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Selected AbstractsDivanadium(V) and Trapped Valence Linear Tetravanadium(IV,V,V,IV) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2009Anindita Sarkar Abstract In an acetonitrile/water mixture, reactions of the N,N,-bis(diacetyl)hydrazine (H2diah), bis(acetylacetonato)oxidovanadium(IV) [VO(acac)2] and monodentate N -coordinating heterocycles (hc) in a 1:2:2 mol ratio provide yellow divanadium(V) complexes of formula [(hc)O2V(,-diah)VO2(hc)] (1, hc = imidazole; 2, hc = pyrazole; 3, hc = 3,5-dimethyl pyrazole). On the other hand, in the same solvent mixture reactions of the same reagents in a 1:4:2 mol ratio produce green linear tetravanadium(IV,V,V,IV) complexes of formula [(acac)2OV(,-O)VO(hc)(,-diah)(hc)OV(,-O)VO(acac)2] (4, hc = imidazole; 5, hc = pyrazole; 6, hc = 3,5-dimethyl pyrazole). The complexes 1,6 have been characterized by elemental analysis, magnetic susceptibility, and various spectroscopic and electrochemical measurements. The X-ray crystal structures of 1, 3 and 6 have been determined. In all three structures, the diazine ligand diah2, is in trans configuration. Metal-centred bond parameters are consistent with the localized electronic structure of the two trans -bent {OV(,-O)VO}3+ cores present in 6. The pentavalent metal centres in 1, 3 and 6 are in a distorted trigonal-bipyramidal N2O3 coordination environment, while the terminal tetravalent metal centres in 6 are in a distorted octahedral O6 coordination sphere. The eight-line EPR spectra of the tetravanadium species (4,6) in dimethyl sulfoxide at ambient temperature indicate the rare valence localized electronic structure in the fluid phase. All the complexes are redox active and display metal-centred electron transfer processes in dimethyl sulfoxide solution. A reduction within ,0.78 to ,0.94 V (vs. Ag/AgCl) is observed for the divanadium(V) species 1,3, while a reduction and an oxidation are observed in the potential ranges ,0.82 to ,0.90 V and 0.96 to 1.12 V (vs. Ag/AgCl), respectively, for the tetravanadium species 4,6. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Selective control of voltage polarity in a single-chamber solid-oxide fuel cell using the same catalytic electrodes with different sizesIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 5 2008Akiyoshi Nagata Member Abstract The selective control of the voltage polarity in a single-chamber solid-oxide fuel cell (SC-SOFC) constituting the anode and cathode arranged at the same electrolyte surface of yttria-stabilized zirconia (YSZ) or samaria-doped ceria (SDC) and which can operate in a flowing mixture of hydrogen and oxygen is discussed on the basis of the dissociation and adsorption reactions due to the catalytic materials and electrode configurations. The open circuit voltage (OCV) of SC-SOFC showed the highest value when the H2:O2 ratio was around 2:1, which might be equal to the mol ratio of oxygen and hydrogen based on the reaction of water formation by the electrochemical reaction in the cell. The voltage polarity of the cell using the Pt and LSM (La0.7Sr0.3MnO3) catalysts was the same as in the conventional SOFC such that in the Pt catalysis the anode became negative whereas in the LSM catalysis the cathode was independent of the electrode configurations. In SC-SOFC using the same Pt catalyst, the larger Pt electrode functioned as the cathode desorbing the oxide ion conducting in YSZ or SDC. As a result, it was confirmed that the voltage polarity of SC-SOFC could be selectively controlled by making use of the same catalytic electrodes with different sizes, and that the I,V characteristic of the cell improved by using SDC with Pt electrodes with a surface area ratio of 2:1. © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Hydrolysis-improved thermosensitive polyorganophosphazenes with ,-amino-,-methoxy-poly(ethylene glycol) and amino acid esters as side groupsPOLYMER INTERNATIONAL, Issue 9 2005Sang Beom Lee Abstract A series of hydrolysis-improved thermosensitive polyorganophosphazenes with ,-amino-,-methoxy-poly(ethylene glycol) (AMPEG) and amino acid esters (AAEs) of ,N,N -systems' was synthesized, and their properties were evaluated in comparison with the thermosensitive polyorganophosphazenes with methoxy-poly(ethylene glycol) (MPEG) and AAEs of ,O,N -systems', by means of 31P NMR spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). Most of the present polymers showed a lower critical solution temperature (LCST) in the range 32.0,79.0 °C, depending on the kinds of AAE, length of AMPEG and the mol ratio of the two substituents. These polymers exhibited higher LCSTs and faster degradation rates than the MPEG-based polymers. The aqueous solution of poly(ethyl glycinate phosphazene)- graft -poly(ethylene glycol) [NP(GlyEt)0.94(AMPEG350)1.06]n did not show an LCST, which is presumed to be due to its high hydrophilicity, in contrast to [NP(GlyEt)1.01(MPEG350)0.99]n which showing an LCST at 77.5 °C. On the other hand, the polymers with a high content of AAE or with hydrophobic amino acids such as L -aspartic acid and L -glutamic acid, have shown a similar LCST to those of the MPEG-based polymers. The half-lives (t1/2) for hydrolysis of [NP(AMPEG350)1.06(GlyEt)0.94]n at pH 5, 7.4 and 10 were 9, 16, and 5 days, respectively, which are almost 2.5 to 4 times faster than that of the MPEG-based polymers. The LCST of the present N,N -polymers has been shown to be more influenced by salts such as NaCl (,salting-out' effect) and tetrapropylammonium bromide (TPAB) (,salting-in' effect) compared with the ,O,N -system'. Such differences of the ,N,N -systems' from the ,O,N -systems' in thermosensitivity, hydrolysis behavior and salt effect seem to be due to the higher hydrophilicity of the amino group in AMPEG. Copyright © 2005 Society of Chemical Industry [source] Temperature and pH sensitive ionic hydrogels based on new crosslinkersPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2005Ayman M. Atta Abstract New crosslinkers were synthesized from reaction of melamine with acryloyl and methacryloyl chloride in the presence of 1-methyl-2-pyrrolidone as a solvent and triethyl amine as acid acceptor. The chemical structures of the prepared crosslinkers were elucidated from FT-IR, 1H-NMR and 13C-NMR analyses. Linear 2-acrylamido-2-methyl-1-propane sulfonic acid and methacrylic acid (AMPS/MAA) copolymers were prepared and their viscometric properties in aqueous solution were investigated. Different weight percentages of the prepared crosslinkers were used as crosslinking agent (AMPS/MAA) to prepare ionic copolymers using ammonium persulfate as initiator. The percentage of crosslinkers was varied from 0.5 to 4,wt%. The swelling behaviors of crosslinked AMPS/MAA gels in deionized water were measured at different pH and temperatures. All AMPS/MAA copolymers exhibit faster deswelling rate at 50°C except for the copolymer containing 0.9 (mol ratio) AMPS. Copyright © 2005 John Wiley & Sons, Ltd. [source] Gas-phase hydrodechlorination of chlorobenzenes over silica-supported palladium and palladium,ytterbium,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 6-7 2003Satyakrishna Jujjuri Abstract A 5% w/w palladium loading on silica has been achieved via impregnation of the support with Pd(C2H3O2)2 and { (DMF)10Yb2[Pd(CN)4]3} , precursors to deliver monometallic (Pd/SiO2) and bimetallic (Yb,Pd/SiO2) catalyst systems respectively. The catalytic action of each has been assessed in the continuous gas-phase hydrodechlorination (HDC) of chlorobenzene (CB) and 1,2-dichlorobenzene (1,2-DCB) (T = 423 K, inlet chlorine/palladium mol ratio of 5 × 103 h,1) and the hydrogenation of benzene (T = 423 K, inlet C6H6/palladium mol ratio of 35 h,1). Activation of both catalysts delivered similar palladium crystallite size distributions with an average palladium diameter of 5,6 nm where the ytterbium component (in Yb,Pd/SiO2) was present as a thin surface coating. The Pd,Yb bimetallic exhibited significantly higher HDC and hydrogenation activities, the former manifested by significantly greater fractional dechlorinations and benzene selectivities/yields. Yb/SiO2 proved inactive in terms of promoting hydrogen scission or addition and the promotional effect of ytterbium in Yb,Pd/SiO2 is discussed in terms of electron donation and hydrogen transfer via surface YbH2. Under identical reaction conditions, a lower HDC activity was recorded for 1,2-DCB compared with CB, a response that is attributed to steric constraints allied to the deactivating effect of the second chlorine substituent. Both Pd/SiO2 and Yb,Pd/SiO2 exhibited a decline in HDC activity with time-on-stream, but the bimetallic was significantly more resistant to deactivation. Copyright © 2003 John Wiley & Sons, Ltd. [source] Anti-Inflammatory and Anti-Tumor-Promoting Effects of Triterpene Acids and Sterols from the Fungus Ganoderma lucidumCHEMISTRY & BIODIVERSITY, Issue 2 2007Toshihiro Akihisa Abstract A series of lanostane-type triterpene acids, including eleven lucidenic acids (3, 4, 9, 10, 13,19) and six ganoderic acids (20,22, 24, 26, 27), as well as six sterols (28,33), all isolated from the fruiting bodies of the fungus Ganoderma lucidum, were examined for their inhibitory effects on the induction of Epstein,Barr virus early antigen (EBV-EA) by 12- O -tetradecanoylphorbol-13-acetate (TPA) in Raji cells, a known primary screening test for anti-tumor promoters. All of the compounds tested, except for ganolactone (27) and three sterols (29,31), showed potent inhibitory effects on EBV-EA induction, with IC50 values of 235,370,mol ratio/32,pmol TPA. In addition, nine lucidenic acids (1, 2, 5,8, 11, 12, 18) and four ganoderic acids (20, 23,25) were found to inhibit TPA-induced inflammation (1,,g/ear) in mice, with ID50 values of 0.07,0.39,mg per ear. Further, 20-hydroxylucidenic acid N (18) exhibited inhibitory effects on skin-tumor promotion in an in vivo two-stage mouse-skin carcinogenesis test based on 7,12-dimethylbenz[a]anthracene (DMBA) as initiator, and with TPA as promoter. [source] | |||||||||||||