Membrane processes for the facilitated extraction of disaccharide sugars: Parameters and mechanism

• The methyl cholate is a potential carrier for the selective transport of disaccharide sugars.
• Determination of the parameters: macroscopic (P and J0) and microscopic (Kass and D∗).
• Molecular recognition phenomenon for special values of Kass and D∗ parameters.
• Molecular recognition phenomenon for the selective extraction of Lactulose.

A supported liquid membrane (SLM) containing a lipophilic agent methyl cholate as carrier, previously used for the facilitated transport of monosaccharides, has been used for the selective extraction of some disaccharides: Lactulose, Lactose, Maltose, Melezitose, Sucrose and Trehalose. The membrane is made of a micro porous poly(vinylidene difluoride) film (PVDF), impregnated with a 0.01 M solution of the carrier in xylene. This prepared SLM is remarkably stable for at least 20 days. The parameters, permeabilities (P) and initial fluxes (J0) on the facilitated extraction across the studied SLM, for these sugars, were determined. On the basis of the flux dependence on the initial concentrations of carrier and transported substrate, the rate-determining step in the transport mechanism is shown to be the migration of the sugar–carrier complex (ST) in the membrane organic phase. The initial flux of transported sugar is related to the initial concentration of this substrate in feed phase by a saturation law, which has allowed the determination of the parameters, apparent diffusion coefficient D∗ and the association constant Kass of the formed complex (ST) in the SLM organic phase. The results clearly indicate that these all sugar-carrier complexes are unstable, which results in higher coefficients D∗ and thus a high permeability of this membrane type to facilitated extraction of these disaccharides. While, the stability of these complexes varies widely depending on the molecular structure of each disaccharide, confirming the molecular recognition phenomenon by the carrier and can identify interaction sites (substrate–carrier) involved during the extraction these carbohydrates

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