Carboxyester hydrolysis promoted by novel nano-sized macrocyclic Zn(II) complexes

A novel series of nano-sized Zn(II) macrocyclic complexes has been synthesized using the template method, i.e. by the in situ reaction of Schiff bases (derived from 1,4-bis(4-amino-5-mercapto-1,2,4-triazol-3-yl)alkanes/ phenylene with salicylaldehyde/2-hydroxyacetophenone) and 1,4-dibromobutane in the presence of zinc(II) acetate dihydrate in ethanol. The complexes have been characterized using elemental analysis, infrared and NMR spectroscopies, scanning electron microscopy and thermal analysis. The catalytic properties of these complexes have been investigated kinetically for the hydrolysis of p-nitrophenylacetate (PNPA) at 25°C in aqueous dimethylsulfoxide using phosphate buffer (pH = 7.0-8.5). During the reaction, absorbance of p-nitrophenolate increases linearly with time (i.e. increase of p-nitrophenolate concentration) which indicates that the rate of the reaction increases linearly with time. On the basis of these results, a plausible mechanism for the hydrolysis of PNPA is proposed. It is shown that coordinated water may serve as a good nucleophile that effectively catalyses PNPA hydrolysis. Therefore, these complexes may serve as model compounds for hydrolytic enzymes. Copyright © 2014 John Wiley & Sons, Ltd.