摘要:

AbstractLaser techniques are used to enlarge the range of application of crossed‐beam experiments and to increase their resolution, via excitation of atomic/molecular reagents on well‐defined quantum states and characterization of reaction products by L.I.F. and R.E.M.P.I. Detailed applications are described in the case of the Cs + H2→ CsH + H photochemical reaction for which a complete set of experimental data was obtained and interpreted by quasi‐classical trajectories.To apply these techniques precise spectroscopic data are required, which are obtained from high resolution, Doppler‐free beam experiments. In turn, reaction dynamics experiments provide out‐of‐equilibrium light sources which can be used to extend spectroscopic analyses. It is shown how the high resolution study of the TiO molecule leads to a new description of its electro

ISSN:0009-4536    

DOI:10.1002/jccs.199800036

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractFragmentation frequently accompanies intact laser desorption ionization of a parent non‐volatile compound, desorption and dissociation dynamics has been a subject of intense studies over the past decade. As a preliminary lest system for future laser desorption study of energetic compounds such as explosives and propellents, we studied UV laser desorption ionization of melamine at a laser power density of approximately 4.4 MW/cm2. Several gas‐phase dissociation channels of the parent and fragment ions formed in UV laser desorption ionization of melamine films can be identified from their velocity distributions. A phenomenological desorption temperature of the order of 20000 K is estimated from fitting the experimental velocity distributions to Maxwellian functi

ISSN:0009-4536    

DOI:10.1002/jccs.199800037

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe absorption and fluorescence properties of a series of 18 indocarbocyanine dyes in organic solvents have been determined. The wavelengths of the absorption and fluorescence maxima, the fluorescence lifetimes and the fluorescence quantum yields relative to the benzo‐15‐crown‐5‐substituted phthalocyanine have been measured. The results are discussed in relation to the molecular structures or the dye

ISSN:0009-4536    

DOI:10.1002/jccs.199800038

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe exchange kinetics of TI+complexes with hexacyclen and hexamethylhexacyclen were studied in 70% methanol solution by proton NMR line‐shape analysis. In TI+‐hexacyclen system, a dissociative mechanism is found to be predominant at higher temperatures, while a bimolecular pathway may become more important at lower temperatures. In contrast, the TI+‐hexamethylhexacyclen system solely prefers a dissociative exchange mechanism in entire temperature range studied. The corresponding exchange rates and the activation parameters Ea, ΔH‡, ΔS‡and ΔG‡for the exchange have been determined, and the possible parameters controlling the exchange rates and mechanisms

ISSN:0009-4536    

DOI:10.1002/jccs.199800039

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe main difficulty inmicro‐HPLC separation is the manipulation with the composition of the mobile phase (degassing of solvents and a slow establishment of equilibrium) but the problem of elution can be solved by temperature optimalization. The effect of temperature inmicro‐HPLC separation of the 16 polycyclic aromatic hydrocarbons (PAHs) (mixture SRM 1647 of the US EPA) has been studied using conventional C18and new developed AP phase (an amide group localized in the hydrophobic ligands). All the investigations have been performed under isocratic conditions (binary hydroorganic mobile phase: acetonitrile/water). The results have shown that, in the case of AP phase, application of temperature gradient (from 298 to 303 K), enabled the attainment of complete 16 PAHs separation (especially of the first 4 solut

ISSN:0009-4536    

DOI:10.1002/jccs.199800040

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractIntroduced in this article is fabrication of an integrated capillary for the applications of electrochemical detection in capillary electrophoresis. The separation section, voltage decoupler, and working electrode were composed into a single section of capillary. The porous decoupler was constructed by HF etching till the thickness of the capillary wall less than 20 μm. The working electrode was prepared by sputtering Au‐films on the outlet of the capillary. The integration of the separation capillary with a complete detection assembly improves the convenience for the routine application of electrochemical measurements in capillary electrophoresis. For a 100‐μm‐i.d. capillary, the theoretical plate number of catechol and the migration time reproducibility can reach 120,000 and 1.9% RSD, respectively. The linear range exceeds 3 order of magnitude and the detection limit is lower than

ISSN:0009-4536    

DOI:10.1002/jccs.199800041

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe quadruply bonded complexes containing bridging acetate and polydentate phosphine ligands of the type Mo2(O2CCR3)XJ(η3‐etp) (R = H, X = Br, 1; R = F, X = CI, 2; R = F, X = Br, 3; etp = Ph2PCH2CH2P(Ph)CH2CH2PPh2) were prepared by reactions of Mo2(O2CCR3)X2(PPh3)2with etp in CH2X2. Their UV‐vis and31P{1H}‐NMR spectra have been recorded, and the structure of 1 has been determined by X‐ray crystallography. Crystal data for 1·2CH2Br2: space group P21/c, a = 13.924(7) Å, b = 21.157(4) Å, c = 14.427(5) Å, β = 101.82(3)°, V = 4159(2) Å3, Z = 4, with final residuals R = 0.0797 and Rw = 0.0793. The absorption wavelengths of the δ → δ* transitions and the chemical shifts and the coupling constants of the31P{1H}‐NMR spectra of these complexes are dependent on the natures of the halogen atoms an

ISSN:0009-4536    

DOI:10.1002/jccs.199800042

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe reactions of Schiff bases, derived by the condensation of thiophene‐2,5‐dicarbaldehyde and furan‐2,5‐dicarbaldehyde with 2‐thienylmethylamine or 2‐furanmethylamine, with silver nitrate have been studied in refluxing anhydrous methanol under nitrogen atmosphere. Complexes thus formed have been isolated and characterized by elemental analysis, electrical conductance, cyclic voltammetry, and1H NMR,13C NMR, IR, LTV‐Vis, and mass spectroscopic studies. The experimental results reveal that the complexes are primarily ionic in nature, consisting of (L)3Ag2dication and Ag(NO3)3negatively charged dianions. The molecular structure of one of the complexes, [((C4H3O)CH2NCH(C4H2S)CHNCH2(C4H3O))3Ag2] [Ag(NO3)3] has been studied in the solid state. The complex is crystallized in the triclinic space group\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm P}\bar 1 $\end{document}with a = 12.889(7) Å, b = 14.884(5) Å, c = 15.084(6) Å, α = 92.18(4)°, β = 79.78(4)°, γ = 110.92(4)°. The structure is disordered. Each Ag in dication is tri‐coordinated by three azomethine N atoms from three ligands, and each ligand employs two azomethine N atoms to coordinate to two Ag ions such that the geometry around the Ag ⃜Ag axis conforms to a propeller‐shape. The two Ag ions are between the two N3planes with Ag ⃜ Ag distance ca. 4.8.1 Å. There is no bonding between any Ag ion and any thiophene of the three ligands. However, two Ag ions and three thiophene S atoms f

ISSN:0009-4536    

DOI:10.1002/jccs.199800043

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractDiazepam(1)is a frequently prescribed hypnotic/anxiolytic drug in worldwide use. Compound1is hydrolyzed in alkaline medium to form 2‐methylamino‐5‐chlorobenzophenone imine(2)and 2‐methylamino‐5‐chlorobenzophenone(3); the ratio of2:3increases with increasing NaOH concentration (J. Pharm. Sci.85, 745–748, 1996). The mechanism in the conversion of1to2and3via various intermediates is the subject of this report. Results of hydrolysis kinetics and structural identification of some intermediate products indicated an initial hydroxide attack at the C2‐carbonyl carbon of1, resulting in the formation of a dioxide (7, 7‐chloro‐1,3‐dihydro‐1‐methyl‐5‐phenyl‐2H‐1,4‐benzodiazepin‐2,2‐dioxide). Compound7was characterized by proton NMR spectroscopy and via its monomethyl ether (8, 7‐chloro‐1,3‐dihydro‐2‐hydroxy‐2‐methoxy‐l‐methyl‐5‐pheny]‐2H‐1,4‐benzodiazepine). The seven‐member diazepine ring of7opened at the N1‐C2 bond to form a glycinate [5, 2‐methylamino‐5‐chloro‐α‐(phenylhenzylidene)glycinate]. Compound7(and/or5) underwent an additional hydroxide attack at the

ISSN:0009-4536    

DOI:10.1002/jccs.199800044

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractA solution of γ‐crystallin became turbid upon beating at 65 °C for 30 minutes; however, addition of α‐crystallin suppressed this thermal aggregation. It was found the effective chaperone function could be achieved with the molar ratio of α/γ greater than 1/20. In terms of crystallin subunit, five molecular α‐crystallin subunits could afford chaperone for one molecular γ‐crystallin. The gel filtration profile of the sample solution, containing α‐ and γ‐crystallins and preincubation at 65 °C for 30 minutes, showed complex formation between α‐ and γ‐crystallins, indicating α‐crystallin was bound to thermally denatured γ‐crystallin. A 1‐anilinonaphthalene‐8‐sulfonic acid (ANS) fluorescence study showed that α‐crystallin has more hydrophobic regions exposed after thermal incubation. In the presence of urea, both the α‐crystallin chaperone activity and the ANS fluorescence intensity decreased. Accordingly, hydrophobic regions of α‐crystallin play

ISSN:0009-4536    

DOI:10.1002/jccs.199800045

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY