A simple strategy for the delivery of active ingredients is to physically complex them with other molecules to obtain better solubility or increase the chemical stability of the complex system. Such as the molecular complex formed by cyclodextrin and essential oil components.
Cyclodextrin is a natural macrocyclic oligosaccharide, which is famous for its ring structure with rigid lipophilic cavity and hydrophilic outer surface, which ensures the good dissolution of the complex in the water environment. They can wrap highly hydrophobic molecules in a hydrophobic cavity to form a true molecular encapsulation. The main advantage of using cyclodextrin molecular complex is that it can protect active ingredients from decomposition due to light, heat, and oxygen, eliminate or reduce bad odors, relieve gastrointestinal irritation, and prevent drugs from decomposing due to light, heat and oxygen. It can also convert oily and liquid medicines into solid powders to reduce microbial contamination and reduce hygroscopicity.
In addition, the formation of the inclusion compound increases the stability of the guest in the body, thereby improving the bioavailability and biological efficacy. There are three main types of cyclodextrins: α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin, which correspond to 6, 7, and 8 glucosyl groups connected by α-(1,4) bonds, respectively. The size of the cavity is 0.5-0.8 nm, which is very important for the "encapsulation" of guest molecules.
In recent years, by chemically modifying the hydroxyl groups, their physical and chemical properties have been improved, thereby enhancing their inclusion capacity. In addition to natural cyclodextrins, more and more semi-synthetic derivatives and copolymers have been prepared and entered the market, such as hydroxypropyl beta cyclodextrin, betadex sulfobutyl ether sodium, methyl beta cyclodextrin and so on. Many of them are used as structural and chiral selectors, and the type and number of substituents give them new properties. Semi-synthetic cyclodextrin derivatives have good solubility in water, can reduce and adjust the release rate of water-soluble molecules, can improve the dissolution rate and inclusion capacity, and can also reduce the side effects of some molecules.