Chemical method and pathway of CD modification

Chemical modification was first investigated. Researchers began to study the modified CD to expand the applications of native CDs. Although CDs contained 

All the chemical modification depends on the structure of basic unit D-glucose and the chemical characters of bond. Most of the CCDs were prepared by reacting with the hydroxyl in C-2, C-3, C-6 or other kinds of bonds, including C-0 and C-H [2]. 

Almost all the CDs are modified through chemical reactions on the hydroxyl groups. The reactivity of the three kinds of hydroxyls follows the order C-6 C-2 C-3. The acidities sequence is C-2 C-3jJ C-6. The C-6 hydroxyl is most easily replaced via the reaction of CDs with reagent in a strong alkaline environment. However, in the weak alkahne environment, the C-2 hydroxyl is easier to be activated and replaced. Because of the steric hindrance, the large molecular size reagent is more convenient to attack the C-6 hydroxyl. The C-3 hydroxyl can be replaced only if the C-2 and C-6 hydroxyls are shielded. When the CDs are used to encapsulate the guest, the dimension of the cavity plays the key role in the stability of the complexes. But the main factor of unstable complexes is nucleophilicity. In addition, the reaction medium and cavity size both had effect on the structure of the reaction product. 

Hydroxyl could always react with alkyl halide, epoxide and a series of halides to obtain the ester, ether and even the polymers or CCDs. An electron withdraw group is needed to activate the oxygen atom while the C-OH bond crashes. 

3 C-C bond can be oxidatively cleaved by periodate or iodate to obtain aldehyde group macrocycle compounds. Then aldehyde group can be further reduced to alcohol, or involved in other reactions. 

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