Structural and dynamic properties of polyoxyethylene sorbitan monooleate micelle in water dispersion studied by pulsed field gradient NMR

Abstract

The diffusion phenomenon of a nonionic surfactant, polyoxyethylene sorbitan monooleate (POE-SMO), micelle in aqueous solution was investigated by pulsed field gradient nuclear magnetic resonance (PFG NMR) with a high gradient strength of 17.4 T/m at the diffusion time t d varied from 3 to 300 ms. This high gradient strength allowed us to measure the slow self-diffusion coefficient of POE-SMO micelle, and the short diffusion time below 10 ms showed the restricted diffusion of the micelle. At the short t d the self-diffusion of the miceUe was restricted and the restricted sizes were 1.8, 1.5, and 0.8 gm for the POE-SMO concentration of 100, 200 and 300 mM, respectively, and 0.6 gm for the POE-SMO only. The possible reason of this restriction was assumed to be the formation of a spatial network ora micellar clustering. Furthermore, a proton exchange between water molecule and surfactant OH group on the micelle surface was proposed. With respect to this proposal, the residence time of the proton at the micelle surface and the thickness of the surface were investigated from proton self-diffusion coefficients by PFG NMR.

Self-Diffusion Coefficient of Water in Tofu Determined by Pulsed Field Gradient Nuclear Magnetic Resonance

“…The slow water diffusion coefficients below 10 -11 m 2 /s could be measured by our PFG-NMR, showing the microscopic water diffusion. The high maximum gradient strength should be used to measure the water diffusion coefficients below 10 -9 m 2 /s due to the fast exchange between exchangeable protons and water molecules as reported in our previous study (the water exchange in surfactant-water micelle systems) (27). Therefore, the two water states around the protein matrix were well-characterized by the Ka ¨rger model (22), even though the chemical exchange on the pore surfaces with water molecules in the tofu was not measured due to the inhomogeneity.…”

MR imaging and diffusion studies of soaked rice

“…Overlooking lipid diffusion could result in a reduction of the self-diffusion coefficient of water in starch granule by an order of magnitude of 10 À11 m 2 /s compared to that of 10 À10 m 2 /s in this study. Hong, Kim, Volkov, Skirda, and Lee (2005) reported that proton exchange between a water molecule and a surfactant OH group on the micelle surface was observed using PFG-NMR with a maximum gradient strength of 17.4 T/m and with the shortest diffusion time of 3 ms. Proton exchange on the micelle was proposed in the region of restricted diffusion with the size of 0.8-1.8 lm where the spatial network or the micellar clustering could be form. Furthermore, the exchange lifetime of the proton on the micelle surface was estimated to be about 8.0 ms, based on the longitudinal magnetization decay with the spin-lattice relaxation time (T 1 ).…”

Molecular and Ionic Diffusion in Ion Exchange Membranes and Biological Systems (Cells and Proteins) Studied by NMR

“…Another reason of population p 1 reducing is a spin–lattice relaxation. Therefore, the p 1 ( t d ) is a biexpontial shape [ 178 ]: where τ is the lifetime of the molecule; T 1 is a spin–lattice relaxation time, which is ≈600 ms; p s , p f are the weights of a slow and fast components, respectively. Figure 64 shows the dependence p 1 (t d ) and its decomposition into components in accordance with Equation (11).…”