ISSN:0005-9021    

DOI:10.1002/bbpc.19840880602

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe dynamical properties of hydrated di‐myristoyl‐phosphatidylcholin were studied at microwave frequencies. The relaxation frequency and the energy of bound water were determined: the properties of bound water vary quasi‐continuously with the amount of bound water. Water is stronger bound in the fluidlike than in the gel phase. For the first time we could measure directly the trans‐gauche isomerization rotation of the alcyl chains. It was observed that two mechanisms are separately operating at the phase transition of the hydrated bilayers: 1. a change of hydration coupled with a change of headgroup conformation and 2. the chain melting. The binding or release of water is preceding the chain melting or freezing by 1 K. It was found that hysteresis effects of the phase transition depend strongly on the rate of hy

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880603

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

年代:1984

数据来源: WILEY

摘要:

AbstractMultilamellar liposomes of dimyristoylphosphatidylcholine in excess water have been investigated by differential temperature scanning calorimetry. The heat, ΔQ, that is exchanged between the environment and the sample at its main phase transition (fluid ↔ ordered) has been determined as a function of the sample volume, lipid concentration, and scanning rate. No variation of the transition heat is found for sample volumes ranging from 35 μl to 785 μl and for lipid concentrations ranging from 3 mM to 300 mM. For low scanning rates α(α ≤ 0.02 K · min−1) a constant transition heat of ΔQ= 23.4 kJ · mol−1is found that increases around α = 0.1 K · min−1to ΔQ= 27.2 kJ · mol−1which remains constant for higher α. We interpret this finding as being evidence for non‐equilibrium transitions at high scanning rates due to relaxation process in the lipid‐water‐system tha

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880604

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

年代:1984

数据来源: WILEY

摘要:

AbstractSyntheses of the trimer (n= 3), tetramer (n= 4) and the pentamer (n= 5) of the p‐oxybenzoate series C6H5CO(–OC6H4CO)n‐2‐OC6H5are reported. Densities and thermal expansion coefficients of the neat liquids were measured and phase transitions in the pure compounds and their binary mixtures were investigated by differential scanning calorimetry (DSC). The nematic‐isotropic transition is directly accessible only in the case of the tetramer (melting point 181°C, nematic‐isotropic transition temperatureTNI= 254°); the trimer melts to an isotropic liquid at 136°C and the nematic‐isotropic transition of the pentamer (melting point 224°C) lies above the range of thermal stability. DSC results for the binary mixtures show the coexistence range of the nematic and the isotropic phases to be very small; it is obscured by pre‐ and post‐transition effects. In satisfactory approximation therefore, the binary mixtures can be treated as one‐component systems, andTNImay be identified with the maximum of the DSC peak. Values ofTNIthus obtained are linear with respect to composition and may be extrapolated to obtainTNI= 100°C for the pure trimer and 464°C for the pure pentamer. As shown by conformational analysis, all conformers of a given homolog have virtually the same axial ratio. These compounds therefore can

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880605

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

年代:1984

数据来源: WILEY

摘要:

AbstractCharacteristic temperaturesT* have been evaluated for the oligomeric p‐oxybenzoates, C6H5CO(‐OC6H4CO)n‐2‐OC6H5from the transition temperaturesTNIpresented in the preceding paper. Forn= 3, 4 and 5 they are, respectively, 343, 316 and 306 K. These parameters that measure the intensities of the orientation‐dependent intermolecular interactions are correlated with the optical anisotropy Δα and the average intermolecular cohesive energy expressed by the characteristic pressurep*. The characteristic temperatureT* decreases slightly with chain length. The lattice theory of nematic fluids is extended to include mixtures of rodlike molecules having different characteristic temperaturesT* in order to treat binary and ternary mixtures of the p‐oxybenzoate oligomers. The wide biphasic gaps predicted for the several binary systems and the concomitant pronounced partitioning of the components between the nematic and isotropic phases are not confirmed by experiments. Compositions of the coexisting phases in ternary systems were found to be identical within limits of experimental determinations. These marked departures from theory are explicable on the premise that facile rotational diffusion of the nematogens here considered, which are of comparatively low chain length, leads to rapid generation of ordered domains of large dimensions. Subsequent diffusional transport over the required distances consequently is very slow. The transition temperatures observed in binary systems are in excellent agreement with calculations carried out in the “single component” approximation using mean values of the axial ratio and ofT* for the mixture, these being taken to be the same in the two phases at equ

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880606

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

年代:1984

数据来源: WILEY

摘要:

AbstractOne of the possible mechanisms operating in ion‐exchange kinetics is film‐diffusion. The typical rate law describing this process can also be derived by viewing the exchange system as an electrical circuit containing a seat of emf, a resistor and a capacitor. The loading of the ion exchanger can be likened to the charging of the capacitor, and a qualitative description is given of the influence of the chemical potential as the driving force for the ion exchange proc

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880607

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

年代:1984

数据来源: WILEY

摘要:

AbstractBy using perturbation theory it is shown that the lattice theory of Guggenheim applied to molecules of equal size makes good predictions for the excess Helmholtz energyaηEand the excess energyuηEfor mixing at constant density. The differences ofaηEanduηEto the excess quantitiesgpEandhpEfor mixing at constant pressure, however, can be considerably large and are expressed analytically. These results are also essential for understanding new computer simulations. Finally, the applicability of the lattice theory to molecules of different sizes is investiga

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880608

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe intermolecular structure functions for liquid chloroform of various isotopic composition have been calculated from an MD simulation. Good agreement was found with the x‐ray measurement and four of the five experimental neutron structure functions. Strong disagreement, however, exists between the atom atom correlation functions derived from the neutron scattering experiments with the isotopic substitution method and the MD results. It seems possible that the atom atom correlation functions from the neutron scattering experiments, which are not without difficulties, might have suffered from experimental uncertaintie

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880609

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe temperature dependences of proton spin‐lattice relaxation time,T1and of the second moment of1H NMR absorptions were studied in dimethylammonium hexachlorostannate(IV), hexachlorotellurate(IV), and their partially deuterated analogs. From X‐ray powder patterns taken at room temperature, the tellurium(IV) complex was found to be isomorphous with the tin(IV) complex. For the tellurium complex, a phase transition was located at 169 K by DTA experiments. By1H NMR, two kinds of motions, the reorientation of the methyl groups about their respective C ‐ N bond axis and the 180° flip motion of the whole cation about its two fold pseudosymmetry axis, were observed for the cation in the crystals. The activation energies were evaluated for these motional modes. Besides these two motions, large‐amplitude librations or small angle reorientations of the cation about its pseudosymmetry axis are deduced to take place at high temp

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880610

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

年代:1984

数据来源: WILEY

摘要:

AbstractSolid Cu—Ni alloys have been investigated thermodynamically within the whole range of composition by Knudsen Cell Mass Spectrometry. The “Algebraic Intensity‐Ratio”‐method (A.I.R.) has been used for the determination of the thermodynamic mixing behavior. The thermodynamic activitiesajshow positive deviations from Raoult's law. The molar enthalpies of mixingHEand the molar excess Gibbs energiesGEare positive over the whole range of composition. At 1350 K the maximum value ofHEis 2420 J/mol (59.48 at‐% Ni), and the maximum value ofGEis 3220 J/mol (53 at‐% Ni). The excess entropiesSEare negative over the whole range of composition with a minimum value of — 0.719 J/mol · K at 36.71 at‐% Ni. The phase diagram has been re‐evaluated by using an analytical procedure which is based on the generalized Newton method for the numerical solution of equations. The calculations are based on the thermodynamic data obtained in this study, on the thermodynamic results from mass spectrometric studies on liquid Cu—Ni alloys, and on literature data for the heat capacities and the heats o

ISSN:0005-9021    

DOI:10.1002/bbpc.19840880611

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

年代:1984

数据来源: WILEY