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A study on a primitive artificial esterase model: Reactivity of a calix[4]resorcinarene bearing carboxyl groups
(2008) Cevasco, Giorgio; Galatini, Andrea; Pirinççioğlu, Necmettin; Thea, Sergio; Williams, Andrew; 0000-0001-9805-9745
The host molecule octacarboxymethyl calix[4]resorcinarene 1 catalyses the hydrolysis of substituted phenyl N-methylpyridinium-4-carboxylate esters 3a-f by complexation followed by intracomplex reaction via an anhydride intermediate. The reactivity in the presence of 1 is higher than that of the background at low pH; at high pH an inversion of reactivity occurs, the background becomes predominant since the host inhibits hydrolysis of the esters. The reactivity of esters 3a-f complexed with the host suffers little change in effective charge on the phenolic oxygen (-0.15 units) in contrast with the changes observed in alkaline hydrolysis (-0.28 units) and in the hydrolysis of the model monoaryl glutarate esters (-1.02 units). The less negative effective charge in the transition state for host 1 catalysis compared with that in the glutarate case is ascribed to stronger solvation by water molecules in the complex compared with that due to water molecules in the bulk solvent.