Β-Cyclodextrin


β-Cyclodextrin sometimes abbreviated as β-CD, is a heptasaccharide derived from glucose. The α-, β-, and γ- cyclodextrins correspond to six, seven, and eight glucose units, respectively. β-Cyclodextrin is the most used natural cyclodextrin in marketed medicines. The reason for this lies in the ease of its production and subsequent low price.

Structure

In β-cyclodextrin, the seven glucose subunits are linked end to end via α-1,4 linkages. The result has the shape of a tapered cylinder, with seven primary alcohols on one face and fourteen secondary alcohol groups on the other. The exterior surface of cyclodextrins is somewhat hydrophilic whereas the interior core is hydrophobic.

Physical properties

β-Cyclodextrin exists as a white powder or crystals. The density of its saturated hydrate crystal is 1.46 g/cm3. β-Cyclodextrin is moderately soluble in water and glycerin; well soluble in dimethyl sulfoxide, dimethylformamide, pyridine, HFIP, and ethylene glycol; and insoluble in ethanol and acetone.
It has an optical rotation of D/25 + 160° to + 164°

Applications

β-Cyclodextrin is widely used in medicine, pharmacy, food industry, textiles. Its molecules can accommodate various biomolecules and hence are also used as a complexing agent. Hydrophobic forms of β- CD have been used as sustained release drug carriers. In addition to improving the solubility of compounds, complexation with cyclodextrin has been used to improve the stability of many drugs by inclusion of the compound and protecting certain functional groups from degradation.
β-Cyclodextrin is also beginning to be used in environmental chemistry. Its unique structure allows it to form inclusion complexes with various pollutants and decrease the concentration of the pollutant.

Inclusion Complexes

β-Cyclodextrin can form inclusion complexes where molecules including organic pollutants, pesticides, pharmaceuticals, and hydrocarbons can be trapped within the cavity of the β-Cyclodextrin molecule through non-covalent bonds. This property of forming inclusion complexes can be utilized in removing pollutants from water.
β-Cyclodextrin can be modified through crosslinking β-cyclodextrin and linecaps to increase the materials, including the uptake of certain metals, that can be trapped within the molecules cavity.

Derivatives

β-cyclodextrin has relatively low solubility in water, and hence industry uses its derivatives, such as 2-hydroxypropyl-β-cyclodextrin, randomly methylated β-cyclodextrin, and β-cyclodextrin sulfobutyl ether sodium salt.

History

β-cyclodextrin was first discovered in 1891 by Antoine Villers who studied enzymatic degradation of potato starch in bacteria. Villers first gave them the name “cellulosines” due to their similar properties to cellulose. Later Franz Schardinger renamed these two compounds dextrins leading to the modern name cyclodextrin. Karl Freudenberg and his co-workers, in 1939, published a full description of the two separated compounds, and it wasn't until 1954 when there was a focus on separating and purifying cyclodextrins naturally and their guest inclusion complexes by Friedrich Cramer.