Research on the Vesicle−Micelle Transition by ¹H NMR Relaxation Measurement

Abstract

We have investigated how the dynamics of surfactant molecules changes with the vesicle-micelle transition by (1)H NMR relaxation studies on the sodium decyl sulfate (SDeS)-decyltrimethylammonium bromide (DeTAB)-deuterium oxide system. The study has been planned with reference to the phase diagram of the SDeS-DeTAB-water system deduced from thermodynamic analysis of the surface tension data. The spin-lattice relaxation time (T(1)) and the spin-spin relaxation time (T(2)) are measured at 90 and 400 MHz at various total molalities, m, and compositions, X(2), of the surfactants. The data were analyzed according to the "two-step" model developed by Wennerström et al. and molecular dynamics of the surfactant is discussed from the viewpoint of correlation time tau(f) associated with the local fast motion of the surfactant molecule, correlation time tau(s) associated with the slow overall motions of the aggregate and surfactant molecules within it, and local order parameter S. We find tau(s) of vesicles is an order of magnitude larger than that of micelles signifying that the tumbling of vesicle particles and surfactant diffusion over the vesicle are much slower than those for micelle. Tau(f) and S for vesicles are also larger than those for micelles. Molecular environments of the surfactant are also discussed from the dependence of the chemical shifts on m at constant X(2) or from that on X(2) at constant m. When the chemical shifts in vesicle and micelle are compared at constant m, the chemical shifts in vesicle are displaced to a lower magnetic field than those in micelle, which implies that the surfactant molecules are arranged more closely to each other in the vesicle than in the micelle.

Effect of Vitamin E and a Long-Chain Alcohol n-Octanol on the Carbohydrate-Based Nonionic Amphiphile Sucrose Monolaurate—Formulation of Newly Developed Niosomes and Application in Cell Imaging

“…The formation of rigid self-organized protocell membranes, such as niosomes, renders the hindered movement and shorter relaxation times of the nuclei which is manifested in the certain broadening of peaks in the NMR spectra. 50 By applying the 1 H NMR relaxation methodology, Villeneuve et al 51 investigated the morphological transformation of the aqueous mixture of common cationic and anionic surfactants. Their study revealed that the liquid-crystal-like nature in the vesicle interior, various curvatures of the bilayered vesicles, and the induced polydispersity of the vesicular aggregates are responsible for the broadening of the NMR peaks in vesicular solutions.…”

Molecular Conformation-Controlled Vesicle/Micelle Transition of Cationic Trimeric Surfactants in Aqueous Solution

“…The 2D DOSY PGSE NMR spectra and spin−spin relaxation time measurement were utilized to achieve further understanding of the unique vesicle to micelle transition. , Because DTAD and DDAD carry the similar molecular structure and show similar aggregation behavior and ability as discussed above, DDAD has been investigated as an example by these two NMR techniques. The 2D DOSY NMR spectra of DDAD at different concentrations are presented in the Supporting Information (Figure S5).…”

Quantitative Determination of Relative Permittivity Based on the Fluorescence Property of Pyrene Derivatives: An Interpretation of Hydrophobicity in Self-Assembled Aggregates of Nonionic Amphiphiles

“…The molecular mobility of amphiphilic molecules is different within aggregates. Molecular mobility of the micelle-forming molecules is higher than that of the vesicle-forming molecules. , Therefore, the evaluation of Laurdan, an environmentally responsive fluorescence probe, shows that the hydrophobic region of micelles is more hydrophilic than that of vesicles . However, the estimated relative permittivity is similar within the aggregates.…”

“…The electric surface potential is challenging to measure, and the most probable alternate value is the zeta potential, which describes many phenomena related to surface charge. Liquid-state nuclear magnetic resonance (NMR) is a powerful technique for evaluating molecular mobility, and the relaxation time indicates the degree of molecular mobility .…”