Interactions of some amino acids and glycine peptides with aqueous sodium dodecyl sulfate and cetyltrimethylammonium bromide at T=298.15 K: a volumetric approach

The apparent molar volumes V_φ of glycine, alanine, valine, leucine, and lysine have been determined in aqueous solutions of 0.05, 0.5, 1.0 mol · kg⁻¹ sodium dodecyl sulfate (SDS) and 1.0 mol · kg⁻¹ cetyltrimethylammonium bromide (CTAB) by density measurements at T=298.15 K. The apparent molar volumes have also been determined for diglycine and triglycine in 1 mol · kg⁻¹ SDS and CTAB solutions. These data have been used to calculate the infinite dilution apparent molar volumes V₂⁰ for the amino acids and peptides in aqueous SDS and CTAB and the standard partial molar volumes of transfer (Δ_trV_2,m⁰) of the amino acids and peptides to these aqueous surfactant solutions. The linear correlation of V₂⁰ for a homologous series of amino acids has been utilized to calculate the contribution of the charged end groups (NH₃⁺, COO⁻), CH₂ group and other alkyl chains of the amino acids to V₂⁰. The results on the partial molar volumes of transfer from water to aqueous SDS and CTAB have been interpreted in terms of ion–ion, ion–polar and hydrophobic–hydrophobic group interactions. The volume of transfer data suggests that ion–ion or ion–hydrophilic group interactions of the amino acids and peptides are stronger with SDS compared to those with CTAB. Comparison of the hydration numbers of amino acids calculated in the present studies with those in other solvents from literature shows that these numbers are almost the same at 1 mol · kg⁻¹ level of the cosolvent/cosolute. Increasing molality of the cosolvent/cosolute beyond 1 mol · kg⁻¹ lowers the hydration number of the amino acids due to increased interactions with the solvent and reduced electrostriction.     

Volumetric, viscometric and refractive index behavior of some α-amino acids in aqueous tetrapropylammonium bromide at different temperatures

Densities, ρ, viscosities, η, and refractive indices, n _D, of glycine (Gly), DL-alanine (Ala), DL-valine (Val) (0.05, 0.10, 0.15, 0.20, 0.25 mol kg^?1), and L-leucine (Leu) (0.02, 0.05, 0.10 mol kg^?1) in water and in 0.20 mol kg^?1 aqueous tetrapropylammonium bromide (TPAB) have been measured at 298.15, 303.15, 308.15, and 313.15 K. The density data have been utilized to calculate apparent molar volumes, ?_v, partial molar volumes at infinite dilution, ?_v°, and partial molar volumes of transfer, ? _v°(tr) of amino acids. The viscosity data have been analyzed by means of Jones-Dole equation to obtain Falkenhagen coefficient, A, and Jones-Dole coefficient, B, free energy of activation of viscous flow per mole of solvent, Δµ₁°*, and solute, Δµ₂°*, and enthalpy, ΔH*, and entropy of activation, ΔS*, of viscous flow. The refractive index data have been used to calculate molar refractivity, R _D, of amino acids in aqueous tetrapropylammonium bromide solutions. It has been observed that ?_v°, B-coefficient and Δµ₂°* vary linearly with increasing number of carbon atoms in the alkyl chain of amino acids, and they were split to get contributions from the zwitterionic end groups (NH₃ ⁺, COO^-) and methylene group (CH₂) of the amino acids. The behavior of these parameters has been used to investigate the solute-solute and solute-solvent interactions as well as the effect of tetrapropylammonium cation (C₃H₇)₄N⁺ on these interactions.     

Effects of concentration and temperature on molar volumes of L-serine, L-isoleucine, and L-glutamine in aqueous NaCl and NaNO3 solutions

Densities of L-serine, L-isoleucine, L-glutamine in 1.5 mol kg^?1 aqueous NaCl, and NaNO₃ solutions have been measured for several molal concentrations of amino acids at temperatures from 298.15 to 323.15 K. The partial molar volumes (? _v ⁰ ) of L-serine, L-isoleucine, and L-glutamine in 1.5 mol kg^?1 aqueous NaCl/NaNO₃ solutions have been computed using density data. The transfer partial molar volumes (Δ_tr? _v ⁰ ) of L-serine, L-isoleucine, and L-glutamine from water to 1.5 mol kg^?1 aqueous NaCl/1.5 mol kg^?1 aqueous NaNO₃ solutions have been determined at 298.15 K. The trends of variation of ? _v ⁰ and Δ_tr? _v ⁰ with change in temperature have been discussed in terms of ion-ion, ion-hydrophilic, and ion-hydrophobic interactions operative in solutions.     

Apparent Molar Volumes of Some Sodium Sulfonamides in Water at Several Molalities and Temperatures

In this article, measured densities of aqueous solutions of sodium sulfadiazine, sodium sulfamerazine and sodium sulfamethazine are reported as a function of molality from 0.0500 to 0.5000 mol?kg^?1 and as a function of temperature at (278.15, 283.15, 288.15, 293.15, 298.15, 303.15, 308.15 and 313.15) K. The apparent molar volumes, partial molar volumes at infinite dilution and partial molar expansibilities were calculated. The dependence of these properties upon temperature is shown. The results are interpreted in terms of solute-solvent interactions.     

Temperature-dependent volumetric and viscometric properties of amino acids in aqueous solutions of an antibiotic drug

Volumetric and viscometric properties of glycine and methionine (amino acids) in a 0.2 vol. % amikacin sulphate (antibiotic drug) aqueous solution with the molality range of 0.025 mol kg^?1–0.25 mol kg^?1 were measured over the temperature range of 20°C–40°C at the interval of 5°C. Different parameters like apparent molar volume (? _V), apparent molar adiabatic compression (? _κ ), isentropic compression (κ _S) along with other acoustical parameters were calculated. Parameters like viscous relaxation time (τ), free volume (V _F), internal pressure (Π _I), and molar cohesive energy (MCE) were calculated from dynamic viscosity measurements. The ? _V values are positive in both cases, but with higher magnitude observed in methionine. These positive values of ? _V are indicative of strong solute-solvent interactions at all temperatures. In case of methionine there is a sharp initial increase in the ? _V values which become almost constant with further additions of the amino acid. Structural differences in the two amino acids studied are clearly reflected in the different nature of the plots of different parameters. In case of an amino acid-drug system, dynamic viscosity increase has been attributed to the increase in the hydrophilic-ionic and hydrophilic-hydrophilic interactions with the increase in the amino acid concentration which in turn may cause more frictional resistance to the flow of the solution. All other parameters are discussed in terms of solute-solvent and solvent-solvent interactions.     

Standard Partial Molar Volumes of Aqueous 2- and 3-Hydroxypropionic Acid from 100 to 325 °C: Functional Group Additivity in Isomers with Closely Spaced Polar Groups

Apparent molar volumes have been determined using a high-pressure vibrating-tube densimeter for aqueous solutions of 2- and 3-hydroxypropionic acid, at temperatures from 100?°C to 325?°C and pressures as high as 15 MPa. The results were corrected for acid ionization and extrapolated to infinite dilution to obtain the standard partial molar volumes, V ₂ ^o . The standard partial molar volumes of both isomers increase with temperature towards a positive discontinuity at the critical point, which is typical for almost all non-electrolytes. The temperature dependence of V ₂ ^o for the sodium salts of the acids is consistent with a negative discontinuity at the critical point, as displayed by all other aqueous electrolytes. Values of the apparent molar volumes of 2-hydroxypropionic acid are more positive than 3-hydroxypropionic acid by ～2 cm³?mol^?1, both in the neutral form and as the sodium carboxylate salt. This is the first demonstration at such high temperatures that functional group additivity in alkyl organic solutes with closely spaced polar groups is preserved to within such small differences. The onset of thermal decomposition prevented measurements at temperatures above 325?°C.     

Effect of sodium caproate on the volumetric and viscometric properties of glycine,dl-α-alanine,and dl-α-amino-n-butyric acid in aqueous solutions

The apparent molar volumes (V_m,2) and relative viscosities (η_r) at T=(298.15 and 308.15) K have been obtained for glycine, dl-α-alanine, and dl-α-amino-butyric acid in aqueous sodium caproate solutions from measurements of density and the flow time. The standard partial molar volumes (V^∘_m,2), standard volumes of transfer (Δ_tV^∘), the viscosity B-coefficients, and the activation thermodynamic quantities (Δμ₂^∘≠ and ΔS₂^∘≠) of viscous flow have been calculated for the amino acids. It is shown that the standard partial molar volumes, viscosity B-coefficients, and activation free energies for viscous flow increase with increasing number of carbon atoms in the alkyl chain of the amino acids. An increase in V^∘_m,2 and Δ_tV^∘ with increasing electrolyte concentrations have been explained due to the interactions of sodium caproate with the charged center of zwitterions for the amino acids. A comparison of the V^∘_m,2 values for glycine, dl-α-alanine, and dl-α-aminon-n-butyric acid in different aqueous salts solutions showed that carboxylate ions have stronger interactions with amino acid than chloride, thiocyanate, and nitrate ions. Results of viscosity are discussed in terms of changes in solvent structure.     

Interactions of Some Amino Acids with Aqueous N,N-Dimethylacetamide Solutions at 298.15 and 308.15 K: A Volumetric Approach

The apparent molar volumes, V _φ , of glycine, L-alanine and L-serine were obtained in aqueous 0 to ∼4 mol⋅kg⁻¹ N,N-dimethylacetamide (DMA) solutions from density measurements at 298.15 and 308.15 K. The standard partial molar volume, V _φ ^o, and standard partial molar volumes of transfer, Δ_tr V _φ ^o, were determined for these amino acids. It has been shown that hydrophilic-hydrophilic interactions between charged groups of the amino acids and the —CON= group of DMA are predominant in the case of glycine and L-serine, but for L-alanine the interactions between its side group (—CH₃) and DMA are predominant. An increase in temperature increases the standard partial molar volumes but decreases the transfer volumes of the amino acids. The results have been interpreted in terms of cosphere overlap model.     

Density and viscosity of α-amino acids in aqueous solutions of cetyltrimethylammonium bromide

The densities and viscosities of aqueous solution of cetyltrimethylammonium bromide (0.01 mol kg⁻¹) (CTAB) and solutions of CTAB containing amino acids, viz., glycine, l-serine, and l-valine (0.01–0.05 mol kg⁻¹), were determined in the temperature range 298.15—313.15 K. Apparent molar volumes of the amino acids were calculated from the density and viscosity values. The calculated apparent molar volumes were used to calculate standard partial molar volumes (-V ₂⁰) and standard partial molar volumes of transfer of amino acids from water to an aqueous solution of CTAB. The viscosity values were used for the calculation of the viscosity coefficients A and B in the Jones—Dole equation. The linear dependences of -V ₂⁰ and B on the number of carbon atoms in the alkyl chains of the amino acids were found. The results obtained were used in analysis of hydrophilic-hydrophilic, hydrophilic-hydrophobic, and hydrophobic-hydrophobic interactions that occur during dissolution of amino acids in an aqueous solution of CTAB.     

Thermodynamic characteristics of solution and viscous flow of amino acids in water at 298.15 K

Thermodynamic and transport properties of aqueous solutions of 13 amino acids at 298.15 K are analyzed in relation to the structure of the side chains of the biomolecules on the basis of the newly obtained and published data. The standard enthalpies of solution (Δ_sol H ⁰), partial molar volumes (V _2,φ ⁰ ), and partial molar contributions to the molar Gibbs free energy of activation of the viscous flow (Δμ ₂ ^0≠ ) were determined for the amino acids in water. Correlation equations were suggested to describe the relationship between the enthalpy characteristics of hydration of amino acids, viscous flow parameters, and bulk properties of their aqueous solutions.     

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.     

Apparent molar volumes and apparent molar heat capacities of aqueous solutions ofN,N- dimethylformamide andN,N- dimethylacetamide at temperatures from 278.15 to 393.15 K and at the pressure 0.35 MPa

Apparent molar heat capacities C_{p, φ}and apparent molar volumesV_φ were determined for aqueous solutions of N, N - dimethylformamide andN , N - dimethylacetamide at temperatures from 278.15 to 393.15 K and at the pressure 0.35 MPa. The molalities investigated ranged from 0.015 mol ·kg ^− 1to 1.0 mol · kg ^− 1. We used a vibrating-tube densimeter (DMA 512P, Anton PAAR, Austria) to determine the densities and volumetric properties. Heat capacities were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences Corporation, Spanish Fork, UT, U.S.A.). The results were fit by regression to equations that describe the surfaces (V_φ,T , m) and (C_{p, φ}, T, m). Infinite dilution partial molar volumes V₂^oand heat capacitiesC_p,2^o were obtained over the range of temperatures by extrapolation of these surfaces to m =  0.     

Apparent molar volumes and apparent molar heat capacities of aqueous solutions ofα- andβ-cyclodextrins at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

Apparent molar heat capacities C_{p, φ}and apparent molar volumesV_φ were determined for aqueous solutions of α - and β -cyclodextrins at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa. The molalities investigated ranged from 0.008 mol · kg ^− 1to 0.12 mol · kg ^− 1forα -cyclodextrin and from 0.004 mol · kg ^− 1to 0.014 mol · kg ^− 1for β -cyclodextrin. We used a vibrating-tube densimeter (DMA 512P, Anton PAAR, Austria) to determine the densities and volumetric properties. Heat capacities were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences Corporation, Spanish Fork, UT, USA). Equations were fit by regression to our experimental (V_φ, T, m) and (C_{p, φ},T , m) results. Infinite dilution partial molar volumes V₂^oand heat capacities C_p,2^owere obtained over the range of temperatures by extrapolation of these surfaces to m =  0.     

Thermodynamic Properties of Aqueous Electrolyte Solutions. Compressibility Studies in 0.1, 0.5 and 1.0 mol⋅kg−1 Lithium Chloride Solutions at Temperatures from 278.15 to 323.15 K

Sound velocities in aqueous 0.1, 0.5 and 1.0 mol?kg^?1 lithium chloride solutions were determined at 1 K temperature intervals from 278.15 to 323.15 K. These velocities served to evaluate the isentropic compressibilities κ _S , the isothermal compressibilities κ _T , the apparent molar compressibilities K _2,φ , the isochoric thermal pressure coefficients (? P/? T) _V , the change of cubic expansion coefficients with pressure at constant temperature (? α/? P) _T , and the changes of heat capacities C _V with volume (? C _V /? V) _T and C _P with pressure (? C _P /? P) _T .     

Apparent molar volumes and apparent molar heat capacities of aqueous d-lactose · H2O at temperatures from (278.15 to 393.15) K and at the pressure 0.35 MPa

Apparent molar volumes V_φ and apparent molar heat capacities C_p,φ were determined for aqueous solutions of d-lactose · H₂O at molalities (0.01 to 0.34) mol · kg⁻¹ at temperatures (278.15 to 393.15) K, and at the pressure 0.35 MPa. Our V_φ values were calculated from densities obtained using a vibrating tube densimeter, and our C_p,φ values were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter. Our results for d-lactose(aq) and for d-lactcose · H₂O were fitted to functions of m and T and compared with the literature results for aqueous d-glucose and d-galactose solutions. Infinite dilution partial molar volumes V₂^∘ and heat capacities C_p,2^∘ are given over the range of temperatures.     

Volumetric Properties of Amino Acids in Aqueous N-methylacetamide Solutions at 298.15 K

The apparent molar volumes (V _φ ) of glycine, L-alanine and L-serine in aqueous 0 to 4 mol⋅kg⁻¹ N-methylacetamide (NMA) solutions have been obtained by density measurement at 298.15 K. The standard partial molar volumes (V_f⁰)V_{\phi}^{0}) and standard partial molar volumes of transfer (D_trV_f⁰)\Delta_{\mathrm{tr}}V_{\phi}^{0}) have been determined for these amino acids. It has been show that hydrophilic-hydrophilic interactions between the charged groups of the amino acids and the –CONH– group of NMA predominate for glycine and L-serine, but for L-alanine the interactions between its side group (–CH₃) and NMA predominate. The –CH₃ group of L-alanine has much more influence on the value of D_trV_f⁰\Delta_{\mathrm{tr}}V_{\phi}^{0} than that of the –OH group of L-serine. The results have been interpreted in terms of a co-sphere overlap model.     

Effect of Amino Acids and Sodium Chloride on <Emphasis Type="SmallCaps">d</Emphasis>-Sorbitol in Aqueous Solutions at Different Temperatures: Volumetric and Acoustic Approach

Apparent molar volumes and apparent molar compressibilities for d-sorbitol in (0.05, 0.1, 0.2 and 0.3) mol·kg^?1 aqueous solutions of l-alanine, l-cysteine and l-histidine and NaCl have been determined from measurements of solution density at T?=?(288.15, 298.15, 308.15 and 318.15) K and sound velocity at T?=?298.15 K, as a function of the concentration of the sugar alcohol. The data were used to obtain the limiting apparent molar volumes, limiting apparent molar compressibilities and the corresponding transfer parameters. Limiting apparent molar expansibilities and their second order derivatives and volume interaction coefficients were also estimated. These parameters are discussed in terms of d-sorbitol and co-solute (amino acid or sodium chloride) interactions in aqueous solutions.     

Apparent and partial molar volumes of long-chain alkyldimethylbenzylammonium chlorides and bromides in aqueous solutions at T=15 °C and T=25 °C

Density measurements of dodecyl- (C₁₂DBACl), tetradecyl- (C₁₄DBACl), hexadecyldimethylbenzylammonium chloride (C₁₆DBACl) and of decyl- (C₁₀DBABr) and dodecyldimethylbenzylammonium bromide (C₁₂DBABr) in aqueous solutions at T=15 °C and T=25 °C have been carried out. From these results, apparent and partial molar volumes were calculated. Positive deviations from the Debye-Hückel limiting law provide evidence for limited association at concentrations below the critical micelle concentration. The change of the apparent molar volume upon micellization was calculated. The relevant parameters have been presented in function of the alkyl chain length. Apparent molar volumes of the present compounds in the micellar phase, V_φ^m, and the change upon micellization, ΔV_φ^m, have been discussed in terms of temperature and type of counterion.     

Partial Molar Volumes of Amino Acids and Peptides in Aqueous Salt Solutions at 25°C and a Correlation with Stability of Proteins in the Presence of Salts

Partial molar volumes for a homologous series of amino acids and peptides have been measured in aqueous 1M sodium acetate, sodium thiocyanate, and sodium sulfate at 25^°C. These data have been utilized in conjunction with the data in water to deduce partial molar volumes of transfer V _2,m ⁰(tr) from water to these aqueous salt solutions. The volumes of transfer for the amino acids and peptides are found to be positive. The interpretation is that this result arises from the dominant interaction of the sodium salts with the charged centers of amino acids and peptides. Thermal denaturation of the structurally homologous proteins lysozyme and -lactalbumin has been studied in the presence of these salts. Significant thermal stabilization of hen egg-white lysozyme has been observed in the presence of sodium acetate and sodium sulfate. However, the thermal stabilization observed for -lactalbumin is very small in the presence of these salts and sodium thiocyanate leads to a lowering of its thermal denaturation temperature. The rise in the surface tension of aqueous salt solutions with salt concentration has been correlated with the calorimetric and volumetric measurements. The results show that V _2,m ⁰(tr) depends less on the type of electrolyte than on the ionic strength of the solution. The V _2,m ⁰(tr) values correlate very well with the increase in the surface tension of aqueous salt solutions, indicating significant role of surface tension in interactions of amino acids, peptides, or protein with the salts.