Synthesis of a Dinuclear ZnII–Calix[4]arene Enzyme Model with Additional General Base Groups – Catalytic Activity in Phosphate Diester Transesterification

Abstract

Calix[4]arenes modified at the upper rim with two pairs of functional groups were synthesized and were used as starting materials for the synthesis of an enzyme model 3‐Zn2 that has two ZnII centers and two dimethylamino groups. Under neutral conditions, this dinuclear metallo‐enzyme model is catalytically active in the cleavage of the phosphate diester bond of the RNA model substrate 2‐hydroxypropyl‐p‐nitrophenyl phosphate (HPNP). The kinetics of 3‐Zn2 were compared with a mononuclear complex 1‐Zn and a dinuclear complex 2‐Zn2 that lack the dimethylamino groups. A catalysis mechanism is proposed where the ZnII centers of 3‐Zn2 cooperate in the activation of the phosphoryl group while one of the dimethylamino groups acts as a general base in the deprotonation of the hydroxyl group of HPNP.

Artificial enzymes based on supramolecular scaffolds

“…1). 99,100 The catalytic activities of calix [4]arenes 21-24 are investigated toward the transesterification of the RNA model substrate HPNP in an acetonitrile and aqueous buffer mixture. The experiment shows that the catalytic moiety itself has a lower catalytic activity than its mononuclear calixarenebased mimic 21, indicating that the calixarene cavity is involved in the catalysis.…”

Dinuclear metallo-phosphodiesterase models: application of calix[4]arenes as molecular scaffolds

“…Although many calix [4]arene-based molecular receptors have been reported, 12,13 calix [4]arene-based enzyme models are little developed. [14][15][16][17][18][19] A notable example is reported by the group of Mandolini, 20 who modified the calix [4]arene lower rim with a crown ether (4). Upon the addition of Ba II ions a crown ether-Ba II complex 4-Ba is formed that exhibits transacylase activity in the methanolysis of p-nitrophenyl acetate.…”

Molecular host–guest complexes: Shielding of guests on semiconductor surfaces

“…Calixarenes have found extensive applications in chemistry, from sensors for heavy metal ions to the development of fluorescent probes, to enzyme mimetics. 90,91 Modification of metal oxides with calixarenes for sensitization processes, however, was unexplored until recently. Katz and coworkers had first explored binding of t-Bu-calixarenes and encapsulation of small organic guests onto insulating silica surfaces, Fig.…”

“…20 Chemical structure of calixarenes and adsorption of a guestt-Bu-calix [4]arene complex onto silica surface. 90,91 calixarene-TiO 2 hybrids are potentially very interesting new materials for semiconductor sensitization processes, as well as for the development of sensors.…”