7 research outputs found
Coordinationâcageâcatalysed hydrolysis of organophosphates : cavityâ or surfaceâbased?
The hydrophobic central cavity of a waterâsoluble M8L12 cubic coordination cage can accommodate a range of phosphoâdiester and phosphoâtriester guests such as the insecticide âdichlorvosâ (2,2âdichlorovinyl dimethyl phosphate) and the chemical warfare agent analogue di(isopropyl) chlorophosphate. The accumulation of hydroxide ions around the cationic cage surface due to ionâpairing in solution generates a high local pH around the cage, resulting in catalysed hydrolysis of the phosphoâtriester guests. A series of control experiments unexpectedly demonstrates thatâin marked contrast to previous casesâit is not necessary for the phosphoâtriester substrates to be bound inside the cavity for catalysed hydrolysis to occur. This suggests that catalysis can occur on the exterior surface of the cage as well as the interior surface, with the exteriorâbinding catalysis pathway dominating here because of the small binding constants for these phosphoâtriester substrates in the cage cavity. These observations suggest that cationic but hydrophobic surfaces could act as quite general catalysts in water by bringing substrates into contact with the surface (via the hydrophobic effect) where there is also a high local concentration of anions (due to ion pairing/electrostatic effects)