Separation of poly- and disaccharides by biphasic systems based on ionic liquids

In this work, separation of poly- and disaccharides is achieved by means of novel biphasic systems based on ionic liquids as alternative to the volatile organic compounds used in large amounts for precipitation of the polysaccharides produced from disaccharides in microbial culture broths. Xanthan and maltose are employed to represent a charged (anionic) polysaccharide and a neutral disaccharide. For the separation. two kinds of systems are applied, a specially designed biphasic system of water/1-hexyl-3-methylimidazolium tetrafluoroborate ([C(6)min][BF4]), and an aqueous biphasic system of 3-methyl-1-octylimidazolium chloride/K2HPO4. In the system of [C(6)min][BF4] the effects of the alcohol (isopropyl), added as modifier, and of the temperature on the system volume partitioning and separation are investigated. Recycling and reuse of the [C(6)mim][BF4] are shown. In both ionic liquid-based systems, complete isolation with simultaneous concentration of the polysaccharide in the upper phase of the system is obtained, and 80% of the initial disaccharide is retained in the lower phase. The mechanism of the polysaccharide transfer is revealed in terms of the possible interactions of the xanthan polyanion with the imidazolium cations assisted by the polymer dehydration caused under the addition of isopropyl alcohol or kosmotropic K2HPO4. Drawbacks of the ionic liquid-based biphasic systems are also discussed. (C) 2012 Elsevier B.V. All rights reserved.