Cooperation of β-Cyclodextrin with Macrocyclic Metal Centers in the Action of Artificial Metalloesterases Built on Poly(ethylenimine)

β-Cyclodextrin (CD) was attached to poly(ethylenimine) (PEI), and then macrocyclic metal centers were constructed on the polymer by condensation with glyoxal or butanedione in the presence of metal (ZnII, NiII, or CoII) templates. The resulting polymers were treated with acetic anhydride to block primary or secondary amines. Hydrolysis of two nitrophenyl esters containing t-butylphenyl residues in the acyl moieties was catalyzed by the PEI derivatives containing both CD cavities and macrocyclic metal centers. Analysis of the kinetic data indicated that the CD cavities and the metal centers provided binding sites and catalytic sites, respectively, for the ester substrates, mimicking metalloesterases. Although the content of metal center was much smaller for the ZnII-containing artificial enzyme compared with the NiII and CoII analogs, catalytic efficiency was greater for the ZnII derivative. Kinetic data indicate high reactivity of the metal center in the productive complex formed between the catalyst and the substrate, when the unproductive binding by the CD cavities is considered.