The alkali metal ions Li(+), Na(+) and K(+) have a profound influence on the stoichiometry of the complexes formed in uranyl(VI)-peroxide-hydroxide systems, presumably as a result of a templating effect, resulting in the formation of two complexes, M[(UO2)(O2)(OH)]2(-) where the uranyl units are linked by one peroxide bridge, μ-η(2)-η(2), with the second peroxide coordinated "end-on", η(2), to one of the uranyl groups, and M[(UO2)(O2)(OH)]4(3-), with a four-membered ring of uranyl ions linked by μ-η(2)-η(2) peroxide bridges. The stoichiometry and equilibrium constants for the reactions: M(+) + 2UO2(2+) + 2HO2(-) + 2H2O → M[(UO2)(O2)(OH)]2(-) + 4H(+) (1) and M(+) + 4UO2(2+) + 4HO2(-) + 4H2O → M[(UO2)(O2)(OH)]4(3-) + 8H(+) (2) have been measured at 25 °C in 0.10 M (tetramethyl ammonium/M(+))NO3 ionic media using reaction calorimetry. Both reactions are strongly enthalpy driven with large negative entropies of reaction; the observation that ΔH(2) ≈ 2ΔH(1) suggests that the enthalpy of reaction is approximately the same when peroxide is added in bridging and "end-on" positions. The thermodynamic driving force in the reactions is the formation of strong peroxide bridges and the role of M(+) cations is to provide a pathway with a low activation barrier between the reactants and in this way "guide" them to form peroxide bridged complexes; they play a similar role as in the synthesis of crown-ethers. Quantum chemical (QC) methods were used to determine the structure of the complexes, and to demonstrate how the size of the M(+)-ions affects their coordination geometry. There are several isomers of Na[(UO2)(O2)(OH)]2(-) and QC energy calculations show that the ones with a peroxide bridge are substantially more stable than the ones with hydroxide bridges. There are isomers with different coordination sites for Na(+) and the one with coordination to the peroxide bridge and two uranyl oxygen atoms is the most stable one.
The first cobalt‐catalyzed direct methylation of a C(sp2)−H bond using dicumyl peroxide (DCP) as both the methylating reagent and hydrogen acceptor has been established. The reaction proceeded without the use of any additives, and was proven to be applicable to various amides bearing a 2‐pyridinylisopropyl (PIP) directing group, providing an efficient access to o‐methyl aryl amides with high functional‐group tolerance. Preliminary mechanistic studies suggest a radical process would be involved in the catalytic process. C−H functionalization: A cobalt‐catalyzed direct methylation of the C(sp2)−H bond by using dicumyl peroxide (DCP) as both the methylating reagent and hydrogen acceptor has been established (see scheme; acac=acetylacetone). The reaction proceeded without the use of any additives, and was proven to be applicable to various amides bearing a 2‐pyridinylisopropyl (PIP) directing group.
O2 takes activation lessons: OO bond activation can be achieved depending on the nature of the heterometal M in [LNi(μ,η2:η2‐O2)M] complexes. The reduction of the nickel(II) superoxide 1 with potassium affords the peroxide 2, which, upon replacement of the K+ ion in 2 by the non‐redox‐active L′Zn+ ion, leads to transient 3, which subsequently s two solvent hydrogen atoms to give the heterobimetallic complex 4. L, L′=β‐diketiminates.
Hair follicles are a promising target for the administration of drugs to treat diseases associated with the pilosebaceous unit, such as acne. For solid lipid microparticle dispersions a successful and selective delivery of adapalene via targeted erosion of the particles in sebum has been shown. By embedding nanoparticulate benzoyl peroxide in lipid microparticles, the therapeutic potency of adapalene can be further increased by improving follicular deposition of benzoyl peroxide and minimizing direct contact between benzoyl peroxide and stratum corneum, which is responsible for the irritating potential of this active agent. The aim of this study was to develop a novel nanoparticulate formulation for benzoyl peroxide suitable for the incorporation in solid lipid microparticles. In this contribution, a wet grinding process using liposomal dispersions of fully hydrated phosphatidylcholine was developed, upscaled and optimized for solid content and stabilizer concentration. The resulting novel nanosuspension was characterized by particle size and morphology and examined for chemical and physical stability as well as solubility and polymorphism. During the process development a dependency between the colloidal microstructure of the stabilizer dispersion and milling efficiency was found: while physical mixtures fail to deliver nanosuspensions, liposomal dispersions succeed with the same amount of stabilizer.
Epoxides are an important class of industrial chemicals that have been used as chemical intermediates. Catalytic epoxidation of olefins affords an interesting production technology. We found a widely usable green route to the production of epoxides: A silicotungstate compound, , is synthesized by protonation of a divacant, lacunary, Keggin-type polyoxometalate of and exhibits high catalytic performance for the epoxidation of various olefins, including propylene, with a hydrogen peroxide (H O ) oxidant at 305 kelvin. The effectiveness of this catalyst is evidenced by ≥ 99% selectivity to epoxide, ≥ 99% efficiency of H O utilization, high stereospecificity, and easy recovery of the catalyst from the homogeneous reaction mixture.
Nitric oxide (NO) is a bioactive molecule that functions in numerous physiological and developmental processes in plants, including lateral root development. In this study, we used biochemical and genetic approaches to analyze the function of Arabidopsis thaliana mitogen-activated protein kinase 6 (MPK6) in the regulation of NO synthesis in response to hydrogen peroxide (H₂O₂) during lateral root development. In both mpk6 mutants studied, H₂O₂-induced NO synthesis and nitrate reductase (NR) activity were decreased dramatically. Furthermore, one NR isoform, NIA2, was required for the MPK6-mediated production of NO induced by H₂O₂. Notably, NIA2 interacted physically with MPK6 in vitro and in vivo and also served as a substrate of MPK6. Phosphorylation of NIA2 by MPK6 led to an increase in NR activity, and Ser-627 was identified as the putative phosphorylation site on NIA2. Phenotypical analysis revealed that mpk6-2 and mpk6-3 seedlings produce more and longer lateral roots than wild-type plants did after application of the NO donor sodium nitroprusside or H₂O₂. These data support strongly a function of MPK6 in modulating NO production and signal transduction in response to H₂O₂ during Arabidopsis root development.
Reactive oxygen species (ROS) play important roles in the development and progression of cancer and other diseases, motivating the development of translatable technologies for biological ROS imaging. Here we report Peroxy-Caged-[18F]Fluorodeoxy thymidine-1 (PC-FLT-1), an oxidatively immolative positron emission tomography (PET) probe for H2O2 detection. PC-FLT-1 reacts with H2O2 to generate [18F]FLT, allowing its peroxide-dependent uptake and retention in proliferating cells. The relative uptake of PC-FLT-1 was evaluated using H2O2-treated UOK262 renal carcinoma cells and a paraquat-induced oxidative stress cell model, demonstrating ROS-dependent tracer accumulation. The data suggest that PC-FLT-1 possesses promising characteristics for translatable ROS detection and provide a general approach to PET imaging that can be expanded to the in vivo study of other biologically relevant analytes.
Thorn-like Ni@TiC NAs and flake-like Co@TiC NAs electrodes without any conductive agent and binder are simply fabricated by the potentiostatic electrodeposition of Ni and Co catalysts on the TiC nanowire arrays (NAs). The electrocatalytic activity of H O oxidation on the Ni@TiC NAs electrodes is better than that on the Co@TiC NAs electrodes. The Ni@TiC NAs electrodes demonstrate a rough surface and have many nano-needles on the rod edges, which assures the high utilized efficiency of Ni catalysts. These particular three-dimensional structures may be very suitable for H O electrooxidation. The anodic current of Ni@TiC NAs anode reaches 0.32 A cm at 0.3 V in 1.0 M H O + 4 M KOH solution. The DPFCs employing Ni@TiC NAs anodes display the peak power density of 30.2 mW cm and open circuit voltage of 0.90 V at 85.1 mA cm with desirable cell stability at 10 mL min flow rate and 20 °C, which is much higher than those previously reported.
The formation, the adsorption and the degradation of H O on different commercial TiO samples (anatase, rutile) and on ZnO have been investigated to better understand its participation in the photocatalytic reactions. The Langmuir and Langmuir–Hinshelwood models have been used for determining the adsorption constants and the rate constants of H O disappearance on these different photocatalysts both in the dark and under UV-A irradiation. Interaction between H O and TiO has been investigated by UV–vis spectroscopy. The adsorption of H O on TiO samples is discussed in term of surface area and nature of TiO including the number of OH groups present on the photocatalysts. The nature of the yellow complex formed between H O and TiO is discussed taking into account its stability, and the coverage rate of OH groups. The kinetic of H O disappearance on the different photocatalysts is related to the adsorption but also the energy of conduction band of anatase and rutile photocatalysts. The results of the formation and decomposition of H O under UV-A irradiation in the presence of ZnO photocatalyst are explained in light of its adsorption.