Copper–Oxygen Dynamics in the Tyrosinase Mechanism

The dinuclear copper enzyme, tyrosinase, activates O₂ to form a (μ-η²:η²-peroxido)dicopper(II) species, which hydroxylates phenols to catechols. However, the exact mechanism of phenolase reaction in the catalytic site of tyrosinase is still under debate. We herein report the near atomic resolution X-ray crystal structures of the active tyrosinases with substrate l -tyrosine. At their catalytic sites, CuA moved toward l -tyrosine (CuA1 → CuA2), whose phenol oxygen directly coordinates to CuA2, involving the movement of CuB (CuB1 → CuB2). The crystal structures and spectroscopic analyses of the dioxygen-bound tyrosinases demonstrated that the peroxide ligand rotated, spontaneously weakening its O−O bond. Thus, the copper migration induced by the substrate-binding is accompanied by rearrangement of the bound peroxide species so as to provide one of the peroxide oxygen atoms with access to the phenol substrate's ϵ carbon atom.     

Effect of Oxygen and Bacteria on the Property of Polymer Gel

The viscosity property of Cr~(3 ),Al~(3 ),and compound ion cross-linked polymer gel solution in the anaerobic and aerobic environment was investigated aiming at meeting the practical demand of the oil field.The viscosity reserving effect after adding the biocide and the gelation in the anaerobic and aerobic environments was also studied in the paper.The results indicate that the viscosity of the cross-linked polymer gel solution caused by the water produced in aerobic environment is higher than that in anaerobic environment,and that the viscosity value of the cross-linked polymer gel solutions after adding biocides has improved to some extent and polymer gel has gelated well in anaerobic environment.     

Oxygen vacancies enable the visible light photoactivity of chromium-implanted TiO2 nanowires

Although computational studies have demonstrated that metal ion doping can effectively narrow the bandgap of TiO₂,the visible-light photoactivity of metal-doped TiO₂ photoanodes is still far from satisfactory.Herein,we report an effective strategy to activate the visible-light photoactivity of chromiumimplanted TiO₂ via the incorporation of oxygen vacancies.The chromium-doped TiO₂ activated by oxygen vacancies(Cr-TiO₂-vac)exhibited an incident photon-to-electron conversion efficiency(IPCE)of~6.8%at450 nm,which is one of the best values reported for metal-doped TiO₂.Moreover,Cr-TiO₂-vac showed no obvious photocurrent decay after 100 h under visible-light illumination.     

Isotopic Exchange and Oxygen Diffusion in the La0.88Sr0.12Ga0.82Mg0.18O3 – α–Molecular Oxygen System

The oxygen isotopic exchange kinetics in La_0.88Sr_0.12Ga_0.82Mg_0.18O_{3 –} and in the same electrolyte whose surface layer is enriched with cobalt ions is studied. Rates of different types of exchange and oxygen isotope diffusion coefficients in oxide are determined at 970–1200 K and oxygen pressures of 400–1200 Pa. The activation energy for the interphase oxygen exchange and the order of heteroexchange vs. oxygen pressure relationship are determined. The presence of cobalt ions in the near-surface layer alters the surface exchange parameters, such as the oxygen heteroexchange rate (which increases), order of the heteroexchange vs. oxygen pressure relationship, and the ratio between rates of different exchange types. The oxygen isotope diffusion coefficients coincide in both electrolytes but differ from those calculated from the electroconductivity data with the Nernst–Einstein equation.     

Unravelling the Complex LiOH-Based Cathode Chemistry in Lithium–Oxygen Batteries**

The LiOH-based cathode chemistry has demonstrated potential for high-energy Li−O₂ batteries. However, the understanding of such complex chemistry remains incomplete. Herein, we use the combined experimental methods with ab initio calculations to study LiOH chemistry. We provide a unified reaction mechanism for LiOH formation during discharge via net 4 e⁻ oxygen reduction, in which Li₂O₂ acts as intermediate in low water-content electrolyte but LiHO₂ as intermediate in high water-content electrolyte. Besides, LiOH decomposes via 1 e⁻ oxidation during charge, generating surface-reactive hydroxyl species that degrade organic electrolytes and generate protons. These protons lead to early removal of LiOH, followed by a new high-potential charge plateau (1 e⁻ water oxidation). At following cycles, these accumulated protons lead to a new high-potential discharge plateau, corresponding to water formation. Our findings shed light on understanding of 4 e⁻ cathode chemistries in metal–air batteries.     

One-Dimensional Covalent Organic Frameworks for the 2e− Oxygen Reduction Reaction

Two-dimensional covalent organic frameworks (2D COFs) are often employed for electrocatalytic systems because of their structural diversity. However, the efficiency of atom utilization is still in need of improvement, because the catalytic centers are located in the basal layers and it is difficult for the electrolytes to access them. Herein, we demonstrate the use of 1D COFs for the 2e⁻ oxygen reduction reaction (ORR). The use of different four-connectivity blocks resulted in the prepared 1D COFs displaying good crystallinity, high surface areas, and excellent chemical stability. The more exposed catalytic sites resulted in the 1D COFs showing large electrochemically active surface areas, 4.8-fold of that of a control 2D COF, and thus enabled catalysis of the ORR with a higher H₂O₂ selectivity of 85.8 % and activity, with a TOF value of 0.051 s⁻¹ at 0.2 V, than a 2D COF (72.9 % and 0.032 s⁻¹). This work paves the way for the development of COFs with low dimensions for electrocatalysis.     

Homogeneous and Polymer-Supported Catalysts in the Oxidation of α-Pinene with Oxygen

The catalytic activities of nitrogen-containing cobalt complexes, polymer (AN-251 anion exchanger)-supported cobalt complex, and a polymer–salt composition containing molybdenum salt and nonionogenic water-soluble polymers were compared in the oxidation of -pinene.     

Some Attempts to Employ the Singlet Oxygen Generated from H2O2

Some attempts to employ the singlet oxygen generated from molybdate-catalyzed decomposition of hydrogen peroxide are presented. Reduction of ascaridole with diimide is also described, along with the preliminary results of the cleavage study using Fe-cysteinate as a simple model for Fe-S type redox species. There were strong indications that S-alkylation occurred as observed in similar cleavage of the potent antimalarial qinghaosu.     

Influence of the Lone Electron Pairs of the Ether Oxygen Atom on the Electron Density Distribution in α-Chloro Ethers

The axial and equatorial C-Cl bonds in cyclic -chloro ethers are polarized differently because of different orientation of the lone electron pair of oxygen relative to these bonds.     

Ab Initio Study of the Oxygen Atom Abstracting Hydrogen from Difluoromethane and Dichloromethane

ThemajorfiresuppressionagentsusedinconfinedspacesortoprotectelectronicsareCFsBrandCF2ClBr.Howeverbecauseoftheirozonedepletionpotential,theirproductionisnowbanned.Thesearchfornewflamesuppressantswhichareeffective,nontoxicandhaveIowglobalenvironmentalimpacthassparkedincreasedinterestinthemechanismsoffiresuppressionandthedevelopmentofpredictiveflamemodels1-2.KineticdataforthereactionsofOatomswithhalogenatedmethanesareneededtomodelthecombustionchendstry.Manystudiesaboutithavebeencarriedoutbyex…     

The Effect of the Oxygen Preadsorption on the Adsorption of Nitric Oxide on Mo (111)

The adsorption of nitric oxide adsorption on clean Mod(111), Mo(111)/O2-(4×4), Mo(111)/O2-(1×3), Mo(111)/O2-(112) facets and Mo(111) oxide surfaces was studied. Mass 28 (N2) desorption spectra show two high temperature peaks at approximate 1030 (β1) and 1200K (β2). For NO exposures less than 0. 1 L only the ft peak was observed. At higher exposures, the ft peak appeared and small amounts of N2O as well as NO desorbed. The preadsorption of oxygen blocked the β2 desorption partially on the (4×4) and (1×3) surfaces and fully on the (112) facet and oxide surfaces. In addition, the β1 desorption peak shifted to higher temperatures with increasing oxygen preexposure.     

How Does the Exchange of One Oxygen Atom with Sulfur Affect the Catalytic Cycle of Carbonic Anhydrase?

We have extended our investigations of the carbonic anhydrase (CA) cycle with the model system [(H(3)N)(3)ZnOH](+) and CO(2) by studying further heterocumulenes and catalysts. We investigated the hydration of COS, an atmospheric trace gas. This reaction plays an important role in the global COS cycle since biological consumption, that is, uptake by higher plants, algae, lichens, and soil, represents the dominant terrestrial sink for this gas. In this context, CA has been identified by a member of our group as the key enzyme for the consumption of COS by conversion into CO(2) and H(2)S. We investigated the hydration mechanism of COS by using density functional theory to elucidate the details of the catalytic cycle. Calculations were first performed for the uncatalyzed gas phase reaction. The rate-determining step for direct reaction of COS with H(2)O has an energy barrier of deltaG=53.2 kcal mol(-1). We then employed the CA model system [(H(3)N)(3)ZnOH](+) (1) and studied the effect on the catalytic hydration mechanism of replacing an oxygen atom with sulfur. When COS enters the carbonic anhydrase cycle, the sulfur atom is incorporated into the catalyst to yield [(H(3)N)(3)ZnSH](+) (27) and CO(2). The activation energy of the nucleophilic attack on COS, which is the rate-determining step, is somewhat higher (20.1 kcal mol(-1) in the gas phase) than that previously reported for CO(2). The sulfur-containing model 27 is also capable of catalyzing the reaction of CO(2) to produce thiocarbonic acid. A larger barrier has to be overcome for the reaction of 27 with CO(2) compared to that for the reaction of 1 with CO(2). At a well-defined stage of this cycle, a different reaction path can emerge: a water molecule helps to regenerate the original catalyst 1 from 27, a process accompanied by the formation of thiocarbonic acid. We finally demonstrate that nature selected a surprisingly elegant and efficient group of reactants, the [L(3)ZnOH](+)/CO(2)/H(2)O system, that helps to overcome any deactivation of the ubiquitous enzyme CA in nature.     

Rocket Engine with Continuous Detonation Combustion of the Natural Gas–Oxygen Propellant System

In a demonstrator of a detonation rocket engine (DRE) using the natural gas–oxygen propellant system, a high (270 s) specific impulse at sea level at a low (32 atm) mean combustor pressure was experimentally obtained for the first time. Comparison of these characteristics with the respective ones (263 s and 61 atm) of the well-known Russian RD 170-A liquid-propellant rocket engine using deflagration combustion of the kerosene–oxygen propellant system showed that the specific impulse at sea level in the DRE is close to that in the deflagration-combustion engine but is produced at half as high a mean combustor pressure. This indicates that the energy efficiency of detonation combustion exceeds that of deflagration combustion, and that there is room to improve the weight–size characteristics of the turbopump unit in the DRE.     

In Situ Confocal Microprobe Raman Spectroscopy Study of the Oxygen Species over Cerium Oxide

Ｃｏ￣ｎｄｅｎｃｅａｕｔｈｏｒ．Ｏａｆ（（ｋ６＜ｌ）ａｄｓｐｅｃｉｅｓＰｅａｋｓｗｅｒｅｆｏｕｎｄｔｏｄｉｓａｐｐｅａｒａｔ５７３＇Ｋ．Ｄｕｒｉｎｇｔｈｅｔｅｍｐｅｒａｔｕｒｅｅｌｅｖａｔｉｏｎ，ｔｈｅＣｅＯＺＦＺｇａｎｄＯ２－Ｐｅａｋｓｗｅｒｅｆｏｕｎｄｔｏｂｒｏａｄｅｎａｎｄｓｈｉｆｔｔｏｌｏｗｅｒｗａｖｅｎｕｍｂｅｒｓ．ＴｈｅｆｈａｌｕｅｎｃｙｓｈｉｆｔｗｉｌｈｒｅｓｅｃｔｔｏｔｅｍｐｅｒａｔｕｒｅｉｓａｗｅｌｌｋｎｏｗｎｐｈｅｎｏｍｅｎｏｎｉｎＲａｍａｎｓｐｅｃｔｒｏｓｃｏｐｙｏｆｓｏｌｉｄｓａｎｄｉｔｉｓｒｅｌａｔｅｄｔｏｔｈｅｔｈｅｒｍａ］ｅｘｐａｎｓｉｏｎｏｆｌａｔｔｉｃｅｐａｒａｍｅｔｅｒｓ．Ａｔ１０２３＇Ｋ，ｔｈｅＯ２－ａｄｓｐｅｃｉｅｓ（ａｔ１１５９ｃｍ－ｌ）ａｎｄＣｅＯＺＦ２，（ａｔ４４９ｃｍ－ｌ）ｐｅａｋｓｗｅｒｅｆｏｕｎｄｔｏｒｅｍａｉｎｅｘｉｓｔｉｎｇｏｎｔｈｅｓｕｒｆａｃｅｏｆｃｅｒｉｕｍｏａｌｄｅ．ＷｈｅｎｔｈｅＯＺ－ｐｒｅｔｒｅａｔｅｄＣｅＯＺｓａｍｐｌｅｗａｓｗａｒｍｅｄｓｕｃｃｅｓｓｉｖｅｌｙｉｎａｆｌｏｗｏｆＣｄ，ｔｈｅｒｅａｃｈｏｎｓｏｆＣａｂｗｉｔｈｌａｎｉｃｅｏ     

Methanol Tolerant FeTPP—Pt／C Co—catalysts for the Electroreduction of Oxygen

It was found for the first time that iron tetraphenylporphyrin(FeTPP)-Pt/C showed the good activity for the electroreduction of oxygen and methanol tolerant abitity,Their perfor-mances were related to the heat-treatment temperature.     

Ethylene Conversion to Higher Hydrocarbon over Copper Loaded BZSM-5 in the Presence of Oxygen

The successful production of higher hydrocarbons from methane depends on the stability or the oxidation rate of the intermediate products. The performances of the BZSM-5 and the modified BZSM-5 catalysts were tested for ethylene conversion into higher hydrocarbons. The catalytic experiments were carried out in a fixed-bed micro reactor at atmospheric pressure. The catalysts were characterized using XRD, NH3-TPD, and IR for their structure and acidity. The result suggests that BZSM-5 is a weak acid. The introduction of copper into BZSM-5 improved the acidity of BZSM-5. The conversion of ethylene toward higher hydrocarbons is dependent on the acidity of the catalyst. Only weaker acid site is required to convert ethylene to higher hydrocarbons. The loading of Cu on BZSM-5 improved the selectivity for higher hydrocarbons especially at low percentage. The reactivity of ethylene is dependent on the amount of acidity as well as the presence of metal on the catalyst surface. Cu1%BZSM-5 is capable of converting ethylene to higher hydrocarbons. The balances between the metal and acid sites influence the performance of ethylene conversion and higher hydrocarbon selectivity. Higher loading of Cu leads to the formation of COx.     

Kinetics of Gaseous Product Formation in the Surface Treatment of Polypropylene with Nitrogen–Oxygen Plasmas

The results of measurements on the composition and the formation rates of gaseous products in the surface treatment action of polypropylene with a low-temperature dc discharge plasma in a nitrogen–oxygen mixture are reported. The amount of oxygen in the mixture was varied within 0–100%. It was found that almost stoichiometric plasma-induced oxidative degradation occurred in an oxygen plasma, whereas the buildup of oxygen-containing functional groups on the surface took place in a mixed nitrogen–oxygen plasma at a nitrogen content of 10–60%.     

An ESR Study on Singlet Oxygen Photoproduction of the Meso-Tetrakis-(Substituted Phenyl) Porphine Derivatives

The ability of meso-tetrakis- (substituted phenyl) porphine derivatives for photo-generating singlet oxygen (O2) is studied by ESR spectrometry. The results show that the singlet oxygen yields of most of porphine derivatives are higher than that of HPD. It is also exhibited that the nature and structure of the substituent at the meso position are closely related to the photo-sensitizing ability of meso-tetrakis-(substituted phenyl) porphine.     

Understanding the Activity of Co-N4−xCx in Atomic Metal Catalysts for Oxygen Reduction Catalysis

Atomic metal catalysis (AMC) provides an effective way to enhance activity for the oxygen reduction reaction (ORR). Cobalt anchored on nitrogen-doped carbon materials have been extensively reported. The carbon-hosted Co-N₄ structure was widely considered as the active site; however, it is very rare to investigate the activity of Co partially coordinated with N, for example, Co-N_4−xC_x. Herein, the activity of Co-N_4−xC_x with tunable coordination environment is investigated as the active sites for ORR catalysis. The defect (di-vacancies) on carbon is essential for the formation of Co-N_4−xC_x. N species play two important roles in promoting the intrinsic activity of atomic metal catalyst: N coordinated with Co to manipulate the reactivity by modification of electronic distribution and N helped to trap more Co to increase the number of active sites.