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991.
The electrochemical oxidation of sulfur amino acids has been investigated by ac measurements and cyclic voltammetry at solid electrodes (Au, vitreous carbon). Electrochemical oxidation proceeds first in the adsorbed state and second by diffusion at metal electrodes. Electrochemical oxidation is catalyzed by a labile metal oxide. At vitreous carbon electrode oxidation in the adsorbed state is only present in the case of methionine. XPS studies have shown the presence of
as intermediate species. To explain the experimental results a reaction path is proposed.  相似文献   
992.
The results of the extraction of HCl by TDPO in benzene and the co-extraction of water are discussed. From the infrared spectra of normal (HCl-H2O) and deuterated (DCl-D2O) systems it may be concluded that TDPO·HCl·H2O is formed in the organic phase on extraction from aqueous solutions with cHCl≤5M, and TDPO·HCl with cHCl>5M. Compounds such as TDPO·2HCl are found in the organic phase if there is an excess of HCl in the organic phase. From cryoscopic and viscosity measurements of the organic phase, conclusions can be made about the presence of polymeric compounds in this phase.  相似文献   
993.
The distribution of valency electron density in Cu2As (C38) has been determined by Fourier synthesis using as coefficients the values ΔF = Fobs ? Fcore (Fcore corresponds to the structure factors of the inner orbitals). The bonding between the pyramidal-site copper atoms and the arsenic atoms is exposed, as well as the bonding between tetrahedral-site and pyramidal-site copper atoms.The structural evolution of the unit cell from the Cu2Sb-type (C38) to the Fe2P-type (C22) and Co2P-type (C23) can be related to the metal-metalloid interaction. This interaction mainly involves the pyramidal-site metal atoms in the Cu2Sb-type, and the tetrahedral-site metal atoms in the Fe2P- and Co2P-types.  相似文献   
994.
The stacked foil technique was used in combination with γ-ray spectroscopy to obtain excitation functions for the production of different nuclei using natural vanadium as target and 85 MeV α-particles and 46.5 MeV deuterons as projectiles. The data are compared with theoretical predictions provided by an equilibrium and pre-equilibrium reaction model. In most cases the theoretical predictions seriously under-estimated the measured cross sections.  相似文献   
995.
The principles and techniques of dynamic light scattering (DLS) are outlined and its application to the study of suspensions of interacting colloidal particles is discussed. We show how, under appropriate conditions, DLS can measure long-time collective and self-diffusion coefficients as well as study short-time motions (characterized by the cumulants). These theoretical considerations are illustrated by experimental data. Finally, we discuss the relevance of certain characteristic timescales to theories of the diffusion of interacting particles.  相似文献   
996.
A series of sulphide-containing pyridines of general formula ? (CH2)x? S? R where R = CH3, C2H5, CH2CH2OH and x = 1, 2 has been prepared and studied potentiometrically in the presence of Ag+ in 0.5 M (K)NO3 medium at 25°C. The complex formation is discussed in terms of the Taft σ*-parameters for the substituents. In acid region, where the complexes AgLH2+ and AgL2H23+ were formed, coordination occurs through the thioether group. In neutral and alkaline medium their was evidence for the species AgL2H2+, AgL+, AgL2+, Ag2L22+ and Ag2L2+ in which Ag+? S and Ag+? bonds are involved. The five membered chelate rings for the AgL+ and AgL2+ species are found to be more stable than the six-membered ones.  相似文献   
997.
The influence of rhenium on the behavior of a Pt/Al2O3 catalyst was studied in n-hexane reaction by means of dilution of the catalyst bed with Re/Al2O3. Parallel to activity, selectivity and ageing data obtained in slug pulse and continuous flow reactors, the amount of the surface carbon formed during the reaction was determined and its reactivity in hydrogen atmosphere was also studied. It is suggested that in the presence of rhenium due to the increase in the amount of hydrogen available for hydrogen consuming reactions including hydrodepolymerization of the carbonaceous surface overlayer, the routes of ageing processes are changed, resulting in lower carbon content on the catalyst and less pronounced catalyst deactivation.
Pt/Al2O3 -, Re/Al2O3. , , , , . , , , , , , , .
  相似文献   
998.
The effect of a range of 10 organic nitriles on the radiation-induced polymerization of styrene was studied. A dose rate of 4.4 rad s?1 was used. A rate of polymerization of styrene (1.744 mol L?1 of toluene solution) of 5.0 × 10?7 mol L?1 s?1 was found. With organic nitriles present (styrene:nitrile ratio of 1:0.28) the rate of polymerization increased. Rates in the range of 5.5 × 10?7 ?5.2 × 10?6 mol L?1 s?1, depending on the nitrile present, were obtained. The polymers were partially characterized and evidence of involvement of each of the nitriles in the polymer chains was revealed. The increase in rate of polymerization has been attributed to the part played by nitrile radicals in the initiation of styrene polymerization. Radical yield values [as G(nitrile radical)] were derived from the relevant rate expressions. Values ranged from 2.7 to 49.5, depending on the particular nitrile. Corresponding values of G(nitrile radical) in the range of 5.1–129.4 were obtained by the manipulation of number-average molar mass data. Values of kpkt of approximately 2 × 10?5 L mol?1 s?1 were found. Trommsdorff types of effect are absent from these systems.  相似文献   
999.
The influence of catalysis on chemical modification of 1,2-polybutadienes (Mn < 10,000) by CX3Z reagents (X = halogen; Z = functional group or halogen), in order to obtain polymers soluble in common solvents, has been studied. The work has been carried out with carbon tetrachloride, trichloromethylphosphonyldichloride (CCl3POCl2) and ethyl trichloroacetate (CCl3CO2Et) in the presence of solvents such as C6H6, CH2Cl2. Among the compounds tested as catalysts for the addition of CX3Z to 1,2-polybutadiene (transition metal salts and complexes; radical initiators) only the systems formed with metal salts such as CuCl2, FeCl3, RuCl3 3H2O, Fe2(CO)9 and Cl2Ru(PPh3)3 were found to show high catalytic activity. The most active is Cl2Ru(PPh3)3: used without or with cocatalysts (Et3NHCl/benzôin, alcohols), it leads always, to the best yields whatever the nature of CX3Z. The activity of the other catalysts is generally dependent on CX3Z structure. Some secondary reactions (cross-linking, cyclization, transesterification) have been found.  相似文献   
1000.
We report on the luminescence of doped and undoped PbMoO4 and PbWO4 single crystals; a red emission is found for the first time for PbMoO4. The degree of polarization of both the emissions of PbWO4 and of the shorter-wavelength emission of PbMoO4 is measured. The shorter-wavelength emissions are assigned to the 3T11A1 transition in the tetrahedral MoO42?(WO42?) group. It is assumed that the 3T1 level is split due to spin-orbit coupling. The longer-wavelength emissions are assigned to a transition in a molybdate (tungstate) group lacking an oxygen ion, i.e., a MoO3(WO3) group.  相似文献   
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