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991.
Russier-Antoine I Jonin C Nappa J Bénichou E Brevet PF 《The Journal of chemical physics》2004,120(22):10748-10752
The wavelength dependence of the quadratic hyperpolarizability of 11 nm diam gold nanoparticles, is reported as measured by hyper Rayleigh scattering. An important photoluminescence background underlying the hyper Rayleigh signal is observed, a contribution attributed to radiative electron-hole recombinations following multiphoton excitation favored by adsorbed organic compound like citrate on the surface of the nanoparticles. The absolute value of the quadratic hyperpolarizability of gold spherical nanoparticles is determined and a strong enhancement is observed for harmonic frequencies in resonance with the dipolar surface plasmon excitation. No contribution of the interband transition is observed. The absolute values reported, beta(C)=5.1x10(-26) esu at the second harmonic energy 2.39 eV, have been measured with femtosecond long laser pulse, and are 1 order of magnitude weaker that the one previously reported with nanosecond long pulses. This difference can be related to similar measurements performed on the second order hyperpolarizability of gold nanoparticles and may be attributed to different electronic relaxation regimes. Finally, the spectrum of the quadratic hyperpolarizability is compared to the theoretically expected one. 相似文献
992.
Barragán P Errea LF Macías A Méndez L Rabadán I Riera A Lucas JM Aguilar A 《The Journal of chemical physics》2004,121(23):11629-11638
The lowest two ab initio potential energy surfaces (PES), and the corresponding nonadiabatic couplings between them, have been obtained for the H3+ system; the molecular data are compared to those calculated with the diatomic in molecules (DIM) method. The form of the couplings is discussed in terms of the topology of the molecular structure of the triatomic. The method of Baer is employed to generate "diabatic" states and the residual nonadiabatic couplings are calculated. The ab initio results for these are markedly different from the corresponding DIM data, and show the need to consider the third PES. 相似文献
993.
Furuta P Brooks J Thompson ME Fréchet JM 《Journal of the American Chemical Society》2003,125(43):13165-13172
The site isolation of two dyes capable of electronic interaction via Forster energy transfer has been studied with the two dyes coumarin 343 and pentathiophene encapsulated by dendrons containing both solubilizing and electroactive moieties. Photoluminescence studies of mixtures of the dendritic dyes show that at high dendron generation, significant site isolation is achieved with relative emission characteristics influenced by both the degree of site isolation and the emission quantum yield of the dyes. Electroluminescence studies carried out in organic light emitting diode devices confirm that color tuning may be achieved by mixing the two encapsulated dyes in a single layer. However, selective carrier trapping by one of the core component dyes can dramatically influence the effectiveness of other components in the device. 相似文献
994.
Boron subhalide cluster dianions B6X 2- 6 (X = Cl, Br, I) are electrochemically oxidized in two steps. According to cyclic voltammograms, the first step is chemically reversible and yields the corresponding radical anions B6X .- 6. The electron transfer is nearly diffusion controlled. The second, slower electron-transfer step leads to a species which we assume to be the hitherto not yet described neutral compounds B6X 2- 6. The voltammograms indicate a coupled fast catalytic reaction, producing the radical anions in a reduction by an electrolyte component. Computer simulations of the cyclic voltammograms reveal mechanistic details of the redox reactions, as well as quantitative values for formal potentials, rate constants, and diffusion coefficients. The results are compared to other BnXn redox systems. 相似文献
995.
Mikkelsen LM Hernáiz MJ Martín-Pastor M Skrydstrup T Jiménez-Barbero J 《Journal of the American Chemical Society》2002,124(50):14940-14951
The conformational properties of the C-glycosyl analogue of the core trisaccharide alpha-D-Man-(1 --> 3)-[alpha-D-Man-(1 --> 6)]-D-Man in solution have been carefully analyzed by a combination of NMR spectroscopy and time-averaged restrained molecular dynamics. It has been found that both the alpha-1,3- and the alpha-1,6-glycosidic linkages show a major conformational averaging. Unusual Phi ca. 60 degrees orientations for both Phi torsion angles are found. Moreover, a major conformational distinction between the natural compound and the glycomimetic affects to the behavior of the omega(16) torsion angle around the alpha-1 --> 6-linkage. Despite this increased flexibility, the C-glycosyl analogue is recognized by three mannose binding lectins, as shown by NMR (line broadening, TR-NOE, and STD) and surface plasmon resonance (SPR) methods. Moreover, a process of conformational selection takes place, so that these lectins probably bind the glycomimetic similarly to the way they recognize the natural analogue. Depending upon the architecture and extension of the binding site of the lectin, loss or gain of binding affinity with respect to the natural analogue is found. 相似文献
996.
Some polymer melts (of high viscosity ) can wet completely the surface of a non miscible, simple liquid. We discuss here the laws of spreading for a macroscopic droplet of this type, when the internal friction of the droplet dominates. We predict a droplet radius increasing liket
1/4 wheret is the spreading time, or equivalently a droplet curvature decreasing liket
–1. The droplet should be surrounded by a precursor film, which is not discussed in the present note. 相似文献
997.
An enzyme-immunoassay for the detection of the mycotoxin zearalenone by use of yolk antibodies 总被引:1,自引:0,他引:1
H. Pichler R. Krska A. Székács M. Grasserbauer 《Fresenius' Journal of Analytical Chemistry》1998,362(1):176-177
The development of an enzyme-immunoassay (ELISA) for the detection of the Fusarium mycotoxin zearalenone (ZON) is described. In contrast to the common antibody isolation from mammal serum, chicken were immunized
in order to isolate specific antibodies from the egg yolk. Five weeks after the start of the immunization a titer of 1:76 000
resulted from three injections without any adverse effects for the animals. Utilizing the indirect competitive assay format
ZON could be detected in a concentration range between 10 and 200 μg/L.
Received: 3 January 1998 / Revised: 16 March 1998 / Accepted: 20 March 1998 相似文献
998.
Péter R. Surján 《Journal of mathematical chemistry》1991,8(1):151-160
Nonlinear time-independent Schr6dinger equations arise if the model Hamiltonian depends on the wave function. This may occur if certain interactions are accounted for in an averaged manner, for example, if a moleule is embedded into a polarizable medium. Arguments are given in favor of the perturbational solution which facilitate the treatment of nonlinearity effects. Two examples are discussed: the case of a polarizable environment and the effective correction of the basis set superposition error. 相似文献
999.
Arturo Zizumbo Rosa Maria Félix-Navarro Jorge Cervantes-Jáuregui Felípe Avalos-Belmontes 《Silicon Chemistry》2005,2(5-6):265-269
Electrochemical formation of poly(phenylmethylsilane) in a divided cell containing a Teflon® neutral membrane was studied. The electrolysis of dichlorosilanes was carried out in a solution containing tetrahydrofuran + hexamethylphosphoramide as the solvent, tetrabutylammonium perchlorate as the support electrolyte and stainless steel as the cathode, with Pt and graphite as the resistant anodes or stainless steel as the sacrificial anode. Polysilanes with a number-average molecular weight in the range from 2,600 to 130,000 g/mol were obtained, depending on the conditions used. 相似文献
1000.
Knecht MR Sewell SL Wright DW 《Langmuir : the ACS journal of surfaces and colloids》2005,21(5):2058-2061
One of the most significant challenges facing the biomimetic synthesis of materials is achieving the requisite level of dimensional and spatial control. Typical reaction conditions for biomimetic silica synthesis allow for continued growth and ripening leading to the formation of larger nanospheres on the order of 200-600 nm in diameter. Herein, we have used polyamidoamine and polypropylenimine dendrimers as templates to expand the reaction conditions of biogenic silica production to produce a more robust synthesis leading to size-selective precipitation of silica nanospheres. Through the use of defined concentrations of phosphate buffer and main group metal chloride salts, we have shown that the biomimetic silica growth process is controlled by cationic neutralization of the anionic silica nanosphere surface. Neutralization minimizes electrostatic repulsions, allowing for agglomerization and continued growth of nanospheres. By controlling these concentrations, we can selectively produce silica nanospheres of desired dimensions between 30 and 300 nm without adversely affecting the template's activity. 相似文献