Dextrin cyclodextrin

Cyclodextrins are the products of starch hydrolysis catalyzed by cyclodextrin glucanotransferase (CGTase); they are cyclic oligosaccharides composed of six or more glucose units linked by α-1,4-glycosidic bonds. The most common and extensively studied types are α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin, which consist of six, seven, and eight glucose units, respectively, and are relatively large and flexible molecules. X-ray diffraction and nuclear magnetic resonance studies have demonstrated that cyclodextrin molecules adopt a conical or truncated-cone-shaped ring structure, featuring numerous rotatable bonds and hydroxyl groups, with an internal cavity whose external appearance resembles a rubber stopper used in tubing. Within the cavity, glycosidic oxygen atoms are arranged such that the lone pairs on these oxygen atoms point toward the center, resulting in a high electron density inside the cavity and imparting partial Lewis-base character. The molecular configuration is that of the C-1 chair conformation of glucose, with the O atom of the glycosidic bond located within the cylindrical interior, thereby conferring hydrophobicity. The 2- and 3-hydroxyl groups of glucose are situated at one end of the cylinder, while the 6-hydroxyl group is at the opposite end; consequently, both ends of the cylinder are hydrophilic. Thus, the inner upper, middle, and lower regions of the cyclodextrin’s cylindrical structure are composed of distinct functional groups.

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Types of cyclodextrins

Physicochemical Properties of Cyclodextrins Cyclodextrin is the English name for cyclodextrin, abbreviated as CD. In the pharmaceutical industry, cyclodextrin is commonly referred to as CD, with the abbreviation “Xidi.” Substances prepared using cyclodextrin inclusion technology are generally designated as “CD + substance name,” abbreviated as “Xidi + substance name.” Cyclodextrin is a pharmaceutical excipient obtained by enzymatic hydrolysis and cyclization of starch, resulting in cyclic oligomers composed of six or more glucose units. The most common types are α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), and γ-cyclodextrin (γ-CD). In the pharmaceutical industry, β-cyclodextrin is typically preferred. β-Cyclodextrin has a cyclic molecular structure: its outer surface is hydrophilic, while its interior is hydrophobic. This structural feature enables it to accommodate hydrophobic molecules or functional groups of appropriate shape and size within its internal cavity, thereby forming inclusion complexes. The β-cyclodextrin inclusion technique is widely used in the formulation industry due to the following advantages: ① It enhances drug stability; after being included in β-cyclodextrin, certain drugs can be protected from volatilization, sublimation, oxidation, light exposure, and degradation. ② It improves bioavailability. ③ It reduces toxic side effects by diminishing drug irritation and masking unpleasant tastes. ④ The volatility of volatile liquids, solids, and oily liquids is significantly reduced upon inclusion in cyclodextrin. ⑤ It does not alter the physicochemical properties of the drug and does not affect its therapeutic efficacy.

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