Studies on sugars extraction across a supported liquid membrane: Complexation site of glucose and galactose with methyl cholate

A supported liquid membrane (SLM) containing methyl cholate as carrier 1b has been used for the facilitated transport of monosaccharides from concentrated (0.4-0.025 M) aqueous solutions. The SLM is made of a microporous poly(vinylidene difluoride) film impregnated with a 0.1 M solution of the carrier in cyclohexane. The SLM prepared with cyclohexane is remarkably stable for at least 23 days. The permeabilities of the SLM for various sugars were determinated. On the basis of the flux dependence on the initial concentrations of sugar, the rate-determining step in the transport mechanism is shown to be migration of a carrier-sugar complex within the SLM. The flux of sugar is related to the initial concentration of sugar in the feed phase by a saturation law, which allowed the determination of the apparent diffusion coefficient D* and the stability constant K of the methyl cholate complexes of sugars formed in the liquid membrane. The variation of K with structure of sugars confirm molecular recognition by the carrier and show that the complexation sites are HO-2,3,6 for glucose and HO-1,2,6 for galactose.