Strategies to Achieve a Ferrocene-Based Polymer with Reversible Redox Activity for Chiral Electroanalysis of Nonelectroactive Amino Acids

Abstract

In the past, various chiral isomers accompanied by electroactive units have been distinguished using electrochemical techniques, which can produce electrochemical signals by themselves. However, it is still difficult to use an electrochemical technique to detect nonelectroactive samples. To address this bottleneck, an electroactive chiral polymer (S,S)-p-CVB-Fc that contains one redox-active ferrocene unit was designed and synthesized in this study. The electroactive polymer can give electrochemical signals as an alternative to the tested chiral samples, regardless of whether the isomers have electroactive units. Then, it was fixed on the surface of a glassy carbon electrode as an electrochemical chiral sensor. When nonelectroactive amino acids including proline, threonine, and alanine were examined by the sensor, clear discrimination in the response of peak current could be observed toward l- and d-isomers at pH 6.5. The peak current ratios (I L/I D) for proline and alanine were 1.47 and 1.48, respectively. In contrast, for threonine, the d-isomer exhibited a higher peak current than the l -isomer with a ratio of 2.59. In summary, the results ensure that the current work can enlarge the testing scope of chiral samples in the field of chiral electroanalysis using an electroactive sensor.

Competitive Self-Assembly Interaction between Ferrocenyl Units and Amino Acids for Entry into the Cavity of β-Cyclodextrin for Chiral Electroanalysis

“…The XPS spectra of SiO 2 @Fc and SiO 2 @Fc-CD are presented in Figure A,B. For SiO 2 @Fc (Figure A), the elements including C 1s, O 1s, N 1s, Si 2s (Si 2p), Br 3d, and Fe 2p are located at 285.2, 532.3, 402.1, , 153.8 (103.6 eV), , 25.2, , and 689.8 eV, , respectively. It should be noted that the peak at 402.1 eV belongs to the carbon–cationic-nitrogen bond, rather than the carbon–nitrogen bond.…”

“…To detect nonelectroactive chiral compounds, it is natural to seek suitable mediators as an alternative to support the electron transfer. The mediators can be divided into two categories: organic dyes (such as phenazine methosulfate and 1,4-benzoquinone) and organometallic complexes (such as Fe and Ru complexes). − Among them, chiral ferrocene (Fc) derivatives have been reported as a suitable enantioselective sensor for chiral electroanalysis, undergoing a reversible redox reaction between ferrous and ferric iron (Fc + ). − The electrochemical signal will therefore decrease when the Fc derivatives interact with the testing isomers. However, to obtain better recognition efficiency, the Fc derivatives need specific functional groups, like boric acid and aldehyde group, leading to covalent bond formation with the testing isomers.…”

An electrochemical chiral sensor based on competitive host–guest interaction for the discrimination of electroinactive amino acids

“…Recently, electrochemical chiral discrimination of electroinactive proline (Pro) with a ferrocene (Fc) derivative modified electrode has been reported by our group, in which the polymeric Fc derivative (( S,S )-poly-(1-(chloromethyl)-4-vinylbenzene)-Fc), with reversible redox activity, was utilized as the electroactive unit and preferentially combined with l -Pro. 11…”

“…Recently, electrochemical chiral discrimination of electroinactive proline (Pro) with a ferrocene (Fc) derivative modified electrode has been reported by our group, in which the polymeric Fc derivative ((S,S)-poly-(1-(chloromethyl)-4-vinylbenzene)-Fc), with reversible redox activity, was utilized as the electroactive unit and preferentially combined with L-Pro. 11 β-Cyclodextrin (β-CD) has hydrophobic inner cavities and a hydrophilic outer surface. 12 It has been used in chiral discrimination because it can form inclusion complexes with guest molecules and display different association constants with the isomers of chiral guest molecules.…”

A Real-Time Strategy for Chiroptical Sensing and Enantiomeric Excess Determination of Primary Amines via an Acid–Base Reaction

“…Chiral amines are important chemical and pharmaceutical intermediates for the synthesis of bioactive compounds. To date, various analytical techniques, including chromatography, − NMR, − fluorescence, − circular dichroism (CD), − and electrochemistry, − have been widely exploited to determine the absolute configuration or enantiomeric excess (ee) values of chiral amines. There is no doubt that different chiral recognition techniques have their own specific requirements.…”