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Spectroscopic Evidence (spectroscopic + evidence)
Selected AbstractsA Rigid Molecular Scaffold Affixing a (Polypyridine)ruthenium(II)- and a Nickel(II)-Containing Complex: Spectroscopic Evidence for a Weakly Coupled Bichromophoric SystemEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2003Yann Pellegrin Abstract The synthesis of DppztBuSalH2 (7), a rigid conjugated ditopic ligand containing a Dppz (dipyrido[3,2- a:2,,3,- c]phenazine) skeleton and a salophen-type chelate, is reported. The complexes DppztBuSalNi (10), [Ru(bpy)2(DppztBuSalH2)]2+ (11), and [Ru(bpy)2(DppztBuSalNi)]2+ (12) have been prepared and characterised using common spectroscopic methods. Electrochemical, UV/Vis spectroelectrochemical and EPR studies were conducted on compounds 7, 10, 11, and 12. The singly reduced radical forms of 7 and 10 can be generated electrochemically, with the lone electron located on the low-lying phenazine ,*-molecular orbital. Complexes 11 and 12 show several reduction waves and electronic and EPR data obtained for the electrogenerated singly reduced species show them to be closely related to the radical species 7·, and 10·,, respectively. The presence of nickel(II) in compound 12 renders the addition of the second electron on the phenazine group reversible. Both 11 and 12 show common features on the cathodic side of their cyclic voltammograms, with reversible one-electron ruthenium-centred oxidation. An additional low-potential reversible-oxidation wave is observed for 12, and this is ascribed to oxidation of the nickel(II) ion. The combined spectroscopic data best describe the ruthenium-containing complexes as weakly coupled bichromophoric systems. Photophysical studies attest to the formation of a charge-separated state for 11, whereas a strong quenching is detected for 12. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Direct Spectroscopic Evidence that the Photochemical Outcome of Flutamide in a Protein Environment is Tuned by Modification of the Molecular Geometry: A Comparison with the Photobehavior in Cyclodextrin and VesiclesHELVETICA CHIMICA ACTA, Issue 2 2003Salvatore Sortino The photoreactivity of the phototoxic anticancer drug flutamide (FM) in the presence of bovine serum albumin (BSA) has been investigated. The presence of BSA induces a remarkable modification of the photochemical outcome of the drug with respect to that observed in aqueous solution. Induced circular dichroism (ICD) measurements combined with theoretical calculations provide strong evidence that the new photochemical scenario is tuned by changes of the molecular geometry of FM when incorporated in the protein microenvironment. This behavior presents close analogies to that found in the presence of either cyclodextrin or phospholipid vesicles, chosen as models for biological systems, and delineates a quite general photochemical picture that can be useful for a more appropriate understanding of the adverse phototoxic effects induced by this drug. [source] Direct Spectroscopic Evidence for a Photodoping Mechanism in Polythiophene and Poly(bithiophene- alt -thienothiophene) Organic Semiconductor Thin Films Involving Oxygen and Sorbed MoistureADVANCED MATERIALS, Issue 46 2009Jing-Mei Zhuo Direct infrared spectroscopic evidence has been obtained for photodoping of high mobility regioregular poly(3-alkylthiophene) and poly[2,5-bis(3-alkyllthiophen-2-yl) thieno (3,2-b)thiophene] with the attendant formation of hydroxide counter-ions. This reveals the central role of dissolved water, explains the key features of degradation of the electrical characteristics of organic semiconductors in the ambient (see figure), and points to possible strategies to further improve their stability. [source] Direct Solid-State NMR Spectroscopic Evidence for the NH4AlF4 Crystalline Phase Derived from Zeolite HY Dealuminated with Ammonium HexafluorosilicateCHEMINFORM, Issue 48 2006Hsien-Ming Kao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Spectroscopic Evidence for a Dinitrogen Complex of Gallium and Estimation of the Ga,N2 Bond Strength.CHEMINFORM, Issue 7 2006Hans-Joerg Himmel Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access the actual ChemInform Abstract, please click on HTML or PDF. [source] Highly Active and Recyclable Heterogeneous Iridium Pincer Catalysts for Transfer Dehydrogenation of AlkanesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Zheng Huang Abstract Pincer-ligated iridium complexes have proven to be highly effective catalysts for the dehydrogenation and transfer-dehydrogenation of alkanes. Immobilization onto a solid support offers significant potential advantages in the application of such catalysts particularly with respect to catalyst separation and recycling. We describe three approaches toward such immobilization: (i) covalent attachment to a Merrifield resin, (ii) covalent bonding to silica via a pendant alkoxysilane group, and (iii) adsorption on ,-alumina (,-Al2O3), through basic functional groups on the para- position of the pincer ligand. The simplest of these approaches, adsorption on ,-Al2O3, is also found to be the most effective, yielding catalysts that are robust, recyclable, and comparable to or even more active than the corresponding species in solution. Spectroscopic evidence (NMR, IR) and studies of catalytic activity support the hypothesis that binding occurs at the para- substituent and that this has only a relatively subtle and indirect influence on catalytic behavior. [source] Linear Coinage Metal Complexes Stabilized by a Group 13 Metalloid LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 28 2010Ganesan Prabusankar Abstract The synthesis and structural characterization of the linear, cationic complex [{(DDP)Ga}2Cu][OTf]·2C6H5F (2, Tf = O2SCF3) stabilized by the monodentate, gallium-based ligand Ga(DDP) (DDP = [HC{(CMe)N(2,6- iPr2C6H3)}2],), as well as NMR spectroscopic evidence for the formation of the corresponding silver compound [{(DDP)Ga}2Ag][Al(hfip)4] (3, hfip = [OC(H)(CF3)2]), are reported. The remarkable steric properties of this gallium-based ligand permit the stabilization of 2, which exhibits an unusual linear geometry and a coordination number of two. [source] Four New Triterpenes from Anchusa azurea var. azureaHELVETICA CHIMICA ACTA, Issue 3 2010e Kuruüzüm-Uz Abstract Four new triterpene glycosides, named oleanazuroside 1 (1), oleanazuroside 2 (2), ursolazuroside 1 (3), and ursolazuroside 2 (4), together with the seven known compounds 5,11, were isolated from the MeOH extract of the aerial parts of Anchusa azureaMiller var. azurea. Their structures were elucidated by means of spectroscopic evidence (UV, IR, MALDI-MS, and 1D- and 2D-NMR). The radical-scavenging activities against 2,2-diphenyl-1-picrylhydrazyl (DPPH) of the BuOH extract and of 8 and 10 were very strong (Table,5). [source] Selenium-Containing Heterocycles from Isoselenocyanates: Base-Catalyzed Reaction of Malononitrile with Phenyl Isoselenocyanate and Bromoacetonitrile or , -Halogenated KetonesHELVETICA CHIMICA ACTA, Issue 10 2007Geoffroy Abstract The reaction of phenyl isoselenocyanate (1a) with malononitrile (=propanedinitrile) in DMF in the presence of Et3N leads to the intermediate ketene N,Se-hemiacetal 6a, which can be trapped with bromoacetonitrile or , -halogenated ketones 12a and 12b (Scheme,3). The products are [(alkylseleno)(phenylamino)methylene]malononitriles 10 and 13, which are obtained in good yield. In the case of the (2-oxoalkyl)seleno derivatives 13, they are in equilibrium with the cyclic hemiacetals 14. Chemical and spectroscopic evidence for the structures of the new compounds are described. The structure of 14a was established by X-ray crystallography. [source] Selenium-Containing Heterocycles from Isoselenocyanates: Synthesis of 1,3-Selenazinane and 1,3-Selenazinanone DerivativesHELVETICA CHIMICA ACTA, Issue 3 2007Geoffroy Abstract The reaction of the intermediate ketene N,Se-hemiacetal 3, prepared from cyanomethylene derivatives 1 by treatment with Et3N and aryl isoselenocyanates 2, with bis-electrophiles 6, 7, 9, and 11 in DMF affords tetrahydro-1H -1,3-selenazine (=1,3-selenazinane) derivatives 8, 10, and 12 in good yield (Scheme,2 and Tables,1,3). Chemical and spectroscopic evidence for the structures of the new compounds are described. The structures of 8d and 12e are established by X-ray crystallography (Figs.,1 and 2). [source] Phenyl and Phenylethyl Glycosides from Picrorhiza scrophulariifloraHELVETICA CHIMICA ACTA, Issue 3 2004Sheng-Xiong Huang Three new phenyl glycosides, scrophenoside A (1), B (2), and C (3), and two new phenylethyl glycosides, scroside D (4) and scroside E (5), were isolated from the stem of Picrorhiza scrophulariifloraPennell (Scrophularlaceae), besides five known compounds. On the basis of spectroscopic evidence, the structures of the new compounds were elucidated as 4-acetyl-2-methoxyphenyl 6- O -[4-(, - D -glucopyranosyloxy)vanilloyl]- , - D -glucopyranoside (1), 4-acetylphenyl 6- O -[(E)- p -coumaroyl]- , - D -glucopyranoside (2), 4-[(1R)- and (1S)-1-hydroxyethyl]-2-methoxyphenyl , - D -glucopyranoside (3a and 3b, resp.), 2-(3,4-dihydroxyphenyl)ethyl O - , - D -glucopyranosyl-(1,3)-4- O -[(E)-feruloyl]- , - D -glucopyranoside (4), and 2-(3,4-dihydroxyphenyl)ethyl O - , - D -glucopyranosyl-(1,3)-6- O -[(E)-feruloyl]- , - D -glucopyranoside (5). [source] Direct Spectroscopic Evidence for a Photodoping Mechanism in Polythiophene and Poly(bithiophene- alt -thienothiophene) Organic Semiconductor Thin Films Involving Oxygen and Sorbed MoistureADVANCED MATERIALS, Issue 46 2009Jing-Mei Zhuo Direct infrared spectroscopic evidence has been obtained for photodoping of high mobility regioregular poly(3-alkylthiophene) and poly[2,5-bis(3-alkyllthiophen-2-yl) thieno (3,2-b)thiophene] with the attendant formation of hydroxide counter-ions. This reveals the central role of dissolved water, explains the key features of degradation of the electrical characteristics of organic semiconductors in the ambient (see figure), and points to possible strategies to further improve their stability. [source] Tyrosinase inhibitors isolated from the roots of Paeonia suffruticosaINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 2 2010H. -Y. J. Cosmet. Sci., 60, 347,352 (May/June 2009) Accepted for publication November 6, 2008. Synopsis The inhibition of mushroom tyrosinase by Paeonia suffruticosa root-derived materials was evaluated. Six tyrosinase inhibitors were isolated by ethanol extraction, n -hexane, ethyl acetate, n -BuOH, and water partition, silica gel column chromatography, Sephadex LH-20, Lobar PR-8, and high-performance liquid chromatography methods, and they were identified as kaempferol (I), quercetin (II), mudanpioside B (III), benzoyloxypaeoniflorin (IV), mudanpioside H (V), and pentagalloyl-,-D-glucose (VI) on the basis of spectroscopic evidence. The inhibitory activities of compounds I to VI against mushroom tyrosinase were determined with IC50 values of 0.120, 0.108, 0.368, 0.453, 0.324, and 0.063 mM, respectively. The kinetic study indicated that all purified inhibitors acted competitively for the L-dopa binding site of the enzyme, with an exception of compound VI, which acted non-competitively. [source] Highly Ordered Interstitial Water Observed in Bone by Nuclear Magnetic Resonance,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2005Erin E Wilson Abstract NMR was used to study the nanostructure of bone tissue. Distance measurements show that the first water layer at the surface of the mineral in cortical bone is structured. This water may serve to couple the mineral to the organic matrix and may play a role in deformation. Introduction: The unique mechanical characteristics of bone tissue have not yet been satisfactorily connected to the exact molecular architecture of this complex composite material. Recently developed solid-state nuclear magnetic resonance (NMR) techniques are applied here to the mineral component to provide new structural distance constraints at the subnanometer scale. Materials and Methods: NMR dipolar couplings between structural protons (OH, and H2O) and phosphorus (PO4) or carbon (CO3) were measured using the 2D Lee-Goldburg Cross-Polarization under Magic-Angle Spinning (2D LG-CPMAS) pulse sequence, which simultaneously suppresses the much stronger proton-proton dipolar interactions. The NMR dipolar couplings measured provide accurate distances between atoms, e.g., OH and PO4 in apatites. Excised and powdered femoral cortical bone was used for these experiments. Synthetic carbonate (,2-4 wt%)-substituted hydroxyapatite was also studied for structural comparison. Results: In synthetic apatite, the hydroxide ions are strongly hydrogen bonded to adjacent carbonate or phosphate ions, with hydrogen bond (O-H) distances of ,1.96 Å observed. The bone tissue sample, in contrast, shows little evidence of ordered hydroxide. Instead, a very ordered (structural) layer of water molecules is identified, which hydrates the small bioapatite crystallites through very close arrangements. Water protons are ,2.3-2.55 Å from surface phosphorus atoms. Conclusions: In synthetic carbonated apatite, strong hydrogen bonds were observed between the hydroxide ions and structural phosphate and carbonate units in the apatite crystal lattice. These hydrogen bonding interactions may contribute to the long-range stability of this mineral structure. The biological apatite in cortical bone tissue shows evidence of hydrogen bonding with an ordered surface water layer at the faces of the mineral particles. This structural water layer has been inferred, but direct spectroscopic evidence of this interstitial water is given here. An ordered structural water layer sandwiched between the mineral and the organic collagen fibers may affect the biomechanical properties of this complex composite material. [source] Photosensitized DNA Damage: The Case of Fluoroquinolones,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Virginie Lhiaubet-Vallet This review focuses on DNA damage photosensitized by the fluoroquinolone (FQ) antibacterial drugs. The in vivo evidence for photocarcinogenesis mediated by FQs is presented in the introduction. The different methods employed for detection of DNA-photodamage mediated by FQs are then summarized, including gel electrophoresis (with whole cells, with isolated DNA and with oligonucleotides) and chromatographic analysis (especially HPLC with electrochemical and MS/MS detection). The chemical mechanisms involved in the formation of the reported lesions are discussed on the basis of product studies and transient spectroscopic evidence. In general, the literature coverage is limited to the last decade, although some earlier citations are also included. [source] Porphyrin Bleaching and PDT-induced Spectral Changes are Irradiance Dependent in ALA-sensitized Normal Rat Skin In Vivo,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2001Jarod C. Finlay ABSTRACT Photobleaching kinetics of aminolevulinic acid,induced protoporphyrin IX (PpIX) were measured in the normal skin of rats in vivo using a technique in which fluorescence spectra were corrected for the effects of tissue optical properties in the emission spectral window through division by reflectance spectra acquired in the same geometry and wavelength interval and for changes in excitation wavelength optical properties using diffuse reflectance measured at the excitation wavelength. Loss of PpIX fluorescence was monitored during photodynamic therapy (PDT) performed using 514 nm irradiation. Bleaching in response to irradiances of 1, 5 and 100 mW cm,2 was evaluated. The results demonstrate an irradiance dependence to the rate of photobleaching vs irradiation fluence, with the lowest irradiance leading to the most efficient loss of fluorescence. The kinetics for the accumulation of the primary fluorescent photoproduct of PpIX also exhibit an irradiance dependence, with greater peak accumulation at higher irradiance. These findings are consistent with a predominantly oxygen-dependent photobleaching reaction mechanism in vivo, and they provide spectroscopic evidence that PDT delivered at low irradiance deposits greater photodynamic dose for a given irradiation fluence. We also observed an irradiance dependence to the appearance of a fluorescence emission peak near 620 nm, consistent with accumulation of uroporphyrin/coproporphyrin in response to mitochondrial damage. [source] Solution NMR evidence for a cis Tyr-Ala peptide group in the structure of [Pro93Ala] bovine pancreatic ribonuclease APROTEIN SCIENCE, Issue 2 2000Ying Xiong Abstract Proline peptide group isomerization can result in kinetic barriers in protein folding. In particular, the cis proline peptide conformation at Tyr92-Pro93 of bovine pancreatic ribonuclease A (RNase A) has been proposed to be crucial for chain folding initiation. Mutation of this proline-93 to alanine results in an RNase A molecule, P93A, that exhibits unfolding/refolding kinetics consistent with a cis Tyr92-Ala93 peptide group conformation in the folded structure (Dodge RW, Scheraga HA, 1996, Biochemistry 35:1548,1559). Here, we describe the analysis of backbone proton resonance assignments for P93 A together with nuclear Overhauser effect data that provide spectroscopic evidence for a type VI ,-bend conformation with a cis Tyr92-Ala93 peptide group in the folded structure. This is in contrast to the reported X-ray crystal structure of [Pro93Gly]-RNase A (Schultz LW, Hargraves SR, Klink TA, Raines RT, 1998, Protein Sci 7:1620,1625), in which Tyr92-Gly93 forms a type-II ,-bend with a trans peptide group conformation. While a glycine residue at position 93 accommodates a type-II bend (with a positive value of ø93), RNase A molecules with either proline or alanine residues at this position appear to require a cis peptide group with a type-VI ,-bend for proper folding. These results support the view that a cis Pro93 conformation is crucial for proper folding of wild-type RNase A. [source] Neutron powder diffraction study of orthorhombic and monoclinic defective silicaliteACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2000G. Artioli The crystal structure of silicalite (SiO2) with a substantial amount of structural hydroxyl groups [Si(1,x)O(2,4x)(OH)4x, with 0.08 < x < 0.10] has been refined from neutron powder diffraction data measured using the HRPD instrument at the ISIS pulsed neutron source. Powder data were collected on the as-synthesized orthorhombic sample at 298,K, and on the deuterated monoclinic sample at 100,K. Preferential location of Si-atom vacancies was found on four out of 12 independent T sites in the orthorhombic silicalite [Si(6), Si(7), Si(10) and Si(11)], although the H atoms of the substituting hydroxyl groups could not be located because of the low statistical site occupancy on multiple sites. No significant population of D atoms or of Si vacancies was found in the tetrahedral sites of the monoclinic sample. The detected long-range order of adjacent Si atoms in defective orthorhombic [MFI] structures is compatible with a mechanism of Si vacancy clustering and with the model of hydroxyl nests assumed in the literature on the basis of IR spectroscopic evidence. Crystal data: orthorhombic, Pnma, Z = 8, a = 20.0511,(1), b = 19.8757,(1), c = 13.36823,(9),Å, V = 5327.62,(5),Å3, Dx = 1.798,g,cm,3, Mr = 721.01; monoclinic, P21/n, Z = 4, a = 19.8352,(2), b = 20.0903,(2), c = 13.3588,(1),Å, , = 90.892,(1)°, V = 5322.78,(6),Å3, Dx = 1.799,g,cm,3, Mr = 1442.02. [source] Synthesis and characterization of some dibutylbis{5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoato}tin(IV) compounds.APPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2003Toxicity studies of di-, tri-organotin complexes on the second instar of Aedes aegypti mosquito larvae Abstract The preparation and spectroscopic characterization of some complexes of the type Bu2Sn(LH)2 (LH = 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoate) are reported. On the basis of spectroscopic evidence (1H, 13C, 119Sn NMR, IR and 119mSn Mössbauer) the compounds were judged to adopt the usual dicarboxylato structural type with a skew trapezoidal arrangement. This was further confirmed by X-ray crystallography in the case of Bu2Sn(L5H)2 (L5H = 5-[(E)-2-(4-chlorophenyl)-1-diazenyl]-2-hydroxybenzoate). Toxicity studies of the di- and tri-organotin compounds on the second larval instar of Aedes aegypti mosquito larvae are reported. Copyright © 2003 John Wiley & Sons, Ltd. [source] Synthesis of the First Chiral Bidendate Bis(trifluoromethyl)phosphane Ligand through Stabilization of the Bis(trifluoromethyl)phosphanide Anion in the Presence of AcetoneCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2006Berthold Hoge Priv.-Doz. Abstract Lewis acid/Lewis base adduct formation of the P(CF3)2, ion and acetone leads to a reduced negative hyperconjugation and, therefore, limits the CF bond activation. The resulting increased thermal stability of the P(CF3)2, ion in the presence of acetone allows selective substitutions and enables the synthesis of the first example of a chiral, bidentate bis(trifluoromethyl)phosphane ligand: a DIOP derivative, [(2,2-dimethyl-1,3-dioxolane-4,5-diyl)bis(methylene)]bis(diphenylphosphane), in which the phenyl groups at the phosphorus atoms are replaced by strong electron-withdrawing trifluoromethyl groups. The resulting high electron-acceptor strength of the synthesized bidentate (CF3)2P ligand is demonstrated by a structural and vibrational study of the corresponding tetracarbonyl,molybdenum complex. The stabilization of the P(CF3)2, ion in the presence of acetone is based on the formation of a dynamic Lewis acid/Lewis base couple, (CF3)2PC(CH3)2O,. Although there is no spectroscopic evidence for the formation of the formulated alcoholate ion, the intermediate formation of (CF3)2PC(CH3)2O, could be proved through the reaction with (CF3)2PP(CF3)2, which yields the novel phosphane,phosphinite ligand (CF3)2PC(CH3)2OP(CF3)2. This ligand readily forms square-planar Pt(II) complexes upon treatment with solid PtCl2. [source] | |||||||||||||||||||||||||