(2-Hydroxypropyl)-beta-cyclodextrin

General description.
Cyclodextrins are cyclic oligosaccharides composed of 6, 7 or 8 glucopyranose units, usually called α -, β-or γ-cyclodextrins, respectively. These compounds have a rigid ring structure, making them natural complexing agents. Intramolecular hydrogen bonds are easily formed between the C2-and C3-hydroxyl groups of the adjacent glucopyranose units of these compounds, which makes their unique structures stable. The molecule has a circular shape, its C2-and C3-hydroxyl groups are located around the larger open end, and the more reactive C6-hydroxyl groups are arranged around the smaller open end. The C6-hydroxyl arrangement opposite to the hydrogen-bonded C2-and C3-hydroxyl groups forces the oxygen bonds to close together in the cavity, resulting in an electron-rich hydrophobic interior. The size of the hydrophobic cavity is a function of the number of glucopyranose units forming cyclodextrins. The solubility of natural cyclodextrins is very low. In the late 1960s, it was found that the chemical substitution of 2, 3 and 6 hydroxyl sites could greatly increase the solubility. Most chemically modified cyclodextrins can reach a concentration of 50% (w / w) in water. The size of the cavity is the main factor in determining which cyclodextrin is used for complexation. The cavity diameters of β-cyclodextrin or β-glucopyranose unit compounds are very suitable for molecules of similar size to hormones, vitamins and many compounds commonly used in tissue and cell culture. Therefore, β-cyclodextrin is most commonly used as a complexing agent.

Application.
Because HBC forms a complex with the drug, the solubility of lipophilic drugs in aqueous solution increases linearly with the concentration of hydroxypropyl-β-cyclodextrin (HBC). The guest-host complex is formed between the drug and the non-polar cavity of HBC, which can cause solubilization. The solution can be freeze-dried to form a soluble powder. It is not toxic to rabbits and mice.

Points for attention in preparation.
The solution can be stored at 4 °C for several months. Solids should be kept sealed at room temperature.