Water-Sorption Properties and Stability of Inclusion Complexes of Thymol and Cinnamaldehyde with β-Cyclodextrins
â-Cyclodextrins ( â - CDs), macrocyclic oligosaccharides formed by seven glucopyranose units, have a rigid lipophilic cavity and can form host - guest inclusion complexes with suitably sized hydrophobic molecules. Water content infl uences the structure of â - CDs and affects the chemical and physic...
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| Autores principales: | , , |
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| Formato: | CHAP |
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| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_97808138_v_n_p149_Ponce |
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| Sumario: | â-Cyclodextrins ( â - CDs), macrocyclic oligosaccharides formed by seven glucopyranose units, have a rigid lipophilic cavity and can form host - guest inclusion complexes with suitably sized hydrophobic molecules. Water content infl uences the structure of â - CDs and affects the chemical and physical stability of complexed compounds. This work investigated the relationship between the sorption characteristics of â - CDs and complexes formed with thymol and cinnamaldehyde and their release. The complexes were obtained by coprecipitation, fi ltered, freeze - dried, and stored at constant relative humidity (RH) in evacuated chambers (22% - 97%) at 25 ° C. The release of encapsulated compounds was determined after equilibration by differential scanning calorimetry (DSC) following the enthalpy of the fusion peak at 50 ° C (thymol) and 7.5 ° C (cinnamaldehyde). DSC thermograms of complexes after freeze drying showed the disappearance of fusion peaks of thymol and cinnamaldehyde, indicating complex formation. Water - sorption isotherms for â - CD and the complexes showed constant and low water sorption at an RH of less than 80%, and then the uptake of water increased abruptly. At 95% RH, the water adsorbed was in the order â - CD (12.5 mol water/mol â - CD) â - CD - thymol (8.5 mol water/mol complex) â - CD - cinnamaldehyde (7 mol water/mol complex). The guest molecules displaced water molecules from inside the cavity of â - CD. At an RH of less than 84%, thymol and cinnamaldehyde were not released. The percent of released compound abruptly increased from 84% RH, coinciding with the abrupt increase of water. Water sorption signifi cantly affected thymol and cinnamaldehyde complexes with â - CD, and complex stability was thus governed by the shape of the water -sorption isotherm. © 2010 Blackwell Publishing. |
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