Home About us Contact
|
Home About us Contact | ||
|
|
||
Electronic Absorption (electronic + absorption)
Terms modified by Electronic Absorption Selected AbstractsPreparation, physicochemical and third order nonlinear optical properties of bis(tetrabutylammonium)bis(2-thioxo-1,3-dithiole-4,5-dithiolato)mercurate(II)CRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2009X. Q. Wang Abstract Bis(tetrabutylammonium)bis(2-thioxo-1,3-dithiole-4,5-dithiolato)mercurate(II) was prepared and characterized by elemental analyses, electronic absorption, infrared and X-ray powder diffraction spectroscopy. The specific heat of the crystal was measured to be 1878.2 J.mol,1K,1 at 300 K. The thermal decomposition process was investigated by means of thermogravimetric analysis and differential thermal analysis measurements in air together with infrared and X-ray powder diffraction spectra. The third-order nonlinear optical properties at 800 nm were measured by femtosecond optical Kerr gate technique by using CS2 as reference. The third-order optical susceptibility of its acetone solution at the concentration of 9.27 × 10,4 M was obtained to be 2.53 × 10,14 esu. The second-order hyperpolarizability was estimated to be 1.7 × 10,32 esu and the response time was about 226 fs. The third order nonlinear optical properties at 532 nm were investigated by using the Z-scan technique with 20 ps. It exhibited self-focusing effect and saturable absorption. The second molecular hyperpolarizability was estimated to be 8.4 × 10,32 esu. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and Characterization of a Series of New Luminescent NHC-Coordinated AuI,AgI Tetra- and Polymetallic Complexes Containing Benzoate-Bridged Ag2 DimersEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2009Amit K. Ghosh Abstract The reaction of [Au(CH3impy)2]PF6 (2), with substituted silver benzoate salts bearing different halide substituents produced a series of new mixed-metal species having two different structural motifs. One structural motif contains discrete tetrametallic Ag2Au2 diamond cores, whereas the other motif contains the same tetrametallic diamond core interconnected by benzoate-bridged silver dimers to form polymers. All the complexes are substitution-inert and stable both in the solid state as well as in solution. We also report the synthesis of oxidative addition products of [Au(CH3impy)2]PF6, which were also obtained during our attempts to oxidize the above-mentioned multimetallic assembly with bromine and iodine. Compounds 3,7 are intensely luminescent in frozen acetonitrile solution, but surprisingly no luminescence is observed at room temperature. All the complexes were completely characterized by 1H, 13C NMR, electronic absorption, emission spectroscopy, elemental analysis and X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Synthesis, Characterization, and Photophysical Properties of Some Heterodimetallic Bisporphyrins of Ytterbium and Transition Metals , Enhancement and Lifetime Extension of Yb3+ Emission by Transition-Metal Porphyrin SensitizationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2007Feng-Lei Jiang Abstract A series of d-f heterodimetallic bisporphyrin complexes (YbZn, YbPd, and YbPt), in which a YbIII porphyrinate moiety is linked to a transition-metal porphyrinate moiety by a flexible three-carbon chain, were synthesized. They were fully characterized by high-resolution mass spectrometry, 1H and 31P NMR spectroscopy, electronic absorption, andfluorescence methods. Variable-temperature near-infrared photoluminescence studies showed that the transition-metal porphyrinate moiety would enhance the ytterbium(III) emission centered at about 998 nm and extend its emission lifetime. YbPd and YbPt showed large two-photon absorption cross-section values because of the interaction between the porphyrin units, which caused a loss of centrosymmetry. Optical limiting investigation demonstrated that [Yb(TPP)(LOMe)] and YbPt have comparable performance to C60 by virtue of their heavy-metal effect. Our results indicate that these bisporphyrin dimetallic complexes will find valuable applications in the field of nonlinear optics. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Binding of Oxovanadium(IV) to Tripeptides Containing Histidine and Cysteine Residues and Its Biological Implication in the Transport of Vanadium and Insulin-Mimetic CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2005Eugenio Garribba Abstract The complexation of VIVO ion with three tripeptides of biological importance containing L -histidine or L -cysteine (HisGlyGly, GlyGlyHis and GlyGlyCys) has been studied. This study was performed in aqueous solution by the combined application of potentiometric and spectroscopic (electronic absorption and EPR) techniques. The results indicate that these oligopeptides, if a ligand-to-metal molar ratio of 10 or 15 is used, can keep VIVO ion in solution until the deprotonation of the amide group with the donor set (NH2, CO, Nimax) for HisGlyGly or (COO,, CO) for GlyGlyHis and GlyGlyCys. In all the systems, at pH values around neutrality, a VOLH,2 species is formed with an (NH2, N,, N,, COO,) donor set for HisGlyGly, (NH2, N,, N,, Nim) for GlyGlyHis and (NH2, N,,N,, S,) for GlyGlyCys. These species, and those with onedeprotonated amide group coordinated to the VIVO ion, can be detected by EPR spectroscopy. The N,(amide) contribution to the hyperfine coupling constant along the z axis, Az, depends on the total charge of the donor atoms in the equatorial plane. The participation of albumin in the transport of vanadium and insulin-mimetic VIVO compounds is reconsidered based on these results. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] A spectroscopic study of the reaction of NAMI, a novel ruthenium(III)anti-neoplastic complex, with bovine serum albuminFEBS JOURNAL, Issue 4 2000Luigi Messori The reaction of Na[transRuCl4Me2SO(Im)] (NAMI; where Im is imidazole), a novel anti-neoplastic ruthenium(III) complex, with BSA, was studied in detail by various physico-chemical techniques. It is shown that NAMI, following chloride hydrolysis, binds bovine serum albumin tightly; spectrophotometric and atomic absorption data point out that up to five ruthenium ions are bound per albumin molecule when BSA is incubated for 24 h with an eightfold excess of NAMI. CD and electronic absorption results show that the various ruthenium centers bound to albumin exhibit well distinct spectroscopic features. The first ruthenium equivalent produces a characteristic positive CD band at 415 nm whereas the following NAMI equivalents produce less specific and less marked spectral effects. At high NAMI/BSA molar ratios a broad negative CD band develops at 590 nm. Evidence is provided that the bound ruthenium centers remain in the oxidation state +3. By analogy with the case of transferrins it is proposed that the BSA-bound ruthenium ions are ligated to surface histidines of the protein; results from chemical modification experiments with diethylpyrocarbonate seem to favor this view. Spectral patterns similar to those shown by NAMI are observed when BSA is reacted with two strictly related ruthenium(III) complexes Na[transRuCl4(Me2SO)2] and H(Im)[transRuCl4(Im)2] (ICR), implying a similar mechanism of interaction in all cases. It is suggested that the described NAMI-BSA adducts may form in vivo and may be relevant for the biological properties of this complex; alternatively NAMI/BSA adducts may be tested as specific carriers of the ruthenium complex to cancer cells. Implications of these findings for the mechanism of action of NAMI and of related ruthenium(III) complexes are discussed. [source] Palladium Nanowire from Precursor Nanowire: Crystal-to-Crystal Transformation via In,Situ Reduction by Polymer Matrix,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2007S. Porel Abstract Precursor nanowires of potassium palladium(II) chloride crystallized inside a poly(vinyl alcohol) film are reduced to palladium nanowires by the polymer itself under mild thermal annealing. The chemical reaction occurring in situ inside the polymer film, including byproduct formation, is investigated through electronic absorption and X-ray photoelectron spectroscopy together with atomic force and electron microscopy. The overall process can be described as a novel case of crystal-to-crystal transformation at the nanoscopic level. Optical limiting characteristics of the nanowire-embedded polymer film are explored. The fabrication procedure developed, involving chemistry inside a polymer matrix mediated by the polymer, opens up a convenient route to the fabrication of free-standing metal nanowire-embedded thin films. [source] Fluorescence and photoisomerization studies of p -nitrophenyl-substituted ethenylindolesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2006Anil K. Singh Abstract The synthesis, electronic absorption, fluorescence (,f, ,ex, ,f, ,f) and photoisomerization (,t,c, photostationary state composition) properties of 3-(4-nitrophenylethenyl- E)-NH-indole (1), 3-(4-nitrophenylethenyl- E)- N -ethylindole (2) and 3-(4-nitrophenyl ethenyl- E)- N -benzenesulfonylindole (3) in organic solvents of varying polarity are reported. The absorption maximum of these compounds undergoes a moderate red shift with increasing solvent polarity. However, the fluorescence maximum becomes highly red shifted with increasing solvent polarity. Whereas 1 and 2 show broad fluorescence bands, 3 exhibits dual fluorescence. Further, 1 and 2 fluoresce much more efficiently than 3. Correlation of the Stokes shift with solvent polarity parameters such as ,f and ET(30) and excited-state dipole moment indicate a highly polar excited state for 1,3. Time-resolved fluorescence studies show that the fluorescence decays are single- and multi-exponential type, depending on the solvent polarity. Further, 1 and 2 do not show photoisomerization on irradiation. However, 3 is photoactive and shows efficient photoisomerization in non-polar heptane. The sensitivity (,) of the photoreaction is determined in various solvent in terms of the Hammett plot, which showed that the excited states involved are electron deficient in nature and consequently stabilized more by an electron sufficient polar solvent and electron donating substituent. These results led us to suggest the existence of three types of excited states, namely the locally excited state, the intramolecular charge-transfer excited state and the conformationally relaxed intramolecular charge-transfer excited state in the photoprocesses of these compounds. Copyright © 2005 John Wiley & Sons, Ltd. [source] Photoreduction of iron protoporphyrin IX chloride in non-ionic triton X-100 micelle studied by electronic absorption and resonance Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2001P. K. Shantha Resonance Raman and electronic absorption studies of iron protoporphyrin IX chloride (hemin) in non-ionic Triton X-100 micelle in the absence and presence of hindered imidazole (2-methylimidazole and 1,2-dimethylimidazole) and unhindered imidazole under various experimental conditions are reported. Hemin undergoes photoreduction at the metal center, both in the absence and presence of hindered imidazole, in anaerobic, alkaline and neutral pH conditions on photoexcitation by laser radiation at 441.6 and 457.9 nm. It is inferred from this study that only the monomer hemin encapsulated within the micelle under the alkaline pH conditions is photoreducible. The photoreduction of hemin in this micelle occurs from an electron transfer as a result of dissociation of coordinated hydroxyl ion to the iron atom in the photoexcited state, which may also involve the OH,Fe charge transfer transition around 360 nm. Copyright © 2001 John Wiley & Sons, Ltd. [source] pH sensor based on polyaniline and aniline,anthranilic acid copolymer films using quartz crystal microbalance and electronic absorption spectroscopyPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2008M. M. Ayad Abstract The pH sensitivity based on conducting polyaniline (PANI) and copolymer of aniline and o -anthranilic acid (AA) films were studied using quartz crystal microbalance (QCM) technique and UV,Vis spectroscopy. The sensor was constructed from these polymer films coated on the electrode of the QCM. The resonant frequency changes as a function of pH in the range of 2,12 were measured. These changes are quantitative indication of the degree of dedoping or redoping of the polymer films upon the subsequent exposure of the electrode to 0.25,M sulfuric acid and different pH solutions. There are two linear regressions between the frequency change and pH with two different and opposite slopes in the regions from 2 to 9 and 9 to 12. The pH sensitivity of the copolymer film was found to be less than using the PANI film. Thin films of PANI and copolymer, which were chemically polymerized in a sulfuric acid solution, were deposited onto the inner walls of the quartz cuvettes. The UV,Vis absorption spectra of these films were measured in different pH solutions. Relations between the maximum absorption and its wavelength versus pH were constructed. The copolymer film shows some advantages over the PANI film. The difference between the PANI and copolymer films as pH sensors using the QCM and electronic absorption extends from the determination of pKa for both films. Copyright © 2008 John Wiley & Sons, Ltd. [source] Spectroscopic study on structure of horseradish peroxidase in water and dimethyl sulfoxide mixtureBIOPOLYMERS, Issue 2 2002Yasushi Maeda Abstract The structure of horseradish peroxidase (HRP) in phosphate buffered saline (PBS)/dimethyl sulfoxide (DMSO) mixed solvents at different compositions is investigated by IR, electronic absorption, and fluorescence spectroscopies. The fluorescence spectra and the amide I spectra of ferric HRP [HRP(Fe3+)] show that overall structural changes are relatively small up to 60% DMSO. Although the amide I band of HRP(Fe3+) shows a gradual change in the secondary structure and a decrease in the contents of , helices, its fluorescence spectra indicate that the distance between the heme and Trp173 is almost constant. In contrast, the changes in the positions of the Soret bands for resting HRP(Fe3+) and catalytic intermediates (compounds I and II) and the IR spectra at the CO stretching vibration mode of carbonyl ferrous HRP [HRP(Fe2+)-CO] show that the microenvironment in the distal heme pocket is altered, even with low DMSO contents. The large reduction of the catalytic activity of HRP even at low DMSO contents can be attributed to the structural transition in the distal heme pocket. In PBS/DMSO mixtures containing more than 70 vol % DMSO, HRP undergoes large structural changes, including a large loss of the secondary structure and a dissociation of the heme from the apoprotein. The presence of the components of the amide I band that can be assigned to strongly hydrogen bonding amide CO groups at 1616 and 1684 cm,1 suggests that the denatured HRP may aggregate through strong hydrogen bonds. © 2002 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 67: 107,112, 2002 [source] Mutation of residues critical for benzohydroxamic acid binding to horseradish peroxidase isoenzyme CBIOPOLYMERS, Issue 5 2001Barry D. Howes Abstract Aromatic substrate binding to peroxidases is mediated through hydrophobic and hydrogen bonding interactions between residues on the distal side of the heme and the substrate molecule. The effects of perturbing these interactions are investigated by an electronic absorption and resonance Raman study of benzohydroxamic acid (BHA) binding to a series of mutants of horseradish peroxidase isoenzyme C (HRPC). In particular, the Phe179 , Ala, His42 , Glu variants and the double mutant His42 , Glu:Arg38 , Leu are studied in their ferric state at pH 7 with and without BHA. A comparison of the data with those previously reported for wild-type HRPC and other distal site mutants reaffirms that in the resting state mutation of His42 leads to an increase of 6-coordinate aquo heme forms at the expense of the 5-coordinate heme state, which is the dominant species in wild-type HRPC. The His42Glu:Arg38Leu double mutant displays an enhanced proportion of the pentacoordinate heme state, similar to the single Arg38Leu mutant. The heme spin states are insensitive to mutation of the Phe179 residue. The BHA complexes of all mutants are found to have a greater amount of unbound form compared to the wild-type HRPC complex. It is apparent from the spectral changes induced on complexation with BHA that, although Phe179 provides an important hydrophobic interaction with BHA, the hydrogen bonds formed between His42 and, in particular, Arg38 and BHA assume a more critical role in the binding of BHA to the resting state. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 261,267, 2001 [source] Spectroelectrochemical and Computational Studies on the Mechanism of Hypoxia Selectivity of Copper RadiopharmaceuticalsCHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2008Jason Abstract Detailed chemical, spectroelectrochemical and computational studies have been used to investigate the mechanism of hypoxia selectivity of a range of copper radiopharmaceuticals. A revised mechanism involving a delicate balance between cellular uptake, intracellular reduction, reoxidation, protonation and ligand dissociation is proposed. This mechanism accounts for observed differences in the reported cellular uptake and washout of related copper bis(thiosemicarbazonato) complexes. Three copper and zinc complexes have been characterised by X-ray crystallography and the redox chemistry of a series of copper complexes has been investigated by using electronic absorption and EPR spectroelectrochemistry. Time-dependent density functional theory (TD-DFT) calculations have also been used to probe the electronic structures of intermediate species and assign the electronic absorption spectra. DFT calculations also show that one-electron oxidation is ligand-based, leading to the formation of cationic triplet species. In the absence of protons, metal-centred one-electron reduction gives the reduced anionic copper(I) species, [CuIATSM],, and for the first time it is shown that molecular oxygen can reoxidise this anion to give the neutral, lipophilic parent complexes, which can wash out of cells. The electrochemistry is pH dependent and in the presence of stronger acids both chemical and electrochemical reduction leads to quantitative and rapid dissociation of copper(I) ions from the mono- or diprotonated complexes, [CuIATSMH] and [CuIATSMH2]+. In addition, a range of protonated intermediate species have been identified at lower acid concentrations. The one-electron reduction potential, rate of reoxidation of the copper(I) anionic species and ease of protonation are dependent on the structure of the ligand, which also governs their observed behaviour in vivo. [source] An Experimental and Computational Study on Intramolecular Charge Transfer: A Tetrathiafulvalene-Fused Dipyridophenazine MoleculeCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2007Chunyang Jia Prof. Abstract To study the electronic interactions in donor,acceptor (D,A) ensembles, D and A fragments are coupled in a single molecule. Specifically, a tetrathiafulvalene (TTF)-fused dipyrido[3,2- a:2,,3,- c]phenazine (dppz) compound having inherent redox centers has been synthesized and structurally characterized. Its electronic absorption, fluorescence emission, photoinduced intramolecular charge transfer, and electrochemical behavior have been investigated. The observed electronic properties are explained on the basis of density functional theory. [source] Supramolecular Assembly of 2,7-Dimethyldiazapyrenium and Cucurbit[8]uril: A New Fluorescent Host for Detection of Catechol and DopamineCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2005Vladimir Sindelar Dr. Abstract The formation of a highly stable inclusion complex between 2,7-dimethyldiazapyrenium (Me2DAP2+) and the cucurbit[8]uril host (CB8) was demonstrated by X-ray crystallography; MALDI-TOF mass spectrometry; and 1H NMR, electronic absorption, and emission spectroscopy. The equilibrium association constant was determined to be 8.9(±0.2)×105 L,mol,1 from UV-visible data and 8.4(±1.5)×105 L,mol,1 from fluorescence data. The Me2DAP2+,CB8 inclusion complex acted as a host to bind compounds containing aromatic ,-donor moieties (D), such as catechol and dopamine. This point was demonstrated by 1H NMR spectroscopy, and electrochemical and emission measurements. Fluorescence detection of the Me2DAP2+,D,CB8 ternary complexes was evident in aqueous solution and on the surface of silica particles, to which fluorescent diazapyrenium units had been covalently immobilized. [source] Electronic Structure, Spectra, and Magnetic Circular Dichroism of Cyclohexa-, Cyclohepta-, and CyclooctapyrroleCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2005Alexander Gorski Abstract Three recently obtained expanded porphyrins represent nice examples of compounds for which the electronic and spectral properties can be predicted from symmetry considerations alone. Perimeter-model-based theoretical analysis of the electronic structure of doubly protonated cyclo[6], cyclo[7], and cyclo[8]pyrrole leads to the anticipation of qualitatively the same electronic absorption and magnetic circular dichroism patterns for all three compounds. These predictions are fully confirmed by experiments, as well as DFT and INDO/S calculations. Due to a characteristic pattern of frontier molecular orbitals, a degenerate HOMO and a strongly split LUMO pair, the three cyclopyrroles show comparable absorption intensity in the Q and Soret regions. Magnetic circular dichroism spectra reveal both A and B Faraday terms, of which the signs and magnitudes are in remarkably good agreement with theoretical expectations. The values of the magnetic moments of the two lowest degenerate excited states have also been obtained. [source] Electronic and Vibrational Properties of Fluorenone in the Channels of Zeolite LCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2004André Devaux Dr. Abstract Fluorenone (C13H8O) was inserted into the channels of zeolite L by using gas-phase adsorption. The size, structure, and stability of fluorenone are well suited for studying host,guest interactions. The Fourier transform IR, Raman, luminescence, and excitation spectra, in addition to thermal analysis data, of fluorenone in solution and fluorenone/zeolite L are reported. Normal coordinate analysis of fluorenone was performed, based on which IR and Raman bands were assigned, and an experimental force field was determined. The vibrational spectra can be used for nondestructive quantitative analysis by comparing a characteristic dye band with a zeolite band that has been chosen as the internal standard. Molecular orbital calculations were performed to gain a better understanding of the electronic structure of the system and to support the interpretation of the electronic absorption and luminescence spectra. Fluorenone shows unusual luminescence behavior in that it emits from two states. The relative intensity of these two bands depends strongly on the environment and changes unexpectedly in response to temperature. In fluorenone/zeolite L, the intensity of the 300 nm band (lifetime 9 ,s) increases with decreasing temperature, while the opposite is true for the 400 nm band (lifetime 115 ,s). A model of the host,guest interaction is derived from the experimental results and calculations: the dye molecule sits close to the channel walls with the carbonyl group pointing to an Al3+ site of the zeolite framework. A secondary interaction was observed between the fluorenone's aromatic ring and the zeolite's charge-compensating cations. [source] Luminescent Molecular Copper(I) Alkynyl Open Cubes: Synthesis,,Structural,Characterization, Electronic Structure, Photophysics, and PhotochemistryCHEMISTRY - AN ASIAN JOURNAL, Issue 1-2 2006Chui-Ling Chan Dr. Abstract A novel class of tetranuclear copper(I) alkynyl complexes with an "open-cube" structure was synthesized. The crystal structure of [Cu4{P(p -MeC6H4)3}4(,3 -,1,,1,,2 -C,C- p -MeOC6H4)3]PF6 was determined. These complexes were found to display dual emission behavior. Through systematic comparison studies on the electronic absorption and photoluminescence properties of a series of [Cu4(PR3)4(,3 -,1,,1,,2 -C,CR,)3]+ complexes, together with density functional theory (DFT) calculations at the PBE1PBE level on the model complex [Cu4(PH3)4(,3 -,1,,1,,2 -C,C- p -MeOC6H4)3]+, the nature of their emission origins was probed. Their photochemical properties were also investigated by oxidative quenching experiments and transient absorption spectroscopy. [source] Synthesis and Characterization of Mixed Phthalocyaninato and meso -Tetrakis(4-chlorophenyl)porphyrinato Triple-Decker Complexes , Revealing the Origin of Their Electronic AbsorptionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2004Xuan Sun Abstract Two series of mixed phthalocyaninato and porphyrinato rare earth(III) triple-decker complexes [M2(Pc)(TClPP)2] (1a,10a) and [M2(Pc)2(TClPP)] (1b,11b) [M = Y, La,Er except Ce and Pm; Pc = phthalocyaninate; TClPP = tetrakis(4-chlorophenyl)porphyrinate] have been prepared by treating the half-sandwich complexes [M(TClPP)(acac)] (acac = acetylacetonate), generated in situ from [M(acac)3]·nH2O and H2(TClPP), with Li2(Pc). All the triple-decker complexes have been characterized by a wide range of spectroscopic and electrochemical methods. The molecular structures of [M2(Pc)(TClPP)2] (M = Y, Ho) have also been determined, and show a symmetrical disposition of ligands, with two outer domed TClPP and one inner Pc rings. A systematic investigation of the optical and electrochemical data of these complexes has revealed the nature of the HOMO and LUMO, as well as the origin of the electronic absorptions of these triple-decker complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] | |||||||||||||||||||||||||