Reversible Redox Systems Research Articles

Synthesis and Characterization of A Fascinating Coordination Polymer Metal-Organic Framework Featuring Cobalt (II) and 4,4'-Bipyridine

ABSTRACT. This investigation delineates the fabrication, comprehensive characterization, and electrochemical evaluation of a one-dimensional Cobalt-based Metal-Organic Framework (Co-MOFs), constructed from 4,4’-Bipyridine ligands and Cobalt (II) ions. The study aimed to perfect the synthesis protocol, elucidate the structural and compositional attributes of the resultant MOF, and probe its electrochemical performance. Utilizing the reflux method, renowned for its efficacy and eco-compatibility, we synthesized the MOF and affirmed its formation through a suite of analytical techniques, including Infrared (IR) spectroscopy, Ultraviolet-Visible (UV-Vis) spectroscopy, Atomic Absorption Spectroscopy (AAS), and electrical conductivity measurements. The synthesized Co-MOFs, chemically notated as [Co2(4,4'-bpy)2(SO4)(H2O)2]SO4·H2O, manifested as a one-dimensional coordination polymer. X-ray Diffraction (XRD) analysis unveiled its monoclinic crystallinity within the C2 space group. Electrochemical characterization uncovered a reversible redox system, evidenced by a robust peak current ratio (IPa/IPc = 7.5), indicative of efficient electron transfer processes. Furthermore, the Co-MOFs significantly augmented the kinetics of the oxygen evolution reaction (OER) in an alkaline aqueous solution, highlighting its potential as a superior catalyst in energy-related electrochemical applications. This work not only contributes to the field of MOF synthesis but also sets the stage for future explorations into their practical applications in sustainable energy systems. Keywords: Electrochemical properties, metal-organic framework, oxigen evolution reaction catalyst, 4,4’-bipyridine.

Synthesis, Electronic, and Antibacterial Properties of 3,7-Di(hetero)aryl-substituted Phenothiazinyl N-Propyl Trimethylammonium Salts.

In this study, a library of 3,7-di(hetero)aryl-substituted 10-(3-trimethylammoniumpropyl)10H-phenothiazine salts is prepared. These title compounds and their precursors are reversible redox systems with tunable potentials. The Hammett correlation gives a very good correlation of the first oxidation potentials with σp parameters. Furthermore, the title compounds and their precursors are blue to green-blue emissive. Screening of the salts reveals for some derivatives a distinct inhibition of several pathogenic bacterial strains (Mycobacterium tuberculosis, Staphylococcus aureus, Escherichia coli, Aconetobacter baumannii, and Klebsiella pneumoniae) in the lower micromolar range.

Dicationic Acridinium/Carbene Hybrids as Strongly Oxidizing Photocatalysts.

A new design concept for organic, strongly oxidizing photocatalysts is described based upon dicationic acridinium/carbene hybrids. A highly modular synthesis of such hybrids is presented, and the dications are utilized as novel, tailor-made photoredox catalysts in the direct oxidative C-N coupling. Under optimized conditions, benzene and even electron-deficient arenes can be oxidized and coupled with a range of N-heterocycles in high to excellent yields with a single low-energy photon per catalytic turnover, while commonly used acridinium photocatalysts are not able to perform the challenging oxidation step. In contrast to traditional photocatalysts, the hybrid photocatalysts reported here feature a reversible two-electron redox system with regular or inverted redox potentials for the two-electron transfer. The different oxidation states could be isolated and structurally characterized supported by NMR, EPR, and X-ray analysis. Mechanistic experiments employing time-resolved emission and transient absorption spectroscopy unambiguously reveal the outstanding excited-state potential of our best-performing catalyst (+2.5 V vs SCE), and they provide evidence for mechanistic key steps and intermediates.

Electrochemistry of Al3+- Catechol System: Kinetics Vs. Thermodynamics (A1-Triple I)

Carbonyls, and quinones among them in particular, occupy a place of choice among organic reversible redox systems for electrocatalysis [1] and energy storage [2]. Their electrochemical behavior is marked by coupled proton and electron transfer (CPET) [3-5]. We have studied this subject in the context of flow batteries [6] and hydrogen carriers [7]. On the other hand, metal ion – catecholate (o-dioxolene) binding [8] attracts attention in different and rather independent domains, including active materials for metal-ion and redox flow batteries [2]. Redox transformations of o-dioxolene-metal complexes are therefore coupled to competitive binding with metal ion and proton at the electrochemical timescale, raising the complexity in the system above that of CPET. These effects have not received proper attention e.g. in aqueous metal-ion battery research.The subject of this communication is the electrochemistry of Al3+ - catechol system in aqueous solution. We discuss the conditions and measurable electrochemical signatures of complex formation, as well as the role of buffer. We explain why our observations are contrasting those on catechol containing polymers proposed for universal metal-ion batteries [9, 10] by considering which reactions attain equilibrium and which are obeying kinetics only.[1] K. Tammeveski et al. J. Electroanal. Chem. 2001, 515 , 101; DOI: 10.1016/S0022-0728(01)00633-7[2] B. Häupler et al. Adv. Energy Mater. 2015, 5 , 1402034; DOI: 10.1002/aenm.201402034[3] M. Quan et al. J. Am. Chem. Soc. 2007, 129 , 12847; DOI: 10.1021/ja0743083[4] J. Wang et al. J. Electroanal. Chem. 2007, 601 , 107; DOI: 10.1016/j.jelechem.2006.10.036[5] Q. Lin et al. J. Phys. Chem. C 2015, 119 , 1489; DOI: 10.1021/jp511414b[6] H. Ghorbani Shiraz et al. J. Energy Chem. 2022, 73 , 292; DOI: 10.1016/j.jechem.2022.06.015[7] M. Vagin et al. Adv. Funct. Mat. 2020, 30 , 2007009; DOI: 10.1002/adfm.202007009[8] R. Maskey et al. Encycl. Inorg. Bioinorg. Chem.; DOI: 10.1002/9781119951438.eibc2810[9] N. Patil et al. ACS Appl. Energy Mater. 2019, 2, 3035; DOI: 10.1021/acsaem.9b00443[10] K. Pirnat et al. Macromolecules 2019, 52, 8155; DOI: 10.1021/acs.macromol.9b01405

Electrochemical polymerization, characterization and spectroelectrochemical studies of a N-substituted-2,5-dithienil-pyrrole bearing an aniline moiety for cross-linking (TPTBA)

N-substituted-2,5-dithienil-pyrroles have demonstrated to be an interesting alternative for the preparation of π-conjugated polymers with good electrochromic properties. Herein the 4-(4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzyl)aniline (TPTBA) was chemically synthetized and its electrochemical behavior and polymerization was studied. The obtained film was characterized by electrochemical and spectroelectrochemical methods. Poly-TPTBA presents a quasi-symmetrical reversible redox system characteristic to well-ordered systems. This explained by the presence of the aniline moiety which can favor a cross-linking of the polymer backbone. Spectroelectrochemical studies reveal a moderate rapid electrochromic transition between both redox states, requiring 2 seconds to alternate between each color: 430 nm (discharged state) and 800 nm (charged state).

Synthesis and Electronic Properties of Conjugated syn,syn‐Dithienothiazine Donor‐Acceptor‐Donor Dumbbells

AbstractA series of conjugated syn,syn‐dithienothiazine donor‐acceptor‐donor dumbbells is readily synthesized by Suzuki coupling or a one‐pot α‐lithiation‐zincation‐Negishi coupling sequence in moderate to good yield. The title compounds are all electron‐rich reversible oxidizable redox systems with a relatively narrow range of oxidation potentials according to cyclic voltammetry. UV/Vis and fluorescence spectroscopy however show a significant effect of the electronic nature of the conjugated bridging system on absorption and emission characteristics. Furthermore, a highly polar excited state can be corroborated by Lippert‐Mataga analysis of the emission solvatochromicity as well as by TD‐DFT calculation of absorption and emission maxima, which classify these dumbbell systems as redox active, luminescent low band gap chromophores with experimentally determined optical band gaps between 2.20 and 2.50 eV.

Reversible Redox System of 2-Oxypyritriphyrin(1.2.1) Accompanying Interconversion between 3-Pyridone and 3-Hydroxypyridine Units.

To develop a system in which a π-conjugation circuit switched by a redox reaction between 3-pyridone and 3-hydroxypyridine, a ring-contracted analog of oxypyriporphyrin, 2-oxypyritriphyrin(1.2.1) was synthesized for the first time. 2-Oxypyritriphyrin(1.2.1) contains a 14π aromatic conjugation circuit with the keto-form of the 3-oxypyridine ring. When 2-oxypyritriphyrin was treated with NaBH4 , not only the 3-oxypyridine group, but also the meso-carbons were also reduced to give a colorless porphyrinogen analog. The reduced compound could be oxidized again to provide 2-oxypyritripyhrin in a reversible manner.

Poly(benzoquinonyldisulfide) as organic positve electrode for Mg and Li batteries

The study of innovative solutions to replace current lithium technology is being carried out at a rapid pace. One of the proposed solution is the development of magnesium batteries, especially organic positive electrode which can exhibit high capacity and capacity retention. In this field, the electrochemical responses of poly(benzoquinonyldisulfide) (PBQDS) in lithium and magnesium cells were investigated in diglyme and sulfolane based electrolytes. Using cavity micro-electrode, similar response was obtained by cyclic voltammetry with the presence of a reversible redox system at 3.5 V vs. Li+/Li or 2.2 V vs. Mg2+/Mg. Using sulfolane + LiTFSI (bis(trifluoromethane)sulfonamide lithium salt) electrolyte, the PBQDS active material achieves a stable capacity of 140 mAh g−1 at C/20. In Mg cell, even if the starting capacity is high, a capacity decrease is noticed along time presumably due to the progressive Mg2+ trapping within the quinone structure. The addition of solvating additive permits to partially mitigate this drawback.

A new electrochemical sensor based on oxidized capsaicin/multi-walled carbon nanotubes/glassy carbon electrode for the quantification of dopamine, epinephrine, and xanthurenic, ascorbic and uric acids

Abstract Capsaicin (CAP) was used as a redox mediator and added to multi-walled carbon nanotubes (MWCNT) modified glassy carbon electrode (GCE), to be used in the quantitation of xanthurenic (XA), ascorbic (AA) and uric (UA) acids, along with the neurotransmitters dopamine (DA) and epinephrine (EP), one at a time, using cyclic voltammetry and chronoamperometry, in buffered aqueous solutions, pH 7.0. The presence, after oxidation of CAP on MWCNT/GCE, of two reversible redox systems, which can be understood through the formation of a reversible surface-confined quinone systems, is important for the redox catalysis. The obtained analytical curves for XA, AA, DA, EP and UA showed linear ranges, between 10 and 95, 5–75, 5–115, 50–1150 and 5–70 μmol L−1, respectively. The detection limits were 8.76, 1.95, 1.80, 7.20 and 1.56 μmol L−1 for XA, AA, DA, EP and UA, respectively. This oxidized CAP-based platform is reported for the first time and is able to detect the analytes at a micromolar level.

Anti‐migration and Combustion Catalytic Performances of Ferrocenyl Compounds of Anilines and Alkylamines Synthesized by Click Reaction

To enhance anti‐migratory performance and combustion catalytic activities of neutral ferrocene‐based burning rate catalysts (BRCs), nine ferrocenyl 1,2,3‐triazolyl compounds of anilines and aliphatic amines (Fc‐ATAZs, 1–9) were synthesized by click reaction and characterized by NMR, UV/Vis, FT‐IR, and MS. TG and DSC studies confirmed that the Fc‐ATAZs are highly thermal stable. Cyclic voltammetry results implied that 1 and 6 are reversible redox systems. The anti‐migration and anti‐volatility tests showed that the Fc‐ATAZs are low‐migratory and low‐volatile compounds.Combustion catalytic activity results of the Fc‐ATAZs revealed that they are highly active for promoting thermal disintegration of AP, RDX and HMX. Compounds 3, 2 and 8 can increase released heats of AP, RDX and HMX, respectively, by 132 %, 112 % and 36 %, respectively, being the highest in each case. Most of them are more active than the reported analogs derived from phenols and benzoic acids. They, except 9, are more active than catocene and can be used as potential BRCs in composite solid propellants.

Enhancing segmental compatibility and tuning the structure-property relationship in ferrocenylsilane tethered polyurethane

This article addresses the effect of enhanced segmental mixing on various physical properties of ferrocenylsilane tethered polybutadiene based polyurethane (PU). To study this, 2-(ferrocenylpropyl) dimethylsilane (FPDS) has been grafted to the pendant vinyl double bond of hydroxyl terminated polybutadiene (HTPB) and 2, 4-dinitrobenzene attached HTPB (HTPB-DNB) through hydrosilylation reaction and then this resulting diols (FPDS-g-HTPB and FPDS-g-HTPB-DNB) were polymerized with isophorone diisocyanate (IPDI) to obtain FPDS-g-HTPB-PU and FPDS-g-HTPB-DNB-PU. Spectral (NMR, IR) analysis, molecular weight measurements and estimation of free hydroxyl contents were carried out to confirm the formation of these new diols. The careful variation of the grafting condition altered the extent of FPDS tethering on the diols which resulted varying amount of Si and Fe contents in these modified HTPBs. Density functional theory (DFT) calculation revealed the presence of various interactions of Si with various functionalities including ferrocene of the chain which resulted highly cross-linked polymer matrix. Cyclic voltammetry (CV) measurements of FPDS-g-HTPB-DNB displayed non-Nerstain reversible redox system with slow electron transfer process owing to the presence of DNB. Further, the PUs obtained from these HTPBs were prepared and characterized thoroughly in terms of thermal, mechanical, structural and tensile properties to study the segmental mixing between hard and soft segments of PUs owing to the presence of Si, Fe and DNB in the PU chain. Higher degree of segmental mixing was noticed when Si, Fe in the diol increased and also presence of DNB in the diol played a significant role in inducing the segmental mixing. The co-existence of segmental mixing and phase separation has been confirmed by small-angle x-ray scattering studies which further reaffirmed by FESEM analysis. Finally, composite solid propellants (CSPs) were prepared from these modified HTPBs and burn rate measurements were carried out. We found that CSPs obtained from FPDS-g-HTPB-DNB displayed ~10% higher burn rate than the CSP made from bare HTPB-DNB.

Electrochemical oxidation of o-phenylenediamine and 1,3 dihydrospiro[benzo[d]imidazole-2,1′-cyclohexane]. A comprehensive study and introducing a novel case of CE mechanism

Electrochemical behavior of o-phenylenediamine (PDA) and 1,3-dihydrospiro[benzo[d]imidazole-2,1′-cyclohexane] (DBI) was extensively studied in water and water/ethanol mixture using different voltammetric techniques. Our data showed that the oxidation of PDA is highly dependent on pH, follows a complex pattern and participate in following chemical reactions such as polymerization. Unlike acidic and neutral solutions, in highly alkaline solutions (pH ≥ 11), however, PDA shows a simple reversible redox system. Contrary to PDA, the presence of the cyclohexyl group in the structure of DBI makes its oxidation pattern less complex than that of PDA and causes the molecule less susceptible to participate in the following chemical reactions. Our results showed that DBI in aqueous solutions is unstable and undergoes acid catalyzed hydrolysis to give PDA. The instability of DBI in acidic solutions is so high that it turns completely into PDA in the time scale of the voltammetric experiments. Different from acidic media, in alkaline solutions (pH ≥ 9.0), the hydrolysis rate is slow, so that DBI shows a reversible redox couple. The kinetic of DBI hydrolysis using differential pulse voltammetry method was studied and the apparent hydrolysis rate constants (khobs) were found by assuming the pseudo-first order rate kinetics. In addition, in this work, adsorption activity, diffusion coefficient and pKa values of DBI and PDA species were determined and the Pourbaix diagrams for these compounds were constructed. The most important part of this paper is devoted to introducing a rare type of mechanism in electrochemical reactions. In this way, the rarely studied mechanism has been introduced in relation to the reaction of PDA with cyclohexanone and the formation of DBI.

Electrochemistry of bi-redox ionic liquid from solution to bi-functional carbon surface

In this work, bi-redox molecule based ionic liquid was synthesized. Ferrocene donor group and anthraquinone acceptor group were linked to imidazolium cation. Next, the electrochemistry of the as synthesized molecule was investigated demonstrating the presence of two reversible redox systems. Furthermore, the diffusion coefficient and electron transfer rate constant were measured using the ferrocene oxidation and the anthraquinone reduction. Besides that, the bi-redox molecule was immobilized onto carbon electrode using two steps procedure based on the oxidative grafting of primary layer bearing diazonium head group followed by Gomberg-Bachmann coupling surface reaction. The surface characterization confirms the attachment of the imidazolium bi-redox molecule as well as the presence of the labile anion within the layer. Interestingly, the electrochemical investigations confirm the bi-redox grafting with an equi-distribution of the electron donor and acceptor within the attached layer. Finally, the attached layer exhibits an enhancement of double-layer capacitance which is correlated to the increase of the charge density and ionic property of the layer.

Connection of CVs and impedance spectra of reversible redox systems, as used for the validation of a dynamic electrochemical impedance spectrum measurement system

With the purpose of fast characterization of electrode reactions, a dynamic electrochemical impedance spectrum (dEIS) measurement system has been assembled which permits the continuous collection of audio-frequency impedance spectra while performing cyclic voltammetry measurements with the usual scan rates of up to 200 mV/s. The performance of this system was tested by analyzing the CV curves and impedance spectra taken simultaneously in ferro-/ferricyanide containing aqueous solutions yielding an experimental demonstration of the connection of the semi-integrated reversible voltammograms and the Warburg coefficients.Graphical abstract

2‐[(4‐Aminobutyl)ferrocenylmethylidene]‐5,6‐dimethoxy‐1‐indanone derivatives: Synthesis, characterization, and investigation of electro‐optical properties

A ferrocenyl‐based, chromophore‐containing 1‐indanone derivative was synthesized through crotonic condensation between 4‐chlorobutylferrocenecarboxaldehyde and 5,6‐dimethoxy‐1‐indanone followed by the nucleophilic substitution of chlorine atom of the obtained dyad with different aromatic and aliphatic amines. The electrochemical and optical properties of the synthesized compounds were investigated to explore the relationship between their structures and optical and electrochemical properties. The bandgaps determined from optical absorption spectra ranged from 2.05 to 2.15 eV. The important electrochemical parameters, including the peak potential separation, peak current ratios, and the dependence of peak currents on the scan rate, were studied. Results showed an electrochemically reversible redox system with diffusion‐controlled redox process for the synthesized compounds. The study of quantum chemistry was performed on the synthesized compounds using the density functional theory approach. The B3LYP method and 6‐311 G(d) basis set were used for optimizing the structures in the gas phase. The theoretical and experimental results show that these compounds can be considered as candidates to be used in optical applications.

Novel ferrocene-based 1,2,3-triazolyl compounds: Synthesis, anti-migration properties and catalytic effects on oxidizers during combustion

To tackle high-migratory and high-volatility problem of marketed neutral ferrocene-based burning rate catalysts, twenty-one ferrocene-based 1,2,3-triazolyl compounds (Fc-TAZs) were synthesized by click reaction and characterized completely by NMR, FT-IR, UV–Vis and elemental analysis. In addition, four compounds were structurally confirmed by single crystal X-ray diffraction. TG and DSC analysis showed that the new Fc-TAZs are of high thermal stability. Cyclic voltammetry investigations suggested that more than half of the Fc-TAZs are reversible redox systems. Anti-migration and anti-volatility tests revealed that all the Fc-TAZs display, on comparison with Catocene, extremely low volatility and migration tendency due to the appearance of polar oxygen and nitrogen atoms in their molecules. Catalytic activity tests of the novel Fc-TAZs towards the thermal decomposition of oxidizers, evaluated by TG and DSC techniques, indicated that all Fc-TAZs exert great effects on the thermal disintegration of AP and compounds 5, 7 and 11 can promote the thermal decomposition of HMX during combustion.

Formation and Isolation of a Four-Electron-Reduced Porphyrin

Porphyrins are well known as 18π conjugated aromatic macrocycles with high stability and also as redox-active compounds exhibiting reversible multi-redox processes. In this study, we demonstrated that the two-electron reduction of a diprotonated dodecaphenylporphyrin derivative by Na2S2O4 in DMSO afforded the corresponding isophlorin (Iph) selectively. Formation of Iph was confirmed by spectroscopic measurements and the isolation of tetra-methylated Iph. Further two-electron reduction of Iph was examined using excess Na2S2O4 in DMSO to obtain an unprecedented four-electron reduced porphyrin (IphH2 ), which was successfully characterized by spectroscopic analysis and X-ray crystallography. IphH2 showed a unique conformation and could be oxidized to reproduce the starting porphyrin by the chemical oxidation, allowing us to establish a proton-coupled four-electron reversible redox system.

Three-dimensional electrocatalytic surface based on an octasilsesquioxane dendrimer for sensing applications

Ferrocenyl dendrimers based on octasilsesquioxane cores electrodeposited on the electrode surface form a 3D structured film with an interesting highly effective surface. This property, together with the presence of interacting ferrocenes, make these films useful electrode materials for two-electron exchanges. This work presents the morphologic and kinetic studies of electrodes modified with a second-generation octasilsesquioxane dendrimer with 32 ferrocenyl terminal groups and their application in the determination of l-tryptophan (TR). The modified electrode shows a reversible redox system without kinetic limitations and allows to determine TR in two wide linear ranges (from 0.06 to 100μM and from 100 to 440μM), with low detection limit (0.01μM). In addition, the modified electrode is successfully applied to detect TR in presence of ascorbic acid, dopamine and uric acid and to their simultaneous determination. The new device has been also applied to the direct determination of TR in pharmaceutical and biological samples with satisfactory results.

Fabrication of silver nanoparticles in titanium dioxide/poly(vinyl alcohol) alternate thin films: A nonenzymatic hydrogen peroxide sensor application

Silver nanoparticles (AgNPs) were readily synthesized in TiO2/poly(vinyl alcohol) (PVA) ultrathin films, which is alternately assembled with Ti(O-nBu)4 and PVA via a surface sol-gel process. The photochemical reduction of as-embedded Ag+ ions in the film led to the formation of well-controllable AgNPs in size, distribution and electrochemical properties. AgNP-immobilized TiO2/PVA films were characterized by quartz crystal microbalance measurements, ultraviolet–visible (UV–vis) spectroscopy, atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical measurements. The increase in thickness of TiO2/PVA hybrid films led to an increase in the surface plasmon resonance peak, showing a blueshift in UV–vis absorption. As the alternate cycles of TiO2/PVA thin film increased (3.5-, 5.5-, and 10.5-cycle), the sizes of prepared AgNPs gradually decreased (9.3, 8.0, and 6.2 nm, respectively) and the distributions of the AgNPs become narrower, correspondingly. Regarding its electrochemical properties, the TiO2/PVA hybrid films showed a well-defined reversible redox system on gold electrodes (GEs), as observed by a pair of current peaks, and further exhibited electrocatalytic activity, and a low limit of detection (LOD) for hydrogen dioxide (H2O2). A lower cycle of thinner hybrid film, 1.5-cycle TiO2/PVA, showed relatively higher electrochemical and amperometric responses than those of 3.5-, 5.5-, and 10.5-cycle films. Based on the amperometric response of the AgNP-incorporated 1.5-cycle TiO2/PVA film, the linear regression equation was acquired as I(μA) = −0.0481 [H2O2] (μM) + 0.4099, with a correlation coefficient of 0.9872. Thus, the significant sensitivity to H2O2 up to 0.0481 μA/μM and LOD of 0.11 μM were achieved, respectively.

Phenol based redox mediators in electroanalysis

The building of chemically modified electrodes is attracting increasing interest over the past decades, with a large number of publications, in different applications. The present review focuses on a special class of surface modifiers based on activated phenols, which work as redox mediators, with most of the more recent materials applied in electroanalysis. Common remarks in this specific subject are reported, like the generation, on the majority of cases, of a reversible quinonoid redox system, able to mediate fast electron transfer toward a series of analytes, the use of carbon nanotubes and graphenes to avoid passivation and to obtain electroanalytical synergism. The steadily increasing number of examples of phenol-based redox catalysis demonstrates that the principle finds wide application in electroanalysis and related fields. This is, mainly, due to the fact that mediated processes frequently afford higher and/or different selectivity than a direct process. In addition, electrode reactions are accelerated and the overall energy consumption reduced, while reagent waste and difficult separation procedures can be avoided.Drawbacks in the area, like heterogeneity of surface, structural complexity of the phenol-based electrogenerated polymers/oligomers, doubts about covalent linkage or not to the surface modifiers, lixiviation, evaluation based on trial and error, are still present and need to be solved for a better and more efficient use of this kind of redox mediators. There is still a demand for more powerful characterization methods to eliminate experimental uncertainties. Electrochemical screening, using special devices, should be implemented in the area, to facilitate the choice of the best mediator. Rationalization based on computational/theoretical methods would help in terms of a well-designed phenol-structure directed to a special electroanalytical function.