Guest-guest interactions in urea inclusion compounds

Different types of urea inclusion compounds have been studied to test the importance of the molecular interactions between the guests. Experimental evidence has been obtained from the EPR spectra of radicals derived from guests by room temperature gamma-ray irradiation of the inclusion compounds. The guest-guest intra-channel interactions are very important in the case of tridecanedioic and tetradecanedioic dicarboxylic acid guests which give rise to strong intermolecular hydrogen bonding between the carboxylic groups. It is found that the molecular conformation of the tetradecanedioic acid is strongly distorted to fit in the host channel dimensions. The interactions between guest molecules included in adjacent host channels have been modulated by varying the relative guest composition in a mixed nonadecan-10-one-nonadecane inclusion compound. It is shown that the molecular reorientation of the nonadecan-10-one guest becomes faster by increasing the nonadecane percentage as a consequence of the reduced inter-channel interactions.