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21.
[reaction: see text] [carboxyl-(11)C]Carboxylic acids were prepared from alkyl iodides via photoinitiated radical reactions using 10(-)(8) mol of [(11)C]carbon monoxide in binary and ternary homogeneous solvent mixtures. Short- (isobutyric), medium-, and long-chain saturated fatty acids (heptadecanoic) were labeled with isolated decay-corrected radiochemical yields ranging from 55% to 70% in 5-7-min reactions. The conversion of [(11)C]carbon monoxide to products reached 80-90%. To obtain good yields in the reactions performed in water-acetonitrile and water-THF mixtures, the addition of tetrabutylammonium hydroxide or potassium hydroxide was essential. The carboxylation was efficient for primary and secondary alkyl iodides. The carboxylation of tertiary iodides was feasible for 1-iodoadamantane but not for tert-butyl iodide. The dependence of the radiochemical yields on reaction time, photoirradiation conditions, and organic and inorganic additives was studied. The method provides a one-step route to [carboxyl-(11)C]carboxylic acids; traditional methods, in contrast, would require several steps. For example, using the devised reaction conditions, 3.19 GBq of purified [1-(11)C]1,10-decanedicarboxylic acid (specific radioactivity 188 GBq/mumol) was obtained within 35 min of the end of 10 muAh bombardment. (1-(13)C)4-Phenylbutyric acid was synthesized using ((13)C)carbon monoxide for identifying the labeling position with (1)H and (13)C NMR. 相似文献
22.
Clegg AD Rees NV Klymenko OV Coles BA Compton RG 《Journal of the American Chemical Society》2004,126(19):6185-6192
The validity of Marcus theory for outer-sphere heterogeneous electron transfer for the electro-oxidation of a range of anthracene derivatives in alkyl cyanide solvents is investigated. The precision measurement of these fast electron transfers (k(0) >or= 1 cm s(-1)) is achieved by use of the high-speed channel electrode and, where necessary, fast-scan cyclic voltammetry. First, the solvent effect on the rate of electron transfer is studied by considering the first oxidation wave of 9,10-diphenylanthracene in the alkyl cyanide solvents: acetonitrile, propionitrile, butyronitrile, and valeronitrile. Second, the variation of k(0) for a series of substituted anthracenes is investigated by analyzing the voltammetric response of the one-electron oxidations of 9-phenylanthracene, 9,10-dichloroanthracene, 9-chloroanthracene, 9,10-dicyanoanthracene, 9-cyanoanthracene, 9-nitroanthracene, 9,10-diphenylanthracene, and anthracene in acetonitrile. It is shown that the rate of electron transfer of a single compound in different alkyl cyanides is determined by the longitudinal dielectric relaxation properties of the solvent, while differences in rate between the substituted anthracenes in acetonitrile can be quantitatively rationalized by considering their relative hydrodynamic radii. This makes possible the accurate prediction of electron-transfer rates for a molecule by interpolation of rate constants known for related molecules. 相似文献
23.
Forryan CL Klymenko OV Wilkins SJ Brennan CM Compton RG 《The journal of physical chemistry. B》2005,109(44):20786-20793
In this paper we present a mathematical model for the surface-controlled dissolution of cylindrical solid particles. This is employed to interpret experimental data published previously for the dissolution of potassium bicarbonate in dimethylformamide at elevated temperatures. Significant kinetic differences in assuming cylindrical rather than spherical shapes are reported with the former representing a closer approximation to the true shape of the particles as revealed by scanning electron microscopy. From the fits of experimental data to the cylindrical model for the surface-controlled dissolution, the dissolution rate constant, k, for the dissolution of KHCO(3) in DMF was found to be (9.6 +/- 1.6) x 10(-9) mol cm(-2) s(-1) at 100 degrees C, and the activation energy for the dissolution was 34.5 kJ mol(-1) over the temperature range of 60-100 degrees C. Comparison between cylindrical and spherical dissolution theory highlights the importance of considering the particle shapes for realistic modeling of surface-controlled dissolution kinetics. 相似文献
24.
Langner A Panarello A Rivillon S Vassylyev O Khinast JG Chabal YJ 《Journal of the American Chemical Society》2005,127(37):12798-12799
Immobilization of indene ligands onto two types of hydrogen-terminated surfaces, oxide-free Si [H/Si(111)] and oxidized Si [H/SiO2/Si], has been investigated by infrared absorption spectroscopy. The activity of a common catalyst (H2PtCl6) is shown to depend critically on the nature of the solvent. For instance, 2-propanol preferentially reacts with the surface, preventing any ligand attachment. Chlorobenzene is more stable, allowing some ligand attachment, but the H2PtCl6 catalyst also fosters silicon oxidation. In contrast, UV irradiation on oxide-free surfaces promotes a cleaner and more efficient reaction, leading to ligand attachment without substrate oxidation. The complete inactivity of H-terminated surfaces with a thin oxide layer [H/SiO2/Si] suggests that the UV-induced immobilization is mediated solely by the excitation of electron-hole pairs (excitons) in the substrate and is not the result of direct Si-H bond breaking. 相似文献
25.
Mykhailo V. Klymenko Ivan M. Safonov Oleksiy V. Shulika Igor A. Sukhoivanov Rainer Michalzik 《Optical and Quantum Electronics》2008,40(2-4):197-204
In this paper, we have developed new design of the injector for quantum cascade structures based on the effective mass superlattice. The transmission spectra of the conventional injector and effective-mass injector have been compared. Advantage of the effective-mass injector is more uniform spectrum of pass-band. This feature allows to improve controllability of the quantum cascade laser, to increase stability of its operation and to decrease sensitivity to noise in applied voltage bias. Also, we have computed geometrical parameters for effective-mass injector which is appropriate to provide inverted population in existing quantum-cascade lasers. Such injector should be characterized by 15–25 numbers of layers with widths of layers up to 2 nm. 相似文献
26.
Alexander O. Ignatyev Oleksiy A. Ignatyev 《Journal of Mathematical Analysis and Applications》2006,313(2):678-688
In this paper we consider the system of difference equations
27.
Monatshefte für Mathematik - For any polynomial $$P(x)in {mathbb {Z}}[x],$$ we study arithmetic dynamical systems generated by $$displaystyle {F_P(n)=mathop {prod nolimits _{kle... 相似文献
28.
Ivachtchenko A Kovalenko S Tkachenko OV Parkhomenko O 《Journal of combinatorial chemistry》2004,6(4):573-583
The parallel solution-phase synthesis of more than 3000 substituted thienopyrimidin-4-ones has been accomplished. Key reactions include assembly of the 2-thioxopyrimidin-4-one ring by condensation of isomeric aminothiophenecarboxylates or their appropriate reactive derivatives (isothiocyanates or dithiocarbamates) with the corresponding isothiocyanates or amines. The libraries from libraries were then obtained in good yields and purities using solution-phase alkylation and acylation methodologies. Simple manual techniques for parallel reactions using special CombiSyn synthesizers were coupled with easy purification procedures (crystallization from the reaction mixtures) to give high-purity final products. The scope and limitations of the developed approach are discussed. 相似文献
29.
Magdalena Ćwikowska Florian P. Pruchnik Oleksiy Pavlyuk Frédéric Lafolet Sylvie Chardon-Noblat Alain Deronzier 《Polyhedron》2010
Binuclear Rh(II) compounds [Rh2(μ-OOCCH3)2(dbbpy)2(H2O)2](CH3COO)2 (1) (dbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine), [Rh2(μ-OOCCH3)2(dbbpy)2(H2O)2](BF4)2·H2O·CH3CN (2), [Rh2(CH3COO)2(C18H24N2)2(CH3CN)2](BF4)2·4CH3CN (3) and {[Rh2(μ-OOCCH3)2(dbbpy)2][BF4]}n (4) have been synthesized and characterized with spectroscopic methods. Structure of complex 3 has been determined using X-ray crystallography. Rhodium atoms in compound 3 have distorted octahedral coordination with O and N atoms in equatorial positions and Rh atom and CH3CN molecule in axial coordination sites. Reduction of rhodium(II) compounds with aqueous 2-propanol leads to the formation of polymetallic compound {[Rh2(μ-OOCCH3)2(dbbpy)2][BF4]}n (4) containing [Rh2]3+ core. Compound 4 shows strong antiferromagnetic properties, μ = 0.18–1.73 M.B. in the range 1.8–300 K, J = −597 cm−1. Electrochemistry of compounds 3 and 4 in CH3CN has been investigated. Compound 4 exhibits a poorly reversible oxidation system at E1/2 = −0.92 V (ΔEp = 0.19 V) and in solution in DMF is slowly oxidized to 3 even in total absence of oxygen. Complex 3 is irreversibly oxidized to Rh(III) compound at Epa = 1.48 V and irreversibly reduced at Epc = −1.02 V to lead to the unstable polynuclear complex 4 in CH3CN. 相似文献
30.
Dr. Oleksiy V. Klymenko Dr. Irina Svir Dr. Alexander Oleinick Dr. Christian Amatore 《Chemphyschem》2012,13(3):845-859
A new simulation algorithm is presented for describing the dynamics of diffusion reactions at the most common microelectrode 1D (planar, cylindrical, spherical) and 2D geometries (band, disk) for electrochemical mechanisms of any complexity and involving fast homogeneous reactions of any kind. A series of typical electrochemical mechanisms that create the most severe simulation difficulties is used to establish the exceptional performance and accuracy of this algorithm, which stem from the combination of (quasi)conformal transformation of space and a new method for auto‐adaptive grid compression. 相似文献