Molecular Oxygen In Aqueous Solution Research Articles

The solubility of oxygen in water and saline solutions

Oxygen is one of the key reaction partners for many redox reactions also in the context of nuclear waste disposal. Its solubility influences radionuclides’ behavior, corrosion processes and even microbial activity. Therefore, a reliable calculation of the solubility of molecular oxygen in aqueous solutions is relevant for any safety assessment. Available geochemical speciation and reactive transport programs handle these data very differently. In some codes, the hypothetical equilibrium between dissolved oxygen and water is used to balance redox reactions. Equilibrium constants are given in “temperature grids” for up to 573.15 K. In other cases, temperature functions for the solubility of gaseous oxygen in water are given, without any reference to a valid temperature range. These settings become even more complicated when used in the context of modeling equilibria in high-saline solutions applying the Pitzer formalism. This raised the question about the experimental foundation of equilibrium constants given in such data files and their validity for the solubility of molecular oxygen in saline solutions. For this article, a thorough literature review was conducted with respect to the solubility of molecular oxygen in pure water and saline solutions. From these primary experimental O2 solubility data a temperature-dependent Henry’s law function as well as temperature-dependent binary and ternary Pitzer ion-interaction coefficients were derived. An internally consistent set of thermodynamic data for dissolved oxygen is presented, along with statements about its validity in terms of temperature and, as far as Pitzer interaction coefficients are concerned, of solution composition. This self-consistent activity-fugacity model containing thermodynamic data, Henry’s law temperature equation, and Pitzer interaction coefficients is capable of providing a more accurate description of redox transformations, allowing a reduction of conservatism in safety assessment calculations, not only in the context of a nuclear repository. The model reproduces well the reliable experimental data available, and is capable to predict the oxygen solubility in complex solution media. The temperature functions used to describe Henry’s constant and the Pitzer interaction coefficients are consistent with the implementation in commonly used geochemical computational programs, allowing direct use without further modification.

Influence of Local Environments in Pores of Different Size on the Catalytic Liquid-Phase Oxidation of d-Glucose by Au Nanoparticles Supported on Nanoporous Carbon

Inorganic nanoparticles (NPs) dispersed on the surface of porous support materials play a dominant role in heterogeneous catalysis. Especially in liquid-phase catalysis, support materials may lead to nanoconfinement of solvent molecules, and the solute and can thus influence their local concentration and structure. This further affects the surface coverage of nanoparticles with reactants and other species, but these influences remain poorly understood—in particular under experimental conditions. Nanoconfinement effects are of particular importance in reactions such as liquid-phase oxidation with oxygen, i.e., when one reactant is a gas that has to be dissolved before reaching the NP surface. The significant influence of the pore structure of carbon materials on the catalytic activity of gold nanoparticles (AuNPs) with nearly similar size (4.1–4.7 nm) is demonstrated in this study. Experimental results on the oxidation of d-glucose with molecular oxygen in aqueous solution show that the “apparent catalytic activity” of AuNPs is a function of the carbon pore size and geometry. The architecture of the carbon pore size is determining the local concentration of reactants. Nanoconfinement of water in carbon nanopores can lead to enhanced solubility of reactants and therefore to their higher local concentration in proximity to the catalytically active sites. In contrast to purely microporous carbon support with the less wettable internal surface without any detectable catalytic activity, AuNPs supported on mesoporous carbons show a much higher metal time yield between 3.8 and 60.6 molGlc min–1 molAu–1, depending on volume and geometry of the mesopores.

Oxygen-releasing manganese clay hybrid complex triggers p53-mediated cancer cell death in hypoxia

Hypoxia in tumor microenvironment is responsible for resistance to conventional modes of cancer therapeutics. A manganese-clay hybrid compound MHC was shown to generate molecular oxygen in aqueous solution. In this study we have shown that MHC, in hypoxia, causes cancer cell death, through release of molecular oxygen and via p53-dependent apoptosis. MHC treatment of cells results in depletion of mitochondrial membrane potential and inhibition of ROS production, in a cell-specific manner. In hypoxia, the oxygen from MHC releases cells from S-phase arrest thus causing p53-dependent apoptosis. The induction of apoptosis by MHC is higher in p53 Wt/Wt cells when it is compared with p53 Mt/Mt cells. The released oxygen from MHC triggers apoptosis via p53 activation through its enhanced homo-oligomerization, post-translational modifications and nuclear localization. Thus MHC as a cellular oxygen-releasing compound has high potential as a drug for hypoxic tumor regression.

Photonics of Molecular Oxygen in Aqueous Solutions

The main stages in the development of research in the field of molecular-oxygen photonics and the most important methodical approaches to investigation of the lowest singlet states of oxygen molecules in organic and aqueous solutions are briefly outlined. The contemporary views on the kinetic and radiative parameters of singlet oxygen in water and deuterium oxide as well as the results of most recent studies of the red and IR absorption bands of oxygen molecules dissolved in water under normal conditions are presented. The data are compared with the absorption and luminescence parameters of oxygen in the gas phase and in organic media. The importance of the results of these studies for specialists in various fields of knowledge from molecular photophysics and spectroscopy to photodynamic and laser medicine is emphasized.

A chemiresistor sensor based on a cobalt(salen) metallopolymer for dissolved molecular oxygen

A resistance detection device for dissolved molecular oxygen in aqueous solutions is prepared using a chemiresistor material as sensor platform. The chemiresistive circuit element is fashioned from a thin film of a cobalt-salen metallopolymer electrodeposited on a platinum electrode. Electrochemical impedance spectroscopy shows that the resistive and capacitive properties of the sensor platform depend on the presence of dissolved oxygen. The electrical circuit models are R(Q/R)(Q/R) and R(Q/R)(Q/RW) in the absence and presence of oxygen, respectively. The chemiresistor sensor exhibits good sensitivity (0.483 kΩ L mg−1), excellent reversibility and excellent linearity over a range of dissolved oxygen concentrations typically found under environmental conditions (2.72–40.9 mg L−1). The sensor fabricated in this work can potentially serve as an alternative sensor for the detection of dissolved oxygen in environmental samples.

Oxidation of 5-aminouracil with molecular oxygen in aqueous solution in the presence of copper(II) chloride

5-Aminouracil was found to form a six-coordinate copper(II) complex in aqueous solution and undergo oxidation to 5,5,6-trihydroxypyrimidine-2,4(1H,3H)-dione in the presence of molecular oxygen. A scheme was proposed for the fixation and activation of molecular oxygen on six-coordinate copper(II) complex with 5-aminouracil. The effect of the ligand structure on the rate of its oxidation with molecular oxygen in aqueous solution in the presence of copper(II) ions was shown.

Degradation of contaminants by Cu+-activated molecular oxygen in aqueous solutions: Evidence for cupryl species (Cu3+)

Copper ions (Cu2+ and Cu+) have shown potential as Fenton-like activators for the circumneutral removal of organic contaminants from aqueous solutions. However, the major active species (cupryl species (Cu3+) versus hydroxyl radical (OH)) produced during the activation of hydrogen peroxide by Cu+ remain unclear. In this study, Cu+-O2 oxidation, in which hydrogen peroxide is produced via the activated decomposition of dissolved molecular oxygen, was used to degrade sulfadiazine, methylene blue, and benzoic acid. The results showed that both sulfadiazine and methylene blue could be efficiently degraded by Cu+-O2 oxidation in a wide effective pH range from 2.0 to 10.0. Quenching experiments with different alcohols and the effect of Br− suggested that Cu3+ rather than OH was the major active species. Electron paramagnetic resonance detected 5,5-dimethyl-2-hydroxypyrrolidine-N-oxyl (DMPO-OH), which was probably produced by the oxidation of DMPO by Cu3+ or OH formed as a product of Cu3+ decomposition. 4-hydroxybenzoic acid was produced during the degradation of benzoic acid by Cu3+. The findings of this study may help to explain the inconsistency regarding the dominant active species produced by the interaction of Cu+ and hydrogen peroxide.

The role of copper(II) ions in the oxidation of 5-hydroxy-6-methyluracil in the ground and electronically excited states with molecular oxygen in aqueous solutions

A spectral fluorescence study of photoinduced reactions in aqueous solutions has been carried out in order to examine the mechanisms of the oxidation of 5-hydroxy-6-methyluracil (I) in the ground and electronically excited states by molecular oxygen in the presence of copper(II) chloride. It has been found that 5,5,6-trihydroxy-6-methylpyrimidine-2,4-dione (II) is formed upon the photolysis of I. The spectral parameters (λmax) and the quantum yields (φ) of fluorescence (FL) of compounds I (φ = 8 × 10–4; λmax = 362 nm) and II (φ = 17 × 10–4; λmax = 306, 330 nm) have been determined. A reaction scheme was proposed, according to which the photooxidation of I occurs through the steps of the generation of the radical cation I •+ and the superoxide anion О 2 •- with the subsequent formation of 5,5,6-trihydroxy-6-methylpyrimidine-2,4-dione. The catalytic and inhibitory effects of Cu(II) ions on the oxidation of 5-hydroxy-6-methyluracil in the ground and electronically excited states, respectively, by the oxygen radical anion О 2 •- have been revealed.

Low-temperature oxidation of methanal on nanostructured silver–amino anion exchanger catalysts

Nanostructured silver–amino anion exchanger composites have been synthesized as catalysts for the low-temperature oxidation of methanal with molecular oxygen in aqueous solution. The oxidative conversion of methanal reaches 80–100% at 298 K. The methanal oxidation reaction is size-dependent, and its rate increases with a decrease in the silver nanoparticle size. The fixed amino groups of anion-exchange matrix play the role of additional active sites for the adsorption of methanal in the form of methylene glycolate–anions, which facilitates the reaction.

Colloidal Gold Nanoparticles: An Unexpected Catalytic Activity in Aqueous Phase with Dioxygen

Selective oxidations of alkenes were investigated using molecular oxygen in aqueous solution under mild conditions. Colloidal gold nanoparticles are particularly versatile catalysts for oxidation reaction with exceptionally high efficiency and significant selectivity. Gold nanorods (Au NRs) exhibited a slightly enhanced activity compare to gold nanospheres.

Platinum/Gold Alloy Nanoparticles-Supported Hydrotalcite Catalyst for Selective Aerobic Oxidation of Polyols in Base-Free Aqueous Solution at Room Temperature

As-prepared platinum/gold alloy nanoparticles-supported hydrotalcites (PtxAuy–starch/HTs) by using a soluble starch as a green reducing and a stabilizing agent are found to be truly effective heterogeneous catalysts for the selective aerobic oxidation of glycerol (GLY) and 1,2-propanediol (PG) in base-free aqueous solution using molecular oxygen in atmospheric pressure at room temperature. The PtxAuy–starch/HTs exhibited higher selectivities for oxidation of the primary hydroxyl group in GLY and PG toward glyceric acid (GA) and lactic acid (LA), respectively, with molecular oxygen in aqueous solution than those reactions over monometallic Pt–starch/HT or Au–starch/HT. Pt60Au40–starch/HT was found to be the most active catalyst for selective aerobic oxidation of polyols. It showed 73% GLY conversion with 57% GA yield and 63% PG conversion with 47% LA yield and retained high selectivity in recycling experiments. XRD patterns of the PtxAuy–starch NPs indicated the d-spacing of Pt atoms was changed by alloyin...

Gold nanoparticles catalyst with redox-active poly(aniline sulfonic acid): application in aerobic dehydrogenative oxidation of cyclic amines in aqueous solution

The catalysis of poly(2-methoxyaniline-5-sulfonic acid) (PMAS)/gold nanoparticles catalyst was demonstrated for the dehydrogenative oxidation reaction of 2-substituted indoline and dihydropyridine under molecular oxygen in aqueous solution. This catalyst was recyclable. Redox mediating function of PMAS was revealed by following the UV–vis spectra.

Low-temperature oxidation of sulfur dioxide by molecular oxygen in aqueous solutions of non-transition metals trifluoroacetates

Oxidation of SO2 was shown to occur in aqueous solutions of Li, Na, and K trifluoroacetates at room temperature. Oxidative activity of the non-transition metal trifluoroacetates increases on decreasing pH of solution and at equal pH values, it follows the sequence: Li < Na < K.

Selective catalytic conversion of biobased carbohydrates to formic acid using molecular oxygen

A new and straightforward method to transform carbohydrate-based biomass to formic acid (FA) by oxidation with molecular oxygen in aqueous solution using a Keggin-type H5PV2Mo10O40 polyoxometalate as catalyst is presented. Several water-soluble carbohydrates were fully and selectively converted to formic acid and CO2 under very mild conditions. It is worth noting, even complex biomass mixtures, such as poplar wood sawdust, were transformed to formic acid, giving 19 wt% yield (11% based on the carbon atoms in the feedstock) under non-optimized conditions.

ChemInform Abstract: Kinetics of the Reactions Between Alkyl Radicals and Molecular Oxygen in Aqueous Solution

The rate constant for the reaction R{sup {sm bullet}} + O{sub 2} {yields} ROO{sup {sm bullet}} in aqueous solution was determined for 18 alkyl radicals by laser flash photolysis. The values are all at the diffusion-controlled limit and lie in the range (1.6-4.9) {times} 10{sup 9} L mol{sup {minus}1} s{sup {minus}1}. The radicals studied are primary, substituted primary, secondary, and benzyl radicals.

Octahedral molecular sieves of the type K-OMS-2 with different particle sizes and morphologies: Impact on the catalytic properties in the aerobic partial oxidation of benzyl alcohol

Abstract Manganese-based octahedral molecular sieves of the type K-OMS-2 (cryptomelane structure) with different morphologies and specific surface areas in the range of 20–135 m2 g−1 were prepared via synproportionation of KMnO4 and Mn2+ salts, either in acidic aqueous suspension (reflux method) or by a solid-state reaction, and via oxidation of MnSO4 either by K2Cr2O7 or by molecular oxygen in aqueous solution. For the reflux method, the influence of K+ cations for the formation of the OMS-2 structure was proven. When KMnO4 is replaced by Ba(MnO4)2, the anion in the Mn2+ salt exerts a strong influence on the synthesis product. All materials were characterized by elemental analysis (ICP-OES), XRD, nitrogen sorption, scanning electron microscopy and TGA. For the oxidation of benzyl alcohol with molecular oxygen in liquid toluene at 110 °C, the catalytic activity of the K-OMS-2 materials is directly correlated to their specific surface area ABET. Since ABET increases with decreasing average crystallite diameter, the catalytic conversion presumably occurs at the outer crystallite surface. These relations are independent of morphology or synthesis procedure. The K-OMS-2 materials are more active than crystalline manganese oxides (MnO, Mn2O3, Mn3O4, β-MnO2), but less active than amorphous MnO2. Regeneration of deactivated K-OMS-2 catalysts can be achieved by calcining at 300 °C in air, partly due to the reversible desorption of water.

Influence of the Potassium Chloride Concentration on the Physical Properties of Electrodeposited ZnO Nanowire Arrays

The structural, electrical, and optical properties of zinc oxide nanowire arrays electrodeposited from the reduction of molecular oxygen in aqueous solutions containing zinc chloride and potassium chloride are studied as a function of the potassium chloride concentration. The concentration is varied in a wide range (from 5 × 10−5 to 3.4 M). The evolution of the lattice parameters suggests the formation of zinc interstitials, especially for [KCl] > 1 M. The donor density of the as deposited nanowires, which was determined from electrochemical impedance spectroscopy (EIS), varies between 7 × 1018 and 4 × 1020 cm−3. Annealing in air (1 h at 450 °C) decreases the donor density to 1017−1018 cm−3, weakening the dependence on KCl concentration. The line width of the near-band-edge photoluminescence shows a correlation with the donor density. By correlating the variation of the lattice parameters, the donor density and the line width of the photoluminescence, we conclude that intrinsic defects play a dominant rol...

Oxidation of 5-hydroxy-6-methyluracil to 5,5,6-trihydroxy-6-methylpyrimidine-2,4-dione with molecular oxygen

The oxidation of 5-hydroxy-6-methyluracil with molecular oxygen in aqueous solutions in the presence of copper(II) chloride gave 5,5,6-trihydroxy-6-methylpyrimidine-2,4-dione in a quantitative yield.

Spiroiminodihydantoin nucleoside formation from 2′‐deoxyguanosine oxidation by [18O‐labeled] singlet molecular oxygen in aqueous solution

The main singlet molecular oxygen ((1)O(2)) oxidation products of free 2'-deoxyguanosine (dGuo) in aqueous solution were identified as a pair of diastereomeric spiroiminodihydantoin 2'-deoxyribonucleosides (dSp) together with 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo). In the present work, evidence is provided from (18)[(1)O(2)] and H(2) (18)O labeling experiments, using HPLC-ESI-MS/MS, that the formation of dSp is explained by the addition of water to a reactive quinonoid intermediate, and a second reaction pathway leading to dSp involves (1)O(2) oxidation of initially generated 8-oxodGuo.

Analysis of fluorescence quenching of pyronin B and pyronin Y by molecular oxygen in aqueous solution

The fluorescence quenching of pyronin B and pyronin Y molecules by molecular oxygen in aqueous solution was studied by using steady-state and time-resolved fluorescence and UV–Vis absorption spectroscopy techniques. In order to understand the quenching mechanism, fluorescence decays, absorption and fluorescence spectra of the probes were recorded as a function of the oxygen concentration and temperature. The quenching was found to be appreciable and shows positive deviation in the Stern–Volmer representation obtained from the fluorescence intensity ratio. Fluorescence quenching constants ( k q) were calculated from the τ o/ τ vs. [ Q] plots having linear correlation and compared with calculated diffusion-controlled rate constants ( k diff) values. Experimental results were in good agreement with the simultaneous dynamic and static quenching model.