Final Oxidation Products Research Articles

Aerobic Oxidation of Hydrocarbons Catalyzed by Mn-Doped Nanoporous Aluminophosphates(I): Preactivation of the Mn Sites

We apply state of the art electronic structure techniques, based on hybrid exchange-functionals in DFT and periodic boundary conditions, to unravel the reaction mechanism responsible for the initial stages of the aerobic oxidation of hydrocarbons catalyzed by Mn-doped aluminophosphates. In this preactivation step of the catalyst, which precedes the catalytic propagation cycle in which the final oxidation products (alcohol, aldehyde, and carboxylic acid) are formed, the MnIII ions initially present in the activated (calcined) catalyst are transformed by interaction with one alkane and one O2 molecule into new Mn-bearing species: a reduced MnII site and a MnIII···peroxo complex, which are active for the subsequent propagation cycle. The preactivation step has a high activation energy, calculated as 135 kJ/mol, explaining the long induction time observed experimentally. Our results further show that MnIII sites are able to produce the hydroperoxide intermediate from the reactants; however, this intermediate can be transformed into the oxidative products only through reduced MnII sites. The latter are formed from MnIII in the preactivation step, via a H-abstraction from the hydrocarbon, also yielding an alkyl radical (R•) that subsequently adds O2 in a stereospecific way to form a free peroxo radical, ROO•. Migration of ROO• in the AlPO nanopores frees MnII for the propagation cycle and forms MnIII···ROO• complexes also needed for propagation. We demonstrate the essential role of MnIII active sites at the initial stages of the reaction for activating the hydrocarbon molecules; such hydrocarbon activation catalyzed by Mn requires much lower activation energies than through noncatalytic pathways, where the hydrocarbon is activated by O2 alone.

In VitroStudies of DNA Damage Caused by Tricyclic Antidepressants: A Role of Peroxidase in the Side Effects of the Drugs

Studies show that tricyclic antidepressants prescribed for migraines, anxiety, and child enuresis have numerous adverse effects in living cells. One of the undesired outcomes observed under treatment with these drugs is DNA damage. However, the mechanisms underlying damage have yet to be elucidated. We performed in vitro studies of the DNA damage caused by four tricyclic antidepressants: imipramine, amitriptyline, opipramol, and protriptyline. We focused particularly on the DNA damage aided by peroxidases. As a model of a peroxidase, we used horseradish peroxidase (HRP). At pH 7, reactions of HRP with excess hydrogen peroxide and imipramine yielded an intense purple color and a broad absorption spectrum with the maximum intensity at 522 nm. Reactions performed between DNA and imipramine in the presence of H(2)O(2) and HRP resulted in the disappearance of the DNA band. In the case of the other three drugs, this effect was not observed. Extraction of the DNA from the reaction mixture indicated that DNA is degraded in the reaction between imipramine and H(2)O(2) catalyzed by HRP. The final product of imipramine oxidation was identified as iminodibenzyl. We hypothesize that the damage to DNA was caused by an imipramine reactive intermediate.

An Investigation on the Principal Paths to Plasma Oxidation of Propylene and NO

Hydrocarbons plasma oxidation combined with fast selective catalytic reduction is a promising technology for treating the diesel exhausts with high sulfur content. In this study, propylene (C3H6) oxidation in a nonthermal plasma process and its effects on NO transition were investigated. The experimental results and the results from simulation based on a simplified model indicated that the binding reactions of O radicals ionizing from O2 with C3H6 are the trigger reactions, from which carbonyl (HCO) and ethyl radicals (C2H5) are produced and play crucial roles in C3H6 and NO oxidation. It was found that carbon monoxide (CO), carbon dioxide (CO2), formaldehyde (HCHO), acetaldehyde (CH3CHO), formic acid (HCOOH), etc. are the final oxidation products of C3H6 oxidation in the absence of NO. With the presence of NO, peroxy (CH3O2 and C2H5O2), and hydroperoxy radical (HO2) that come from C3H6 oxidation are able to oxidize NO to NO2 efficiently and, meanwhile, induce the reactions that would lead to the formatio...

ChemInform Abstract: Growth Conditions, Electrical Resistivity, Microhardness, and Thermal Properties of Nb5Sn2Ga Single Crystals Synthesized from High-Temperature Tin Solutions.

Abstract Single crystals of a new ternary intermetallic compound Nb 5 Sn 2 Ga were prepared from high-temperature tin solutions by a self flux method using Nb and Ga metals as starting materials under a He gas. The crystal was examined by X-ray diffraction and chemical analyses. The ternary single crystals Nb 5 Sn 2 Ga were generally obtained in the form of prismatic shape extending in the [001] direction, and with (100) and (110) faces. The Vickers microhardness value on (001) plane and (100) or (110) planes of crystals is in the range of 8.5–10.1 GPa. The electrical resistivity determined on crystal is in the range of 253.1–276.7 μΩ cm. The oxidation of Nb 5 Sn 2 Ga crystal starts at about 562°C. The final oxidation products were NbO 2 , Nb 12 O 29 , Nb 2 O 5 , SnO 2 and Ga 2 O 3 .

Hydrogen Production via Photolytic Oxidation of Aqueous Sodium Sulfite Solutions

Sulfur dioxide (SO(2)) emission from coal-burning power plants and refinery operations has been implicated as a cause of acid rain and other air pollution related problems. The conventional treatment of SO(2)-contaminated air consists of two steps: SO(2) absorption using an aqueous sodium hydroxide solution, forming aqueous sodium sulfite (Na(2)SO(3)), and Na(2)SO(3) oxidation via air purging to produce sodium sulfate (Na(2)SO(4)). In this process, the potential energy of SO(2) is lost. This paper presents a novel ultraviolet (UV) photolytic process for production of hydrogen from aqueous Na(2)SO(3) solutions. The results show that the quantum efficiency of hydrogen production can reach 14.4% under illumination from a low pressure mercury lamp. The mechanism occurs via two competing reaction pathways that involve oxidation of SO(3)(2-) to SO(4)(2-) directly and through the dithionate (S(2)O(6)(2-)) ion intermediate. The first route becomes dominant once a photostationary state for S(2)O(6)(2-) is established. The initial pH of Na(2)SO(3) solution plays an important role in determining both the hydrogen production rate and the final products of the photolytic oxidation. At initial solution pH of 9.80 Na(2)SO(3) photo-oxidation generates Na(2)SO(4) as the final reaction product, while Na(2)S(2)O(6) is merely a reaction intermediate. The highest hydrogen production rate occurs when the initial solution pH is 7.55. Reduction in the initial solution pH to 5.93 results in disproportionation of HSO(3)(-) to elemental sulfur and SO(4)(2-) but no hydrogen production.

Mild Oxidation of C−C Bonds of Benzoiridacycles

We describe herein the formation of two metallacyclic derivatives, 4b and 5b, which contain a coordinated ketone functionality (from an α-keto ester metallacyclic substituent). An iridafuran, 6, that results from the reaction of TpMe2Ir(Ph)2(N2) (TpMe2 = hydrotris(3,5-dimethylpyrazolyl)borate) with di-tert-butyl acetylenedicarboxylate (DTAD) and oxygen is also reported. Our results reveal that the reactions proceed through iridacycle intermediates (detected by NMR) resulting formally from the coupling of one (in the case of 6) or two (for 4b and 5b) molecules of DTAD, with the metal unit “TpMe2Ir(C6H4)” derived from the iridium precursor. These intermediates experience very mild and selective oxidation by air to incorporate one (4b and 5b) or three (6) oxygen atoms in the final oxidation products.

DDQ oxidation of hydroxyisochromans and homologues

Some hydroxyisochromans and hydroxyphthalans are tested under oxidative conditions obtaining hydroxybenzophenone derivatives. All reactions were followed by 1H NMR spectroscopy. Some final main oxidation products were also isolated and characterised.

Interactions between DNA Purines and Ruthenium Ammine Complexes within Nanostructured Sol−Gel Silica Matrixes

The interactions between DNA purines (guanine and adenine) and three ruthenium ammine complexes (hexaammineruthenium(III) chloride, hexaammineruthenium(II) chloride, and ruthenium-red) were studied in a confined environment, within sol-gel silica matrixes. Two encapsulation methods were rehearsed (differing in temperature and condensation pH), in order to analyze the effects of the sol-gel processes on the purines and on the Ru complexes separately. The extent of decomposition of the Ru complexes, as well as the interactions established with the purine bases, proved to be determined by the coencapsulation method. Combined results by diffuse reflectance UV-vis and infrared spectroscopies showed that, when coencapsulation is carried out at 60 degrees C, specific H bonding interactions are established between the amine group of Ade and the ammine groups of the Ru complex or the hydroxo group of an early decomposition product. These are responsible for the important role of the purine in inhibiting the oxidation reactions of the Ru(II) and Ru(III) complexes. In contrast, Gua establishes preferential H bonds with the matrix (mainly due to the carbonyl group), leading to higher yields in the final oxidation products of the Ru complexes, namely, trimers and dimers. Direct covalent bonding of either purine to the metal was not observed.

Recovery of plutonium from carbonate wash solutions

A novel method has been developed for recovery of plutonium and uranium from carbonate wash solutions generated during solvent wash process involved in the reprocessing of high burn up FBTR fuel. The proposed method involves a selective coprecipitation of Pu and U by adding ammonium hydroxide to the pre acidified carbonate wash solution. Substantial removal of DBP by successive steps of coprecipitation, completely eliminates the possibility of undesired solid formation which is mainly due to the presence of high content of DBP. By adopting this method, an excellent decontamination factor for DBP has been achieved without any crud/solid formation. Phosphate content in the final oxide product meets the product specifications. Flowsheet condition necessary for the recovery process for plutonium from the aqueous carbonate solution is formulated and adopted in the CORAL facility.

Oxidation Reactions of Cytosine DNA Components by Hydroxyl Radical and One-Electron Oxidants in Aerated Aqueous Solutions

Indirect evidence strongly suggests that oxidation reactions of cytosine and its minor derivative 5-methylcytosine play a major role in mutagenesis and cancer. Therefore, there is an emerging necessity to identify the final oxidation products of these reactions, to search for their formation in cellular DNA, and to assess their mutagenic features. In this Account, we report and discuss the main *OH and one-electron-mediated oxidation reactions, two of the most potent sources of DNA damage, of cytosine and 5-methylcytosine nucleosides that have been recently characterized. The addition of *OH to the 5,6-unsaturated double bond of cytosine and 5-methylcytosine generates final degradation products that resemble those observed for uracil and thymine. The main product from the oxidation of cytosine, cytosine glycol, has been shown to undergo dehydration at a much faster rate as a free nucleoside than when inserted into double-stranded DNA. On the other hand, the predominant *OH addition at C5 of cytosine or 5-methylcytosine leads to the formation of 5-hydroxy-5,6-dihydro radicals that give rise to novel products with an imidazolidine structure. The mechanism of the formation of imidazolidine products is accounted for by rearrangement reactions that in the presence of molecular oxygen likely involve an intermediate pyrimidine endoperoxide. The reactions of the radical cations of cytosine and 5-methylcytosine are governed by competitive hydration, mainly at C6 of the pyrimidine ring, and deprotonation from the exocyclic amino and methyl group, leading in most cases to products similar to those generated by *OH. 5-Hydroxypyrimidines, the dehydration products of cytosine and uracil glycols, have a low oxidation potential, and their one-electron oxidation results in a cascade of decomposition reactions involving the formation of isodialuric acid, dialuric acid, 5-hydroxyhydantoin, and its hydroxyketone isomer. In biology, GC --> AT transitions are the most common mutations in the genome of aerobic organisms, including the lacI gene in bacteria, lacI transgenes in rodents, and the HPRT gene in rodents and humans, so a more complete understanding of cytosine oxidation is an essential research goal. The data and insights presented here shed new light on oxidation reactions of cytosine and 5-methylcytosine and should facilitate their validation in cellular DNA.

Oxidation pathways of natural dye hematoxylin in aqueous solution

The oxidation mechanism of hematoxylin was studied in phosphate buffers and 0.1 M KCl by cyclic voltammetry and UV-Vis spectroscopy under deaerated conditions. The redox potential of hematoxylin in buffered solution strongly depends on pH. A two electron oxidation is preceded by deprotonation. The homogeneous rate of deprotonation process of hematoxylin in 0.1 M phosphate buffer is kd = (2.5 ± 0.1) × 104 s–1. The cyclic voltammetry under unbuffered conditions shows the distribution of various dissociation forms of hematoxylin. The dissociation constants pK1 = 4.7 ± 0.2 and pK2 = 9.6 ± 0.1 were determined using UV-Vis spectroscopy. The final oxidation product was identified by gas chromatography with mass spectrometry detection as hemathein. The distribution of oxidation products differs under buffered and unbuffered conditions. The dye degradation in natural unbuffered environment yields hemathein and hydroxyhematoxylin, which is absent in buffered solution.

Preparation and morphology of porous SiO2 ceramics derived from fir flour templates

The preparation of SiO2 ceramics with controllable porous structure from fir flour templates via sol-gel processing was investigated. The specific size the fir flour, which was treated with 20 % NaOH solution, was infiltrated with a low viscous silica sol and subsequently calcined in air, which resulted in the formation of highly porous SiO2 ceramics. X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM) were employed to investigate the microstructure and phase formation during processing as well as of the SiO2 ceramics. N2 adsorption measurements were used to analyze the pore size distributions (PSD) of the final ceramics. The results indicated that the surface topography was changed and the proportion of the amorphous material was increased in NaOH-treated fir flour. The final oxide products retained ordered structures of the pores and showed unique pore sizes and distributions with hierarchy on the nanoscale derived from the fir flour.

Preparation and morphology of porous SiO2 ceramics derived from fir flour templates

The preparation of SiO2 ceramics with controllable porous structure from fir flour templates via sol-gel processing was investigated. The specific size the fir flour, which was treated with 20 % NaOH solution, was infiltrated with a low viscous silica sol and subsequently calcined in air, which resulted in the formation of highly porous SiO2 ceramics. X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM) were employed to investigate the microstructure and phase formation during processing as well as of the SiO2 ceramics. N2 adsorption measurements were used to analyze the pore size distributions (PSD) of the final ceramics. The results indicated that the surface topography was changed and the proportion of the amorphous material was increased in NaOH-treated fir flour. The final oxide products retained ordered structures of the pores and showed unique pore sizes and distributions with hierarchy on the nanoscale derived from the fir flour.

Earthworm cast as a promising filter bed material and its methanotrophic contribution to methane removal

The use of biocovers is a promising strategy toward mitigating CH 4 emission from smaller and/or older landfills. In this study, a filter bed material consisting of a mixture of earthworm cast and rice paddy soil in a biocover was evaluated. Although the CH 4 oxidation rate of the enriched paddy soil was 4.9 μg g-dry soil −1 h −1, it was enhanced to 25.1 μg g-dry soil −1 h −1 by adding an earthworm cast with a 3:7 ratio of earthworm cast:soil (wet weight). CO 2 was found as the final oxidation product of CH 4, and the mole ratio of CO 2 production to CH 4 consumption was 0.27. At a moisture content range of 15–40% and a temperature range of 20–40 °C, the CH 4 oxidation rates of the enriched mixture were more than 57% of the maximum rate obtained at 25% moisture content and 25 °C. By denaturing gradient gel electrophoresis analysis employing primers for the universal bacterial 16S rRNA gene, and terminal-restriction fragment length polymorphism analysis using primers for the pmoA gene, the bacterial and methanotrophic communities in the enriched mixture were mainly originate from paddy soil and earthworm cast, respectively. Both type I (mainly Methylocaldum) and type II methanotrophs (mainly Methylocystis) played important roles in CH 4 oxidation in the enriched mixture.

Factors That Affect the Nature of the Final Oxidation Products in “Peroxo‐Shunt” Reactions of Iron–Porphyrin Complexes

The present study focuses on the oxidation of the water-soluble and water-insoluble iron(III)-porphyrin complexes [Fe(III)(TMPS)] and [Fe(III)(TMP)] (TMPS = meso-tetrakis(2,4,6-trimethyl-3-sulfonatophenyl)porphyrinato, TMP = meso-tetrakis(2,4,6-trimethylphenyl)porphyrinato), respectively, by meta-chloroperoxybenzoic acid (m-CPBA) in aqueous methanol and aqueous acetonitrile solutions of varying acidity. With the application of a low-temperature rapid-scan UV/Vis spectroscopic technique, the complete spectral changes that accompany the formation and decomposition of the primary product of O-O bond cleavage in the acylperoxoiron(III)-porphyrin intermediate [(P)Fe(III)-OOX] (P = porphyrin) were successfully recorded and characterized. The results clearly indicate that the O-O bond in m-CPBA is heterolytically cleaved by the studied iron(III)-porphyrin complexes independent of the acidity of the reaction medium. The existence of two different oxidation products under acidic and basic conditions is suggested not to be the result of a mechanistic changeover in the mode of O-O bond cleavage on going from low to high pH values, but rather the effect of environmental changes on the actual product of the O-O bond cleavage in [(P)Fe(III)-OOX]. The oxoiron(IV)-porphyrin cation radical formed as a primary oxidation product over the entire pH range can undergo a one- or two-electron reduction depending on the selected reaction conditions. The present study provides valuable information for the interpretation and improved understanding of results obtained in product-analysis experiments.

Fourier Transform Infrared Spectroscopy Study of CO Electro-oxidation on Pt(111) in Alkaline Media

In this work we investigate the electro-oxidation of CO on Pt(111) in alkaline solution by using Fourier transform infrared spectroscopy (FTIRS), to determine the adsorption sites of the CO, the intermediate species and the final oxidation product as a function of the applied potential. Multiple CO vibration bands (on-top, bridge and 3-fold hollow site) are observed on the Pt(111) electrode, their distribution and potential dependence being strongly dependent on the surface treatment. Spectroscopic results show that the final reaction product is carbonate and suggest that adsorbed carbonate blocks the access of CO from the (111) terrace to the active sites (i.e., step and kink sites).

Competition between Photoisomerization and Photocyclization of the Cis Isomers of n-Styrylnaphthalenes and -Phenanthrenes

The isomerization and cyclization photoreactions of the cis (Z) isomers of n-styrylnaphthalenes (n = 1 and 2), n-styrylphenanthrenes (n = 1, 2, 3, 4, and 9), and two related compounds, 3-styrylchrysene and 3-styrylbenzo[c]phenanthrene, were investigated by spectrophotometric and chromatographic techniques. The quantum yields of the two photoreactions were measured in aerated and deaerated nonpolar solvent at room temperature and compared with those reported in the literature for some of the molecules investigated and other related compounds. The combined use of high-performance liquid chromatographic and spectrophotometric techniques made easier the separation of the components of the photoreaction mixtures thus simplifying the study of the isomerization/cyclization competition and the measurement of the UV-vis absorption spectra and the thermal decay kinetics of the dihydrophenanthrene-type intermediates. The conformational equilibria in the ground state and the positional isomerism (n values) notably affect the prevalence of one or the other competitive photoreaction. Oxygen also plays an important role: practically it does not affect the quantum yield of the Z --> E process but has a drastic effect on the formation of the final oxidation product which can proceed even in the presence of traces of air. In three cases, non-negligible formation of a side colorless product was detected. It was assigned to an isomer of the normal photocyclization intermediate (4a,4b-dihydrophenanthrene-type), formed by shift of one or both hydrogen atom(s) to other positions of the rings. Parallel ab initio calculations of the potential energy of the possible conformers helped to explain the structure effects on the competitive photoreactive relaxation pathways. Some correlations between the computed reagent/product energy difference in the ground state and the photocyclization yield and thermal stability of the intermediates were also verified.

Mechanisms of sulfide ion oxidation during cyanidation. Part II: Surface catalysis by pyrite

The mechanisms and the reaction products for the oxidation of sulfide ions in the presence of pyrite have been established. When the leach solution contains free sulfide ions, oxidation occurs via electron transfer from the sulfide ion to dissolved oxygen on the pyrite mineral surface, with polysulfides being formed as an intermediate oxidation product. In the absence of cyanide, the polysulfides are further oxidised to thiosulfate, whilst with cyanide present, thiocyanate and sulfite are also formed from the reaction of polysulfides with cyanide and dissolved oxygen. Polysulfide chain length has been shown to affect the final reaction products of polysulfide oxidation by dissolved oxygen. The rate of pyrite catalysed sulfide ion oxidation was found to be slower in cyanide solutions compared to cyanide free solutions. Mixed potential measurements indicated that the reduction of oxygen at the pyrite surface is hindered in the presence of cyanide. The presence of sulfide ions was also found to activate the pyrite surface, increasing its rate of oxidation by oxygen. This effect was particularly evident in the presence of cyanide; in the presence of sulfide the increase in total sulfur from pyrite oxidation was 2.3 mM in 7 h, compared to an increase of <1 mM in the absence of sulfide over 24 h.

Transformation of vivianite by anaerobic nitrate‐reducing iron‐oxidizing bacteria

In phosphate-rich environments, vivianite (Fe(II)(3)(PO(4))(2), 8H(2)O) is an important sink for dissolved Fe(II) and is considered as a very stable mineral due to its low solubility at neutral pH. In the present study, we report the mineralogical transformation of vivianite in cultures of the nitrate-reducing iron-oxidizing bacterial strain BoFeN1 in the presence of dissolved Fe(II). Vivianite was first transformed into a greenish phase consisting mostly of an amorphous mixed valence Fe-phosphate. This precipitate became progressively orange and the final product of iron oxidation consisted of an amorphous Fe(III)-phosphate. The sub-micrometer analysis by scanning transmission X-ray microscopy of the iron redox state in samples collected at different stages of the culture indicated that iron was progressively oxidized at the contact of the bacteria and at a distance from the cells in extracellular minerals. Iron oxidation in the extracellular minerals was delayed by a few days compared with cell-associated Fe-minerals. This led to strong differences of Fe redox in between these two types of minerals and finally to local heterogeneities of redox within the sample. In the absence of dissolved Fe(II), vivianite was not significantly transformed by BoFeN1. Whereas Fe(II) oxidation at the cell contact is most probably directly catalyzed by the bacteria, vivianite transformation at a distance from the cells might result from oxidation by nitrite. In addition, processes leading to the export of Fe(III) from bacterial oxidation sites to extracellular minerals are discussed including some involving colloids observed by cryo-transmission electron microscopy in the culture medium.

Efficient Photocatalytic Removal of NO in Indoor Air with Hierarchical Bismuth Oxybromide Nanoplate Microspheres under Visible Light

In this study, hierarchical bismuth oxybromide (BiOBr) nanoplate microspheres were used to remove NO in indoor air under visible light irradiation. The BiOBr microspheres were synthesized with a nonaqueous sol-gel method by using bismuth nitrate and cetyltrimethyl ammonium bromide as the precursors. On degradation of NO under visible light irradiation (lambda > 420 nm) at 400 part-per-billion level, which is typical concentration for indoor air quality, these nonaqueous sol-gel synthesized hierarchical BiOBr microspheres exhibited superior photocatalytic activity to the chemical precipitation synthesized counterpart BiOBr bulk powder and Degussa TiO2 P25 as well as C doped TiO2. The excellent catalytic activity and the long-term activity of nonaqueous sol-gel synthesized BiOBr microspheres were attributed to their special hierarchical structure, which was favorable for the diffusion of intermediates and final products of NO oxidation. Ion chromatograph results confirmed that nitric acid was produced on the surface of BiOBr microspheres during the photooxidation of NO in gas phase. This work suggests that the nonaqueous sol-gel synthesized BiOBr nanoplate microspheres are promising photocatalytic materials for indoor air purification.