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31.
Poulsen MD Peronne E Stapelfeldt H Bisgaard CZ Viftrup SS Hamilton E Seideman T 《The Journal of chemical physics》2004,121(2):783-791
The rotational revival structure of asymmetric top molecules, following irradiation by an intense picosecond laser pulse, is explored theoretically and experimentally. Numerically we solve nonperturbatively for the rotational dynamics of a general asymmetric top subject to a linearly polarized intense pulse, and analyze the dependence of the dynamical alignment on the field and system parameters. Experimentally we use time-resolved photofragment imaging to measure the alignment of two molecules with different asymmetry, iodobenzene, and iodopentafluorobenzene. Our numerical results explain the experimental observations and generalize them to other molecules. The rotational revival structure of asymmetric tops differs qualitatively from the intensively studied linear top case. Potentially it provides valuable structural information about molecules. 相似文献
32.
Revillod G Russier-Antoine I Benichou E Jonin C Brevet PF 《The journal of physical chemistry. B》2005,109(11):5383-5387
We report the use of the nonlinear optical technique of hyper-Rayleigh scattering to investigate the interaction of the cationic probe molecule crystal violet with micelles of sodium dodecyl sulfate. An absolute value of (847 +/- 80) x 10(-30) esu is measured at the fundamental wavelength of 870 nm for the molecular hyperpolarizability of crystal violet free in pure aqueous solutions. In aqueous solutions of sodium dodecyl sulfate, above and below the critical micelle concentration, the measured hyperpolarizability of crystal violet is weaker than in the solution free of sodium dodecyl sulfate. From the comparison with linear optical photoabsorption spectroscopy data, this difference is attributed to electrostatic interactions between the cationic crystal violet molecules and the negatively charged sodium dodecyl sulfate surfactant molecules present in excess. Polarization resolved hyper-Rayleigh scattering measurements are then performed to show that, below and above the critical micelle concentration, crystal violet molecules also undergo symmetry changes upon interaction with sodium dodecyl sulfate. Above the critical micelle concentration, the minimum fraction of micelles interacting with at least one CV molecule is estimated. For instance, for a crystal violet aqueous concentration of 150 microM, this fraction is larger than 7%. 相似文献
33.
Astuti Y Topoglidis E Briscoe PB Fantuzzi A Gilardi G Durrant JR 《Journal of the American Chemical Society》2004,126(25):8001-8009
In this paper, we report a spectroelectrochemical investigation of proton-coupled electron transfer in flavodoxin D. vulgaris Hildenborough (Fld). Poly-L-lysine is used to promote the binding of Fld to the nanocrystalline, mesoporous SnO(2) electrodes. Two reversible redox couples of the immobilized Fld are observed electrochemically and are assigned by spectroelectrochemistry to the quinone/semiquinone and semiquinone/hydroquinone couples of the protein's flavin mononucleotide (FMN) redox cofactor. Comparison with control data for free FMN indicates no contamination of the Fld data by dissociated FMN. The quinone/semiquinone and semiquinone/hydroquinone midpoint potentials (E(q/sq) and E(sq/hq)) at pH 7 were determined to be -340 and -585 mV vs Ag/AgCl, in good agreement with the literature. E(q/sq) exhibited a pH dependence of 51 mV/pH. The kinetics of these redox couples were studied using cyclic voltammetry, cyclic voltabsorptometry, and chronoabsorptometry. The semiquinone/quinone reoxidation is found to exhibit slow, potential-independent but pH-sensitive kinetics with a reoxidation rate constant varying from 1.56 s(-)(1) at pH 10 to 0.0074 s(-)(1) at pH 5. The slow kinetics are discussed in terms of a simple kinetics model and are assigned to the reoxidation process being rate limited by semiquinone deprotonation. It is proposed that this slow deprotonation step has the physiological benefit of preventing the undesirable loss of reducing equivalents which results from semiquinone oxidation to quinone. 相似文献
34.
[reaction: see text] A stereoselective synthesis of (-)-ilimaquinone (4) is presented. The synthetic strategy is based on a novel radical decarboxylation and quinone addition methodology that produces quinone 7 from reaction of thiohydroxamic acid derivative 8 with benzoquinone (9). Final functionalization of 7 to ilimaquinone (4) is achieved by exploring the electronic effects of the residual thiopyridyl group. 相似文献
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37.
G. Clouet P. Chaumont P. Corpart 《Journal of polymer science. Part A, Polymer chemistry》1993,31(11):2815-2824
The thermal bulk polymerization of methyl methacrylate (MMA) in a wide range of temperatures has been studied using a dilatometric reactor. It is shown that, irrespective of the care taken to purify the MMA, the evolution of the time-conversion curve can be explained only if we account for the presence of an impurity associated with the monomer acting as a free radical initiator. The activation energy for the decomposition of this impurity has been estimated as 98 kJ/mol. Having accounted for this impurity, the activation energy for the real thermal polymerization of the MMA has been estimated to be 75 kJ/mol. © 1993 John Wiley & Sons, Inc. 相似文献
38.
Emmanuel Beyou Pierre Babin Bernard Bennetau Jacques Dunogues Dominique Teyssie Sylvie Boileau 《Journal of polymer science. Part A, Polymer chemistry》1994,32(9):1673-1681
Unsaturated perfluoroalkyl esters derived from undecylenic acid: CH2?CH? (CH2)8? COO? CH2? CH2? RF (with RF?C6F13, 2a and RF?C8F17, 2b ) and C8F17? (CH2)10? COO? CH2? CH?CH2, 2c were prepared with excellent yields. Their hydrosilylation by methylhydrodimethylsiloxane copolymers of various Si? H contents gives new fluorinated polysiloxanes which were examined by 1H- and 13C-NMR, GPC, differential scanning calorimetry, and optical polarizing microscopy. Polymers derived from compounds 2a and 2b exhibit mesomorphic structures. © 1994 John Wiley & Sons, Inc. 相似文献
39.
Emmanuel Blas Patricio-Rangel Margarita Tlahuextl Hugo Tlahuext Antonio Rafael Tapia-Benavides 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(4):322-327
The synthesis and characterization of two new 1,3,5‐triazines containing 2‐(aminomethyl)‐1H‐benzimidazole hydrochloride as a substituent are reported, namely, 2‐{[(4,6‐dichloro‐1,3,5‐triazin‐2‐yl)amino]methyl}‐1H‐benzimidazol‐3‐ium chloride, C11H9Cl2N6+·Cl? ( 1 ), and bis(2,2′‐{[(6‐chloro‐1,3,5‐triazine‐2,4‐diyl)bis(azanediyl)]bis(methylene)}bis(1H‐benzimidazol‐3‐ium)) tetrachloride heptahydrate, 2C19H18ClN92+·4Cl?·7H2O ( 2 ). Both salts were characterized using single‐crystal X‐ray diffraction analysis and IR spectroscopy. Moreover, the NMR (1H and 13C) spectra of 1 were obtained. Salts 1 and 2 have triclinic symmetry (space group P) and their supramolecular structures are stabilized by hydrogen bonding and offset π–π interactions. In hydrated salt 2 , the noncovalent interactions yield pseudo‐nanotubes filled with chloride anions and water molecules, which were modelled in the refinement with substitutional and positional disorder. 相似文献
40.