Dimeric beta-cyclodextrin-based supramolecular ligands and their copper(II) complexes as metalloenzyme models

Abstract

New supramolecular ligands possessing linear 13- and 15-membered pyridine diamidetriamine chelators between the primary sides of two beta-cyclodextrin cavities were synthesized, and characterized by MALDI-MS, NMR, IR and UV-Visible spectroscopy. Fluorescence and pH-metric titration were carried out in order to ascertain their behavior as bifunctional hosts for fluorescent guests and Cu(II) ion. The pK(a) value for the Cu(II) promoted deprotonation of amide ligands was determined to be 6.2 from pH-absorbance profile. Above pH 8.0, two deprotonated amides and three amino groups chelated Cu(II) ion, and yielded penta-coordinated Cu(II) complexes. The Cu(II) complexes catalyzed the hydrolysis of p-nitrophenyl acetate, adamantate and amino acids. Especially, the complex containing 13-membered chelator is an artificial metalloesterase with catalytic rate constant k(cat) = 3.8 x 10(-3) min(-1) and Michaelis constant K-m = 3.5 x 10(-4) M for the hydrolysis of p-nitrophenyl adamantate via metal-hydroxide mechanism. (C) 1998 Elsevier Science Inc. All rights reserved.