摘要:

AbstractThe organometallic radical: (3,5‐di‐t‐butyl‐0‐benzoquinone)tetracarbonyl‐rhenium(0) and its triphenylphosphine substituted derivatives were studied by EPR spectroscopy. The unpaired electron is shown to be localized in the organic 1,2‐diketone ligand. The rate of carbonyl substitution by triphenylphosphine at the unsubstituted rhenium radical indicates a second order reaction. The activation parameters are ΔH* =19.1±0.8Kcal/moleand ΔS

ISSN:0009-4536    

DOI:10.1002/jccs.198600013

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractElectron spin resonance (ESR) spectra of carbon radicals on Ru/Al2O8, catalysts have been studied. Carbon monoxide treatment resulted in three kinds of sorbed species: a weakly sorbed CO species associated with the anisotropic spectrum; a more tightly sorted carbon species, perhaps amorphous carbon; and another carbon species, which is essentially unreactive with oxygen and may be graphitic carbon.

ISSN:0009-4536    

DOI:10.1002/jccs.198600014

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractA method is developed for the determination of trace amounts of selenium by flow injection analysis based on the catalytic effect of this element. Catalytic enhancement by selenium for the reduction of picrate ion by sodium sulfide was used and photometrically measured at the wavelength, 470nm.Optimum conditions were determined for temperature,pH, the concentrations of picrate and sodium sulfide, and also the conditions of the flow system; injection of sample volume, flow rate and mixing coil length.With these conditions a good linear relationship was obtained for selenium in the range from 0.1ppmto 1.0ppmand the detection limit was about 5ppb(two times of the noise). Interference by the diverse ions can be avoided with the use of a precolumn cation exchanger (Dowex 50) and by masking with EDTA in the conditional stream.

ISSN:0009-4536    

DOI:10.1002/jccs.198600015

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractPolyaniline has been synthesized by the chemical and electrochemical oxidation of aniline. The conductivities increase by seven order of magnitude upon protonation. The IR absorption band near 1590cm−1shifts to a lower frequency upon protonation. Visible spectra vary with the degree of protonation and the applied potential. Cyclic voltammetry indicates that polyaniline exists in several form

ISSN:0009-4536    

DOI:10.1002/jccs.198600016

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractThe electrochemical behaviour of several derivatives containing the sequence S‐C‐CO‐N in their structure presented as such or in masked form in both aqueous and non‐aqueous media are reported. The results of electrooxidation indicated that when the S atom is present as hetero atom in the structure of the molecule the main product will be the sulphone derivative, on the other hand when present in the form C=S the preferential product is the dimer. The overall redox study indicated that the azo group at C‐2 is very active in both aqueous and non aqueous media. On the other hand derivatives substituted at C‐2 the preferential electrochemical step is the attack of the hetero

ISSN:0009-4536    

DOI:10.1002/jccs.198600017

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractBenzophenone is produced in the photocatalytic oxidation of diphenylmethane in an oxygen saturated TiO2suspension. The yield is found to increase with increasing solvent polarity. An electron transfer mechanism is proposed in which a pair of electron‐positive holes generated initially by illumination may transfer an electron to O2and abstract an electron from diphenylmethane to form O2−and ϕ2CH2+; subsequently, ϕ2CH2+will react with O2−to give the

ISSN:0009-4536    

DOI:10.1002/jccs.198600018

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

Abstract2,5‐Dimethoxy‐2,5‐dihydrofuran (DDF) reacts with dichloroketene to give 7,9‐dimethoxy‐3,3,5,5‐tetrachloro‐8‐oxabicyclo[4,3,0]‐noan‐2,4‐dione (I), and methyl chloro‐(2,5‐dihydro‐5‐methoxy‐2‐furanylidene) acetate (II). The reactions of 2,5‐dihydrofuran and 2,5‐dimethoxy‐tetrahydrofuran with dichloroketene were also‐studied for comparison. Compound II was derived from the insertion of a molecule of dichloroketene into the C‐O bond of DDF with subsequent dehydrochlorination. Compound I resulted from the cycloaddition of two molecules of dichloroketene to the C=C bond of DDF. A mechanism involving a 1,5‐dipolar intermediate i

ISSN:0009-4536    

DOI:10.1002/jccs.198600019

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractTo study the role of glycine residues in stabilizing the collagen triple helix, the glycine residues in the polytripeptide (Pro‐Ala‐Gly)nwere partially replaced by alanine. The proline content was kept constant. The stability of the helical conformation of these polypeptides was studied by IR‐ and X‐ray measurements in the solid state and by ORD, CD and viscometry in solution. The renaturation was followed as a function of time. All the polytripeptides studied, with the exception of (‐Pro‐Ala‐Ala‐)nattained the polyproline II conformation. However the stability decreased with increasing alanine content. Obviously the molecules of (‐Pro‐Ala‐Gly‐) are highly associated by intermolecular hydrogen bonds and one may therefore suppose that a triple‐stranded helix aggregation occurs. The results of the refolding process show that the stability of the helices seems to also affect the refolding rate in terms of the optical rotation, Two transitions appeared: the first one is responsible for a rapid reversible change in conformation and the second one for a further slow and irreversible change in the hydrodynamic shape. The latter seems to be due to the partial helical nature, leading

ISSN:0009-4536    

DOI:10.1002/jccs.198600020

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractTwo pairs of isomers of 3‐ and 2‐phthalimido‐3(2)benzimidazolylpropanoic acid (V and VI) and 2‐ and 3‐phthalimidobenzimidazopyrrolone (VII and VIII) were produced from the reaction of phthaloylaspartic anhydride (I) witho‐phenylenediamine (II). The13C‐NMR spectra of V and VI both showed 11 carbon signals indicating that the structures of their benzimidazole groups were symmetric. Isomers V and VI were easily distinguished from each other by the chemical‐shift‐differences (Δδ) of the methylene carbon and the methine carbon. Compounds VII and VIII displayed 14 carbon signals and no longer showed the symmetric structure of the benzimidazole moity, The chemical‐shift‐differences (Δδ) between methylene carbon and methine carbon in pyrrolones of VII and VIII can also be used to distinguish VII from VIII. The Δδ of compound VII is less

ISSN:0009-4536    

DOI:10.1002/jccs.198600021

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractIn‐beam and matrix‐isolation techniques have been used in the mass spectral studies of several categories of biologically significant compounds. These include amino acids, quaternary ammonium salts, vitamins and nucleosides. Molecular ions and/or (M+H)+ions are obtained, together with useful fragmentations, all of which are valuable in structural elucidations. Spectra obtained by this version of the in‐beam technique are similar but not identical with those obtained by field desorption and secondary ion mass spectrometry. Ammonium and sodium chlorides, ammonium sulfate,p‐toluenesulfonic and hydrochloric acids can all be used as a room temperature matrix. The detection limits for vitamin E and 2′‐deoxyguanosine have been determined as 1ngand 5 μg,

ISSN:0009-4536    

DOI:10.1002/jccs.198600022

出版商:WILEY‐VCH Verlag    

年代:1986

数据来源: WILEY