Cyclodextrins Research Paper
Cyclodextrins (CDs) are most important carriers because of their semi-natural property as it is produced from a natural material i.e. starch, by simple enzymatic conversion. Solubility and dissolution rate of BCS class II drugs can be improved by addition or by complexation with hydrophilic carriers like cyclodextrins. Cyclodextrins have the capability to form inclusion complexes with the guest molecules i.e. poorly water soluble drugs. The formed inclusion complex shows significant changes physicochemical properties of drugs with respect to its solubility and dissolution rate.
2.1.2. Chemistry of cyclodextrins
Three major CDs are crystalline, homogeneous, non-hygroscopic substances, which are torus-like macro-rings built up from glucopyranose units. The a-cyclodextrin (Schardinger’s a-dextrin, cyclomaltohexaose, cyclohexaglucan, cyclohexa-amylose, a-CD, ACD, C6A) consists of six glucopyranose units. The b-CD (Schardinger’s b-dextrin, cyclomaltoheptaose, cycloheptaglucan, cycloheptaamylose, b-CD, BCD, and C7A) has seven such units. The g-CD (Schardinger’s g-dextrin, cyclomaltooctaose, cyclooctaglucan, cyclooctaamylose, g-CD, GCD and C8A) comprises eight such units …show more content…
1.3.: Chemical structure of a, b, g CDs.
The characteristic structural features of CDs are depicted in Figure 1.3. On the side where the secondary hydroxyl groups are situated, the cavity is wider than on the other side where free rotation of the primary hydroxyls reduces the effective diameter of the cavity. The approximate dimensions of CDs are shown in Figure 1.4.
For a long time, only the three CDs (a-,b-, and g-CD) were known and well characterized. In early 1950, French scientist observed the existence of some larger CDs (, etc.), but it was not clear whether they were really 9, 10, etc., membered rings, or glucosyl-, maltosyl-, or diglucosyl-branched CDs. During the past decade, a series of the larger CDs has been isolated and