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991.
The UV and IR absorption spectra and the NMR and NQR spectra of certain isocyanates of three- and four-coordinated phosphorus have been investigated. The reciprocal effect of the phosphorus atom and the NCO group is discussed on the basis of spectral analysis, quantum chemical calculations of the electron systems, and calculations of the normal vibrational forms. Comparison of the (PO) frequencies in the IR spectra of the phosphorus isocyanates with the Taft gives a linear relationship which testifies to the predominant inductive effect of the NCO group on the P(O)R1R2 grouping. A similar relationship is observed between the resonance frequency res in the NMR spectra and for C1P(O)R1R2 compounds. The effect of the phosphorus atom on the electronic system in the NCO group is shown by the hypsochromic shift of the absorption band in the210-m region and an appreciable increase in its intensity, compared with alkyl isocyanates. This fact, which agrees with the NMR spectral data and the quantum chemical calculations, indicates the presence of conjugation in the P-N bond. We found the order of the P-N bond to be approximately 1.2. This partial double-bond nature of the P-N bond results from the interaction of the p electrons of nitrogen in the NCO group with the d orbitals of the phosphorus atom.We are grateful to our colleagues at the Kazan Physicotechnical Institute AS USSR A. I. Rivkind, S. G. Salikhov, and I. A. Safin for recording the spectra.  相似文献   
992.
The formation kinetics and mechanism were studied for the intermediate and final products of degradation of aqueous phenol solutions in air and oxygen low-temperature dielectric-barrier discharge plasmas in a reactor with different geometric arrangements of electrodes. It was shown that the plasma-enhanced oxidation of phenol could be described in the general form by the well-known mechanism of enzymatic oxidation of toxic pollutants (-mechanism). The estimated effective rate constant of phenol degradation in an aqueous solution in an 2 plasma in reactors with the parallel-plate and coaxial arrangement of electrodes was 2.2 × 10–3 s–1 and 5.8 × 10–2 s–1, respectively. It was found that the potential toxicity of solutions after treatment was 7.5 times lower than that of the untreated solutions.  相似文献   
993.
We present a comparative golden rule analysis of the dynamics of the intramolecur (IM) hydrogen atom and proton transfer in the photochemical cycles of 2-(2′-hydroxyphenyl)benzoxazole (HBO) and 5,8-dimehtyl-1-tetralone (DMT). Two major effects are taken into consideration: the promoting effect of the IM vibrations which are symmetrically coupled to the reaction coordinate,and the suppressing effect resulting from the reorganization of both the molecule and solvent.

Semiempirical quantum-chemical calculations at the AM1 level were carried out to study the energy levels of all states involved in the photochemical cycles, including the effects of solvation in a polar protic solvent in the case of DMT. Two rotamers EI and EII for the enol form of DMT were located corresponding to different positions of the H atom in the hydroxyl group. In the group state the first is more stable both in the gas phase and in polar protic solvents such as diethyl ether—isopentane—ethanol (5:2:5 by volume). Therefore the reketonization reaction is treated as one-step tunneling from the rotamer EI to the keto form, i.e. without the activated rotational equilibrium EI↔EII proposed by Grellmann and coworkers in an earlier study. The steep slope of the kinetic curve of this reaction is attributed to the additional activation energy resulting from the final reorganization of the low frequency oscillators, both intramolecular and solvent. For the dynamic calculations, the standard AM1 output (structural and force field data) was used as the input, and good agreement with the available kinetic experiments was reached for both compounds. No special reasons were found for the similarity of the kinetic curves for triplet excited-state intramolecular proton transfer in HBO and DMT.  相似文献   

994.
A new spectrophotometric method was developed to determine vanadium using tannic acid as a complexing reagent to form a coloured reaction product which can easily be extracted by 1-pentanol in the presence of cetylpyridinium. The developed method can successfully be applied to determine trace levels of 10 ng/ml of vanadium in natural waters without any preconcentration step. It can also determine less than 1 mg/kg of vanadium in edible oils and petroleum products.  相似文献   
995.
Shihabi ZK 《Electrophoresis》2000,21(14):2872-2878
Discontinuous buffers for capillary zone electrophoresis (CZE) can be used under less rigid conditions compared to those for isotachophoresis for stacking. They can be prepared simply by modifying the sample itself, either by addition of small inorganic ions, low conductivity diluents, or both, and also by adjusting its pH, meanwhile injecting a large volume on the capillary. Zwitterionic and organic-based buffers such as triethanolamine and tris(hydroxymethyl)aminomethane (Tris) are well suited for stacking due to their low conductivity, provided the buffer is discontinuous as demonstrated here. A simple mechanism based on discontinuous buffers is described to explain many of the observed stacking types in CZE, pointing out the many similarities to transient isotachophoresis.  相似文献   
996.
The use of photosensitizing dyes having intense absorption bands in the 600-900 nm spectral interval opens up new prospects in the field of photochemotherapy, because it allows the illumination of relatively large tissue volumes with no significant damage to photosensitizer-free tissues. Special interest is currently focused on the photodynamic therapy of solid tumors, because of the property of several dyes with a macrocyclic chemical structure (porphyrins, chlorins, phthalocyanines, xanthenes) to accumulate in significant amounts and be retained for prolonged periods of time by neoplastic lesions. Strategies are being developed for enhancing the selectivity of tumor targeting by photosensitizers through the exploitation of functional or biochemical differences between normal and malignant cells.  相似文献   
997.
998.
The electron impact mass spectra of the acetates of zinc, magnesium, cobalt and manganese have been investigated using a direct inlet probe. Volatile tetrahedral complexes are produced on heating, and ions of the form [M4(OCOCH3)6O] (M = Co and Mn) and [N4(OCOCH3)5O]+ (N = Zn or Mg) are observed. A mixture of magnesium and cobalt acetates produces ions of the form [MgnCo4–n(OCOCH3)6O].  相似文献   
999.
The interaction between an antibody molecule and a protein antigen is an example of "natural" protein modelling. Amino acids of the antigen-binding site consisting of three hypervariable segments (L1, L2, L3) of the light (L) and three (H1, H2, H3) of the heavy (H) chain of an antibody molecule interact with amino acids present in an epitope of a protein. A ten-residue peptide was synthesized with an amino acid sequence analogous to the hypervariable L3 segment of a monoclonal antibody directed against lysozyme. The peptide was immobilized on CH-Sepharose 4B and the affinity adsorbent was used to purify lysozyme added to a detergent extract of insect cells infected with a recombinant baculovirus. This methodology may also be applicable to other antigen-antibody combinations, in immunoaffinity chromatography for selective purification of a protein or in an immunosensor for detection of a protein.  相似文献   
1000.
Summary The quantitative oxidation of thiocyanate by ceric sulphate has been studied and the method utilised for the determination of small quantities of cerium by back titrating the excess (unreacted) KSCN against standard mercuric nitrate with diphenylcarbazone as the internal indicator. Accurate results are obtained under the specified experimental conditions and the procedure is more simple and direct than that adopted during earlier studies of the above redox reaction.Grateful thanks of the author are due to Professor S. S. Joshi for facilities during the work and to the National Institute of Sciences of India for award of a Research Fellowship.  相似文献   
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