MOLECULAR RECOGNITION OF PYROPHOSPHATE BY 1,13-DIOXA-4,7,10,16,19,22-HEXAAZACYCLOTETRACOSANE (OBISDIEN) AND BY ITS MONONUCLEAR AND DINUCLEAR COPPER(II) COMPLEXES - A THERMODYNAMIC AND MOLECULAR MECHANICS STUDY

摘要

The hexabasic macrocyclic ligand 1,13-dioxa-4,7,10,16,19,22-hexaazacyclotetracosane ([24]aneN(6)O(2) or OBISDIEN) forms a variety of cationic species including mono- through hexaprotonated forms of the macrocycle in the absence of metal ions as well as both mononuclear and dinuclear copper(IT) complexes. The Cu(II) complexes also form protonated, unprotonated, and hydroxylated species. These cationic hosts ''recognize'' certain bridging groups that have the suitable size and shape to bridge the two metal ions and coordinate them simultaneously. This paper describes the ability of OBISDIEN and its mononuclear and dinuclear Cu(II)-OBISDIEN complexes to ''recognize'' the pyrophosphate bridging group and to form complexes that exist in a number of protonated forms. In all, 48 individual species are identified. The nature of the bonding between the pyrophosphate, OBISDIEN, copper(II) ion, and one or more hydrogen ions is discussed. Molecular mechanics calculations show that the dicopper(II) OBISDIEN complex is able to adopt several low energy conformers with widely differing Cu to Cu separations that allow for coordination of bridging ligands of differing lengths. [References: 23]