Cyclodextrin binding

Abstract: A β-cyclodextrin dimer with a linking bipyridyl group is synthesized as a catalyst precursor, a holoenzyme mimic. It binds both ends of potential substrates into the two different cyclodextrin cavities, holding the substrate ester carbonyl group directly above a metal ion bound to the bipyridyl unit. The result is very effective ester hydrolysis with good turnover catalysis. For example, a Cu(II) complex accelerates the rate of hydrolysis of several nitrophenyl esters by a factor of 104−105, with at least 50 turnovers and no sign of product inhibition. In the best case, with an added nucleophile that also binds to the metal ion, a rate acceleration of 1.45 × 107 over the background reaction rate was observed. Hydrolysis by a catalyst with only one cyclodextrin binding group is significantly slower than in the bidentate binding cases. As expected, the binding of a transition state analogue to these catalysts is stronger with the metal ion present than without. This and kinetic evidence point to a mechanism...

Abstract: The cyclization/cleavage of 3',5'-uridyluridine to form 2',3'-cyclic uridylic acid is very effectively catalyzed by Eu3+, and the cyclization/cleavage of the 1-p-nitrophenyl phosphate ester of propane-1,2-diol also shows strong metal ion catalysis by Eu3+, Tb3+, and Yb3+. It also shows moderate catalysis by Mg2+, but not by Ca2+; Zn2+ and Pb2+ are also good catalysts. Various ligands activate these reactions further, and imidazole apparently acts as an additional base catalyst. Some cyclodextrin derivatives act to bind both the substrate and the metal ion but, contrary to what is reported elsewhere, there is no strong selectivity among nucleotides that can be ascribed to cyclodextrin binding.