Presence Of Atmospheric Oxygen Research Articles

Thermal stability of porphyrins with chemicaly active NH bond and their associates with electron-donor solvents

The composition and stability of the crystalline H associates of NH active tetrapyrroles with electron-donor solvents were investigated by thermogravimetry. It was found that common porphyrins and their analogs can form 1: 1 and 1: 2 macrocycle solvent H associates whose energy of formation depends on their composition and ranges from 20 to 115 kJ/mol. Based on the results from an analysis of the Stokes shifts, we concluded that the formation of H associates in a solution is accompanied by variations in the degree of macrocycle nonplanarity. The stability of a series of tetrapyrroles with regard to thermal destruction in argon atmosphere and in the presence of atmospheric oxygen was shown to drastically vary.

Single-step incorporation of oh groups into the monosubstituted dodecahydro-closo-dodecaborate(2-) anion derivatives [B12H11SCN]2−, [B12H11I]2−, and [B12H11OC(O)CH3]2−

We have studied the reactions of the monosubstituted derivatives [B12H11X]2− (X = SCN, I, OC(O)CH3) with acetic acid in the presence of atmospheric oxygen and moisture. The results demonstrate that a hydroxyl group can be embedded in a single step, without formation of any acetoxy derivatives. The synthesized compounds were identified by elemental analysis, IR spectroscopy, and NMR. A mechanism of the process has been proposed.

Production of dihydrodaidzein and dihydrogenistein by a novel oxygen-tolerant bovine rumen bacterium in the presence of atmospheric oxygen

The original bovine rumen bacterial strain Niu-O16, capable of anaerobically bioconverting isoflavones daidzein and genistein to dihydrodaidzein (DHD) and dihydrogenistein (DHG), respectively, is a rod-shaped obligate anaerobic bacterium. After a long-term domestication, an oxygen-tolerant bacterium, which we named Aeroto-Niu-O16 was obtained. Strain Aeroto-Niu-O16, which can grow in the presence of atmospheric oxygen, differed from the original obligate anaerobic bacterium Niu-O16 by various characteristics, including a change in bacterial shape (from rod to filament), in biochemical traits (from indole negative to indole positive and from amylohydrolysis positive to negative), and point mutations in 16S rRNA gene (G398A and G438A). We found that strain Aeroto-Niu-O16 not only grew aerobically but also converted isoflavones daidzein and genistein to DHD and DHG in the presence of atmospheric oxygen. The bioconversion rate of daidzein and genistein by strain Aeroto-Niu-O16 was 60.3% and 74.1%, respectively. And the maximum bioconversion capacity for daidzein was 1.2 and 1.6 mM for genistein. Furthermore, when we added ascorbic acid (0.15%, m/v) in the cultural medium, the bioconversion rate of daidzein was increased from 60.3% to 71.7%, and that of genistein from 74.1% to 89.2%. This is the first reported oxygen-tolerant isoflavone biotransforming pure culture capable of both growing and executing the reductive activity under aerobic conditions.

A new approach for reduction of methylene green withascorbic acid by de-oxygenation through carbondioxide

Reduction kinetics of the methylene green (MG) with ascorbic acid (AA) in acidic medium at λmax 660 nm was monitored through visible spectrophotomtry in absence and presence of sodium carbonate. CO2 release through reaction of sodium carbonate and oxalic acid, created deoxygenated atmosphere for reduction of dye which greatly boosted the reaction rate. Initially slow reaction in presence of atmospheric oxygen proceeded rapidly when sodium carbonate was added. The reaction followed fractional order kinetics with AA and zero order kinetics with MG. The rate of reaction shows no linear dependence on [H+] concentration as an acidic medium. The rate of reaction is directly related with the elevated concentration of salt, which suggests that the two same charged species are involved in the rate determining step. Secondary reactions at elevated temperature showed complex kinetics.

ChemInform Abstract: An Investigation into the Unusual Formation of an Isocoumarin by Acylation of 2,3,6-Trimethoxytoluene with (E)-2-Methylbut-2-enoic Acid and Trifluoroacetic Anhydride.

Prolonged reaction of 2,3,6-trimethoxytoluene with an excess of premixed (E)-2-methylbut-2-enoic acid and trifluoroacetic anhydride in air affords 5,6,8-trimethoxy-3,4,7-trimethylisocoumarin 11 in 66% yield as the sole product isolated, the structure of which was confirmed by X-ray crystallography. Shorter reaction times afford products which enable the identification of the reaction mechanism. This involves initial regioselective acylation, cyclisation of the derived α,β-unsaturated aryl ketone 5 to the cis/trans mixture of indanones 18 and 19 and O-acylation of these indanones to yield the indenyl ester 17. The indanones and compound 17 can all react with trifluoroacetic acid in the presence of atmospheric oxygen to afford the isocoumarin by a mechanism which requires the intermediacy of an α-keto indanyl hydroperoxide, which in turn undergoes an acid-catalysed Baeyer–Villiger-type rearrangement to incorporate oxygen, thereby giving the isocoumarin.

EFFECT OF KCL EXCESS AND INERT CARRIER ON THE YIELD OF KVO3 SYNTHESIS

Investigation was carried out on the optimal conditions of the synthesis of KVO3 and Cl2 from KCl and V2O5 in the presence of atmospheric oxygen. The influence of the excess of KCl relative to V2O5 was investigated. Also, the effect of quartz sand introduced into the reaction mixture on the yield of KVO3 synthesis was determined. The obtained product of synthesis was isolated from the post-reaction mixture.

Experimental Design in the Preparation of Modified HEMA-Based Superporous Hydrogels in an Aqueous Medium

Due to a relatively large number of excipients and their concentrations, which can be used effectively in the preparation of superporous hydrogels, an experimental design based on the Taguchi matrix has proven to be a very valuable tool in screening and narrowing down the final formulation. In this study, the effect of starting materials, their concentrations as well as the starting reaction temperature, were examined in the preparation of superporous hydrogels based on hydroxyethyl methacrylate. A large number of possible formulations and conditions might lead to the production of a reasonable hydrogel network, but some formulations produce stronger or faster swelling superporous hydrogels than others. The final properties of the superporous hydrogels depend upon the events that occur during formation of the gel, including the presence of atmospheric oxygen, which is responsible for the inhibition period seen at the start of the reaction, and also including the change in temperature at which the reaction starts. These events can be largely affected by the choice of ingredients used in the reaction. For this study, eight variables were chosen, and their effects were examined using a Taguchi matrix. The parameters examined were the maximum temperature during the reaction, the time corresponding to the maximum temperature, and the reaction yield which is represented by the weight of the dry final SPH.

Oxidation of an Oligonucleotide‐Bound CeIII/Multiphosphonate Complex for Site‐Selective DNA Scission

Oligodeoxyribonucleotide conjugates of ethylenediamine-N,N,N',N'-tetrakis(methylenephosphonic acid) (EDTP) have been used to place a Ce(III)/EDTP complex in close proximity to predetermined phosphodiester linkages of a complementary target oligonucleotide. In the presence of atmospheric oxygen, the Ce(III) is oxidized into Ce(IV) which, in turn, efficiently cleaves the target phosphodiester linkage. No cleavage occurs at the other single-stranded regions, which suggests that the catalytic Ce species is strictly localized next to the target phosphodiester linkage. No decrease in the reaction rate is observed upon introduction of scavengers for hydroxyl radicals (such as DMSO or MeOH) or singlet oxygen (such as NaN(3)) to the system; this indicates that the reaction proceeds via a hydrolytic pathway. Any significant contribution by an oxidative pathway is further ruled out by the observation that nucleosides remain intact after incubation with Ce(IV)/EDTP complex for extended periods.

Effect of Sea Salts on Structural Concrete in a Tidal Environment

SummaryStructural concrete exposed to the tidal/splash zone of marine environments is always subjected to ambient external, as well as internal, action of seawater over its entire lifespan. The environmental loading causes maximum damage to structural concrete in the tidal/splash zone of marine environments where it experiences the concentrated effect of salt ions found in seawater in presence of atmospheric oxygen, carbon dioxide and other harmful gases. The gradual penetration of sea salt ions and the formation of expansive/leachable compounds leads to cracking, spalling and even structural distress. This paper presents a part of a durability study on the effect of sea salts on structural concrete exposed to simulated tidal/splash zone marine conditions over a period of one year. The concrete specimens cast from two different grades of concrete were exposed to seawater of different concentration under submerged, alternate wetting-drying and atmospheric state of exposure in a controlled humidity and temperature environment. Using accelerated test techniques, the deteriorative effects were measured by studying visual appearance, weight and volume change, compressive strength, permeability and stress-strain characteristics, and x-ray diffraction patterns of salt-attacked concrete specimens. The test data provide useful information regarding the durability of structural concrete exposed to the tidal/splash zone of marine environments.

Analysis and optimization of copper-catalyzed azide-alkyne cycloaddition for bioconjugation.

Since its discovery in 2002, the copper-catalyzed azide-alkyne cycloaddition (CuAAC)[1] reaction—the most widely recognized example of click chemistry[2]—has been rapidly embraced for applications in myriad fields.[3] The attractiveness of this procedure (and its copper-free strained-alkyne variant[4]) stems from the selective reactivity of azides and alkynes only with each other. Because of the fragile nature and low concentrations at which biomolecules are often manipulated, bioconjugation presents significant challenges for any ligation methodology. Several different CuAAC procedures have been reported to address specific cases involving peptides, proteins, polynucleotides, and fixed cells, often with excellent results,[5] but also occasionally with somewhat less satisfying outcomes.[6] We describe here a generally applicable procedure that solves the most vexing click bioconjugation problems in our laboratory, and therefore should be of use in many other situations. The CuAAC reaction requires the copper catalyst, usually prepared with an appropriate chelating ligand,[7] to be maintained in the CuI oxidation state. Several years ago we developed a system featuring a sulfonated bathophenanthroline ligand,[8] which was optimized into a useful bioconjugation protocol.[9] A significant drawback was the catalyst’s acute oxygen sensitivity, requiring air-free techniques which can be difficult to execute when an inert-atmosphere glove box is unavailable or when sensitive biomolecules are used in small volumes of aqueous solution. We also introduced an electrochemical method to generate and protect catalytically active CuI–ligand species for CuAAC bioconjugation and synthetic coupling reactions with miminal effort to exclude air.[10] Under these conditions, no hydrogen peroxide was produced in the oxygen-scrubbing process, resulting in protein conjugates that were uncontaminated with oxidative byproducts. However, this solution is also practical only for the specialist with access to the proper equipment. Other protocols have employed copper(I) sources such as CuBr for labeling fixed cells[11] and synthesizing glycoproteins.[12] In these cases, the instability of CuI in air imposes a requirement for large excesses of Cu (greater than 4 mm) and ligand for efficient reactions, which raises concerns about protein damage or precipitation, plus the presence of residual metal after purification. The most convenient CuAAC procedure involves the use of an in situ reducing agent. Sodium ascorbate is the reductant of choice for CuAAC reactions in organic and materials synthesis, but is avoided in bioconjugation with a few exceptions.[13] Copper and sodium ascorbate have been shown to be detrimental to biological[14] and synthetic[15] polymers due to copper-mediated generation of reactive oxygen species.[16] Moreover, dehydroascorbate and other ascorbate byproducts can react with lysine amine and arginine guanidine groups, leading to covalent modification and potential aggregation of proteins.[6a,17] We hoped that solutions to these problems would allow ascorbate to be used in fast and efficient CuAAC reactions using micromolar concentration of copper in the presence of atmospheric oxygen. This has now been achieved, allowing demanding reactions to be performed with biomolecules of all types by the nonspecialist. For purposes of catalyst optimization and reaction screening, the fluorogenic coumarin azide 1 developed by Wang et al. has proven to be invaluable (Scheme 1).[18] The progress of cycloaddition reactions between mid-micromolar concentrations of azide and alkyne in aqueous buffers was followed by the increase in fluorescence at 470 nm upon formation of the triazole 2. Scheme 1 Top: Reaction used for screening CuAAC catalysts and conditions. Below: Accelerating ligand 3 and additive 4 used in these studies. DMSO=dimethylsulfoxide.

Organosilane self-assembled multilayer formation based on activation of methyl-terminated surface with reactive oxygen species generated by vacuum ultra-violet excitation of atmospheric oxygen molecules

A xenon excimer lamp which irradiates vacuum ultra-violet (VUV) light at 172 nm in wavelength was applied to the photochemical surface conversion of n-octadecyltrimethoxysilane self-assembled monolayer (ODS-SAM) in the presence of atmospheric oxygen and subsequent multilayer fabrication. The terminal functional groups of ODS-SAM, –CH 3 groups, were converted into polar functional groups, like –COOH, by the reaction with atomic oxygen species generated photochemically through VUV excitation of atmospheric oxygen molecules. The structure of the resulting organosilane multilayer with different numbers of superimposed monolayers (from 1 to 11), prepared on a smooth and hydrophilic silicon substrate by the layer-by-layer (LbL) approach, was examined in terms of molecular organization as well as the intra- or interlayer binding modes in such novel films. Ellipsometry and grazing angle X-ray reflectivity measurements revealed that multilayer films of up to 11 discrete monolayers were successfully obtained, indicating that the self-assembly is a viable technique for the construction of relatively thick (16 nm and above) multilayer films.

Reduction Kinetics of Thionine in Aerobic Condition with D‐Galactose

AbstractReduction kinetics of thionine (Th) with D‐galactose (RH) was observed on a UV/Visible 1601 Shimadzu spectrophotometer at λmax 599 nm. The results showed that the initially slow reduction kinetics got enhanced and proceeded to completion within a few minutes. A pseudo first order kinetics was observed when influence of different parameters like concentration of dye and reductant, ionic strength and temperature was investigated. A significant shift in wave length from 599 to 517 nm was observed at alkaline pH whereas addition of a small amount of acid caused a shift in equilibrium. This resulted in the generation of oxidized form of thionine which was pragmatic in the presence of atmospheric oxygen. Change in ionic strength at elevated temperature lied to decrease in the rate constant. Thermodynamics activation parameters like Ea reflects a high amount of energy required for reduction of Th with RH whereas entropy of activation (ΔS⊖) and free energy of activation (ΔG⊖) show the highly solvated states of transient complex which was less disorderly arranged than the oxidized form of dye. A mechanism consistent with above findings has been discussed in the relevant section of paper.

A study of the reaction of propane dehydrogenation on a Cr,Co,Ni,Bi,K/γ-Al2O3 catalyst in the presence of atmospheric oxygen

Effect of the C3H8 dehydrogenation temperature (560–650°C) and oxygen on the rates of C3H8 conversion and C3H6 formation was studied using a catalyst prepared under lowered or atmospheric pressure.

Modified method for synthesis of detonation nanodiamonds and their real elemental composition

Modified technique for synthesis of detonation nanodiamonds by exploding a charge of high explosives in a water shell is described. Reducing agents are introduced into water. Their use enables solution of a number of problems: the carbon content of nanodiamonds is raised from 90 to 96 wt %, the content of incombustible admixtures is dramatically diminished from 3 to 0.1 wt %, and the yield of detonation nanodiamonds becomes two times higher. A new method for determining the elemental composition is described and the oxidation of nanodiamonds under heating in the presence of atmospheric oxygen is analyzed.

CuI complexes with 2,2′-biquinolyl-containing polymeric ligands as electrocatalysts for the oxidative coupling of alkynes in the presence of dioxygen

Electrocatalytic oxidative coupling of terminal alkynes in the presence of atmospheric oxygen catalyzed by CuI complexes with polymeric biquinolyl ligands leads to the corresponding diynes in high yield. The reaction proceeds under mild conditions at a potential of CuII/CuI electroreduction (−0.55 V vs. Ag/AgCl/KCl) and is accompanied by O2 reduction to H2O.

Photochemical surface modification and characterization of double-decker-shaped polysilsesquioxane hybrid thin films

The surface modification of a double-decker-shaped polysilsesquioxane (DDPSQ) film by deep ultraviolet (UV) irradiation (λ = 185 and 254 nm) was studied in the presence of atmospheric oxygen at room temperature. The change in the surface structure of a DDPSQ hybrid film was observed by means of contact angle measurements, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Exposure to deep UV light was found to convert the surface of DDPSQ film from hydrophobic to hydrophilic due to the formation of silanol groups (Si–OH) on the DDPSQ film. Measurements of FT-IR and XPS indicate that the Si–O–Si cage structure of DDPSQ was converted to the Si–O–Si network structure of SiO2 through cleavage of the Si–O–Si cage with deep UV irradiation. The irradiated DDPSQ film surface is very smooth with a root-mean-square (RMS) roughness of 0.34 nm. Moreover, to demonstrate the effect of surface modification of a DDPSQ film on the adhesion of metals, we fabricated silver (Ag) micropatterns on the deep UV modified DDPSQ film by laser-induced pyrolysis of a film prepared from liquid-dispersed Ag nanoparticles. The Ag micropatterns show an excellent adhesion to the modified DDPSQ surface as assessed by the Scotch tape test.

Highly Stable 3,4,9,10-Perylenediimide Radical Anions Immobilized in Robust Zirconium Phosphonate Self-Assembled Films

Self-assembled thin films of 3,4,9,10-perylenediimides (PDIs) containing up to 50 PDI layers were grown on quartz slides using the zirconium phosphonate technique. When the films were immersed in aqueous solutions of the sodium dithionite reducing agent, in situ reduction of the dye was observed, generating a purple film containing PDI radical anions. The PDI radical anions formed within the films were rather stable, persisting for several minutes in the presence of atmospheric oxygen. Atomic force microscopy (AFM) images showed that the film surface was rather smooth and pinhole-free.

Photopolymerization of acrylates in the presence of bipyridinium salts

The photopolymerization of acrylic monomers initiated by bipyridinium salts has been studied. It has been shown that active radicals are produced more efficiently in the presence of atmospheric oxygen than in vacuum. A scheme of the process including one-electron transfer involving oxygen has been proposed.

S-Acyl and N-Acyl Derivatives of Benzothiazole-2-thiol: An Example of Acyl Group Rearrangement

Amides, thioamides and carbamates are versatile intermediates in the synthesis of natural products. Among the most well-known procedures to make amides and thioamides are the reactions between amines and acyl halides, or between amines and thioacyl halides. Acyl halides and thioacyl halides are, however, not easy to handle in general or available in stock most of the time. For instance, thiobenzoyl chloride, a purple liquid collection and purification via vaccum distillation, undergoes decomposition very easily in the presence of atmospheric oxygen at 78 C or above. Thus, effective acylating reagents or acylating intermediates such as acylimidazole, a reaction product of trisdialkylaminoborane and carboxylic acid, acyloxyborane, 1,1'-[carbonyldioxy]dibenzotriazole convertible into 1-acyloxybenzotriazole, and benzotriazole-1-yl diethyl phosphate have been carefully developed for the syntheses of amides. Moreover, the utility of thioacylimide explored by Geordeler, the usage of N-thiobenzoylbenztriazole, the reaction between diimidazole sulfide and dithiobenzoic acid reported by Walter, and Lawesson’s reagent played a key role for syntheses of thioamides. As for using leaving groups containing sulfur for the preparation of amides, 3-acylthiazolidine-2-thione by Y. Nagao, and utility of 2-mercaptobenzoxazole (MBO) by Ueda have been previously explored. In a previous paper, we have reported the syntheses for a variety of phenylamides, thiobenzamides and various carbamates by adopting S-benzoyl derivative of benzothiazole-2thiol, so called 2-mercaptobenzothiazole (MBT) as a good leaving group moiety. Here, we wish to report the phenomenon of the acyl group rearrangement between derivatives of MBT, the quantitative isolation of each derivative of MBT, and their chemical properties. Both acyl derivatives of MBT have demonstrated that they can be used in the facile syntheses of other alkylamides (alkyl = methyl, benzyl, cinnamyl) and benzylthioamide. Although Ueda observed the formation of S-acyl derivative and N-acyl derivative of MBO as result of the acyl group rearragement during the reaction, there was no mention of the ratio distribution of derivatives or mechanistic details. For a comparison to S-acyl/N-acyl rearrangement of MBO, Ueda also reported that the acylating reagent, derived from 1,2-benzisothiazol-3-ol and benzoyl chloride, also gives the benzoyl group rearrangement between the O-

Substrate Profiling of Protein Tyrosine Phosphatase PTP1B by Screening a Combinatorial Peptide Library

Protein tyrosine phosphatases (PTPs) are a large family of enzymes that catalyze the hydrolytic removal of the phosphoryl group from phosphotyrosyl (pY) proteins. To date, the in vivo substrates and physiological functions of PTPs remain poorly defined. In this work, we have developed a novel combinatorial library method to systematically determine the substrate specificity of PTPs. A one-bead-one-compound peptide library containing five randomized residues, Fmoc-XXXXXpYAA (where X is norleucine or 17 proteinogenic amino acids excluding Tyr, Cys, and Met), was chemically synthesized on 90-μm TentaGel resin by the split-and-pool method. Limited treatment of the library with a PTP removed the phosphoryl group from beads that carry the most preferred substrates. The exposed tyrosine side chain was selectively oxidized into an orthoquinone by the treatment with tyrosinase in the presence of atmospheric oxygen. The orthoquinone was then selectively derivatized with biotin-hydrazide, followed by on-bead colorim...