1H NMR and calorimetric study on binding ability of cyclodextrins to isomeric pyridinecarboxylic acids in aqueous solution

• Published in: Journal of Inclusion Phenomena and Macrocyclic Chemistry 2008-12, Vol.62 (3-4), p.363-370
• Main Authors: Terekhova, Irina V., Kumeev, Roman S., Alper, Gennady A.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Crystallography and Scattering Methods; Food Science; Organic Chemistry; Original Article
• ISSN: 0923-0750; 1573-1111
• DOI: 10.1007/s10847-008-9479-4

Complex formation of α- and β-cyclodextrins with isomeric pyridinecarboxylic acids (picolinic, nicotinic and isonicotinic acids) in water were studied by calorimetry and 1 H NMR at 298.15 K. The obtained results revealed the weak 1:1 complex formation governed by the cavity dimensions and position of the carboxylic group in the pyridine ring. It was found that selective inclusion complex formation of α- and β-cyclodextrins with nicotinic and isonicotinic acids takes place. In the case of picolinic acid, the considerable role of external interactions and formation of less stable complexes were detected. The location of the carboxylic group in the meta -position of pyridine ring is more favorable for the effective binding. The pyridinecarboxylic acids are shallow inserted into α-cyclodextrin cavity possessing the smaller diameter, while they are deeply included into β-cyclodextrin cavity. Thermodynamic parameters of complex formation (K, Δ c G 0 , Δ c H 0 and Δ c S 0 ) were calculated and discussed in terms of influence of reagents structure.