Cyclic voltammetry (CV) and controlled potential electrolysis (CPE) experiments revealed that at a Pt electrode, pyridoxine undergoes a one-electron chemically irreversible oxidation at approximately 0.50 V versus Fc/Fc⁺, likely generating a dimeric product. Fouling of the electrode surface could be detected with repeated scans during CV and during preparative scale CPE oxidation experiments. These adsorption effects were overcome by performing bulk oxidation of pyridoxine with NOSbF₆ as a chemical oxidant. At Pt electrodes, a cathodic wave associated with the reduction of pyridoxine was detected at approximately −1.60 V versus Fc/Fc⁺. The reduction process appeared to be chemically reversible on the shorter timeframe of CV, but not under the prolonged timescale of CPE. The reduction of pyridoxine involves a direct discharge of pyridoxine at the Pt surface, generating an oxide anion, which upon treatment with iodomethane yields N-methylated pyridoxine rather than its O-methylated analogue.

Carbon nanotubes (CNTs) possess well-defined structural and chemical characteristics coupled with a large surface area that makes them ideal as sorbent materials for applications where adsorption processes are required. The adsorption properties of carboxylated derivatives of multiwalled carbon nanotubes (COOH-MWCNT) and singlewalled carbon nanotubes (COOH-SWCNT), together with their nonfunctionalized counterparts (MWCNT and SWCNT) for 48 common atmospheric volatile organic compounds (VOCs) were determined using thermal desorption–gas chromatography/mass spectrometry (TD-GCMS). The CNTs exhibited similar recoveries for many of the VOCs compared to the standard sorbent materials, Carbopack X and Tenax TA. However, VOCs with electron donor–acceptor (EDA) properties such as carbonyls, alkenes, and alcohols exhibited poorer recoveries on all CNTs compared to Carbopack X and Tenax TA. The poor recoveries of VOCs from the CNTs has important implications for the long term use and storage of CNTs, because it demonstrates that they will become progressively more contaminated with common atmospheric VOCs, therefore potentially affecting their surface-based properties.

Voltammetric experiments with 9,10-anthraquinone and 1,4-benzoquinone performed under controlled moisture conditions indicate that the hydrogen-bond strengths of alcohols in aprotic organic solvents can be differentiated by the electrochemical parameter ΔE_p^red=|E_p^red(1)−E_p^red(2)|, which is the potential separation between the two one-electron reduction processes. This electrochemical parameter is inversely related to the strength of the interactions and can be used to differentiate between primary, secondary, tertiary alcohols, and even diols, as it is sensitive to both their steric and electronic properties. The results are highly reproducible across two solvents with substantially different hydrogen-bonding properties (CH₃CN and CH₂Cl₂) and are supported by density functional theory calculations. This indicates that the numerous solvent–alcohol interactions are less significant than the quinone–alcohol hydrogen-bonding interactions. The utility of ΔE_p^red was illustrated by comparisons between 1) 3,3,3-trifluoro-n-propanol and 1,3-difluoroisopropanol and 2) ethylene glycol and 2,2,2-trifluoroethanol.

Ten 1,4-phenylenediamines were studied using electrochemical techniques (voltammetry and controlled potential electrolysis) and UV/Vis spectroscopy under ambient conditions. All compounds demonstrated vibrant color changes upon one-electron electrochemical oxidation in acetonitrile, with most displaying a primary color (red, green, blue, or yellow) in their oxidized state. The four electrochromes that exhibited the most intense color changes were examined by using a gold micromesh electrode laminated inside a polymer film to determine their electrochromic properties in solution (contrast ratios, chromatic efficiency, and cycle life). Their colored radical cations were also characterized by electron paramagnetic resonance spectroscopy as well as monitored for color retention over a period of 24 hours. Notably, only relatively small potentials were required to initiate the chromatic changes and the oxidized forms of the compounds were long-lived and unaffected by atmospheric oxygen or moisture.

The drop-casting method for the suspension of nanomaterials on conducting surfaces is a commonly used procedure for evaluating the electrochemical properties of the drop-cast materials. In this study, we pinpoint a key limitation of the method, which may lead to misinterpretation of the obtained data, especially when evaluating heterogeneous electron-transfer rates. The electrochemical responses recorded at 1 mm-diameter copper electrodes modified with porous layers of drop-cast multiwalled carbon nanotubes (MWCNTs) in 0.1 M Na₂SO₄ aqueous solutions were examined. Standard amounts of the MWCNTs that are typically used for the drop-casting procedure (1 mg MWCNT in 1 mL of dimethylformamide) were deposited drop wise on the surface of the copper electrodes. Layers of MWCNTs were progressively built up on the electrode surface by varying the number of drops from 0 to 10. The ability of the MWCNTs to cover and prevent diffusion to the base copper electrode was assessed by performing oxidative cyclic (CV) and linear-sweep voltammetry (LSV) experiments in the presence of aggressive SO₄²⁻ supporting electrolyte, where a large oxidative current indicated the occurrence of corroding copper metal. It was demonstrated that a total of 10 drops of the coating solution (equivalent to 640 μg cm⁻² of MWCNTs per unit area) was still insufficient in providing complete coverage over the underlying electrode surface (as a corrosion current was still observed), even though considerably lower CNT loadings have been applied in many literature reports. The electrochemical results indicate that, for experiments that utilize the drop-casting procedure to modify electrode surfaces, it cannot be assumed that the base electrode, nor the pore structure of the coating material, does not significantly contribute to the overall observed voltammetric response.

Caffeine (CAF) undergoes a one-electron oxidation in acetonitrile to form a cation radical, with variable scan rate CV experiments indicating that the lifetime of the cation radical improves as the trace water content of the solvent is decreased. Electrochemical oxidation (and chemical oxidation with NOSbF₆) of CAF in CH₃CN leads to the generation of the protonated CAF cation as the long-term product in high yield, whose structure is confirmed by single-crystal X-ray crystallography and NMR spectroscopy. The protonated cation is able to be electrochemically reduced back to CAF under electrolysis conditions. The formation of the protonated cation involves the initial one-electron oxidation of CAF to form the cation radical, which undergoes a hydrogen atom abstraction reaction. Digital simulations of the CV data show that the rate and equilibrium constants for the hydrogen atom abstraction step are k_f=1.0×10² L mol⁻¹ s⁻¹ and K_eq=1.0×10².

A review summarizing the voltammetric literature of the liposoluble vitamins A, D, E and K in organic solvents containing supporting electrolyte is presented. Electrochemical studies that were performed by attaching the vitamins to electrode surfaces and performing voltammetric scans in aqueous solutions are also summarized. Vitamins A (retinol and retinal) and D (cholecaliferol and ergocalciferol) undergo chemically irreversible voltammetric oxidation processes in organic solvents to form complicated or unknown compounds that cannot be electrochemically converted back to the starting materials. In contrast to vitamins A and D, vitamins E and K undergo chemically reversible electron-transfer processes that are often coupled to proton-transfer reactions. Vitamin E (a phenol) is voltammetrically oxidized in aprotic organic solvents in a −2e^-/−H⁺ process to form a diamagnetic cation, which is unusually long-lived compared to the analogous cations produced during the oxidation of other phenols. In an aqueous environment, vitamin E is electrochemically oxidized to the hydroquinone in a chemically irreversible −2e^- process. In low moisture content aprotic solvents, vitamin K (a quinone) is reduced in two one-electron chemically reversible steps to form first a radical anion (semiquinone, at E₁) and then at more negative potentials a dianion is formed (at E₂). The dianion is especially prone to strong hydrogen-bonding interactions with trace water present in the organic solvents, resulting in a shift in the formal reduction potential of E₂ to more positive potentials as more water is added to the solvent. DOI 10.1002/tcr.201100005

Dopamine was electrochemically oxidized in aqueous solutions and in the organic solvents N,N-dimethyl-formamide and dimethylsulfoxide containing varying amounts of supporting electrolyte and water, to form dopamine ortho-quinone. It was found that the electrochemical oxidation mechanism in water and in organic solvents was strongly influenced by the buffering properties of the supporting electrolyte. In aqueous solutions close to pH 7, where buffers were not used, the protons released during the oxidation process were able to sufficiently change the localized pH at the electrode surface to reduce the deprotonation rate of dopamine ortho-quinone, thereby slowing the conversion into leucoaminochrome. In N,N-dimethylformamide and dimethylsulfoxide solutions, in the absence of buffers, dopamine was oxidized to dopamine ortho-quinone that survived without further reaction for several minutes at 25 °C. The voltammetric data obtained in the organic solvents were made more complicated by the presence of HCl in commercial sources of dopamine, which also underwent an oxidation process.