Presence Of Molecular Oxygen Research Articles

Tuning of Activated Carbon for Solvent-Free Oxidation of Cyclohexane

Activated carbon (AC) was prepared from carbonization of phosphoric acid soaked peanut shell at 380°C under inert atmosphere followed by activation with hydrogen peroxide. The AC was characterized by SEM, EDX, FTIR, TGA, and BET surface area and pore size analyzer. The potential of AC as a catalyst for solvent-free oxidation of cyclohexane to cyclohexanol and cyclohexanone (the mixture is known as KA oil) in the presence of molecular oxygen at moderate temperature was investigated in a self-designed double-walled three-necked batch reactor. The effect of different reaction parameters/additive was optimized. The maximum productivity value (2.14 mmolg−1 h−1, without base, and 4.85 mmolg−1 h−1, with 0.2 mmol NaOH) of the desired product was achieved under optimal reaction parameters: vol 12.5 mL, cat 0.4 g, time 14 h, oxygen flow 40 mL/min (pO2 760 Torr), stirring 1100 rpm, and temp 75°C. The AC shows recyclability for multiple runs without any significant loss in activity. Thus, the AC can be an efficient catalyst, due to low cost, ease of synthesis, easy recovery, nonleaching, and recyclability for multiple uses for the solvent-free oxidation of cyclohexane.

Structure evalution of electron irradiated borosilicate glass simuluated by molecular dynamics

Sodium borosilicate (NBS) glass is one of the candidate materials for high-level waste glass immobilization. A large number of experiments are performed to study the effect of irradiation by electrons or heavy ions on this type of glass. However, only a few researches of numerically investigating the effect of irradiated NBS glass have been reported. Furthermore those studies mainly focus on heavy-ion irradiation, and none of them is devoted to simulating the effects of electron irradiation on glass that has been irradiated by electrons, especially for structure evolution. In this paper, we propose a novel method of using molecular dynamics (MD) to simulate structure evolution of electron-irradiated NBS glass with compositions of 67.73% SiO2, 18.04% B2O3 and 14.23% Na2O, in mol.%. This method is based on the previous experimental results of Raman spectra and mechanism of structure transformation in irradiated glass. The Raman spectra confirm that the peak indicating the existence of molecular oxygen appears at 1550 cm-1 in irradiated glass. It is assumed that those oxygen atoms do not have any interactions with other adjacent atoms nor participate in the glass network recombination. This assumption is reasonable, for molecular oxygen mainly exists as dissolved oxygen instead of oxygen bubble and is located at interstice of glass network. Thus the presence of molecular oxygen does not have any effect on glass network structure. Then irradiated glass can be obtained by gradually randomly removing a certain number of oxygen atoms from the pristine glass. The glass with removed oxygen atoms is regarded as an irradiated glass which is considered as one irradiated by electrons in experiments. The results derived from MD simulation include average SiOSi bond angle, ring size distribution, sodium profile, evolution of [BO4] units, and [BO3] units. With the increase of removed oxygen atoms, the average bond angle of SiOSi decreases and the number of small rings gradually increases in irradiated glass. Besides, sodium phase separation is observed obviously after extensively removing oxygen. Moreover, in the process of removing oxygen, some [BO4] units transform into [BO3] units, and the transformation process reaches a saturation state finally. Those effects derived from MD such as decrease of SiOSi bond angle, increase of small rings in number, phase separation of sodium and structure change between [BO4] units and [BO3] units, are consistent with those of glass irradiated by electrons in previous experiments. Therefore, the method proposed in this paper will provide a new perspective to understand the mechanism of structure evolution in sodium borosilicate glass after being irradiated by electrons.

UV photodissociation dynamics of CHI2Cl and its role as a photolytic precursor for a chlorinated Criegee intermediate.

Photolysis of geminal diiodoalkanes in the presence of molecular oxygen has become an established route to the laboratory production of several Criegee intermediates, and such compounds also have marine sources. Here, we explore the role that the trihaloalkane, chlorodiiodomethane (CHI2Cl), may play as a photolytic precursor for the chlorinated Criegee intermediate ClCHOO. CHI2Cl has been synthesized and its UV absorption spectrum measured; relative to that of CH2I2 the spectrum is shifted to longer wavelength and the photolysis lifetime is calculated to be less than two minutes. The photodissociation dynamics have been investigated using DC slice imaging, probing ground state I and spin-orbit excited I* atoms with 2 + 1 REMPI and single-photon VUV ionization. Total translational energy distributions are bimodal for I atoms and unimodal for I*, with around 72% of the available energy partitioned in to the internal degrees of freedom of the CHICl radical product, independent of photolysis wavelength. A bond dissociation energy of D0 = 1.73 ± 0.11 eV is inferred from the wavelength dependence of the translational energy release, which is slightly weaker than typical C-I bonds. Analysis of the photofragment angular distributions indicate dissociation is prompt and occurs primarily via transitions to states of A'' symmetry. Complementary high-level MRCI calculations, including spin-orbit coupling, have been performed to characterize the excited states and confirm that states of A'' symmetry with highly mixed singlet and triplet character are predominantly responsible for the absorption spectrum. Transient absorption spectroscopy has been used to measure the absorption spectrum of ClCHOO produced from the reaction of CHICl with O2 over the range 345-440 nm. The absorption spectrum, tentatively assigned to the syn conformer, is at shorter wavelengths relative to that of CH2OO and shows far weaker vibrational structure.

Photochemically-induced anti-syn isomerization of quinazolinone-derived Schiff's bases: EPR, NMR and DFT analysis

Two quinazolinone-based Schiff's bases (1 and 2) have been studied by UV/vis, EPR, and NMR spectroscopic methods, as well as DFT calculations. UV/vis spectroscopy confirmed that both compounds undergo significant changes upon UV irradiation in DMSO solutions in the presence of molecular oxygen. EPR spectroscopy proved generation of reactive radical intermediates via the interaction of activated molecular oxygen with the solvent molecules upon UV irradiation. Furthermore, photochemically-induced electron transfer led to isomerization from anti to syn-isomer when irradiated by UV light as demonstrated by NMR spectroscopy. The process is relatively slow, the isomerization takes up to 6 h and the conversion reaches about 40%. The original equilibrium was re-established within 30 days. Theoretical and experimental data also showed that the degree of conversion and the rotational energy barriers are affected by substitution at the aromatic rings.

The production of reduced-alcohol wines using Gluzyme Mono® 10.000 BG-treated grape juice

High alcohol wines have become a major challenge in the international wine trade. Several physical processes are used to produce wines with reduced-alcohol content, all of which involve the selective extraction of ethanol based on volatility or diffusion. In this study, the possibility of Gluzyme Mono® 10.000 BG (Gluzyme) (Novozymes, South Africa) to reduce the glucose content of synthetic grape juice before fermentation was investigated in order to produce wine with reduced-alcohol content. Gluzyme is a glucose oxidase preparation from Aspergillus oryzae, currently used in the baking industry. Glucose oxidase catalyses the oxidation of glucose to gluconic acid and hydrogen peroxide (H2O2) in the presence of molecular oxygen. Gluzyme was initially used in synthetic grape juice, where different enzyme concentrations and factors influencing its efficiency were investigated under winemaking conditions. The results showed up to 0.5% v/v less alcohol at an enzyme concentration of 20 kU compared to the control samples. This reduction in alcohol was increased to 1 and 1.3% v/v alcohol at pH 3.5 and pH 5.5 respectively in aerated (8 mg/L O2) synthetic grape juice using 30 kU enzyme. Secondly, Gluzyme was used to treat Pinotage grape must before fermentation. Gluzyme-treated wines at 30 kU enzyme concentration after fermentation contained 0.68% v/v less alcohol than the control wines. A decrease in acetic acid concentration of the treated compared to control wines was also observed.

Inter-Kingdom Modification of Metabolic Behavior: [GAR+] Prion Induction in Saccharomyces cerevisiae Mediated by Wine Ecosystem Bacteria

The yeast Saccharomyces cerevisiae has evolved to dominate grape juice fermentation. A suite of cellular properties, rapid nutrient depletion, production of inhibitory compounds and the metabolic narrowing of the niche, all enable a minor resident of the initial population to dramatically increase its relative biomass in the ecosystem. This dominance of the grape juice environment is fueled by a rapid launch of glycolysis and energy generation mediated by transport of hexoses and an efficient coupling of transport and catabolism. Fermentation occurs in the presence of molecular oxygen as the choice between respiratory or fermentative growth is regulated by the availability of sugar a phenomenon known as glucose or catabolite repression. Induction of the [GAR+] prion alters the expression of the major hexose transporter active under these conditions, Hxt3, reducing glycolytic capacity. Bacteria present in the grape juice ecosystem were able to induce the [GAR+] prion in wine strains of S. cerevisiae. This induction reduced fermentation capacity but did not block it entirely. However, dominance factors such as the rapid depletion of amino acids and other nitrogen sources from the environment were impeded enabling greater access to these substrates for the bacteria. Bacteria associated with arrested commercial wine fermentations were able to induce the prion state, and yeast cells isolated from arrested commercial fermentations were found to be [GAR+] thus confirming the ecological relevance of prion induction. Subsequent analyses demonstrated that the presence of environmental acetic acid could lead to [GAR+] induction in yeast strains under certain conditions. The induction of the prion enabled yeast growth on non-preferred substrates, oxidation and reduction products of glucose and fructose, present as a consequence of bacterial energy production. In native ecosystems prion induction never exceeded roughly 50-60% of the population of yeast cells suggesting that the population retains the capacity for maximal fermentation. Thus, the bacterial induction of the [GAR+] prion represents a novel environmental response: the query of the environment for the presence of competing organisms and the biological decision to temper glucose repression and dominance and enter a metabolic state enabling coexistence.

Pd/ZrO2: An Efficient Catalyst for Liquid Phase Oxidation of Toluene in Solvent Free Conditions

Abstract 0.1 % Pd/ZrO2 was synthesized and characterized by various physicochemical techniques and was successfully used as catalyst for solvent free oxidation of toluene in the presence of molecular oxygen using batch reactor. The catalytic performance of Pd/ZrO2 was explored in terms of effect of catalyst loading, reaction time, temperature and partial pressure of oxygen on oxidation of toluene in solvent free conditions. Pd/ZrO2 was found as a stable catalyst under the reaction conditions. Used catalyst exhibited the same catalytic efficiency as fresh catalyst under similar reaction conditions. Reaction was taking place according to Langmuir-Hinshelwood type of mechanism.

Visible-Light-Induced Efficient Selective Oxidation of Nonactivated Alcohols over {001}-Faceted TiO2 with Molecular Oxygen.

In the presence of molecular oxygen, a {001}-faceted nanocrystalline anatase TiO2 catalyst enabled the selective oxidation of nonactivated aliphatic alcohols to the corresponding aldehydes or ketones under visible light. The reaction shows excellent conversion and selectivity towards the formation of the carbonyl products without over-oxidation to the corresponding carboxylic acids. The exceptional reactivity of the catalyst is possibly due to the absorption of visible light originating from a stronger interaction of alcohol with the {001} facet, which facilitates the modification of the band structure of TiO2 , thus facilitating the photogenerated hole transfer and subsequent oxidation processes. The experimental results have also been corroborated by first-principles quantum chemical DFT calculations.

CuCl2-Mediated Oxidative Coupling of N,N-Dimethylanilines with [60]Fullerene in the Presence of Molecular Oxygen

An efficient and simple copper-mediated oxidative coupling of N,N-dimethylanilines with [60]fullerene was employed to obtain a high yield of scarce 6-membered-ring [60]fullerene-fused tetrahydroquinolines. The reaction occurred through sp3 C–H bond activation under mild reaction conditions with molecular oxygen as the oxidant. A plausible reaction pathway was proposed, and the electrochemistry of the fullerene products was investigated.

Understanding paper degradation: identification of products of cellulosic paper decomposition at the wet-dry "tideline" interface using GC-MS.

Cellulose paper degradation products forming in the "tideline" area at the wet-dry interface of pure cellulose paper were analyzed using gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) and high-resolution electrospray ionization-mass spectrometry (ESI-MS, LTQ Orbitrap) techniques. Different extraction protocols were employed in order to solubilize the products of oxidative cellulose decomposition, i.e., a direct solvent extraction or a more laborious chromophore release and identification (CRI) technique aiming to reveal products responsible for paper discoloration in the tideline area. Several groups of low molecular weight compounds were identified, suggesting a complex pathway of cellulose decomposition in the tidelines formed at the cellulose-water-oxygen interface. Our findings, namely the appearance of a wide range of linear saturated carboxylic acids (from formic to nonanoic), support the oxidative autocatalytic mechanism of decomposition. In addition, the identification of several furanic compounds (which can be, in part, responsible for paper discoloration) plus anhydro carbohydrate derivatives sheds more light on the pathways of cellulose decomposition. Most notably, the mechanisms of tideline formation in the presence of molecular oxygen appear surprisingly similar to pathways of pyrolytic cellulose degradation. More complex chromophore compounds were not detected in this study, thereby revealing a difference between this short-term tideline experiment and longer-term cellulose aging.

Isotope-Labeling Studies Support the Electrophilic Compound I Iron Active Species, FeO(3+), for the Carbon-Carbon Bond Cleavage Reaction of the Cholesterol Side-Chain Cleavage Enzyme, Cytochrome P450 11A1.

The enzyme cytochrome P450 11A1 cleaves the C20-C22 carbon-carbon bond of cholesterol to form pregnenolone, the first 21-carbon precursor of all steroid hormones. Various reaction mechanisms are possible for the carbon-carbon bond cleavage step of P450 11A1, and most current proposals involve the oxoferryl active species, Compound I (FeO(3+)). Compound I can either (i) abstract an O-H hydrogen atom or (ii) be attacked by a nucleophilic hydroxy group of its substrate, 20R,22R-dihydroxycholesterol. The mechanism of this carbon-carbon bond cleavage step was tested using (18)O-labeled molecular oxygen and purified P450 11A1. P450 11A1 was incubated with 20R,22R-dihydroxycholesterol in the presence of molecular oxygen ((18)O2), and coupled assays were used to trap the labile (18)O atoms in the enzymatic products (i.e., isocaproaldehyde and pregnenolone). The resulting products were derivatized and the (18)O content was analyzed by high-resolution mass spectrometry. P450 11A1 showed no incorporation of an (18)O atom into either of its carbon-carbon bond cleavage products, pregnenolone and isocaproaldehyde . The positive control experiments established retention of the carbonyl oxygens in the enzymatic products during the trapping and derivatization processes. These results reveal a mechanism involving an electrophilic Compound I species that reacts with nucleophilic hydroxy groups in the 20R,22R-dihydroxycholesterol intermediate of the P450 11A1 reaction to produce the key steroid pregnenolone.

Oxidative Depolymerization of Lignin Using a Novel Polyoxometalate-Protic Ionic Liquid System

Oxidative depolymerization of lignin obtained from pine and willow can be achieved in a novel system encompassing the ionic liquid (IL) 1-butylimidazolium hydrogensulfate coupled with a vanadium based polyoxometalate (POM) under oxygen rich conditions. Along with an array of phenols and functionalized aromatics, vanillin and syringaldehyde were the main products extracted from the IL. The overall yield of aldehyde products were shown to be higher on lignin samples obtained with shorter pretreatment times, with vanillin being the exclusive aldehyde product obtained from pine. In the presence of molecular oxygen, the highest yield of aldehyde products was obtained when 5 wt % of the POM relative to the IL was employed and constituted the major product in the extracted oils. This system succeeds in exploiting the ability of ILs to depolymerize lignin and the remarkable properties of the POM to oxidize the lignin fragments into useful platform chemicals.

In Situ ATR-FTIR Investigation of the Effects of H2o and D2o Adsorption on the TiO2 Surface

Surface hydroxyl groups on TiO2 play an important role for the photoinduced hydrophilicity as well as for photocatalytic reactions. Adsorbed species such as water and organic compounds are expected to affect the hydroxyl group behaviour on the TiO2 surface, however, their influences have to date not been clearly determined. Herein, a detailed investigation of H2O and D2O adsorption on the TiO2 surface (anatase) in the dark and under UV(A) irradiation is reported using ATR-FTIR spectroscopy. The adsorption and photocatalytic degradation of acetate on the TiO2 surface was also investigated in H2O and D2O. Adsorption of H2O with different ratios of D2O revealed an isotopic exchange reaction occurring on the surface of TiO2 in the dark. This isotopic exchange leads to a change in the behaviour of acetate with the intensity of the OH bending band between the carboxylate and the OH group at 900 cm-1 decreasing and ultimately disappearing in the dark. Upon illumination with UV(A) light both, OH and OD groups are formed, which in turn increase the hydrophilicity of the TiO2 surface. The amount of OH and OD groups was found to increase in the presence of molecular oxygen. This increase is most likely caused by the photoadsorption of H2O and D2O due to photoinduced charge transfer processes [1]. On the other hand, the investigations show that during UV(A) irradiation the acetate molecules can adsorb again on the TiO2 surface which is explained by an increased surface area due to a de-aggregation of the particles agglomerates [2]. Based upon the observed correlation between the carboxylate and the OH and/or OD groups at neutral pH (pH ≈ pHzpc) it is obvious that acetate preferentially adsorbs on the positively charged anatase in a monodentate structure. As an in-situ technique, ATR-FTIR studies provide evidence of the adsorption behaviour of water and D2O on TiO2 surfaces thus yielding new insights into the mechanism of photoinduced hydrophilicity and of photocatalytic reactions.

ChemInform Abstract: Propargylation of 1,3‐Dicarbonyl Compounds Catalyzed by 2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone and Sodium Nitrite in the Presence of Molecular Oxygen and Formic Acid.

Catalyzed by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and sodium nitrite, the coupling reaction of 1,3-diarylpropynes and 1,3-dicarbonyl compounds using molecular oxygen as a terminal oxidant was developed. The reaction was promoted dramatically in the presence of HCOOH. The corresponding products were obtained within half an hour in 37–87% yields.

Nanoscale upconversion for oxygen sensing

Optical oxygen sensors have many promising qualities but rely on excitation by violet or blue wavelengths that suffer from high levels of scattering and absorption in biological tissues. Here we demonstrate an alternative method using 980nm near-infrared light to initially stimulate ceramic upconverting nanoparticles (UCNPs) contained within a novel form, electrospun core-shell fibers. The emission of the UCNPs excites a molecular optical oxygen sensor, the subsequent phosphorescent emission being dynamically quenched by the presence of molecular oxygen. The potential for use of such an energy transfer within electrospun fibers widely used in biological applications is promising. However, current knowledge of such ‘handshake’ interactions is limited. Fiber-based carriers enabling such optical conversions provide unique opportunities for biosensing as they recapitulate the topography of the extracellular matrix. This creates a wide array of potential theranostic, fiber-based applications in disease diagnosis/imaging, drug delivery and monitoring of therapeutic response. Using a fiber-based vehicle, we observed gaseous oxygen sensing capabilities and a linear Stern-Volmer response allowing highly accurate calibration. Configurational aspects were also studied to determine how to maximize the efficiency of this ‘handshake’ interaction.

Agent-based Model of Oxidation Reactions of Ferrous Ions

Molecules in comets are formed through chemical oxidation reactions induced by radiation. Thesereactions can be simulated in laboratory experiments applying gamma radiation to samples at low temperatures. The kinetics of the induced reactions can be modeled by a system of coupled non-linear ordinary differential equations describing the mass balance of all of the species involved. However, finding a traditional solution to this system is difficult because of the large number of reactions involved, the need to solve all of the equations simultaneously, and the strong dependence on the initial conditions due to the non-linear character of the equations. For each species, the mass-balance equation includes all of the reaction rates leading to production (source terms) and to destruction (sink terms). In this sense, each equation is analogous to the prey-predator model, with the sink terms consider to be the “prey” and the source terms as the “predators”. Due to this, we can use an agent-based model to follow the kinetics of the chemical reactions. In this paper, we present a code in Python for an agent-based model of the chemical oxidation of ferrous ions (Fe2+) induced by gamma radiation and in the presence of molecular oxygen. We compare the results that this code produces for molar concentrations of Fe3+over time with those obtained in the laboratory.

Gold-catalyzed selectivity-switchable oxidation of benzyl alcohol in the presence of molecular oxygen

A selectivity-switchable oxidation of benzyl alcohol by molecular oxygen is achieved with the iron doped graphene (FeGr) supported gold catalysts. The oxidative esterification process is dominant with Au/FeGr and K2CO3 as the catalyst in methanol where a 96.2% conversion of benzyl alcohol and 99.9% selectivity of methyl benzoate were obtained. While, the oxidation of benzyl alcohol is orientated to produce benzaldehyde in n-butanol using AuPd/FeGr as the catalyst, in which an 89.1% conversion and 87.5% selectivity of benzaldehyde was attained. Moreover, the effects of the additive, reaction medium and reaction time were investigated. Also, the oxidation of different benzylic alcohols was successfully performed under the optimal conditions. Furthermore, the used catalysts were characterized by XRD, NH3-TPD, SEM, Roman, TG-DTA and BET techniques. Based on the experimental results and phenomena, a possible reaction mechanism is proposed for the selective oxidation of benzyl alcohol with molecular oxygen in which alkyl benzoate is produce through the hemiacetal intermediate of benzaldehyde with short chain alcohol, and the generation rate of hemiacetal decides the selectivity of product.

Kinetics of the Reaction of CH3O2 Radicals with OH Studied over the 292-526 K Temperature Range.

Reaction of methyl peroxy radicals with hydroxyl radicals, CH3O2 + OH → CH3O + HO2 (1a) and CH3O2 + OH → CH2OO + H2O (1b) was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 292-526 K temperature range and pressure 1 bar (bath gas He). Hydroxyl radicals were generated in the reaction of electronically excited oxygen atoms O((1)D), produced in the photolysis of N2O at 193.3 nm, with H2O. Methyl peroxy radicals were generated in the reaction of methyl radicals, CH3, produced in the photolysis of acetone at 193.3 nm, and subsequent reaction of CH3 with O2. Temporal profiles of OH were monitored via transient absorption of light from a DC discharge H2O/Ar low-pressure resonance lamp at ca. 308 nm. The absolute intensity of the photolysis light was determined by accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The overall rate constant of the reaction is k1a+1b = (8.4 ± 1.7) × 10(-11)(T/298 K)(-0.81) cm(3) molecule(-1) s(-1) (292-526 K). The branching ratio of channel 1b at 298 K is less than 5%.

Redox-Dependent Dynamics in Heme-Bound Bacterial Iron Response Regulator (Irr) Protein.

The iron response regulator (Irr) protein from Bradyrhizobium japonicum mediates iron-dependent regulation of heme biosynthesis. Irr degrades in response to heme availability through a process that involves the binding of heme to Cys-29 in the heme regulatory motif (HRM) in the presence of molecular oxygen. In this work, we assessed the dynamics of one-electron reduction of heme-bound Irr by monitoring the formation of transient intermediates by pulse radiolysis. Hydrated electrons generated by pulse radiolysis reduced heme iron-bound Irr, facilitating the binding of molecular oxygen to the heme iron in Irr through an initial intermediate with an absorption maximum at 420 nm. This initial intermediate was converted to a secondary intermediate with an absorption maximum at 425 nm, with a first-order rate constant of 1.0 × 10(4) s(-1). The Cys-29 → Ala (C29A) mutant of Irr, on the other hand, did not undergo the secondary phase, implying that ligand exchange of Cys-29 for another ligand takes place during the process. Spectral changes during the reduction of the heme-bound Irr revealed that binding of CO to ferrous heme consisted of two phases with kon values of 1.3 × 10(5) and 2.5 × 10(4) M(-1) s(-1), a finding consistent with the presence of two distinct hemes in Irr. In aerobic solutions, by contrast, oxidation of the ferrous heme to the ferric form was found to be a two-phase process. The C29A mutant was similarly oxidized, but this occurred as a single-phase process. We speculate that a reactive oxygen species essential for degradation of the protein is generated during the oxidation process.

Synthesis of 2,4,6-Trisubstituted Pyridines by Oxidative Eosin Y Photoredox Catalysis.

Eosin Y, an organic dye, was activated as a photoredox catalyst in the presence of molecular oxygen using visible light and, when it was used in the reaction of aryl ketones and benzyl amines, afforded good yields (52-87%) of 2,4,6-triarylpyridines (21 examples) at ambient temperature. The aryl groups at the 2- and 6-positions are derived from ketones, while benzyl amine plays the dual role of providing an aryl functionality at the 4-position of pyridine as well as being a nitrogen donor.