SYNTHESIS AND TRANSACYLATING ACTIVITY OF ISOMERIC CO(III)-CYCLODEXTRIN ARTIFICIAL METALLOENZYMES

Although the cyclen-Co(III) complex has exhibited amongst the greatest rate accelerations in acyl and phosphoryl transfer reactions, this catalytic unit has not been used previously in the design of an artificial metalloenzyme. For this study, 6-cyclodextrin derivatives of cyclen-Co(III) with attachments to the primary and secondary sides of the cyclodextrin torus were synthesized. The primary-side cyclodextrin-cyclen-Co(III) conjugate accelerates the hydrolysis of p-nitrophenylacetate by a factor of 1000 (pH 7.0, 25-degrees-C) in comparison with the water-catalyzed reaction. Maximum reactivity occurs at pH 7, consistent with the known pK(a) values and hypothesised mechanism of action of Co(III) complexes. The secondary-side cyclodextrin-cyclen-Co(III) conjugate is less reactive towards p-nitrophenylacetate hydrolysis under saturating conditions. Reactivities towards an azide, a phosphonate and a phosphate,triester were in each case less than five times greater than the buffer-catalyzed rate.