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101.
102.
Wiest O Harrison CB Saettel NJ Cibulka R Sax M König B 《The Journal of organic chemistry》2004,69(24):8183-8185
Two new artificial photolyase models that recognize pyrimidine dimers in protic and aprotic organic solvents as well as in water through a combination of charge and hydrogen-bonding interactions and use a mimic of the flavine to achieve repair through reductive photoinduced electron transfer are presented. Fluorescence and NMR titration studies show that it forms a 1:1 complex with pyrimidine dimers with binding constants of approximately 10(3) M(-1) in acetonitrile or methanol, while binding constants in water at pH 7.2 are slightly lower. Excitation of the complex with visible light leads to clean and rapid cycloreversion of the pyrimidine dimer through photoinduced electron transfer catalysis. The reaction in water is significantly faster than in organic solvents. The reaction slows down at higher conversions due to product inhibition. 相似文献
103.
Ren Fournier 《International journal of quantum chemistry》1994,52(4):973-985
The bonding of acetylene to copper atom, dimer, and trimer was investigated with a Kohn–Sham density functional approach. Full geometry optimization yielded the equilibrium structures of various CunC2H2 species. Gradient corrections were included in the calculation of binding energies (BE ). The Cu—C2H2 complex was found to have a Cs structure and a BE of 10 kcal/mol. Three isomers of Cu2C2H2 have similar total energies: a C2v end-bonded structure with a BE of 18 kcal/mol, and two 1,2-dicupro ethylene isomers—a cis form with a BE of 12 kcal/mol and a trans form with a BE of 15 kcal/mol. Two stable C2v isomers of Cu3C2H2 were found. In both isomers, the Cu3 ring relaxes from its isosceles structure, with two short bonds (2.247 Å) and one long bond (2.478 Å), and adopts a nearly equilateral geometry. In one isomer of Cu3C2H2, the acetylene is bonded to one apex of the Cu3 ring with a BE of 29 kcal/mol. In the other, it is bonded to two copper atoms of one side of the Cu3 ring with a BE of 33 kcal/mol. © 1994 John Wiley & Sons, Inc. 相似文献
104.
Giraud N Blackledge M Goldman M Böckmann A Lesage A Penin F Emsley L 《Journal of the American Chemical Society》2005,127(51):18190-18201
A detailed analysis of nitrogen-15 longitudinal relaxation times in microcrystalline proteins is presented. A theoretical model to quantitatively interpret relaxation times is developed in terms of motional amplitude and characteristic time scale. Different averaging schemes are examined in order to propose an analysis of relaxation curves that takes into account the specificity of MAS experiments. In particular, it is shown that magic angle spinning averages the relaxation rate experienced by a single spin over one rotor period, resulting in individual relaxation curves that are dependent on the orientation of their corresponding carousel with respect to the rotor axis. Powder averaging thus leads to a nonexponential behavior in the observed decay curves. We extract dynamic information from experimental decay curves, using a diffusion in a cone model. We apply this study to the analysis of spin-lattice relaxation rates of the microcrystalline protein Crh at two different fields and determine differential dynamic parameters for several residues in the protein. 相似文献
105.
The solvents o-, m-, p-xylene, p-dichlorobenzene, 1,2,4-trichlorobenzene, and naphthalene were calibrated as condensates used in the thermoporosimetry technique. Exponential relationships were found connecting the pore radii R(p) (in nm) and the freezing-point depression of the swelling solvent deltaT (in degrees C) on the one hand and the apparent energy of crystallization W(a) (in J cm(-3)) and deltaT on the other hand: R(p) = t exp[-1/(c deltaT)]; W(a) = W0 exp(deltaT/f). Pore- or mesh-size distributions can be derived from differential scanning calorimetry results by using the following equation: dV(p)/dR(p) = k{[cY(T)deltaT2]/[W(a)R(p)]}. All the numerical parameters were determined. Polyethylene and polypropylene samples, cross-linked with high-energy electrons or gamma-rays, were submitted to thermoporosimetry study. Relative mesh-size distributions, which depend on the polymer/solvent pair, were calculated for these polyolefins with o-, m-, and p-xylene as solvent and were found to be in the same sequence as those of their degrees of swelling and the irradiation doses received. 相似文献
106.
Rokitamycin and josamycin were successfully derivatized with dansylhydrazine in 20 min at 60 degrees C. Rokitamycin and josamycin levels were determined in plasma after ion-pair extraction into hexane-isoamyl alcohol with lauryl sulphate and precolumn derivatization. Resolution was obtained by liquid chromatography with fluorescence detection (352/537 nm) in 12 min. The limit of detection was 20 ng/ml macrolide starting from 1 ml of plasma, and linearity was demonstrated between 50 and 400 ng/ml. Inter-run coefficients of variation were 10.2% at 100 ng/ml and 9.1% at 300 ng/ml. The system was reliably used for pharmacokinetic studies in plasma. 相似文献
107.
Millot N Cox A Santini CC Molard Y Basset JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(6):1438-1442
The reaction of the Lewis acid B(C(6)F(5))(3) with silanol groups of silica surfaces, dehydroxylated at different temperatures (300, 500, 700, and 800 degrees C), has been investigated in presence of the Br?nsted base NEt(2)Ph. The structure of the resulting modified silica supports [triple bond Si-OB(C(6)F(5))(3)](-)[HNEt(2)Ph](+) (1) has been carefully identified by IR and multinuclear solid-state NMR spectroscopies, isotopic (2)H and (18)O labeling, elemental analysis, molecular modeling, and comparison with synthesized molecular models. Highly dehydroxylated silica surfaces were required to transform selectively each silanol group into unique [triple bond Si-OB(C(6)F(5))(3)](-)[HNEt(2)Ph](+) fragments. For lower dehydroxylation temperatures, two sorts of surface sites were coexisting on silica: the free silanol groups [triple bond SiOH] and the ionic species 1. 相似文献
108.
Polfer NC Haselmann KF Zubarev RA Langridge-Smith PR 《Rapid communications in mass spectrometry : RCM》2002,16(10):936-943
Electron capture dissociation (ECD) of polypeptides has been demonstrated using a commercially available 3 Tesla Fourier transform ion cyclotron resonance (FTICR) instrument. A conventional rhenium filament, designed for high-energy electron impact ionisation, was used to effect ECD of substance P, bee venom melittin and bovine insulin, oxidised B chain. A retarding field analysis of the effective electron kinetic energy distribution entering the ICR cell suggests that one of the most important parameters governing ECD for this particular instrument is the need to employ low trapping plate voltages. This is shown to maximise the abundance of low-energy electrons. The demonstration of ECD at this relatively low magnetic field strength could offer the prospect of more routine ECD analysis for the wider research community, given the reduced cost of such magnets and (at least theoretically) the greater ease of electron/ion cloud overlap at lower field. 相似文献
109.
B. Balestri P. Y. Bertin B. Coupat G. Fournier A. Gérard E. W. A. Lingemann J. Miller J. Picard B. Saghai K. K. Seth P. Vernin 《Czechoslovak Journal of Physics》1982,32(3):255-257
Elastic scattering differential cross section data of
±
d at 65 MeV and
±
4He at 51 MeV are presented and compared respectively to fully relativistic 3-body and optical potential calculations including true pion absorption.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981. 相似文献
110.
Budimir N Fournier F Bailly T Burgada R Tabet JC 《Rapid communications in mass spectrometry : RCM》2005,19(13):1822-1828
The tripodal ligand N,N,N-tris[(1,hydroxy-2-pyridinon-6-yl)amide]propylamine was synthesized. It is composed of an anchor (nitrogen atom), a functional group (hydroxamate), and also a spacer of variable length defined by the number of methylene groups linking the anchor and the functional group. The characterization of this ligand in the presence of several divalent metal cations (Fe(II), Mn(II), Co(II) and Cu(II)), performed by electrospray ionization mass spectrometry (ESI-MS and ESI-MS/MS), allowed elucidation of oxidation states and also of different fragmentation patterns. The importance of the spacer length was studied in the case of the iron binary complex by comparing this ligand with another with a shorter spacer. In this way the stabilizing conditions, in which hydrogen bonds are implicated, were clarified. 相似文献