Temperature dependent dielectric relaxation study of ethylene glycol-water mixtures

Using the picosecond time domain reflectometry method, dielectric relaxation measurements for 13 ethylene glycol (EG)-water mixtures have been studied from 0 to 40°C. The dielectric relaxations in the mixtures show a Debye-type behavior, whereas the relaxation in pure EG can be described by the Cole-Cole model. The static dielectric constant ₀, the relaxation time and the dielectric constant at high frequency have also been determined at various temperatures. The dielectric relaxation data suggests that there is no tendency to form hydrogen bonds with the addition of water to EG unlike other alcoholic systems but this tendency becomes increasingly important with decreasing temperature. The activation energy decreases with increased water content in the mixture as expected.     

Dielectric study of poly(methyl methacrylate) microcapsules in particular reference to the effect of the frequency dependence of the permittivity of the capsule wall

The dielectric behavior of poly(methyl methacrylate) (PMMA) microcapsules was analyzed theoretically by taking account of the frequency dependence of the relative permittivity _s and the electrical conductivity _s of the capsule wall. For comparison, similar analysis was applied to polystyrene (PS) microcapsules which have frequency-independent _s and _s . The behavior of _s and _s of the PMMA microcapsules was assumed to be represented by a dielectric relaxation of them-th power type on the basis of dielectric data on underwater PMMA films. By means of a theory of the interfacial polarization, some consideration was carried out regarding the effect of the frequency dependence of _s and _s on the dielectric behavior of the PMMA microcapsules. The consideration led to predictions that the frequency dependence of _s and _s causes (i) the variation in the relaxation intensity with the change in the conductivity of suspending medium, (ii) the frequency dependence of the permittivity at low frequencies and (iii) the frequency dependence of the conductivity at high frequencies. The theoretical prediction (i) was verified by observed data, (ii) and (iii) remaining unverified owing to the experimental difficulty.     

Determination of various deformation processes in impact-modified PMMA at strain rates up to 105%/min

The deformation processes in impact-modified PMMA, which deforms homogeneously, were determined by means of the stress/strain experiment (, ) with simultaneous lateral strain measurement (_lat) in a wide range of strain rates () up to 10⁵%/min (impact stress). The elastic, plastic cavitation and plastic shear processes were determined as a function of strain. Therefore we calculated the elastic strain ( _el), the elastic volume expansion ( _{vol el}), the cavitation strain ( _cav), which is identical with the plastic volume expansion ( _{vol pl}), the shear strain ( _sh) and the energy densities (W_el, W_cav, W_sh) related to these three processes.For strains of 3 % onward it was found that plastic shear processes and plastic cavitation processes are responsible for a partial loss of elastically stored energy. Both plastic processes turn out to be mostly anelastic deformations, their amount depending strongly on the strain rate. The contributions of the processes to the total deformation of the unmodified PMMA in its strain range are similar to those of the impact-modified PMMA, and the high impact strength is caused by a shift of the catastrophic rupture to very high strains.     

Resonance Raman spectra of tris(acetylacetonato)iron(III) and ruthenium(III) complexes and their solvent effect

The resonance Raman spectra of tris(acetylacetonatoiron(III)) and ruthenium(III) complexes in various solvents and in water-acetonitrile (W-AN) mixtures were measured. The resonance Raman spectra of both complexes indicated peaks near 460 and around 1580 cm^–1. Thev(C-O) peak (around 1580 cm^–1) is shifted to low frequency with an increase in the dielectric constant _T of the solvents, whereas thev(M-O) (M=Fe and Ru, near 460 cm^–1) are constant, independent of _T. It implies that the C-O bond in the acac^– ligand is lengthened by the polarizability effect of the solvents, while both the Fe-O and Ru-O bonds, which are located in the inside of the complexes, are not influenced by the solvents indicating that the interaction does not depend on the properties of individual solvent molecules but on those of the aggregate.     

The relative permittivity of 1,2-dimethoxyethane and N,N-dimethylformamide mixtures from −10 to 40°C

Binary solutions of N,N-dimethylformamide and 1,2-dimethoxyethane have been investigated by means of dielectric measurements at temperatures ranging from –10 to +40°C, and for nine mixtures covering the whole miscibility field expressed by the mole fraction of one component (0X₁1). The experimental data were used to study the dependence of on T and X₁, of the type = (T), = (X₁), and = (T,X₁). Further, the excess mixing function _E has been evaluated in order to identify particular patterns of interaction between unlike molecules and any other factor that could modify such patterns. The minimum in the _E vs. composition plots suggests the formation of an adduct of stoichiometric ratio DMFDME=11 at all the investigated temperatures.     

Molecular dynamics and the structure of macrocycles —Solvent acetonitrile interactions

Microwave complex permittivities,* = -J, are reported in the 1–90 GHz frequency range for the macrocycles 18-crown-6 (18C6) and 15C5 added to acetonitrile in stoichiometric proportions, in the solvent CCl₄ at 25°C. Digitized infrared spectra of the CN stretch ₂ vibration of acetonitrile for the same systems are reported in the 2300–2200 cm^–1 spectral region. The macrocycle 12C4 added to CH₃CN has also been investigated in the infrared. Both the dielectric relaxation and infrared results are interpreted in terms of macrocycle-acetonitrile interactions, probably involving a methyl-hydrogen to ethereal-oxygen interaction. These interactions with CH₃CN diminish in strength according to the sequence: 18C6 > 15C5 > 12C4.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Simple statistical mechanics of electrolytes with a concentration dependent dielectric constant. Part 1. The pressure equation

We have used an approximation of the Adelman's theory of solutions to take into account the non-pairwise additive effects on the interaction potentials for a real electrolyte solution. As a result, a solute concentration dependent dielectric constant appears. The comparison with experimental data is done by means of the pressure equation. The influence of on solution properties is analyzed in two molality ranges using as a reference simplified models but with the dielectric constant of the pure solvent instead of .     

Dielectric study on pure and KOH-doped tetrahydrofuran clathrate hydrates

Complex dielectric permittivities of pure and KOH-doped (x = 1.8 x 10^–4) tetrahydrofuran clathrate hydrates were measured in the temperature range 20–260 K and in the frequency range 20 Hz-1 MHz. The relaxation time of the water reorientational motion was found to decrease drastically as a result of the doping; e.g., the relaxation time of the doped sample was 10^–9 times shorter than that of the pure sample at 70 K. The activation enthalpy of the motion was reduced to 7.4 kJ mol^–1. On cooling the crystal, the value of decreased suddenly at the 62 K phase transition to the ₂ value of the pure sample and at the same time disappeared. No dispersion effect due to the guest reorientation was observed below the transition. These data indicate that both the host and guest molecules become ordered or, at least, change their mobility drastically. In the pure sample, a relaxation phenomenon of ₀₂ was found around the glass transition region. The relaxation times agreed well with those derived from the enthalpy of relaxation in a calorimetric study.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

The general form of pseudopotential operators

The general form of hermitean linear pseudopotential operators, which are independent of the virtual energies, is derived. A special case of this pseudopotential is the usually used one, ¦c>(– _c)<c¦. It is shown that any pseudopotential is of essentially non-local character. The significance of -dependency and non-hermiticity of pseudopotentials is discussed. The advantages of semiempirical model hamiltonians in comparison with exact pseudopotential hamiltonians are stressed.

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Zusammenfassung Die allgemeine Form hermitescher linearer Pseudopotentialoperatoren, die die virtuellen Orbitalenergien nicht enthalten, wird angegeben. Eine spezielle Form hiervon ist das üblicherweise verwendete Potential ¦c>(– _c). Es wird gezeigt, da\ jegliches Pseudopotential wesentlich nichtlokalen Charakter hat. Die Bedeutung von s-AbhÄngigkeit und Nicht-HermitezitÄt von Pseudopotentialen wird diskutiert. Der Vorzug von Modell-Hamiltonoperatoren gegenüber exakten Pseudo-Operatoren wird betont.

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Résumé Expression générale des opérateurs de pseudo-potentiel linéaires hermitiques, indépendants des énergies des orbitales virtuelles. Le pseudo-potentiel ordinairement utilisé ¦c>(– _c) en est un cas particulier. On montre que tout pseudo-potentiel a essentiellement un caractère non local. Discussion de la signification de la dépendance à et de la non-hermiticité des pseudo-potentiels. On souligne les avantages des hamiltoniens modèles semi-empiriques par rapport aux hamiltoniens de pseudo-potentiel exact.

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The pseudo-orbitals so defined are not normalized to unity.     

The golden jubilee of the Coulson-Rushbrooke pairing theorem

The year 1990 marks the fiftieth anniversary of the much celebrated Pairing Theorem of Coulson and Rushbrooke. In its original form, the Theorem stated that for any altemant hydrocarbon: (1) the -electron energy levels are symmetrically distributed about the zero energy level; (2) the LCAO-MO associated with the energy level _i is the same as that belonging to the energy level - _i except for a difference of sign (only) in every other atomic orbital coefficient; (3) the total-electron charge density at any carbon atom in the molecule equals unity. Here, we trace the origins of this Theorem, describe its subsequent development, and outline some of its more significant uses. We conclude by discussing recent applications of the Theorem to positive and negative hydrocarbon ions, Möbius systems, and high-spin hydrocarbon species.     

Isolation,purification, and characterization of cyclomaltodecaose (ε-CD)

-Cyclodextrin (-CD) is a cyclic oligosaccharide, composed of ten -1,4-linked D-glucoses reported by Frenchet al. in 1965¹⁾, but has not been studied because of the difficulty in the preparation and purification of large-ring CDs composed of more than nine -1,4-linked D-glucose units. This report describes the purification and characterization of -CD. Furthermore, the crystal and molecular structure of -CD hydrate -CD 19H₂O) was elucidated by X-ray analysis.     

Microwave dielectric properties of potassium hydroxide aqueous solutions

Microwave dielectric properties of potassium hydroxide aqueous solutions were studied at frequencies of 13 to 25 GHz over a wide range of concentrations and temperatures of 288 to 308 K. Experimental electrical conductivity data were used to determine ionic losses at high frequencies. The static dielectric permittivity σ_s, dielectric relaxation time τ, and thermodynamic activation parameters of dielectric relaxation (ΔH _ɛ⁺⁺, ΔG _ɛ⁺⁺, and ΔS _ɛ⁺⁺) were calculated. These quantities decrease in transfer from water to solutions. Thereby we demonstrate that potassium hydroxide has a disturbing effect on the initial hydrogen-bond network of water.     

Role of electrostatic interaction in the processes of complex formation

Aspects of the theory of associate mixtures formed as a result of electrostatic interaction between their components are discussed. We obtained equations, convenient for comparison with the experiment, that elucidate the dependence of the association constant on the dielectric susceptibility of the solvent. The experimental results of the associates studied, which were composed of a diazo-salt cation and an anion of a xanthene dye, are described satisfactorily by the theoretical dependences, but with a smaller equilibrium distance between the associate component. We have shown that the smaller equilibrium distances are due to the fact that the dependence of the dielectric susceptibility of the solvent on the distance (r) for small distances between the interacting ions is not taken into account in the qualitative theory.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 5, pp. 591–596, September–October, 1986.     

Conformation and hydration of sugars and related compounds in dilute aqueous solution

The effect of hydroxyl substitution on the nature of the hydration of an alkane chain has been studied by calorimetric techniques. Static permittivities (₀) of a range of monosaccharides and related compounds in aqueous solution have also been determined. The (₀) data, suitably processed, have provided information about the solute dipole moments. In conjunction with earlier results from volumetric, compressibility, and relaxation studies, the specific hydration model is further developed and the relationships between solute molecular conformations and solute-water interactions are discussed.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

Effect of dipole position on relaxation parameters

Dielectric absorption studies have been made on numerous monobromoalkanes and two,-dibromoalkanes dispersed in polystyrene and polypropylene matrices in the frequency range 10–10⁵ Hz between 80-285 K. All compounds exhibited two clear cut dispersion regions in polystyrene except 3-bromopentane, 4-bromoheptane and 4-bromooctane. Nevertheless, when these three solute molecules are dispersed in polypropylene, they then show two dispersion regions. The low temperature process (LT) has been attributed to -CHzBr group rotation about the C-C bonds and the high temperature (HT) process to molecular rotation. In the case of,-dibromoalkanes, both -CH₂Br groups contribute to the low temperature absorption. For a bromoalkane of a given chain length the relaxation time alters with variation of the main dipole position from the terminal carbon atom to the middle of the chain for the low temperature absorption; this is related to the change in the size of the reorientating unit containing the -CHzBr group. The effect of the same variation of the dipole position on the high temperature absorption is that the relaxation time decreases which is attributed to the decrease in volume swept out on molecular rotation. The ratio,_maxLT/_(max)HT, increases with the variation of the dipole from the terminal to the middle of the chain.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

Quinazolines

A method was developed for the preparation of 2,3-polymethylene-3,4-dihydro-4-quinazolones with substituents in the benzene and polymethylene chains by reaction of anthranilic acid and its substituted derivatives with -butyro-, 5-phenyl--butyro-, -capro-, and -chloro--caprolactams in the presence of dehydrating agents. The corresponding quinazolines were obtained by reduction of the synthesized quinazolones.See [1] for communication V.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1564–1569, November, 1976.     

Synthesis of substituted lysine-containing oligopeptides

Conclusions Oligopeptides containing lysine and alanine and having the following sequences were obtained: BOC-[(N-Cb)-Lys]₆OCH₃, BOC-[(N-Cb)-Lys]₈OCH₃, BOC-Ala-[(N-Cb)-Lys]₄-Ala-OCH₃, and BOC-Ala-[(N-Cb)-Lys]₆-Ala-OCH₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1858–1860, August, 1972.     

Ionic enthalpies of transfer from water to water-sulfolane mixtures

NaCl, NaBr, NaI, NaClO₄, KCl, KClO₄, NaBPh₄, and Ph₄PBr solution enthalpies were measured in water-sulfolane mixtures at 30°C. Ionic enthalpies of transfer from water to mixed solvents were calculated on the basis of the assumption H _s ^o (BPh ₄ ^– )=H _s ^o (Ph₄P⁺). The variation of the ionic enthalpies of transfer with solvent composition is discussed in terms of ion-solvent interactions and of the effects caused by sulfolane on the structure of water.     

Influence of polarity of medium on the nature of charge transfer complex,kinetics, and mechanism of reaction with a one-electron transfer in a tetracyanoethylene-n-alkyl-substituted aniline system

The influence of the polarity of the medium (B, ) on the thermodynamic characteristics of the formation of a charge transfer complex (CTC) and one electron transfer from a donor D to and acceptor A was studied in N-alkyl-substituted aniline (D) — tetracyanoethylene (A) systems. It was shown that in systems with CTC in which [B]/[D] 1, the limiting step in the reaction with one electron transfer in weakly polar solvents (<20) is the formation of molecular (AD), and in strongly polar sovents (>20), of ionic (AD) CTC. A correlation was established between the spectral (VCT) characteristics of the formation of the CTC and the kinetic parameters (k_eff) of one electron transfer reaction and degrees of charge transfer in molecular and ionic CTC were determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 167–173, March–April, 1989.