Adsorption of difructose dianhydrides on hydrophobic Y-zeolites

Abstract

The chemical conversion of fructose to a mixture of isomeric difructose dianhydrides (DFAs) is limited by thermodynamical reason, and the enzymatic production of DFAIII from inulin is restricted by the yield of the final crystallization. Both processes require a separation process for the isolation of pure samples. Hydrophobic Y-zeolites are shown here to adsorb DFAs from aqueous solution. The interaction of the zeolite with DFAs is significantly greater than the interaction with fructose and higher fructose containing oligosaccharides and varies with the structure of the DFA isomer, the β,β-(1-2':2-1′)-connected difructopyranose dianhydride having an exceptional high affinity. Compared to sucrose the DFA adsorption is significantly slower. Molecular modeling of the DFAs by ab initio (GTO 3-31G*) and MM+ force field revealed a stiff but stretched geometry which enables the molecules to enter the 0.74 nm pore openings without great conformational change. An application of the DFA adsorption was realized for isolating biotechnologically produced DFA III. DFA III can be selectively adsorbed from the residue after its crystallization and desorbed with ethanol. The application of the method to the isolation of DFAs from a mixture of 13 isomers, obtained by chemical condensation of fructose, yields a preferential sorption of 2 DFA isomers. • DFA adsorption by hydrophobic interaction. • Much greater adsorption compared to fructose. • Cylindrical carbohydrate conformation. • Molecular diameter matches pore opening.