Selective Electrochemical Recognition of the α‐Naphthol Isomer and In Situ Immobilization of Naphthoquinones for Tunable Electrocatalysis

Abstract

Fits like a glove: Separationless and selective electrochemical oxidation of the α-naphthol (α-NAP) isomer yields naphthoquinone species on the surface of multiwalled carbon nanotubes, which can further catalyze the electro-oxidation of NADH and hydrazine at different potentials. The β-NAP isomer failed to show any such electro-oxidation.

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

“… Dopamine Au@Dopamine-SAM – 59 ± 0.05 NADH 38 2. α-Naphthol GCE/MWCNT@np-quinone − 100 ± 5 80 NADH, Hyd 39 3. Quinoline GCE/MWCNT@QLO − 450 ± 5 64 Hyd 40 4.…”

In situ stabilization of hydroxylamine via electrochemical immobilization of 4-nitrophenol on GCE/MWCNT electrodes: NADH electrocatalysis at zero potential

“…4 Recently, our group has demonstrated rapid and reversible electrochemical methods for the immobilization of various phenol-based organic compounds via the stabilization of electrogenerated intermediate species onto carbon nanotube (CNT) modied glassy carbon electrodes (GCEs). [10][11][12][13] The phenolic hydroxyl groups and the ortho-or paracarbons of the aromatic ring play key roles in such immobilization processes. In addition, the aromatic nitro groups, along with the phenolic groups, can easily be reduced electrochemically to form aminophenols.…”

In Situ Structural Elucidation and Selective Pb2+ Ion Recognition of Polydopamine Film Formed by Controlled Electrochemical Oxidation of Dopamine

“…Note that both DA-adsorption and -solution based techniques have shown qualitatively similar e-pDA product formation. The following Sauerbrey equation is referred for the conversion of frequency to mass change: − mass change (Δ m ) = (−1/2) f o –2 Δ f A k ρ 1/2 , where A is the area of the EQCM-Au (0.196 cm 2 ), ρ = density of the crystal (2.648 g cm –3 ), k = shear modulus of the crystal (2.947 × 10 11 g cm S 2– ), Δ f = measured frequency change, and f 0 = oscillation frequency of the crystal (8 MHz). A Δ f change of 1 Hz is equivalent to a Δ m value of 1.4 × 10 –9 g in mass.…”

“…4,11,12,24,25 Indeed, based on several ex situ characterizations using instruments like time-of-flight secondary ion mass spectrometry (TOF-SIMS), 26 high-performance liquid chromatography, 27 positive ion mode electrospray (ES+) ionization coupled high-resolution mass spectrometry (HRMS), 23 matrix-assisted laser desorption/ionization (MALDI)-MS, 22 solid state nuclear magnetic resonance, 22 and X-ray photoelectron spectroscopy, 26 the following mechanisms and structural information about pDA have been postulated: oxidation of dopamine to 5,6-dihydroxy (DHI) and 5,6-indolequinone (IDQ) intermediates followed by (i) selfassembling with dopamine via π−π and hydrogen bondings; 22 (ii) covalent linking between the benzene rings of several DHI/ IDQ and dopamine units with different degrees of saturation; 23 In general, the problems faced while characterizing the pDA by conventional techniques are as follows: (i) sample collection methodrather than analysis of the pDA film directly, pDA aggregates collected from the dopamine solution in the presence of dissolved oxygen 22,23 or chemical-oxidant such as ammonium persulfate, 29 Ce(IV) ion, 30 sodium hypochlorite, 22 and periodate 27 and solid surface (TiO 2 and glass) 23,28 have been used; (ii) hygroscopic and insolubility nature of the pDA (it is highly insoluble in water, acid, moderate alkaline conditions, and all common organic solvents); 11,12,22 (iii) disruption of the hydrogen bonding and in turn structure by organic solvent used to isolate the partial structure of the pDA; (iv) ambiguity in the structure of the off-line isolated products/aggregates with the original solid state pDA. 28 Meanwhile, our group has been working with the in situ electrochemical quartz crystal microbalance (EQCM) technique, which contains a sensitive piezoelectric quartz crystal, for identifying intermediates of several complex electro-organic reactions such as phenol oxidation to hydroquinone, 31 azo-bond cleavage via aniline intermediate, 32 and quinoline-quinone product formation from quinoline 33 by performing c...…”

“…In general, the problems faced while characterizing the pDA by conventional techniques are as follows: (i) sample collection methodrather than analysis of the pDA film directly, pDA aggregates collected from the dopamine solution in the presence of dissolved oxygen , or chemical-oxidant such as ammonium persulfate, Ce­(IV) ion, sodium hypochlorite, and periodate and solid surface (TiO 2 and glass) , have been used; (ii) hygroscopic and insolubility nature of the pDA (it is highly insoluble in water, acid, moderate alkaline conditions, and all common organic solvents); ,, (iii) disruption of the hydrogen bonding and in turn structure by organic solvent used to isolate the partial structure of the pDA; (iv) ambiguity in the structure of the off-line isolated products/aggregates with the original solid state pDA . Meanwhile, our group has been working with the in situ electrochemical quartz crystal microbalance (EQCM) technique, which contains a sensitive piezoelectric quartz crystal, for identifying intermediates of several complex electro-organic reactions such as phenol oxidation to hydroquinone, azo-bond cleavage via aniline intermediate, and quinoline-quinone product formation from quinoline by performing controlled electrochemical oxidation/reduction reactions of the precursors on a graphitic carbon electrode, like MWCNT chemically modified electrodes. Due to the strong π–π interaction, MWCNT helps trap the intermediates that have been formed on the interface of the electrochemical reaction.…”