Partial Molar Compressibility Research Articles

Chain Compaction and Synergistic Destabilization of Globular Proteins by Mixture of Denaturants

AbstractCharacterization of unfolded states is essential to understand the mechanism of protein folding. This study examines the unfolded states of RNase A and α‐LA in the mixture of ′′structurally‐similar′′ chemical denaturants, arginine (Arg) and guanidinium chloride (Gdm). Thermal‐ and chemical‐unfolding experiments show that the mixture of denaturants synergistically destabilizes the proteins. Volumetric analysis shows that partial molar volume (V°) and adiabatic compressibility (Ks) of the proteins decreases with increasing [Gdm]. This suggests that the proteins might be gradually losing their intra‐molecular interactions resulting in decreased internal cavity. The addition of Arg to the Gdm‐unfolded states decreases both V° and Ks values indicating compaction of the protein chains. This could be attributed to reduction in the hydration of surface‐exposed residues of the proteins upon direct interaction with Arg and increased non‐native contacts. The results provide a direct experimental evidence for the compaction of unfolded protein chain upon addition of another denaturant.

Volumetric and ultraacoustic properties of sodium salts of ibuprofen/diclofenac drugs in aqueous and aqueous-β-cyclodextrin solution

Present paper reports the study of inclusion complex formation between two non-steroidal anti-inflammatory drugs namely sodium ibuprofen and diclofenac sodium in water and aqueous-β-cyclodextrin solutions through thermodynamic properties like the standard partial molar volumes and the standard partial molar compressibility at 303.15, 308.15 and 313.15 K and at atmospheric pressure. For this, the densities and ultrasonic velocities of ternary sodium ibuprofen/diclofenac-β-cyclodextrin-water mixtures were measured and used for the calculation of apparent molar volume (V2,ϕ) and apparent molar compressibility (κs,2,ϕ). The concentration dependence of apparent properties has been fitted to standard relations and corresponding the standard partial molar volume (V2o) and the standard partial molar compressibility (κs,2o) and respective solute-solute interaction parameters Sv and Sk were graphically determined. The standard transfer volumes (ΔtrV2o) and standard transfer compressibility (Δtrκs,2o) were also computed and these properties have been interpreted in terms of drug hydration, inclusion complex formation, and different interactions involved. The sign of Sv and Sk revealed the weakening of solute–solute interactions in presence of cosolute β-cyclodextrin. Solubilization of hydrophobic parts, expulsion of water from hydrophobic cavity of β-cyclodextrin and inclusion complex formation of these drugs with β-cyclodextrin has been confirmed from partial molar volume and transfer properties.

Volumetric, acoustic and viscometric studies of intermolecular interactions in polyethylene glycol 400 + alkyl acrylate binary mixtures at temperatures from 293.15 to 318.15 K

ABSTRACT Densities, ρ, speeds of sound, u and refractive index, n D of binary solutions of polyethylene glycol 400 with methyl acrylate (MA), ethyl acrylate (EA), n-butyl acrylate (n-BA), including those of pure components, have been measured over the whole composition range at temperatures (293.15–318.15) K and atmospheric pressure. From experimental data, excess molar volume, , excess isentropic compressibility, , excess speed of sound, , excess molar isentropic compressibility, , deviations in refractive indices, and deviations in molar refraction, . The partial and excess molar volumes and compressibilities covering the entire mole fraction range, and at infinite dilution were also calculated. These parameters variation with composition and temperature of mixtures suggest the difference in shape and size of molecules of components and formation of hydrogen bonding between unlike molecules. Moreover, the refractive indices of binary solutions are predicted by various empirical mixing rules and compared with experimental findings.

The (p-Vm-T-x) properties of {water (1) + acetamide (2)} mixtures in the range 278.15–323.15 K and 0.10–100 MPa

The density ρ at atmospheric pressure and compression ratios k=ΔV/Vo of the {water (1) + acetamide (2)} mixture in the range of temperature from 278.15 K to 323.15 K (278.15, 288.15, 298.15, 308.15, 323.15), pressures from 10 to 100 MPa (10, 25, 50, 75 and 100) and in a wide range of compositions (maximum mole fraction of acetamide (AA) x2 = 0.3875) were measured in the work. The partial molar volumes of both components V¯1 and V¯2 in the mixture, molar isothermal compression KT,m, molar isobaric thermal expansion EP,m, isochoric coefficient of thermal pressure βV, and internal pressure of the mixture Pint were calculated. The volume characteristics for an infinitely dilute AA solution in water: limiting partial molar volumes V¯2∞, limiting partial molar isothermal compression K¯T,2∞, and limiting partial molar isobar expansion E¯P,2∞ were calculated. The obtained results are discussed from the standpoint of interactions of solute-solvent and solute-solute. The obtained results are discussed in terms of solute-solvent and solute-solute interactions.

Modulation of molecular interactions of homologous series of amino acids with (sorbitol + glycine betaine) mixture compared to individual osmolytes: Thermodynamic analysis

Sorbitol and glycine betaine (GB) are the important osmolytes which are known to stabilize proteins. To understand the conformational stability of these complex biomolecules and their interactions with solvents in fine details, physico-chemical properties of the homologous series of amino acids were studied. The values of densities (ρ) and speeds of sound (u) of five amino acids: glycine, dl-alanine, dl-α-amino-n-butyric acid, l-valine, and l-leucine were measured in mixtures of {water + sorbitol (0.53 mol·kg−1) + glycine betaine (0.51 mol·kg−1)} and {water + sorbitol (1.12 mol·kg−1) + glycine betaine (1.04 mol·kg−1)} at T = 298.15 K. Heats of dilution (q) of amino acids from water to mixture {water + sorbitol (0.53 mol·kg−1) + glycine betaine (0.51 mol·kg−1)} solution were also measured. These values have been used to find the infinite dilution standard partial molar volume (V2.m0), standard partial molar adiabatic compressibility (Ks,2.m0), enthalpy of dilution (ΔdilH0), standard partial molar volume of transfer (ΔtrV2,m0) and hydration number of amino acids. By linear regression fitting of V2.m0,contributions of zwitterionic and hydrophobic groups of amino acids have been calculated. All these results have been correlated and interpreted in terms of intermolecular interactions on the basis of co-sphere overlap model. In case of all the amino acids except valine and leucine, the dominance of ionic–ionic and hydrophilic–ionic interaction is indicated. The values of (ΔtrΔdilH0) obtained by isothermal titration calorimetry support the volumetric interpretations. An attempt has also been made to find the calorimetric evidences to preferential hydration of lysozyme and preferential exclusion of osmolytes.

On empirical decomposition of volumetric data

Volumetric characterization of proteins and their recognition events has been instrumental in providing information on the role of intra- and intermolecular interactions, including hydration, in stabilizing biomolecules. The credibility of molecular models and interpretation schemes used to rationalize experimental data are essential for the validity of microscopic insights derived from volumetric results. Current empirical schemes used to interpret volumetric data suffer from a lack of theoretical and computational substantiation. In this contribution, we take advantage age of recent MD simulations of proteins in solution coupled with Voronoi-Delaunay tessellation of simulated structures that have provided an exceptional level of structural detail on the nature of protein-water interfaces. We use these structural insights to re-evaluate empirical frameworks used for interpretation of volumetric data. An important issue in this respect is the actual dividing surface between water and protein atoms that is used in volumetric studies when the solute and solvent are treated as hard spheres enclosed within their respective van der Waals surfaces. In one development, using Voronoi tessellation of MD simulated protein-water systems the dividing surface has been defined as the points equidistant from the water and protein atoms. The interstitial void volume between the solute and the dividing surface corresponds to thermal volume envisaged by Scaled Particle Theory. In this communication, we explicitly account for the contributions of thermal volume to the partial molar volume, compressibility, and expansibility of proteins and re-examine and redefine the intrinsic and hydration volumetric contributions. We discuss the implications of our results for protein transitions and association events.

Kirkwood-Buff integration: A promising route to entropic properties?

Kirkwood-Buff integration (KBI) is implemented into the massively-parallel molecular simulation tool ms2 and assessed by molecular dynamics simulations of binary liquid mixtures. The formalism of Krüger et al. (P. Krüger et al., J. Phys. Chem. Lett. 4: 235–238, 2013) that adopts NVT ensemble data to the μVT ensemble is employed throughout. Taking advantage of its linear scaling with inverse system size, the extrapolation to the thermodynamic limit is analyzed. KBI are calculated with standard radial distribution functions (RDF) and two corrected RDF forms. Simulations in the NVT ensemble are carried out in the entire composition range for four Lennard-Jones mixtures, studying system size dependence by varying N = 4000, 8000 and 16000 molecules. Moreover, four mixtures of “real” components are considered with N = 4000. Thermodynamic factor, partial molar volumes and isothermal compressibility are calculated from KBI and compared with benchmark data from NpT ensemble simulations. The assessment shows that the formalism of Krüger et al. greatly improves KBI and that extrapolation is important, particularly for smaller systems.

Molecular Interactions of Pyridoxine Hydrochloride in Aqueous Mixed Solutions of D-Glucose, D-Fructose, and D-Lactose at Different Temperatures

Density and ultrasonic velocity values for solutions of pyridoxine hydrochloride in aqueous mixed solutions containing D-glucose, D-fructose, and D-lactose have been obtained for various concentrations and at temperatures 298.15–313.15 K. Volumetric and acoustic parameters such as partial molar volumes, partial molar adiabatic compressibilities, partial molar expansibilities were determined using density and ultrasonic velocity data. The analysis of the obtained data has been done by using Masson’s equation and interpretation was done in terms of solute–solute and solute–solvent interactions. The pyridoxine hydrochloride acts as a structure breaker in water as well as in binary aqueous mixed solutions of D-glucose, D‑fructose, and D-lactose.

Temperature dependent solution properties of amino acids in colloidal solutions

Volumetric and acoustic studies of amino acids (l‑aspartic acid and l‑serine) in water and in aqueous cetyl trimethyl ammonium bromide (CTAB) solutions were carried out to understand intermolecular interactions in aqueous solutions of amino acids and in colloidal solutions containing cationic micelles. Density and sound velocity of amino acids solutions of different concentrations in water and in colloidal solutions of CTAB were measured at different temperatures (303.15 K–313.15 K). Volumetric and acoustic parameters like apparent and partial molar volume (Vφ and Vφo), expansibility factor (Eφo), transfer volume, compressibility factors (Kφ and Kφo) and intermolecular free length (Lf) were calculated using measured density and sound velocity data of amino acids solutions. Positive values of Vφ and negative values of Kφ are indicative of strong intermolecular electrostatic interactions among ions of amino acids and water molecules. Presence of CTAB molecules in micellar form in amino acids solutions causes an overall increase in the degree of intermolecular interactions among components of solutions. Moreover, positive values of expansibility factor showed the structure making behavior of amino acids both in water and in aqueous CTAB solutions.

Partial Molar Volumes, Partial Molar Compressibilities, and Viscosities of α,ω-Amino Acids in Water and in Aqueous Solutions of Sodium Chloride over a Temperature Range of 293.2–333.2 K

Density, sound velocity, and viscosity were measured in the temperature range of 288.15–308.15 K at intervals of 5 K for glycine, 3-aminopropanoic acid, 4-aminobutanoic acid, 5-aminopentanoic acid,...

Densities, speeds of sound, refractive indices, excess and partial molar properties of polyethylene glycol 200 + methyl acrylate or ethyl acrylate or n-butyl acrylate binary mixtures at temperatures from 293.15 to 318.15 K

The densities, ρ, speeds of sound, u and refractive indices, nD of binary mixtures of polyethylene glycol 200 with methyl acrylate, ethyl acrylate, n-butyl acrylate, including those of pure liquids, over the entire composition range were measured at temperatures (293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K and atmospheric pressure. Using the experimental data, the excess molar volume, VmE, excess molar isentropic compressibility, Ks, mE, excess speed of sound, uE, deviations in refractive index, ΔϕnD, deviations in molar refraction, ΔRM have been calculated. The partial molar volumes and compressibilities, excess partial molar volumes and compressibilities over the whole composition range, and at infinite dilution have also been calculated. The excess properties were correlated by the Redlich–Kister polynomial equation. The variations of these parameters with composition and temperature are discussed in terms of intermolecular interactions in these mixtures. Moreover, the values of ultrasonic speeds for these mixtures were also calculated by using scaled particle theory and the results are compared with the experimentally measured values.

A volumetric and acoustic study of pseudo-binary mixtures of (water + 1,3-propanediol + 3-butoxypropan-1-amine) from T = (283.15 to 303.15) K

Due to the relevant role that polyols play either as solvents or additives in many industries thermodynamic properties of aqueous mixtures of these compounds have been largely studied. In this work we aim to study the effect of adding a small amount of 3-butoxypropan-1-amine on the volumetric properties of the binary (water + 1,3-propanediol) mixture. Densities and speeds of sound of the ternary (pseudo-binary) mixture, (water + 1,3-propanediol + 3-butoxypropan-1-amine), were measured at five different temperatures ranging from T = (283.15 to 303.15) K. Excess molar, volumes, isobaric expansions and isentropic compressions of the system, as well as the excess partial molar, volumes and isentropic compressions for water and 1,3-propanediol were derived. Some functions of transference of the 1,3-propanediol and water from the binary{water + 1,3-propanediol} to the ternary mixtures were estimated. The interpretation of the results was made in terms of changes in aggregation patterns and hydration.

Effect of temperature on thermo-acoustical parameters of arginine in colloidal solutions

Volumetric and acoustic studies of l‑arginine in water and in aqueous sodium dodecyl sulphate (SDS) solutions were carried out to understand intermolecular interactions in solutions of arginine with water and colloidal solutions containing anionic micelles. Density and ultrasonic velocity data for arginine in water and in aqueous colloidal solutions were measured over a temperature range (288.15 K–308.15 K). The experimental data have been used to calculate apparent and partial molar volume (Φv, Φvο), apparent and partial molar compressibility (Φk, Φko), transfer volume (Φνto), partial molar expansibility (ΦE°), acoustic impedance (Z) and relative association (τ) etc. to comprehend inter and intra molecular interactions. The above mentioned parameters have been used to explore the arginine-surfactant interactions among ions of arginine and water molecules. The trends of transfer volumes have been interpreted by the cosphere overlap model. Moreover, the expansibility factor showed the structure making the behavior of arginine both in water and in aqueous SDS solutions.

Volumetric behaviour and isentropic compressibility of formamide with 2-dialkylaminoethanols

The volumetric properties and isentropic compressibilities of binary mixtures of formamide (FA) with 2-dialkylaminoethanols viz. 2-dimethylaminoethanol (2-DMAE) and 2-diethylaminoethanol (2-DEAE) were evaluated over the entire composition range at 303.15, 313.15 and 323.15 K and at atmospheric pressure. The excess partial molar volumes (V¯m,1E and V¯m,2E), excess isentropic compressibility (κsE), excess partial molar compressions (K¯s,m,1E and K¯s,m,2E) are deduced. The partial molar volumes (V¯m,1∘ and V¯m,2∘), partial molar compressions (K¯s,m,1∘ and K¯s,m,2∘), excess partial molar volumes (V¯m,1∘E and V¯m,2∘E), and excess partial molar compressions (K¯s,m,1∘E and K¯s,m,2∘E), at infinite dilution, over the entire composition range are also calculated. The knowledge of the volumetric properties and molar compression aids to understand specific molecular interactions existing between the FA and 2-DMAE/2-DEAE molecules of the binary system. The strength of intermolecular interactions in these mixtures follows the order: FA + 2-DEAE > FA + 2-DMAE. The required experimental data are used from our earlier work on the volumetric and acoustic study published in J. Mol. Liqs. 219 186 (2016).

Partial molar volumes and compressibilities of α-amino acids from aqueous to aqueous-disodium tartrate solutions at T = (303.15, 308.15 and 313.15) K

Present work reports the densities (ρ) and ultrasonic velocities (u) of four α-amino acids (viz. glycine, l-proline, l-arginine and l-asparagine) in aqueous disodium tartrate (Na2Tar) (0.50, 1.00 and 1.50 mol·kg−1) solutions at T = (303.15, 308.15 and 313.15) K. Apparent molar volumes (V2, ϕ) and apparent molar isentropic compressibilities (κS, 2, ϕ) of amino acids have been calculated from density and ultrasonic velocity data respectively. Standard molar volumes (V2, ϕo) and standard molar compressibilities (κS, 2, ϕ0) were determined from the graphical fittings using standard relations and corresponding standard transfer volumes (ΔtV2, ϕo) and standard transfer compressions (ΔtκS, 2, ϕ0) were calculated. Different thermodynamic parameters have been used to explore solute-solute, solute-solvent interactions and effect of disodium tartrate salt on the hydration and electrostriction behavior of amino acids. A significant effect of added salt on the volumetric and acoustic behavior of studied amino acids through ion-ion, ion hydrophilic-hydrophilic and hydrogen bonding interactions has been observed.

Effects of Isentropic and Partial Molar Compressibility of Propiophenone with 1-Alkanols Binary Mixtures at 303.15 to 318.15 K

Effects of Isentropic and Partial Molar Compressibility of Propiophenone with 1-Alkanols Binary Mixtures at 303.15 to 318.15 K

Densities, ultrasonic speeds, excess and partial molar properties of binary mixtures of acetonitrile with some alkyl methacrylates at temperatures from 293.15 K to 318.15 K

The densities, ρ, and speed of sound, u, of the binary mixtures of acetonitrile with alkyl methacrylates (methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, including those of pure liquids, over the entire composition range were measured at temperatures (293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K and atmospheric pressure. Using the experimental data, the excess molar volumes, VmE, excess speeds of sound, uE, excess isentropic compressibilities, κsE and excess molar isentropic compressibilities, Ks,mE have been calculated. The partial molar volumes and compressibilities and excess partial molar volumes and compressibilities of the components of the mixtures over the whole composition range; and at infinite dilution have also been calculated. The excess properties were correlated by the Redlich–Kister polynomial equations. The variations of these parameters with composition and temperature have been discussed in terms of intermolecular interactions prevailing in these mixtures.

Structural changes of water caused by non-electrolytes: Volumetric and compressibility approach for urea-like analogues

Hydration of thiourea (TU), hydroxyurea (HU, hydroxycarbamide), acetone (AC, 2-propanone) and dimethyl sulfoxide (DMSO) has been investigated with the help of the volumetric and compression measurement. The apparent molar volumes and the apparent molar isentropic (adiabatic) compression have been calculated from the density and speed of sound data at temperatures ranging from 288.15 to 308.15 K at atmospheric pressure (0.1 MPa). From these data the standard partial molar volumes and the standard partial molar isentropic compressions have been calculated.The properties of the hydration spheres formed around investigated solutes have been characterised based on four parameters: (i) empirical slope for the dependency of the apparent molar volume on the concentration, (ii) difference between standard partial molar volume and van der Waals volume, (iii) standard partial molar compression, (iv) temperature dependency of the standard partial molar compression. The obtained results have been discussed and compared with the solvation properties of the N-alkyl derivatives of urea.

Physicochemical properties of L-carnitine in aqueous solution and its interaction with trimethylamine N-oxide, sodium chloride and dextrose: Volumetric and calorimetric insights

Abstract L -carnitine plays physiologically important roles specifically to decrease triglycerides, very low density lipoprotein (VLDL) and cholesterol. Considering these facts, it is believed to be helpful in the reduction of cardiovascular diseases and diabetes. Physicochemical properties of L -carnitine in aqueous or mixed aqueous solutions are scarcely available in literature. Such properties will be useful in understanding the interactions of L -carnitine with other cellular components like trimethylamine-N-oxide (TMAO), dextrose ( D -glucose) and NaCl. The values of densities (ρ) and speeds of sound (u) of L -carnitine were measured over the molality range of m = 0.05 mol·kg−1 to m = 0.3 mol·kg−1 at temperature T = 293.15 K to T = 313.15 K in water and in aqueous solutions of TMAO, dextrose, and NaCl. Using these data, values of apparent molar volume (V2,m,φ) and apparent molar adiabatic compressibility (Ks,2,m,φ) have been determined. The results obtained from these measurements have been used to derive the standard partial molar volume ( V 2 , m o ), standard partial molar adiabatic compressibility ( K s , 2 , m o ), standard partial molar volume of transfer ( Δ tr V 2 , m o ) and standard partial molar isentropic compressibilities of transfer ( Δ tr K S , 2 , m o ) from water to aqueous solutions of TMAO, dextrose, and NaCl. Through Isothermal Titration Calorimetry (ITC), the enthalpies of dilution ( Δ dil H m ) of L -carnitine in water (over a temperature range of T = 293.15 K to T = 313.15 K) and in aqueous solutions of TMAO, dextrose, and NaCl have been determined. The values of standard molar enthalpy of dilution ( Δ dil H m o ) and their transfer values ( Δ tr Δ dil H m o ) have been derived from these measurements. The results have been discussed in terms of possible intermolecular interactions. The data suggest that there is overall balancing of hydrophobic and hydrophilic interactions in system containing L -carnitine and TMAO in aqueous solution, but hydrophobic effect dominates when the co-solute is NaCl or dextrose.

Density and volumetric properties of the aqueous solutions of urea at temperatures from T = (278 to 333) K and pressures up to 100 MPa

Abstract This paper highlights the values of densities of aqueous solutions of urea in the concentration range m (from 0.1809 to 12.801) mol·kg−1 at T = (278.15, 288.15, 298.15, 308.15, 323.15 and 333.15) K and at p = (0.101, 10, 25, 50, 75 and 100) MPa. The densities were also measured for dilute aqueous solutions m (from 0.093 to 2.505) mol·kg−1 with temperature from 274.15 to 283.15 K, with increment of 1 K at atmospheric pressure, in order to study the effect of urea on the temperature of the maximum water density. Volumetric properties calculated from the density, such as apparent molar volumes of urea, Vɸ,2, molar isothermal compressions, KT,m, and molar isobaric thermal expansions, EP,m, of solution are considered depending on concentration, temperature and pressure. Also, certain volumetric characteristics for infinitely diluted urea in water were obtained: the limiting partial molar volumes, V 2 ∞ ; limiting partial molar isothermal compressions, K T , 2 ∞ ; and limiting partial molar isobaric thermal expansions, E P , 2 ∞ . Obtained results are discussed from the standpoint of solute – solute and solute – solvent interactions. With the help of various approaches based on volumetric characteristics, the character of the disturbing effect of urea on the water structure was described.