Hydrogen ion titration of lysozyme in alcohol-water solutions

H+ titration curves of hen egg-white lysozyme were obtained at 0.15 I in the presence of small amounts (less than 15%) of methanol, ethanol and n-propanol. The acidity constants of two groups (whose pK values in water are, respectively, 4.2 and 3.5) are increased in water-alcohol mixtures in comparison to water. From the evaluation of these constants as a function of alcohol concentration and hydrocarbon chain length, it is suggested that these alcohols interact specifically with lysozyme. As pK values of 4.2 and 3.5 in water are generally assigned to Asp-101 and Asp-52 respectively, it seems that interaction occurs within the active site of the enzyme. © 1975.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Enthalpies of micellization of quaternary tetradecyl- and cetyltrimethylammonium

Direct enthalpies of micellization (AHm°) of cetyltrimethylammonium salts (CTAX, X = OH", F", Cl", Br", and N03") and tetradecyltrimethylammonium hydroxide (TTAOH) have been measured by using a microcalorimeter method. The dilution of the detergent solution was carried out in the calorimeter chamber in where heats of dilution were detected. The chamber was fed with two peristaltic pumps, one pump delivered the solvent and the other the detergent solution whose concentration varied continuously. The concentration gradient was obtained by inserting a flask containing solvent in the detergent pump path followed by a flask containing the detergent solution at a concentration about ten times its critical micelle concentration (cmc). When the dilution in the calorimeter chamber is done with water and the resulting solution is above the cmc of the given detergent, the heat detected arises from the heat of demicellization and the heat of micellar dilution. On the other hand, when the dilution is done with a solution just above the cmc, the heat detected would only correspond to the heat of micellar dilution. The standard enthalpies of micellization (AHm°) obtained in this manner are discussed in terms of hydrophobic and electrostatic contributions. The AHm° values and the standard free energies of micellization obtained from the cmcs were used to calculate the standard entropies of micellization (AS^0). A linear trend between ASm° and AHm° was obtained which was interpreted in terms of dehydration of ions when they are transfered from the water to the micellar phase. It is concluded that the binding of small ions to micelles would be promoted mainly by entropic factors. It is also concluded that the thermodynamic behavior of micellar solutions is esentially determined by the nature and properties of the counterions

Enthalpies of micellization of quaternary tetradecyl- and cetyltrimethylammonium

Direct enthalpies of micellization (ΔHm°) of cetyltrimethylammonium salts (CTAX, X = OH-, F-, Cl-, Br-, and NO3-) and tetradecyltrimethylammonium hydroxide (TTAOH) have been measured by using a microcalorimeter method. The dilution of the detergent solution was carried out in the calorimeter chamber in where heats of dilution were detected. The chamber was fed with two peristaltic pumps, one pump delivered the solvent and the other the detergent solution whose concentration varied continuously. The concentration gradient was obtained by inserting a flask containing solvent in the detergent pump path followed by a flask containing the detergent solution at a concentration about ten times its critical micelle concentration (cmc). When the dilution in the calorimeter chamber is done with water and the resulting solution is above the cmc of the given detergent, the heat detected arises from the heat of demicellization and the heat of micellar dilution. On the other hand, when the dilution is done with a solution just above the cmc, the heat detected would only correspond to the heat of micellar dilution. The standard enthalpies of micellization (ΔHm°) obtained in this manner are discussed in terms of hydrophobic and electrostatic contributions. The ΔHm° values and the standard free energies of micellization obtained from the cmcs were used to calculate the standard entropies of micellization (ΔSm°). A linear trend between ΔSm° and ΔHm° was obtained which was interpreted in terms of dehydration of ions when they are transfered from the water to the micellar phase. It is concluded that the binding of small ions to micelles would be promoted mainly by entropic factors. It is also concluded that the thermodynamic behavior of micellar solutions is esentially determined by the nature and properties of the counterions. © 1984 American Chemical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A microcalorimetric method of determination of critical micellar concentration and enthalpy of micellization

A method is proposed for the analysis of dilution heats of micellar systems. Simultaneous determination of critical micellar concentration and of micellization enthalpy can be derived from measurements performed at a single temperature. This method, when applied to ionic and non-ionic detergents, supplies results in good agreement with those published for detergents in aqueous solutions at 25 °C. Determination of these two parameters should thus be possible for any type of solvent; further measurements were extended to detergents in solutions 0.001, 0.01 and 0.1 M in NaCl. © 1976 Dr. Dietrich Steinkopff Verlag GmbH & Co. KG.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Kinetics of purple membrane dark-adaptation in the presence of Triton X-100

The kinetics of purple membrane dark adaptation were studied at pH 5 and 7, in the presence and absence of the nonionic detergent Triton X-100. The effect of both sublytic and lytic surfactant concentrations has been considered. Our results show that: (a) dark adaptation is faster at pH 5 than at pH 7, (b) dark adaptation is slower, and of smaller amplitude, in the presence than in the absence of Triton X-100. The data may be interpreted in terms of a simple first-order kinetic model, according to which light-dark adaptation would depend basically on the equilibrium between the 13-cis-and the all-trans-isomers. The experiments also suggest that at pH 5, but not at pH 7, solubilizing surfactant concentrations produce a considerable increase in the velocity of the dark adaptation reaction, perhaps through changes in the microenvironment of a protonable group. © 1990.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Binding of Triton X-100 to bovine serum albumin as studied by surface tension measurements

A previously published computerized drop-weight technique for surface tension measurements, not involving the use of radioactively labelled compounds, has been applied to the study of detergent binding to proteins. The procedure is based on the observation that the protein-surfactant complex is no longer surface-active. As an example, the binding of Triton X-100 to bovine serum albumin has been studied, and the results were found to be in good agreement with those obtained through established but less convenient methods. Our procedure should be useful for measurements of detergent binding to biomembranes. © 1991.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Solubilization of phospholipid bilayers by surfactants belonging to the Triton X series: Effect of polar group size

Various effects of Triton X-114, Triton X-100, Triton X-102, Triton X-165, and Triton X-305 (written in increasing order of cmc, hydrophile/lipophile balance, and number of ethylene oxide units, i.e. polar group size) have been tested on large unilamellar vesicles made of egg phosphatidylcholine. For both lytic and sublytic effects, Triton X-102 appears to be the most efficient member of the series. Leakage and solubilization parameters confirm the previous suggestion that these are two independent surfactant-induced processes.SCOPUS: ar.jinfo:eu-repo/semantics/publishe