Due to the large number of hydroxyl groups in the cyclodextrin molecule (18, 21 and 24 hydroxyl groups in ?-cyclodextrin, ?-cyclodextrin and ?-cyclodextrin respectively), the number of possible derivatives of natural cyclodextrins is very high. The hydroxyl groups can be converted to different functional groups in a variety of ways. In the production of methylated cyclodextrins, the degree of substitution can be controlled via the choice of reaction conditions. The scientific name heptakis(2,6-di-O-methyl) ?-cyclodextrin describes the cyclodextrin derivative in which the hydroxyl groups at carbon atoms 2 and 6 have been replaced by methoxy groups. The name of this derivative can be abbreviated to dimethyl-?-cyclodextrin. Similarly, heptakis(2,3,6-tri-O-methyl) ?-cyclodextrin is the fully methylated cyclodextrin derivative otherwise known as trimethyl-?-cyclodextrin. The introduction of the methyl groups increases water solubility until 2/3rds of the hydroxyl groups have been substituted. If the methylation continues, the product then becomes less water-soluble again. However, even trimethyl-?-cyclodextrin is more soluble than natural ?-cyclodextrin