Current oscillatory phenomena based on electrogenerated superoxide ion at the HMDE in dimethylsulfoxide

Superoxide Anion Chemistry-Its Role at the Core of the Innate Immunity

Classically, superoxide anion O₂^•- and reactive oxygen species ROS play a dual role. At the physiological balance level, they are a by-product of O₂ reduction, necessary for cell signalling, and at the pathological level they are considered harmful, as they can induce disease and apoptosis, necrosis, ferroptosis, pyroptosis and autophagic cell death. This revision focuses on understanding the main characteristics of the superoxide O₂^•-, its generation pathways, the biomolecules it oxidizes and how it may contribute to their modification and toxicity. The role of superoxide dismutase, the enzyme responsible for the removal of most of the superoxide produced in living organisms, is studied. At the same time, the toxicity induced by superoxide and derived radicals is beneficial in the oxidative death of microbial pathogens, which are subsequently engulfed by specialized immune cells, such as neutrophils or macrophages, during the activation of innate immunity. Ultimately, this review describes in some depth the chemistry related to O₂^•- and how it is harnessed by the innate immune system to produce lysis of microbial agents.

In Situ Electrosynthesis of Peroxydicarbonate Anion in Ionic Liquid Media Using Carbon Dioxide/Superoxide System

Climate engineering solutions with emphasis on CO₂ removal remain a global open challenge to balancing atmospheric CO₂ equilibrium levels. As a result, warnings of impending climate disasters are growing every day in urgency. Beyond ordinary CO₂ removal through natural CO₂ sinks such as oceans and forest vegetation, direct CO₂ conversion into valuable intermediaries is necessary. Here, a direct electrosynthesis of the peroxydicarbonate anion (C₂O₆^2-) was investigated by the reaction of CO₂ with the superoxide ion (O₂^·-), electrochemically generated from O₂ reduction in bis(trifluoromethylsulfonyl)imide [TFSI^-] anion derived ionic liquid (IL) media. This is the first time that the IL media were employed successfully for CO₂ conversion into C₂O₆^2-. Moreover, the charge transfer coefficient for the O₂^·- generation process in the ILs was less than 0.5, indicating that the process was irreversible. Voltammetry experiments coupled with global electrophilicity index analysis revealed that, when CO₂/O₂ was contacted simultaneously in the IL medium, O₂^·- was generated in situ first at a potential of approximately -1.0 V. Also, CO₂ was more susceptible to attack by O₂^·- before any possible interaction with the IL except for [PMIm⁺][TFSI^-]. This was because CO₂ has a higher global electrophilicity index (ω_CO2 = 0.489 eV) than those for the [EDMPAmm⁺][TFSI^-] and [MOEMMor⁺][TFSI^-]. By further COSMO-RS modeling, CO₂ absorption was proven feasible at the COSMO-surface of the [TFSI^-] IL-anion where the charge densities were σ = -1.100 and 1.1097 e/nm². Therefore, the susceptible competitiveness of either IL cations or CO₂ to the nucleophilic effects of O₂^·- was a function of their positive character as estimated by their electrophilicity indices. As determined by experimental attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and DFT-FTIR computation, the reaction yielded C₂O₆^2- in the ILs. Consequently, the presence of O=O symmetric stretching FTIR vibrational mode at ∼844 cm^-1 coupled with the disappearance of the oxidative cyclic voltammetry waves when sparging CO₂ and O₂ confirmed the presence of C₂O₆^2-. Moreover, based on DFT/B3LYP/6-31G, pure C₂O₆^2- has symmetric O=O stretching at ∼805 and ∼844 cm^-1 when it is in association with the IL-cation. This was the first spectroscopic observation of C₂O₆^2- in ILs, and the O=O symmetric stretching vibration has peculiarity for identifying C₂O₆^2- in ILs. This will open new doors to utilize CO₂ in industrial applications with the aid of reactive oxygen species.

Superoxide Ion: Generation and Chemical Implications

Superoxide ion (O2(•-)) is of great significance as a radical species implicated in diverse chemical and biological systems. However, the chemistry knowledge of O2(•-) is rather scarce. In addition, numerous studies on O2(•-) were conducted within the latter half of the 20th century. Therefore, the current advancement in technology and instrumentation will certainly provide better insights into mechanisms and products of O2(•-) reactions and thus will result in new findings. This review emphasizes the state-of-the-art research on O2(•-) so as to enable researchers to venture into future research. It comprises the main characteristics of O2(•-) followed by generation methods. The reaction types of O2(•-) are reviewed, and its potential applications including the destruction of hazardous chemicals, synthesis of organic compounds, and many other applications are highlighted. The O2(•-) environmental chemistry is also discussed. The detection methods of O2(•-) are categorized and elaborated. Special attention is given to the feasibility of using ionic liquids as media for O2(•-), addressing the latest progress of generation and applications. The effect of electrodes on the O2(•-) electrochemical generation is reviewed. Finally, some remarks and future perspectives are concluded.

Eccentric Phenomena at Liquid Mercury Electrode/Solution Interfaces: Upward, Downward, and Circular Motions

The present paper describes a visualization of unidirectional and circular motions triggered by an electrochemical redox reaction at a charged, bent, and streamed liquid electrode/liquid solution interface. The novel circular motion that induces a conversion of electrochemical energy into mechanical energy could be visualized for the first time at a hanging mercury drop electrode (HMDE)/dimethyl sulfoxide (DMSO) solution interface via the electrochromic reaction of 2,1,3-benzothiadiazole (BTD) by using a CCD-color video camera. The observed motions are self-insisting in nature and are tunable into upward, downward, clockwise, and anticlockwise ones by an appropriate choice of the experimental conditions. This circular motion is visualized for the first time as the cause of the well-known cyclic voltammetric anodic current oscillation at the HMDE. Several small perturbations, for example, surface tension, surface motion, bulk motion, diffusional mass transport, and surface electrochemical potential are considered to be endlessly amplified by their coupling in a cyclic chain, resulting in such macroscopic motions at the electrode/solution interface. All of the phenomena can be explained on the basis of the modern theory proposed by Aogaki et al. for the polarographic streaming maxima of the first kind.