Light Emission Resulting from Hydroxylamine-Induced Singlet Oxygen Formation of Oxidizing LDL Particles

Abstract— Oxidation of low-density lipoprotein (LDL) by low amounts of cupric ions resulted in the formation of singlet oxygen (₁O₂, ₁DL_g) when hydroxylamine (NH2OH) was added. Direct evidence on this excited species came from partial spectral resolution of the emitted light in the red spectral region (634 nm and 703 nm), which can be attributed to the dimol decay of singlet oxygen. Additional evidence for the existence of singlet oxygen came from the enhancing effect of deuterium oxide buffer (D20) on chemiluminescence intensity and the quenching effect of sodium azide. A linear correlation between NH2OH-de-pendent chemiluminescence intensity and the amount of diene conjugates (DC) formed in this reaction was observed. Removal of adventitious transition metals by adequate chelators prevented chemiluminescence in this system; NH2OH was also found to efficiently decrease metabolites of lipid peroxidation (LPO). Our findings are consistent with a sequence of reactions in which NH2OH first converts transition metals to their reduced state, thereby stimulating the formation of alkoxy- and peroxy-radicals. Peroxyradicals decompose in a bimolecular Russel reaction to hydroxyl compounds and singlet oxygen while the majority of alkoxy radicals are eliminated by a secondary reaction with NH2OH. Identical effects were observed when reducing antioxidants such as ascorbic acid or trolox C were used instead of hydroxylamine.     

Indirect Electrooxidation of Organic Substrates by Hydrogen Peroxide Generated in an Oxygen Gas-Diffusion Electrode

Indirect electrooxidation of phenol, formaldehyde, and maleic acid in cells with and without a cation-exchange membrane, with a platinum anode and a gas-diffusion carbon black cathode, which generates hydrogen peroxide from molecular oxygen, proceeds with high efficiency and various oxidation depths, which depend on the intermediate nature: the process involving HO ₂ ^- occurs selectively and yields target products, while the formation of HO₂ ^· and HO^· leads to the destruction of organic compounds to CO₂ and H₂O.     

Influence of Hydrogen and Oxygen on Porous Silicon Light Emission

The effect of oxygen and hydrogen on the photoluminescence intensity of porous silicon was examined. The results indicate that the presence of oxygen is necessary for visible light emission. In contrast, high hydrogen passivation is unfavorable for visible light emission.     

Promoting Solar-driven Hydrogen Peroxide Production over Thiazole-based Conjugated Polymers via Generating and Converting Singlet Oxygen

Solar-driven synthesis of hydrogen peroxide (H₂O₂) from water and air provides a low-cost and eco-friendly alternative route to the traditional anthraquinone method. Herein, four thiazole-based conjugated polymers (Tz-CPs: TTz , BTz , TBTz and BBTz ) are synthesized via aldimine condensation. BBTz exhibits the highest H₂O₂ production rate of 7274 μmol g⁻¹ h⁻¹ in pure water. Further, the reaction path is analyzed by electron paramagnetic resonance (EPR), in situ diffuse reflectance infrared Fourier transform (DRIFT) and theoretical calculation, highlighting the prominent role of singlet oxygen (¹O₂). The generation of ¹O₂ occurs through the oxidation of superoxide radical (⋅O₂⁻) and subsequent conversion into endoperoxides via [4+2] cycloaddition over BBTz , which promotes charge separation and reduces the barrier for H₂O₂ production. This work provides new insight into the mechanism of photocatalytic O₂ reduction and the molecular design of superior single-polymer photocatalysts.     

Sensor System for Simultaneous Measurement of Oxygen and Hydrogen Peroxide Concentration During Glucose Oxidase Activity

An amperometric sensor system, based on a repetitive double step potential method at a glassy carbon electrode, has been developed for the simultaneous measurement of hydrogen peroxide and oxygen concentrations. The current measured at a potential of –1 V (vs. Ag/AgCl/saturated Cl^–) corresponds to the sum of the reduction currents of hydrogen peroxide and dissolved oxygen. The current measured at –0.55 V (vs. Ag/AgCl/saturated Cl^–) is due to the reduction of dissolved oxygen to hydrogen peroxide. Alternatively, the concentration of dissolved oxygen can also be determined using a Clark electrode. The concentration of hydrogen peroxide and dissolved oxygen during enzymatic conversion of glucose can be followed on line and be used to control the process.     

Sunlight‐Driven Hydrogen Peroxide Production from Water and Molecular Oxygen by Metal‐Free Photocatalysts

Design of green, safe, and sustainable process for the synthesis of hydrogen peroxide (H₂O₂) is a very important subject. Early reported processes, however, require hydrogen (H₂) and palladium‐based catalysts. Herein we propose a photocatalytic process for H₂O₂ synthesis driven by metal‐free catalysts with earth‐abundant water and molecular oxygen (O₂) as resources under sunlight irradiation (λ>400 nm). We use graphitic carbon nitride (g‐C₃N₄) containing electron‐deficient aromatic diimide units as catalysts. Incorporating the diimide units positively shifts the valence‐band potential of the catalysts, while maintaining sufficient conduction‐band potential for O₂ reduction. Visible light irradiation of the catalysts in pure water with O₂ successfully produces H₂O₂ by oxidation of water by the photoformed valence‐band holes and selective two‐electron reduction of O₂ by the conduction band electrons.     

Inhibition by Hydrogen Peroxide in the Radical Chain Oxidation of Hydrocarbons by Molecular Oxygen

Theoretical and Experimental Chemistry - Inhibition by hydrogen peroxide in the radical chain aerobic oxidation of alkylarenes is reported. A kinetic scheme for this process and an equation...     

CO2 Laser-Induced Graphene with an Appropriate Oxygen Species as an Efficient Electrocatalyst for Hydrogen Peroxide Synthesis

Oxygen species functionalized graphene (O−G) is an effective electrocatalyst for electrochemically synthesizing hydrogen peroxide (H₂O₂) by a 2 e⁻ oxygen reduction reaction (ORR). The type of oxygen species and degree of carbon crystallinity in O−G are two key factors for the high catalytic performance of the 2 e⁻ ORR. However, the general preparing method of O−G by the precursor of graphite has the disadvantages of consuming massive strong oxidant and washing water. Herein, the biomass-based graphene with tunable oxygen species is rapidly fabricated by a CO₂ laser. In a flow cell setup, the laser-induced graphene (LIG) with abundant active oxygen species and graphene structure shows high catalytic performance including high Faraday efficiency (over 78 %) and high mass activity (814 mmolg_catalyst⁻¹ h⁻¹), superior to most of the reported carbon-based electrocatalysts. Density function theory demonstrates the meta-C atoms at nearby C−O, O−C=O species are the key catalytic sites. Therefore, we develop one facile method to rapidly convert biomass to graphene electrocatalyst used for H₂O₂ synthesis.     

White‐Light Emission from a Single Polymer with Singlet and Triplet Chromophores on the Backbone

Summary: A strategy to generate an efficient white‐light emission has been developed by mixing fluorescence and phosphorescence emission from a single polymer. Fluorene is used as the blue‐emissive component, benzothiadiazole (BT) and the iridium complex [(btp)₂Ir(tmd)] are incorporated into a polyfluorene backbone, respectively, as green‐ and red‐emissive chromophores by Suzuki polycondensation. By changing the contents of BT and [(btp)₂Ir(tmd)] in the polymer, the electroluminescence spectrum from a single polymer can be adjusted to achieve white‐light emission. A white polymeric light‐emitting diode (WPLED) with a structure of ITO/PEDOT:PSS/PVK/PFIrR1G03/CsF/Al shows a maximum external quantum efficiency of 3.7% and the maximum luminous efficiency of 3.9 cd · A⁻¹ at the current density of 1.6 mA · cm⁻² with the CIE coordinates of (0.33, 0.34). The maximum luminance of 4 180 cd · m⁻² is achieved at the current density of 268 mA · cm⁻² with the CIE coordinates of (0.31, 0.32). The white‐light emissions from such polymers are stable in the white‐light region at all applied voltages, and the electroluminescence efficiencies decline slightly with the increasing current density, thus indicating that the approach of incorporating singlet and triplet species into the polymer backbone is promising for WPLEDs.

Structure of PFIrR1G04 and the EL spectra of its devices under various voltages. Device structure: ITO/PEDOT:PSS/PVK/polymer/CsF/Al.     

Xanthine Sensors Based on Anodic and Cathodic Detection of Enzymatically Generated Hydrogen Peroxide

A xanthine biosensor was fabricated by the covalent immobilization of xanthine oxidase (XO) onto a functionalized conducting polymer (Poly‐5, 2′: 5′, 2″‐terthiophine‐3‐carboxylic acid), poly‐TTCA through the formation of amide bond between carboxylic acid groups of poly‐TTCA and amine groups of enzyme. The immobilization of XO onto the conducting polymer (XO/poly‐TTCA) was characterized using cyclic voltammetry, quartz crystal microbalance (QCM), and X‐ray photoelectron spectroscopy (XPS) techniques. The direct electron transfer of the immobilized XO at poly‐TTCA was found to be quasireversible and the electron transfer rate constant was determined to be 0.73 s^?1. The biosensor efficiently detected xanthine through oxidation at +0.35 V and reduction at ?0.25 V (versus Ag/AgCl) of enzymatically generated hydrogen peroxide. Various experimental parameters, such as pH, temperature, and applied potential were optimized. The linear dynamic ranges of anodic and cathodic detections of xanthine were between 5.0×10^?6?1.0×10^?4 M and 5.0×10^?7 to 1.0×10^?4 M, respectively. The detection limits were determined to be of 1.0×10^?6 M and 9.0×10^?8 M with anodic and cathodic processes, respectively. The applicability of the biosensor was tested by detecting xanthine in blood serum and urine real samples.     

Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen Using Tailored Pd Nanocatalysts: A Review of Recent Findings

Direct synthesis of hydrogen peroxide from hydrogen and oxygen is being actively studied as an alternative to the current manufacturing process. The direct synthesis route has not reached the point of commercialization because of low yields, but significant effort is being spent on enhancing the productivity. With advances in computational capacity, simulation studies based on DFT calculations now offer directions for catalyst improvement, but such modifications can only be realized through the application of nanoparticle synthesis techniques that allow for nanocrystal morphology and size control and unique immobilization. To date, there have only been a small number of studies on such nanoparticles with size and crystallographic homogeneity for the direct hydrogen peroxide synthesis. According to our knowledge no other group has systematically investigated application of nanoparticles in direct synthesis of hydrogen peroxide, and thus included in this review are primarily previous studies conducted by our group. In this review, we discuss the utilization of nanotechnology for the synthesis of Pd catalysts and its effect on the direct synthesis of hydrogen peroxide, and we suggest a direction for future studies.     

High‐Yield Electrosynthesis of Hydrogen Peroxide from Oxygen Reduction by Hierarchically Porous Carbon

H₂O₂ production by electroreduction of O₂ is an attractive alternative to the current anthraquinone process, which is highly desirable for chemical industries and environmental remediation. However, it remains a great challenge to develop cost‐effective electrocatalysts for H₂O₂ synthesis. Here, hierarchically porous carbon (HPC) was proposed for the electrosynthesis of H₂O₂ from O₂ reduction. It exhibited high activity for O₂ reduction and good H₂O₂ selectivity (95.0–70.2 %, most of them >90.0 % at pH 1–4 and >80.0 % at pH 7). High‐yield H₂O₂ generation has been achieved on HPC with H₂O₂ concentrations of 222.6–62.0 mmol L^?1 (2.5 h) and corresponding H₂O₂ production rates of 395.7–110.2 mmol h^?1 g^?1 at pH 1–7 and ?0.5 V. Moreover, HPC was energy‐efficient for H₂O₂ production with current efficiency of 81.8–70.8 %. The exceptional performance of HPC for electrosynthesis of H₂O₂ could be attributed to its high content of sp³‐C and defects, large surface area and fast mass transfer.     

Visible Light and Microwave-Mediated Rapid Trapping and Release of Singlet Oxygen Using a Coordination Polymer

Due to its high reactivity and oxidative strength, singlet oxygen (¹O₂) is used in a variety of fields including organic synthesis, biomedicine, photodynamic therapy and materials science. Despite its importance, the controlled trapping and release of ¹O₂ is extremely challenging. Herein, we describe a one-dimensional coordination polymer, CP1 , which upon irradiation with visible light, transforms ³O₂ (triplet oxygen) to ¹O₂. CP1 consists of Cd^II centers bridged by 9,10-bis((E)-2-(pyridin-4-yl)vinyl)anthracene ligands which undergo a [4+2] cycloaddition reaction with ¹O₂, resulting in the generation of CP1−¹O₂ . Using microwave irradiation, CP1−¹O₂ displays efficient release of ¹O₂, over a period of 30 s. In addition, CP1 exhibits enhanced fluorescence and has an oxygen detection limit of 97.4 ppm. Theoretical calculations reveal that the fluorescence behaviour is dominated by unique through-space conjugation. In addition to describing a highly efficient approach for the trapping and controlled release of ¹O₂, using coordination polymers, this work also provides encouragement for the development of efficient fluorescent oxygen sensors.     

Kinetics of Hydrogen Peroxide Accumulation in Electrosynthesis from Oxygen in Gas-Diffusion Electrode in Acidic and Alkaline Solutions

Accumulation of H₂O₂ in aqueous solutions with various pH values in electroreduction of oxygen in carbon-black gas-diffusion hydrophobized electrodes was studied. The effect of various parameters of the process on its electrochemical component and decomposition rate of the H₂O₂ formed was analyzed.     

Biphasic Synthesis of Hydrogen Peroxide from Carbon Monoxide,Water, and Oxygen Catalyzed by Palladium Complexes with Bidentate Nitrogen Ligands

Effective and stable Pd catalysts for the biphasic synthesis of hydrogen peroxide from carbon monoxide, oxygen, and water [Eq. (a)] can be obtained by the right choice of bidentate nitrogen ligand. The best turnover numbers (578) for this reaction have been achieved with palladium complexes with 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline ligands.     

The Reaction of Singlet and Triplet Oxygen with 2-Phenylnorbornene

The reaction of singlet oxygen with 2-phenylnorbornene ( 1 ) in aprotic solvents gives 3-formylcyclopentyl phenyl ketone ( 2 ) (10%) and uncharacterized polymer (90%). When methanol is used as solvent, endo-2-phenyl-exo-2-methoxy-exo-3-hydroperoxynorbornane ( 4 ) and endo-2-(anti-1′, 4′-epidioxy-5′,6′-epoxycyclohex-2′-enyl)-exo-2,3-epoxynorbornane ( 6 and 7 ) are obtained in addition to 2 . Triplet oxygen with 1 gave 2 , endo-2-phenyl-exo-2,3-epoxynorbornane ( 8 ), and the trimer 9 or 10 of exo-2,3-epidioxy-endo-2-phenylnorbornane. With protic solvents the amount of epoxide increased at the expense of trimer. The singlet and triplet oxygen reactions are discussed in the light of possible intermediates.