Characterization of Inherently Chiral Electrosynthesized Oligomeric Films by Voltammetry and Scanning Electrochemical Microscopy (SECM)

• Published in: Molecules (Basel, Switzerland) Vol. 25; no. 22; p. 5368
• Main Authors: Donnici, Margherita, Toniolo, Rosanna, Arnaboldi, Serena, Mussini, Patrizia R, Benincori, Tiziana, Cirilli, Roberto, Daniele, Salvatore
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 17.11.2020; MDPI
• Subjects: Aqueous solutions; chiral electroactive probes; Coated electrodes; Competition; Electrochemistry; Electrochemistry - methods; Electrodes; enantiodiscrimination in electrochemistry and electroanalysis; Experiments; Feedback; Ferricyanide; Gold - chemistry; Inherently chiral oligomer films; Iron cyanides; Microscopy; Microscopy, Electrochemical, Scanning - methods; Negative feedback; Oxidation; Oxidation-Reduction; Polymers; Positive feedback; Potassium chloride; Reagents; Scanning; scanning electrochemical microscopy; Silver chloride; Stereoisomerism; Voltammetry; scanning electrochemical microscopy; enantiodiscrimination in electrochemistry and electroanalysis; Inherently chiral oligomer films; chiral electroactive probes
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules25225368

A voltammetric and scanning electrochemical microscopy (SECM) investigation was performed on an inherently chiral oligomer-coated gold electrode to establish its general properties (i.e., conductivity and topography), as well as its ability to discriminate chiral electroactive probe molecules. The electroactive monomer ( )-2,2'-bis(2,2'-bithiophene-5-yl)-3,3'-bibenzothiophene (( )-BT T ) was employed as reagent to electrodeposit, by cyclic voltammetry, the inherently chiral oligomer film of ( )-BT T (oligo-( )-BT T ) onto the Au electrode surface (resulting in oligo-( )-BT T -Au). SECM measurements, performed in either feedback or competition mode, using the redox mediators [Fe(CN) ] and [Fe(CN) ] in aqueous solutions, and ferrocene (Fc), ( )-FcEA, ( )-FcEA and FcEA (FcEA is , -dimethyl-1-ferrocenylethylamine) in CH CN solutions, indicated that the oligomer film, as produced, was uncharged. The use of [Fe(CN) ] allowed establishing that the oligomer film behaved as a porous insulating membrane, presenting a rather rough surface. This was inferred from both the approach curves and linear and bidimensional SECM scans, which displayed negative feedback effects. The oligomer film acquired semiconducting or fully conducting properties when the Au electrode was biased at potential more positive than 0.6 V vs. Ag|AgCl|KCl. Under the latter conditions, the approach curves displayed positive feedback effects. SECM measurements, performed in competition mode, allowed verifying the discriminating ability of the oligo-( )-BT T film towards the ( )-FcEA and ( )-FcEA redox mediators, which confirmed the results obtained by cyclic voltammetry. SECM linear scans indicated that the enantiomeric discriminating ability of the oligo-( )-BT T was even across its entire surface.