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41.
Infrared multiple-photon dissociation of CTCl3 was investigated using a pulsed CO2 laser-pumped NH3 laser at 12.08 μm. No evidence of any CDCl3 depletion or decomposition product was observed in photolyzed CTCl3/CDCl3 mixtures. A lower limit of the single-step T/D enrichment factor, β, was found to be ≈ 165, based on the sensitivity in measuring CDCl3 depletion. The low-fluene CTCl3/CDCl3 optical selectivity in absorptions is > 9000 at the 835 cm?1 CTCl3 ν4 peak. 相似文献
42.
Raman and IR spectra of methylarsonic acid, CH3AsO3H2, trideuteromethylarsonic acid, CD3AsO3H2 and their anions in aqueous solution and the solid state are discussed. Some results of a general valence force field and a Urey-Bradley force field are reported. 相似文献
43.
The vibrational spectra (IR and Raman) of CHCl2PO3H2 and its anions in H2O and D2O solutions are reported. The IR spectra of the solid dibasic sodium and potassium salts, the solid normal and O-deuterated monobasic sodium and potassium salt and the solid normal and O-deuterated acid are discussed. The principal results of the normal coordinate analysis of the compounds are tabulated. 相似文献
44.
Pinheiro JP Minor M van Leeuwen HP 《Langmuir : the ACS journal of surfaces and colloids》2005,21(19):8635-8642
In this work we propose a dynamic metal speciation theory for colloidal systems in which the complexing ligands are localized on the surface of the particles; i.e., there is spatial heterogeneity of binding sites within the sample volume. The differences between the complex formation and dissociation rate constants of complexes in colloidal dispersions and those in homogeneous solutions originate from the differences in kinetic and mass transport conditions. In colloidal systems, when the effective rate of dissociation of the surface complexes becomes fully diffusion controlled, its value is defined via the geometrical parameters of the particle. We assess the extent to which the conventional approach of assuming a homogeneously smeared-out ligand distribution overestimates the lability of surface complexes in colloidal ligand dispersions. The validity of the theory is illustrated by application to binding of lead and cadmium by carboxyl modified latex particles: our approach correctly predicts the formation/dissociation rate constants, which differ by several orders of magnitude from their homogeneous solution counterparts. 相似文献
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47.
Spyros P. Perlepes Frank J. Quaeyhaegens Herman O. Desseyn 《Transition Metal Chemistry》1990,15(2):132-140
Summary The new complexes K2[ML2]·2H2O (M=Ni, Cu), K2[PdL2]·H2O, K2[CuL2(H2O)2]·H2O, [Ni(LH2)Cl2]x ·xH2O and [Ni(LH2)Br2]x·1,5xH2O, where LH2= oxalyldihydrazide, have been prepared. Emphasis has been put on determining the conditions for the synthesis of both deprotonated and non-deprotonated NiII complexes. They were characterized by analyses, conductivity measurements, thermogravimetry, magnetic susceptibility and spectroscopic methods like i.r. and far-i.r., diffuse reflectance u.v. vis, and e.s.r. Monomeric square planar and distorted octahedral structures were found for the deprotonated complexes in the solid state while the non-deprotonated NiII complexes appeared to be pseudo-tetrahedral polymers. The doubly deprotonated L2-ion exhibits a bidentate N(amide), N(amide)-coordination, while the neutral LH2 molecule behaves as a N(amino), N(amino)-bidentate ligand forming polymeric structures. Vibrational analysis of the complexes was carried out, using hydrogen and metal isotopic substitution. 相似文献
48.
Codée JD Stubba B Schiattarella M Overkleeft HS van Boeckel CA van Boom JH van der Marel GA 《Journal of the American Chemical Society》2005,127(11):3767-3773
A novel flexible assembly strategy is described for the modular synthesis of heparin and heparan sulfates. The reported strategy uses monomeric building blocks to construct the oligosaccharide chain to attain a maximum degree of flexibility. In the assembly, 1-hydroxyl glucosazido- and 1-thio uronic acid donors are combined in a sequential glycosylation protocol using sulfonium triflate activator systems. The key 1-thio uronic acids were obtained in an efficient manner from diacetone glucose employing a chemo- and regioselective oxidation of partially protected glucose and idose thioglycosides. 相似文献
49.
The nonadiabatic surface hopping Herman-Kluk (HK) semiclassical initial value representation (SC-IVR) method for nonadiabatic problems is reformulated. The method has the same spirit as Tully's surface hopping technique [J. Chem. Phys. 93, 1061 (1990)] and almost keeps the same structure as the original single-surface HK SC-IVR method except that trajectories can hop to other surfaces according to the hopping probabilities and phases, which can be easily integrated along the paths. The method is based on a rather general nonadiabatic semiclassical surface hopping theory developed by Herman [J. Chem. Phys. 103, 8081 (1995)], which has been shown to be accurate to the first order in h and through all the orders of the nonadiabatic coupling amplitude. Our simulation studies on the three model systems suggested by Tully demonstrate that this method is practical and capable of describing nonadiabatic quantum dynamics for various coupling situations in very good agreement with benchmark calculations. 相似文献
50.
Antonie J. W. G. Visser Jan L. De Wit Franz Müller Herman J. C. Berendsen 《Helvetica chimica acta》1982,65(8):2422-2430
The water relaxation rates of several flavoproteins in the semiquinone state have been investigated by the spin echo technique. The results indicate a rather unspecific interaction between water and the protein-bound flavosemiquinones. An average interaction distance of 0.3-0.5 nm has been estimated. From the temperature dependence of the rate constants the free energy of activation for proton exchange is calculated to be about 17 kJ/mol. The rate of proton exchange is around 1011 s?1 for the flavosemiquinones investigated are accessible to water regardless of their ionic state. The large difference in relaxation rates of water protons between D - and L - amino-acid oxidases is noticeable. Oxynitrilase exhibits the highest whereas Azotobacter vinelandii flavodoxin shows the lowest water relaxation rate of the flavoproteins studied. The results are discussed in relation to the visible-light absorption properties of the flavoproteins. 相似文献