Investigation of buffer-cyclodextrin systems

Abstract

Equilibrium constants for the formation of inclusion compounds of 3-hydroxy-2-naphthoic acid with β-cyclodextrin were determined in aqueous solutions, in the absence and presence of buffers, by the steady-state fluorescence Benesi–Hildebrand method. Almost all the buffers that are usually used have been tested and they are found to have an influence on the formation constants. We suggest that buffers should not be used in aqueous solutions of cyclodextrins unless the experimental error is unacceptable. Furthermore, we obtained the inclusion compound formation constants (K_salt) of β-CD with some buffer components by using a fluorescence competitive inhibition technique. NaClO₄, KClO₄, KCl, KHC₈H₄O₄, KH₂C₆H₅O₇ and NaHC₄H₄O₆ can form 1:1 inclusion complexes with β-cyclodextrin (K_salt>0) while KF, K₂SO₄, NaH₂PO₄, NaAc, Na₂HPO₄ and NaHCO₃ cannot (K_salt<0).