INTERACTION OF CALIX(N)ARENES WITH UREA, DIBENZOYLUREA AND 4,5-DIPHENYLIMIDAZOLIN-2-ONE

Interaction of urea, dibenzoylurea and 4,5-diphenylimidazolin-2-one wi th calix(n)arenes has been investigated by ultraviolet, infrared and N MR spectroscopy. It appears that urea can get incorporated into the ca vity of p-tert-butyl-25,26,27,28-tetrahydroxycalix(4)arene (1) and -bu tyl-37,38,39,40,41,42-hexahydroxy-calix(6)arene (2) and is held in pos ition through hydrogen bonding. Analysis with CPK models evinces that the interaction of urea is stronger in the case of 1,2- and 1,3-partia l cone conformations of 1 and 2 but it fits tighter into the cone conf ormation of calix(4)arene 1. In the case of 2, urea, though hydrogen b onded, seems to be more free probably due to greater flexibility of ca lix(6)arene architecture. On the contrary, dibenzoylurea and 4,5-diphe nylimidazolone are very weakly bound to these calix(n)arenes.