Aqueous Guanidine Hydrochloride Solutions Research Articles

Solvation behavior of some nucleic acid bases and nucleosides in water and in aqueous guanidine hydrochloride solutions: Viscometric, calorimetric and spectroscopic approach

Viscosity, η and enthalpy of dilution, q of studied nucleic acid bases (uracil, cytosine, thymine) and nucleosides (uridine, cytidine and thymidine) in water and in aqueous solutions of (0.10, 0.25, 0.50, 0.75 and 1.00)mol·kg−1 guanidine hydrochloride (GnHCl) have been determined over a temperature range (288.15-318.15)K at (101.3±0.5)kPa. These data have been used to calculate viscosity B-coefficients and standard molar enthalpy of dilution, ΔdilHo which have further been used to evaluate corresponding transfer parameters ΔtrB and ΔtrΔdilHo, respectively. Positive ΔtrB values and negative ΔtrΔdilHo values indicate the predominance of hydrophilic–ionic interactions in these systems. Temperature dependence of B-coefficient and ΔdilHo has also been discussed. Spectroscopic studies have been carried out to further investigate the structural changes and the interactions involved in the mixed aqueous solutions.

Volumetric studies on nucleic acid bases and nucleosides in aqueous guanidine hydrochloride solutions at T = (288.15 to 318.15) K and at atmospheric pressure

Apparent molar volumes (V2,ϕ) have been determined from density measurements for some nucleic acid bases (uracil, cytosine, thymine), and nucleosides (uridine, cytidine and thymidine) in water and in aqueous solutions of (0.10, 0.25, 0.50, 0.75 and 1.00)mol⋅kg−1 guanidine hydrochloride (co-solute) over the temperature range (288.15 to 318.15)K, at atmospheric pressure using vibrating-tube digital densimeter. These data have further been used to calculate apparent molar volumes V2,ϕo at infinite dilution and the corresponding apparent molar volumes of transfer ΔtrV2,ϕo at infinite dilution from water to aqueous solutions of guanidine hydrochloride (GnHCl). Apparent molar expansibilities (E2,ϕo), second-order derivative ∂2V2,ϕo/∂T2p and volumetric interaction coefficients have also been calculated. Co-sphere overlap model has been used to rationalize the data in terms of molecular interactions (hydrophilic, hydrophobic and ionic interactions). The present data have been compared and discussed for the systems studied with those reported in the presence of other co-solutes. The contributions of –CH2 group to V2,ϕo have also been calculated at different temperatures and concentrations of GnHCl.

Ultrasonic Studies of Some Biomolecules in Aqueous Guanidine Hydrochloride Solutions at 298.15 K

Ultrasonic velocity (U), viscocity (η) and density (ρ) of L ‐ ascorbic acid, dextrose and sucrose in aqueous guanidine hydrochloride (0.3 m) have been measured at 298.15 K. The derived acoustical parameters namely adiabatic compressibility (β), apparent molal compressibility (ΨK) apparent molal volume (ΨV) limiting apparent molal compressibility (Ψ0K) limiting apparent molal volume (Ψ0V) and their constants (SK, Sv) and viscosity B‐ coefficient and hydration number (nH) have been computed from the experimental data. The variation of these parameters with respect to the molality of solutes have been explained on the basis of solute‐solvent interaction and structure making tendency of the solutes in solvents.

The failure of simple empirical relationships to predict the viscosity of mixed aqueous solutions of guanidine hydrochloride and glucose has important implications for the study of protein folding.

Viscosities of aqueous solutions of guanidine hydrochloride (GuHCl) were measured in the presence of varying amounts of glucose. At high concentrations of glucose or GuHCl, the measured viscosities showed significant deviation from the values computed using a method proposed by Tanford (1966, J Biol Chem 241:3228-3232). This method was originally derived to allow the calculation of the effects of buffer or low concentrations of salts and other additives on the density and viscosity of aqueous solutions of urea or GuHCl. Recently it has been used to estimate the viscosity of denaturant solutions that contain high concentrations of viscogens. Our results show that the extrapolation of this approach to solutions of highly concentrated viscous co-solutes leads to significant errors. The implications for experimental studies of the viscosity dependence of conformational transitions in proteins is discussed.

Apparent Molar Volume of some ω-Amino Acids in Aqueous Guanidine Hydrochloride Solutions at 15 and 25°

Apparent Molar Volume of some ω-Amino Acids in Aqueous Guanidine Hydrochloride Solutions at 15 and 25°

Osmotic and activity coefficients of aqueous guanidine hydrochloride solutions at 25.degree.C

Osmotic and activity coefficients of aqueous guanidine hydrochloride solutions at 25.degree.C

Denaturation of subtilisin BPN′ and its derivatives in aqueous guanidine hydrochloride solutions

The denaturation of subtilisin BPN′ (EC 3.4.21.14) in guanidine hydrochloride was studied in order to find possible reasons for the exceptional stability of this enzyme against the action of denaturing agents including guanidine hydrochloride. Chemically modified subtilisins, i.e., phenylmethanesulfonylsubtilisin and thiol-subtilisin, were completely denatured in 2 M guanidine hydrochloride at pH 7 without autolysis but they were stable in 0.5 M guanidine hydrochloride for at least 60 h. On the other hand, once completely denatured, the subtilisins remained inactive and in highly unfolded conformations for 60 h or longer after transfer into 0.5 M guanidine solution at pH 7 or 9. No enzymatic activity was regained when the guanidine concentration was lowered to almost zero. We concluded from these and other results described in this paper that this enzyme was thermodynamically unstable in 2 M guanidine hydrochloride at 20°C and at pH 7. We wish to point out the possibility that the denaturation of this enzyme could indeed be irreversible.

Solvation of lysozyme and β-lactoglobulin in aqueous guanidine hydrochloride solutions

The preferential interaction of the solvent components with lysozyme and β-lactoglobulin was determined in aqueous guanidine·HCl solutions by means of equilibrium dialysis and differential refractometry. It has been found that on the molal scale at all concentrations studied the denaturant was preferentially bound. Using a modified equilibrium dialysis technique the total denaturant binding to the two proteins was also estimated. The binding increases with increasing denaturant concentration. In 6 M guanidine·HCl where both proteins are completely denatured one denaturant molecule is bound per three amino acid residues. An attempt is also made to correlate the observed values of total binding for lysozyme with volume and enthalpy changes determined in previous studies.

Equilibrium and kinetics of the unfolding of α-lactalbumin by guanidine hydrochloride

The reversible unfolding of α-lactalbumin by guanidine hydrochloride has been studied at 25.0°C by means of difference spectra and optical rotation. At about pH 5.50, two tryptophanyl residues buried in the interior of the native protein were considered to be exposed on its surface in the denaturated state. The dependence of the equilibrium constant of the unfolding reaction in aqueous solutions of guanidine hydrochloride on pH can be described in terms of abnormal histidyl residues. The dependence on guanidine hydrochloride concentration results in a smaller intrinsic binding constant of the denaturant with the protein, a smaller difference between the numbers of the sites on the denaturated and the native protein molecules, and a more unstable structure in the native state, than for lysozyme. On the other hand, from kinetic measurements, the unfolding was considered to be an apparent two-state transition. Apparent rate constants and half-times of the transition suggest a faster transition than in the case of lysozyme.

Ultrasonic examination of the hemoglobin dissociation process in aqueous solutions of guanidine hydrochloride.

The ultrasonic absorption was determined, in aqueous solutions of hemoglobin undergoing dissociation as a function of the strong electrolyte guanidine hydrochloride (GuHCl), up to 5.4M (molar), over the frequency range 1–50 MHz. With increasing GuHCl concentration to 0.7M, the Hb molecule dissociates into half-molecules without loss of tertiary structure, and at GuHCl concentrations greater than 2.5M, the Hb molecule dissociates further into its four individual polypeptide chains with complete loss of tertiary structure. The ultrasonic absorption coefficient appears to be insensitive to the dissociation process, though a small contribution appears at the lower frequencies, owing to the expansion of the polypeptide molecule. A maximum in the absorption occurs near 2M GuHCl concentration, which does not correspond to dissociation or expansion of the Hb molecule, and it is thought to be associated with the proton transfer reaction.

The Solubility of Amino Acids, Diglycine, and Triglycine in Aqueous Guanidine Hydrochloride Solutions

Abstract The solubilities of amino acids, diglycine, and triglycine have been measured in water and 1 m to 6 m guanidine hydrochloride solutions. Free energies of transfer of amino acid side chains and backbone peptide units from water to guanidine hydrochloride solutions have been calculated from these data. The results show similarity between the patterns of solubilizing effects of guanidine hydrochloride and urea, although guanidine hydrochloride is 2 to 3 times more effective than urea at the same concentrations.