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471.
J. Lipkowski A. Grabowska J. Waluk G. Calestani B. A. Hess Jr. 《Journal of chemical crystallography》1992,22(5):563-572
The crystal structures of two molecules undergoing fast intramolecular excited state proton transfer (2,2-bipyridyl-3,3-diol, BP(OH)2, and 2,2-bipyridyl-3-ol, BP(OH)) are reported and compared with the results ofab initio and molecular mechanics calculations. Strong intramolecular hydrogen bonding is observed in both cases. The pyridyl rings are coplanar in BP(OH)2, whereas in BP(OH) they form an angle of 3.7°.Dedicated to Prof. R. Zahradnik on the occasion of his birthday. 相似文献
472.
Measurements of fluorescence quantum yield D/oD of Na-fluorescein (donor; D) versus concentration of rhodamine B (acceptor; A) in viscous solutions have been carried out. The donor concentration in these solutions was as follows:C
D=2·10–2
M (system I), 1.5·10–2
M (II), 10–2
M (III), 3·10–3
M (IV), and 5·10–5
M (V). The experimental results have been compared with current theories of nonradiative electronic energy transfer (NEET). In the case of very strong migration (systems I, II, and III), a significant influence of correlations (between configurations of D and A molecules in the surroundings of successively excited donors) on quantum yield D/oD has been determined. Experimental values have been found to be clearly higher in comparison with those predicted theoretically. The influence of possible factors on the decrease in the effectiveness of excitation energy transport to traps-acceptors in systems of very strong migration has been discussed.Dedicated to Professor A. Kawski on the occasion of his 65th birthday. 相似文献
473.
We derive herein the limiting laws for certain stationary distributions of birth-and-death processes related to the classical model of chemical adsorption-desorption reactions due to Langmuir. The model has been recently considered in the context of a hybridization reaction on an oligonucleotide DNA-microarray. Our results imply that the truncated-gamma- and beta-type distributions can be used as approximations to the observed distributions of the fluorescence readings of the oligo-probes on a microarray. These findings might be useful in developing new model-based, probe-specific methods of extracting target concentrations from array fluorescence readings. 相似文献
474.
475.
Andrzej Nowakowski Iwona Nowakowska 《Journal of Mathematical Analysis and Applications》2008,338(2):771-783
We discuss the solvability of the Dirichlet problem for the semilinear equation of the vibrating string xtt(t,y)−Δx(t,y)+f(t,y,x(t,y))=0 in higher dimensions with sides length being irrational numbers and superlinear nonlinearity. To this effect we derive a new dual variational method. 相似文献
476.
Iwona Podgórska-Brzdękiewicz 《PAMM》2009,9(1):717-718
The work refers to stability and free vibrations of discrete, two-part planar frame with three degree of freedom. For the considered frame the total mechanical energy is determined on the basis of the external load of the structure, whose direction of action depends on geometry of loading and receiving head. Adequate relationships describing stability of the considered frame are obtained taking into account potential energy of the system (static criterion) or total mechanical energy (kinetic criterion). An influence of geometrical parameters of loading head and rigidity of rotational springs modelling the finite stiffness of structural constraints on the critical load is analyzed. The courses of natural vibration frequencies in relation to the external loads are determined for the assumed values regarding geometry and physical constants of the system. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
477.
In this article a solid lead electrode (PbE) was utilized for the first time for determination of organic substances by means of adsorptive stripping voltammetry. A new procedure of simultaneous determination of rutin and folic acid was developed. Two well shaped and well separated reduction signals of rutin and folic acid were obtained with the use of PbE. The optimization of analytical procedure was presented. The calibration graphs for rutin and folic acid for an accumulation time of 120 s were linear in the ranges from 2×10?9 to 1×10?7 mol L?1 and from 2×10?9 to 5×10?8 mol L?1, respectively. The obtained detection limits for rutin and folic acid determination following accumulation time of 120 s were 7.9×10?10 and 8.4×10?10 mol L?1. Potential interference effects were investigated. The proposed procedure was used for analysis of pharmaceutical preparations with satisfactory results showing practical applications. The analytical parameters of the proposed procedure were compared with other voltammetric procedures of mentioned substances determination. 相似文献
478.
Barbara Wozniak Iwona MatraszekZuchowska Alicja Klopot Andrzej Posyniak 《Journal of separation science》2019,42(21):3319-3329
For the detection of 19 steroid hormones in bovine muscle, a fast and sensitive liquid chromatography with electrospray ionization tandem mass spectrometry method was developed using both positive and negative ionization mode. Chromatographic separation on Poroshell 120‐EC C18 column was achieved in less than 10 min using isocratic elution of mobile phase of acetonitrile/methanol/water. The compounds were extracted from muscle tissue using ethyl acetate and quick, easy, cheap, effective, rugged, and safe technique. The purification of the obtained extract was performed by dispersive solid‐phase extraction with sorbents C18, primary secondary amine and magnesium sulphate. The method was validated in accordance with the Commission Decision 2002/657/EC. For all steroids tested good recoveries were obtained (from 51.2 to 121.4%) in the concentration range from decision limits until 5 µg/kg. The values of decision limits and the detection capabilities for individual compounds were in the range 0.10–0.48 and 0.17–0.95 µg/kg, respectively. The method was characterized by satisfactory linearity for most compounds (correlation coefficients > 0.99) and the reproducibility was lower than 35%. The elaborated procedure has met the criteria for confirmatory methods and is currently used in the official control of hormones. 相似文献
479.
Wrona IE Gabarda AE Evano G Panek JS 《Journal of the American Chemical Society》2005,127(43):15026-15027
Enantioselective total synthesis of reblastatin is described. The synthesis highlights hydrozirconation, transmetalation, aldehyde addition sequence to install E-trisubstituted olefin and C7 stereocenter, and the first use of an intramolecular Buchwald-like amidation reaction to close the 19-membered macrolactam. 相似文献
480.
Janusz Trawczyski Andrzej Kubacki Józef Wrzyszcz Mirosaw Zawadzki Hanna Grabowska Wodzimierz Mita 《Reaction Kinetics and Catalysis Letters》2002,76(2):259-264
Surface behavior of zinc aluminates prepared according to three different methods has been investigated by TPD NH3 and IR spectroscopy and compared with properties of alumina. It was stated that zinc affects the strength and distribution of acidic sites as well as HDS activity of Mo (CoMo) catalysts supported on Zn doped Al2O3. 相似文献