An allosteric supramolecular hydrolase model: Combination of a guanidinium function with a metal center in cyclodextrin scaffold

Abstract

An allosteric hydrolase model ( 1) with cooperativity between a metal center and an allosteric site has been constructed through supramolecular assembly of an adamantanyl guanidinium and a copper (II) complex of tris(2-aminoethyl)amine modified cyclodextrin (tren-CD). The structure of the supramolecular inclusion has been determined by 1H NMR and selective NOESY measurement. Furthermore, the allosteric role of the guanidinium group was unambiguously demonstrated by the catalytic behaviors of the allosteric model 1, the kinetics studies for the allosteric model revealed that the allosteric guanidinium group strongly influences catalytic behaviors of the supramolecular catalyst in the cleavage of 4,4′-dinitrodiphenyl carbonate (DNDPC). For example, the turnover number k cat of catalyst 1 was 20 min −1 and the second-order rate constant of 14,080 M −1 min −1 was observed for the hydrolysis of DNDPC, catalyst 1 exhibits higher activity than catalyst 2 without an allosteric site, and its activity is similar to that for copper (II) complex of tris(2-aminoethyl)amino-cyclodextrin (Cu-tren-CD) which possesses a free cavity as a substrate binding site. Obviously, this result revealed that the presence of guanidinium group led to change of the catalytic mechanism and efficiency in the hydrolytic process.