Enthalpy dodecyl sulfate

Where this factor plays a role, the hydrophobic interaction between the hydrocarbon chains of the surfactant and the non-polar parts of protein functional groups are predominant. An example of this effect is the marked endothermic character of the interactions between the anionic CITREM and sodium caseinate at pH = 7.2 (Semenova et al., 2006), and also between sodium dodecyl sulfate (SDS) and soy protein at pH values of 7.0 and 8.2 (Nakai et al., 1980). It is important here to note that, when the character of the protein-surfactant interactions is endothermic (/.< ., involving a positive contribution from the enthalpy to the change in the overall free energy of the system), the main thermodynamic driving force is considered to be an increase in the entropy of the system due to release into bulk solution of a great number of water molecules. This entropy... 

The reaction of Problem 10 was studied at two different temperatures, and, from the temperature dependence of the rate constants, the authors determined AH% and ASJ, the enthalpy and entropy of activation, respectively. The following values of these parameters were obtained in pure water and in 0.01 M sodium dodecyl sulfate (NaLS) and 0.01 M hexadecyl trimethyl ammonium bromide (CTABr) ... 

The activation parameters for the acid-catalyzed hydrolysis of long chain alkyl sulfates compared to those for non-micellar ethyl sulfate calculated from potentiometric data indicate that the rate acceleration accompanying micellization is primarily a consequence of a decrease in the enthalpy of activation rather than an increase in the entropy (Kurz, 1962). However, the activation energies for the acid-catalyzed hydrolysis of sodium dodecyl sulfate calculated from spectrophotometric data have been reported to be identical (Table 8) for micellar and non-micellar solutions, but the entropy of activation for the hydrolysis of the micellar sulfate was found to be 6 9 e.u. greater than that for the non-micellar system (Motsavage and Kostenbauder, 1963). This apparent discrepancy may be due to the choice of the non-micellar state as the basis of comparison, i.e. ethyl sulfate and non-micellar dodecyl sulfate, to temperature dependent errors in the values of the acid catalyzed rate constant determined potentiometrically, or to deviations in the rate constants from the Arrhenius equation. 

Enthalpy of Micelle Formation of Mixed Sodium Dodecyl Sulfate and Sodium Deoxycholate Systems in Aqueous Media... 

Figure 1. Sodium dodecyl sulfate enthalpy curves at various temperatures...

The real breakthrough in terms of kinetic theory was published in 1973 by Aniansson and Wall [80, 81], who provided much more applicable kinetic equations for stepwise micelle formation using a polydisperse model. In a substantial paper two years later they were able to predict the first-order rate constants for the dis-sociation/association of surfactant ions to and from micelles (and hence residence times/lifetimes of surfactant monomers within micelles) [82]. They found values for the association and dissociation of surfactants into/from micelles (Ar and k , respectively) for sodium dodecyl sulfate (SDS) as 1 x 10 s and 1.2 x 10 mok s". Their kinetic model still remains essentially unchanged as a basis for the kinetics of micellar formation and breakdown. Modifications made to existing theory also allowed them to offer a significant thermodynamic explanation for the low enthalpy change upon micellization. 

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