“Inherently Chiral” Ionic‐Liquid Media: Effective Chiral Electroanalysis on Achiral Electrodes

Abstract

To achieve enantioselective electroanalysis either chiral electrodes or chiral media are needed. High enantiodiscrimination properties can be granted by the "inherent chirality" strategy of developing molecular materials in which the stereogenic element responsible for chirality coincides with the molecular portion responsible for their specific properties, an approach recently yielding outstanding performances as electrode surfaces. Inherently chiral ionic liquids (ICILs) have now been prepared starting from atropisomeric 3,3'-bicollidine, synthesized from inexpensive reagents, resolved into antipodes without need of chiral HPLC and converted into long-chain dialkyl salts with melting points below room temperature. Both the new ICILs and shorter family terms, solid at room temperature, employed as low-concentration additives in achiral ILs, afford impressive enantioselection for the enantiomers of different probes on achiral electrodes, regularly increasing with additive concentration.

Influence of Chiral Compounds on the Oxygen Evolution Reaction (OER) in the Water Splitting Process

“…Indeed, it is known that the presence in bulk solution of chiral compounds is able to “induce” an enantio-selective or generate local spatial chirality effects: See for instance results obtained in chiral ionic liquids and enantio-recognition effects in achiral ionic liquids, this latter induced by the presence of suitable bulk chiral compounds (even in a low concentration) [ 25 ]. In principle, this allows an efficient production of hydrogen through the water splitting, but using a simpler and cheaper system (i) in terms of manufactory costs, being based only on preparing a bulk solution, and (ii) natural chiral compounds, tartaric acid in this specific case, are rather cheap when compared to metallic nanoparticles obtained by both expensive and environmentally-dangerous (for example the cadmium based nanoparticles [ 11 , 26 ]).…”

“Inherently Chiral” Ionic‐Liquid Media: Effective Chiral Electroanalysis on Achiral Electrodes

“…Alkylation makes pyridine rings electron poorer, and therefore more easily reducible than the parent scaffold:two [12] Scheme 2. N,N'-dialkyl-3,3'-bicollidiniumsalts 2 and N-alkyl-3,3'-bicollidinium salts 4.…”

Widening the Scope of “Inherently Chiral” Electrodes: Enantiodiscrimination of Chiral Electroactive Probes with Planar Stereogenicity

“…In such selectors both chirality and main functional properties originate from the same element, coinciding in all so far considered examples with the main molecular backbone, which features a tailored torsion with a very high racemization barrier. [35][36][37][38][39][40][41][42][43][44] A thoroughly investigated model example is provided by the 2,2'-bis[2-(5,2-bithienyl)]-3,3'-bi-thianaphthene (BT 2 T 4 ) electroactive monomer, inherently chiral on account of its atropisomeric bibenzothiophene core (i. e., with sterically hindered rotation between its two halves). By electrooxidation it enables fast, reproducible electrode modification with films constituted by a mixture of open and cyclic inherently chiral electroactive oligomers (Figure 1), [35,45] resulting in effective enantiodiscrimination of chiral electroactive probes of different nature.…”

“…[35][36][37][38] Remarkably, the same inherent chirality strategy has proved successful with other inherently chiral electrodeposited films, either based on different atropisomeric cores, i. e. bithiophene [39] and biindole, [40] or on a helical element as tetrathia [7]helicene [41] (carbohelicene films [46] could be also tested). It even held when implemented in ionic liquid media or related additives, again either on account of atropisomeric elements, i. e. bipyridinium [42] or bibenzimidazolium [43] salts, or of a helical tetrathiahelicene element. [44] Thus, the inherent chirality strategy has been shown to be of general character, a given selector (be it electrode surface or medium) being able to discriminate the enantiomers of redox probes with different chemical and electrochemical properties.…”

“…[44] Thus, the inherent chirality strategy has been shown to be of general character, a given selector (be it electrode surface or medium) being able to discriminate the enantiomers of redox probes with different chemical and electrochemical properties. [35][36][37][38][39][40][41][42][43][44] However, in such works only three out of the four kinds of rigid stereogenic elements (see key concepts and definitions at SI.1) have been considered in the chiral probes and/or chiral selectors, namely stereocenters (A), stereogenic axes (B), and helices (D, Figure 2).…”