Investigation of the inclusion of the herbicide metobromuron in native cyclodextrins by powder X-ray diffraction and isothermal titration calorimetry

We report the formation of inclusion complexes between the phenylurea herbicide metobromuron [3-(p-bromophenyl)-1-methoxy-1-methylurea] and β- and γ-cyclodextrin in the solid state. Formation of crystalline inclusion complexes by the kneading method was confirmed by powder X-ray diffraction and further structural characterization using the principles of isostructurality followed. In addition, ΔH°, ΔS°, ΔG° and the association constants (K) at 298 K were determined for complex formation in solution using isothermal titration calorimetry. The magnitudes of K for the formation of 1:1 complexes between metobromuron and α-, β- and γ-CD were estimated as 598, 310 and 114, respectively.

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