What can isothermal titration microcalorimetry experiments tell us about the self‐organization of surfactants into micelles?

Abstract

The aim of the present review is to give a concise analysis of the thermodynamic parameters obtained from isothermal titration microcalorimetry (ITC) experiments for the characterization of the self-organization of surfactants into micelles. This review is also focused on works describing some methods allowing to overcome ITC limitation and to extract accurate thermodynamic values from ITC data.

Evaluation of the Micellization Mechanism of an Amphipathic Graft Copolymer with Enhanced Solubility of Ipriflavone

“…ITC is a powerful tool for obtaining calorimetric information about the self-organization of surfactants into micelles and can quantify the enthalpy derived from the micellization of a surfactant and amphiphilic polymer in a single experiment without the necessity of a probe. 22,23,27) In the case of conventional surfactants such as sodium dodecyl sulfate or cetyltrimethylammonium bromide, the ITC thermograms display sigmoidal curves and three concentration ranges: (i) the dissociation range of micelles with repeated dilution of a titrated solution, (ii) the micellization range of surfactant molecules, and (iii) the dilution of micelles. 22,28) In (i), an exothermic reaction could occur because of the breakup of micelles into unimers and dilution of the resultant unimers when the final concentration of surfactant was below the CMC in the sample cell.…”

“…Under this experimental condition, thermodynamic reactions derived from the phase of (ii) and (iii) may be observed. The non-sigmoidal thermograms were analyzed according to a method that has been reported by many authors 23,29,30) and enables a rough estimation to be made of the start of transition (ST) and end of transition (ET) corresponding to the start and end of the micellization process. As shown in Fig.…”

“…[18][19][20][21][22] The ITC method has been used to characterize micellar-based systems because the detailed thermodynamic behavior of micellization could be determined by a single experiment, without the need of a probe. 22,23) The main objective of this study was to evaluate the micellization properties of Soluplus ® in water and its solubility enhancement effect on an amorphous solid dispersion (ASD) system. Ipriflavone was selected as a model compound of a poorly water-soluble compound, which is generally used in the treatment of post-menopausal and senile osteoporosis by oral administration.…”

Automated analysis of calorimetric demicellization titrations

“…Here, we show that a combination of both approaches provides an unbiased and reproducible data analysis strategy without the need for user input other than the calorimetric data proper. The approach is explained and exemplified using demicellization isotherms of the fluorinated surfactant F 6 OPC (3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-n-octylphosphocholine) and the zwitterionic detergent CHAPSO (3-([3-cholamidopropyl]dimethylammonio)-2-hydroxy-1-propanesulfonate).…”

“…Thus, the CMC can be experimentally determined using a variety of methods, including surface tension and conductivity measurements, dye binding experiments, and nuclear magnetic resonance spectroscopy [3]. However, isothermal titration calorimetry (ITC) is the method of choice [4] for the accurate and precise determination of CMC values because it is highly sensitive and noninvasive and offers superior resolution and reproducibility [5]. Moreover, ITC provides additional thermodynamic information, namely, the molar enthalpy and entropy changes accompanying micellization.…”