Application of supported liquid membranes containing methyl cholate in cyclohexane for the carrier-mediated transport of sugars

A supported liquid membrane (SLM) containing methyl cholate, a bile acid ester, as carrier for the facilitated transport of sugars has been prepared with cyclohexane as a solvent instead of the previously used aromatic solvents, opening the way to industrial applications. The SLM consists of a microporous poly(vinylidene difluoride) support impregnated with a solution of carrier (C). The transport of several commercial sugars and deoxy-sugars has been studied. The initial flux J(i) of sugar (S) shows a linear dependence on [C](0), the concentration of carrier, but behaves according to the saturation law with respect to c(0), the initial concentration of sugar in the feed phase. Thus, the rate-determining step of the transport is the migration within the SLM of a carrier-sugar complex (CS) formed rapidly at the interface between the SLM and the feed solution. The apparent diffusion coefficient D* and the equilibrium constant K of the complex have been determined for each sugar, revealing noticeable differences that confirm molecular recognition by the HO-3,7,12 triol system of methyl cholate. The complexes Of D-xylose, L-rhamnose and L-fucose, three sugars that do not possess an HO-6 group, are weaker than those of the corresponding hexoses, i.e. glucose, mannose and galactose. The importance of the presence of the exocyclic HOCH2 group for efficient binding of the sugar may be related to the long distance between HO-3,12 of the carrier.