Structure-breaking Effect Research Articles

Analysis of the Temperature and Composition Dependence of Viscosimetric Properties of 2-Butanone + 2-Butanol Solvent Mixtures

Kinematic viscosities were measured for 2-butanone + 2-butanol binary liquid mixtures with a capillary Ubbelohde routine viscometer in the temperature range from 273.15 to 353.15 K at atmospheric pressure, and covering the whole miscibility field (0⩽x i ⩽1). Experimental data have been correlated by means of different empirical or semiempirical relationships, such as ν=ν(T), ν=ν(x i ), and ν=ν(T, x i ). Viscosity deviations, Δν, from ideal behavior are negative at all experimental conditions, confirming that structure breaking effects prevail in the liquids. Furthermore, the thermodynamics of viscous flow and excess Gibbs energy of activation of viscous flow, G* E , have been calculated. As an alternative and complementary approach to such investigations, the fluidity (ϕ) of this binary system has been analyzed by the modified—Batschinski theory. The results are discussed in terms of the specific molecular interactions between the mixture components.

The power of tests of predictive ability in the presence of structural breaks

This paper presents analytical, Monte Carlo, and empirical evidence on the effects of structural breaks on tests for equal forecast accuracy and encompassing. We show that out-of-sample predictive content can be hard to find because out-of-sample tests are highly dependent on the timing of the predictive ability. Moreover, predictive content is harder to find with some tests than others: in power, F-type tests of equal forecast accuracy and encompassing often dominate t-type alternatives. Based on these results and evidence from an empirical application, we conclude that structural breaks under the alternative may explain why researchers often find evidence of in-sample, but not out-of-sample, predictive content.

Hyper-Mobile Water Is Induced around Actin Filaments

When introduced into water, some molecules and ions (solutes) enforce the hydrogen-bonded network of neighboring water molecules that are thus restrained from thermal motions and are less mobile than those in the bulk phase (structure-making or positive hydration effect), and other solutes cause the opposite effect (structure-breaking or negative hydration effect). Using a method of microwave dielectric spectroscopy recently developed to measure the rotational mobility (dielectric relaxation frequency) of water hydrating proteins and the volume of hydration shells, the hydration of actin filament (F-actin) has been studied. The results indicate that F-actin exhibits both the structure-making and structure-breaking effects. Thus, apart from the water molecules with lowered rotational mobility that make up a typical hydration shell, there are other water molecules around the F-actin which have a much higher mobility than that of bulk water. No such dual hydration has been observed for myoglobin studied as the representative example of globular proteins which all showed qualitatively similar dielectric spectra. The volume fraction of the mobilized (hyper-mobile) water is roughly equal to that of the restrained water, which is two-thirds of the molecular volume of G-actin in size. The dielectric spectra of aqueous solutions of urea and potassium-halide salts have also been studied. The results suggest that urea and I − induce the hyper-mobile states of water, which is consistent with their well-known structure-breaking effect. The molecular surface of actin is rich in negative charges, which along with its filamentous structure provides a structural basis for the induction of a hyper-mobile state of water. A possible implication of the findings of the present study is discussed in relation to the chemomechanical energy transduction through interaction with myosin in the presence of ATP.

Observations of Water Monomers in Supersaturated NaClO4, LiClO4, and Mg(ClO4)2 Droplets Using Raman Spectroscopy

Salts of the same anions of Mg2+, Na+, and Li+ have been found to exhibit different hygroscopic properties. These differences are attributed to the molecular structural properties of the hydrogen bonding network of the water molecules in the second and first hydrated layers of Mg2+, Na+, and Li+. To study the structures of water molecules, in particular, the presence of water monomers, Raman spectra of single levitated droplets of aqueous NaClO4, LiClO4, and Mg(ClO4)2 solutions from diluted concentrations to high supersaturations were measured. Because heterogeneous nucleation was suppressed in these levitated droplets, supersaturated droplets with a water-to-solute ratio (WSR) as low as 2 was achieved. Taking advantage of the structure breaking effect of ClO4- on the hydrogen bonding network of water molecules, Raman spectra of water monomers in these highly supersaturated droplets were observed. At a low WSR, two peaks at 3549 and 3588 cm-1 for water monomers with one and two weak hydrogen bonds with Cl...

Anionic Effects on Raman OD Stretching Spectra for Alcoholic LiX Solutions ( X = Cl − , Br − , I − , ClO 4 − , NO 3 − , and CH 3 COO − )

Raman OD stretching spectra of alcoholic LiX (X = Cl−, Br−, I−, ClO4 −, NO3 −, and CH3COO−) solutions (alcohols = methanol and ethanol) were measured in the liquid state at room temperature and in the glassy state at liquid nitrogen temperature. The effects of the anions on the Raman OD stretching spectra in these alcoholic solutions are investigated and the structural changes of the solutions are discussed. It is shown that the structure-breaking effects of anions on the intrinsic alcoholic structure increase in the order: Cl− < Br− < I− < ClO4 −. From spectral changes, it seems that CH3COOLi exerts little effect on the liquid structure of the alcohol.

Multivariate-based causality tests of twin deficits in the US

This paper provides an alternative methodology for testing the causality direction between twin deficits in the US. Rao's multivariate F-test combined with the bootstrap simulation technique has appealing properties, especially when the data-generating process is characterized by unit roots. In addition the results show that the effect of structural breaks are of paramount importance when the causality tests are conducted. In much contemporary applied econometrics there is all-too-little attention given to the possibility of changes in the economic process.

Forecast-Based Model Selection in the Presence of Structural Breaks

This paper presents analytical, Monte Carlo, and empirical evidence on the effects of structural breaks on tests for equal forecast accuracy and forecast encompassing. The forecasts are generated from two parametric, linear models that are nested under the null. The alternative hypotheses allow a causal relationship that is subject to breaks during the sample. With this framework, we show that in-sample explanatory power is readily found because the usual F-test will indicate causality if it existed for any portion of the sample. Out-of-sample predictive power can be harder to find because the results of out-of-sample tests are highly dependent on the timing of the predictive ability. Moreover, out-of-sample predictive power is harder to find with some tests than with others: The power of F-type tests of equal forecast accuracy and encompassing often dominates that of the more commonly-used t-type alternatives. Overall, out-of-sample tests are effective at revealing whether one variable has predictive power for another at the end of the sample. Based on these results and additional evidence from two empirical applications, we conclude that structural breaks can explain why researchers often find evidence of in-sample, but not out-of-sample, predictive content.

Using simulation to study solvation in water

Abstract Simulations of simple solutes (charged and uncharged spheres) in model water have been performed in order to elucidate aspects of solvation in water at ambient and supercritical states. The variation of solvation entropy as a function of solute charge has been used to investigate hydrophobic and hydrophilic ordering and the structure-making and structure-breaking effects of ions. Simulations with model solvents, which differ from water in certain features, have been used to try to identify the particular properties of water that are associated with these phenomena.

Dielectric Spectroscopy of Solutions of Some Alkylammonium Salts in Chloroform and 1-Octanol

Abstract Dielectric loss spectra between 1 MHz and 36 GHz have been measured at 20°C for solutions of hexadecyl trimethylammonium bromide and chloride, tetrahexylammonium bromide and tetrabutylam-monium bromide in chloroform and 1-octanol (three solutes per solvent) at moderate and high concen-trations. The discussion is aimed at identifying relaxation processes involving ions. Describing the relax -ational part of the spectra (after subtraction of the conductivity contribution) by a sum of spectral com-ponents, the lowest frequency component can be attributed to the solute in all cases. Its concentration dependence is indicative of two ionic relaxation processes differing in physical nature. The solvent is partly involved in those processes; moreover a structure breaking effect is likely to occur in case of the alcoholic solvent. The results are also discussed in comparison with a molten alkylammonium salt and with solutions of this and of inorganic salts.

Study of Intermolecular Interaction in Dimethylsulphoxide + 1-Alkanols (1-Butanol, 1-Hexanol, 1-Octanol) At 303.15 K

The ultrasonic velocity, u, viscosity, η, and density, ρ of dimethylsulphoxide (DMSO), 1-butanol, 1-hexanol, 1-octanol, and of their binary mixtures, where DMSO is common component, have been measured at 303.15 K. From the experimental data, excess isentropic compressibility, K E s, excess intermolecular free length, LE f, excess velocity, u E, excess acoustic impedance, Z E, excess viscosity, ηE, excess free energy of activation of viscous flow, G*E, and excess rheochore, [R E] have been calculated. The behaviours of excess functions with composition of the mixtures suggest that the structure-breaking effect dominates over the interaction effect between the component molecules. Furthermore, the experimental values of u and η were fitted by empirical equations stating their dependence on composition of the mixtures. The experimental values of u have been compared with those calculated by using Nomoto and Van Dael relations.

Regionalisation versus globalisation in European financial market integration: Evidence from co-integration analyses

Motivated by recent regulatory changes, this study investigates the degree of integration in retail lending in six core European Union (EU) countries using co-integration methodology which allows to investigate the presence and effects of structural breaks. While in the pre-break period we could detect integration to a limited degree, the evidence for integration weakened in the post-1992 period. This could however reflect a convergence process, particularly with respect to spreads. This result is clearly a regional, not a global phenomenon. As European lending rates are not yet fully integrated, the still segmented financial markets pose a challenge for a unified monetary policy.

NMR studies on hydrophobic interactions in solution Part 5. Effect of urea on the hydrophobic self-association of tert-butanol in water at different temperatures

An NMR A22 parameter study of the effect of urea on the hydrophobic self-association of tert-butanol in aqueous solutions is presented. One aim of the present paper is to contribute to the understanding of the urea effect in protein denaturation. The experimental data used for the computation of the A22 parameters, namely the self-diffusion coefficients and the intermolecular 1H relaxation rates of tert-butanol in the ternary system, together with the additionally measured self-diffusion coefficients of water, are also examined with respect to a possible structure-breaking effect of urea on the aqueous phase which has been discussed in the literature. We obtain the remarkable result that in a certain mixture range addition of urea can increase the translational mobility of the solute tert-butanol, whereas it always decreases the mobility of bulk water. Thus, we could not detect a structure-breaking effect of urea on the aqueous phase. The urea content was varied up to 12 mol% in the temperature range 10–40°C. It is found that low urea concentrations enhance the hydrophobic self-association in the water-rich region in the whole temperature range. With low tert-butanol concentrations this enhancement effect reaches a pronounced maximum. At higher urea concentrations a destabilisation of the hydrophobic interaction is observed. This latter result is in agreement with the need for relatively high urea concentrations to achieve protein denaturation. Obviously, the same basic mechanism controls the effect of urea not only on the stability of hydrophobic association of comparatively small molecules but also on the conformation of large biomolecules.

Hexadecylpyridinium Chloride + Trimethyltetradecylammonium Bromide Mixed Micelles in Polyethylene Glycol + Water Mixtures

Abstract The conductances of hexadecylpyridinium chloride (HPyCl) + trimethyltetradecylammonium bromide (TTAB) mixtures over the entire mole fraction range of HPyCl (αHPyCl) were measured in aqueous binary mixtures of polyethylene glycol (PEG) 200, 400, 600, and 4000 containing different amounts of each PEG in their respective binary mixtures at 30 °C. Each conductivity curve showed a single break, except in the presence of PEG 4000 where two breaks were observed. From the conductivity (κ) data, the critical micellar concentration (cmc), degree of counter ion association (χ), the equivalent conductivities (Λ) from the slope of κ versus C plots, and the standard Gibb’s free energy of transfer of the surfactant hydrocarbon chain from the medium to the interior of the micelle (ΔGHP°) were computed. It was observed that micelle–PEG interactions in the case of HPyCl and TTAB were quite similar to mixed micelle–PEG interactions especially in the presence of PEG 200, 400, and 600. The results were explained on the basis of medium structure-breaking effects of PEG and adsorption of PEG on the micelle–solution interface. In the presence of PEG 4000, the micelle formation corresponding to the first break was found to be similar to that in the presence of PEG 200, 400, and 600. The second break was designated to the polymer bound micellar aggregates, which became more stable as the amount of PEG 4000 was increased.

International evidence on shock persistence: structural change, nonlinearities and subsample robustness

Testing for unit roots and the related issue of measuring shock persistence has attracted considerable theoretical and applied econometric interest. The issue of the size of the random walk component raised by Cochrane (Journal of Political Economy, 96, 893-920, 1988) has been extended in the work of other authors. Leung (Economics Letters, 40, 435-44, 1992), in particular, considers the effects of structural breaks on measures of persistence. In this paper we consider new results for the effects of structural change, nonlinearities and subsample robustness on spectral-based measures of persistence illustrating the potential problems via an updated and extended version of the Cogley (Journal of Political Economy, 98, 501-18, 1990) data set. We find that significant structural breaks exist in the majority of the series investigated. Furthermore, measured persistence differs markedly across distinct periods with the assumption of common growth rates over very long periods leading on occasions to potentially erroneous conclusions on the degree of persistence. Nonlinearities measured by the significance of time squared (TSQ), seem important in many cases, particularly post-World War Two (WW2), potentially explaining the apparently high levels of post-WW2 persistence. The paper concludes with a warning on the use of measures of persistence when the data include structural change and/or nonlinearities, highlighting the importance of the correct choice for breakpoints and second sub-sample start points.

Apparent molar volumes of glycine, L-alanine, and L-serine in water + ethanol mixtures at 298.15 K

Densities of glycine, L-alanine, and L-serine have been measured with an oscillating-tube densimeter at 298.15 K in water + ethanol (EtOH) mixtures ranging from pure water to 45% ethanol by mass. From these densities, apparent molar volumes and limiting apparent molar volumes of the three amino acids in the mixtures have been calculated. Transfer volumes are interpreted in terms of the structure-making or structure-breaking effects of water on addition of these amino acids in the mixtures. The relative contributions of hydrophilic and hydrophobic interactions in these solutions have been inferred.Key words: glycine, L-alanine, L-serine, water + ethanol mixtures, densities.

Dynamical structure of water in aqueous solutions of LiCl, NaCl, and KCl by low-frequency Raman scattering: Comparison between the multiple random telegraph model and Cole-Cole relaxation

Depolarized low-frequency Raman spectra of aqueous solutions of LiCl, NaCl, and KCl have been investigated over a wide concentration range. The spectra were analyzed with one relaxation mode and two damped harmonic oscillators. We applied two types of relaxation model: the multiple random telegraph (MRT) model and the Cole-Cole-type relaxation. Each relaxation time becomes longer than that of liquid water in both relaxation models. Structure making (Li, Na) and structure breaking (K) effects were concluded from a fitting parameter corresponding to the modulation speed in the MRT model.

Apparent Molar Volumes of l-Glycine, l-Alanine, and l-Serine in Water + Dimethylformamide Mixtures at 298.15 K

Densities of l-glycine, l-alanine, and l-serine have been measured with an oscillating-tube densimeter at 298.15 K in water + dimethylformamide (DMF) mixtures ranging from pure water to 45% DMF by mass. From these densities, apparent molar volumes and limiting apparent molar volumes of the three amino acids in the mixtures have been calculated. Transfer volumes were interpreted in terms of the structure-making or structure-breaking effects of these amino acids in the mixtures.

Dielectric Spectroscopy of Binary Liquid Mixtures of Methanol with Morpholine, Pyrrolidine and some of their Derivatives

Abstract Dielectric spectra (up to 72 GHz) have been measured at 20 °C for mixtures of methanol and one of the following substances: morpholine, N-methyl morpholine, N-cyano morpholine, pyrrolidine and N-cyano pyrrolidine. The composition dependence of the relaxation parameters shows close similarities for the morpholines and, on the other hand, for the pyrrolidines, which indicates that a structure breaking effect on methanol is exerted by the former but not by the latter group of substances.

NMR studies on hydrophobic interactions in solution Part 2.—Temperature and urea effect on the self-association of ethanol in water

A. Sacco and M. Holz, J. Chem. Soc., Faraday Trans., 1997, 93, 1101 DOI: 10.1039/A605867A

EFFECTS OF PRESSURE AND TEMPERATURE ON THE VISCOSITY B COEFFICIENT FOR POTASSIUM CHLORIDE IN WATER

Viscosity of aqueous potassium chloride (KCl) solution was measured at temperatures of 283.2 and 323.2K and pressures up to 375MPa by means of a rolling-ball viscometer. The Jones-Dole B coefficient of KCl at both temperatures increased with increasing pressure and then decreased after passing over a maximum as well as previously observed one at 298.2K. The maximum became more pronounced at lower temperatures. In comparison with the dielectric friction theory, the observation of the maximum is ascribed to a balance between two contributions; pressure breaks any water structure (B increases) and reduces the dielectric friction between ion and solvent (B decreases). The temperature coefficient ∂B/∂T was observed to be positive at all pressures and decreases with increasing pressure. The fact suggests that the structure-breaking effect of KCl for water reduces with increasing pressure, and the reduction of the effect may be ascribed that the water structure which should be broken by addition of the electrolyte is already broken by pressure.