D. K. Chattoraj

Biopolymer–surfactant interactions: 5: Equilibrium studies on the binding of cetyltrimethyl ammonium bromide and sodium dodecyl sulfate with bovine serum albumin, β-lactoglobulin, hemoglobin, gelatin, lysozyme and deoxyribonucleic acid

The equilibrium binding of cetyltrimethyl ammonium bromide (CTAB) with bovine serum albumin, β-lactoglobulin, hemoglobin, lysozyme, gelatin and deoxyribonucleic acid, and of sodium dodecyl sulfate (SDS) with lysozyme, has been studied by an electrometric method mainly with variation of pH and ionic strength. The reversibility of the interaction has been established by studying the association and dissociation processes. The isotherms obtained are of the co-operative type; DNA, β-lactoglobulin and bovine serum albumin have shown strong binding of CTAB; the binding of SDS with lysozyme is also fairly strong and greater than that of CTAB. Ionic strength and pH influence the interaction process. The free energies of binding are distinctly of two categories. The low and high free energies (ΔGI° and ΔGII°) correspond to normal and co-operative binding processes respectively, their difference being identified with the free energy of co-operative association.

Thermodynamics of adsorption of inorganic electrolytes at air/water and oil/water interfaces

Abstract Extensive surface and interfacial tension data for air/water and oil/water systems in the presence of high concentrations of inorganic salts were presented. The boundary tensions increased considerably in all cases in the presence of electrolytes, except in the nitro benzene/water case where a decrease was observed in the presence of KSCN. From thermodynamic analysis, the absolute amount of water and electrolyte present at the interface was determined. In most cases the amount of water and electrolyte present at the interface was of the order of 10 −9 and 10 −11 mole/cm 2 , respectively. The interface was found to contain almost a monolayer of water in most cases, although a multilayer was also found in the presence of some salts. The interfacial region of the oil/water system in the presence of several salts was found to contain an appreciable amount of oil. Based on the integration of the Gibbs adsorption equation followed by a hypothetical dilution process, the standard free energy of transfer of 1 mole of water from bulk phase to the interface in the presence of various inorganic salts has been calculated for the change of a bulk mole fraction of water from 1.0 to 0.5. These free energies, which are all positive, are strictly comparable for different salts and for different types of interfaces under identical states of reference.

Biopolymer - Surfactant Interaction: 4 Kinetics of Binding of Cetyltrimethyl Ammonium Bromide with Gelatin, Hemoglobin, β-lactoglobulin and Lysozyme

The binding of CTAB with the proteins, gelatin, hemoglobin, beta-lactoglobulin and lysozyme follow first order kinetics and occurs either in two or three distinct stages. The number of stages depends on the overall configuration of the biopolymers. The denatured protein, gelatin has shown three-stage kinetics under all conditions, whereas the native proteins, hemoglobin, beta-lactoglobulin and lysozyme have exhibited two stage kinetics. Heat treated lysozyme in 8 mol dm-3 urea medium has also shown a two-stage kinetics. On the basis of non interacting binding sites on the proteins and independent sequential binding, the rates of reaction have been observed to increase with temperature and follow the trend k1 >> k2 > k3. The interaction of CTA+ with the proteins is both electrostatic and hydrophobic. Hemoglobin has shown maximum reaction rate whereas, beta-lactoglobulin has shown a minimum. The activation parameters for the kinetic process have exhibited almost non-variant delta G++ and delta H++ < T delta S++. The formation of activation complex in the Eyring model is entropy controlled so also the overall kinetics. An isokinetic entropy-enthalpy compensation phenomenon has been observed for the respective kinetic stages.

BIOPOLYMER-SURFACTANT INTERACTION : 3 KINETICS OF BINDING OF CETYLTRIMETHYL AMMONIUM BROMIDE TO DEOXYRIBONUCLEIC ACID

Abstract By using a surfactant ion-selective membrane electrode, the kinetics of binding of cetyltrimethyl ammonium bromide with deoxyribonucleic acid (DNA) were studied. The binding followed first-order kinetics and appeared to occur in three stages for native DNA. Denatured DNA (caused by heat, acid and alkali) exhibited two-stage first-order kinetics. The multi-stage rate constants followed the order k 1 > k 2 > k 3 or k 1 > k 2 ; they were energetically well separated. The three-stage kinetics at ionic strength μ =0.05 was reduced to a two-stage one at μ =0.001. The enthalpies of activation of all three stages were low whereas the entropy values were reasonably high, and varied in a narrow range. The Δ H ‡ T Δ S ‡ manifestation suggested the kinetic process to be essentially entropy controlled. An isokinetic enthalpy–entropy compensation phenomenon was observed.

Excess adsorption of lysozyme and water at solid-liquid interfacesα

Abstract Adsorption isotherms of lysozyme at solid-water interfaces have been studied as a function of protein concentration, ionic strength of the medium, pH and temperature using silica, alumina, carbon, chromium and Sephadex as solid surfaces. Adsorption of lysozyme is affected strongly by change of pH, temperature and ionic strength. In most cases adsorption isotherms attained a state of adsorption saturation. On chromium, lysozyme is either expanded laterally or negatively adsorbed. In some cases, adsorption isotherms were S shaped, showing the existence of some kind of interactions within the adsorbed protein layer. Adsorption of lysozyme on Sephadex at pH 5.0 and 7.5 is negative due to the excess adsorption of water by this material. The standard free energies (Δ G °) of positive and negative adsorption of lysozyme per square meter, signifying the relative affinity of adsorption in the state of monolayer saturation, have been calculated. The magnitude of the standard free energy of transfer (Δ G B °) of one mole of protein from solution to the surface is observed to be 40.3 kJ mol −1 and the value is independent of pH, ionic strength, nature of the surface and temperature.

A GENERALIZED SCALE FOR FREE ENERGY OF ADSORPTION FROM GIBBS ADSORPTION EQUATION

Abstract From analytical and isopiestic vapor pressure techniques, a substantial amount of experimental data on the extent of adsorption Γ 2 1 of solute (surfactants, fatty acids, inorganic salts) at liquid as well as solid surfaces suspended in aqueous media at different bulk solute activities ( a 2 ) are obtained for calculation of free energy of adsorption. Values of Γ 2 1 change with increase of solute activity. Using all these experimental values in the integrated forms of the Gibbs adsorption equations for multicomponent solutions, the standard free energy change Δ G o in kJ m −2 unit have been evaluated for different solid–liquid systems for the change of bulk solute activity from zero to unity in the rational scale. For surfactants, Δ G o is negative since Γ 2 1 is positive whereas for inorganic salts Δ G o is positive since Γ 2 1 is negative. All values of Δ G o , positive or negative refer to unit solute activity in this generalized scale of free energy of adsorption and hence the order of their values expresses the relative measure of affinities of solutes and solvents for different types of solid surfaces. Also using the Gibbs adsorption equation in an alternative form, the excess free energies of hydration of different solid surfaces in a different thermodynamic scale may be evaluated.

Thermodynamics of interaction of water vapour with 20 different poly-l-amino acids

The uptake of water vapour by 20 different polyaminoacids have been evaluated by an isopiestic vapour pressure technique in absence of solute at three different temperatures (22 degrees C, 30 degrees C and 37 degrees C). The water vapour adsorption isotherm for different polyaminoacids in the range of water activity varying between zero and unity apparently agreed with that expected from a type III BET isotherm. From the linear BET plots, obeyed in the lower range of water activity, the BET constants n(m) and Qm for different polyamines have been evaluated. The amount of water vapour adsorbed (n1) was calculated in moles/kg of polyaminoacids as well as in moles/mole of amino acid residue. Its value at unit water activity (deltan(o)1) has been evaluated by an extrapolation method and the results support that the multilayer adsorption of water vapour at the interface of polyaminoacids takes place. Values of deltan(o)1 are strictly comparable in terms of moles per kg rather than mole per mole unit. In case of beta lactoglobulin (betalg), lysozyme and BSA, theoretically obtained deltan(o)1 values were observed to be considerably larger than experimental values of deltan(o)1. This indicated that amino acid residues in the polypeptide release a large amount of water due to the formation of a globular structure. Using the Bull equation in the integrated form, standard free energies, deltaGo(w) for water-polyamino acid binding interaction at two different temperatures have been evaluated. Based on the Clausius-Clapeyron equation in an integrated form, the integral enthalpy for water-polyamino acid interaction has also been evaluated.

Standard Free Energy of Adsorption at Liquid Interfaces

Based on the Gibbs adsorption equation appropriate relation has been determined for the calculation of the change in free energy (ΔGb o) for the positive adsorption of one mole of surfactant or negative adsorption of one mole of inorganic salt at air-liquid or liquid-liquid interface when the bulk concentration of the surfactant or salt altered fron zero to unit mole fraction hypothetically. For this purpose previously measured boundary tension (γ) data for various aqueous concentrations of organic monobasic and dibasic acids and their salts, SDS, DTAB and CPC1 respectively are used to calculate ΔGb o for excess positive adsorption of solute using the Gibbs adsorption equation. Boundary tension data for various aqueous concentrations of inorganic salts like NaCl, LiCl, CaCl2, A1C13, Na2SO4 and Al2(SO4)3 are used for calculation of ΔGb o for excess negative adsorption of salts at the interface. Values of ΔGb o, however, for different systems are not comparable since they do not include the effect of maximum packing of adsorbed surfactant or salt and water molecules at the interface It is, therefore, proposed that standard free energy (ΔGo) of adsorption of solutes for all cases may be taken to be equal to product, ΔGb o. Γ R,m where Γ R,m stands for the maximum amount of solute in moles transferred as positive or negative excess per square centimeter of liquid surface when the solute concentration in the bulk is altered from zero to unity. Values of ΔG° expressed in calories per square centimeter for positive adsorption of different surfactants and negative adsorption of inorganic salts at air-liquid or liquid -liquid interfaces of various types are comparable in this proposed universal scale of thermodynamics. Air-water, benzene-water, petroleum ether-water, heptane-water, nitrobenzene-water and toluene-water interfaces have been used in all these studies.