“Inherently chiral” thiophene-based electrodes at work: a screening of enantioselection ability toward a series of pharmaceutically relevant phenolic or catecholic amino acids, amino esters, and amine

Abstract

"Inherently chiral" thiophene-based electroactive oligomer films have recently been shown to exhibit outstanding chirality manifestations. One of the most exciting among them is an unprecedented enantioselection ability as electrode surfaces. In fact, in preliminary chiral voltammetry experiments, the new electrodes have been shown to both discriminate the enantiomers of chiral probes (either enantiopure or in a mixture, in terms of large differences in peak potentials) and quantify them (in terms of linear dynamic ranges in peak currents), without the need for preliminary separation steps. Such ability has now been tested on a series of chiral DOPA-related molecules, from phenolic amino acid tyrosine (together with its methyl ester) to catecholic amino acid DOPA (together with its methyl ester), to catecholamine epinephrine (adrenaline). The wide-range enantioselectivity of the new inherently chiral electrode surfaces is fully confirmed, as large peak potential differences are obtained for probe enantiomers of the whole series working in common aqueous buffers. Moreover, interesting modulating effects on enantiodiscrimination can be observed as a function of both molecular structure and pH. Graphical abstract Inherently chiral thiophene-based electrodes at work with pharmaceutically relevant probes.

Self‐Standing Membranes Consisting of Inherently Chiral Electroactive Oligomers: Electrosynthesis, Characterization and Preliminary Tests in Potentiometric Setups

“…[18] The resulting modified electrodes showed impressive enantiodiscrimination performances with different chiral probes in voltammetric experiments. [18][19][20] Most interestingly, we are now showing that electrosynthesized oligo-BT 2 T 4 films can be peeled off from the electrode surface after their growth, yielding self-standing chiral membranes. Consisting of open and closed oligomers combining inherent chirality with electroactivity, with both features being indissolubly connected with the π-conjugated oligomeric backbone, they can indeed be regarded as an attractive tool for electroanalytical applications.…”

“…with λ = ion molar conductances, approximating λ values with tabulated λ°ones, we get for KCl [Eq. (20)]:…”

“…[16,17] In "inherently chiral" polyconjugated molecular materials both chirality and key functional properties originate from the same structural element, which can coincide with the whole main molecular scaffold, featuring a tailored torsion with an energy barrier too high to be overcome at room temperature; regioregularity enables propagating such property into foldamer-/helical-like macro-or supramolecular structures. [16,17] Large potential differences have been observed between enantiomers of various chiral probes in voltammetry experiments implementing inherent chirality at electrode j solution interphases by modifying achiral electrodes with enantiopure inherently chiral electroactive films electrodeposited from different heterocycle-based monomers with atropoisomeric cores (i. e. consisting of two moieties with hindered reciprocal rotation) [18][19][20][21][22] or with helical shape (i. e. tetrathiahelicene). [23] Among them, the parent and so far more extensively studied one is 2-[5-(2,5'-bithienyl)]thianaphthene BT 2 T 4 (Scheme 1) [18][19][20] consisting of a bibenzothiophene atropoisomeric core (with approximately 80°torsional angle and 167 kJ mol À 1 related energy barrier [18] ) and two bithiophene wings with homotopic α thiophene terminals available for oligomerization.…”

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

“…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.…”

“…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.…”