摘要:

AbstractThe electronic structure of tungsten carbide was investigated by EHMO semiempirical method. The most stable structure of the carbide was predicted on the basis of binding energy calculations. The W‐C bonding is covalent in nature with some charge transfer from the W to the C atoms. The increase in the occupancy of the d shell of the W atoms and the position of the Fermi level may account for the platinum‐like catalytic behavior of tungsten carb

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090201

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper presents an experimental procedure to study state‐to‐state collisional dynamics by using tunable and pulsed laser techniques and time‐resolved and dispersed fluorescence methods. For the first time, the decay processes of electronically excited iodine,B3IIou+(v′ = 19), to the adjacent vibrational states in collisions with He molecules have been directly observed in real time. The rate constants for the state‐to‐state vibrational energy transfer obtained are,k,vHe(19→18) = (2.76±0.05)x10−11cm3s−1molecule−1andkvHe(19→20) = (1.65±0.04) × 10−11cm3s−1molecule−1. These results are in satisfactory agreement with

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090202

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractUsing tetrapropylammonium bromide (TPABr) as a template, molecular sieve Ni‐ZSM‐5 and its single crystals were synthesized in a nonalkaline system in the presence of fluoride ions. By means of XRD, IR, EPMA, MAS NMR, EPR, DTA and H2‐TPR techniques, it is proved that the hetero‐atom, nickel, is really located in the zeolite framework. And finally, Ni‐ZSM‐5 was found to have high catalytic cracking

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090203

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractA reflux‐treatment of soluble polyaniline (SPA) in dimethylformamide (DMF) containing CoCl2yields an active catalyst for dioxygen reduction which can be adsorbed on the electrode surface firmly. The catalytic reduction of dioxygen at the glassy carbon (GC) electrode modified by the catalyst was studied with cyclic voltammetry (CV), rotating disk electrode (RDE) and rotating ring‐disk electrode (RRDE). The kinetic process of dioxygen reduction at the modified electrode was analyzed with a new RRDE theory dealing with a nondiffusion‐controlled process on ring electrode. The rate constants for each scheme of dioxygen reduction were calculated, showing that only 2‐electron reduction to H2O2was conducted at the modified electrode. The effect of solution acidity on the electrocatalytic behaviour for dioxygen reduction was investigated. A possibility of initiating catalytic activity for dioxygen reduction was explored with ESCA

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090204

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractThree different kinds of rare‐earth metal phthalocyanine complexes (Pc2LuH, Pc3Gd2, R12Pc3Dy2) were synthesized. Their ultra‐thin films were prepared by the Langmuir‐Blodgett technique. Crystallites were observed in Langmuir film of Pc3Gd2by means of transmission electron microscopy. The limiting molecular areas of the phthalocyanine derivatives on pure water increased in the order mono‐, di‐ and triphthalocyanine, implying that these phthalocyanine molecules are stacked with a face‐to‐face orientation and edge‐on to the water surface. By using scanning tunneling microscopy individual molecules of lutetium diphthalocyanine adsorbed on graphite surfaces were imaged for

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090205

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractFrom the acetone extract of the root ofEuphorbia sieboldiana, a newent‐atis‐16‐ene type diterpenol was isolated and its structure was demonstrated asent‐atis‐16‐ene‐13 α‐hydroxy‐3,14‐dione (1) based on the chemical as well as NMR and MS spectroscopic evidences, and finally confirmed

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090206

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractThree pyrrololactam alkaloids have been isolated from the marine spongePhacellia fuscaSchmidt collected from the South China Sea, and their structures were determined as1–3, on the grounds of spectral data. This is the first report of these compounds from this sponge. The structure of1was confirmed by X‐ray analy

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090207

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractThe kinetics for the reaction of ascorbyl palmitate and 4‐hydroxy‐TEMPO, 4‐methoxy‐TEMPO or 4‐hexanoyloxy‐TEMPO in CTAB and SDS micelles was studied by ESR spectroscopy. It was found that the behavior of ascorbyl palmitate is remarkably different from ascorbic acid in their antioxidant activity in micelles. The predominant factors governing the activity in micelles involve the lipophilicity of the antioxidant and the oxidant, the charge type of the substrates and the concentration of the surfactant. As high as 2 × 104fold rate variation was observed by changing the lipophilicity of the antioxidant and the microenvironment of the rea

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090208

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractThe gel‐liquid crystal phase transitions (PT) in bilayers formed from a series of synthetic sodium dialkylmethyl sulphates have been studied by both fluorescence and differential scanning calorimetry (DSC) methods, which are between the transitions of the corresponding phospholipids and the quarternary ammonium salt bilayers possessing the same hydrocarbon chains. The fluorescenceI3/I2ratio (R) of probe pyrene in the bilayers decreases below and increases above the transitions respectively with increasing the chain length of the surfactants in the series SUDS, SPHS, and SHOS. In addition, the difference between theRabove and below the transition (ΔR) is larger in the suspension prepared at the temperature above that of the transition than in that formed at room temperature. Intermembrane transfer and transbilayer migration (flip‐flop) evaluated by means of DSC of a mixture of equimolar aqueous dispersions of SHOS and SPHS as well as by ESR of bilayer embedding the stable free radical 4‐HD‐TEMPO in the presence and absence of excess ascorbic acid take place noticeably only at the temperature above that of the transitions. Cholesterol has shown the same effect onΔRas to decrease the length of the alkyl chain of the surfactants. It also causes a decrease of the fluorescence Intensity ratio of excimer to monomer of pyrene,Ie/Im(S), in both phase. The results are discussed in terms of bilayer structure, chain fluidity, and permeability

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090209

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY

摘要:

AbstractThree substitutedα, β, β‐trifluorostyrenes (TFS's),i. e., p‐thiomethyltrifluorostyrene (4),p‐cyclopropyltrifluorostyrene (5) andp‐t‐butyltrifluorostyrene (6), have been synthesized. The rate constants (k2) of the thermal cyclodimerization of these compounds have been measured in the temperature range 120–160°C. The polar parameters σmbof these TFS's calculated from19F NMR chemical shifts are: forp‐thiomethyl, ‐0.18;p‐cyclopropyl, ‐0.31 andp‐t‐butyl, ‐0.22. The spin delocalization substituent parameters σ′T(140°) ofp‐thiomethyl, cyclopropyl andt‐butyl groups are 0.59, 0.27 and 0.30 respectively. Thus all of these groups act as electron‐donating groups whi

ISSN:1001-604X    

DOI:10.1002/cjoc.19910090210

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1991

数据来源: WILEY