Enzymatic modification reactions, cyclodextrin

Cyclodextrins are included here as water-soluble supports. They will also be mentioned in Chap. 7 on separations and in Chap. 8 on running reactions in water instead of organic solvents. Cyclodextrins221 are made by the enzymatic modification of starch.222 They are made commercially by Cer-estar and Wacker Chemie. They have conical structures of six, seven, and eight glucose units in rings, denoted a- /3-, and y-cyclodextrin, respectively. Mercian Corporation has a process for /3-cyclodextrin, which is more selective than usual, that produces no a- and only a small amount of the y-product.223 The insides are apolar and hydrophobic, whereas the outsides are hydrophilic (Table 5.2). 

As the native cyclodextrins (CDs) exhibit some limitations in application, they need to be modified to improve the properties. All the modification methods could be divided into two kinds, chemical modification and enzymatic modification. Based on the stable cyclic structure, CDs could be modified via etherification, esterification, oxidation and crosslinking reactions. The chemical modification has a special purpose of introducing novel functional group. CDs modified by chemical means were named as cyclodextrin chemical derivatives (CCDs). 

Variations of this method are possible in several ways. First of all, cyclodextrin which is available on a large scale by enzymatically catalyzed modification of starch can be tailored by chemical reactions. Furthermore, copolymerizations between different host-guest complexes are possible whereby in some cases the reactivity ratios differ from those reported in literature. 

Abstract. The first successful method for modification of dimethyl-) -cyclodextrin 0 -DMCD) was demonstrated by the synthesis of a new artificial hydrolase (2) and the enzymatic activities of 2 were investigated. 2 caused an 1100-fold increase in the rate of hydrolysis of / -nitrophenyl acetate at pH 7.2, whereas unmodified p-DMCD depressed the reaction. The kinetic pK of 2 was 7.2, and the of 2 was... 

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