Interaction of bovine serum albumin with anionic surfactants

The effect of binding and conformational changes induced by anionic surfactants sodium dodecyl sulfate (SDS) and sodium octyl sulfate (SOS) on bovine serum albumin (BSA) have been studied using differential scanning calorimetry (DSC), circular dichroism (CD), fluorescence and UV spectroscopic methods. The denaturation temperature, van't Hoff enthalpy and calorimetric enthalpy of BSA in the presence of SDS and SOS and urea at pH 7 have been determined. The results indicate that SDS plays two opposite roles in the folding and stability of BSA. It acts as a structure stabiliser at a low molar concentration ratio of SDS/BSA and as a destabilizer at a higher concentration ratio as a result of binding of SDS to denatured BSA. The Brandts and Lin model has been used to simulate the results

Anomalous Thermoelectric power of over-doped Bi2Sr2CaCu2O8 superconductor

Temperature dependence of thermoelectric power S(T) of three differently processed Bi2Sr2CaCu2O8 (Bi2212) samples, viz. as-processed melt quenched (Bi2212-MQ), 6000C N2-annealed (Bi2212-N2) and 6000C O2-annealed (Bi2212-O2) is reported here. All the samples possess single-phase character and their superconducting transition temperatures (TcR=0) are 85 K, 90 K and 72 K respectively for Bi2212-MQ, Bi2212-N2 and Bi2212-O2. While Bi2212-MQ and Bi2212-N2 samples are in near optimum doping regime, Bi2212-O2 is an over-doped sample. TcS=0 values obtained through S(T) data are also in line with those deduced from the temperature dependence of resistance and DC magnetization. Interestingly, S(T) behaviour of the optimally-doped Bi2212-MQ and Bi2212-N2 samples is seen to be positive in whole temperature range, it is found negative for the over-doped Bi2212-O2 sample above TcS=0. These results have been seen in the light of the recent band structure calculations and the ensuing split Fermi surface as determined by angle-resolved photoelectron spectroscopy (ARPES).Comment: 11 Pages Text + Figs: comments welcome ([email protected]

Effect of osmoregulatory solutes on the stability of proteins

The thermal denaturation of ribonuclease A and lysozyme in aqueous solutions of osmoregulatory solutes methylamines [trimethylamine N-oxide, betaine (trimethylammonioacetate) and sarcosine] and urea have been investigated by differential scanning calorimetry (DSC). The transition temperature, heat capacity and enthalpy of denaturation in aqueous solutions of ribonuclease A and lysozyme at pH 6.00 have been determined by a least-squares fit of the excess heat capacity data to the two-state model. Thermodynamic functions of denaturation, ΔG°, ΔH° and ΔS° at various temperatures have also been evaluated. The methylamines increase the thermal stability of ribonuclease A and lysozyme in the order : trimethylamine N-oxide > sarcosine > betaine. The stabilizing effect of methylamines when compared with that of amino acids follows the order : trimethylamine N-oxide > glycine > β-alanine > gamma-aminobutyric acid > sarcosine > serine > α-alanine > betaine > proline. The structure-stabilizing effect of methylamines and structure-destabilizing effect of urea on ribonuclease A are nearly additive. No net effect on the stability of ribonuclease A is observed in a 2 :1 mixture of urea and methylamines

Thermodynamics of transfer of sorbitol and mannitol from water to aqueous solutions of urea, guanidine hydrochloride and sodium chloride

Integral enthalpies of solution at 298.15 and 308.15 K and densities at 298.15 K for sorbitol and mannitol in aqueous solutions of urea (2, 4 and 6 mol kg-1), guanidine hydrochloride (2 and 4 mol kg-1) and sodium chloride (2 and 4 mol kg-1) have been determined. These data have been used to derive thermodynamic functions (viz. enthalpy, heat capacity and partial molal volumes) for transfer from water to aqueous solutions of urea, guanidine hydrochloride and sodium chloride. The thermodynamic data have been rationalized in terms of polyol-cosolute interactions. The difference in the behaviour of sorbitol and mannitol has been explained in terms of a specific hydration model

Enthalpies and heat capacities of transfer of sodium decanoate, sodium dodecanoate and sodium dodecyl sulphate from water to aqueous urea solutions

Integral enthalpies of solution at very low concentrations of sodium decanoate (NaC<SUB>10</SUB>) and sodium dodecyl sulphate (NaDDS) in 2 and 6 mol kg<SUP>-1</SUP> aqueous urea solutions at 298.15, 308.15 and 318.15 K and of sodium dodecanoate (NaC<SUB>12</SUB>) in 2 mol kg<SUP>-1</SUP> aqueous urea solution at 298.15 and 308.15 K were determined calorimetrically. Enthalpies and heat capacities of transfer of these compounds from water to aqueous urea solutions were derived from integral enthalpies of solution. The results show that the enthalpies of transfer of NaC<SUB>10</SUB> and NaC<SUB>12</SUB> from water to 2 mol kg<SUP>-1</SUP> aqueous urea solution at 298.15 K are positive while that of NaDDS is negative. These values decrease at higher temperatures. The heat capacities of transfer of all these solutes from water to aqueous urea solutions at 303.15 K are negative and increase with increasing temperature. The results are discussed in terms of the structural effects of urea and of the constituent hydrophobic and hydrophilic groups of the solutes in aqueous solutions

Enthalpies, heat capacities and apparent molal volumes of transfer of some amino acids from water to aqueous t-butanol

Integral enthalpies of solution at 298 and 308 K and densities at 298 K of some amino-acid solutions in aqueous t-butanol were measured as a function of t-butanol mole fraction. The integral enthalpies, heat capacities, and apparent molal volumes of transfer of amino acids from water to aqueous t-butanol solutions were derived from these data. The results are discussed in terms of solute-solute and solute-solvent interactions. Coefficients of pair, triplet and higher-order interactions involving solute and cosolvent molecules have been calculated from the transfer functions. The relative contribution of various hydrophilic and hydrophobic interactions in these solutions have been inferred from the sign and magnitude of the interaction coefficients

Apparent molal volumes of amino acids, N-acetylamino acids, and peptides in aqueous solutions

This article does not have an abstract

Nuclear magnetic resonance and thermochemical studies on the influence of urea on water structure

This article does not have an abstract

Thermodynamic studies of transfer of some amino acids and peptides from water to aqueous glucose and sucrose solutions at 298.15 K

Partial molar heat capacities and volumes for a homologous series of amino acids and dipeptides have been measured in aqueous 1 mol kg<SUP>-1</SUP> glucose and sucrose solutions at 298.15 K using flow microcalorimetry and densimetry, respectively. These data have been utilized, in conjunction with the data obtained for them in water earlier, to deduce the partial molar heat capacities and volumes of transfer from water to 1 mol kg<SUP>-1</SUP> aqueous glucose and sucrose solutions. A comparison of these transfer parameters with similar ones in aqueous sodium chloride and calcium chloride solutions is made. The results are explained using the cosphere overlap model and the factors governing the stability of proteins in these sugar solutions have been discussed