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An experimental study of static magnetic field effect on free diffusion of saccharides in aqueous solution

University of British Columbia

The purpose of this work was to investigate experimentally the effects of an externally applied magnetic field on free diffusion of saccharides in aqueous solution. The diffusion coefficients of simple saccharides (deoxyribose, D(-)ribose, D(+)xylose, D-glucose, D-galactose, D(-)fructose, lactose, sucrose, maltose, raffinose) diffusing through a 0.4 micron pore diameter Nuclepore membrane were measured in applied magnetic field strengths ranging from zero to 1.1 T. The applied magnetic field strength was the only variable in these experiments. The initial saccharide concentration difference across the membrane was one percent by weight. The experiments were conducted at a constant temperature of 25 ±0.1° C. The diffusion coefficient was obtained by means of a modified Rayleigh interferometer-laser system. A Rayleigh interferometer measured refractive index profiles of dilute saccharide solutions contained in a diffusion cell. Refractive index profiles were converted to concentration profiles which were then used to calculate mass fluxes and the corresponding binary diffusion coefficients. A study of saccharide-water interactions indicates that these interactions are very complex in nature and that saccharide hydration depends not only on the number of equatorial hydroxyl (e-OH) groups in a saccharide molecule but also on their spatial orientation. The saccharide-water solutions exhibit properties that are considered to be the result of two factors (1) the elongated (non-spherical) shape of the oligosaccharides (2) effect of monosaccharides on the local water structure (i.e their ability to either enhance or destroy the local water structure). The observed magnetic field effect on diffusion coefficients of saccharides shows a strong dependency on these two factors. A decrease in binary diffusion coefficients ranging from two to eighteen percent has been observed for applied magnetic fields up to 1.1 T. The diffusion coefficients evaluated at zero field strength (earth's magnetic field) agreed with literature values to within one percent. The noted decrease in diffusivity of monosaccharides (ribose, xylose, galactose, glucose) becomes larger with an increase in the number of equatorial hydroxyl (e-OH number) groups in the saccharide molecule. This is because an increase in e-OH number increases the microviscosity of the saccharide molecule (structure making or stabilising effect). Deoxyribose and fructose, on the other hand, are considered to be structure breakers. The observed decrease in diffusivity for these saccharides induced by the applied magnetic field seem to be the result of a general stabilizing effect of the applied field on the originally less stable saccharide-water solution. The effect of applied magnetic field on the binary diffusion coefficients of oligosaccharides (sucrose, lactose, maltose, raffinose) correlates with the e-OH numbers as well. In this case, however, the observed decrease in diffusivities is due directly to the orientation of these molecules by the externally applied magnetic field (Cotton-Mouton effect). The same membrane was used to study one complete saccharide system, six runs, (made possible by the changes introduced into the design of diffusion cell and diffusion cell holder in this work) so that variation between membranes would not be a factor. The new experimental procedure resulted in significant reduction in data scatter and highly improved measurement accuracy. Finally, it was shown that the membrane only presented an area reduction to diffusion i.e. the transport process through the membrane followed the assumption of free diffusion.

Text

2011-01-10

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http://hdl.handle.net/2429/30560

Chemical and Biological Engineering

University of British Columbia

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