ISSN:0005-9021    

DOI:10.1002/bbpc.19820860802

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

年代:1982

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19820860803

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

年代:1982

数据来源: WILEY

摘要:

AbstractThe oxidation kinetics of several N‐ and ring‐alkylated p‐phenylenediamines with hexacyanoferrate(III) (F3) was studied in the pH‐range 2,5 – 9 by means of a multimixing stopped flow technique which is described in detail. The p‐phenylene diamine‐derivatives (R) are oxidized via reversible one‐electron steps to the semiquinone diimine radical S (rate constantsk1,k−1) and the quinone diimine T (rate constantsk2,k−2). –k1andk−1could be measured directly for all compounds,k2andk−2for two derivatives. – Only the unprotonated species of R, S, T, F3are reactive. The reduction is possible by the unprotonated Fe(CN)4‐6(F2) and by its protonated form F2H. The complexes of F2with alkali ions are inactive. In this way the respective association constants could be calculated. The kinetics of the reaction was compared with the thermodynamics, represented by potential‐pH‐diagrams. – The activation parameters of the reaction of p‐phenylene diamine‐derivatives with F3, F2and also with iodine were measured. The activation energies of the second step (k2,k−2) are negligible. – Both oxidants attack the alkylated aminogroup of the p‐phenylene diamine derivatives. The radical

ISSN:0005-9021    

DOI:10.1002/bbpc.19820860804

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

年代:1982

数据来源: WILEY

摘要:

AbstractAn electrochemical method for the determination of the local hydrogen activity, and indirectly the local hydrogen concentration, in a metal sample is described. The sample is employed as part of a concentration cell, with the remainder of the cell contained in a movable probe designed so that the electrolyte contacts only a small portion of the sample surface. Two such probes are described, one using an aqueous electrolyte, the other a solid proton conductor. As examples of the method, activity measurements are reported for a palladium wire nonuniformly loaded with hydrogen, and for pressed pellets of Zr powder and crystalline and amorphous samples of intermetallic compounds loaded with hydrogen by both physical and electrochemical means.

ISSN:0005-9021    

DOI:10.1002/bbpc.19820860805

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

年代:1982

数据来源: WILEY

摘要:

AbstractCyclic electrochemical intercalation/deintercalation of anions fromaqueous salt solutionsin crystalline graphite electrodes has been investigated. The practical electrode was polypropylene bound natural graphite “CPP”. The main candidates for the salts were NaClO4, NaBF4, Na2SO4and KF in the concentration range of 0.1 – 12 M. –Current efficienciesα with ClO−4and BF−4are lower as in aqueous acids due to side reactions, which increase with increasing dilution and temperature. No pH‐effect on α has been found between pH 1 – 12. Under favourable conditions (8 M NaClO4at 20 °C or 4 M NaClO4at 0 °C), α's as high as 80% have been observed. A pronounced formation effect is found upon galvanostatic cycling. In Na2SO4, α drops to zero at pH 3 due to the lack of HSO−4‐ions. No intercalation of F−ions is detected from aqueous KF. –Intercalation potentialE1shows Nernst behaviour with regard to anions in solution and intercalated anions. The slope of Nernst curve is 59 mV per decade as expected.E1is much more positive than in aqueous acid of the same concentration due to the absence of solvate acid depolarization. The anions are desolvated, but not discharged upon intercalation. No indication of an in situ formation of solvate acid has been found. – For comparison, intercalation of anions from perchlorates in CH3OH, CH3COOH, and CH3CN has been investigated. – The potential application in an aqueous Zn/graphite accumulator is discussed. This battery has – with 4 M NaClO4

ISSN:0005-9021    

DOI:10.1002/bbpc.19820860806

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

年代:1982

数据来源: WILEY

摘要:

AbstractTwo 4‐cyano‐4′‐alkoxybiphenyl derivatives (3 COB‐8 COB) have been used as fluorescent micellar probes in four different surfactants (SDS, CTAB, NPh‐EO‐9, and NPh‐EO‐30) the concentration [S] of which varies in a broad range around the CMC. The distribution constantKfor the solubilization of the probes between micelles and water and the solubilitySin the surfactant are obtained from the absorption spectra after saturation of the sample either by stirring at room temperature or by ultrasonication. CMC values in agreement with those reported in the literature are determined from the curves λmax=f[S]. According to the saturation method, a different type of aggregate is formed below the CMC in the case of 8 COB. The emission spectra demonstrate that the COB derivatives are preferentially solvated in polar environment (polarity>ethanol). The assignment of the observed enhanced line width as compared to homogeneous solutions reveals the existence of several types of sites with different polarities and indicates inhomogeneous locations in the micelle with exchange times slower than about 1 nanosecond. – The results are tentatively interpreted according to the Fromherz's surfactant‐bloc

ISSN:0005-9021    

DOI:10.1002/bbpc.19820860807

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

年代:1982

数据来源: WILEY

摘要:

AbstractThe trans‐isomers of certain thioindigoid dyes in dilute solutions can be completely converted to the cis‐isomer by selective excitation of the trans‐isomer. At higher dye concentrations the conversion is limited. The corresponding photostationary state is determined by two processes in opposite directions: (i) by the usual trans→cis photoisomerization and (ii) by an inverse cis→trans isomerization initiated by excitation of the trans‐isomer. An analysis of this peculiar effect has shown that the trans‐triplet catalyses the cis→tran

ISSN:0005-9021    

DOI:10.1002/bbpc.19820860808

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

年代:1982

数据来源: WILEY

摘要:

AbstractIn the present paper we report on the discovery and some initial investigations of sustained limit cycle oscillations in the stirred flow oxidation of cerous ions by acidic bromate. In order to find and measure the region of oscillations in the parametric plane of the inflow concentrations of bromate and bromide, a linear concentration gradient method was applied. At present the described flow oxidation is the simplest chemical oscillator fully understood in terms of elementary reaction steps.

ISSN:0005-9021    

DOI:10.1002/bbpc.19820860809

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

年代:1982

数据来源: WILEY

摘要:

AbstractThe monolayer phase transition from the liquid‐condensed to the liquid‐expanded phase of the unusual synthetic phospholipid DPPA has been studied with the Langmuir film balance and compared with literature data of DPPC. DPPA and DPPC have different head groups. DPPA has a quarternary acridine orange (AO) residue instead of the quarternary nitrogen atom of DPPC. – The equilibrium pressure π of the phase transition of DPPA increases linearly with the transition temperatureTu: dπ/dTu= 3.1 · 10−5N cm−1K−1. The area change ΔFu= 6.6 · 10−16cm2per molecule DPPA at the phase transition is within the limits of error independent of π, in contrast to DPPC and other phospholipids. The transition entropy ΔSu= 125 J K−1mol−1and transition enthalpy ΔHu= 38 kJ mol−1are large in comparison to DPPC under equal experimental conditions. The difference is related to the association of the head groups of DPPA in condensed phase. It agrees qualitatively with the thermodynamic parameters of the dissociation of d

ISSN:0005-9021    

DOI:10.1002/bbpc.19820860810

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

年代:1982

数据来源: WILEY

摘要:

AbstractBetaine B (8‐amino‐5‐ethyl‐3‐oxido‐6‐phenylphenanthridinium‐betaine) is bound to DNA as protonated cation BH⊕(8‐amino‐5‐ethyl‐3‐hydroxy‐6‐phenylphenanthridinium‐cation). BH⊕is a hydroxy derivative of the ethidium cation E. Its binding to calf thymus DNA has been investigated by means of absorption spectroscopy. From binding isotherms we determined the binding constants of the non‐competitive binding (intercalation)K1= 0.9 · 104M−1and the competitive binding (external binding)K2= 1.0 · 106M−1using NaCl as competitor,T= 298 K. The constantK1of the intercalation is much more smaller than the constantK2of the external binding. Similar properties has the ethidium cation E. – Unprotonated betaine B isn't bound to DNA. In a range of middle pH‐values there exists an equilibrium in solution between the free unprotonated betaine B and the protonated bound betaine BH⊕. The free enthalpy of binding

ISSN:0005-9021    

DOI:10.1002/bbpc.19820860811

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

年代:1982

数据来源: WILEY