A computational study of the inclusion processes of cyclodextrins and cyclodextrin polymers

Cyclodextrins (CDs) are molecules that are composed of glucopyranose rings. Cyclodextrins can be formed from either 6, 7, or 8 glucopyranose units yielding, α-, β-, or y-Cyclodextrins respectively. Cyclodextrin polymers (COPs) can occur when glyceryl linkers are added to the previously mentioned cyclodextrins. CDs and COPs are hydrophilic, yet contain a hydrophobic cavity. This cavity allows for the binding of numerous guest molecules. Some practical purposes resulting from the host-guest interactions can be seen in cosmetology, food science, and pharmacy. Using the MacroModel Interactive Molecular Modeling System Version 5.0 we studied the binding of guest molecules to α-, β-, and y-CDs and CDPs. P-nitrophenol and p-hydroxylmethyl benzoate are bound to α-CD and α-CDP, a single pyrene is bound to β-CD and β-CDP, while two pyrenes can bind to the large cavity of y-CD and y-CDP. For all three CDPs, the number of glyceryl linker unit& was systematically varied from one to ten to look at the effect of chain length on the stability of clam-shell versus open-binding. Each structure is minimized in both a clam shell conformation, with the guest surrounded by two CDs connected by glyceryl linker units and in an open conformation, with the guest bound to only one CD of the CDP. An inverted position for open binding was also studied in α-CD and α-CDP. This position occurs when the ester group of p-hydroxylmethyl benzoate and rutro group of p-nitrophenol bind to the CD or COP as opposed to the hydroxyl groups. The results obtained show that open binding is most stable for α-, β-, and y-CDPs for all chain lengths, and that there is no optimal value or glyceryl units for dam-shell binding. The determination of whether the inverted position in open binding is preferable to the normal position is inconclusive