysis, and different spectroscopic and magnetic techniques. The thermal and redox behavior of the complexes was also evaluated. Complexes 1, 2, 5, and 6 show better nuclease activity than [Cu(phen)2]2+. Inaddition, crystals were isolated in the cases of [Cu(HAm4DH)Cl2]2 (5a), 1,[Cu(Am4DH)Cl] (5b), 1,[Cu(Am4DH)Br] (6a), and [Cu(HAm4DH)(H2O)(ClO4)2]·MeOH·H2O (9a) and these structures were analyzed by X-ray diffraction. Compound 5a has a dimeric structure with chlorine bridges and shows weak antiferromagnetism (J = ,12.2 cm,1). Complexes 5b and 6a are one-dimensional polymers formed through halogen bridges and the deprotonated thiosemicarbazone in the thiolate form. In compound 9a the copper(II) is in a distorted octahedral environment with two ClO4 units coordinated to the metal center. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Star-Shaped D-,-A Molecules Containing a 2,4,6-Tri(thiophen-2-yl)-1,3,5-triazine Unit: Synthesis and Two-Photon Absorption PropertiesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 32 2009Li Zou Abstract A series of new star-shaped donor-,-acceptor (D-,-A) molecules containing the 2,4,6-tri(thiophen-2-yl)-1,3,5-triazine unit were synthesized and characterized. The 1,3,5-triazine group, as a strong electron-accepting center, is connected to three electron-donating end groups through ,-conjugated bridges. As a result of the coexistence of the electron acceptor and donor, these compounds show reversible or quasireversible redox behavior. Through changing the peripheral end group the optical properties can be modified. All compounds exhibit two-photon absorption activity in the range of 720,880 nm and show large two-photon absorption cross sections that are closely related to the intramolecular charge transfer and ,-conjugated length of the molecule.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Polycationic States of Oligoanilines Based on Wurster's BlueEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 26 2009Akihiro Ito Abstract Polycations of two oligoanilines based on Wurster's blue,N,N,,N, -tris[4-(dimethylamino)phenyl]- N,N,,N, -trimethyl-1,3,5-benzenetriamine (2) and N,N, -bis(3-{N -[4-(dimethylamino)phenyl]- N -methylamino}phenyl)- N,N, -dimethyl- p -phenylenediamine (3), have been generated efficiently by a stepwise oxidation procedure. Their redox behavior was characterized in terms of the embedded p -phenylenediamine (PD) units and their intramolecular connectivity. EPR analysis of the oxidized 2 and 3 species revealed the existence of high-spin species in solution. It was found that spin multiplicities of the dominant polycationic species of 2 and 3 formed by 3 equiv. of oxidant can be assigned to quartet and doublet states, respectively on the basis of pulsed EPR spectroscopy. These results demonstrate that the intramolecular connectivity between the spin-containing units decisively influences the spin preference of the multispin systems based on oligoanilines.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Resonance Raman study of multihemic c -type cytochromes from Desulfuromonas acetoxidansFEBS JOURNAL, Issue 4 2000Geneviève Chottard Two multihemic cytochromes c from the sulfur reducing bacteria Desulfuromonas acetoxidans have been studied by optical and resonance Raman spectroscopy: cytochrome c551.5, a trihemic cytochrome and cytochrome c Mr 50 000, a recently isolated high molecular mass cytochrome. The redox and Raman characteristics of cytochrome c551.5 are compared to those of the tetrahemic cytochromes c3 from Desulfovibrio. While the redox behavior, followed by spectroelectrochemistry, is similar to that of cytochrome c3, showing the same conformational change after reduction of the highest potential heme, the Raman data show a contribution from a His, form of the axial ligands and lead to the assignment of a band at 218 cm,1 to the Fe(III),(His)2 stretching vibration. The Raman data on cytochrome c Mr 50 000 are in favor of an entirely low spin species with two different sets of axial ligands. A partially reduced state is easily accessible by ascorbate addition. [source] Syntheses, structures, and supramolecular properties of giant ,-expanded macrocyclic oligothiophenesHETEROATOM CHEMISTRY, Issue 5 2007Masahiko Iyoda Fully conjugated ,-expanded macrocyclic oligothiophenes with 60,-, 90,-, 120,-, 150,-, and 180,-electron systems (1,5) were synthesized using modified McMurry coupling reaction as a key step. Compound 1 was converted into macrocyclic oligo(2,5-thienylene-ethynylene) 6 using bromination-dehydrobromination procedure. X-ray analysis of 1 revealed a unique molecular and packing structure, reflecting a round, planar shape with nanoscale inner cavity. Interestingly, 2 and 3 self-aggregate in the solid state to form nanowires. The structure of fibrous aggregates was established by scanning electron microscopic and atomic force microscopic analyses. Compounds 1,6 exhibit multi-step reversible redox behavior with fairly low first oxidation potentials, reflecting their cyclic conjugation. Doping of 1,3 with iodine gives semiconductors owing to their ,-donor properties and ,,, stacking ability. © 2007 Wiley Periodicals, Inc. 18:460,466, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20337 [source] Multi-Input/Multi-Output Molecular Response System Based on the Dynamic Redox Behavior of 3,3,4,4-Tetraaryldihydro[5]helicene Derivatives: Reversible Formation/Destruction of Chiral Fluorophore and Modulation of Chiroptical Properties by Solvent PolarityCHEMISTRY - A EUROPEAN JOURNAL, Issue 37 2009Takanori Suzuki Prof. Abstract 3,3,4,4-Tetaaryldihydro[5]helicenes (1) and 1,1,-binaphthyl-2,2,-diylbis(diarylcarbenium)s (22+) can be reversibly interconverted upon electron transfer, which is accompanied by a vivid color change (electrochromism) as well as by the formation/cleavage of a CC bond ("dynamic redox behavior"). Because only the neutral donor 1 exhibits strong fluorescence, electrochemical input can further modify the fluorescent properties of the pair. Due to the configurational stability of the helicity in 1 and axial chirality in 22+, the redox reaction of optically pure material proceeds stereospecifically, which induces a chiroptical change such as circular dichroism (CD) as an additional output. The CD spectra of dications 22+ exhibit solvent dependency (chiro-solvatochromism), which is accompanied by solvatochromic behavior based on the ,,, interaction of the two cationic chromophores as well as coordinative interaction of the Lewis basic solvent to the Lewis acidic triarylcarbenium moieties. Thus, the present system is endowed with multi-input functionality for modifying multiple output signals. [source] | ||||||||||