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U Baltensperger - One of the best experts on this subject based on the ideXlab platform.
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development of a sensitive long path absorption photometer to quantify Peroxides in aerosol particles peroxide lopap
Atmospheric Measurement Techniques, 2012Co-Authors: Peter Mertes, L Pfaffenberger, J Dommen, Markus Kalberer, U BaltenspergerAbstract:Abstract. A new off-line instrument to quantify Peroxides in aerosol particles using iodometry in long path absorption spectroscopy has been developed and is called peroxide long path absorption photometer (Peroxide-LOPAP). The new analytical setup features important technical innovations compared to hitherto published iodometric peroxide measurements. Firstly, the extraction, chemical conversion and measurement of the aerosol samples are performed in a closed oxygen-free (~ 1 ppb) environment. Secondly, a 50-cm optical detection cell is used for an increased photometric sensitivity. The limit of detection was 0.1 μM peroxide in solution or 0.25 nmol m−3 with respect to an aerosol sample volume of 1 m3. The test reaction was done at a constant elevated temperature of 40 °C and the reaction time was 60 min. Calibration experiments showed that the test reaction with all reactive Peroxides, i.e. hydrogen peroxide (H2O2), peracids and Peroxides with vicinal carbonyl groups (e.g. lauroyl peroxide) goes to completion and their sensitivity (slope of calibration curve) varies by only ±5%. However, very inert Peroxides have a lower sensitivity. For example, tert-butyl hydroperoxide shows only 37% sensitivity compared to H2O2 after 1 h. A kinetic study revealed that even after 5 h only 85% of this inert compound had reacted. The time trends of the peroxide content in secondary organic aerosol (SOA) from the ozonolysis and photo-oxidation of α-pinene in smog chamber experiments were measured. The highest mass fraction of Peroxides with 34% (assuming a molecular weight of 300 g mol−1) was found in freshly generated SOA from α-pinene ozonolysis. Mass fractions decreased with increasing NO levels in the photo-oxidation experiments. A decrease of the peroxide content was also observed with aging of the aerosol, indicating a decomposition of Peroxides in the particles.
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Development of a sensitive long pathlength absorbance photometer to quantify Peroxides in aerosol particles (Peroxide-LOPAP)
Copernicus Publications, 2012Co-Authors: Peter Mertes, L Pfaffenberger, J Dommen, Markus Kalberer, U BaltenspergerAbstract:A new off-line instrument to quantify Peroxides in aerosol particles using iodometry in long pathlength absorption spectroscopy has been developed and is called peroxide long pathlength absorbance photometer (Peroxide-LOPAP). The new analytical setup features important technical innovations compared to hitherto published iodometric peroxide measurements. Firstly, the extraction, chemical conversion and measurement of the aerosol samples are performed in a closed oxygen-free (∼1 ppb) environment. Secondly, a 50-cm optical detection cell is used for an increased photometric sensitivity. The limit of detection was 0.1 μM peroxide in solution or 0.25 nmol m<sup>−3</sup> with respect to an aerosol sample volume of 1000 l. The test reaction was done at a constant elevated temperature of 40 °C and the reaction time was 60 min. <br><br> Calibration experiments showed that the test reaction with all reactive Peroxides, i.e. hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), peracids and Peroxides with vicinal carbonyl groups (e.g. lauroyl peroxide) goes to completion and their sensitivity (slope of calibration curve) varies by only ±5%. However, very stable Peroxides have a lower sensitivity. For example <i>tert</i>-butyl hydroperoxide shows only 37% sensitivity compared to H<sub>2</sub>O<sub>2</sub> after 1h. A kinetic study revealed that even after 5 h only 85% of this stable compound had reacted. <br><br> The time trends of the peroxide content in secondary organic aerosol (SOA) from the ozonolysis and photo-oxidation of α-pinene in smog chamber experiments were measured. The highest amount of Peroxides with 34% (assuming a MW of 300 g mol<sup>−1</sup>) was found in freshly generated SOA from α-pinene ozonolysis. Contents decreased with increasing NO levels in the photo-oxidation experiments. A decrease of the peroxide content was observed with aging of the aerosol indicating a decomposition of Peroxides in the particles
Y. John Wang - One of the best experts on this subject based on the ideXlab platform.
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Peroxide formation in polysorbate 80 and protein stability.
Journal of pharmaceutical sciences, 2002Co-Authors: Y. John WangAbstract:Nonionic surfactants are widely used in the development of protein pharmaceuticals. However, the low level of residual Peroxides in surfactants can potentially affect the stability of oxidation-sensitive proteins. In this report, we examined the peroxide formation in polysorbate 80 under a variety of storage conditions and tested the potential of Peroxides in polysorbate 80 to oxidize a model protein, IL-2 mutein. For the first time, we demonstrated that Peroxides can be easily generated in neat polysorbate 80 in the presence of air during incubation at elevated temperatures. Polysorbate 80 in aqueous solution exhibited a faster rate of peroxide formation and a greater amount of Peroxides during incubation, which is further promoted/catalyzed by light. Peroxide formation can be greatly inhibited by preventing any contact with air/oxygen during storage. IL-2 mutein can be easily oxidized both in liquid and solid states. A lower level of Peroxides in polysorbate 80 did not change the rate of IL-2 mutein oxidation in liquid state but significantly accelerated its oxidation in solid state under air. A higher level of Peroxides in polysorbate 80 caused a significant increase in IL-2 mutein oxidation both in liquid and solid states, and glutathione can significantly inhibit the peroxide-induced oxidation of IL-2 mutein in a lyophilized formulation. In addition, a higher level of Peroxides in polysorbate 80 caused immediate IL-2 mutein oxidation during annealing in lyophilization, suggesting that implementation of an annealing step needs to be carefully evaluated in the development of a lyophilization process for oxidation-sensitive proteins in the presence of polysorbate.
John Y Wang - One of the best experts on this subject based on the ideXlab platform.
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peroxide formation in polysorbate 80 and protein stability
Journal of Pharmaceutical Sciences, 2002Co-Authors: Emily Ha, John Y WangAbstract:Abstract Nonionic surfactants are widely used in the development of protein pharmaceuticals. However, the low level of residual Peroxides in surfactants can potentially affect the stability of oxidation‐sensitive proteins. In this report, we examined the peroxide formation in polysorbate 80 under a variety of storage conditions and tested the potential of Peroxides in polysorbate 80 to oxidize a model protein, IL‐2 mutein. For the first time, we demonstrated that Peroxides can be easily generated in neat polysorbate 80 in the presence of air during incubation at elevated temperatures. Polysorbate 80 in aqueous solution exhibited a faster rate of peroxide formation and a greater amount of Peroxides during incubation, which is further promoted/catalyzed by light. Peroxide formation can be greatly inhibited by preventing any contact with air/oxygen during storage. IL‐2 mutein can be easily oxidized both in liquid and solid states. A lower level of Peroxides in polysorbate 80 did not change the rate of IL‐2 mutein oxidation in liquid state but significantly accelerated its oxidation in solid state under air. A higher level of Peroxides in polysorbate 80 caused a significant increase in IL‐2 mutein oxidation both in liquid and solid states, and glutathione can significantly inhibit the peroxide‐induced oxidation of IL‐2 mutein in a lyophilized formulation. In addition, a higher level of Peroxides in polysorbate 80 caused immediate IL‐2 mutein oxidation during annealing in lyophilization, suggesting that implementation of an annealing step needs to be carefully evaluated in the development of a lyophilization process for oxidation‐sensitive proteins in the presence of polysorbate. © 2002 Wiley‐Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:2252–2264, 2002
Scott W Walsh - One of the best experts on this subject based on the ideXlab platform.
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AA-2414, an antioxidant and thromboxane receptor blocker, completely inhibits peroxide-induced vasoconstriction in the human placenta.
The Journal of pharmacology and experimental therapeutics, 1999Co-Authors: Scott W Walsh, Yuping Wang, Anthony KillianAbstract:We hypothesized that AA-2414, a novel thromboxane receptor blocker with antioxidant properties, would inhibit peroxide-induced vasoconstriction in the isolated perfused human placental cotyledon. In study 1, placental cotyledons (n = 5) were perfused serially for 20- min intervals with control KrebsRinger-bicarbonate (KRB) buffer, t-butyl hydroperoxide (Px; 100 microM), KRB buffer, and KRB buffer containing Px to which progressively increasing concentrations of AA-2414 were added (1 x 10(-8) to 1 x 10(-4) mol/l). In study 2, placental cotyledons (n = 6) were perfused with control KRB buffer, Px alone, KRB buffer, 1 x 10(-5) mol/l AA-2414 alone, Px plus AA-2414, and Px alone. Compared with control, perfusion with Px significantly increased perfusion pressure, vascular resistance, and the maternal and fetal secretion rates of lipid Peroxides, thromboxane B2 (TXB2) and 6-keto prostaglandin F1alpha. In study 1, AA-2414 + Px produced a dose-response inhibition of Px-induced increases in perfusion pressure, vascular resistance, and maternal secretion of lipid Peroxides and TXB2. In study 2, perfusing AA-2414 at a dose of 1 x 10(-5) mol/l completely inhibited Px-induced vasoconstriction and increases in lipid peroxide and TXB2 secretion rates, but only partially inhibited the increase in 6-keto prostaglandin F1alpha secretion. We conclude that AA-2414 inhibited peroxide-induced vasoconstriction in the human placenta, as well as peroxide- induced increases in the placental secretion rates of lipid Peroxides and thromboxane, but only partially inhibited peroxide-induced increases in the placental secretion rate of prostacyclin.
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β-Carotene Attenuates Peroxide-Induced Vasoconstriction in the Human Placenta
The Journal of the Society for Gynecologic Investigation: JSGI, 1997Co-Authors: Sylvia M. Cueto, Yuping Wang, Angele D. Romney, Scott W WalshAbstract:Objective Placental lipid Peroxides and thromboxane are abnormally increased in preeclampsia. Peroxides stimulate thromboxane to increase placental vasoconstriction. Antioxidants, such as β-carotene, control lipid peroxidation. Reduced levels of β-carotene (0.25 μmol/L) have been found in preeclamptic women. We hypothesized that normal (0.5 μmol/L) or elevated (1.0 μmol/L) levels of β-carotene would attenuate peroxide-induced vasoconstriction in the human placenta, whereas low levels would not. Methods Isolated human placental cotyledons ( n = 8) were sequentially perfused with control Krebs-Ringer-bicarbonate buffer, 200 μmol/L t-butyl hydroperoxide, and then with progressively increasing concentrations of β-carotene (0.25, 0.5, and 1 μmol/L) plus t-butyl hydroperoxide. Fetal perfusion pressure was monitored continuously, and maternal and fetal effluent samples were collected for each treatment. Samples were analyzed for lipid Peroxides and for thromboxane and prostacyclin by their stable metabolites thromboxane B_2 (TXB_2) and 6-keto-prostaglandin (PG)F_1α. Results Compared with control, t-butyl hydroperoxide significantly increased perfusion pressure, vascular resistance, and the secretion rates of lipid Peroxides, TXB_2 and 6-keto-PGF_1α. Perfusion with normal (0.5 μmol/L) or increased (1 μmol/L) levels of β-carotene significantly or completely inhibited t-butyl hydroperoxide-induced vasoconstriction and the increases in lipid peroxide and TXB_2 secretion, but did not inhibit peroxide-induced increases in 6-keto-PGF_1α secretion. Reduced levels of β-carotene (0.25 μmol/L) did not inhibit t-butyl hydroperoxide-induced vasoconstriction or the increases in lipid peroxide secretion. Conclusions β-carotene at levels found in normal pregnant women (0.5 μmol/L) or at levels achieved with β-carotene supplementation (1 μmol/L) inhibited peroxide-induced vasoconstriction and lipid peroxide and thromboxane secretion. Levels of β-carotene found in preeclamptic women (0.25 μmol/L) did not inhibit peroxide-induced vasoconstriction or lipid peroxide secretion.
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deficient glutathione peroxidase activity in preeclampsia is associated with increased placental production of thromboxane and lipid Peroxides
American Journal of Obstetrics and Gynecology, 1993Co-Authors: Scott W Walsh, Yuping WangAbstract:Objective: Thromboxane and lipid peroxide levels are abnormally increased in preeclamptic placentas. The cause of this increase is not known. Peroxides stimulate prostaglandin H 2 synthase to increase thromboxane and oxygen radicals, which increase lipid Peroxides. Glutathione peroxidase inactivates Peroxides, thereby decreasing peroxide stimulation of prostaglandin H synthase. If glutathione peroxidase activity were deficient, then Peroxides could increase, leading to increased stimulation of prostaglandin H synthase, resulting in increased production of thromboxane and lipid Peroxides. The following study tested this hypothesis. Study Design: Placental tissues from 11 normal and 11 preeclamptic women were immediately frozen in liquid nitrogen after delivery. One gram of tissue from each placenta was homogenized for analysis. Placental tissues were also obtained from six normal pregnancies for incubation with a glutathione peroxidase inhibitor, N-ethylmaleimide. Samples were analyzed for glutathione peroxidase activity, lipid Peroxides by hydrogen peroxide equivalents, thromboxane by thromboxane B 2 , and prostacyclin by 6-keto-prostaglandin F 1α . Results: Glutathione peroxidase activity was significantly lower in preeclamptic than in normal placentas (9.41 ± 0.05 vs 13.41 ± 0.63 units/gm, p p 2 215 ± 31 vs 138 ± 15 ng/gm, p p Conclusions: Glutathione peroxidase activity is significantly lower, and lipid Peroxides and thromboxane are significantly higher, in preeclamptic placentas compared with normal placentas. Inhibition of glutathione peroxidase activity in normal placentas results in significantly increased production of lipid Peroxides and thromboxane and an increase in the thromboxane to prostacyclin ratio. We speculate that in normal placentas, glutathione peroxidase limits prostaglandin H synthase activity by reducing the amount of peroxide present, thus reducing peroxide stimulation of prostaglandin H synthase. In preeclampsia deficient glutathione peroxidase activity results in increased peroxide levels leading to increased stimulation of prostaglandin H synthase, which results in increased production of lipid Peroxides and thromboxane.
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Secretion of lipid Peroxides by the human placenta
American journal of obstetrics and gynecology, 1993Co-Authors: Scott W Walsh, Yuping WangAbstract:Objective: We attempted to determine whether the human placenta secretes lipid Peroxides. If it does, then it could be a source of lipid Peroxides in maternal blood. Study design: In study 1 isolated human placental cotyledons ( n = 7) were perfused serially for 20-minute intervals with control Krebs-Ringer-bicarbonate buffer gassed with 95% oxygen and 5% carbon dioxide and Krebs-Ringer-bicarbonate buffer with progressively increasing concentrations of t-butyl hydroperoxide added (10, 25, 50, and 100 μmol/L) to stimulate endogenous lipid peroxide production. In study 2 placental cotyledons ( n = 6) were perfused serially for 20-minute intervals with control Krebs-Ringer:bicarbonate buffer, t-butyl hydroperoxide (100 μmol/L), low-dose aspirin (5 × 10 −5 mol/L), and low-dose aspirin plus t-butyl hydroperoxide. Maternal and fetal effluent samples were analyzed for lipid Peroxides by hydrogen peroxide equivalents. Results: In study 1, compared with control Krebs-Ringer-bicarbonate perfusion, peroxide perfusion significantly increased, in a dose-response manner, placental lipid peroxide secretion. In study 2, aspirin completely blocked the ability of peroxide to increase the secretion of lipid Peroxides. In both studies placental secretion of lipid Peroxides was significantly greater toward the maternal side of the placenta than toward the fetal side. Conclusions: (1) The human placenta secretes lipid Peroxides primarily into the maternal effluent. (2) Exogenous peroxide stimulates endogenous lipid peroxide production, which is blocked by aspirin, suggesting cyclooxygenase is involved in lipid peroxide production. (3) The placenta could be a source of circulating lipid Peroxides in pregnant women.
Jan H. Näsman - One of the best experts on this subject based on the ideXlab platform.
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Changes in Peroxide Melt-Modified Poly(L-lactide)
Industrial & Engineering Chemistry Research, 1995Co-Authors: Anders Södergård, Maria Niemi, Johan-fredrik Selin, Jan H. NäsmanAbstract:Poly(L-lactide) (PLLA), prepared in a tin octoate-catalyzed reaction, was modified with various types and amounts of Peroxides in the melt during mixing in an extruder or in a kneader. The modified material was analyzed using size exclusion chromatography (SEC), X-ray photoelectron spectroscopy (XPS), a differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA) and by microscopic studies. HydroPeroxides, peroxy acid, peroxy ester, dialkanoyl peroxide, diaroyl peroxide, and dialkyl peroxydicarbonate stabilized the melt during mixing. Nonstabilizing Peroxides were dialkyl and diaralkyl peroxide. The binding energy for the electrons in the Sn 3d level increased for the stabilized PLLA. Thus, the stabilization mechanism was deactivation of the species that catalyzes the reversible esterification reaction. The decomposition temperature of the peroxide-modified polymer increased, and the crystallinity decreased. However, annealing the peroxide-modified poly(L-lactide) resulted in almost the same degree of crystallinity as that of the unmodified polymer. This behavior was due to a slower crystallization rate for the stabilized PLLA
