Enzyme mimics hydrogen-transfer reactions

The hydride-donating properties of 1,4-dihydropyridine derivatives have obvious analogies with the well-known coenzymes, NADH and NADPH. The incentive to incorporate 1,4-dihydropyridine residues into crown ethers comes [68] from the knowledge that positive ions (e.g. Mg ) can catalyse hydride transfers 

Activation parameters for hydride transfers in the crown-assisted reaction (dGjso = 

Complexes between iV-(w-aminoalkyl)pyridinium salts (50) and (51) and the 18-crown-6 derivative l,l-(52), synthesised from L-tartaric acid and carrying four 

Inhibition is observed when excess of KBF4 is added the hydrogen transfer becomes intermolecular and follows second-order kinetics with identical rate constants (kj = 1.2 X 10 /M/sec) for hydrogen transfers between l,l-(52) and (50) and l,l-(52) and (51). This results from the exclusion of the substrates from the crown ether-receptor sites by the more strongly complexed ion. When inhibition is caused by a 

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Many of the most successful enzyme mimics have involved functionalised cyclodextrins, and the work of Breslow in particular is familiar to anyone who has followed the field. [24] These hosts bind aromatic rings within a hydrophobic cavity. In another seminal contribution Lehn [25,26] has used polyammonium macrocycles to catalyse phosphate transfer reactions of ATP, demonstrating that multiple hydrogen-bonds can also be an effective source of binding between flexible systems in aqueous solution. 

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