Stepwise encapsulation of sulfate ions by ferrocenyl-functionalized tripodal hexaurea receptors

Three ferrocenyl-functionalized tripodal hexaurea anion receptors with ortho- (L(2)), meta- (L(3)), and para-phenylene (L(4)) bridges, which showed strong binding affinities toward sulfate ions, have been designed and synthesized. In particular, meta-phenylene-bridged ligand L(3), owing to its trigonal bipyramidal structure, can encapsulate two SO4(2-) ions in its "inner" and "outer" tripodal clefts, respectively, as supported by their clearly distinct NMR resonances and by molecular modeling. The sulfate complex of ortho-ligand L(2), (TBA)2[SO4⊂L(2)]·2H2O (1), displays a caged tetrahedral structure with an encapsulated sulfate ion that is hydrogen bonded by the six urea groups of ligand L(2). CV studies showed two types of electrochemical response of the ferrocene/ferrocenium redox couple upon anion binding, that is, a shift of the wave and the appearance of a new peak. Quantitative binding data were obtained from the NMR and CV titrations.

Electrochemical method for the determination of enantiomeric excess of binol using redox-active boronic acids as chiral sensors

A chiral ferrocene-based boronic acid interacts with (R)- and (S)-Binol to form two complexes that exhibit significantly different ferrocene-based electrode potentials. This difference in redox behavior can be exploited to demonstrate in principle how high levels of enantiomeric excess in a mixture of enantiomers can be quantified and read-out using an electrochemical method.