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Title: Studies of some properties of lecithin micelles
Author: McIntosh, Donald S.
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1964
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Part 1. Introduction and Theory of Experimental Techniques. In the introductory section of this thesis, the elucidation of the structure of lecithin, lecithin purification methods (with emphasis on more recent developments) and some routes to its synthesis are outlined. Micellisation and solubilisation in aqueous and non-aqueous solutions are discussed, the effects in aqueous solution being only briefly mentioned, fuller accounts being given of the two properties with respect to non-aqueous solutions and lecithin micellar systems. The structure of myelin is considered, attention being directed to its phosphatide content. The theories of the two main experimental techniques used, light-scattering and restricted, diffusion, are presented. The relationship between the viscosity of solutions of macromolecular particles and the particle shape and salvation is outlined. Part 2. Experimental Results, and Discussion. The development and calibration of a light-scattering photometer are described, together with a new type of cell. An assessment was made of some errors in the light-scattering method of molecular weight determination using a polystyrene fraction in methyl ethyl ketone and in toluene. The total error in a molecular weight determination was dependent upon the solvent, the error range being +/- 8 to 13% (P = 0.95) A Rayleigh interference refractometer with a specially adapted cell holder was used to determine diffusion coefficients. Light-scattering was used to determine the micelles size of lecithin in a series of eleven solvent systems whose dielectric constant, epsilon, ranged from 2.3 (benzene) to 4208 (84.0% V/V methanol/Water). Over this range the micelles decreased in size from aggregates of 80 monomers in benzene to monomers at E. 29.0 (93.4% V/V ethanol/water); the size then increased to aggregates of 80 monomers, at epsilon= 42.8. It was thought that on changing from the non-polar to the polar solvents, the micelles structure was reversed, i.e. the lecithin polar head groups were in the interior of the micelle in the non-polar solvents, and on the exterior where epsilon > 29.0. To confirm the micelles weights from light-scattering in solvent mixtures, some micelles weights were determined by a combination of diffusion and viscosity results. From the comparison of micelles weights and viscosity intercept to model structures, it appeared that on increasing epsilon from 2.3, and reaching the range epsilon= 18-25, the micelle structure changed from a bimolecular to a monomolecular leaflet. A similar transition was thought to occur in the more polar solvents where epsilon > 29.0. Interpretation of results in these latter solvents was more difficult due to hydration effects confusing those of asymmetry when considering the viscosity intercepts. The solubilisation, by lecithin micelles in benzene, of cholic acid and four bis-quaternary ammonium compounds was investigated. For cholic acid, the ratio of the number of molecules solubilised per molecule of lecithin was 0.64, and methods were suggested for the incorporation of this solubilisate in the micelle. Because of the small solubilisation ratios observed for the bis-quaternary ammonium compounds, no solubilisate-micelle structure was suggested. A study was made of the interaction of water and lecithin micelles in benzene. Light-scattering and diffusion-viscosity measurements indicated that the number of monomers per micelle remained constant as the micellar water content increased. In such systems it was shown that all the water present could be assumed to be solubilised. Viscosity intercepts showed an increase from 2.87, at zero water content, to a peak of 4.00 at 0.058 g. water/g. lecithin. Further addition of water to the micelles caused a gradual decrease in the viscosity intercept till at 0.33 g. water/g, lecithin the value was 3.33. This latter intercept was characteristic of hydrated spheres having a calculated water content of 0.33g, water/g. lecithin. Comparison to molecular models seemed to indicate that the micelles resembled oblate ellipsoids, and that the addition of water initially increased their asymmetry (up to 0.058g./g.), while further water tended to cause the particles to become spherical. The maximum uptake of water by 1% lecithin solutions in benzene was shown to be 0.33g. water/g. lecithin.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available