Degradation of Supramolecular Host-Guest Complexes Induced by Hydroxyl Radicals - Effect of the Host on the Guest Reactivity

Abstract

The article deals with photoinduced degradation of two supramolecular host-guest complexes of naphthalene with a-cyclodextrin and of 4-chloroaniline with tetrasulfonated calix[4]arene. The properties of both the complexes were studied by UV/VIS and NMR spectroscopy and also theoretically using quantum-chemical calculations. Degradation of both the guests induced by attack of hydroxyl radicals was accelerated due to the formation of the complexes. It can be assumed that transient products formed after the initial attack induce secondary decomposition of other guest molecules in consecutive radical reactions. The protective effect of a-cyclodextrin manifests itself by slowing down reactions of naphthalene in triplet state (oxygen quenching, triplet-triplet annihilation). In addition, in the case of the 4-chloraniline - calix[4]arene complex, an influence of the host on the population of individual degradation products was observed: while the reactions leading to the formation of oligomeric products were inhibited, transformations of the host were accelerated.