Hydrogen bond lifetimes in supercritical methanol–water mixtures via MD simulation

Dynamical features of hydrogen bonds in methanol–water mixtures have been analysed in terms of lifetime in the wide range of conditions, including supercritical states, using a molecular dynamics simulation with flexible potential models. Hydrogen bond characteristics in methanol–water mixtures were investigated by considering the combination of molecular species and donor–acceptor of hydrogen-bonded molecules. The hydrogen bond lifetimes mainly depend on temperature, and those in supercritical condition were about 1/10th of that at ambient condition. Focusing on the composition dependence of the hydrogen bond lifetime, the unique behaviour of that resulting from hydration structure was observed. Moreover, the molecular combination, which showed the largest hydrogen bond lifetime, was different for ambient and high temperature and high pressure conditions. The relationship between hydrogen bond lifetime and molar volume was also calculated to discuss the hydrogen bond lifetime in terms of the collision frequency of molecules and the intermolecular distance.     

Selective recognition of CG interruption by 2′,4′-BNA having 1-isoquinolone as a nucleobase in a pyrimidine motif triplex formation

To develop a novel nucleoside analogue for the effective recognition of CG interruption in a homopurine-homopyrimidine tract of double-stranded DNA (dsDNA), we succeeded in the synthesis of a triplex-forming oligonucleotide (TFO) containing a novel 2′,4′-BNA (Q^B) bearing 1-isoquinolone as a nucleobase, and the triplex-forming ability and sequence-selectivity of the TFO (TFO-Q^B) were examined. On melting temperature (T_m) measurements, it was found that the TFO-Q^B formed a stable triplex DNA in a highly sequence-selective manner under near physiological conditions.     

Phonon drag conductivity in the Fröhlich-Peierls phase in quasi-one-dimensional electron phonon systems with impurities

The effect of impurities on the static conductivity in the Fröhlich-Peierls phase is discussed by using the technique of the temperature Green function. The diagrams of the phonon drag type especially are shown to give the most important contribution to the static conductivity at low temperatures. The temperature dependence of this contribution is of the activation type with an activation energy equal to the pinning frequency of the phase mode of the charge density wave. The dependence of the preexponential factor on the impurity concentrations is also discussed.On leave of absence     

Computer calculation of tensors in Riemann normal coordinates

A new method of calculation is given for arbitrary tensors in Riemann normal coordinates. Inventing a compact notation for an abstract form of tensors which is suitable to a noncommutative algebra system, we carry out the computer calculations to obtain coefficients of the Taylor expansion of tensors in Riemann normal coordinates. Explicit forms are given up to the tenth order for the metric tensor.     

Magnetothermal resistivity of antiferromagnetic insulator

Magnetothermal resistivity of an antiferromagnetic insulator is calculated by assuming that the thermal energy is carried mainly by phonons which are scattered by spin fluctuations. The spin system is treated by the Green function method.     

Some fatty acids having an O-heterocycle in their terminal positions. I. ω-(3-Chromonyl)alkanoic acids

Some ω-(3-chromonyl)alkanoic acid derivatives, 1a and 2a , n = 4, 5; 3a, 4a and 5a , n = 2-6, were synthesized by cyclization of corresponding methyl ω-(2-hydroxybenzoyl)alkanoates 7b or ethyl ω-(2,4-dihydroxybenzoyl)alkanoates 8b with N,N-dimethylformamide-dimethyl acetal or acetic anhydride-DBU followed by hydrolysis.     

Simultaneous measurements of stress and infrared dichroism on polymers

Summary In order to obtain informations on the molecular nature and mechanism of rheological processes on polymers, simultaneous measurements of stress and infrared dichroism were made of polychloroprene (Neoprene Type AC) films during the course of continuous elongation at the constant rate 25%/min and of stress relaxation at 400% elongation. The time dependence of the infrared dichroism was obtained by measuring the intensity change at fixed wavenumbers of absorption band maxima on the differential polarized infrared spectra. Both the degree of crystallinity of sample films and the orientation function of transition moments were calculated from the results of the infrared dichroic measurements under the assumption of uniaxial orientation, which was confirmed to be the case by X-ray diffraction and birefringence measurements.In the continuous elongation experiments, it was found that the orientation functions for crystalline-sensitive bands showed maxima at 25% elongation and then decreased rapidly, changing their signs from positive to negative. There also appeared the yield point in the stress-strain curve and the beginning of sharp decrease of crystallinity at the same degree of elongation 25%. These facts were interpreted in terms of the orientation of the crystalline phase followed by the degradation of crystallites and drawing out of the molecular chain from the crystallites. In the stress relaxation experiments, moderate changes in the orientation functions were found for various characteristic absorption bands. Little difference was observed between changes in the orientation functions for the amorphous and crystalline-sensitive bands. This makes a contrast with the previous results for vulcanized natural rubber, where the orientation of the crystalline phase was completed almost immediately after elongation, while in the amorphous phase the molecular chains were oriented gradually during the course of stress relaxation.

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Zusammenfassung Um Informationen über die molekulare Natur und den Mechanismus rheologischer Prozesse von Polymeren zu erhalten, wurden gleichzeitige Messungen der Spannung und des Infrarot-Dichroismus an Polychloropren-Filmen (Typ AC-Neopren) während der kontinuierlichen Verstreckung bei konstanter Verstreckungsgeschwindigkeit von 25%/min und während der Spannungsrelaxation bei 400% Verlängerung durchgeführt. Die Zeitabhängigkeit des Infrarot-Dichroismus wurde aus der Intensitätsänderung im festen Wellenzahlbandmaximum eines Kristallisationsbandes mit einem differenz-polarisierten Infrarot-Spektrographen festgestellt. Beide, der Kristallanteil der Probe und die Orientierungsfunktion für die Übergangsmomente lassen sich aus den Resultaten unter Annahme einachsiger Orientierung auswerten. Letztere, die einachsige Orientierung, wurde mit Röntgenbeugung und Doppelbrechung sichergestellt.In den Experimenten mit kontinuierlicher Verlängerung zeigten die Orientierungsfunktionen der Kristallempfindlichen Banden bei 25% Verlängerung ein Maximum. Danach sanken sie rasch unter Wechsel ihres Vorzeichens von positiv nach negativ ab. Der Fließpunkt in der Spannungs-Dehnungs-Kurve und der Beginn des scharfen Abfalls der Kristallinität zeigen sich vom gleichen Verlängerungsgrad 25% ab.Diese Tatsachen werden aufgrund der Orientierung der kristallinen Phase erklärt, gefolgt von einem Abbau der Kristallite und einem Herausziehen der Molekülketten aus den Kristalliten. In den Spannungsrelaxationsversuchen wurden gewisse Änderungen der Orientierungsfunktionen für die verschiedenen charakteristischen Absorptionsbanden gefunden. Es ergaben sich geringe Differenzen in der Änderung der Orientierungsfunktionen für die amorphen und kristallempfindlichen Banden. Das steht im Gegensatz zu früheren Resultaten an vulkanisiertem Naturkautschuk. Bei letzteren war die Orientierung der Kristallphase beinahe unmittelbar nach der Dehnung vollständig, während in der amorphen Phase die molekularen Ketten nach und nach im Laufe der Spannungsrelaxation orientiert wurden.

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With 8 figures in 9 details and 1 table