2.1.7 Cyclodextrins
Cyclodextrins invariably consist of 6, 7 or 8 molecules (viz. α, β and γ cyclodextrin) in a 1, 4-configuration to result into the formation of rings having various diameters. In fact, based on the geometry of the chiral isomer, only one would possibly gain entry into the cavity in the ring while the other is excluded evidently.
Synonyms Cyloamyloses; Cycloglycans; Schardinger dextrins.
Biological Source Starch on being treated with the amylase of Bacillus macerans, a specific enzyme, gives rise to a mixture of cyclodextrins. They are naturally occuring carbohydrates.
Preparation It is obtained from the action of B. macerans amylase on starch to yield homogeneous cyclic α – (1→4) linked D-gluco-pyranose units.
Description The various rings constituting the cyclodextrins appear to be as doughnut shaped. However, α-cyclodextrin i.e., the smallest of the lot, has a diameter about two times that of 18-crown–6 (viz., as crown ethers) and its hole (4.5ºA across) is approximately two times as broad.
Chemical Constituents Cyclodextrins mainly are comprised of three different types, as detailed below:

The structure of α-cyclodextrin may be represented in Figure 3.2, in two different manners, namely:

(a) Chair-conformation based cyclic structure, and
(b) Doughnut shaped or like a tiny-pail with the bottom knocked out.

1. As enzyme models based on the fact that , like enzymes, they first and foremost bind the substrate and then, through substituent groups, act on it.
2. As a complexing agent to explore the various types of enzyme action.
3. It may be employed as an additive to the mobile phase (in HPLC*), but it invariably gets bound to an innert support material.

Source: Pharmacognosy And Pharmacobiotechnology By Ashutosh Kar

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