Inverted Micelle‐in‐Micelle Configuration in Cationic/Carbohydrate Surfactant Mixtures. Issue 1 (11th November 2016)

• Record Type: Journal Article
• Authors: Das, Saikat; Xu, Wenjin; Lehmler, Hans‐Joachim; Miller, Anne‐Frances; Knutson, Barbara L.; Rankin, Stephen E.
• Is Part Of: Chemphyschem. Volume 18:Issue 1(2017)
• Page Start: 79
• Page End: 86
• Publication Date: 2016-11-11
• Subjects: asymmetric vesicles -- micelle structure -- mixed surfactants -- nuclear magnetic resonance spectroscopy -- self-assembly; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.201600908
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: Nuclear magnetic resonance is applied to investigate the relative positions and interactions between cationic and non‐ionic carbohydrate‐based surfactants in mixed micelles with D2 O as the solvent. This is accomplished by using relaxation measurements [spin‐lattice ( T 1 ) and spin‐spin ( T 2 ) analysis] and nuclear Overhauser effect spectroscopy (NOESY). This study focuses on the interactions of n‐octyl β‐d ‐glucopyranoside (C8G1) and β‐d ‐xylopyranoside (C8X1) with the cationic surfactant hexadecyltrimethylammonium bromide (C16 TAB). Whereas the interactions between carbohydrate and cationic surfactants are thermodynamically favorable, the NOESY results suggest that both of the sugar head groups are located preferentially at the interior core of the mixed micelles, so that they are not directly exposed to the bulk solution. The more hydrophilic sugar headgroups of C8G1 have more mobility than sugar heads of C8X1 owing to increased hydration. Herein, an inverted carbohydrate configuration in mixed micelles is proposed for the first time and supported by fluorescence spectroscopy experiments. This inverted carbohydrate headgroup configuration would limit the use of these mixed surfactants when access to the carbohydrate headgroup is important, but may present new opportunities where the carbohydrate‐rich core of the micelles can be exploited. Abstract : Sweet Surprise : NMR and fluorescence spectroscopy show that the surfactant n‐octyl β‐d ‐glucopyranoside (C8G1) segregates with its sugar headgroups clustered at the interior of mixed micelles formed with the cationic surfactant hexadecyltrimethylammonium bromide (C16 TAB) (see picture). This configuration is a surprise because favorable thermodynamics of mixing might suggest that the headgroups should mix at the exterior of micelles.