Competitive Self-Assembly Interaction between Ferrocenyl Unitsand Amino Acids for Entry into the Cavity ofβ-Cyclodextrin forChiral Electroanalysis

At present, chiral electroanalysis of nonelectroactivechiral compounds still remains a challenge because they cannotprovide an electrochemical signal by themselves. Here, a strategybased on a competitive self-assembly interaction of a ferrocene(Fc) unit and the testing isomers entering into the cavity of beta-cyclodextrin (beta-CD) was carried out for chiral electroanalysis. Firstof all, the Fc derivative was directly bridged to silica microspheres,followed by inclusion into the cavity of beta-CD. As expected, once itwas modified onto the surface of a carbon working electrode as anelectrochemical sensor, SiO2@Fc-CD-WE, its differential pulsevoltammetry signal would markedly decrease compared with theuncovered Fc. Next, whenL- andD-isomers of amino acids thatincluded histidine, threonine, phenylalanine, and glutamic acidwere examined using SiO2@Fc-CD-WE, it showed an enantioselective entry of amino acids into the cavity of beta-cyclodextrin insteadof Fc, resulting in the release of Fc with signal enhancement. For histidine, glutamic acid, and threonine,L-isomers showed a higherpeak current response compared withD-isomers. The peak current ratios betweenL- andD-isomers were 2.88, 1.21, and 1.40,respectively. At the same time, the opposite phenomenon occurred for phenylalanine with a peak current ratio of 3.19 betweenD-andL-isomers. In summary, we are assured that the recognition strategy based on the supramolecular interaction can enlarge thedetection range of chiral compounds by electrochemical analysis

Automated summary

This study presents a strategy for chiral electroanalysis using a competitive self-assembly interaction of a ferrocene unit and testing isomers. The strategy involves the use of beta-cyclodextrin as a cavity for the inclusion of the isomers. The study successfully demonstrated enantioselective entry of amino acids into the cavity, leading to the release of ferrocene and signal enhancement.