Thermodynamic study on inclusion complex formation of riboflavin with hydroxypropyl-β-cyclodextrin in water
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The inclusion complex formation of riboflavin (RF) with hydroxypropyl-β-cyclodextrin (HP-β-CD) in water was investigated by 1H NMR, UV-vis spectroscopy, and solubility methods. A 1:1 stoichiometry and thermodynamic parameters of complex formation (K, Δc G 0, Δc H 0, and Δc S 0) were determined. Complexation was characterized by negative enthalpy and entropy changes due to prevalence of van der Waals interactions and hydrogen bonding between polar groups of the solutes. A partial insertion of RF into macrocyclic cavity was revealed on the basis of 1H NMR data and molecular mechanics calculation. Location of benzene ring of RF molecule inside the hydrophobic cavity of HP-β-CD results in an increase of aqueous solubility of the former.
KeywordsInclusion complex formation Hydroxypropyl-β-cyclodextrin Riboflavin Thermodynamics
We thank the Russian Foundation for Basic Research for financial support of this study (grant No. 09-03-97563). This study was also possible thank to the agreement between Russian and Polish Academies of Sciences. We thank Tikhova M.N. for her help with some measurements.
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