Facilitated transport of aldoses by methyl cholate through supported liquid membranes impregnated with various solvents

Supported liquid membranes (SLMs) have been prepared that contain methyl cholate as a novel type of supramolecular carrier designed for the transport of sugars. This commercial amphiphilic sterol ester probably binds sugars at its HO-3,7,12 triol system, allowing their extraction in apolar solvents. The support was a poly(vinylidene difluoride) flat-sheet microporous film. Experiments with glucose revealed very large differences in sugar permeability due to the solvent, hence special attention was paid to the choice of the organic solvent. No transport occurred with aliphatic hydrocarbons. With aromatics, SLMs prepared with benzene had the largest permeabilities. The rate laws of the transport were compared for the three aldoses: glucose, galactose and mannose. In all cases, the transport kinetics showed a linear dependence of the flux with the carrier concentration, but a saturation law with the aldose concentration, in agreement with a mechanism in which the rate-determining step is the migration of a sugar-carrier complex in the SLM. Molecular recognition of the aldoses by methyl cholate was demonstrated by determining noticeable differences between the stability constants of the corresponding complexes.