Standard Partial Molar Volumes Research Articles

A volumetric, ultraacoustical study and computational study of molecular interactions in 4-aminoantipyrine-aqueous-β-cyclodextrin solutions

Present work reports experimental densities and corresponding apparent and standard partial molar volumes, ultrasonic velocities and isentropic, apparent and standard partial molar compressibilities of 4-Aminoantipyrine-aqueous-β-cyclodextrin (0.000 mol∙kg−1, 0.001 mol∙kg−1, 0.005 mol∙kg−1, 0.010 mol∙kg−1and 0.015 mol∙kg−1) solutions at different temperatures. Transfer properties like transfer volumes and compressions were calculated. The refractive indices of these systems were also measured. The computational properties such as solvation energy (ΔESol), relative stabilization energy (ΔERel), complexation energy (ΔEComp) and change in volume (ΔV) were computed using DFT. The results from volumetric and acoustical studies have been evaluated in terms of molecular interactions and their existence confirmed from experimental and computational studies. The values of transfer volumes and compressibilities indicate the hydrophilic-hydrophilic interactions between polar groups of 4-Aminoantipyrine and hydroxyl groups of β-cyclodextrin dominating over hydrophobic-hydrophobic interactions between the phenyl group of 4-Aminoantipyrine and hydrophobic interior of β-cyclodextrin.

Solute–solvent interactions of glycine, L–alanine, and L–valine in aqueous 1–butyl–3–methylimidazolium methylsulfate ionic liquid solutions at different temperatures

The intermolecular interactions of amino acids (glycine, L–alanine, and L–valine) in aqueous solutions of an ionic liquid, 1–butyl–3–methylimidazolium methylsulfate [Bmim][MeSO4] as a function of temperature have been investigated by combination of volumetric and acoustic methods. The density, ρ, and speed of sound, u, of glycine, L–alanine and L–valine in aqueous 1–buytl–3–methylimidazolium methylsulfate solutions have been measured in the temperature interval T = (288.15, 298.15, and 308.15) K and atmospheric pressure. These data have been used to calculate apparent molar volume (V∅), and apparent molar adiabatic compressibility (K∅,s) of these mixtures at different temperatures. Later, the standard partial molar volume (V∅0), standard partial molar volumes of transfer (ΔV∅0), standard partial molar adiabatic compressibility (K∅,s0), and standard partial molar adiabatic compressibility (ΔK∅,s0) of transfer have been determined for these amino acid solutions from density and speed of sound data. Also, hydration number (nH) and various group contribution have been calculated. Finally the results have been interpreted in terms of solute - solvent interactions that exist among the currently investigated systems.

Volumetricand ultrasonic properties of thiamine hydrochloride drug in aqueous solutions of choline-based deep eutectic solvents at different temperatures

Important efforts have been made over the past years to improve the drug acts, which leads to the discovery of novel drug preparations and delivery systems. The optimal design of such processes requires a molecular-level understanding of the interactions between drug molecules and biological membranes. The thermodynamic investigation provides deep and complete knowledge of interactions and the choice of appropriate and suitable production compounds in pharmaceutical fields. Particularly, the analysis of drugs + co-solvents in aqueous media is the central issue in many types of research because they exert their impact by interacting with biological membranes. This work is aimed to measure the density and speed of sound for the thiamine hydrochloride in water + deep eutectic solvents (DESs) mixtures (choline chloride/urea, choline chloride/ethylene glycol and choline chloride/glycerol) at temperature range (293.15–308.15) K. By correlation of the evaluated parameters in some standard relations, the partial molar parameters i.e. apparent molar volumes, Vφ,m, and apparent molar isentropic compression, κs,φ,m, are calculated. In addition, apparent molar isobaric expansion, Eφ,m0, and Hepler’s constant are computed from the density and speed of sound data. For fitting the experimental Vφ,m and κs,φ,m the Redlich-Meyer equation was employed that the important quantities; standard partial molar volume, Vm0, and partial molar isentropic compression, κs,m0, were obtained. The thermodynamic analysis of the studied system also plays a crucial role in the pharmaceutical industry.

Thermodynamic study of calcium d-pantothenate drug in the presence of aqueous solutions including some amino acids: Volumetric and compressibility properties

The impressive and remarkable efforts have been made over the past years to improve the production, formulation and purification of active ingredients pharmaceutical which leads to the discovery of novel drug preparations and delivery systems. The optimal design of such processes requires a molecular-level understanding of the interactions between drug molecules and biological membranes. The thermodynamic investigation provides deep and complete knowledge of interactions and the choice of appropriate and suitable compounds in pharmaceutical fields. Particularly, the analysis of drugs + biomolecules in aqueous solutions is the central issue in many types of research because they exert their impact by interacting with biological membranes. This work is aimed to measure the density and speed of sound for the calcium d-pantothenate, vitamin B5 calcium salt (CDP) in aqueous solutions of amino acids (glycine, l-alanine, and l-leucine) at temperature ranges (293.15 to 308.15) K. By correlating of the measured physical quantities in with standard relations, apparent molar volumes, Vϕ,m, and apparent molar isentropic compression, κs,ϕ,m, are calculated. In addition, apparent molar isobaric expansion, Eϕ,m0, and Hepler’s constant are computed. For fitting the experimental Vϕ,m and κϕ the Redlich-Meyer equation was employed that the important quantities; standard partial molar volume, Vϕ0 , and partial molar isentropic compression, κϕ0, were obtained.

Complex Protein Retention Shifts with a Pressure Increase: An Indication of a Standard Partial Molar Volume Increase during Adsorption?

Studies of protein adsorption on reversed-phase and ion exchange stationary phases demonstrated an increase in retention with increasing pressure, which is interpreted as a standard partial molar volume decrease during the transition of the protein from a mobile to a stationary phase. Investigation of the pressure effect on the retention of lysozyme and IgG on a cation exchange column surprisingly revealed a negative retention trend with the increase of pressure. Further investigation of this phenomenon was performed with β-lactoglobulin, which enabled adsorption to be studied on both cation and anion exchange columns using the same mobile phase with a pH of 5.2. The same surface charge and standard partial molar volume in the mobile phase allowed us to examine only the effect of adsorption. Interestingly, a negative retention trend with a pressure increase occurred on an anion exchange column while a positive trend was present on a cation exchange column. This indicates that the interaction type governs the change in the standard partial molar volume during adsorption, which is independent of the applied pressure. Increasing the protein charge by decreasing the pH of the mobile phase to 4 reversed the retention trend (into a negative) with a pressure increase on the cation exchange column. A further decrease of the pH value resulted in an even more pronounced negative trend. This counterintuitive behavior indicates an increase in the standard partial molar volume during adsorption with the protein charge, possibly due to intermolecular repulsion of adsorbed protein molecules. While a detailed mechanism remains to be elucidated, presented results demonstrate the complexity of ion exchange interactions that can be investigated simply by changing the column pressure.

Effect of choline lactate ionic liquid as entrainer on the thermodynamic properties of alcohols + water azeotropic mixtures

Ionic liquids could be used as entrainer in the azeotropic mixture separation process efficiently. Accordingly, the thermodynamic properties of ionic liquid choline lactate ([Ch][Lac]) as a potential entrainer have been studied in different azeotropic mixtures. In this respect, the density and speed of sound for binary systems containing (water + [Ch][Lac]) (ethanol/ 1-propanol/ 2-propanol) + [Ch][Lac])] and also ternary systems with different mass percent from alcohol-containing (water + alcohol + [Ch][Lac]) have been measured under a pressure 871 hPa at different temperatures T = (288.15 to 318.15) K. These data are used to calculate standard partial molar volume (Vφ0), and the limiting apparent molar compressibility (κφ0) using the Redlich-Mayer model besides the intermolecular free length (Lf) and relative association (RA) to interpret the existing interaction in the azeotropic mixture of the studied alcohols. Also, the scaled particle theory is used as a microscopic approach. All of the properties have been analyzed to interpret the interactions between the components of the mixture and 2-propanol has stronger interactions with the [Ch][Lac] in the azeotrope composition. The results suggest that the [Ch][Lac] could be used as an entrainer to separate 2-propanol more efficiently rather than the other studied alcohols.

Study of the interactions of monosaccharides D(+)-glucose and D(−)-fructose in aqueous diammonium hydrogen phosphate over the temperature range T=(288.15–318.15) K

The interactions of monosaccharides D(+)-glucose and D(−)-fructose in aqueous solutions of diammonium hydrogen phosphate (DAP) as a function of temperature have been investigated. The values of densities and speeds of sound have been measured for the system of monosaccharides and salt in aqueous solution. Densities and speed of sound for D(+)-glucose and D(−)-fructose in (0.5, 1.0, 1.5 and 2.0) mol⋅kg−1 aqueous solutions of diammonium hydrogen phosphate (DAP) are measured at T = (288.15, 298.15, 308.15 and 318.15) K and experimental pressure p = 0.1 MPa. The apparent molar volume,Vφ the partial molar volume, VφO and standard partial molar volumes of transfer, Δ VφO for D(+)-glucose and D(−)-fructose in aqueous solutions of diammonium hydrogen phosphate (DAP) have been calculated from density data. Apparent molar isentropic compression,Kϕ,s partial molar isentropic compression, Kϕ,so and partial molar isentropic compression of transfer, ΔKϕ,so have been calculated from speed of sound measurements. The expansibility parameter (∂Vϕ0 /∂T)p and its derivative (∂2 Vϕ0 /∂2 T)p along with pair (VAB, KAB) and triplet (VABB, KABB) interaction coefficients have also been calculated. The results have been interpreted in terms of solute − solute and solute–solvent interactions prevailing in these ternary systems.

Volumetric and acoustic properties of L-phenyl glycine and L-phenylalanine in aqueous solution of 1-dodecyl-3-methylimidazolium bromide [C12mim] [Br

To study the molecular interactions between the ternary mixtures containing long chain imidazolium based ionic liquid as a common solvent with substituted amino acids L-phenyl glycine and L-phenylalanine respectively, densities and speed of sound have been measured at three different temperatures viz. T = 288.15 K, 298.15 K, 318.15 and 318.15 K under 0.1 MPa pressure. The density and speed of sound data have been further utilized to calculate the apparent molar volume and apparent molar isentropic compression. From the data obtained, apparent molar volume (Vϕ), partial molar volume (Vϕ0), and standard partial molar volumes of transfer (ΔVϕ0). Positive values of apparent molar volume indicate strong interactions. Also, partial molar isentropic compression of transfer (ΔKϕ,S0) and partial molar isentropic compression (Kϕ,s) have been calculated from the sound of speed. Furthermore, structure making and structure breaking ability of solute have been discussed by evaluation of apparent molar expansivity, (ϕE0), Hepler's constant values ∂/∂Tp. The obtained results have been discussed in terms of solvation behavior, structural changes and various interactions present in different ternary mixtures (1-dodecyl-3-methylimidazolium bromide + amino acids + water).

Investigation of the inter-ionic interactions of an imidazolium-based ionic liquid with the aqueous solutions of tripotassium citrate and trisodium citrate through volumetric, acoustic and FTIR routes

Volumetric, acoustic and spectroscopic characteristics of an imidazolium-based ionic liquid, 1-Butyl-3-methylimidazolium chloride ([bmim][Cl]) in water and aqueous solutions of tri-potassium citrate, K3Cit, and tri-sodium citrate, Na3Cit were studied at five different temperatures T = (298.15 K, 303.15 K, 308.15 K, 313.15Kand 318.15 K) and atmospheric pressure (0.1Mpa). The apparent molar volume,Vϕ, and apparent molar compressibility, Kϕ,S were computed from the experimental data of densities and ultrasonic speeds. The derived properties such as standard partial molar volume, Vϕ0 , partial molar compressibilities, Kϕ,S0, limiting apparent molar expansivity, Eϕ0, and their corresponding transfer volumes, ΔtrVϕ0, transfer compressibilities, ΔtrKϕ,S0, of [bmim][Cl] from water to aqueous potassium/sodium citrate solutions were also determined. The transfer properties have been used to discuss the solute-solvent interactions that exist in the solutions. The positive value of Hepler’s constant indicates that the IL has structure-making ability in the studied solutions. In addition, FTIR spectroscopy was executed on the systems. Based on these data, the predominant molecular interactions occurring between [bmim][Cl] and water and in between [bmim][Cl] and K3Cit/Na3Cit were found to be hydrogen bonds.

Volumetric properties, conductivity and computation analysis of selected imidazolium chloride ionic liquids in ethylene glycol

In this paper, the influence of the side chain length of five ionic liquids (ILs): 1-methylimidazolium chloride ([C0mim][Cl]), 1,3-dimethylimidazolium chloride (([C1mim][Cl]), 1-ethyl-3-methylimidazolium chloride (([C2mim][Cl]), 1-butyl-3-methylimidazolium chloride (([C4mim][Cl]) and 1-hexyl-3-methylimidazolium chloride (([C6mim][Cl]) on the interactions with ethylene glycol (EG) was studied. Based on the measurement of density and electrical conductivity of the ionic liquid + EG mixture in the temperature range (278.15–313.15) K, the values of apparent molar volume, standard partial molar volumes, apparent molar volume at infinite dilution, Masson’s interaction coefficient, thermal expansion coefficient, limiting apparent molar expansibilities, Heppler’s coefficient, ion association constants, thermodynamic parameters of ion-pair formation as well as diffusion coefficient was calculated. Experimental results were supported by molecular dynamic simulations. With the increase of the side chain length, from C0mim+ to C6mim+ cation, ion–dipole interactions on the solvation process decrease, and the influence of solvophobic solvation increases. Ionic liquids [C0mim][Cl] and [C1mim][Cl] show structure-breaker properties, [C4mim][Cl] and [C6mim][Cl] structure-making properties in EG solutions, while [C2mim][Cl] is borderline. The values of ion association constants in EG are higher than in water. The ion association process is spontaneous for all ionic liquids and entropy-driven.

Deep eutectic solvents for antiepileptic drug phenytoin solubilization: thermodynamic study

Thermodynamic investigations provide information about the solute-solvent interactions in the selection of the proper solvent for different fields of pharmaceutical sciences. Especially, the study of antiepileptic drugs in solutions (ethanol/co-solvent) has been a subject of interest owing to their effect in the systems using interaction with a number of important biological membranes. This work focuses on the measurement of density and speed of sound of the phenytoin (PTH) in ethanol/deep eutectic solvents (choline chloride:ethylene glycol, and choline chloride:glycerol) solutions as the innovative class of green solvents at temperature range (288.15 to 318.15) K. It was determined Hansen solubility parameters for assessment of PTH interactions in the solvent media. Some thermophysical parameters including apparent molar volumes Vϕ, apparent molar isobaric expansion E_varphi^0, and Hepler’s constant, apparent molar isentropic compressibility κφ were obtained and calculated using these data. To correlate the Vϕ and κφ values, the Redlich-Meyer equation was used to calculate the number of quantities containing standard partial molar volume and partial molar isentropic compressibility. Finally, Delta delta values showed a strong interaction between PTH and solvent (ethanol/DES (ChCl:EG)). The thermodynamic analysis of the studied system also plays a crucial role in the pharmaceutical industry.

Some thermodynamic properties and computational study of DESs (choline chloride/ethylene glycol and choline chloride/malonic acid) in lithium nitrate + propylene carbonate solutions at T = 298.15 K

Deep eutectic solvents (DESs) with propylene carbonate represent an appealing alternative for organic solvents and ionic liquids to dissolve lithium salts. The present research reports the effect of deep eutectic solvents {DESs (choline chloride/ethylene glycol with the molar ratio of 1.00:2.00) and (choline chloride/malonic acid with the molar ratio of 1.00:1.00) on the thermodynamic and transport properties of solutions of lithium nitrate (LiNO3) in propylene carbonate (PC). To evaluate solute–solvent interactions in the above systems first the volumetric, ultrasonic, and viscometric properties were studied. For this purpose, the density (d), speed of sound (C) and viscosity (η) were measured for the binary solutions of (LiNO3 + PC) and quaternary solutions containing (LiNO3 + PC) and DES in different mass fraction of, w = (0.05, 0.010, 0.015 and 0.020), at 298.15 K under ambient pressure. The measured data were used for calculation of the apparent molar volume (Vφ), standard partial molar volume (Vφ0), apparent molar isentropic compressibility (κϕ), partial molar isentropic compressibility (κφ0), partial molar volumes of transfer (ΔtrVφ0) and viscosity B-coefficient of (LiNO3 + PC + DES) solutions. Then, to evaluate the interaction energies, the density functional theory (DFT) of LiNO3 with DESs in PC has also been studied. The thermodynamic and transport investigations indicated that the choline chloride/ethylene glycol interactions are more favorable than choline chloride/malonic acid with LiNO3 in the presence of PC. Generally, the additions of these DESs on the solution of LiNO3 + PC lead to enhancing of the solute–solvent interactions. Also, the DFT results revealed that the interaction between the ChCl/EG with LiNO3 in PC is stronger than ChCl/MA with LiNO3 in PC confirming the result deduced from our experimental studies.

Interaction studies of diglycine with aqueous solutions of sulphathiazole drug at different temperatures

The interactions of diglycine with sulphathiazole drug as a function of temperatures have been studied using volumetric and acoustic parameters. Densities and speeds of sound of diglycine in (0.001, 0.002,0.005, and 0.010) mol·kg-1 aqueous solutions of sulphathiazole drug have been measured at five different temperatures of (288.15,293.15,298.15,303.15 and 308.15) K under 0.1MPa pressure. From density data, the apparent molar volume (Vf), the partial molar volume ( ) and the standard partial molar volume of transfer ( ) for glycine from water to aqueous sulphathiazole solutions have been calculated. Partial molar isentropic compression and partial molar isentropic compression of transfer ( ) have been calculated from the speed of sound data. Transfer parameters by using cosphere overlap model have been explained from the point of view of concentration dependence of solute-solute and solute-solvent interactions. To draw the conclusion from the volumetric and acoustic data, limiting apparent molar expansion , as well as hydration numbers, have been studied. The calculated values of thermal expansion coefficient, , have small and positive values. All of these derived or calculated parameters are explained to understand the solvation behavior, mixing aspects and various types of interactions born in the ternary solutions of (drug + water + dipeptide) due to change in structure. We have also attempted to examine the temperature and concentration dependence of such interactions.

Effect of choline chloride based deep eutectic solvents on lithium perchlorate + propylene carbonate solutions: Thermodynamic, transport, electrochemical and computational study

BackgroundThe influence of deep eutectic solvents (DESs) {(choline chloride (ChCl): lactic acid (LA) and choline chloride: malonic acid (MA)} with different mass fractions of DES on the thermodynamic, transport and electrochemical properties of lithium perchlorate (LiClO4) in propylene carbonate (PC) systems were studied. These investigations are in line with proposing new green electrolyte solutions for future electrochemical applications. MethodsDensity, speed of sound and viscosity at T = 288.15–318.15 K of (LiClO4 + PC + DESs) solutions have been measured from which the apparent molar volume, apparent molar isentropic compressibility, standard partial molar volume, partial molar isentropic compressibility, partial molar volumes of transfer, partial molar isentropic compressibility of transfer and viscosity B-coefficient were calculated. Also density functional theory (DFT) of LiClO4 with DESs in PC solvent was applied. As well as linear sweep voltammetry (LSV) measurements were performed. Significant findingsThe calculated thermodynamic and transport parameters indicated that interactions of ChCl/LA with LiClO4 in the presence of PC are more favorable than ChCl/MA. Then, the DFT was applied to find further evidence for these solute-solvent interactions and confirmed the thermodynamic and transport results. Finally, LSV measurements were performed for investigating the electrochemical potential windows of the systems.

Standard Partial Molar Heat Capacities and Volumes of Aqueous N,N-Dimethylethanolamine and N,N-Dimethylethanolammonium Chloride from 283.15 to 393.15 K, and Ionization Constants to 598.15 K

Standard Partial Molar Heat Capacities and Volumes of Aqueous <i>N</i>,<i>N</i>-Dimethylethanolamine and <i>N</i>,<i>N</i>-Dimethylethanolammonium Chloride from 283.15 to 393.15 K, and Ionization Constants to 598.15 K

Densities and Apparent Molar Volumes of Aqueous Solutions of NaClO4, KClO4, and KCl at Temperatures from 293 to 343 K

Densities of aqueous solutions of the strong electrolytes sodium perchlorate, potassium perchlorate, and potassium chloride have been measured by vibrating-tube densimetry at 5 K intervals over the temperature range 293.15 ≤ T (K) ≤ 343.15 up to near-saturation concentrations (for NaClO4 and KClO4) or to about 2 mol·kg–1 (for KCl) at 0.1 MPa pressure. Particular attention was paid to solute purity and solution composition. The densities were used to calculate the corresponding apparent molar volumes, Vϕ, which considerably extend and improve the quality of the volumetric database for these salts, especially with respect to temperature. Where comparisons were possible, the present Vϕ results agreed well with most literature data, with the significant exception of NaClO4(aq) at higher temperatures. The Vϕ values were extrapolated to infinite dilution using an extended Redlich–Rosenfeld–Meyer equation to yield the standard state partial molar volumes (V2o). A combination of these values with relevant literature data and a well-established extra-thermodynamic assumption was used to estimate the standard molar volumes, V2o(ion), of several key monovalent ions as functions of temperature. These values appear to be more reliable than existing estimates based on older data, and will be useful for determining volumes of other ions in aqueous solution.

Effect of some choline based deep eutectic solvents on volumetric and ultrasonic properties of gabapentin drug in water at T = (288.15 to 318.15) K

A key part of the drug preparation process is the optimization of molecular interactions between drugs and solvents. Thermodynamic properties provides complete information on interactions and the selection of suitable solvents for various pharmaceutical processes. Especially, the investigation of antiepileptic drugs in aqueous solutions has been a subject of interest because they employ their effect by interaction with biological membranes. In this study, the density and speed of sound for the gabapentin (GBP) in aqueous deep eutectic solvents (DESs), (choline chloride/ethylene glycol (ChCl/EG), choline chloride/glycerol (ChCl/Gly), and choline chloride/urea (ChCl/U)) as novel category of green solvents were measured at temperature range 288.15 K to 318.15 K. The apparent molar volumes Vφ, apparent molar isobaric expansion Eφ0, Hepler’s constant and apparent molar isentropic compressibility κφ were calculated from the density and speed of sound data. Findings show that Vφ values are higher for binary systems compared to ternary systems. The order of Vφ values for aqueous DESs solutions are as follows: ChCl/EG > ChCl/U > ChCl/Gly. The standard partial molar volume Vφ0 and partial molar isentropic compressibility κφ0 were obtained by using the Redlich-Meyer equation. The obtained results for the Vφ0 quantity indicate a strong interaction between the GBP drug and the ChCl/Gly. Finally, using the results of Eφ0, it is understood that GBP has acted as a structure maker in the presence of all DESs.

Thermophysical and taste behavior of sucrose in aqueous solution of some deep eutectic solvents at T= (288.15 to 318.15) K

Saccharide’s behavior in aqueous solutions has become a cornerstone of modern nutritional science, whether in academia or in industry. This study provides an exciting opportunity to advance our knowledge about taste quality by using thermophysical properties. So, the densities, speeds of sound, viscosities and refractive indices of sucrose in the aqueous solutions of choline chloride/urea, choline chloride/ethylene glycol, choline chloride/oxalic acid, dimethyl ammonium chloride/ethylene glycol as deep eutectic solvents (DESs) have been measured at T = (288.15–318.15) K and P = 86.6 kPa. Standard partial molar volumes, standard transfer volumes, and partial molar isentropic compressibility, have been calculated from the experimental data also, interaction volumes, and cavity volumes, have been computed from scaled particle theory. Taste quality data show that the studied DESs do not affect on the taste quality and sucrose falls in the sweet range and also, thermophysical properties suggest that solute-solvent interactions in choline chloride-ethylene glycol are stronger and strengthened with increasing the concentration of DESs and temperature.

Effect of the Temperature and Solvents on the Solvolysis of Barium Bromide in Aqueous-Organic Solutions: Volumetric and Viscometric Study

Volumetric and viscometric properties of solutions containing barium bromide in an aqueous solution of ethylene glycol and 1,4-dioxane have been discussed at different temperatures such as 298.15K 303.15K, 308.15K, and 313.15K. The Masson’s equation was used to determine the apparent molar volume, V_ϕ, standard partial molar volume, V_ϕ^0, molar expansibilities,E_ϕ^0 by taking the density data. The values of viscosity and density were used in the Jones-Dole equation to find the viscosity B coefficients, which were used to estimate the ion-solvent interactions. The values of Hepler’s constant (∂^2 V_ϕ^0/ ∂T2)p and the viscosity B-coefficients have been used to deduce the solvent structure-promoting or structure breaking tendency of the salt in the studied mixtures. In the current study, the positive values of Hepler’s constant and the negative values of dB/dT show that barium bromide in the considered solvents mainly behaves as a structure promoter.

Understanding the interactions between protein stabilizers and the peptide bond through the analysis of the volumetric and compressibility properties for the model systems

This work confirms our earlier supposition, that volumetric and acoustic parameters for simple model proposed by us are directly related to stabilizing/destabilizing effect of osmolytes on proteins structure. The apparent molar volumes, VΦ, and the apparent molar isentropic compressions, KS, Φ, of glycine and N,N,N –trimethylglycine (betaine) were determined from densities and speed of sound measurements in aqueous solution of N-methylacetamide (as a model of peptide bond of protein). The standard molar parameters for osmolytes were obtained from concentration dependence of the calculated quantities at NMA concentration equal 2, 4, 6 and 8 (mol/kg) and at temperature T = (288.15, 298.15 and 308.15) K. The standard values were combined with volumetric and compressibility data for amino acids in pure water to obtain transfer properties from water to aqueous N-methylacetamide solutions. The standard partial molar volume of transfer of studied osmolytes, ΔtVΦ0, seems to be related mainly to hydrophilic/hydrophobic features of molecules. The stabilizing/destabilizing effect of solute on protein structure is reflected in temperature influence on the limiting partial molar quantities.