摘要:

AbstractThe dipole moments of two aliphatic imines and their hydrogen bonded phenol complexes were determined experimentally. A value of 1.63D was found for isopropyl, N isopropyl imine and 1.60 D for tertio butyl, N isobutyl imine. Their complexes with phenol, 3,5 dichloro‐ and para nitro phenol are respectively of 3.45, 4.57 and 6.99 D for the first and 3.69, 4.67 and 7.10 D for the second. This experimental study was completed by a theoretical study of model imines and their complexes with watermethanol and formic acid. The theoretical results explain through structural and electronic arguments the variation of the dipole moments. They furnish also values of the angles which are indispensable for the discussion of experimental dipole increments. The dipole increments obtained show clearly the strength of the H‐bond obtained with imine bases as well as its sensibility to the strength of the associated a

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950101

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe conductances of silver (I) perchlorate, nitrate and bromate have been determined in water‐dimethylsulfoxide (DMSO) mixtures at 30°C over the complete range of solvent compositions. The data were analyzed by the 1980 Fuoss equation and the limiting molar conductances (<Λ0) and association constants (KA) of the salts were evaluated at all compositions. TheΛ0values have been split into their ionic values and the ionic Walden products of all the ions were calculated using the transference number data derived from a concentration cell with transference. The initial increase of the Walden product of silver ion up to 20 wt% DMSO and its subsequent decrease beyond this composition with addition of DMSO, indicates that it is preferentially solvated by water at high compositions of water and subsequently by DMSO. For anions, the Walden products vary in a complex manner and seem to be strongly influenced by solvent‐solvent intera

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950102

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe curvature of the line of critical points in a reentrant ternary mixture is determined by approaching the double critical point (DCP) extremely closely. The results establish the continuous and quadratic nature of this line. Out study encompasses as small a loop size (ΔT) as 663 mK. The DCP is realized when ΔTbecomes zer

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950103

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe pressure dependence of the critical temperature is used to bring a homogeneous 2‐butoxyethanol/ water mixture of critical composition (xc= 0.0598; mole fraction of 2‐butoxyethanol; critical temperatureTc(P= 1 bar) = 49.39°C) from a state away from its critical temperature to a state close to the critical temperature. This is accomplished by fast pressure jumps (expansions) with an amplitude in the range of −50 bar<ΔP<−5 bar (ΔP= (Pf‐Pi);Pf, hydrostatic pressure in the final state (Pf= 1 bar);Pi, hydrostatic pressure in the initial state) and a characteristic time constant of τp≃ 0.3 ms. The coefficient characterizing the pressure dependence of the critical temperature has a value of (dTc/dP)c.l.= 43 mK bar−1. The delayed increase of the intensity of scattered light (“critical opalescence”) is measured as function of time at different scattering angles (10° ≤ θ ≤ 60°) and different temperature differences (Tc‐Tf) (Tc. critical temperature;Tf, final temperature after the pressure jump). The fast pressure jump leads to a small decrease of the temperature of the sample ((∂T/∂P)s= 6 mK bar−1). The measured relaxation curves are found to be single exponentials for times short compared with the relaxation time τTof the heat conduction process bringing the system back to its initial temperatureTf(τTis in the order of seconds). – For small values of the scaling variable (qζf)0.7) the structure factor relaxes more slowly than theoretically expected (i.e. τhyd/τexp<1). This behaviour is similar to that of the systems 3‐m

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950104

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

年代:1991

数据来源: WILEY

摘要:

AbstractTheoretical relationships for the kinetics of two‐step charge transfer of bivalent metal were derived taking into account the adsorption of the intermediate according to the Langmuir isotherm. The polarization transients can exhibit inductive behaviour in two anodic and two cathodic particular cases. Inductive transients in the range of low Tafel slope are exclude

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950105

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe implement a ϕ4‐model to analyze the localization of energy in collective modes along the sugar‐phosphate backbone of RNA strands. We focus on the relevance of soliton‐like excitations in the site‐specificity of intramolecular nucleophilic attacks leading to transesterifications in the sugar‐phosphate backbone. We provide evidence supporting the view that hot spots for transesterification of catalytic RNA are caused by a combination of two factors: nonlinear energy transfer and intra‐chain folding. In particular, our results might help understanding the physics of covalent cyclization and cycle‐reopening in the catalytic intervening sequence (IVS) of ribosomal RNA fromTetrahymenaand also they might help identifying the nucleophilic agents and cosubstrate in IVS RNA exci

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950106

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

年代:1991

数据来源: WILEY

摘要:

AbstractMean dynamic dipole polarizabilities α0(λ,T) and second thermodynamic virial coefficientsB(T) of meth‐ane have been determined for the first time in the extended temperature range 128 K ≦T≦ 890 K by means of only one apparatus using interferometric low‐pressure measurements (p≦ 03 MPa) of the refractive indexn(λ,T, p) in the visible wavelength range (λ = vacuum wavelength). α0(λ,T) is in good accordance with previously measured values, but an obvious small minimum at the critical temperatureTcseems to occur. TheB(T)‐data determined in the low‐temperature range ΔT1(128 K ≦T≦ 298 K) are in fair agreement with other published data. The high‐temperatureB(T)‐values of the range ΔTII(760 K ≦T≦ 890 K) have been measured for the first time. They are in good accordance with extrapolated low‐temperature virial coefficients. The mean standard deviation | ΔB| ≈ 8 cm3mol−1of the measuredB(T)‐values may be further reduced by means

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950107

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

年代:1991

数据来源: WILEY

摘要:

AbstractSputtering yields of polycrystalline samples of V, Co, Ni, Cu, Zn, Pd, Pt and Ag were investigated as a function of oxygen pressure from residual gas conditions (po2≦ 0.002 mPa) to 6 mPa. Ar+ions (2 keV; 35μA/cm2; incidence angle θ = 45°) were used for bombardment. Also sputtering yields of Fe, Nb and Ta were observed at residual gas conditions and for 2 mPa of O2and for Ti, Cr and Cd under 2 mPa of O2. The sputtering yields were found to decrease with increasing oxygen pressure. This decrease is most pronounced for metals which are easily oxidized. Sputtering yields of V, Ni, Zn, Pd and Ag were also found to decrease under N2, N2O and NO. Using linear cascade theory the sputtering yields under oxygen were estimated and compared with experimental data. Satisfying correspondence was achieved, if different surface binding energies were assumed for clean and oxidized surfaces respecti

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950108

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe35Cl NQR spectra of the mono‐, di‐, and trichloroacetates of 4‐methylaniline and 3,4‐dimethylaniline, [4‐(CH3)C6H4NH3⊕] [Cl3‐nHnCCOO⊖] and [3,4‐(CH3)2C6H3NH3⊕] [Cl3‐nHnCCOO⊖],n= 0, 1, 2, were studied in the range 77 ≦T/K ≦TdecompositionorTbleaching out. Whereas for the monochloroacetates of both aniline derivatives the35Cl NQR is observable up toT>353 K, broadening of the35Cl NQR lines of both groups, ‐CHCl2and ‐ CCl3, lead to a bleaching of the NQR signals in the range 114 ≦T/K ≦ 280, far below the decomposition temperature of the respective compound. The crystal structures of [4‐(CH3)C6H4NH3⊕] [Cl2HCCOO⊖] and of [3,4‐(CH3)2C6H3NH3+] [Cl3‐nHnCCOO⊖],n= 0, 1 were determined at room temperature. The results of both, diffraction exp

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950109

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

年代:1991

数据来源: WILEY

摘要:

AbstractHNO3and HClO4were intercalated into the graphite lattice by means of chemical oxidants and by electrochemical oxidation. In both cases the potential variation versus time was recorded in order to trace the intercalation process. Compared with H2SO4, the intercalation reactions of nitric and perchloric acid proved to be fast. Impedance measurements indicated that the penetration of the phase boundary by acid anions, acid molecules and water as well as intercalate nucleation determine the reaction rate of the chemical insertion reactions. Biintercalation and cointercalation compounds with HNO3and HClO4were prepared for the first time.

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950110

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

年代:1991

数据来源: WILEY