Comparative study of molecular recognition of folic acid subunits with cyclodextrins.

The complexation of pteroic acid and pterine, subunits of folic acid, with native cyclodextrins (α‒, β‒, and γ‒CDs) was studied in solution (UV-vis), and in the solid state (thermal analysis, IR and Raman). UV-vis titrations at pH = 7.4 provided data regarding stoichiometry of the formed complexes as well as their associations constants. Stability of the complexes increases in the series: γ‒CD < β‒CD << α‒CD for pterine, and γ‒CD < α‒CD << β‒CD for pteroic acid. The mode of complexation was further exploited by molecular modeling studies (docking studies, PM6) showing additionally changes in conformation of pteroic acid upon complexation. Comparison of the association constants of the complexes of pterine and pteroic acid with native cyclodextrins with data obtained for analogous complexes with folic acid shows that all folic acid complexes are less stable than those formed from its subunits.