Thromboxane B2 biosynthesis and phospholipids hydrolysis in platelets from hypercholesterolemic rabbits

Thromboxane B₂ biosynthesis from arachidonic acid was increased in platelets from hypercholesterolemic rabbits. The enzymic activity of phospholipase A₂ which releases arachidonic acid, the precursor for the biosynthesis of thromboxane B₂, showed hardly any change in hypercholesterolemic platelets. Phospholipase C and diglyceride lipase activities also were not changed in platelets from hypercholesterolemic rabbits. Furthermore, phospholipid concentration in platelets were not increased in this state. Thus, we conclude that the supply of precursor for thromboxane B₂ biosynthesis was not increased in platelets from hypercholesterolemic rabbits as compared to controls. These results suggest that the enzyme activity of thromboxane B₂ biosynthesis may be enhanced in platelets from hypercholesterolemic rabbits.     

Low concentration of oxidized low density lipoprotein suppresses platelet reactivity <Emphasis Type="Italic">in vitro</Emphasis>: An intracellular study

The intracellular mechanisms underlying oxidized low density lipoprotein (oxLDL)-signaling pathways in platelets remain obscure and findings have been controversial. Therefore, we examined the influence of oxLDL in washed human platelets. In this study oxLDL concentration-dependently (20–100 μg/mL) inhibited platelet aggregation in human platelets stimulated by collagen (1 μg/mL) and arachidonic acid (60 μM), but not by thrombin (0.02 U/mL). The activity of oxLDL was greater at 24 h in inhibiting platelet aggregation than at 12 h. At 24 h, oxLDL concentration-dependently inhibited intracellular Ca²⁺ mobilization and thromboxane B₂ formation in human platelets stimulated by collagen. In addition, at 24 h oxLDL (40 and 80 μg/mL) significantly increased the formation of cyclic AMP, but not cyclic GMP or nitrate. In an ESR study, 24 h-oxLDL (40 μg/mL) markedly reduced the ESR signal intensity of hydroxyl radicals (OH⁻) in both collagen (2 μg/mL)-activated platelets and Fenton reaction (H₂O₂+Fe²⁺). The inhibitory effect of oxLDL may induce radical-radical termination reactions by oxLDL-derived lipid radical interactions with free radicals (such as hydroxyl radicals) released from activated platelets, with a resultant lowering of intracellular Ca²⁺ mobilization followed by inhibition of thromboxane A₂ formation, thereby leading to increased cyclic AMP formation and finally inhibited platelet aggregation. This study provides new insights concerning the effect of oxLDL in platelet aggregation.     

Transformation of Prostaglandin D2 to 11-Dehydro Thromboxane B2 by Baeyer-Villiger Oxidation

Prostaglandin D₂ is one of five chief prostanoids formed in the cyclooxygenase pathway of arachidonic acid oxidation. Except for a single oxygen atom, PGD₂ is structurally identical to 11-dehydro thromboxane B₂ (11d-TxB₂), a urinary metabolite of the pro-aggregatory platelet activator, thromboxane A₂. The close structural relationship suggested that one might be transformed to the other. Accordingly, we tested whether the cyclopentanone of PGD₂ can be expanded to the δ-lactone of 11d-TxB₂ in a Baeyer-Villiger oxidation. Oxidation of PGD₂ with two standard oxidants showed that 11d-TxB₂ was formed only with H₂O₂ but not with peracetic acid. Byproducts of the H₂O₂-mediated oxidation were hydroperoxide derivatives and isomers of PGD₂. Chemical oxidation of PGD₂ to 11d-TxB₂ may be a model for an equivalent enzymatic transformation, suggesting a possible link in the metabolism of PGD₂ and thromboxane A₂.     

A sintering strategy for lithium zinc ferrite with a high saturation magnetization and low ferromagnetic resonance line-width

Based on the activation energy and diffusion kinetics theory of grain growth, Li_0.42Zn_0.28Ti_0.1Fe_2.2O₄ ceramics with a low ferromagnetic resonance line-width (ΔH) and high saturation magnetization (Ms) were synthesized by adopting LTCC (low-temperature cofired ceramics) technology. The critical sintering temperature of ferrite synthesis was reduced to 925 °C due to activation energy reduction and the liquid phase sintering mechanism of Bi₂O₃. The sintering agent B₂O₃ further improved the grain size, homogeneity, density and properties. EDS and XRD refinement showed that Bi³⁺ and B³⁺ ions did not enter lattices, but Ti⁴⁺ ions entered lattices and replaced part of the Fe³⁺ ions, leading to the lattice expansion. Finally, homogeneous and compact Li_0.42Zn_0.28Ti_0.1Fe_2.2O₄ ferrite with Ms up to 354.6 kA/m and ΔH as low as 184.2 Oe was synthesized at temperatures as low as 925 °C by adding an appropriate content of Bi₂O₃ and B₂O₃. In the present study, the exploration and practice of reducing the sintering temperature and improving the material properties based on sintering agents is a beneficial supplement and improvement to the wider application of the LTCC technique.     

Effect of Hydrogen Peroxide on the Biosynthesis of Heme and Proteins: Potential Implications for the Partitioning of Glu-tRNAGlu between These Pathways

Glutamyl-tRNA (Glu-tRNA^Glu) is the common substrate for both protein translation and heme biosynthesis via the C₅ pathway. Under normal conditions, an adequate supply of this aminoacyl-tRNA is available to both pathways. However, under certain circumstances, Glu-tRNA^Glu can become scarce, resulting in competition between the two pathways for this aminoacyl-tRNA. In Acidithiobacillus ferrooxidans, glutamyl-tRNA synthetase 1 (GluRS1) is the main enzyme that synthesizes Glu-tRNA^Glu. Previous studies have shown that GluRS1 is inactivated in vitro by hydrogen peroxide (H₂O₂). This raises the question as to whether H₂O₂ negatively affects in vivo GluRS1 activity in A. ferrooxidans and whether Glu-tRNA^Glu distribution between the heme and protein biosynthesis processes may be affected by these conditions. To address this issue, we measured GluRS1 activity. We determined that GluRS1 is inactivated when cells are exposed to H₂O₂, with a concomitant reduction in intracellular heme level. The effects of H₂O₂ on the activity of purified glutamyl-tRNA reductase (GluTR), the key enzyme for heme biosynthesis, and on the elongation factor Tu (EF-Tu) were also measured. While exposing purified GluTR, the first enzyme of heme biosynthesis, to H₂O₂ resulted in its inactivation, the binding of glutamyl-tRNA to EF-Tu was not affected. Taken together, these data suggest that in A. ferrooxidans, the flow of glutamyl-tRNA is diverted from heme biosynthesis towards protein synthesis under oxidative stress conditions.     

15-hydroperoxyeicosatetraenoic acid inhibits human platelet aggregation

Using human platelets isolated from their plasma, we showed that 15-hydroperoxy-eicosatetraenoic acid (15-HPETE) inhibits platelet aggregation induced either by arachidonic acid or prostaglandin H₂ analog. 15-HPETE does not modify platelet prostaglandin and thromboxane formation from exogenous arachidonic acid but does decrease platelet lipoxygenase activity.     

Ammonia synthesis over the Ba-promoted ruthenium catalysts supported on boron nitride

Barium promoted ruthenium catalysts deposited on the boron nitride supports were characterised (XRD, O₂ and CO chemisorption) and tested in NH₃ synthesis. Prior to use, the raw BN materials marked as BNS (Starck, 96 m²/g) and HCV (Advanced Ceramics Corporation Cleveland USA, 40 m²/g) were heated in an ammonia stream at 700–800 °C for 120 h. As a result, the oxygen content was reduced from 7.0 at% (BNS) to 3.5 at% (BNS_NH3) and from 3.8 to 2.7 at% (HCV_NH3), as evidenced by XPS. The kinetic studies of NH₃ synthesis (63 or 90 bar; H₂:N₂ = 3:1) revealed that the catalysts based on the modified supports were more active, respectively, than those derived from starting nitrides, the difference being especially pronounced in the case of BNS and BNS_NH3. Studies of the catalysts activation have shown, in turn, that the stabilisation in a H₂:N₂=3:1 mixture at 1bar is very slow, i.e. the reaction rate increases slowly versus time on stream even at a high temperature of 550 – 600°C. Stabilisation is faster and the NH₃ synthesis rates are higher when the activation is performed with an ammonia rich mixture (10% NH₃ in H₂:N₂=3:1) flowing under high pressure of 90 bar. It is suggested that boron oxide (an impurity) acts as a deactivating agent for Ba–Ru/BN and that the reaction between NH₃ and B₂O₃ (B₂O₃+2NH₃=2BN +3H₂O) is responsible for the activity increase. A poisoning mechanism of B₂O₃ is discussed.     

White‐emitting phosphor Ba2B2O5:Ce3+, Tb3+, Sm3+: Luminescence,energy transfer,and thermal stability

A series of Ba₂B₂O₅: RE (RE=Ce³⁺/Tb³⁺/Sm³⁺) phosphors were synthesized using high‐temperature solid‐state reaction. The X‐ray diffraction (XRD), luminescent properties, and decay lifetimes are utilized to characterize the properties of the phosphors. The obtained phosphors can emit blue, green, and orange‐red light when single‐doped Ce³⁺, Tb³⁺, and Sm³⁺. The energy can transfer from Ce³⁺ to Tb³⁺ and Tb³⁺ to Sm³⁺ in Ba₂B₂O₅, but not from Ce³⁺ to Sm³⁺ in Ce³⁺ and Sm³⁺ codoped in Ba₂B₂O₅. However, the energy can transfer from Ce³⁺ to Sm³⁺ through the bridge role of Tb³⁺. We obtain white emission based on energy transfer of Ce³⁺→Tb³⁺→Sm³⁺ ions. These results reveal that Ce³⁺/Tb³⁺/Sm³⁺ can interact with each other in Ba₂B₂O₅, and Ba₂B₂O₅ may be a potential candidate host for white‐light‐emitting phosphors.     

Mitochondrial Protection and Anti-aging Activity of Astragalus Polysaccharides and Their Potential Mechanism

The current study was performed to investigate mitochondrial protection and anti-aging activity of Astragalus polysaccharides (APS) and the potential underlying mechanism. Lipid peroxidation of liver and brain mitochondria was induced by Fe²⁺–Vit C in vitro. Thiobarbituric acid (TBA) colorimetry was used to measure the content of thiobarbituric acid reactive substances (TBARS). Mouse liver mitochondrial permeability transition (PT) was induced by calcium overload in vitro and spectrophotometry was used to measure it. The scavenging activities of APS on superoxide anion (O₂^•−) and hydroxyl radical (•OH), which were produced by reduced nicotinamide adenine dinucleotide (NADH)—N-Methylphenazonium methyl sulfate (PMS) and hydrogen peroxide (H₂O₂)–Fe²⁺ system respectively, were measured by 4-nitrobluetetrazolium chloride (NBT) reduction and Fenton reaction colorimetry respectively. The Na₂S₂O₃ titration method was used to measure the scavenging activities of APS on H₂O₂. APS could inhibit TBARS production, protect mitochondria from PT, and scavenge O₂^•−, •OH and H₂O₂ significantly in a concentration-dependent manner respectively. The back of the neck of mice was injected subcutaneously with D-galactose to induce aging at a dose of 100 mg/kg/d for seven weeks. Moreover, the activities of catalase (CAT), surperoxide dismutase (SOD) and glutathione peroxidase (GPx) and anti-hydroxyl radical which were assayed by using commercial monitoring kits were increased significantly in vivo by APS. According to this research, APS protects mitochondria by scavenging reactive oxygen species (ROS), inhibiting mitochondrial PT and increasing the activities of antioxidases. Therefore, APS has the effect of promoting health.     

Direct synthesis of hydrogen peroxide from hydrogen and oxygen: An overview of recent developments in the process

Hydrogen peroxide (H₂O₂) is an important commodity chemical and its demand is growing significantly in the chemical synthesis due to its “green” character. Currently, H₂O₂ is produced almost exclusively by the anthraquinone auto-oxidation (AO) process. The AO process involves indirect oxidation of hydrogen and thus avoids potentially explosive H₂/O₂ mixture. However, this large-scale process presents significant safety issues associated with the transport of bulk H₂O₂. Moreover, the AO process can hardly be considered an environmentally friendly method. In view of this, more economical and environmentally cleaner routes have been explored for the production of H₂O₂. The liquid-phase catalytic direct synthesis of H₂O₂ from H₂ and O₂ offers an attractive green technology for small-scale/on-site production of H₂O₂. However, the direct synthesis process suffers from two major drawbacks: (i) potential hazards associated with H₂/O₂ mixtures and (ii) poor selectivity for H₂O₂ because the catalysts used for H₂O₂ synthesis are also active for its decomposition and hydrogenation to water as well as for H₂ combustion. These serious issues and the recent developments in the direct H₂O₂ synthesis are discussed in this review. The roles of protons (H⁺) and halide ions in promoting the H₂O₂ selectivity are also examined in detail.     

Intracellular Ca2+ concentration and H2O2 production in mouse peritoneal macrophages are stimulated by platelet activating factor

The intracellular calcium concentration ([Ca²⁺]i) in mouse peritoneal macrophages cultured on a coverglass was measured in the superfusion system using fura-2 as a fluorescent calcium probe and platelet activating factor (PAF) as a stimulant. In the presence of extracellular Ca²⁺, 10⁻⁷M PAF sharply increased [Ca²⁺]i from a basal level of 90 nM to 340 nM. Thereafter, the [Ca²⁺]i level gradually decreased in two phases, in an initial rapid phase and a subsequent slow phase of decrease. The calcium response was dependent on the PAF concentration. In the absence of extracellular Ca²⁺, a single sharp peak was observed, suggesting two different modes of Ca²⁺ movement, one from intracellular stores and the other from the extracellular medium. A simple, sensitive fluorometric assay system was developed for measuring H₂O₂ in the superfusate of macrophages after stimulation by use of immobilized peroxidase and 3-(p-hydroxyphenyl)propionic acid as a fluorogenic substrate. With this system, as little as 2 pmol of H₂O₂ could be measured. PAF (1 μM) increased H₂O₂ production in peritoneal macrophages in the presence of extracellular Ca²⁺, but H₂O₂ production was not observed in the absence of extracellular Ca²⁺. Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989.     

Study of the two pathways for arachidonate oxygenation in blood platelets

During collagen-induced blood platelet aggregation, arachidonic acid is set free from membrane phospholipids and subsequently converted into 12-hydroxyeicosatetraenoic acid by arachidonate lipoxygenase and into thromboxane A₂, 12-hydroxyheptadecatrienoic acid (HETE) and malondialdehyde by cyclooxygenase and thromboxane synthase. Lipoxygenase and cyclooxygenase have optimal activity at neutral to basic pH, while the thromboxane synthase is pH-independent between 5 and 9. These enzymes are membrane-bound. The cyclooxygenase is rapidly inactivated upon membrane disruption by nonionic detergents or phospholipid degradation with phospholipase A₂. It was found that platelet phospholipase A₂ preferentially splits off fatty acid with four double bonds. Eicosatetraynoic acid was used to investigate the physiological function of the arachidonate lipoxygenase during collagen-induced aggregation of rat blood platelets. This fatty acid is a more efficient inhibitor of lipoxygenase than of cyclooxygenase. At an inhibitor concentration of 0.6 μg/ml, platelet aggreation, 12-hydroxyeicosatetraenoic acid production as well as 15-hydroxytryptamine release are completely inhibited, while there is an apparent stimulation of the cyclooxygenase. These results indicate that arachidonate lipoxygenase is essential for irreversible blood platelet aggregation.     

Effect of UV Radiation on the Removal of Carboxylic Acids from Water by H2O2 and O3 in the Presence of Metallic Ions

The effect of UV radiation on the removal of formic, oxalic and maleic acids from water by metallic ion (Fe²⁺ or Cu²⁺)/H₂O₂ and metallic ion/O₃ was studied and compared. The results showed that metallic ion/O₃/UV has higher efficiency than metallic ion/H₂O₂/UV for oxalic acid removal. UV radiation significantly increases the efficiency of metallic ion/H₂O₂ for formic and maleic acids removal while its effect on the efficiency of metallic ion/O₃ for formic acid removal is minor_. However, at pH 2, O₃ alone showed higher efficiency than metallic ion/H₂O₂/UV for formic acid removal. Contrary to the relative efficiency of metallic ions in the previous systems, Cu²⁺ exhibited higher rate than Fe²⁺ for the removal of the degradation products of maleic acid by O₃. UV radiation exhibited a minor effect on the efficiency of Cu²⁺/O₃, while it exhibited a large effect on the efficiency of Fe²⁺/O₃ for the removal of the degradation products of maleic acid.     

PAMAM Dendrimer-Derived Ir/Al2O3 Catalysts: An EXAFS Characterization

Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to characterize several synthesis stages of hydroxyl-terminated generation four (G4OH) PAMAM dendrimer-derived Ir/γ-Al₂O₃ catalyst. The EXAFS results indicate that Ir³⁺ forms complexes with dendrimer functional groups through displacement of two Cl^? ion ligands. These complexes are very stable in solution, and no reduction of Ir³⁺ to Ir nanoparticles or clusters is observed after introduction of reducing agents such as NaBH₄ or H₂. These Ir³⁺-dendrimer complexes remain essentially intact after support impregnation. The formation of 1–2 nm particles occurs when the catalysts are treated with O₂/H₂ or H₂, and the dendrimer-derived catalysts exhibit a lower degree of metal support interaction.     

Luminescent properties of Sr2B2O5: Tm,Na blue phosphor

A novel blue phosphor, Sr₂B₂O₅: Tm³⁺, Na⁺ for white light-emitting diodes (W-LEDs) was prepared by solid-state synthesis and its structure and luminescence properties were investigated. This phosphor can be effectively excited within the broad near ultraviolet (NUV) wavelength region, from 340 nm to 370 nm, and exhibits a satisfactory blue performance. The emission peaks are observed at 457 nm (blue) and 475 nm (blue), due to the respective transitions of ¹D₂→³F₄ and ¹G₄→H₆. Seven mole percent of doping concentration of Tm³⁺ was shown to be optimal. Concentration quenching occurs when Tm³⁺ concentration is beyond 7 mol%, its mechanism being explained by dipole–dipole interaction of Tm³⁺ and being confirmed by decay property measurements. We have made a deep analysis on the effect of charge compensation reagent on luminescence intensity. Good blue emissions with the CIE chromaticity coordinates (0.173, 0.165) could be achieved. Our results suggest that the Sr₂B₂O₅: Tm³⁺, Na⁺ phosphor is a potential blue-emitting material.     

Red-shift and improved afterglow of Sr3Al2-xBxO5Cl2:Eu2+, Dy3+ phosphors via a cation substitution strategy

Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ (x = 0, 0.2, 0.4) long persistent phosphors were prepared via solid-state process. The pristine Sr₃Al₂O₅Cl₂:Eu²⁺, Dy³⁺ phosphor exhibits orange/red broad band emission around 609 nm, which can be attributed to the electric radiation transitions 4f⁶5 d¹→4f⁷ of Eu²⁺. Upon the same excitation, the B³⁺-doped Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ phosphors display red-shift from 609 nm to 625 nm with increasing B³⁺ concentrations. The XRD patterns show that Al³⁺ can be replaced by B³⁺ in the host lattice at the tetrahedral site, which causes lattice contraction and crystal field enhancement, and thereafter achieves the red-shift on the emission spectrum. The XPS investigation provides direct evidence of the dominant 2-valent europium in the phosphor, which can be ascribed for the broad band emission of the prepared phosphors. The afterglow of all phosphors show standard double exponential decay behavior, and the afterglow of Sr₃Al₂O₅Cl₂:Eu²⁺, Dy³⁺is rather weak, while the sample co-doped with B³⁺shows longer and stronger afterglow, as confirmed after the curve simulation. The analysis of thermally stimulated luminescence showed that, when B³⁺ is introduced, a much deeper trap is created, and the density of the electron trap is also significantly increased. As a result, B³⁺ ions caused redshift and enhanced afterglow for the Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ phosphor.     

Performance and transition mechanism from acidity to basicity of amphoteric oxides (Al2O3 and B2O3) in SiO2–CaO–Al2O3–B2O3 system: A molecular dynamics study

Amphoteric oxides (Al₂O₃ and B₂O₃) represent opposite effects on the structure and properties of silicate melts in different conditions, while the understanding about the transition from acidity to basicity is far from complete. Molecular dynamics simulation was adopted in the present study to investigate the performance and acidity-basicity transformation of Al₂O₃ and B₂O₃ in the SiO₂–CaO–Al₂O₃–B₂O₃ system. The results showed that, different from Ca²⁺ ions, excessive Al³⁺ or B³⁺ ions tend to destroy the bridge oxygen structures, showing the function of basic oxide. This is similar to the behavior of Ca²⁺ ions and other basicity ions. It was found that, on the one hand, B³⁺ ions tend to form [BO₃]^3- planar triangular structures with the increase of B³⁺ ions contents, on the other hand, B³⁺ ions could reduce the stability of Si–O bonds. Therefore, B³⁺ ions could make the system structure less stable, which is the reason why the B₂O₃ is a kind of active agent. In addition, because of the significant differences in lattice energy and atomic structure between Al₂O₃ and B₂O₃, the effects of Al₂O₃ and B₂O₃ on the thermodynamic properties of silicate melts are quite different.     

Form of the catalytically active Pd species during the direct synthesis of hydrogen peroxide

Direct synthesis of H₂O₂ could produce H₂O₂ at lower cost than the Riedl–Pfleiderer process, which would enable the broader use of H₂O₂ for industrial oxidations. The addition of inorganic acids and halides to the solvent increase H₂O₂ selectivities on Pd nanoparticles but also dissolve Pd and produce dynamic mixtures of complexes including heterogeneous (Pd⁰) and homogeneous (Pd²⁺) species, any of which may contribute to H₂O₂ formation. We combine kinetic measurements and in operando UV–vis spectroscopy to determine how H₂O₂ rates and selectivities depend on concentrations of these forms of Pd. Introducing HCl to the solvent increases the concentration of Pd²⁺ complexes by oxidizing Pd⁰ nanoparticles. The rates of primary H₂O₂ formation and H₂O₂ selectivities do not depend directly on the population of the Pd²⁺ species for catalysts tested in water or methanol. These results suggest that Pd nanoparticles form H₂O₂ and detectable homogeneous complexes do not act as catalysts.     

ESR Study of a Complex Formation Between HO2 Radical and Peroxy-Vanadium (V) Ion

HO₂ radicals were generated in a flow system by the reaction: Ce⁴⁺ + H₂O₂→ Ce³⁺ +HO₂ + H⁺. The HO₂ radicals were mixed with V - H₂O₂ solutions and ESR spectroscopy was used to follow the reaction. It was shown that HO₂ reacts with both VO(O₂)⁺ and VO(O₂)^?₂ complexes. The ESR signal of the complexed radical consists of eight lines, indicating that the unpaired electron interacts with the Vanadium nucleus. The kinetics of the formation and decay reactions of the complexed radical were studied.     

Intensifying graft-polymerization in the process of modifying polycaproamide fibres

Conclusions -- The kinetics of the graft polymerization of dimethylaminoethyl methacrylate to polycaproamide fibre initiated by the redox systems Fe²⁺ - H₂O₂, Cu²⁺ - H₂O₂, and by an ROC containing a complex copper compound (Cu _c ²⁺ - H₂O₂) has been studied.-- An increase in the rate of graft polymerization, in the amount of grafted component, and the degree of useful conversion of the monomer has been found when the reaction is initiated by the ROS Cu _c ²⁺ - H₂O₂.Moscow Textile Academy. Translated from Khimicheskie Volokna, No. 3, pp. 11–12, May–June, 1992.