Effective Enantiodiscrimination in Electroanalysis Based on a New Inherently Chiral 1,1′-Binaphthyl Selector Directly Synthesizable in Enantiopure Form

Abstract

Enantioselective electroanalysis, which aims to discriminate the enantiomers of electroactive chiral probes in terms of potential difference, is a very attractive goal. To achieve this, its implementation is being studied for various "inherently chiral" selectors, either at the electrode surface or in the medium, yielding outstanding performance. In this context, the new inherently chiral monomer Naph2T4 is introduced, based on a biaromatic atropisomeric core, which is advantageously obtainable in enantiopure form without HPLC separation steps by a synthetic route hinging on enantiopure 2,2’-dibromo-1,1’-binaphthalenes. The antipodes of the new inherently chiral monomer can be easily electrooligomerized, yielding inherently chiral electrode surfaces that perform well in both cyclic voltammetry (CV) enantiodiscrimination tests with pharmaceutically interesting molecules and in magnetoelectrochemistry experiments.

Modulating the Enantiodiscrimination Features of Inherently Chiral Selectors by Molecular Design: A HPLC and Voltammetry Study Case with Atropisomeric 2,2’‐Biindole‐Based Monomers and Oligomer Films

“…A peculiarity of 2,2′‐biindole monomers[ 1 , 12 ] is that, unlike other atropisomeric monomer families so far studied,[ 6 , 9 , 10 , 11 ] first oxidations are typically localized mostly in the monomer core, on the two very electron rich pyrrolic units behaving as two equivalent reciprocally interacting redox centers. As a consequence, a twin first oxidation peak system is observed in voltammetry, [27] of reversible character since the radical cations resulting from oxidation are stable being too far from the monomer terminals to give coupling.…”

“…Redox features of the monomers were studied by cyclic voltammetry, also supported by DFT calculations (detailed results and discussion in chapter SI.2 in the Supporting Information), taking as benchmark the prototype case of parent monomer (N-Me-IND) 2 -T 4 in the same conditions . [1] A peculiarity of 2,2'-biindole monomers [1,12] is that, unlike other atropisomeric monomer families so far studied, [6,[9][10][11] first oxidations are typically localized mostly in the monomer core, on the two very electron rich pyrrolic units behaving as two equivalent reciprocally interacting redox centers. As a consequence, a twin first oxidation peak system is observed in voltammetry, [27] of reversible character since the radical cations resulting from oxidation are stable being too far from the monomer terminals to give coupling.…”

“…In fact, unlike the case of for example current or conductivity differences, it can enable direct enantiomer identification (with possible concurrent quantification from the peak current) as well as selective enantiomer electrochemical activation. [5] Focusing on atropisomeric selectors, attractive enantiodiscrimination performances have been observed with 3,3'bibenzothiophene, [6,9] 3,3'-bithiophene [10] and 1,1'-binaphthyl [11] systems, besides the above 2,2'-biindole one. [1,12] However, biindole systems offer a peculiar important advantage, namely, very easy modulation of functional properties through easy design tuning.…”

“…Focusing on atropisomeric selectors, attractive enantiodiscrimination performances have been observed with 3,3′‐bibenzothiophene,[ 6 , 9 ] 3,3′‐bithiophene [10] and 1,1′‐binaphthyl [11] systems, besides the above 2,2′‐biindole one. [ 1 , 12 ] However, biindole systems offer a peculiar important advantage, namely, very easy modulation of functional properties through easy design tuning.…”

Trópos and Átropos Biindole Chiral Electroactive Monomers: A Voltammetry and HPLC Comparative Insight

“…In particular, it has been so far implemented exploiting monomers based on four atropisomeric biheteroaromatic cores, i. e . 3,3’‐bibenzothiophene, [3,9,10] 3,3’‐bithiophene, [4] 2,2’‐biindole [5–7] and 1,1’‐binaphthyl [8] ones, in all cases combined with symmetrical oligothiophene‐based terminals (some examples are reported in Figure 1). Besides their above highly successful application for chiral electroanalysis, such monomers are also attractive model systems in the frame of intramolecular charge communication studies.…”