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961.
Ekaterina I. Goldyreva Ilya A. Leonidov Mikhail V. Patrakeev Victor L. Kozhevnikov 《Journal of Solid State Electrochemistry》2013,17(5):1449-1454
The drift mobility of electron charge carriers in oxygen non-stoichiometric manganite CaMnO3???δ was calculated by combining the total electrical conductivity and oxygen non-stoichiometry data at 700–950 °С and oxygen partial pressure varying between 10?6 and 1 atm. The carrier concentration changes with pressure and temperature were obtained with the help of the earlier-developed defect model involving reactions of oxygen exchange and thermal excitation of manganese sites. The activation energy for mobility is found to increase with oxygen non-stoichiometry. High-temperature electron transport properties of the manganite CaMnO3???δ can be explained in terms of activated jumps of n-type small polarons in adiabatic regime. The relatively small mobility of charge carriers is explained by strong localization of polarons on manganese sites. 相似文献
962.
Lesnichin SB Shenderovich IG Muljati T Silverman D Limbach HH 《Journal of the American Chemical Society》2011,133(29):11331-11338
Using liquid-state NMR spectroscopy we have estimated the proton-donating ability of Zn-bound water in organometallic complexes designed as models for the active site of the metalloenzyme carbonic anhydrase (CA). This ability is important for the understanding of the enzyme reaction mechanism. The desired information was obtained by (1)H and (15)N NMR at 180 K of solutions of [Tp(Ph,Me)ZnOH] [1, Tp(Ph,Me) = tris(2-methyl-4-phenylpyrazolyl)hydroborate] in CD(2)Cl(2), in the absence and presence of the proton donors (C(6)F(5))(3)BOH(2) [aquatris(pentafluorophenyl)boron] and Col-H(+) (2,4,6-trimethylpyridine-H(+)). Col-H(+) forms a strong OHN hydrogen bond with 1, where the proton is located closer to nitrogen than to oxygen. (C(6)F(5))(3)BOH(2), which exhibits a pK(a) value of 1 in water, also forms a strong hydrogen bond with 1, where the proton is shifted slightly across the hydrogen-bond center toward the Zn-bound oxygen. Finally, a complex between Col and (C(6)F(5))(3)BOH(2) was identified, exhibiting a zwitterionic OHN hydrogen bond, where H is entirely shifted to nitrogen. The comparison with complexes of Col with carboxylic acids studied previously suggests that, surprisingly, the Zn-bound water exhibits in an aprotic environment a similar proton-donating ability as a carboxylic acid characterized in water by a pK(a) of 2.2 ± 0.6. This value is much smaller than the value of 9 found for [Zn(OH(2))(6)](2+) in water and those between 5 and 8 reported for different forms of CA. Implications for the biological function of CA are discussed. 相似文献
963.
Chemistry of Heterocyclic Compounds - Microreview summarizes the latest examples on NH-unsubstituted 1,2,3-triazole synthesis. The described methods are categorized according to the used starting... 相似文献
964.
Elles CG Shkrob IA Crowell RA Arms DA Landahl EC 《The Journal of chemical physics》2008,128(6):061102
Time-resolved x-ray absorption spectroscopy has been used to observe the transient species generated by one-photon detachment of an electron from aqueous bromide. The K-edge spectrum of the short-lived Br(0) atom exhibits a resonant 1s-4p transition that is absent for the Br(-) precursor. The strong 1s-4p resonance suggests that there is very little charge transfer from the solvent to the open-shell atom, whereas weak oscillations above the absorption edge indicate that the solvent shell around a neutral Br(0) atom is defined primarily by hydrophobic interactions. These conclusions are in agreement with Monte Carlo and quantum chemical simulations of the solvent structure. 相似文献
965.
Wang G Bohaty AK Zharov I White HS 《Journal of the American Chemical Society》2006,128(41):13553-13558
The interior surface of the glass nanopore electrode was modified with spiropyran moieties to impart photochemical control of molecular transport through the pore orifice (15-90 nm radius). In low ionic strength acetonitrile solutions, diffusion of a positively charged species (Fe(bpy)(3)(2+)) is electrostatically blocked with approximately 100% efficiency by UV light-induced conversion of the neutral surface-bound spiropyran to its protonated merocyanine form (MEH+). Transport through the pore orifice is restored by either irradiation of the electrode with visible light to convert MEH+ back to spiropyran or addition of a sufficient quantity of supporting electrolyte to screen the electrostatic field associated with MEH+. The transport of neutral redox species through spiropyran-modified glass nanopores is not affected by light, allowing photoselective transport of redox molecules to the electrode surface based on charge discrimination. The glass nanopore electrode can also be employed as a photochemical trap, by UV light conversion of surface-bound spiropyran to MEH+, preventing Fe(bpy)(3)(2+) initially in the pore from diffusing through the orifice. 相似文献
966.
Voskressensky LG Vorobiev IV Borisova TN Varlamov AV 《The Journal of organic chemistry》2008,73(12):4596-4601
Reaction of 10-cyanotetrahydrobenzo[b][1,6]naphthyridines (1-6) with activated alkynes affords stable benzo[b]pyrrolo[2,1-f][1,6]naphthyridine-4-ium ylides (7-14) in moderate yields. A proposed mechanism for their formation consists of a new tandem multistage process. 相似文献
967.
968.
Ilya V. Boikov 《分析论及其应用》1996,12(3):59-67
Local splines are presented for the approximation of functions of one and many variables, which are analytic in the domains
, where Ui(zi) is a unit disk in the complex plane Ci,i=1,2,…,l, l=1,2, …. Results are given for functions whose r-order derivatives belong to the Hardy's class Hp,1≤p≤∞. It is shown that the approximation converge to the function at the rate
for functions of one variable and An−(r−1/p)/(l−1) for functions of l variables, where n is the number of points of local splines and A and C are positive constants.
This work was supported by Russian Foundation of Fundumental Inverstigations 相似文献
969.
Arkadi V. Eremenko Alexander Makower Christian G. Bauer Ilya N. Kurochkin Frieder W. Scheller 《Electroanalysis》1997,9(4):288-292
A bienzyme electrode for monitoring biologically important peptides containing tyrosine has been established on the basis of mushroom tyrosinase and quinoprotein glucose dehydrogenase (GDH). Tyrosine residues bound in the peptide chain are oxidized by tyrosinase resulting in consumption of oxygen. Subsequently, the dopaquinone residues are reduced in the GDH catalysed reaction which is driven by an excess of glucose. This reaction cycle leads to a considerable increase of sensitivity. Both enzymes were entraped in poly(vinyl)alcohol matrix and placed on the surface of a Clark-type oxygen electrode (the working platinum electrode was potentiostated at −600 mV) (vs. Ag/AgCl reference electrode) between a polypropylene and cellulose membrane. The bienzyme-modified Clark-type oxygen electrode has a lower detection limit of 0.2 μM for the opioid peptides Tyr-D-Ser-Gly-Phe-Leu-Thr, Leu-enkephalin, Tyr-D-Ala-Gly-Phe-D-Leu and morphiceptin. The dependence of response of the electrode on the length of peptide chain and position of tyrosine residue is discussed. The new electrode has been applied to the quality control of tyrosine containing peptides from pharmaceutical formulations and from peptide synthesis. 相似文献
970.
We show that every two-generated torsion-free one-ended word-hyperbolic group has virtually cyclic outer automorphism group.
This is done by computing the JSJ-decomposition for two-generator hyperbolic groups. We further prove that two-generated torsion-free
word-hyperbolic groups are strongly accessible. This means that they can be constructed from groups with no nontrivial cyclic
splittings by applying finitely many free products with amalgamation and HNN-extensions over cyclic subgroups.
Received June 25, 1998 相似文献