Journal of Molecular Liquids

Published by Elsevier
Print ISSN: 0167-7322
An effective exciton Hamiltonian for all amide bands is used to calculate the linear absorption and photon echo spectra of a 17 residue helical peptide (YKKKH17). The cross peak bandshapes are sensitive to the inter-band couplings. Fluctuations of the local amide frequencies of the all amide fundamental and their overtone and combination states are calculated using the multipole electric field induced by environment employing the electrostatic DFT map of N-methyl acetamide. Couplings between neighboring peptide units are obtained using the anharmonic vibrational Hamiltonian of glycine dipeptide (GLDP) at the BPW91/6-31G(d,p) level. Electrostatic couplings between non-neighboring units are calculated by the fourth rank transition multipole coupling (TMC) expansion including 1/R(3) (dipole-dipole), 1/R(4) (quadrupole-dipole), and 1/R(5) (quadrupole-quadrupole and octapole-dipole) interactions.
The effect of salts on water behavior has been a topic of interest for many years; however, some recent reports have suggested that ions do not influence the hydrogen bonding behavior of water. Using an effective two-state hydrogen bonding model to interpret the temperature excursion infrared response of the O-H stretch of aqueous salt solutions, we show a strong correlation between salt effects on water hydrogen bonding and the Hofmeister order. These data clearly show that salts do have a measurable impact on the equilibrium hydrogen bonding behavior of water and support models which explain Hofmeister effects on the basis of solute charge density.
The dielectric properties of water of various degrees of purity are measured at room temperature between 20 Hz and 1 MHz. Dielectric properties of deionized water containing different concentrations of copper sulphate are also presented. The results are in fair agreement with Coelho's theory of the space charge response of a medium containing mobile ions only when an additional contribution to the permittivity arising from DC conduction in the electrolyte is taken into account. This condition is consistent with the assumption that the carriers are free electrons of high mobility and low number density. It is noted that this is a very surprising result
Computer simulation is used to investigate the statistical correlation between the molecular centre of mass velocity () and molecular angular momentum () of the optically active molecule 1,1 fluoroiodoethane in the liquid state. Of the nine elements of the moving frame correlation matrix <(t)T(o)>m, the diagonal elements vanish by symmetry for all t. The other elements exist, in principle, for t > o, but the (1,3) and (3,1) elements are small in magnitude, and therefore buried in the computer noise, for both the R and S enantiomers and their racemic mixture. The molecular dynamical nature of the two enantiomers is therefore identical in the laboratory and any moving frame of reference. This implies that the laboratory frame autocorrelations of each enantiomer are similar to those in the racemic mixture, in marked contrast to 1,1 fluorochloroethane [12] where differences in the structure of the (1,3) and (3,1) elements for each enantiomer lead to large and observable differences between autocorrelations in either enantiomer and their racemic mixture. These differences are measures of rotation/translation correlation on a fundamental single molecule level.The simulation is supported by measurements in the far infra-red on the (+) enantiomers and racemic mixtures of 3 methyl cyclohexanone and 3 methyl cyclopentanone in the liquid state at 293K.
The kinematic viscosities (ν) of liquid binary mixtures of N,N-dimethylformamide and 1,2-dimethoxyethane were measured at 19 temperatures in the range −10⩽ t / °C ⩽ 80, employing the pure species and 9 their solutions covering the whole miscibility range expressed by the condition 0 ⩽ χi ⩽ 1. The measured values have been used to test some empirical equations of the type ν=ν(T), ν=ν(χi, and ν=ν(T,χi), in order to obtain useful correlation models with predictive ability in correspondence of the experimental data gaps. Starting from the experimental data, the excess kinematic viscosities (νE) have been calculated. Sign and magnitude of these quantities have been discussed in terms of type and nature of specific intermolecular interactions. Some derived quantities such as thermodynamic parameters of the viscous flow (ΔG∗, ΔH∗ and ΔS∗), have been calculated on the basis of Eyring's model. Furthermore, the fluidity of this binary solvent system was analysed and interpreted following Hildebrand and modified-Hildebrand correlation models.
The pioneer experimental results of positron annihilation experiments in non-aqueous solutions of n-hexanol in ethylene glycol (1,2-ethanediol) were compared with the acoustic ones. The changes of annihilation parameters with concentration show that the solute affects strongly the original diol structure. Similarities with the results known for aqueous systems were found, suggesting formation of clathrate-like solvates (the phenomenon here called the hydrophobic-like solvation). The ultrasonic data for the title system do not confirm directly formation of any specific structure. It is possible that compressibility of solvates does not differ from the pure liquids, and/or the solvates are formed in very small amounts. Thus, usefulness of the positron annihilation method in investigation of liquid structure was proven again.
Densities and dynamic viscosities for 1,4dioxane with water, at several temperatures T = 298.15 K have been measured over the whole composition range and 0.1 MPa, along with the properties of the pure components. Excess molar volumes, viscosity deviations, and excess free energy of activation for the binary system at the above-mentioned temperature are deduced.The viscosity of a mixture depends on the molecular interactions between the component mixtures with strong interactions between different molecules show positive viscosity deviations and negative excess molar volume confirming recent works that affirmed the water–1,4dioxane cluster formation.
Electric conductivities of diluted magnesium sulfate solutions in binary mixtures of 1,4-dioxane with water were measured covering a solvent composition range up to 50 wt.% of 1,4-dioxane at temperatures from 5 to 35 °C. Evaluation of the limiting molar conductivity Λ∞ and the association constant KA is based on the chemical model of electrolyte solutions, including short-range forces. From the temperature dependence of the limiting molar conductivities Eyring's enthalpy of activation of charge transport was estimated. The standard Gibbs energy, enthalpy and entropy of the ion-pairing process were calculated from the temperature dependence of the ion-association constants.
The Kirkwood–Buff integrals and the volume-corrected preferential solvation parameters for the first solvation shell are reported for binary mixtures of 1,4-dioxane with many organic solvents. They are calculated from reported thermodynamic data at the temperatures for which these data are available. The co-solvents include n-hexane, n-heptane, c-hexane, methyl-c-hexane, benzene, toluene, ethylbenzene, methanol, ethanol, 1-propanol, 2-propanol, c-pentanol, 1,2-ethanediol, acetic acid, dichloromethane, chloroform, tetrachloromethane, 1,2-dichloroethane, 1,2-dibromoethane, trichloroethene, tetrachloroethene, bromochlorotrifluoroethane (halothane), hexafluorobenzene, acetonitrile, triethylamine, piperidine, formamide, N,N-dimethylformamide, dimethyl sulfoxide, and tetramethylene sulfone (sulfolane). The derived preferential solvation parameters of these mixtures are discussed in terms of the interactions that take place.
The permittivity of 1,4-dioxane and benzene solutions of mono(oxyethylene) glycol, MEG, di(oxyethylene) glycol, DEG, tri(oxyethylene) glycol, TEG and tetra(oxyethylene) glycol, TTEG was measured at 298.15 K. From the experimental data, the apparent molar polarizations at infinite dilution were calculated. The limiting apparent molar polarization for a definite compound depends on the theoretical model used and is the highest for the Kirkwood model relative to the Debye or Onsager approach. The electric dipole moment of the investigated solutes was estimated according to the Debye, Onsager and Kirkwood theoretical approaches. The calculated dipole moments (Debye method) linearly increase with the square root of the number of monomeric units, while the Onsager dipole moments do not show a simple linear relation. The Kirkwood correlation factor depends on the molecular weight of the solute and is close to one. From the group dipole moment of the polar monomeric unit the factor g, which takes into account the degree of flexibility of the chain, was calculated and found to be greater than one for the lower members.
The Polarizable Continuum Solvation Model (PCSM) is extended to include compounds containing halogens. The PCSM analysis has been carried out for ClCH2(CH2)(4)CH2Cl and ICH2(CH2) 4CH2Cl in polar and non-polar solvents of wide range of dielectric constants. The physical properties of the systems, such as free energies, electrostatic interaction, cavitation enthalpy and dipole moment are discussed. The PCSM provides the solvation analysis and explains the properties of the compounds satisfactorily.
We adduce new arguments for the significance of so-called 1.5- (or sesquialteral) molecular light scattering in one-component fluids. For this purpose, we analyze its effect on the Landau-Placzek ratio for the critical opalescence spectrum. The results obtained are used to reveal experimental data which can be interpreted as evidence for its existence and to evaluate both the relative magnitude and the sign of the 1.5-scattering contribution.
Dielectric data from 10−2 Hz to 109 Hz are given for fresh leaves of Crassula portulacea (Jade plant), liquid extracted from such leaves and extracted liquid containing a synthetic polymer film. Features associated with the bulk electrolyte, the cell walls and the electrical double layer at the electrodes of the specimen holder are clearly delineated in the data. A synthetic film is shown to produce interfacial polarization that appears quite similar to that due to cell walls. Interpretation of the data is given in terms of ionic movement through the leaf structure. The data presented here are intended to be a prototype for live tissue data and used, for example, to design synthetic dielectric phantom materials.
The molecular dynamics of water adjacent to hydrophobic and hydrophilic groups of organic molecules is a problem eminently relevant in biophysics. To this end complex permittivities ϵ* = ϵ′ - Jϵ″ in the frequency range 1–90 GHz for 15C5 crown ether-water mixtures of compositions XH2O = 0.034, 0.31 and 0.68 at 25°C are reported. Physical properties of the mixtures such as shear viscosities, densities and static permittivities are also reported. In addition Raman spectra of the crown ether-water mixture have been collected. Both the crown ether bands (COC and CH2 stretch) as well as the water OH stretch have been studied. The crown ether bands have been analyzed. The dielectric relaxation behavior is characterized by the delay time of the polarization remaining almost constant up to XH2O = 0.68 in accord to the viscosity pattern. The relaxation spectrum departs more and more from the Debye model upon addition of water. The Cole-Davidson distribution function seems best able to describe the data.The dielectric data are interpreted qualitatively by a modified Glarum theory envisaging cooperative rotation of the crown ether and collisions with water-molecules.
The frequency dependence of the water oxygen-17 transverse and longitudinal relaxation times is used to investigate the dynamic state of water in a saturated sucrose solution at 298K. Assuming that the observed frequency dependence originates from the slow modulation of the residual quadrupole coupling of the water-sucrose interaction, an anisotropic rotation model is used to extract water rotational correlation times and the order parameter characterizing the water-sucrose dynamic complex. Although the theory succeeds in providing a quantitative fit to the longitudinal data there is an unexpected anomalous dephasing enhancement in the transverse relaxation, and the paper concludes with a discussion of the possible origins of this enhancement and of alternative models for the dynamic state of the water.
A brief historical survey of major contributions coming from the period 1884–1984 century to the theory of associated solutions is presented. The most important topics which are connected with the analysis of associated solutions are considered here: the progress in the mathematical description of molecular models, the applied experimental techniques and the variety of involved chemical systems.
The relative energies and dipolar properties of two conformers of 2,2′-bipyridine (1) were calculated using AM1 and ab initio methods. Dipole moments of 1 and pyridine in many organic solvents were determined. On this basis, the Gibbs energy ΔG(s) for the conformational s-trans⇌s-cis equilibrium of 1 was estimated. The solvent effect on ΔG(s) is discussed quantitatively using the reaction-field model for the continuum dielectric medium, in the framework of which both the dipolar and quadrupolar terms are considered. This simple model works very well when the adopted radius of the solvent cavity is that obtained from the apparent molar volume of 2,2′-bipyridine in solutions. It is also shown that the mean spherical approximation (MSA) model predicts a weaker dependence of ΔG(s) on the solvent's relative permittivity than the continuum model.
The liquid and the glassy phases of 2,2-dimethylbutane have been investigated by isothermal isobaric ensemble Monte Carlo simulation. Thermodynamic Properties and radial distribution functions for both the liquid and the glass have been obtained. The radial distribution functions have been classified into three types based on the accessibility of the group. It has been shown that the structure of the Iiquid and the glass can be understood in terms of the above classification of the radial distribution functions. Molecular reorientation plays an important role in the structural rearrangement accompanying glass formation. As much as 35% of the contribution to the increase in the intermolecular interaction energy on vitrification is due to the reorientation of the neighbouring pairs of molecules. The observed changes in the dimerisation energy and the bonding energy distribution function are consistent with the observed structural changes.
During the nonexponential relaxation of a methyl group both magnetization components MA and MB can be observed. From these, correlation times characterizing the motion of the molecule in solution have been derived and related to the microscopic viscosity.
Stepwise ionization and tautomerism of fluorescein (Fl) and its 2,7-dichloroderivative (2,7-DCFl) were studied using vis-spectroscopy in AOT-stabilized reversed microemulsions of water in n-octane (water:surfactant ratio W = 20). The ‘apparent’ pKaa values of dyes (average confidential interval ± 0.08) in microemulsions, at ionic strength of dispersed aqueous phase I = 0.05 M, are as follows: pKa1a = 6.68, pKa2a = 7.85 for Fl; pKa1a = 6.00, pKa2a = 7.17 for 2,7-DCFl. The state of H2O molecules in dispersed ‘water pools’ was interpreted using IR spectra of O–H stretching at various W = H2O:AOT ratio, as well as by registering fluorescence and excitation spectra and fluorescence lifetimes of the dyes. ‘Unusual’ solvent properties of dispersed water within reversed microemulsions, i.e. micropolarity, microviscosity and pH gradient and inhomogeneous electrical potential within water pool, create favorable conditions for protolytic reactions as compared with aqueous solutions. Conclusions concerning tautomerism of the molecular and ionic species were deduced from the absorption spectra. The neutral (molecular) forms H2R of the studied dyes in reversed microemulsions are highly converted into colorless lactones. The monoanion HR− of the unsubstituted Fl exists both in aqueous solutions and in AOT-stabilized ‘water pools’ as the common carboxylate tautomer. In contrast, the form HR− of 2,7-DCFl in reversed AOT microemulsions exists mainly as a deeply and intensively colored structure, with non-ionized carboxylic and ionized hydroxylic group (phenolate tautomer).
The lattice structure, dynamic and thermal properties of yttria-stabilized zirconia (YSZ) have been investigated by molecular dynamics (MD) simulation between 300 and 2000 K using the Born–Mayer–Huggins interatomic potential. The lattice constant of YSZ with cubic structure increased with temperature and yttria content, and was in good agreement with the one experimentally obtained. The self-diffusion coefficient of O2− ion was much larger than those of Zr4+ and Y3+ ions, and decreased with increasing yttria content. The constant-pressure heat capacity, which was the sum of harmonic and anharmonic terms obtained by the MD simulation, was compared with the experimental data.
The structure and properties of water confined in activated carbon (AC) pores of an average diameter 20 Å have been investigated over a temperature range between 298 K and 228 K by adsorption isotherms, differential scanning calorimetry (DSC), and large-angle X-ray diffraction. The adsorption isotherm at 298 K has shown the V-type one, in which the adsorption of water takes place at a relative pressure (p/p0) ∼ 0.4, increasing rapidly with an increase in the relative pressure to a saturated value at p/p0 = 1. The DSC data of water in AC at p/p0 = 1.0 have shown three steps of vitrification of water, suggesting different pore sizes of AC. The X-ray diffraction data on confined water at p/p0 = 1.0 have revealed that the ice-like tetrahedral network of water is slightly perturbed from bulk water structure, but not to such an extent as found for water confined in hydrophilic pores of MCM-41 previously reported [P. Smirnov, T. Yamaguchi, S. Kittaka, S. Takahara, Y. Kuroda, J. Phys. Chem. B 104 (2000) 5498]. With decreasing temperature, the hydrogen bonded network of water was enhanced, and at 243 K hexagonal ice Ih was partially formed in the AC pores, in contrast with cubic ice Ic formed in hydrophilic pores (diameter 100 Å) of silica. The microscopic structure of supercooled water confined in hydrophobic AC pores is compared with those in hydrophilic MCM-41 pores.
The effect of uniform and uniaxial d.c. electric field in the range between 0.15×107 and 1.5×107 V/cm on supercooled water at T=250 K is examined by means of molecular dynamics simulations. As in clusters, a change of structure, (not the crystalline one) is identified at a transition field of the order of 1.0×107 V/cm which change is also accompanied by a significant and abrupt slowing of the reorientational and structural relaxation. The electric field induced spatial anisotropy, due to the near alignment of the molecular dipoles along the field direction, was found to significantly affect the dynamics along and perpendicular to the field vector, resulting in stronger hydrogen bonds and in slower diffusion along the field direction.
A combined integral equation and quantum mechanical method, the so-called RISM–SCF method, is used to develop a self consistent effective potential model to describe pure liquid water in accordance with thermodynamic properties like chemical potential or entropy over a wide range of temperature and pressure. Since the thermodynamic excess properties calculated with the SSOZ equation are extremely charge dependent using constant Lennard–Jones parameters, we first developed a new function of the Lennard–Jones parameters of water depending on the partial charges taking into account the charge dependent polarisation which is reflected mainly by the attracting term of the Lennard–Jones potential. We used experimental data of thermodynamic excess functions at three selected temperatures in order to adjust the potential parameters reproducing these thermodynamic functions with an error smaller than 3%. Using this charge dependence of the Lennard–Jones parameters we applied the RISM–SCF method to calculate thermodynamic properties of pure liquid water, especially its vapor pressure, in a temperature range from 273.16 to 423.15 K and a pressure range from 0.5 to 500 kPa. Our calculated values of the vapor pressure agree well with the experimental data, as do our values of chemical potential and entropy as function of temperature.
Densities, ρ, and speeds of sound, u, of 2-propanone + dipropylamine, + dibutylamine or + triethylamine systems have been measured at (293.15, 298.15 and 303.15) K and atmospheric pressure using a vibrating tube densimeter and sound analyser Anton Paar model DSA-5000. The ρ and u values were used to calculate excess molar volumes, VE, and the excess functions at 298.15 K for the thermal expansion coefficient, αPE, and for the isentropic compressibility, KSE at 298.15 K. VE, KSE and αPE are positive magnitudes. When replacing dipropylamine by dibutylamine or triethylamine in the studied mixtures, the excess functions increase. This may be ascribed to the interactions between unlike molecules which are more important in the former solutions. From the comparison with similar data obtained for 2-propanone + aniline, + N-methylaniline, or + pyridine systems, it is concluded that interactions between unlike molecules are stronger in mixtures containing aromatic amines. Free volume effects are present in solutions with dipropyl or dibutylamine as the VE curves are shifted towards higher mole fractions of 2-propanone.
Densities and viscosities of the binary aqueous solutions of 1-propanol and 2-propanol have been measured over the whole composition range at temperatures between 293.15 K and 333.15 K. The energies of activation for viscous flow for aqueous solutions of 1-propanol and 2-propanol were calculated and found to be 17.94 and 22.16 kJ mol− 1, respectively. A polynomial equation and an equation based on the Power Law and Erying's absolute rate theory were used to correlate the viscosity data of the aqueous solutions of 1-propanol and 2-propanol. The average absolute deviations (AAD) for density correlations of aqueous solutions of 1-propanol and 2-propanol are less than 0.07%.
The standard partial molar volumes of univalent ions in a variety of solvents are calculated as the sum of their intrinsic volume and a (negative) electrostrictive volume or, for tetraalkyl- or aryl ions, structural contributions. The shell-by-shell calculation of the electrostriction according to Marcus and Hefter takes into account the mutual dependence of the relative permittivity and the electrical field strength of the solvent around the ion. It leads to good agreement between the calculated and the experimental values for all solvents, both dipolar aprotic and hydrogen bonding, for which data for univalent ions are available. In particular, this approach permits an independent estimation of the standard partial molar volumes of alkali metal halides in anhydrous formic acid, not included in the former comparisons.
The excess molar volumes (VmE) for binary liquid mixtures of (2-alkoxyethanol +N,N-dimethylformamide or N,N-dimethylacetamide) have been measured with a continuous dilution dilatometer at 298.15 K and atmospheric pressure over the entire composition range. The 2-alkoxyethanols were 2-methoxyethanol (CH3OCH2CH2OH), 2-ethoxyethanol (C2H5OCH2CH2OH), and 2-butoxyethanol (C4H9OCH2CH2OH). The excess molar volumes are negative and symmetric over the entire range of composition for all mixtures. The results have been used to estimate the partial molar volumes Vmi of the components. The change of VmE and Vm i with composition and the number of alkyl chain-length in the alkoxyethanol molecule are discussed with reference to the nature of interactions between the component molecules.
Excess molar volumes VmE for binary liquid mixtures of (n-alkanol + 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-propoxy-2-propanol, 1-butoxy-2-propanol, or 1-tert-butoxy-2-propanol) have been measured as a function of composition using a continuous dilution dilatometer at 298.15 K and atmospheric pressure over the full range of composition. The n-alkanols were methanol, ethanol, and 1-propanol. The VmE for each of the mixture studied are negative over the whole mole fraction range. For each case, the VmE increases in a positive direction with increase in chain length of the n-alkanol. The VmE results have been used to estimate the excess partial molar volumes V¯m,iE of the components.
Protonation constants of polyacrylate (MW = 2 kDa) were determined in several mixed LiCl/KCl aqueous mixtures and mole ratios from y = 0 to 1 y = [Li+] / ([Li+] + [K+]) and I = 1 to 3.5 mol L− 1. Different models were tested in calculating protonation constants from ISE-H+ potentiometric data (namely: Henderson–Hasselbalch, Högfeldt and Dicarboxylic-like models). The function log KH vs. y does not follow an ideal behaviour (Young's rule) but can be expressed by a three parameter equation derived by the zeroth Guggenheim approximation. From this equation it is possible to calculate the free energy of mixing. The dependence on ionic strength of protonation constants was modelled by the SIT (Specific ion Interaction Theory) approach.
The electrical conductances of the solutions of sodium chloride (NaCl), potassium chloride (KCl), sodium bromide (NaBr), sodium iodide (NaI), sodium tetraphenylborate (NaBPh4), tetrabutylammonium iodide (Bu4NI) and sodium perchlorate (NaClO4) in water (1) + 2-methoxyethanol (2) mixtures containing 0.01, 0.025, 0.05, 0.075, 0.10, 0.15 and 0.20 mol fractions of 2-methoxyethanol have been reported at 298.15 K. The conductance data have been analyzed by the Fuoss–Justice equation. The individual limiting ionic conductivities of Na+, K+, Bu4N+, BPh4−, I−, Cl−, and Br− ions have been determined using the Fuoss–Hirsch assumption. The dependencies of the limiting molar conductances, Λo, and Walden products, Λoη, versus mixed solvent composition have been discussed.
Densities of the ternary mixtures chlorobenzene + n-hexane + (n-undecane or n-dodecane) have been measured at 298.15 K and atmospheric pressure. The excess molar volumes were computed from the experimental data and were fitted to the Nagata equation. The partial excess molar volumes were calculated, an interpretation in terms of composition and molecular size being made. The molecular radius was derived and compared from different thermodynamic property and models. The Peng–Robinson and Soave–Redlich–Kwong equations of state were applied, in combination with different mixing rules for excess molar volume prediction. The accurate obtained results by means of cubic equations of state show the applicability of binary interaction parameters to estimate multicomponent excess molar volumes or any other properties by means of adequate thermodynamic derivations.
Assuming a quaternary liquid mixture to be made up of six binaries, statistical mechanical theory of Flory has been extended to develop the expression for dynamic viscosity of multi-component systems using the concept of absolute rate and free volume theories of liquid state. A reasonable agreement has been achieved between theory and the experiment for n-hexadecane, carbon tetrachloride, n-benzene and n-hexane quaternary system at 298.15 K. An attempt has also been made to explain the nature of the molecular interactions involved, in the light of excess thermodynamic functions of which sign and magnitude depend upon the chain length of the component liquids.
Ultrasonic velocities of tetrapropylammonium bromide (Pr4NBr), tetrabutylammonium bromide (Bu4NBr), tetrapentylammonium bromide (Pen4NBr), tetrahexylammonium bromide (Hex4NBr), tetraheptylammonium bromide (Hep4NBr), and tetraoctylammonium bromide (Oct4NBr) in N,N-dimethylacetamide have been measured at 298.15 K. Apparent molar isentropic compressibilities κφ of these electrolytes were derived from these data supplemented with their densities. The limiting apparent molar isentropic compressibilities κφo were obtained by extrapolation from the plot of κφ vs. the square root of the molality. The κφo values of the electrolytes were split into approximate limiting ionic compressibilities κφ±o on the basis of the assumption that κφo(Br−)=0. The results have been interpreted in terms of specific constitutional and structural factors of the solvent molecules and of solute ions.
Differential diffusion coefficients of potassium sulfocyanate in water at 298.15 K, and at concentrations from 0.001 M to 1 M, have been measured using a conductimetric cell and an automatic apparatus to follow diffusion. The results are discussed on the basis of the Onsager-Fuoss and Pikal models. The cell uses an open-ended capillary method and a conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries, at recorded times.
The crystallisation enthalpies of NaCl, KCl, LiCl· H2O, MgCl2· 6H2O, CaCl2· 6H2O and BaCl2· 2H2O from aqueous solution were determined by means of different methods. It was concluded that the method of differential enthalpies of solution measurements gives the best results. Therefore, for the equilibrium solid phases occurring in the systems K2SO4 - (NH4)2SO4 - H2O, KCl - KBr - H2O and KNO3 - NH4NO3 - H2O, the concentration dependencies of those enthalpies, within solubility isotherms were measured. It allowed for calculation of the limiting differential solution enthalpies and also the crystallisation enthalpies of the mixed crystals.
The solvate KF.2HF is used in the molten state at 85°C for the production of F2. Water can be present in small quantities in the HF feed for this process and causes various complications such as corrosion of cell components and undesirable formation of F2O. The work described in this paper examines the effects of presence of H2O in KF.2HF melts in a comprehensive way over a wide range of mole fractions of water in the KF.2HF system. The conductivity, viscosity and Walden product are evaluated together with the determination of the density, to provide information on selective solvation, speciation and acidity in the system, as well as volumetric deviations of additivity in the thermodynamic properties of the system. Complete primary hydration of the ionic species appears to be reached at a mole fraction of water around 0.88, i.e. 7 water moles per mole of KF.2HF.
The densities, viscosities, and ultrasonic velocities of pure ethanol, 1-hexanol, 1-octanol, acetonitrile, N,N-dimethylformamide, and of the binary mixtures of ethanol with 1-hexanol and 1-octanol, and those of acetonitrile with N,N-dimethylformamide were determined at 303.15 K. The excess adiabatic compressibility, excess intermolecular free length, excess volume, excess viscosity, excess acoustic impedance, and the molecular association have been calculated from the experimental data. These parameters are used to discuss the nature and the extent of intermolecular interactions in the mixtures.
Isentropic compressibilities, Rao's molar sound functions, molar refractions, excess isentropic compressibilities, excess molar volumes, viscosity deviations and excess Gibbs energies of activation of viscous flow for seven binary mixtures of tetrahydrofuran (THF) with cyclohexane, methylcyclohexane, n-hexane, benzene, toluene, p-xylene and propylbenzene over the entire range of composition at 303.15 K have been derived from experimental densities, speeds of sound, refractive indices and viscosities. The excess partial molar volumes of THF in different solvents have been estimated. The experimental results have been analyzed in terms of the Prigogine–Flory–Patterson theory.
We perform numerical simulations to study static and dynamic critical behaviour of the 3d random-site Ising model. A distinct feature of our approach is a combination of the Metropolis, Swendsen-Wang, and Wolff Monte Carlo algorithms. For the static critical behaviour, these approaches are the complementary ones, whereas in dynamics they correspond to three different types of relaxation, being a particular subject of our study.
The use of the HP 4192A Analyser has made dielectric spectroscopy measurements of liquid crystals much easier for frequencies from 5 Hz to 13 MHz. The value of data obtained at the lowest frequencies is limited because the significance of the measured values of conductivity is open to a number of interpretations. Among these are dipolar relaxation, ionic conductivity, hopping conductivity, as well as a Maxwell Wagner effect caused by an inhomogeneity of the sample and the existence of electrode polarisation. Experimental data taken from a number of materials in solid, liquid and liquid crystalline phases have been analysed to explore this problem.
We describe an experimental set up, which enables precise measurements of the complex permittivity of highly absorbing liquids (20–200 Np/cm) in the frequency range 70–600 GHz as a function of temperature (100–350 K) and pressure (up to 70 bars). The designed measuring cell is particularly well adapted for studying liquid compounds which are gaseous under normal conditions. The precision of the measurements is better than 3 percent in the whole temperature, pressure and frequency ranges. Examples of the results obtained for highly polar liquids CH3F and CHF3 are presented.
The solubilities of acetaminophen and ibuprofen in the mixtures of propylene glycol–water, of polyethylene glycol 600–propylene glycol, and of polyethylene glycol 600–propylene glycol–water at 25 °C are determined and mathematically represented by the Jouyban–Acree model. The solubilities are measured using the shake flask method and the model is used to fit the solubility data of each drug in the solvent mixtures. The density of the solute-free solvent mixtures is measured and employed to train the Jouyban–Acree model and then the density of the saturated solutions is predicted. The obtained overall mean relative deviations (OMRDs) for fitting the solubility data of acetaminophen and ibuprofen in binary mixtures are 1.4% and 11.2%, respectively. The OMRDs for fitting the solubilities in ternary solvent mixtures for acetaminophen and ibuprofen are 16.5% and 37.5%, respectively, and the OMRD values for predicting all solubilities of acetaminophen and ibuprofen by these trained versions of the Jouyban–Acree model were 5.2% and 17.8%, respectively. The prediction of OMRD for the density of saturated solutions was 2.2%.
The time evolution equation of the ensemble averages of the Wigner D-functions is used for describing the non-linear dielectric relaxation of an assembly of polar molecules in the context of the non-inertial rotational diffusion model. These functions are needed when one considers the case where the direction of the dipole moment makes some angle (different from zero) with the long molecular axis of the symmetric-top molecule. Moreover, it is assumed that the external perturbation acting on the liquid medium is due to the simultaneous application of a strong d.c. bias field superimposed on a weak a.c. electric field. Analytical expressions for the first three harmonic components of the electric polarization are derived and the first one is chosen as example of illustration by means of three-dimensional relaxation spectra and Cole–Cole diagrams. These figures clearly show the existence of two distinct relaxation processes along the short and the long molecular axes, respectively. Also, a comparison of our theoretical model with experimental data of the first harmonic component of the electric permittivity (non-linear dielectric increment) for a solution of 5 CB in squalane leads to a satisfactory enough agreement.
Infrared OH stretching spectra of n-butanol in n-hexane mixtures have been measured at three temperatures as a function of mixture composition up to a mole fraction 0.3 of n-butanol. The spectra were analyzed using DFT (B3LYP) and ab initio (MP2) calculations. Hydrogen-bonded n-butanol clusters up to four members have been calculated using DFT and high-level ab initio methods, including cyclic trimers and tetramers. A distinct cooperative effect of the hydrogen bonding energy has been observed. On the basis of these theoretical results, a new modified ERAS (extended real associated solution) model incorporating tetramer cyclic species in addition to the linearly associated species was applied for describing simultaneously the measured monomer concentration of n-butanol obtained from the IR spectra, the chemical shift of the hydroxyl proton of n-butanol (δOH) obtained from 1H NMR measurements, and experimental data of the molar excess enthalpy (HE). 1H NMR- and HE-data covering the whole range of concentration in the mixture have been used.
We present a first principles calculation of the frequency dependence of rotational motion of OD bonds of deuterated water molecules in the liquid phase by means of ab initio molecular dynamics simulations. The fluctuating frequencies of the OD bonds are calculated through a time series analysis of the simulated trajectories and the frequency-resolved rotational dynamics are investigated in terms of the first and second-rank rotational correlation functions of the OD bond vectors. It is found that the short-time dynamics can depend significantly on the frequency which, in turn, is related to different hydrogen bonding environments, whereas the long-time dynamics is essentially frequency independent. A comparison of the current theoretical results with the recent polarization-resolved time dependent infrared spectroscopic results is also presented.
Ab initio molecular dynamics simulations are applied to a study of hydration structure of a chain-like molecule containing vinyl alcohol groups -[CH2-CHOH]n- with n = 4. Partial pair distribution functions and angle distributions are analyzed in order to estimate the features of the hydration shell. It is shown, that hydration process causes essential changes of mutual orientation of hydrophilic groups having on average less than two neighbor water molecules. A tendency of the hydrated poly(vinyl alcohol) chain fragment to backbone torsion is observed.
Interaction of poly(vinyl pyrrolidone) PVP with water molecules is of interest for possible drug applications and other chemical reactions. In this purview, aqueous solutions in 0.1–10 g/dl PVP were studied in terms of the optical absorption spectrum and rheology in this work. The rheology determines a polymer nature of the solutions in the selective concentrations (C). A strong absorption band, which occurs in an asymmetric shape at wavelength maximum λmax = 247 nm (π →π⁎ electronic transition) in 10 g/dl PVP, shifts nonlinearly to a λmax value as small as 222 nm upon decreasing the C-value. The λmax follows a parabolic path as a function of increasing the C-value in this range. The band narrows down from an average 55 nm bandwidth Δλ in 10 g/dl PVP to a value 15 nm in the 0.1 g/dl PVP in predominant intramolecular interactions in selective conformers in dilute solutions. An opposite effect of red-shift and band broadening occurs in solute–solvent interactions. The viscosity thus increased hardly from a value 10 × 10− 4 Pa s in the 0.1 g/dl PVP to as much as 37 × 10− 4 Pa s (i.e., as large a factor ∼ 4) in the 10 g/dl PVP at a shear rate 100 s− 1. A weak concentration-induced viscosification of dispersed PVP molecules in water is important for the medicinal values.
The absorption and fluorescence extents of the dye Safranine T (ST) are influenced by micellar solution. The critical micellar concentration (CMC), aggregation number and micelle-ST binding constant of ionic surfactant, sodium dodecylsulphate (SDS) and nonionic surfactants polyoxyethylene (20) sorbitan -monolaurate, -monopalmitate, -monostearate and -monooleate (Tween-20, Tween-40, Tween-60 and Tween-80) respectively have been determined by exploiting the spectral behaviours of ST in presence of urea and thiourea. The CMC and the aggregation number of the micelles have been found to increase and decrease respectively in presence of the additives urea and thiourea. While thiourea has greater CMC increasing effect than urea, it diminishes the aggregation number of the micelles efficiently than urea. The dye-micelle binding constant has been found to decrease in presence of urea and thiourea. Thiourea also quenches the fluorescence of ST in aqueous as well as in micellar medium.
A spectroscopic method for studying quadrupole formation is described, and experimental results are presented for lithium thiocyanate in a tetrahydrofuran/hexane solvent system. From molar absorptivity equations and an equation by Fuoss and Kraus, a direct relationship is derived between the quadrupole formation constant, KQ, and the dielectric constant of the medium. Experimental results are consistent with the equation and allow an estimate of the distance between lithium and thiocyanate in the ion pair.
Top-cited authors
Vinod K Gupta
  • University of Johannesburg
Mumtaz Ahmad Quraishi
  • Banaras Hindu University
Chandrabhan Verma
  • King Fahd University of Petroleum and Minerals
Eno Ebenso
  • North-West University
Bahram Ramezanzadeh
  • Institute for Color Science and Technology