NMR diffusion studies on lyotropic liquid crystalline systems
Sammanfattning: The pulsed field gradient fourier transform nuclear magnetic resonance (PFG-FTNMR) method to measure translational diffusion coefficients in multicomponent systems has been applied to amphiphilic molecules forming liquid crystalline phases.By analyzing the concentration dependence of the diffusion coefficients of water and amphiphile in a micellar system of N,N-dimethyldodecy lamine oxide (DDAO) in water it was possible to conclude that the micelles formed were polydisperse in size and shape. It was also shown that solubilization of small amounts of hydrophobic molecules into the micelles induces spherical micelles of a narrow size distribution. From the magnitude of the lateral diffusion coefficient in the cubic phase of DDAO/water it was concluded that this phase is built up of bicontinous aggregates.The lipid lateral diffusion in the cubic phase of monooleoylglycerol (MO)/water has been measured. The decrease in the lateral diffusion of MO in this phase, when the water was replaced by glycerol, was ascribed to changes in viscosity in the polar region. Measurements by electron spin resonance and time-resolved fluorescence spectroscopy showed that changes in viscosity of the solvent also affected the motions in the hydrocarbon region.The diffusion coefficients of all three components in the cubic phase located in the lowwater region of the ternary system of diacylglycerol (DAG)/soybean phosphatidylcholine (SPC)/water have been determined. Conclusive evidence was provided for that this cubic phase is built up of reversed micelles containing mainly SPC in a continous matrix of mainly DAG.The effect on the phase properties of DDAO upon incorporation of the peptide gramicidin D has been investigated. It was shown that gramicidin D induces a lamellar phase at all water contents. The change in the order parameter profile of the C-2H bonds in perdeuterated DDAO upon incorporation of gramicidin D is compatible with theoretical calculations for proteins exhibiting a positive hydrophobic mismatch.A method for using the PFG FTNMR technique in measurements of the transmembrane exchange rate of small molecules in vesicular suspensions is discussed and some preliminary data is shown.
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