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71.
Irina Odinets Tamás Kégl Oleg Artyushin Galina Molchanova Tatyana Mastryukova György Keglevich 《Journal of organometallic chemistry》2005,690(14):3456-3464
Asymmetrical cyclic phosphite and phosphinite ligands of a novel type bearing either trifluoromethyl or pentafluorophenyl group were synthesized using >PCl or >PN< species and racemic fluorinated alcohols. The P-ligands were converted to complexes of RhIII(L)(Cp∗)Cl2 type (where L = phosphite or phosphinite) and, in two instances, their stereostructures were evaluated by X-ray analysis. These complexes along with in situ systems, formed from Rh(CO)2(acac) precursor and the corresponding ligand, were tested in the hydroformylation of styrene. Both systems provided excellent hydroformylation activities at 100 °C. Using the RhI in situ systems, moderate and high regioselectivities towards the branched aldehyde (2-phenyl-propanal) were obtained at 100 and 40 °C, respectively. 相似文献
72.
Ayelet Vilan Tatyana A. Bendikov Hagai Cohen 《Journal of Electron Spectroscopy and Related Phenomena》2008
Secondary electron emission (SEE) is a major player in surface charging during X-ray photoelectron spectroscopy (XPS); its characteristics and applicability as a current source for electrical measurements are studied. We employ sample biasing and a top retarding grid to control the photoelectron current, and further compare their I–V characteristics with direct spectroscopy of the secondary electrons. Using silica-coated gold substrates, the effect of sample work function on the emitted secondary electrons is shown and fine control over the surface potential gradients, in the range of 10–100 meV, is achieved. XPS-based chemically resolved electrical measurements (CREM) can thus be extended to the positive current regime. 相似文献
73.
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75.
The addition of monovalent, divalent, and trivalent metal ions to three anionic ethyl meso-thiacarbocyanine dyes, an ethyl meso-oxacarbocyanine, and an imidacarbocyanine in aqueous solution at room temperature results in the production of J-aggregates within the range of tens to hundreds of seconds. The rate of formation of J-aggregates correlates with the rate of decay of dimers or monomers and is dependent on the type of metal ion, dye structure, and temperature. The rate of formation of J-aggregates increases as the temperature decreases and the dye and salt concentrations increase, and the rate is highest for trivalent ions and smallest for monovalent ions, independent of the type of anion. The time course of formation of J-aggregates is described in most cases by a sigmoidal curve, and the kinetics and mechanism are discussed within the framework of autocatalysis. Computer simulations reveal that the sigmoidal time dependence is transferred to an exponential-like curve by substantially increasing the rate constant for the noncatalytic step. The reaction pathway into J-aggregates can be switched from dimeric ion pairs as the reactant to monomeric ion pairs, when the rate constant for the catalytic step via the monomer becomes larger with respect to that via the dimer. 相似文献
76.
Vladimir E. Vigdergauz Tatyana V. Nedosekina 《Journal of Solid State Electrochemistry》1998,2(1):50-57
Experimental methods for the evaluation of the wettability of electrodes made from natural mineral sulfides are discussed
for the case of potentiostatic polarization. The wettability, induced by xanthates with different lengths of the alkyl chain,
was studied for the case of pyrite, chalcopyrite, galena, arsenopyrite and chalcocite. Therefore measurements of the detachment
force of an air bubble (ABDF) and of the induction time (ABIT) were performed. The first of these allows us to estimate the
conditions for the destruction of the bubble-mineral complex, and the second allows us to estimate the conditions of aggregate
formation under collision. The study was carried out at various polarization potentials in a borate buffer solution. The results
of the measurements are compared with thermodynamic data and with experimental results obtained for representative cases such
as xanthate sorption and flotation recovery. A correlation of the flotation experiments with the ABDF results can be demonstrated.
Received: 28 February 1997 / Accepted: 12 August 1997 相似文献
77.
Afiyatullov SSh Kalinovsky AI Pivkin MV Dmitrenok PS Kuznetsova TA 《Natural product research》2006,20(10):902-908
Three new diterpene glycosides, virescenosides V (1), W (2), and X (3) have been isolated from a marine strain of Acremonium striatisporum KMM 4401 associated with the holothurian Eupentacta fraudatrix. Their structures have been elucidated on the basis of high resolution mass spectrometry, 1D and 2D NMR (1H, 13C, DEPT, COSY 45, COSY RCT, HSQC, HMBC, and NOESY spectra) as 19-O-beta-D-altropyranosyl-7-oxo-isopimara-8(14),15-diene-2alpha,3beta-diol (1), 19-O-beta-D-altropyranosyl-isopimara-7,15-diene-2 alpha,3 beta,6 alpha-triol (2), and 19-O-beta-D-altropyranosyl-isopimara-8,15-diene-2 alpha,3 beta,7 alpha-triol (3). 相似文献
78.
Polyakov NE Leshina TV Salakhutdinov NF Kispert LD 《The journal of physical chemistry. B》2006,110(13):6991-6998
The structure, stability, and reactivity of the host-guest complexes between a set of carotenoids and the triterpene glycoside, beta-glycyrrhizic acid (GA), were investigated by different physicochemical techniques: high-performance liquid chromatography, optical absorption, and fluorescence spectroscopy. It has been demonstrated recently that the molecular complexes of GA with a number of drugs are characterized by reduced toxicity and increased therapeutic activity of these drugs. In the present work it was found that carotenoids form 1:2 complexes with GA in aqueous solutions as well as in polar organic solvents, methanol, acetonitrile, and dimethylsulfoxide. We assume that the structure of the complex is a cycliclike dimer of GA encapsulating a carotenoid molecule. The stability constants in all solvents are near 10(4) M(-1). In addition, GA forms inclusion complexes with carotenoid radical cations, which results in their stabilization. Complex formation (a) decreases the rate of electron transfer from carotenoids to electron acceptors (Fe3+ or quinone) and (b) considerably increases the lifetime of the carotenoid-quinone charge-transfer complex and the yield of the major product (a carotenoid-quinone adduct). A thermodynamic study shows that hydrophobic interactions are the main driving force of the carotenoid-GA complex formation. These results are important for understanding both the nature of GA complexes and the influence of GA on the therapeutic activity of some drugs. Furthermore, carotenoid-GA complexes could be used for the design of artificial light-harvesting, photoredox, and catalytic systems. 相似文献
79.
Huang W Schopfer M Zhang C Howell RC Gee BA Francesconi LC Polenova T 《The journal of physical chemistry. B》2006,110(25):12340-12350
Paramagnetic Eu-substituted Keggin oxopolytungstates crystallize in different forms, determined by the nature of the counterions. The crystal packing is in turn responsible for the variations in the geometry of paramagnetic Eu sites with respect to the anion core. We probed the paramagnetic environments in a series of Eu-substituted Keggin solids, by 31P magic angle spinning NMR spectroscopy. 31P spinning sideband envelopes are dominated by the electron-nuclear dipolar interaction. For the compounds under investigation, both the magnitude and the asymmetry parameter of the electron-nuclear dipolar coupling tensor are sensitive to the mutual arrangements of paramagnetic Eu sites in the crystal lattice. and also report on the stoichiometry of the anion. The electron-nuclear dipolar coupling tensors were calculated from the crystallographic coordinates and the experimentally determined effective magnetic moments, assuming a point dipole approximation. The computed tensors are in very good agreement with the experimental spectra. Furthermore, the P-Eu distance estimates, accurate to within 0.06-0.12 A, can be obtained directly from the magnitude of the electron-nuclear dipolar coupling. This work demonstrates that 31P MAS NMR spectroscopy is a useful probe for investigating local environments in paramagnetic Keggin solids. 相似文献
80.
The kinetics of formation of J-aggregates for 3,3'-bis[sulfopropyl]-R-4',5'-dibenzo-9-ethylthiacarbocyanines (R=5-methoxy; R=4,5-dibenzo) and 3,3'-bis[sulfopropyl]-5,5'-diphenyl-9-ethyloxacarbocyanine were studied in aqueous solution in the presence of gelatin at different pH values and at room and elevated temperatures. Addition of gelatin at concentrations of 0.0005-0.05 wt % to solutions of dyes results in the production of J-aggregates in the tens of seconds to tens of minutes range. The rate of J-aggregate formation increases with increasing concentrations of dye and gelatin, correlates with the rate of decay of dimers, and is also dependent on the dye structure, temperature, and pH. The rate of J-aggregation is increased for and decreased for with an increase in temperature. For and, the rate increases with increasing [H+] and reaches the maximum value at pH 3.3-4.3 for 3. The interaction of with gelatin is considered to be a cooperative binding process, and J-aggregation is characterized by the time-dependent rate constant. Sigmoidal- and nonsigmoidal-type kinetic curves of both formation of J-aggregates and decay of the dimers are best fitted with a stretched exponential function. 相似文献