Cyclodextrins (CDs) are a family of water soluble and biocompatible macrocycles that are widely used in the food, agriculture, and pharmaceutical industries for the dissolution and stabilization of (bio)active components through host-guest complex formation. γ-CD is the largest and most water soluble amongst the three more common CDs, i.e., α-, β-, and γ-CDs, and thus is best host for bulky guests, such as vitamins and sensitive dyes. However, the high-water solubility of γ-CD necessitates steam distillation for its purification thus drastically increases its production costs. To address this drawback, we used a photoremovable hydrazone template as a proof-of-concept strategy for improving the yield of the enzymatic synthesis of γ-CD and lowering the associated production costs. We synthesized a hydrazone photoswitch with high water solubility and studied itsphotoisomerization behavior and complexation with CDs in water. We showed that while both the Z and E isomers of the hydrazone switch form low affinity (K = 250–725 M−1) complexes with β-CD (1:1), only the Z isomer of the switch can be included in γ-CD (2:1; K2 = 8,970 M−1). We took advantage of this property to template the synthesis of γ-CD thus increase its yield by 6-fold, and then used the photoremovable nature of the template to isolate the synthesized γ-CD without the need for steam distillation. Considering that only a handful of photoswitches can bind to γ-CDs, we anticipate that this newly discovered host-guest couple will open the way for designing γ-CD-based photo-responsive adaptive materials.

Reversible templated synthesis of γ-Cyclodextrin using a hydrazone photoswitch

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