Enhancement of in vitro fungicidal activity of fuberidazole to Botrytis cinerea by cucurbiturils

The host-guest interaction of fuberidazole (FBZ) fungicide with cucurbituril (CB) macromolecules was characterized in pure water using UV-vis spectrophotometric and NMR techniques. The in vitro applications (at pH 5.5 in pure water) of host-guest complexes were conducted against Botrytis cinerea. While addition of CB5 to FBZ had no significant effect in vitro, mixing CB7 or CB8 with FBZ in a 1:2 ratio improved fungal growth inhibition at least threefold, when compared to the corresponding concentration of the unbound fungicide molecules. Empty CB hosts were completely inactive. Furthermore, the inhibitory activity to B. cinerea was relatively maintained down to a concentration of 5:10 μM of the CB7/8@FBZ complexes, relative to any of controls. Complexation by CB7/8 further improved the photostability of the fungicides with photostabilization factors of 7 and 3, respectively. CB7/8 bound the protonated forms of these guests very strongly but their neutral forms were significantly weaker, which reflects a complexation-induced increase of their pK _a values by 3.8 units with CB7 and 1.4 units with CB8. The present investigation constitutes an innovative, nonclassical, approach to enhance fungicides efficacy utilizing macromolecules with a potential application in crop protection technology.