Oxygen derived free radicals in clinical context

Oxygen derived free radicals have been implicated in a number of clinical disorders including atherosclerosis (1), ischemic heart disease (IHD) (2), post ischemic reperfusion injury (3) and respiratory distress syndrome (4). These radical are generated by sequential reduction of molecular oxygen; the primary product being superoxide anion (O₂ ^.−) which is subsequently reduced to hydrogen peroxide (H₂O₂), hydroxy1 radical (OH^.) and singlet oxygen (¹O₂). However the evidence for ODFR induced cell damage in various clinical disorders is still debated and rests largely on free radical scavenging studies, through electron paramagnetic resonance spectroscopic (EPRS) studies have provided direct evidence for ODFR generation following coronary artery ligation (5). By definition, a free radical is an atom, ion or molecule with one or more unpaired electrons (the presence of unpaired electron in a free radical being represented by a superscribed bold dot-R^.) and may be formed as a result of homolytic fission of a covalent bond or by electron transfer reactions, and may have cationic (NH₃ ⁺), anionic (O₂ ^.−) or neutral (NO) characteristics. The most important in vivo source for these radical species have been found to be univalent biochemical redox reactions involving oxygen. (a) A:B→A^.+B^. (b) A:+B→A^.+B^.     

Oxidative foliar photo-necrosis produced by the bacteria Pseudomonas cedrina

BackgroundAlthough bioactive metabolites capable of causing oxidative photo-necrosis in plant tissues have been identified in fungi, little is known about this type of mechanism in bacteria. These metabolites act as photosensitizers that generate reactive oxygen species (ROS) capable of causing damage to cells. In addition, these metabolites can pass into an energetically excited state when they receive some luminous stimulus, a condition in which they interact with other molecules present in the environment, such as molecular oxygen (O₂), also known as triplet oxygen (³O₂), generating ROS.ResultsThe suspension of the bacterial culture of Pseudomonas cedrina was shown to produce foliar necrosis in papaya leaves (Carica papaya L.) only in the presence of sunlight, which is evidence of photosensitizing mechanisms that generate singlet oxygen (¹O₂). From the chemical study of extracts obtained from this bacteria, 3-(4-(2-carboxipropyl) phenyl) but-2-enoic acid (1) was isolated. This compound, in the presence of light and triplet oxygen (³O₂), was able to oxidize ergosterol to its peroxide, since it acted as a photosensitizer producing ¹O₂, with which it was corroborated that a photosensitization reaction occurs, mechanism by which this bacterium could prove to cause oxidative foliar photo-necrosis.ConclusionsP. cedrina was able to induce oxidative foliar photo-necrosis because of its potential ability to produce photosensitizing metabolites that generate singlet oxygen in the plants it colonizes. Based on the above, it can be proposed that some bacteria can cause oxidative foliar photo-necrosis as an important mechanism in the pathogenesis of host species.How to cite: Mendoza G, Sánchez-Tafolla L, Trigos A. Oxidative foliar photo-necrosis produced by the bacteria Pseudomonas cedrina. Electron J Biotechnol 2020;44. https://doi.org/10.1016/j.ejbt.2020.01.007     

Evidence for oxygenation of Fe-Mg oxides at mid-mantle conditions and the rise of deep oxygen

As the reaction product of subducted water and the iron core, FeO₂ with more oxygen than hematite (Fe₂O₃) has been recently recognized as an important component in the D” layer just above the Earth''s core-mantle boundary. Here, we report a new oxygen-excess phase (Mg, Fe)₂O_3+δ (0 < δ < 1, denoted as ‘OE-phase’). It forms at pressures greater than 40 gigapascal when (Mg, Fe)-bearing hydrous materials are heated over 1500 kelvin. The OE-phase is fully recoverable to ambient conditions for ex situ investigation using transmission electron microscopy, which indicates that the OE-phase contains ferric iron (Fe³⁺) as in Fe₂O₃ but holds excess oxygen through interactions between oxygen atoms. The new OE-phase provides strong evidence that H₂O has extraordinary oxidation power at high pressure. Unlike the formation of pyrite-type FeO₂Hx which usually requires saturated water, the OE-phase can be formed with under-saturated water at mid-mantle conditions, and is expected to be more ubiquitous at depths greater than 1000 km in the Earth''s mantle. The emergence of oxygen-excess reservoirs out of primordial or subducted (Mg, Fe)-bearing hydrous materials may revise our view on the deep-mantle redox chemistry.     

Mineralogy of the deep lower mantle in the presence of H2O

Understanding the mineralogy of the Earth''s interior is a prerequisite for unravelling the evolution and dynamics of our planet. Here, we conducted high pressure-temperature experiments mimicking the conditions of the deep lower mantle (DLM, 1800–2890 km in depth) and observed surprising mineralogical transformations in the presence of water. Ferropericlase, (Mg, Fe)O, which is the most abundant oxide mineral in Earth, reacts with H₂O to form a previously unknown (Mg, Fe)O₂H_x (x ≤ 1) phase. The (Mg, Fe)O₂H_x has a pyrite structure and it coexists with the dominant silicate phases, bridgmanite and post-perovskite. Depending on Mg content and geotherm temperatures, the transformation may occur at 1800 km for (Mg_0.6Fe_0.4)O or beyond 2300 km for (Mg_0.7Fe_0.3)O. The (Mg, Fe)O₂H_x is an oxygen excess phase that stores an excessive amount of oxygen beyond the charge balance of maximum cation valences (Mg²⁺, Fe³⁺ and H⁺). This important phase has a number of far-reaching implications including extreme redox inhomogeneity, deep-oxygen reservoirs in the DLM and an internal source for modulating oxygen in the atmosphere.     

Selective electrochemical production of hydrogen peroxide at zigzag edges of exfoliated molybdenum telluride nanoflakes

The two-electron reduction of molecular oxygen represents an effective strategy to enable the green, mild and on-demand synthesis of hydrogen peroxide. Its practical viability, however, hinges on the development of advanced electrocatalysts, preferably composed of non-precious elements, to selectively expedite this reaction, particularly in acidic medium. Our study here introduces 2H-MoTe₂ for the first time as the efficient non-precious-metal-based electrocatalyst for the electrochemical production of hydrogen peroxide in acids. We show that exfoliated 2H-MoTe₂ nanoflakes have high activity (onset overpotential ∼140 mV and large mass activity of 27 A g⁻¹ at 0.4 V versus reversible hydrogen electrode), great selectivity (H₂O₂ percentage up to 93%) and decent stability in 0.5 M H₂SO₄. Theoretical simulations evidence that the high activity and selectivity of 2H-MoTe₂ arise from the proper binding energies of HOO^* and O^* at its zigzag edges that jointly favor the two-electron reduction instead of the four-electron reduction of molecular oxygen.     

A high-capacity cathode for rechargeable K-metal battery based on reversible superoxide-peroxide conversion

As a promising low-cost energy storage device, the development of a rechargeable potassium-ion battery (KIB) is severely hindered by the limited capacity of cathode candidates. Regarded as an attractive capacity-boosting strategy, triggering the O-related anionic redox activity has not been achieved within a sealed KIB system. Herein, in contrast to the typical gaseous open K-O₂ battery (O₂/KO₂ redox), we originally realize the reversible superoxide/peroxide (KO₂/K₂O₂) interconversion on a KO₂-based cathode. Controlled within a sealed cell environment, the irreversible O₂ evolution and electrolyte decomposition (induced by superoxide anion (O₂⁻) formation) are effectively restrained. Rationally controlling the reversible depth-of-charge at 300 mAh/g (based on the mass of KO₂), no obvious cell degradation can be observed during 900 cycles. Moreover, benefitting from electrolyte modification, the KO₂-based cathode is coupled with a limited amount of K-metal anode (merely 2.5 times excess), harvesting a K-metal full-cell with high energy efficiency (∼90%) and long-term cycling stability (over 300 cycles).     

Cascade-responsive nanobomb with domino effect for anti-tumor synergistic therapies

The development of reactive oxygen species (ROS) generation agents that can selectively produce sufficient ROS at the tumor site without external energy stimulation is of great significance for the further clinical application of ROS-based therapies. Herein, we designed a cascade-responsive ROS nanobomb (ZnO₂@Ce6/CaP@CPPO/BSA, designated as Z@Ce6/CaP@CB) with domino effect and without external stimulation for the specific generation of multiple powerful ROS storms at the tumor site. The calcium phosphate shell and ZnO₂ core gradually degrade and release Ca²⁺, Zn²⁺ and hydrogen peroxide (H₂O₂) under acid stimulation. On the one hand, Zn²⁺ can enhance the generation of endogenous superoxide anions (·O₂^–) and H₂O₂ through the inhibition of the mitochondrial electron transport chain. On the other hand, the generation of large amounts of exogenous H₂O₂ can cause oxidative damage to tumor cells and further activate bis[2,4,5-trichloro-6-(pentyloxycarbonyl)phenyl] oxalate (CPPO)-mediated chemiexcited photodynamic therapy. In addition, the oxidative stress caused by the generated ROS can lead to the uncontrolled accumulation of Ca²⁺ in cells and further result in Ca²⁺ overload-induced cell death. Therefore, the introduction of Z@Ce6/CaP@CB nanobombs triggered the ‘domino effect’ that caused multiple heavy ROS storms and Ca²⁺ overload in tumors and effectively activated anti-tumor immune response.     

塔克拉玛干沙漠腹地太阳紫外辐射特征

本文利用塔克拉玛干沙漠腹地(塔中站:83°40'E,39°01'N)2007年1月-12月紫外辐射和总辐射的观测资料,分析了塔克拉玛干沙漠腹地太阳紫外辐射的气候学特征。结果表明:①本地区太阳紫外辐射年总量为305.64MJ(/m2·a)。年平均日总量为0.84MJ/m2,大于黑河、太湖和青藏高原地区。紫外辐射年平均值在总辐射年平均值中所占比例为4.99%,小于太湖和北京,大于黑河地区和五道梁,月平均日总量7月最大;②其日变化,晴天呈现出标准的倒"U"型,即早晚小、中午大,正午达到一天中的最大值;③紫外辐射受云量、降水和沙尘的影响很大;④紫外辐射在总辐射中所占比例有明显的年、季节和日变化,其年变化分为三个明显不同的阶段,夏季大,冬季小。青藏高原地区春夏大,冬季小,北京地区和黑河地区相近,分别是冬季大,夏季小和冬季大,春夏小。     

Immobilization of horseradish peroxidase on Fe3O4 magnetic nanoparticles

BackgroundIron magnetic nanoparticles have attracted much attention. They have been used in enzyme immobilization because of their properties such as product is easily separated from the medium by magnetic separation. The present work was designed to immobilize horseradish peroxidase on Fe₃O₄ magnetic nanopraticles without modification.ResultsIn the present study, horseradish peroxidase (HRP) was immobilized on non-modified Fe₃O₄ magnetic nanoparticles. The immobilized HRP was characterized by FT-IR spectroscopy, scanning electron microscopy, and energy dispersive X-ray. In addition, it retained 55% of its initial activity after 10 reuses. The optimal pH shifted from 7.0 for soluble HRP to 7.5 for the immobilized HRP, and the optimal temperature shifted from 40°C to 50°C. The immobilized HRP is more thermostable than soluble HRP. Various substrates were oxidized by the immobilized HRP with higher efficiencies than by soluble HRP. K_m values of the soluble and immobilized HRP were 31 and 45 mM for guaiacol and 5.0 and 7.0 mM for H₂O₂, respectively. The effect of metals on soluble and immobilized HRP was studied. Moreover, the immobilized HRP was more stable against high concentrations of urea, Triton X-100, and isopropanol.ConclusionsPhysical immobilization of HRP on iron magnetic nanoparticles improved the stability toward the denaturation induced by pH, heat, metal ions, urea, detergent, and water-miscible organic solvent.     

A highly alkaline-stable metal oxide@metal–organic framework composite for high-performance electrochemical energy storage

Most metal–organic frameworks (MOFs) hardly maintain their physical and chemical properties after exposure to alkaline aqueous solutions, thus precluding their use as potential electrode materials for electrochemical energy storage devices. Here, we present the design and synthesis of a highly alkaline-stable metal oxide@MOF composite, Co₃O₄ nanocube@Co-MOF (Co₃O₄@Co-MOF), via a controllable and facile one-pot hydrothermal method under highly alkaline conditions. The obtained composite possesses exceptional alkaline stability, retaining its original structure in 3.0 M KOH for at least 15 days. Benefitting from the exceptional alkaline stability, unique structure, and larger surface area, the Co₃O₄@Co-MOF composite shows a specific capacitance as high as 1020 F g⁻¹ at 0.5 A  g⁻¹ and a high cycling stability with only 3.3% decay after 5000 cycles at 5 A g⁻¹. The as-constructed solid-state flexible device exhibits a maximum energy density of 21.6 mWh cm⁻³.     

Integration of bio-inspired lanthanide-transition metal cluster and P-doped carbon nitride for efficient photocatalytic overall water splitting

Photosynthesis in nature uses the Mn₄CaO₅ cluster as the oxygen-evolving center to catalyze the water oxidation efficiently in photosystem II. Herein, we demonstrate bio-inspired heterometallic LnCo₃ (Ln = Nd, Eu and Ce) clusters, which can be viewed as synthetic analogs of the CaMn₄O₅ cluster. Anchoring LnCo₃ on phosphorus-doped graphitic carbon nitrides (PCN) shows efficient overall water splitting without any sacrificial reagents. The NdCo₃/PCN-c photocatalyst exhibits excellent water splitting activity and a quantum efficiency of 2.0% at 350 nm. Ultrafast transient absorption spectroscopy revealed the transfer of a photoexcited electron and hole into the PCN and LnCo₃ for hydrogen and oxygen evolution reactions, respectively. A density functional theory (DFT) calculation showed the cooperative water activation on lanthanide and O−O bond formation on transition metal for water oxidation. This work not only prepares a synthetic model of a bio-inspired oxygen-evolving center but also provides an effective strategy to realize light-driven overall water splitting.     

Achieving ultrahigh electrochemical performance by surface design and nanoconfined water manipulation

The effects of nanoconfined water and the charge storage mechanism are crucial to achieving the ultrahigh electrochemical performance of two-dimensional transition metal carbides (MXenes). We propose a facile method to manipulate nanoconfined water through surface chemistry modification. By introducing oxygen and nitrogen surface groups, more active sites were created for Ti₃C₂ MXene, and the interlayer spacing was significantly increased by accommodating three-layer nanoconfined water. Exceptionally high capacitance of 550 F g^–1 (2000 F cm^–3) was obtained with outstanding high-rate performance. The atomic scale elucidation of the layer-dependent properties of nanoconfined water and pseudocapacitive charge storage was deeply probed through a combination of ‘computational and experimental microscopy’. We believe that an understanding of, and a manipulation strategy for, nanoconfined water will shed light on ways to improve the electrochemical performance of MXene and other two-dimensional materials.     

LXYL-P1-2 immobilized on magnetic nanoparticles and its potential application in paclitaxel production

BackgroundLXYL-P1-2 is the first reported glycoside hydrolase that can catalyze the transformation of 7-β-xylosyl-10-deacetyltaxol (XDT) to 10-deacetyltaxol (DT) by removing the d-xylosyl group at the C-7 position. Successful synthesis of paclitaxel by one-pot method combining the LXYL-P1-2 and 10-deacetylbaccatin III-10-β-O-acetyltransferase (DBAT) using XDT as a precursor, making LXYL-P1-2 a highly promising enzyme for the industrial production of paclitaxel. The aim of this study was to investigate the catalytic potential of LXYL-P1-2 stabilized on magnetic nanoparticles, the surface of which was modified by Ni²⁺-immobilized cross-linked Fe₃O₄@Histidine.ResultsThe diameter of matrix was 20–40 nm. The K_m value of the immobilized LXYL-P1-2 catalyzing XDT (0.145 mM) was lower than that of the free enzyme (0.452 mM), and the k_cat/K_m value of immobilized enzyme (12.952 mM s⁻¹) was higher than the free form (8.622 mM s⁻¹). The immobilized form maintained 50% of its original activity after 15 cycles of reuse. In addition, the stability of immobilized LXYL-P1-2, maintained 84.67% of its initial activity, improved in comparison with free form after 30 d storage at 4°C.ConclusionsThis investigation not only provides an effective procedure for biocatalytic production of DT, but also gives an insight into the application of magnetic material immobilization technology.How to citeZou S, Chen TJ, Li DY, et al. LXYL-P1-2 immobilized on magnetic nanoparticles and its potential application in paclitaxel production. Electron J Biotechnol 2021;50.https://doi.org/10.1016/j.ejbt.2020.12.005     

Redox mediators for high-performance lithium–oxygen batteries

Aprotic lithium–oxygen (Li–O₂) batteries are receiving intense research interest by virtue of their ultra-high theoretical specific energy. However, current Li–O₂ batteries are suffering from severe barriers, such as sluggish reaction kinetics and undesired parasitic reactions. Recently, molecular catalysts, i.e. redox mediators (RMs), have been explored to catalyse the oxygen electrochemistry in Li–O₂ batteries and are regarded as an advanced solution. To fully unlock the capability of Li–O₂ batteries, an in-depth understanding of the catalytic mechanisms of RMs is necessary. In this review, we summarize the working principles of RMs and their selection criteria, highlight the recent significant progress of RMs and discuss the critical scientific and technical challenges on the design of efficient RMs for next-generation Li–O₂ batteries.     

DNA combing on low-pressure oxygen plasma modified polysilsesquioxane substrates for single-molecule studies

Molecular combing and flow-induced stretching are the most commonly used methods to immobilize and stretch DNA molecules. While both approaches require functionalization steps for the substrate surface and the molecules, conventionally the former does not take advantage of, as the latter, the versatility of microfluidics regarding robustness, buffer exchange capability, and molecule manipulation using external forces for single molecule studies. Here, we demonstrate a simple one-step combing process involving only low-pressure oxygen (O₂) plasma modified polysilsesquioxane (PSQ) polymer layer to facilitate both room temperature microfluidic device bonding and immobilization of stretched single DNA molecules without molecular functionalization step. Atomic force microscopy and Kelvin probe force microscopy experiments revealed a significant increase in surface roughness and surface potential on low-pressure O₂ plasma treated PSQ, in contrast to that with high-pressure O₂ plasma treatment, which are proposed to be responsible for enabling effective DNA immobilization. We further demonstrate the use of our platform to observe DNA-RNA polymerase complexes and cancer drug cisplatin induced DNA condensation using wide-field fluorescence imaging.     

Comparison of the masses of he and h1 on a mass-spectrograph

The ratio of the masses of He : Ht was measured by comparison of He⁺⁺ with H₂¹⁺ on fourteen spectra, and the measurements give He : H¹ = 3.971283 ± 0.000042. If He = 4.00216 ± 0.00013 on the O¹⁶ scale as given by Aston, then H¹ = 1.007775 ± 0.000035 in excellent agreement with the value 1.00778 reported by Aston.A method is suggested for the determination of the mass of H² in terms of He and C.     

Role of prostaglandin in the regulation of gastric H+—Transporting system

Prostaglandins and (PG) have been reported to be an important gastric acid suppressive factor. However, the mechanism underlying is yet to be clearly established. In vitro study with gastric microsomes in presence of both PGE₂ and PGI₂ shows a stimulation of gastric H⁺ K⁺-ATPase activity below 1X10⁻⁶M and 2.5X10⁻⁷M concentrations respectively. However, with further increase in concentrations of both PGE₂ and PGI₂, H⁺, K⁺-ATPase activity shows an inhibition but PGI₂ completely obliterates the K⁺ stimulated part of H⁺, K⁺-ATPase activity at higher concentration. The H⁺-ion transport study using chambered frog gastric mucosa shows that both PGE₂ and PGI₂ inhibit H⁺-ion transport at 5X10⁻⁶ M and 10X10⁻⁶M concentrations respectively but the effect of PGI₂ is reversible. These differential effects of PGE₂ and PGI₂ on microsomal H⁺, K⁺-ATPase and on H⁺ transport my be caused by the differential effects of these phospholipid mediators with the gastric mucosal cell membrane. This in vitro investigation shows the role of prostaglandin (s) as a physiological switch/regulator of gastric H⁺ ion transport leading to the cessation of gastric acid secretion.     

Free radical injury and antioxidant status in patients with benign prostate hyperplasia and prostate cancer

Reactive oxygen species and other free radicals are known to be the mediators of phenotypic and genotypic changes that lead from mutation to neoplasia. There are some primary antioxidants such as glutathione peroxidase (GPx), glutathione S-transferases (GSTs) and reduced glutathione, which protect against callular and molecular damage caused by the reactive oxygen metabolites (ROMs). The present study was conducted to determine the level of malondialdehyde (MDA), as an index of lipid peroxidation, along with the GPx, GSTs activities and level of reduced glutathione in 45 prostate cancer (PC) patients, 55 benign prostate hyperplasia (BPH) patients as compared to the controls. Significant higher levels of MDA and GSTs activities in the serum, (P<0.005) and significant lower levels of reduced GSH concentration and GPx activity in blood haemolysates (P<0.05) of PC and BPH patients were observed as compared to the controls. The relatively higher GSTs activity and low level of reduced GSH may be due to the response of increased reactive oxygen metabolites production in the blood. The higher MDA and lower GPx activities may be inadequate to detoxify high levels of H₂O₂ into H₂O leading to the formation of the^*OH radical followed by MDA. This result hypothesizes that oxidant-antioxidant imbalance may be one of the major factor responsible for the development of prostate cancer and benign prostate hyperplasia.     

Molecular grafting towards high-fraction active nanodots implanted in N-doped carbon for sodium dual-ion batteries

Sodium-based dual-ion batteries (Na-DIBs) show a promising potential for large-scale energy storage applications due to the merits of environmental friendliness and low cost. However, Na-DIBs are generally subject to poor rate capability and cycling stability for the lack of suitable anodes to accommodate large Na⁺ ions. Herein, we propose a molecular grafting strategy to in situ synthesize tin pyrophosphate nanodots implanted in N-doped carbon matrix (SnP₂O₇@N-C), which exhibits a high fraction of active SnP₂O₇ up to 95.6 wt% and a low content of N-doped carbon (4.4 wt%) as the conductive framework. As a result, this anode delivers a high specific capacity ∼400 mAh g⁻¹ at 0.1 A g⁻¹, excellent rate capability up to 5.0 A g⁻¹ and excellent cycling stability with a capacity retention of 92% after 1200 cycles under a current density of 1.5 A g⁻¹. Further, pairing this anode with an environmentally friendly KS6 graphite cathode yields a SnP₂O₇@N-C||KS6 Na-DIB, exhibiting an excellent rate capability up to 30 C, good fast-charge/slow-discharge performance and long-term cycling life with a capacity retention of ∼96% after 1000 cycles at 20 C. This study provides a feasible strategy to develop high-performance anodes with high-fraction active materials for Na-based energy storage applications.