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 beta- and gamma-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, Delta H degrees, Delta S degrees, Delta G degrees 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 alpha-, beta- and gamma-CD were estimated as 598, 310 and 114, respectively. (C) 2009 Elsevier Ltd. All rights reserved.