Probing inclusion complexes of cyclodextrins with amino acids by physicochemical approach

• α and β-Cyclodextrin form inclusion complex with l-Leu and l-Ile in aqueous media.
• Surface tension and conductivity studies suggest 1:1 stoichiometry of the complex.
• Density, viscosity and refractive index studies show the host-guest interactions.
• Hydration number and solvation number also support the inclusion phenomenon.
• Stability constants are calculated from NMR titration.

Formations of host-guest inclusion complexes of two natural amino acids, viz., l-Leucine and l-Isoleucine as guests with α and β-cyclodextrins have been investigated which include diverse applications in modern science such as controlled delivery in the field of pharmaceuticals, food processing etc. Surface tension and conductivity studies establish the formation of inclusion complexes with 1:1 stoichiometry. The interactions of cyclodextrins with amino acids have been supported by density, viscosity, refractive index, hydration and solvation number measurements indicating higher degree of inclusion in case of α-cyclodextrin. l-Leucine interacts more with the hydrophobic cavity of cyclodextrin than its isomer. With the help of stability constant by NMR titration, hydrophobic effect, H-bonds and structural effects the formations of inclusion complexes have been explained.