DIMERIC BETA-CYCLODEXTRIN-BASED SUPRAMOLECULAR LIGANDS AND THEIR COPPER(II) COMPLEXES AS METALLOENZYME MODELS

New supramolecular ligands possessing linear 13- and 15-membered pyrid ine diamidetriamine chelators between the primary sides of two beta-cy clodextrin cavities were synthesized, and characterized by MALDI-MS, N MR, IR and UV-Visible spectroscopy. Fluorescence and pH-metric titrati on were carried out in order to ascertain their behavior as bifunction al hosts for fluorescent guests and Cu(II) ion. The pK(a) value for th e 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-coordina ted Cu(II) complexes. The Cu(II) complexes catalyzed the hydrolysis of p-nitrophenyl acetate, adamantate and amino acids. Especially, the co mplex containing 13-membered chelator is an artificial metalloesterase with catalytic rate constant k(cat) = 3.8 x 10(-3) min(-1) and Michae lis constant K-m = 3.5 x 10(-4) M for the hydrolysis of p-nitrophenyl adamantate via metal-hydroxide mechanism. (C) 1998 Elsevier Science In c. All rights reserved.