Counterion Binding in the Aqueous Solutions of Bile Acid Salts, as Studied by Computer Simulation Methods

• Published in: Langmuir Vol. 24; no. 19; pp. 10729 - 10736
• Main Authors: Pártay, Lívia B, Sega, Marcello, Jedlovszky, Pál
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 07.10.2008
• Subjects: Bile Acids and Salts - chemistry; Cations - chemistry; Chemistry; Colloidal state and disperse state; Colloids: Surfactants and Self-Assembly, Dispersions, Emulsions, Foams; Computer Simulation; Exact sciences and technology; General and physical chemistry; Micelles. Thin films; Models, Molecular; Molecular Conformation; Probability; Solutions; Surface physical chemistry; Water - chemistry; Binding; Computer simulation; Sodium; Bile salt; Bile acid; Molecular dynamics; Micelle; Freezing point; Counter ion; Nuclear magnetic resonance; Aqueous solution; Electrode potential
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la801352d

We investigate the structural and dynamical properties of counterion binding in sodium cholate and sodium deoxycholate micelles at three different concentration, namely, 30, 90, and 300 mM, by means of molecular dynamics simulations at the atomistic level. The obtained results can resolve a long-standing, apparent contradiction between different experiments that reported discordant values for the degree of counterion binding. Namely, our results suggest that certain experimental techniques, such as freezing point depression, are only sensitive to the contact counterions, and hence, the degree of contact binding of the counterions is measured. On the other hand, in experiments employing, e.g., electrode potential or nuclear magnetic resonance measurements, the solvent-separated counterions also contribute to the signal detected, and hence, the counterions that are measured as bound ones do include the solvent-separated counterions as well.