Partial Molar Compressibility Research Articles

The partial molar heat capacity, expansion, isentropic, and isothermal compressions of thymidine in aqueous solution at T = 298.15 K

Solution densities have been determined for aqueous solutions of thymidine at T = (288.15, 298.15, 303.15, and 313.15) K. The partial molar volumes at infinite dilution, V 2 ∘ , obtained from the density data were used to derive the partial molar isobaric expansion at infinite dilution for thymidine at T = 298.15 K, E 2 ∘ { E 2 ∘ = ( ∂ V 2 ∘ / ∂ T ) p } . The partial molar heat capacity at infinite dilution for thymidine, C p , 2 ∘ , at T = 298.15 K has also been determined. Sound speeds have been measured for aqueous solutions of thymidine at T = 298.15 K. The partial molar isentropic compression at infinite dilution, K S , 2 ∘ , and the partial molar isothermal compression at infinite dilution, K T , 2 ∘ { K T , 2 ∘ = - ( ∂ V 2 ∘ / ∂ P ) T } , have been derived from the sound speed data. The V 2 ∘ , E 2 ∘ , C p , 2 ∘ , and K S , 2 ∘ results for thymidine are critically compared with those available from the literature.

Fluctuation theory of molecular association and conformational equilibria

General expressions relating the effects of pressure, temperature, and composition on solute association and conformational equilibria using the fluctuation theory of solutions are provided. The expressions are exact and can be used to interpret experimental or computer simulation data for any multicomponent mixture involving molecules of any size and character at any composition. The relationships involve particle-particle, particle-energy, and energy-energy correlations within local regions in the vicinity of each species involved in the equilibrium. In particular, it is demonstrated that the results can be used to study peptide and protein association or aggregation, protein denaturation, and protein-ligand binding. Exactly how the relevant fluctuating properties may be obtained from experimental or computer simulation data are also outlined. It is shown that the enthalpy, heat capacity, and compressibility differences associated with the equilibrium process can, in principle, be obtained from a single simulation. Fluctuation based expressions for partial molar heat capacities, thermal expansions, and isothermal compressibilities are also provided.

Partial molar adiabatic compressibilities of transfer of some amino acids from water to aqueous lactose solutions at different temperatures

Apparent molar adiabatic compressibilities ( K ϕ, s ) of glycine, L-alanine, L-valine, and L-leucine have been determined in aqueous and mixed aqueous solutions of lactose (2 to 6 mass%) at T = (293.15, 298.15, 303.15, and 308.15) K. From these data partial molar adiabatic compressibilities at infinite dilution ( K ϕ, s 0) have been evaluated to calculate corresponding transfer function. The transfer partial molar adiabatic compressibilities at infinite dilution ( ΔK ϕ, s 0) are found to be positive. The decrease in the magnitude of transfer partial molar adiabatic compressibilities from glycine to L-leucine indicates the dominance of hydrophobic–hydrophobic interactions between the increasing side chains of amino acids. Also, the contributions of NH 3 + COO − , and CH 2 groups have been calculated by the linear correlation of K ϕ, s 0 with number of carbon atoms in the alkyl chain of amino acids.

Solvation of multivalent cations in methanol – Apparent molar volumes, expansibilities, and isentropic compressibilities

Densities of the solutions of gallium, yttrium, lanthanum, gadolinium, and lutetium trifluoromethanesulfonates in methanol have been determined at temperatures ranging from (283.15 to 313.15)K. The sound velocities in these systems have been measured at T=298.15K. From obtained data the standard partial molar volumes and their temperature derivatives as well as standard partial molar adiabatic compressibilities for ions in solutions have been estimated. The results have been discussed on the basis of the classical model of ion in solution and compared with our earlier findings for divalent cations. The importance of the numbers of solvent molecules in first solvation spheres of ions has been revealed.

Partial Molar Isentropic and Isothermal Compressions of the Nucleosides Adenosine, Cytidine, and Uridine in Aqueous Solution at 298.15 K

Sound speeds have been measured for aqueous solutions of the nucleosides adenosine, cytidine, and uridine at T = 298.15 K and at ambient pressure. For adenosine and uridine, the partial molar isentropic compressions at infinite dilution, KS,2o, were derived from the sound speed data using conventional methods. These KS,2o results were combined with the partial molar heat capacities and partial molar isobaric expansions at infinite dilution available from the literature to evaluate, for the first time, the partial molar isothermal compressions at infinite dilution, KT,2o {KT,2o = −(∂V2o/∂p)T, where V2o is the partial molar volume of the solute at infinite dilution}. An alternative method is described for the calculation of the KS,2o and KT,2o values for cytidine from the sound speed data. The KT,2o results for the nucleosides have been rationalized in terms of the likely solute−water interactions. For cytidine, an analysis of the molality dependence of the partial molar isothermal compression in terms of self-association has also been explored.

Volumetric and Viscometric Studies of Some Amino Acids in Aqueous Solutions of Cadmium Chloride at T = (288.15 to 318.15) K and at Atmospheric Pressure

The apparent molar volumes, apparent molar adiabatic compressibilities, and viscosities of glycine, dl-α-alanine, dl-α-amino-n-butyric acid, l-valine, and l-leucine, in aqueous solutions of cadmium chloride, CdCl2, at different concentrations have been determined in the temperature range (288.15 to 318.15) K from density, sound velocity, and time flow measurements, using a vibrating-tube digital densimeter, ultrasonic multifrequency interferometer, and Ubbelohde type capillary viscometer attached with an automatic viscosity measuring unit, respectively. From these data, partial molar volumes V2o, partial molar adiabatic compressibilities, KoS,2, viscosity B-coefficients, and the corresponding transfer parameters (ΔtVo2, ΔtKoS,2, and ΔtB), hydration numbers, nH, and side chain group contributions, dB/dT have been calculated. Transfer parameters are positive and increase with the concentration of CdCl2.

Ultrasonic and Volumetric Study of N–H Bond Complexes in Binary Mixtures

Experimental values of the density and ultrasonic velocity have been measured for binary mixtures of butylamine with 1-butanol and with tert-butanol at temperatures of 293.15, 303.15 and 313.15 K over the entire mole fraction range. From these data, the excess molar volumes, deviations in isentropic compressibility, excess internal pressures, and excess molar enthalpies have been calculated. All of the excess functions were fitted to Redlich-Kister polynomial relations to estimate the adjustable parameters along with the standard deviations of the fits. The variations of these excess functions with mole fraction of butylamine have been examined. The changes in these parameters with composition suggest that the interaction between butylamine and 1-butanol is strong, whereas its interaction with tert-butanol is weak. Further, the partial molar volumes and partial molar compressibilities at infinite dilution have also been evaluated since these parameters provide better insight for studying intermolecular interactions.

Thermodynamic Study of Some Amino Acids, 2-Aminopropanoic Acid, 2-Amino-3-methylbutanoic Acid, 2-Amino-4-methylpentanoic Acid, and 2-Amino-3-phenylpropanoic Acid in Aqueous Saccharide Solutions at Different Temperatures: Volumetric and Ultrasonic Study

Knowledge of thermodynamic properties of amino acids in aqueous medium can provide valuable information about the stabilization mechanism of proteins. In this study, we report the density and speed of sound of some amino acids (2-aminopropanoic acid, 2-amino-3-methylbutanoic acid, 2-amino-4-methylpentanoic acid, and 2-amino-3-phenylpropanoic acid) in aqueous fructose, d-(+)-cellobiose, and d-melezitose solutions (0.1 mol·kg−1) at (293.15, 298.15, 303.15, and 308.15) K. From these data, the apparent molar volume and apparent molar adiabatic compressibility have been evaluated. The partial molar volume, partial molar adiabatic compressibility, and their corresponding transfer functions were calculated. These results were used to interpret the type of interactions occurring in the ternary mixtures using the cosphere overlap model. The concentration and temperature dependence of solute−solute and solute−solvent interactions in the present study was also discussed.

Partial molar volume and partial molar compressibility of four homologous α-amino acids in aqueous sodium fluoride solutions at different temperatures

Density and ultrasonic speed of four amino acids (glycine, l-alanine, l-valine, and l-leucine) in aqueous sodium fluoride solutions {(0.1 to 0.5) M} have been measured at T = (308.15, 313.15, and 318.15) K. Apparent molar volumes ( V φ ), partial molar volumes V φ 0 , transfer volumes Δ V φ 0 and hydration number ( n H ) are evaluated using density data. Adiabatic compressibility ( β s), change (Δ β s), and relative change in compressibility (Δ β s/ β 0), apparent molar compressibility ( K φ ), partial molar compressibility K φ 0 , transfer compressibility Δ K φ 0 , and hydration number ( n H) have been calculated using ultrasonic speed data. The linear correlation of V φ 0 , Δ V φ 0 , K φ 0 and Δ K φ 0 for a homologous series of amino acids have been used utilised to calculate the contribution of charged end groups ( NH 3 + , COO −), CH 2 group and other alkyl chain of the amino acids. The analysis shows that the ion–ion interactions are much stronger than ion–hydrophobic interactions over the entire concentration range of sodium fluoride. It is observed that sodium fluoride has a strong dehydration effect on amino acids.

High-pressure EPR reveals conformational equilibria and volumetric properties of spin-labeled proteins.

Identifying equilibrium conformational exchange and characterizing conformational substates is essential for elucidating mechanisms of function in proteins. Site-directed spin labeling has previously been employed to detect conformational changes triggered by some event, but verifying conformational exchange at equilibrium is more challenging. Conformational exchange (microsecond-millisecond) is slow on the EPR time scale, and this proves to be an advantage in directly revealing the presence of multiple substates as distinguishable components in the EPR spectrum, allowing the direct determination of equilibrium constants and free energy differences. However, rotameric exchange of the spin label side chain can also give rise to multiple components in the EPR spectrum. Using spin-labeled mutants of T4 lysozyme, it is shown that high-pressure EPR can be used to: (i) demonstrate equilibrium between spectrally resolved states, (ii) aid in distinguishing conformational from rotameric exchange as the origin of the resolved states, and (iii) determine the relative partial molar volume (ΔV°) and isothermal compressibility (Δβ(T)) of conformational substates in two-component equilibria from the pressure dependence of the equilibrium constant. These volumetric properties provide insight into the structure of the substates. Finally, the pressure dependence of internal side-chain motion is interpreted in terms of volume fluctuations on the nanosecond time scale, the magnitude of which may reflect local backbone flexibility.

Partial molar volumes, expansibilities and compressibilities of glyglyglycine in aqueous sucrose and fructose solutions between 288.15 and 308.15 K

Apparent molar volumes ( V ϕ) and apparent molar adiabatic compressibilities ( K ϕ,s ) of triglycine (glyglyglycine) in aqueous and mixed aqueous solutions of fructose and sucrose (2, 4, and 6 mass%) have been determined at 288.15, 293.15, 298.15, 303.15, and 308.15 K. From these data, limiting partial molar volumes ( V ϕ 0 ) and limiting partial molar adiabatic compressibilities ( K ϕ , s 0 ) for glyglyglycine in aqueous sucrose and fructose solutions have been evaluated, together with the standard partial molar properties of transfer Δ tr Y of the glyglyglycine from water to aqueous saccharides solutions. Transfer parameters have been interpreted in terms of solute–cosolute interactions on the basis of a cosphere overlap model. Pair and triplet interaction coefficients have also been calculated from transfer parameter data. The partial molar volume at infinite dilution ( V ϕ 0 ) were used to obtain the partial molar expansion at infinite dilution, E 2 0 , for glyglyglycine to examine the temperature dependence of such interactions.

Volumetric and Viscometric Studies of Molecular Interactions of Binary Liquid Mixtures of Styrene with Acetone and Dimethylsulphoxide at Different Temperatures

The present work reports the results of densities, ρ, viscosities, η, ultrasonic speeds, u, and refractive indices, n, of pure styrene (STY), acetone (ACT) and dimethylsulphoxide (DMSO) and of their binary liquid mixtures over the entire composition range at 298.15, 303.15, 308.15, and 313.15 K. The excess molar volumes, V E , excess intermolecular free lengths, , deviations in isentropic compressibilities, Δk s , viscosities, Δη, and in refractive indices, Δn were calculated from the experimental data. Partial molar volumes, , and partial molar compressibilities, , of ACT and DMSO in styrene at infinite dilution and at different temperatures have been evaluated. Apart from using density data for the calculation of V E , excess molar volumes have also been estimated by using the Flory's statistical theory and refractive index measurements.

Volumetric, Viscometric, and Ultrasonic Properties of Liquid Mixtures of Cyclohexane with Alkanols at Different Temperatures

The densities (ρ), viscosities (η), and ultrasonic speeds (u) of pure cyclohexane, 1-butanol, 2- butanol, and those of their binary mixtures, with cyclohexane as common component, covering the whole composition range have been measured at 293.15, 298.15, 303.15, 308.15, 313.15, and 318.15 K. From the experimental data the excess molar volume (VE), deviations in isentropic compressibility (Δks), deviations in viscosity (Δη), deviations in ultrasonic speed (Δu), deviations in acoustic impedance (ΔZ), deviations in internal pressure (ΔPi), excess Gibbs free energy of activation (ΔG*E), entropies (ΔS*), and enthalpies (ΔH*) of activation of viscous flow have been determined. The sign and magnitude of these parameters were found to be sensitive towards interactions prevailing in the studied systems. Partial molar volumes (V0 φ,2) and partial molar compressibilities (K0 φ,2) of 1-butanol and 2-butanol in cyclohexane have also been evaluated. Moreover, VE values were theoretically predicted by using Flory’s statistical theory. The variations of derived parameters mentioned above with composition offer a convenient method to study the nature and extent of interactions between the component molecules of the liquid mixtures, not easily obtained by other means

Ultrasonic and thermodynamic studies of glycine in aqueous electrolytes solutions at 303 K

Densities and ultrasonic velocities of glycine (0.01–0.09M) in aqueous NaCl and MgCl2 (0.02 and 0.06M) solutions have been measured at 303K. From these experimental data adiabatic compressibility Ks, apparent molar volume, ϕv apparent molar adiabatic compressibility, ϕKs, partial molar volume ϕv0 and partial molar adiabatic compressibility, ϕ0Ks at infinite dilution were calculated for all the ternary systems. The data have been interpreted in terms of solute–solute and solute–solvent interactions. These results show that dipole–dipole and ion–solvent interaction are strong in glycine–aqueous MgCl2 than in glycine–aqueous NaCl.

Urea interactions with protein groups: A volumetric study

We determined the partial molar volumes and adiabatic compressibilities of N-acetyl amino acid amides, N-acetyl amino acid methylamides, N-acetyl amino acids, and short oligoglycines as a function of urea concentration. We analyze these data within the framework of a statistical thermodynamic formalism to determine the association constants for the reaction in which urea binds to the glycyl unit and each of the naturally occurring amino acid side chains replacing two waters of hydration. Our determined association constants, k, range from 0.04 to 0.39 M. We derive a general equation that links k with changes in free energy, DeltaGtr, accompanying the transfer of functional groups from water to urea. In this equation, DeltaGtr is the sum of a change in the free energy of cavity formation, DeltaDeltaGC, and the differential free energy of solute-solvent interactions, DeltaDeltaGI, in urea and water. The observed range of affinity coefficients, k, corresponds to the values of DeltaDeltaGI ranging from highly favorable to slightly unfavorable. Taken together, our data support a direct interaction model in which urea denatures a protein by concerted action via favorable interactions with a wide range of protein groups. Our derived equation linking k to DeltaGtr suggests that DeltaDeltaGI and, hence, the net transfer free energy, DeltaGtr, are both strongly influenced by the concentration of a solute used in the experiment. We emphasize the need to exercise caution when two solutes differing in solubility are compared to determine the DeltaGtr contribution of a particular functional group.

Volumetric, ultrasonic speed, and viscometric studies of salbutamol sulphate in aqueous methanol solution at different temperatures

Values of density, ultrasonic speed, and viscosity of salbutamol sulphate (SBS) have been determined in aqueous methanol solutions at T = (303.15, 308.15, 313.15, and 318.15) K. The apparent molar volume V φ , partial molar volume V ϕ 0 , molar expansivity E 2 0 , isobaric thermal expansion coefficient ( α 2), and second derivative of infinite dilution of partial molar volume with temperature ∂ 2 V ϕ 0 / ∂ T 2 are evaluated using density data. Isentropic compressibility β s , change in isothermal compressibility Δ β s , relative change in isentropic compressibility ( Δ β s / β s 0 ), apparent molar compressibility K φ and partial molar compressibility K ϕ 0 values are calculated by using data on density with ultrasonic speed. Viscosity B-coefficient, variation of B-coefficient with temperature, i.e., dB/dT, free energy of activation per mole of solvent Δ μ 1 0 ∗ and solute Δ μ 2 0 ∗ are evaluated using viscosity data. The above parameters are used to interpret the solute–solute, solute–solvent interactions and structure making/breaking ability of the drug in the given aqueous methanol solution.

Solvation of Hydrophobic Amino Acid Side Chains and Peptide Backbone in Aqueous Glycine Betaine and Trimethylamine N-oxide Solutions

There is a large class of small, water-soluble molecules broadly referred to as osmolytes that may stabilize or destabilize biomacromolecular structures. For example, trimethylamine N-oxide (TMAO) and glycine betaine are prominent stabilizers of proteins, while urea is a strong denaturant. Although these osmolytes have been employed in protein studies for more than 70 years, the mechanisms of their action are still largely unknown. One reason for this deficiency is the lack of direct thermodynamic data that can be used to quantify solute-solvent interactions versus solute-osmolyte interactions. In this work, we use high precision densimetry and ultrasonic velocimetry to examine the solvation properties of amino acid side chains and the peptide group in binary mixtures of water and TMAO or glycine betaine. Specifically, we report the partial molar volume, V°, and adiabatic compressibility, Ks°, of N-acetyl amino acid amides (alanine, valine, leucine, isoleucine, phenylalanine) and oligoglycines (Gly)1-5 in binary mixtures containing 0 to 4 M TMAO or glycine betaine. We use our volumetric results to evaluate the osmolyte-dependent group contributions of amino acid side chains and the peptide group. We analyze these osmolyte-dependent group numbers to evaluate the binding constants and elementary changes in volume and compressibility accompanying the replacement of water of hydration in the vicinity of the solutes with a TMAO or glycine betaine molecule. We compare these data with similar results previously obtained in our laboratory for the interactions of urea with protein groups. In general, we discuss the implications of our results for elucidating the mechanism of stabilization/destabilization of protein structures by osmolytes.

Molecular Mechanism of Urea-Induced Protein Denaturation

For more than half a century, urea has been used as a strong denaturant in protein folding/unfolding studies. However, the molecular mechanisms of urea-induced protein unfolding still remain unclear. This lack of understanding is to some extent reflects the scarcity of direct thermodynamic information that can be used to characterize interactions of urea with amino acid side chains and the peptide group. We recently demonstrated that volumetric measurements combined with statistical thermodynamic approach may represent a novel and effective way to tackle this problem [Lee, S. & Chalikian, T. V. (2009) J. Phys. Chem. B. 113, 2443-2450]. In this work, we employ high precision acoustic and densimetric techniques to quantify the solvation properties of solutes in the presence of urea. Specifically, we report the partial molar volumes, V°, and adiabatic compressibilities, KS°, of N-acetyl amino acid amides containing all 20 naturally existing amino acid side chains and oligoglycines, (Gly)1-5, at urea concentrations ranging from 0 to 8 M. Using our developed statistical thermodynamic approach, that links volumetric observables of a solute with solute-solvent and solute-cosolvent interactions in binary solvents, we evaluate the binding constants, k, and elementary changes in volume, ΔV, and compressibility, ΔKS, accompanying the replacement of water in the vicinity of the solutes with a urea molecule. While the binding constants are essentially similar for all protein groups, the magnitude and the sign of the determined values of ΔV and ΔKS vary markedly. The latter values reflect the nature of urea interactions with specific functional groups and the concomitant changes in hydration. In general, our results are consistent with a picture in which urea interacts with polar, non-polar and charged groups with comparable affinities, although the underlying forces stabilizing each type of interaction depend on the chemical nature of the interacting group.

Thermodynamic properties of peptide solutions 19. Partial molar isothermal compressions at T = 298.15 K of some peptides of sequence gly-X-gly in aqueous solution

The partial molar isobaric expansions at infinite dilution and T = 298.15 K, E 2 ∘ { E 2 ∘ = ( ∂ V 2 ∘ / ∂ T ) p } were determined recently for some tripeptides of sequence glycyl-X-glycine, where X is one of the amino acids alanine, valine, leucine, isoleucine, phenylalanine, methionine, proline, serine, threonine, asparagine, glutamine, histidine, and tyrosine. These quantities, along with partial molar heat capacity data available from the literature, were used to convert the partial molar isentropic compressions at infinite dilution determined previously for these tripeptides into the partial molar isothermal compressions at infinite dilution and T = 298.15 K, K T , 2 ∘ { K T , 2 ∘ = - ( ∂ V 2 ∘ / ∂ p ) T } . These K T , 2 ∘ results, along with that for triglycine, were used to estimate the contributions of the amino acid side-chains to the partial molar isothermal compressions of peptides. The side-chain contributions have been rationalized in terms of the likely peptide–water interactions.

Physicochemical investigation on interactions of some amino acids with aqueous tetra-butyl ammonium bromide solution at 298.15 K

Apparent molar volumes, viscosity B-coefficients, and apparent molar isentropic compressibilities of glycine, L-alanine, L-valine and L-leucine in 0.062, 0.125 and 0.256 mol kg−1 aqueous tetra-butyl ammonium bromide (TBAB) solution have been determined at 298.15 K from their experimental density, flow time and sound speed measurements, respectively. The standard partial molar volumes and compressibilities are used to calculate the corresponding volume of transfer at infinite dilution, from water to aqueous TBAB solutions. The linear correlation of partial molar volumes for a homologous series of amino acids has been utilised to calculate the contribution of charged end groups and other alkyl chains of the amino acids to partial molar volumes. The hydration numbers of amino acids have also been determined. Viscosity B-coefficients have been calculated using the Jones–Dole equation. The values of the charged end groups contribution to the viscosity B-coefficients of the amino acids are calculated.