Regioselective Electrochemical Oxidation of One of the Identical Benzene Rings of Carbazole to 1,4-Quinone on the MWCNT Surface and Its Electrocatalytic Activity

Abstract

Carbazole-1,4-quinone is a key structural unit of naturally occurring carbazole-quinone alkaloids, for instance, 3-methyl carbazole-1,4-quinone (Murrayaquinone), that are widely used in pharmaceutics and medicine. These compounds are generally synthesized from tetrahydro ketone derivatives by multistep synthetic routes. Until now, there is no direct method reported for the partial oxidation of carbazole to carbazole-1,4-quinone by chemical, biochemical, or electrochemical reaction routes. Literature survey on the oxidation of carbazole and its derivatives suggests that polymeric or oligomeric forms are the sole products, but not, monomeric carbazole-1,4-quinone. Herein, we report a simple electrochemical oxidation of surface-confined carbazole to a highly redox active carbazole-mono-1,4-quinone, where only one of the identical benzene rings of carbazole gets selectively oxidized, on a cathodically activated multiwalled carbon nanotube (MWCNT) surface anchored to a glassy carbon electrode (GCE/MWCNT*@Car-Qn; * = cathodically activated, Car-Qn = carbazole-1,4-quinone) in pH 7 phosphate buffer solution, unlike the time consuming conventional multistep synthetic routes. The GCE/MWCNT*@Car-Qn showed a well-defined surface-confined peak at E 1/2 = 215 ± 5 mV versus Ag/AgCl with a Nertisan pH dependence in character. This new hybrid system showed efficient electrocatalytic oxidation and sensing of hydrazine in a neutral pH solution. No such electrochemical features were noticed for carbazole on the GCE surface. Collective physico-chemical (scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, HRMS, and NMR) and electrochemical characterizations of the MWCNT*@Car-Qn formation process revealed that in situ formed H2O2 at cathodic potentials and iron impurity in MWCNT, forming electro-Fenton species, are responsible for the selective electrochemical oxidation of carbazole to carbazole-1,4-quinone on the MWCNT surface.

A prototype device of microliter volume voltammetric pH sensor based on carbazole–quinone redox-probe tethered MWCNT modified three-in-one screen-printed electrode

“… Hemoglobin GCE/GMC/Heme-Nf − 380 30 ± 0.12 H 2 O 2 43 7. Carbazole GCE/MWCNT@Car − 215 ± 5 − 59 Hyd 44 8. Anthraquinone GCE/AQ@f-MWCNT − 285 − 58 DO, H 2 O 2 45 9.…”

Square-Wave Voltammetric Detection of Zn(II) and Cd(II) with a Graphite/Carbon Paste Electrode Decorated with 2-Hydroxy-1,4-naphthoquinone

“…These results highlight the paramount role of π–π stacking in the formation of the supramolecular assemblies and they also confirm that noncovalent interactions rule the adsorption process at the G/HNFQ-CPE/solution interphase. In this regard, Kumar and co-workers suggest that carbazole and multiwalled carbon nanotubes interact through π–π stacking, which represents the unique structural interaction that could lead to the experimentally observed restricted electrooxidation of the carbazole molecule leading to 1,4-quinone …”

“…25−27 GCE electrodes modified with naphthoquinone (anthraquinone) for the detection of [Ni(CN) 4 ] 2− and [Cu(CN) 3 ] 2− , has been recently reported by our group 26,27 Among other supports based on carbons materials modified with Q molecules, we can mention the exfoliated graphite functionalized with redoxactive Q, 28 which enables the electrocatalysis of ascorbic acid oxidation, and the multiwalled carbon nanotubes (MWCNTs) anchored to a glassy carbon electrode, which are able to oxidize carbazole to carbazole-mono-1,4-quinone. 29 For the latter material, it has been proposed that a strong π−π interaction occurs, given the structural compatibility of benzene rings between MWCNTs and Q molecules. In the field of energy storage, it has been demonstrated that electroactive molecules incorporated on carbon materials can significantly improve their charge storage properties.…”

“…Quinone molecules (Q) have demonstrated their adsorption capacity on glassy carbon electrode surfaces (GCE), as well as an electron acceptor behavior in several reactions. − GCE electrodes modified with naphthoquinone (anthraquinone) for the detection of [Ni­(CN) 4 ] 2– and [Cu­(CN) 3 ] 2– , has been recently reported by our group , Among other supports based on carbons materials modified with Q molecules, we can mention the exfoliated graphite functionalized with redox-active Q, which enables the electrocatalysis of ascorbic acid oxidation, and the multiwalled carbon nanotubes (MWCNTs) anchored to a glassy carbon electrode, which are able to oxidize carbazole to carbazole-mono-1,4-quinone . For the latter material, it has been proposed that a strong π–π interaction occurs, given the structural compatibility of benzene rings between MWCNTs and Q molecules.…”

Accelerated Electrosynthesis Development Enabled by High-Throughput Experimentation

“…45 Nevertheless, such a challenge has been greatly alleviated by the recent development of electrocatalysts. 46 Redox-active electrocatalysts can enable the generation of reaction intermediates at reduced potentials with improved chemo-, 47,48 regio-, 49,50 and stereo-selectivity. 51,52 Homogeneous electrocatalysts (sometimes referred as mediators) are often the first option for a variety of electroorganic reactions because of their high adaptability and selectivity.…”