Fructose-Permeable Liquid Membranes Containing Boronic Acid Carriers

Abstract

Liquid membranes that contain boronic acids have potential application in environmentally benign industrial D-fructose production. This review describes our efforts to develop boronic acid carriers that promote high fluxes, that are resistant to leaching, and that are highly selective for fructose over other sugars. Considerable progress has been made with multidentate boronic acid carriers. Initial attempts to transport D-fructose as macrocyclic β-D-fructopyranose diesters appeared to suffer from competitive transport of macrocyclic α-D-glucofuranose diesters, and did not lead to high D-fructose selectivity. On the other hand, carriers that can bind multiple equivalents of D-fructose as tridentate β-D-fructofuranose esters have been much more effective. Unfortunately, D-fructose selectivity is still apparently limited by a competitive and boronic acid-independent non-selective ‘mobile fixed site relay’ transport process. However, further progress will be possible through improved carrier design, careful investigation of the various stages of the transport process, and the use of more industrially useful membrane configurations.