48 chimica oggi CHEMISTRY TODAY September 2003 ABSTRACT Cyclodextrins (CDs) are a family of cyclic oligosaccharides that are composed of α-1,4-linked glucopyranose subunits. They are produced from starch by enzymatic degradation. These macrocyclic carbohydrates with apolar internal cavities can form complexes and solubilize many normally water-insoluble compounds. Cyclodextrins are used in separation science because they have been shown to discriminate between positional isomers, functional groups, homologues and enantiomers. This property makes them a useful agent for a wide variety of separations. The utility of these water-soluble cyclic glucans in a variety of foods, flavors, cosmetics, packaging and textiles is also well known. INTRODUCTION Cyclodextrins (CDs) are cyclic oligosaccharides commonly composed of six, seven or eight α-D-glucose units (α, β and γ respectively) which have an overall shape reminiscent of a truncated cone. On account of their relatively hydrophobic interiors, CDs have the ability to form inclusion complexes with a wide range of substrates in aqueous solution. This property of CDs has led to their application in areas as varied as enzyme mimics, catalysis and the encapsulation of drugs. CDs are naturally occurring water-soluble glucans. They are also known as cycloamyloses, cyclomaltoses and Schardinger dextrins. They are produced as a result of intramolecular transglycosylation reaction from the degradation of starch by cyclodextrin glucanotransferase enzyme (CGTase) (1). They have been known for nearly 100 years. In 1881, Villiers first produced them by digesting the starch with Bacillus amylobacter, and in 1903 Schardinger demonstrated the cyclic structure of these compounds. Cyclodextrins are of three types: α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin, referred to as first generation or parent cyclodextrins. α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin are composed of six, seven and eight α-(1,4) linked glycosyl units, respectively (2). β-Cyclodextrin is the most accessible, the lowest-priced and generally the most useful. Each cyclodextrin is a torus (doughnut- shaped) molecule. The internal cavity of the doughnut is hydrophobic, whereas the external surface is hydrophilic. They act as a host for entrapping other molecules without the formation of covalent bonds (3). Chemical modifications of CDs can alter their physical properties. These modifications can improve solubility, stability against light or oxygen and help control the chemical activity of guest molecules (4). The three major types of cyclodextrins available are crystalline, homogenous and non-hygroscopic substances. α-Cyclodextrin is composed of six glucopyranose units and known as Schardinger’s α-dextrin, cyclomaltohexose, cyclohexaglucan. Similarly β-Cyclodextrin and γ-Cyclodextrin are composed of seven and eight glucopyranose units and known Schardinger’s β-dextrin, cyclomaltoheptose, cycloheptaglucan and Schardinger’s γ-dextrin, cyclomaltooctose, cyclooctaglucan respectively (Figure 1). One of the areas of importance in biotechnology and bioengineering is the phenomenon of molecular complexation (MC), which is useful in selectivity, separation and solubilization of various bio-molecules. Different organic molecular complexing agents such as proteins, antibodies and some inorganic agents like zeolites, fullerenes and crown ethers etc., are also very useful, but are costly to synthesize and have limited capabilities (4). All these posses a cage-like supramolecular structure which is the same as the structures formed from cryptands, calixarenes, cyclophanes, spherands and crown ethers (5). The compounds having supramolecular structures carry out chemical reactions which involve all intramolecular interactions where covalent bonds are not formed with interacting molecules, ions or radicals. Majority of all these reactions are of ‘host–guest’ type. Compared to all the supramolecular hosts mentioned above, cyclodextrins are most important because they can alter the properties of the complex forming materials (1). As a result of molecular complexation phenomenon CDs are widely used in many industrial products, technologies and analytical methods. The negligible B I O T E C H N O L O G Y Cyclodextrins: Emerging applications BRAJESH BARSE PRAVEEN KAUL ANIRBAN BANERJEE C L KAUL U C BANERJEE * Department of Biotechnology National Institute of Pharmaceutical Education and Research Sector-67 Mohali, Punjab - 160 0 62, India * Corresponding author