Water inside β-cyclodextrin cavity: amount, stability and mechanism of binding.

Stiliyana Pereva,Todor Dudev,Tony Spassov,Silvia Angelova,Valya Nikolova

doi:10.3762/bjoc.15.163

Stiliyana Pereva, Todor Dudev + Show 3 more

Open Access

https://doi.org/10.3762/bjoc.15.163

Copy DOI

Abstract

Cyclodextrins (CDs) are native host systems with inherent ability to form inclusion complexes with various molecular entities, mostly hydrophobic substances. Host cyclodextrins are accommodative to water molecules as well and contain water in the native state. For β-cyclodextrin (β-CD), there is no consensus regarding the number of bound water molecules and the location of their coordination. A number of intriguing questions remain: (1) Which localities of the host’s macrocycle are the strongest attractors for the guest water molecules? (2) What are the stabilizing factors for the water clusters in the interior of β-CD and what type of interactions between water molecules and cavity walls or between the water molecules themselves are dominating the energetics of the β-CD hydration? (3) What is the maximum number of water molecules inside the cavity of β-CD? (4) How do the thermodynamic characteristics of β-CD hydration compare with those of its smaller α-cyclodextrin (α-CD) counterpart? In this study, we address these questions by employing a combination of experimental (DSC/TG) and theoretical (DFT) approaches.

Highlights

Cyclodextrins (CDs), a family of enzymatically modified starches, are widely used as host macrocycles in forming inclusion complexes with various molecular entities of interest to food industry, pharmacology, cosmetics, catalysis, and environmental protection [1,2,3,4,5,6,7,8]
The brief literature survey outlined above shows that, a significant body of information has been accumulated on the β-CD hydration/dehydration, the intimate mechanism of the process is still not completely understood leaving several outstanding questions unanswered: 1) Which localities of the host’s macrocycle are the strongest attractors for the incoming water molecules? (2) What are the major factors contributing to the stability of the water clusters entrapped in the β-CD interior and what type of interactions between water molecules and cavity walls or between the water molecules themselves are dominating the energetics of the β-CD hydration? 3) What is the maximum number of water molecules inside the cavity of β-CD? 4) How do the thermodynamic characteristics of β-CD hydration compare with those of its smaller α-CD counterpart?
The first incoming water molecules cluster around the narrow belt due to the higher electron density concentrated in this location

Summary

Introduction

Cyclodextrins (CDs), a family of enzymatically modified starches, are widely used as host macrocycles in forming inclusion complexes with various molecular entities of interest to food industry, pharmacology, cosmetics, catalysis, and environmental protection [1,2,3,4,5,6,7,8]. The results conflict mostly on the number of bound water molecules and the location of their coordination (inside/outside the host cavity).

Results

Conclusion