Abstract
Cyclodextrins are some of the most used carriers for bioactive compounds (as host–guest complex) and many factors influence the association–dissociation of this complex, some of them being related to hydrophobicity. In the solid state, cyclodextrins contain two types of water molecules: “surface” water molecules (especially close to the crystal surface) and “strong-bonded” water molecules (especially from the cyclodextrin cavity), but the classification is hard to do, and the concentration of these water molecules are relatively difficult to estimate by simple methods.
In the present study we used the volumetric Karl Fischer titration to estimate these types of water molecules in cyclodextrins by means of the rate of water reaction (related to diffusion from cyclodextrin crystals). “Surface” water molecules are titrated with rates between 1.8–2.8 mM/s for α-cyclodextrin, while for β-cyclodextrin these rates are little bit higher (2.9–3.4 mM/s). The rates corresponding to “strong-bonded” water molecules are approximately tens fold lower (0.05–0.3 mM/s for α-cyclodextrin and 0.15–0.33 mM/s for β-cyclodextrin). The approximate ratio between “surface” and “strong-bonded” water molecules could also be estimated by this simple and rapid method.
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Abbreviations
- KFT:
-
Karl Fischer titration
- aCD:
-
α-cyclodextrin
- bCD:
-
β-cyclodextrin
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This work was supported by Ministry of Education, Research, Youth, and Sports from Romania, PN2_62072/2008.
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Hădărugă, N.G., Hădărugă, D.I. & Isengard, HD. “Surface water” and “strong-bonded water” in cyclodextrins: a Karl Fischer titration approach. J Incl Phenom Macrocycl Chem 75, 297–302 (2013). https://doi.org/10.1007/s10847-012-0143-7
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DOI: https://doi.org/10.1007/s10847-012-0143-7