Catalysis by Reactive Anion Receptor Molecules

Hydrogen transfer has been induced with macrocyclic receptors bearing 1,4-di-hydropyridyl (DHP) groups. Bound pyridinium substrates are reduced by hydrogen transfer from DHP side chains within the supramolecular species 78 the first-order intracomplex reaction is inhibited and becomes bimolecular on displacement of the bound substrate by complexable cations [5.19]. Reactions with carbonyl or sulphonium substrates have been performed with other DHP containing macrocycles, such as 79 [5.20]. 

The development of anion coordination chemistry and anion receptor molecules has opened up the possibility to perform molecular catalysis on anionic substrates of chemical and biochemical interest, such as adenosine triphosphate. The catalysis of phosphoryl transfer is of particular interest, namely in view of the crucial role of such processes in biology and of the numerous enzymes that catalyse them. 

Multiple recognition and catalysis in ATP hydrolysis with increased ATP/ADP selectivity has been achieved with a multifunctional anion receptor containing a macrocyclic polyamine as anion binding site, an acridine group as stacking site and a catalytic site for hydrolysis (structure 82) [4.27]. Phosphoryl transfer is accelerated by other types of hydrogen-bonding receptors [5.24a]. 

Enolase type activity is displayed in the efficient supramolecular catalysis of H/D exchange in malonate and pyruvate bound to macrocyclic polyamines [5.32]. Other processes that have been studied comprise for instance the catalysis of nucleophilic aromatic substitution by macrotricyclic quaternary ammonium receptors of type 21 [5.33], the asymmetric catalysis of Michael additions [5.34], the selective functionalization of doubly bound dicarboxylic acids [5.35] or the activation of reactions on substituted crown ethers by complexed metal ions [5.36]. 

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