Mechanism of facilitated saccharide transport through plasticized cellulose triacetate membranes

Mechanistic insight is gained for saccharide transport through plasticized cellulose triacetate (CTA) membranes containing lipophilic ion-pair transpo rt carriers. The molecular structures of the different membrane components are systematically varied and diagnostic transport characteristics such as saccharide-carrier diffusion constant and saccharide extraction constant ar e determined. The observed percolation thresholds support a jumping mechani sm, however, the diffusion constants are found to decrease as the size of t he saccharide, carrier cation, and carrier anion increase, indicating that the rate-limiting step in the transport process involves diffusion of a com plex comprised of all three components. The data is reconciled in terms of mobile-site jumping mechanism where the saccharide is relayed along a seque nce of ion-pair carriers that are locally mobile. In an attempt to improve saccharide selectivity, calix-[4]-arene dicarboxylates were evaluated as po tential ditopic transport carriers. This produced no major change in saccha ride extraction constants. (C) 2001 Elsevier Science B.V. All fights reserv ed.