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1
Ellis, Earl F., Lyn Y. Dodson y Richard J. Police. "Restoration of cerebrovascular responsiveness to hyperventilation by the oxygen radical scavenger n-acetylcysteine following experimental traumatic brain injury". Journal of Neurosurgery 75, n.º 5 (noviembre de 1991): 774–79. http://dx.doi.org/10.3171/jns.1991.75.5.0774.
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✓ Previous experiments have shown that, following experimental fluid-percussion brain injury, cyclo-oxygenase-dependent formation of oxygen radicals prevents arteriolar vasoconstriction in response to hyperventilation. The oxygen radical scavengers superoxide dismutase and catalase restore normal reactivity; however, they are not routinely available for clinical use. The present study tested whether n-acetylcysteine (Mucomyst), an agent currently available for acetaminophen toxicity, could be used as a radical scavenger to restore reactivity after brain injury. N-acetylcysteine (163 mg/kg) was given intraperitoneally prior to or 30 minutes after fluid-percussion brain injury (2.6 atm) in cats, and reactivity to hyperventilation was tested 1 hour after injury. The authors found either that pre- or postinjury administration led to normal reactivity. Additional experiments supported the hypothesis that n-acetylcysteine is an oxygen radical scavenger, since it reduced or prevented the free radical-dependent cerebral arteriolar dilation normally induced by the topical application of arachidonic acid or bradykinin. The mechanism by which n-acetylcysteine is effective in trauma may involve direct scavenging of radicals or stimulation of glutathione peroxidase activity. The results suggest that n-acetylcysteine may be useful for treatment of oxygen free radical-mediated brain injury.
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Kuzuya, Masayuki, Shin-ichi Kondo y Yasushi Sasai. "Addendum - Recent advances in plasma techniques for biomedical and drug engineering". Pure and Applied Chemistry 77, n.º 4 (1 de enero de 2005): 667–82. http://dx.doi.org/10.1351/pac200577040667.
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Plasma-induced surface radicals formed on a variety of organic polymers have been studied by electron spin resonance (ESR), making it possible to provide a sound basis for future experimental design of polymer surface processing (i.e., plasma treatment). On the basis of the findings from such studies on the nature of radical formation and radical reactivity, several novel bioapplications in the field of biomedical and drug engineering have been developed. Applications derived from the nature of plasma-induced surface radical formation include the preparation of a reservoir-type drug delivery system (DDS) of sustained and delayed release, and a floating drug delivery system (FDDS) possessing gastric retention capabilities, the combined findings leading to preparation of a novel “patient-tailored DDS” administered under consideration of the fact that the environment (pH and transit time, etc.) in the gastrointestinal (GI) tract varies with each patient. Applications derived from the reactivity of plasma-induced surface radicals include the preparation of composite powders applicable to a matrix-type DDS by making a mechanical application to the surface radical-containing polymer powders with drug powders, plasma-assisted immobilization of oligo-nucleotides (DNA) onto polymer surfaces applicable to constructing a DNA diagnosis system, and basic study of plasma-assisted preparation of a novel functionalized chemo-embolic agent of non-crosslinked hydrogel, vinyl alcohol-sodium acrylate copolymer (PVA-PAANa).
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Ellis, E. F., S. A. Holt, E. P. Wei y H. A. Kontos. "Kinins induce abnormal vascular reactivity". American Journal of Physiology-Heart and Circulatory Physiology 255, n.º 2 (1 de agosto de 1988): H397—H400. http://dx.doi.org/10.1152/ajpheart.1988.255.2.h397.
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Previous studies have shown that after experimental neural trauma or acute hypertension the brain produces superoxide anion radicals, and brain arterioles display endothelial lesions, dilation, and loss of normal reactivity in response to a decrease in CO2 tension. Because these abnormalities are prevented by pretreatment with free radical scavengers or inhibitors of the cyclooxygenase component of prostaglandin (PG) H synthase, arachidonic acid metabolism by PGH synthase with concomitant formation of tissue injuring oxygen radicals causes the vascular damage. The purpose of the present experiments was to determine whether kinins, which are known to stimulate arachidonate metabolism and to induce cerebral arteriolar dilation via production of superoxide anion, may be involved in initiating the cerebrovascular abnormalities produced by neural trauma in cats. The diameter and reactivity of untreated in vivo pial arterioles on one cerebral cortex was compared with the diameter and reactivity of pial arterioles on the contralateral cortex, which were pretreated topically with a competitive receptor antagonist, which is specific for kinins. Before fluid percussion neural trauma was induced, arterioles on both cerebral hemispheres constricted normally to a decrease in CO2 tension. After injury, the arterioles on the untreated cortex dilated and did not constrict in response to a decrease in arterial CO2 tension, whereas the arterioles pretreated with the kinin antagonist dilated less and displayed normal reactivity to CO2. These experiments demonstrate that a specific kinin receptor stimulates PGH synthase-dependent, free radical-mediated cerebrovascular injury. Given the ubiquitous distribution of the kallikrein-kinin system, we propose that kinins may be an important common mediator of systemic vascular injury and abnormal vascular reactivity.
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Stone, Daniel, Lisa K. Whalley, Trevor Ingham, Peter M. Edwards, Danny R. Cryer, Charlotte A. Brumby, Paul W. Seakins y Dwayne E. Heard. "Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy". Atmospheric Measurement Techniques 9, n.º 7 (7 de julio de 2016): 2827–44. http://dx.doi.org/10.5194/amt-9-2827-2016.
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Abstract. OH reactivity (k′OH) is the total pseudo-first-order loss rate coefficient describing the removal of OH radicals to all sinks in the atmosphere, and is the inverse of the chemical lifetime of OH. Measurements of ambient OH reactivity can be used to discover the extent to which measured OH sinks contribute to the total OH loss rate. Thus, OH reactivity measurements enable determination of the comprehensiveness of measurements used in models to predict air quality and ozone production, and, in conjunction with measurements of OH radical concentrations, to assess our understanding of OH production rates. In this work, we describe the design and characterisation of an instrument to measure OH reactivity using laser flash photolysis coupled to laser-induced fluorescence (LFP-LIF) spectroscopy. The LFP-LIF technique produces OH radicals in isolation, and thus minimises potential interferences in OH reactivity measurements owing to the reaction of HO2 with NO which can occur if HO2 is co-produced with OH in the instrument. Capabilities of the instrument for ambient OH reactivity measurements are illustrated by data collected during field campaigns in London, UK, and York, UK. The instrumental limit of detection for k′OH was determined to be 1.0 s−1 for the campaign in London and 0.4 s−1 for the campaign in York. The precision, determined by laboratory experiment, is typically < 1 s−1 for most ambient measurements of OH reactivity. Total uncertainty in ambient measurements of OH reactivity is ∼ 6 %. We also present the coupling and characterisation of the LFP-LIF instrument to an atmospheric chamber for measurements of OH reactivity during simulated experiments, and provide suggestions for future improvements to OH reactivity LFP-LIF instruments.
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Hens, K., A. Novelli, M. Martinez, J. Auld, R. Axinte, B. Bohn, H. Fischer et al. "Observation and modelling of HO<sub>x</sub> radicals in a boreal forest". Atmospheric Chemistry and Physics 14, n.º 16 (26 de agosto de 2014): 8723–47. http://dx.doi.org/10.5194/acp-14-8723-2014.
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Abstract. Measurements of OH and HO2 radicals were conducted in a pine-dominated forest in southern Finland during the HUMPPA-COPEC-2010 (Hyytiälä United Measurements of Photochemistry and Particles in Air – Comprehensive Organic Precursor Emission and Concentration study) field campaign in summer 2010. Simultaneous side-by-side measurements of hydroxyl radicals were conducted with two instruments using chemical ionization mass spectrometry (CIMS) and laser-induced fluorescence (LIF), indicating small systematic disagreement, OHLIF / OHCIMS = (1.31 ± 0.14). Subsequently, the LIF instrument was moved to the top of a 20 m tower, just above the canopy, to investigate the radical chemistry at the ecosystem–atmosphere interface. Comprehensive measurements including observations of many volatile organic compounds (VOCs) and the total OH reactivity were conducted and analysed using steady-state calculations as well as an observationally constrained box model. Production rates of OH calculated from measured OH precursors are consistent with those derived from the steady-state assumption and measured total OH loss under conditions of moderate OH reactivity. The primary photolytic sources of OH contribute up to one-third to the total OH production. OH recycling, which occurs mainly by HO2 reacting with NO and O3, dominates the total hydroxyl radical production in this boreal forest. Box model simulations agree with measurements for hydroxyl radicals (OHmod. / OHobs. = 1.00 ± 0.16), while HO2 mixing ratios are significantly under-predicted (HO2mod. / HO2obs. = 0.3 ± 0.2), and simulated OH reactivity does not match the observed OH reactivity. The simultaneous under-prediction of HO2 and OH reactivity in periods in which OH concentrations were simulated realistically suggests that the missing OH reactivity is an unaccounted-for source of HO2. Detailed analysis of the HOx production, loss, and recycling pathways suggests that in periods of high total OH reactivity there are additional recycling processes forming OH directly, not via reaction of HO2 with NO or O3, or unaccounted-for primary HOx sources. Under conditions of moderate observed OH reactivity and high actinic flux, an additional RO2 source of approximately 1 × 106 molec cm−3 s−1 would be required to close the radical budget. Nevertheless, a major fraction of the OH recycling occurs via the reaction of HO2 with NO and O3 in this terpene-dominated environment.
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Archer, S. L., D. P. Nelson y E. K. Weir. "Simultaneous measurement of O2 radicals and pulmonary vascular reactivity in rat lung". Journal of Applied Physiology 67, n.º 5 (1 de noviembre de 1989): 1903–11. http://dx.doi.org/10.1152/jappl.1989.67.5.1903.
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The role of endogenous radicals in the regulation of pulmonary vascular tone was evaluated by simultaneous measurement of pulmonary artery pressure and lung radical levels during exposure of isolated rat lungs to varying inspired O2 concentrations (0-95%) and angiotensin II. Lung radical levels, measured “on-line” using luminol and lucigenin-enhanced chemiluminescence, decreased in proportion to the degree of alveolar hypoxia. Radical levels fell during hypoxia before the onset of pulmonary vasoconstriction and promptly returned to basal levels with restoration of normoxic ventilation. Mild alveolar hypoxia (10% O2), which failed to decrease chemiluminescence, did not trigger pulmonary vasoconstriction. Although chemiluminescence tended to decrease more as the hypoxic response strengthened, there was not a simple correlation between the magnitude of the change in chemiluminescence induced by hypoxia and the strength of the hypoxic pressor response. Normoxic chemiluminescence was largely inhibited by superoxide dismutase but not catalase. Superoxide dismutase also increased normoxic pulmonary vascular tone and the strength of the pressor response to hypoxia and angiotensin II. Thus the predominant activated O2 species in the lung, during normoxia, was the superoxide anion or a closely related substance. Alteration of endogenous radical levels can result in changes in vascular tone. It remains uncertain whether the decrease in lung radical production during hypoxia caused pulmonary vasoconstriction or was merely associated with hypoxic ventilation.
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Cort, Aysegul, Tomris Ozben, Anna Sansone, Sebastian Barata-Vallejo, Chryssostomos Chatgilialoglu y Carla Ferreri. "Bleomycin-induced trans lipid formation in cell membranes and in liposome models". Organic & Biomolecular Chemistry 13, n.º 4 (2015): 1100–1105. http://dx.doi.org/10.1039/c4ob01924e.
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Bleomycin–iron complexes cause lipidcis–transisomerisation through thiyl radical formation and reactivity with unsaturated phospholipids, revealing membranes as a relevant and novel site of drug effect.
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Hens, K., A. Novelli, M. Martinez, J. Auld, R. Axinte, B. Bohn, H. Fischer et al. "Observation and modelling of HO<sub>x</sub> radicals in a boreal forest". Atmospheric Chemistry and Physics Discussions 13, n.º 11 (1 de noviembre de 2013): 28561–629. http://dx.doi.org/10.5194/acpd-13-28561-2013.
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Abstract. Measurements of OH and HO2 radicals were conducted in a~pine dominated forest in Southern Finland during the HUMPPA-COPEC-2010 (Hyytiälä United Measurements of Photochemistry and Particles in Air – Comprehensive Organic Precursor Emission and Concentration study) field campaign in summer 2010. Simultaneous side-by-side measurements of hydroxyl radicals were conducted with two instruments using chemical ionization mass spectrometry (CIMS) and laser-induced fluorescence (LIF), indicating good agreement. Subsequently, the LIF instrument was moved to the top of a 20 m tower, just above the canopy, to investigate the radical chemistry at the ecosystem–atmosphere interface. Comprehensive measurements including observations of many VOCs and the total OH reactivity were conducted and analysed using steady-state calculations as well as an observationally constrained box model. Production rates of OH calculated from measured OH precursors are consistent with those derived from the steady state assumption and measured total OH loss under conditions of moderate OH reactivity. The primary photolytic sources of OH contribute up to one third to the total OH production. OH recycling, which occurs mainly by HO2 reacting with NO and O3, dominates the total hydroxyl radical production in this boreal forest. Box model simulations agree with measurements for hydroxyl radicals (OHmod./OHobs. = 1.04 ± 0.16), while HO2 mixing ratios are significantly underpredicted (HO2mod./HO2obs. = 0.3 ± 0.2) and simulated OH reactivity does not match the observed OH reactivity. The simultaneous underprediction of HO2 and OH reactivity in periods in which OH concentrations were simulated well, suggests that the missing OH reactivity is an unaccounted source of HO2. Detailed analysis of the HOx production, loss, and recycling pathways suggests that in periods of high total OH reactivity there are additional recycling processes forming OH directly, not via reaction of HO2 with NO or O3. Nevertheless, a major fraction of the OH recycling occurs via the reaction of HO2 with NO and O3 in this terpene dominated environment.
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Martínez-Alonso, Emma, Alejandro Escobar-Peso, Maria I. Ayuso, Rafael Gonzalo-Gobernado, Mourad Chioua, Juan J. Montoya, Joan Montaner, Israel Fernández, José Marco-Contelles y Alberto Alcázar. "Characterization of a CholesteroNitrone (ISQ-201), a Novel Drug Candidate for the Treatment of Ischemic Stroke". Antioxidants 9, n.º 4 (31 de marzo de 2020): 291. http://dx.doi.org/10.3390/antiox9040291.
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Nitrones have a well-recognized capacity as spin-traps and are considered powerful free radical scavengers, which are two important issues in hypoxia-induced oxidative stress and cell death in brain ischemia. Consequently, nitrones have been proposed as therapeutic agents in acute ischemic stroke (AIS). In this paper, we update the biological and pharmacological characterization of ISQ-201, a previously identified cholesteronitrone hybrid with antioxidant and neuroprotective activity. This study characterizes ISQ-201 as a neuroprotective agent against the hypoxia-induced ischemic injury. Transitory four-vessel occlusion and middle cerebral artery occlusion (tMCAO) were used to induce cerebral ischemia. Functional outcomes were determined using neurofunctional tests. Infarct area, neuronal death, and apoptosis induction were evaluated. In addition, ISQ-201 reactivity towards free radicals was studied in a theoretical model. ISQ-201 significantly decreased the ischemia-induced neuronal death and apoptosis, in a dose-dependent manner, showing its therapeutic effect when administered up until 6 h after post-ischemic reperfusion onset, effects that remained after 3 months from the ischemic episode. Furthermore, ISQ-201 significantly reduced infarct volume, leading to recovery of the motor function in the tMCAO model. Finally, the theoretical study confirmed the reactivity of ISQ-201 towards hydroxyl radicals. The results reported here prompted us to suggest ISQ-201 as a promising candidate for the treatment of AIS.
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Schoerpf, Sebastian, Yohann Catel, Norbert Moszner, Christian Gorsche y Robert Liska. "Enhanced reduction of polymerization-induced shrinkage stress via combination of radical ring opening and addition fragmentation chain transfer". Polymer Chemistry 10, n.º 11 (2019): 1357–66. http://dx.doi.org/10.1039/c8py01540f.
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The combination of vinylcyclopropanes with an ester-activated vinyl sulfonate ester in a light-induced radical polymerization shows high reactivity accompanied by a significant increase in conversion and it leads to an enhanced reduction of polymerization-induced shrinkage stress.
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van Vliet, Kaj M., Nicole S. van Leeuwen, Albert M. Brouwer y Bas de Bruin. "Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid". Beilstein Journal of Organic Chemistry 16 (16 de marzo de 2020): 398–408. http://dx.doi.org/10.3762/bjoc.16.38.
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Where monochloroacetic acid is widely used as a starting material for the synthesis of relevant groups of compounds, many of these synthetic procedures are based on nucleophilic substitution of the carbon chlorine bond. Oxidative or reductive activation of monochloroacetic acid results in radical intermediates, leading to reactivity different from the traditional reactivity of this compound. Here, we investigated the possibility of applying monochloroacetic acid as a substrate for photoredox catalysis with styrene to directly produce γ-phenyl-γ-butyrolactone. Instead of using nucleophilic substitution, we cleaved the carbon chlorine bond by single-electron reduction, creating a radical species. We observed that the reaction works best in nonpolar solvents. The reaction does not go to full conversion, but selectively forms γ-phenyl-γ-butyrolactone and 4-chloro-4-phenylbutanoic acid. Over time the catalyst precipitates from solution (perhaps in a decomposed form in case of fac-[Ir(ppy)3]), which was proven by mass spectrometry and EPR spectroscopy for one of the catalysts (N,N-5,10-di(2-naphthalene)-5,10-dihydrophenazine) used in this work. The generation of HCl resulting from lactone formation could be an additional problem for organometallic photoredox catalysts used in this reaction. In an attempt to trap one of the radical intermediates with TEMPO, we observed a compound indicating the generation of a chloromethyl radical.
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Wang, Wenjie, Jipeng Qi, Jun Zhou, Bin Yuan, Yuwen Peng, Sihang Wang, Suxia Yang, Jonathan Williams, Vinayak Sinha y Min Shao. "The improved comparative reactivity method (ICRM): measurements of OH reactivity under high-NO<sub><i>x</i></sub> conditions in ambient air". Atmospheric Measurement Techniques 14, n.º 3 (24 de marzo de 2021): 2285–98. http://dx.doi.org/10.5194/amt-14-2285-2021.
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Abstract. The comparative reactivity method (CRM) was developed more than a decade to measure OH reactivity (i.e., OH loss frequency) in both laboratory and field studies. However, accurate OH reactivity quantification remains challenging under real ambient conditions, especially for OH reactivity measurements in high-NOx (e.g., > 10 ppbv) environments, as ambient NO enhances the regeneration of OH radicals in the CRM reactor. To solve this problem, we design a new and improved CRM reactor (ICRM) and add NO into the system continuously so that the HO2 radical concentration is suppressed. We confirmed the appropriate level of NO by determining the maximum decrease in the pyrrole level caused by regenerated OH radicals from NO + HO2. RO2 radicals induced by volatile organic compounds (VOCs) in the ICRM reactor were also found to react with NO, which led to the regeneration of OH radicals and thus the underestimation of OH reactivity. This effect was quantified by the calibration of representative VOC species at different NO levels, and the correction coefficients obtained were used to correct the measured OH reactivity. All these efforts resulted in reducing the uncertainty of the NO-artifact correction by at least an order of magnitude compared to the original CRM system. Additionally, these technological improvements also considerably reduced the systematic errors from pyrrole photolysis in the original system. A new operation mode was proposed for the ICRM, which is able to avoid the interference resulting from OH radicals produced by photolysis of residual humidity and save time for ambient measurement. The ICRM system was employed in a field campaign to measure OH reactivity and performed well with ambient NO levels ranging from 0 to 50 ppbv, which are typically observed in the urban and suburban atmosphere.
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Schoonderwoerd, Simon A., Gerard M. J. Beijersbergen van Henegouwen y Ivan R. Panday. "UVA-Induced Genetic Effects of Thioridazine, Mesoridazine and Sulforidazine: an in vitro Study". Zeitschrift für Naturforschung C 45, n.º 6 (1 de junio de 1990): 638–44. http://dx.doi.org/10.1515/znc-1990-0613.
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Abstract This in vitro study focuses on the UVA-induced reactions with DNA of thioridazine (TRZ), and two of its major metabolites (TRZ-2-sulfoxide or mesoridazine, MRZ ; and TRZ- 2-sulfone or sulforidazine, SRZ). TRZ binds covalently to DNA upon UVA-irradiation. Under comparable irradiation conditions, MRZ binds to a lesser extent and almost no binding was observed with SRZ. Besides, photo-induced genetic effects were investigated by means of a differential DNA repair test in E. coli. The photo-induced genetic effects in E. coli decreased from TRZ, MRZ to SRZ, which corresponds with their capacity for UVA-induced binding to DNA. TRZ, MRZ and SRZ differed in their rate of photodecomposition rather than in the intrinsic reactivity towards DNA of the instable intermediates formed. Irreversible binding to DNA was also observed upon treatment with peroxidase, which is known to oxidize phenothiazines via the formation of reactive radical cation species. As both the colour of the intermediate and its reactivity towards DNA were comparable for peroxidase treatment and exposure to UVA, we assume that the radical cation is the reactive species in the latter case as well.
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Glatthar, Ralf, Martin Spichty, Andreas Gugger, Rohit Batra, Wolfgang Damm, Matthias Mohr, Hendrik Zipse y Bernd Giese. "Mechanistic Studies in the Radical Induced DNA Strand Cleavage—Formation and Reactivity of the Radical Cation Intermediate". Tetrahedron 56, n.º 25 (junio de 2000): 4117–28. http://dx.doi.org/10.1016/s0040-4020(00)00335-5.
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Torreggiani, Tinti, Jurasekova, Capdevila, Saracino y Foggia. "Structural Lesions of Proteins Connected to Lipid Membrane Damages Caused by Radical Stress: Assessment by Biomimetic Systems and Raman Spectroscopy". Biomolecules 9, n.º 12 (27 de noviembre de 2019): 794. http://dx.doi.org/10.3390/biom9120794.
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Model systems constituted by proteins and unsaturated lipid vesicles were used to gain more insight into the effects of the propagation of an initial radical damage on protein to the lipid compartment. The latter is based on liposome technology and allows measuring the trans unsaturated fatty acid content as a result of free radical stress on proteins. Two kinds of sulfur-containing proteins were chosen to connect their chemical reactivity with membrane lipid transformation, serum albumins and metallothioneins. Biomimetic systems based on radiation chemistry were used to mimic the protein exposure to different kinds of free radical stress and Raman spectroscopy to shed light on protein structural changes caused by the free radical attack. Among the amino acid residues, Cys is one of the most sensitive residues towards the attack of free radicals, thus suggesting that metal-Cys clusters are good interceptors of reactive species in metallothioneins, together with disulfides moieties in serum albumins. Met is another important site of the attack, in particular under reductive conditions. Tyr and Phe are sensitive to radical stress too, leading to electron transfer reactions or radical-induced modifications of their structures. Finally, modifications in protein folding take place depending on reactive species attacking the protein.
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Lew, Michelle M., Pamela S. Rickly, Brandon P. Bottorff, Emily Reidy, Sofia Sklaveniti, Thierry Léonardis, Nadine Locoge et al. "OH and HO<sub>2</sub> radical chemistry in a midlatitude forest: measurements and model comparisons". Atmospheric Chemistry and Physics 20, n.º 15 (5 de agosto de 2020): 9209–30. http://dx.doi.org/10.5194/acp-20-9209-2020.
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Abstract. Reactions of the hydroxyl (OH) and peroxy (HO2 and RO2) radicals play a central role in the chemistry of the atmosphere. In addition to controlling the lifetimes of many trace gases important to issues of global climate change, OH radical reactions initiate the oxidation of volatile organic compounds (VOCs) which can lead to the production of ozone and secondary organic aerosols in the atmosphere. Previous measurements of these radicals in forest environments characterized by high mixing ratios of isoprene and low mixing ratios of nitrogen oxides (NOx) (typically less than 1–2 ppb) have shown serious discrepancies with modeled concentrations. These results bring into question our understanding of the atmospheric chemistry of isoprene and other biogenic VOCs under low NOx conditions. During the summer of 2015, OH and HO2 radical concentrations, as well as total OH reactivity, were measured using laser-induced fluorescence–fluorescence assay by gas expansion (LIF-FAGE) techniques as part of the Indiana Radical Reactivity and Ozone productioN InterComparison (IRRONIC). This campaign took place in a forested area near Indiana University's Bloomington campus which is characterized by high mixing ratios of isoprene (average daily maximum of approximately 4 ppb at 28 ∘C) and low mixing ratios of NO (diurnal average of approximately 170 ppt). Supporting measurements of photolysis rates, VOCs, NOx, and other species were used to constrain a zero-dimensional box model based on the Regional Atmospheric Chemistry Mechanism (RACM2) and the Master Chemical Mechanism (MCM 3.2), including versions of the Leuven isoprene mechanism (LIM1) for HOx regeneration (RACM2-LIM1 and MCM 3.3.1). Using an OH chemical scavenger technique, the study revealed the presence of an interference with the LIF-FAGE measurements of OH that increased with both ambient concentrations of ozone and temperature with an average daytime maximum equivalent OH concentration of approximately 5×106 cm−3. Subtraction of the interference resulted in measured OH concentrations of approximately 4×106 cm−3 (average daytime maximum) that were in better agreement with model predictions although the models underestimated the measurements in the evening. The addition of versions of the LIM1 mechanism increased the base RACM2 and MCM 3.2 modeled OH concentrations by approximately 20 % and 13 %, respectively, with the RACM2-LIM1 mechanism providing the best agreement with the measured concentrations, predicting maximum daily OH concentrations to within 30 % of the measured concentrations. Measurements of HO2 concentrations during the campaign (approximately a 1×109 cm−3 average daytime maximum) included a fraction of isoprene-based peroxy radicals (HO2*=HO2+αRO2) and were found to agree with model predictions to within 10 %–30 %. On average, the measured reactivity was consistent with that calculated from measured OH sinks to within 20 %, with modeled oxidation products accounting for the missing reactivity, however significant missing reactivity (approximately 40 % of the total measured reactivity) was observed on some days.
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Ratushnyy, Maxim, Monika Kamenova y Vladimir Gevorgyan. "A mild light-induced cleavage of the S–O bond of aryl sulfonate esters enables efficient sulfonylation of vinylarenes". Chemical Science 9, n.º 36 (2018): 7193–97. http://dx.doi.org/10.1039/c8sc02769b.
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A new mode of S–O bond activation has been discovered, which constitutes novel reactivity of easily available and bench-stable arylsulfonate phenol esters. This protocol enables access to putative sulfonyl radical intermediates, which enable straightforward access to valuable vinyl sulfones.
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Fuchs, H., B. Bohn, A. Hofzumahaus, F. Holland, K. D. Lu, S. Nehr, F. Rohrer y A. Wahner. "Detection of HO<sub>2</sub> by laser-induced fluorescence: calibration and interferences from RO<sub>2</sub> radicals". Atmospheric Measurement Techniques Discussions 4, n.º 1 (25 de febrero de 2011): 1255–302. http://dx.doi.org/10.5194/amtd-4-1255-2011.
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Abstract. HO2 concentration measurements are widely accomplished by chemical conversion of HO2 to OH including reaction with NO and subsequent detection of OH by laser-induced fluorescence. RO2 radicals can be converted to OH via a similar radical reaction sequence including reaction with NO, so that they are potential interferences for HO2 measurements. Here, the conversion efficiency of various RO2 species to HO2 is investigated. Experiments were conducted with a radical source that produces OH and HO2 by water photolysis at 185 nm, which is frequently used for calibration of LIF instruments. The ratio of HO2 and the sum of OH and HO2 concentrations provided by the radical source was investigated and was found to be 0.50 ± 0.02. RO2 radicals are produced by the reaction of various organic compounds with OH in the radical source. Interferences via chemical conversion from RO2 radicals produced by the reaction of OH with alkanes (H-atom abstraction) are negligible consistent with measurements in the past. However, RO2 radicals from OH plus alkene- and aromatic-precursors including isoprene (mainly OH-addition) are detected with a relative sensitivity larger than 80% with respect to that for HO2 for the configuration of the instrument with which it was operated during field campaigns. Also RO2 from OH plus methyl vinyl ketone and methacrolein exhibit a relative detection sensitivity of 60%. Thus, previous measurements of HO2 radical concentrations with this instrument were biased in the presence of high RO2 radical concentrations from isoprene, alkenes or aromatics, but were not affected by interferences in clean air, when the OH reactivity was dominated by small alkanes. By reducing the NO concentration and/or the transport time between NO addition and OH detection, interference from these RO2 species are suppressed to values below 20% relative to the HO2 detection sensitivity. The HO2 conversion efficiency is also smaller by a factor of four, but this is still sufficient for atmospheric HO2 concentration measurements for a wide range of conditions.
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Fuchs, H., B. Bohn, A. Hofzumahaus, F. Holland, K. D. Lu, S. Nehr, F. Rohrer y A. Wahner. "Detection of HO<sub>2</sub> by laser-induced fluorescence: calibration and interferences from RO<sub>2</sub> radicals". Atmospheric Measurement Techniques 4, n.º 6 (28 de junio de 2011): 1209–25. http://dx.doi.org/10.5194/amt-4-1209-2011.
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Abstract. HO2 concentration measurements are widely accomplished by chemical conversion of HO2 to OH including reaction with NO and subsequent detection of OH by laser-induced fluorescence. RO2 radicals can be converted to OH via a similar radical reaction sequence including reaction with NO, so that they are potential interferences for HO2 measurements. Here, the conversion efficiency of various RO2 species to HO2 is investigated. Experiments were conducted with a radical source that produces OH and HO2 by water photolysis at 185 nm, which is frequently used for calibration of LIF instruments. The ratio of HO2 and the sum of OH and HO2 concentrations provided by the radical source was investigated and was found to be 0.50 ± 0.02. RO2 radicals are produced by the reaction of various organic compounds with OH in the radical source. Interferences via chemical conversion from RO2 radicals produced by the reaction of OH with methane and ethane (H-atom abstraction) are negligible consistent with measurements in the past. However, RO2 radicals from OH plus alkene- and aromatic-precursors including isoprene (mainly OH-addition) are detected with a relative sensitivity larger than 80 % with respect to that for HO2 for the configuration of the instrument with which it was operated during field campaigns. Also RO2 from OH plus methyl vinyl ketone and methacrolein exhibit a relative detection sensitivity of 60 %. Thus, previous measurements of HO2 radical concentrations with this instrument were biased in the presence of high RO2 radical concentrations from isoprene, alkenes or aromatics, but were not affected by interferences in remote clean environment with no significant emissions of biogenic VOCs, when the OH reactivity was dominated by small alkanes. By reducing the NO concentration and/or the transport time between NO addition and OH detection, interference from these RO2 species are suppressed to values below 20 % relative to the HO2 detection sensitivity. The HO2 conversion efficiency is also smaller by a factor of four, but this is still sufficient for atmospheric HO2 concentration measurements for a wide range of conditions.
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Rhodes, Christopher J. "Reactive Radicals on Reactive Surfaces: Heterogeneous Processes in Catalysis and Environmental Pollution Control". Progress in Reaction Kinetics and Mechanism 30, n.º 3 (septiembre de 2005): 145–213. http://dx.doi.org/10.3184/007967405779134038.
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Many reactions that occur on solid surfaces are mediated by free radicals. A review is presented of both mechanistic and practical investigations in relation to catalysis and environmental applications. The review begins with actual imaging of surface adsorbed reactive radicals using scanning tunnelling microscopy (STM), and then discusses a range of examples, mainly as underpinned by electron spin resonance (ESR) measurements. Included are surface defects and their reactions, studies of the redox behaviour of zeolites, and the use of radicals adsorbed in zeolites as molecular surface probes of diffusion and reactivity within these important materials. Photocatalysis, mainly using TiO2-based materials, is reviewed both from the fundamental perspective and in terms of some practical examples relating to pollution control. Other reactive oxide surfaces are considered, including silica, and the nature of paramagnetic centres that may be induced thereon by a variety of activation procedures. Evidence is presented for the formation of radical species during heterogeneous reactions on metal surfaces. Finally, the role of free radical generation in creating and modifying polymer and nanomolecular systems is discussed, and the health implications of the ability of some solids such as quartz to generate reactive oxygen radicals in contact with biological media.
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MEDINA, PASCUAL, PASCUAL CHUAN, ROSA NOGUERA, JOSé M. VILA, MARTíN ALDASORO y SALVADOR LLUCH. "Reactivity of Human Deferential Artery to Constrictor and Dilator Substances". Journal of Andrology 17, n.º 6 (12 de noviembre de 1996): 733–39. http://dx.doi.org/10.1002/j.1939-4640.1996.tb01859.x.
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ABSTRACT: The present study was designed to investigate general morphology and the response of human deferential artery to constrictor and dilator substances with special emphasis on endothelium‐dependent responses. Human deferential artery segments were obtained from patients undergoing radical cystectomy (n = 7), suprapubic prostatectomy (n = 6), or radical prostatectomy (n = 6). Light microscopy revealed that human deferential artery is of muscular type, and fluorescence microscopy showed a dense adrenergic innervation. Paired rings, one normal and the other de‐endothelialized by gentle rubbing, were mounted for isometric recording of tension in organ baths. Vasopressin, endothelin, serotonin, and potassium chloride induced endothelium‐independent contractions, whereas norepinephrine and electrical field stimulation caused frequency‐dependent contractions that were of greater magnitude in arteries denuded of endothelium. In precontracted arterial rings, acetylcholine and substance P induced endothelium‐dependent relaxations. In contrast, papaverine and sodium nitroprusside caused concentration‐dependent relaxations that were similar in the presence and in the absence of endothelium. NG‐nitro‐L‐arginine methyl ester(10−4 M), an inhibitor of nitric oxide synthase, potentiated the responses to norepinephrine in artery rings with endothelium, nearly abolished the acetylcholine‐induced relaxation, and attenuated the relaxation induced by substance P. Incubation with methylene blue (10‐5 M), an inhibitor of guanylate cyclase, completely prevented the relaxation induced by acetylcholine in arteries with endothelium. The results of this study indicate that the human deferential artery has a dense adrenergic innervation and marked ability to contract or relax in response to different agonists. Some of these responses are in part endothelium dependent and mediated through release of nitric oxide. These morphological and pharmacological observations could play an important role in regulating flow or pressure of blood that arrives to the vas deferens.
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Abe, Yasuyuki, Tsuyoshi Sawada, Makoto Takafuji, Tsutomu Mashimo, Masao Ono y Hirotaka Ihara. "Ultrastrong Gravity-induced Unusual Reactivity in Radical Addition of Bromotrichloromethane to Ethyl Cinnamate". Chemistry Letters 39, n.º 3 (5 de marzo de 2010): 174–75. http://dx.doi.org/10.1246/cl.2010.174.
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Kuzuya, Masayuki, Shin-ichi Kondo, Hideki Ito y Akihiro Noguchi. "ESR study on the nature of oxygen plasma-induced surface radicals of Teflon and corresponding peroxy radical reactivity". Applied Surface Science 60-61 (enero de 1992): 416–20. http://dx.doi.org/10.1016/0169-4332(92)90453-5.
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Bsaibes, Sandy, Mohamad Al Ajami, Kenneth Mermet, François Truong, Sébastien Batut, Christophe Hecquet, Sébastien Dusanter et al. "Variability of hydroxyl radical (OH) reactivity in the Landes maritime pine forest: results from the LANDEX campaign 2017". Atmospheric Chemistry and Physics 20, n.º 3 (4 de febrero de 2020): 1277–300. http://dx.doi.org/10.5194/acp-20-1277-2020.
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Abstract. Total hydroxyl radical (OH) reactivity measurements were conducted during the LANDEX intensive field campaign in a coniferous temperate forest located in the Landes area, southwestern France, during July 2017. In order to investigate inter-canopy and intra-canopy variability, measurements were performed inside (6 m) and above the canopy level (12 m), as well as at two different locations within the canopy, using a comparative reactivity method (CRM) and a laser photolysis–laser-induced fluorescence (LP-LIF) instrument. The two techniques were intercompared at the end of the campaign by performing measurements at the same location. Volatile organic compounds were also monitored at both levels with a proton transfer time-of-flight mass spectrometer and online gas chromatography instruments to evaluate their contribution to total OH reactivity, with monoterpenes being the main reactive species emitted in this forest dominated by Pinus pinaster Aiton. Total OH reactivity varied diurnally, following the trend of biogenic volatile organic compounds (BVOCs), the emissions and concentrations of which were dependent on meteorological parameters. Average OH reactivity was around 19.2 and 16.5 s−1 inside and above the canopy, respectively. The highest levels of total OH reactivity were observed during nights with a low turbulence (u*≤0.2 m s−1), leading to lower mixing of emitted species within the canopy and thus an important vertical stratification characterized by a strong concentration gradient. Comparing the measured and the calculated OH reactivity highlighted an average missing OH reactivity of 22 % and 33 % inside and above the canopy, respectively. A day–night variability was observed on missing OH reactivity at both heights. Investigations showed that during daytime, missing OH sinks could be due to primary emissions and secondary products linked to a temperature-enhanced photochemistry. Regarding nighttime missing OH reactivity, higher levels were seen for the stable and warm night of 4–5 July, showing that these conditions could have been favorable for the accumulation of long-lived species (primary and secondary species) during the transport of the air mass from nearby forests.
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Glatthar, Ralf, Martin Spichty, Andreas Gugger, Rohit Batra, Wolfgang Damm, Matthias Mohr, Hendrik Zipse y Bernd Giese. "ChemInform Abstract: Mechanistic Studies in the Radical Induced DNA Strand Cleavage - Formation and Reactivity of the Radical Cation Intermediate." ChemInform 31, n.º 39 (26 de septiembre de 2000): no. http://dx.doi.org/10.1002/chin.200039197.
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Cho, Changmin, Hendrik Fuchs, Andreas Hofzumahaus, Frank Holland, William J. Bloss, Birger Bohn, Hans-Peter Dorn et al. "Experimental chemical budgets of OH, HO2, and RO2 radicals in rural air in western Germany during the JULIAC campaign 2019". Atmospheric Chemistry and Physics 23, n.º 3 (8 de febrero de 2023): 2003–33. http://dx.doi.org/10.5194/acp-23-2003-2023.
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Abstract. Photochemical processes in ambient air were studied using the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich, Germany. Ambient air was continuously drawn into the chamber through a 50 m high inlet line and passed through the chamber for 1 month in each season throughout 2019. The residence time of the air inside the chamber was about 1 h. As the research center is surrounded by a mixed deciduous forest and is located close to the city Jülich, the sampled air was influenced by both anthropogenic and biogenic emissions. Measurements of hydroxyl (OH), hydroperoxyl (HO2), and organic peroxy (RO2) radicals were achieved by a laser-induced fluorescence instrument. The radical measurements together with measurements of OH reactivity (kOH, the inverse of the OH lifetime) and a comprehensive set of trace gas concentrations and aerosol properties allowed for the investigation of the seasonal and diurnal variation of radical production and destruction pathways. In spring and summer periods, median OH concentrations reached 6 × 106 cm−3 at noon, and median concentrations of both HO2 and RO2 radicals were 3 × 108 cm−3. The measured OH reactivity was between 4 and 18 s−1 in both seasons. The total reaction rate of peroxy radicals with NO was found to be consistent with production rates of odd oxygen (Ox= NO2 + O3) determined from NO2 and O3 concentration measurements. The chemical budgets of radicals were analyzed for the spring and summer seasons, when peroxy radical concentrations were above the detection limit. For most conditions, the concentrations of radicals were mainly sustained by the regeneration of OH via reactions of HO2 and RO2 radicals with nitric oxide (NO). The median diurnal profiles of the total radical production and destruction rates showed maxima between 3 and 6 ppbv h−1 for OH, HO2, and RO2. Total ROX (OH, HO2, and RO2) initiation and termination rates were below 3 ppbv h−1. The highest OH radical turnover rate of 13 ppbv h−1 was observed during a high-temperature (max. 40 ∘C) period in August. In this period, the highest HO2, RO2, and ROX turnover rates were around 11, 10, and 4 ppbv h−1, respectively. When NO mixing ratios were between 1 and 3 ppbv, OH and HO2 production and destruction rates were balanced, but unexplained RO2 and ROX production reactions with median rates of 2 and 0.4 ppbv h−1, respectively, were required to balance their destruction. For NO mixing ratios above 3 ppbv, the peroxy radical reaction rates with NO were highly uncertain due to the low peroxy radical concentrations close to the limit of NO interferences in the HO2 and RO2 measurements. For NO mixing ratios below 1 ppbv, a missing source for OH and a missing sink for HO2 were found with maximum rates of 3.0 and 2.0 ppbv h−1, respectively. The missing OH source likely consisted of a combination of a missing inter-radical HO2 to OH conversion reaction (up to 2 ppbv h−1) and a missing primary radical source (0.5–1.4 ppbv h−1). The dataset collected in this campaign allowed analyzing the potential impact of OH regeneration from RO2 isomerization reactions from isoprene, HO2 uptake on aerosol, and RO2 production from chlorine chemistry on radical production and destruction rates. These processes were negligible for the chemical conditions encountered in this study.
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Nölscher, A. C., E. Bourtsoukidis, B. Bonn, J. Kesselmeier, J. Lelieveld y J. Williams. "Seasonal measurements of total OH reactivity emission rates from Norway spruce in 2011". Biogeosciences 10, n.º 6 (26 de junio de 2013): 4241–57. http://dx.doi.org/10.5194/bg-10-4241-2013.
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Abstract. Numerous reactive volatile organic compounds (VOCs) are emitted into the atmosphere by vegetation. Most biogenic VOCs are highly reactive towards the atmosphere's most important oxidant, the hydroxyl (OH) radical. One way to investigate the chemical interplay between biosphere and atmosphere is through the measurement of total OH reactivity, the total loss rate of OH radicals. This study presents the first determination of total OH reactivity emission rates (measurements via the comparative reactivity method) based on a branch cuvette enclosure system mounted on a Norway spruce (Picea abies) throughout spring, summer and autumn 2011. In parallel VOC emission rates were monitored by a second proton-transfer-reaction mass spectrometer (PTR-MS), and total ozone (O3) loss rates were obtained inside the cuvette. Total OH reactivity emission rates were in general temperature and light dependent, showing strong diel cycles with highest values during daytime. Monoterpene emissions contributed most, accounting for 56–69% of the measured total OH reactivity flux in spring and early summer. However, during late summer and autumn the monoterpene contribution decreased to 11–16%. At this time, a large missing fraction of the total OH reactivity emission rate (70–84%) was found when compared to the VOC budget measured by PTR-MS. Total OH reactivity and missing total OH reactivity emission rates reached maximum values in late summer corresponding to the period of highest temperature. Total O3 loss rates within the closed cuvette showed similar diel profiles and comparable seasonality to the total OH reactivity fluxes. Total OH reactivity fluxes were also compared to emissions from needle storage pools predicted by a temperature-only-dependent algorithm. Deviations of total OH reactivity fluxes from the temperature-only-dependent emission algorithm were observed for occasions of mechanical and heat stress. While for mechanical stress, induced by strong wind, measured VOCs could explain total OH reactivity emissions, during heat stress they could not. The temperature-driven algorithm matched the diel variation of total OH reactivity emission rates much better in spring than in summer, indicating a different production and emission scheme for summer and early autumn. During these times, unmeasured and possibly unknown primary biogenic emissions contributed significantly to the observed total OH reactivity flux.
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Feketeová, Linda, Bun Chan, George N. Khairallah, Vincent Steinmetz, Philippe Maître, Leo Radom y Richard A. J. O'Hair. "Gas-phase structure and reactivity of the keto tautomer of the deoxyguanosine radical cation". Physical Chemistry Chemical Physics 17, n.º 39 (2015): 25837–44. http://dx.doi.org/10.1039/c5cp01573a.
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Gas-phase IR spectroscopy, ion–molecule reactions, collision-induced dissociation and computational chemistry in combination form a powerful tool to gain insights into the structure of one-electron oxidised guanine in DNA and its resultant chemistry.
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Cao, Heng, Sheng-Feng Xiong, Li-Long Dong y Zhou-Tong Dai. "Study on the Mechanism of Lipid Peroxidation Induced by Carbonate Radicals". Molecules 29, n.º 5 (2 de marzo de 2024): 1125. http://dx.doi.org/10.3390/molecules29051125.
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Based on the reported research, hydroxyl radicals can be rapidly transformed into carbonate radicals in the carbonate–bicarbonate buffering system in vivo. Many of the processes considered to be initiated by hydroxyl radicals may be caused by carbonate radicals, which indicates that lipid peroxidation initiated by hydroxyl radicals can also be caused by carbonate radicals. To date, theoretical research on reactions of hydrogen abstraction from and radical addition to polyunsaturated fatty acids (PUFAs) of carbonate radicals has not been carried out systematically. This paper employs (3Z,6Z)-nona-3,6-diene (NDE) as a model for polyunsaturated fatty acids (PUFAs). Density functional theory (DFT) with the CAM-B3LYP method at the 6-311+g(d,p) level was used to calculate the differences in reactivity of carbonate radicals abstracting hydrogen from different positions of NDE and their addition to the double bonds of NDE under lipid solvent conditions with a dielectric constant of 4.0 (CPCM model). Grimme’s empirical dispersion correction was taken into account through the D3 scheme. The energy barrier, reaction rate constants, internal energy, enthalpy and Gibbs free energy changes in these reactions were calculated With zero-point vibrational energy (ZPVE) corrections. The results indicated that carbonate radicals initiate lipid peroxidation primarily through hydrogen abstraction from diallyl carbon atoms. The reaction of hydrogen abstraction from diallyl carbon atoms exhibits the highest reaction rate, with a reaction rate constant approximately 43-fold greater than the second-ranked hydrogen abstraction from allyl carbon atoms. This process has the lowest energy barrier, internal energy, enthalpy, and Gibbs free energy changes, indicating that it is also the most spontaneous process.
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Nölscher, A. C., E. Bourtsoukidis, B. Bonn, J. Kesselmeier, J. Lelieveld y J. Williams. "Seasonal measurements of total OH reactivity fluxes, total ozone loss rates and missing emissions from Norway spruce in 2011". Biogeosciences Discussions 9, n.º 10 (5 de octubre de 2012): 13497–536. http://dx.doi.org/10.5194/bgd-9-13497-2012.
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Abstract. Numerous reactive volatile organic compounds (VOCs) are emitted into the atmosphere by vegetation. Most biogenic VOCs are highly reactive towards the atmosphere's most important oxidant, the hydroxyl (OH) radical. One way to investigate the chemical interplay between biosphere and atmosphere is through the measurement of total OH reactivity, the total loss rate of OH radicals. This study presents the first determination of total OH reactivity emission rates (measurements via the Comparative Reactivity Method) based on a branch cuvette enclosure system mounted on a Norway spruce (Picea abies) throughout spring, summer and autumn 2011. In parallel separate VOC emission rates were monitored by a Proton Transfer Reaction-Mass Spectrometer (PTR-MS), and total ozone (O3) loss rates were obtained inside the cuvette. Total OH reactivity emission rates were in general temperature and light dependent, showing strong diel cycles with highest values during daytime. Monoterpene emissions contributed most, accounting for 56–69% of the measured total OH reactivity flux in spring and early summer. However, during late summer and autumn the monoterpene contribution decreased to 11–16%. At this time, a large missing fraction of the total OH reactivity emission rate (70–84%) was found when compared to the VOC budget measured by PTR-MS. Total OH reactivity and missing total OH reactivity emission rates reached maximum values in late summer corresponding to the period of highest temperature. Total O3 loss rates within the closed cuvette showed similar diel profiles and comparable seasonality to the total OH reactivity fluxes. Total OH reactivity fluxes were also compared to emissions from needle storage pools predicted by a temperature-only dependent algorithm. Deviations of total OH reactivity fluxes from the temperature-only dependent emission algorithm were observed for occasions of mechanical and heat stress. While for mechanical stress, induced by strong wind, measured VOCs could explain total OH reactivity emissions, during heat stress they could not. The temperature driven algorithm matched the diel course much better in spring than in summer, indicating a different production and emission scheme for summer and early autumn. During these times, unmeasured and possibly unknown primary biogenic emissions contributed significantly to the observed total OH reactivity flux.
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Bottorff, Brandon, Michelle M. Lew, Youngjun Woo, Pamela Rickly, Matthew D. Rollings, Benjamin Deming, Daniel C. Anderson et al. "OH, HO2, and RO2 radical chemistry in a rural forest environment: measurements, model comparisons, and evidence of a missing radical sink". Atmospheric Chemistry and Physics 23, n.º 18 (15 de septiembre de 2023): 10287–311. http://dx.doi.org/10.5194/acp-23-10287-2023.
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Abstract. The hydroxyl (OH), hydroperoxy (HO2), and organic peroxy (RO2) radicals play important roles in atmospheric chemistry. In the presence of nitrogen oxides (NOx), reactions between OH and volatile organic compounds (VOCs) can initiate a radical propagation cycle that leads to the production of ozone and secondary organic aerosols. Previous measurements of these radicals under low-NOx conditions in forested environments characterized by emissions of biogenic VOCs, including isoprene and monoterpenes, have shown discrepancies with modeled concentrations. During the summer of 2016, OH, HO2, and RO2 radical concentrations were measured as part of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport – Atmospheric Measurements of Oxidants in Summer (PROPHET-AMOS) campaign in a midlatitude deciduous broadleaf forest. Measurements of OH and HO2 were made by laser-induced fluorescence–fluorescence assay by gas expansion (LIF-FAGE) techniques, and total peroxy radical (XO2) mixing ratios were measured by the Ethane CHemical AMPlifier (ECHAMP) instrument. Supporting measurements of photolysis frequencies, VOCs, NOx, O3, and meteorological data were used to constrain a zero-dimensional box model utilizing either the Regional Atmospheric Chemical Mechanism (RACM2) or the Master Chemical Mechanism (MCM). Model simulations tested the influence of HOx regeneration reactions within the isoprene oxidation scheme from the Leuven Isoprene Mechanism (LIM1). On average, the LIM1 models overestimated daytime maximum measurements by approximately 40 % for OH, 65 % for HO2, and more than a factor of 2 for XO2. Modeled XO2 mixing ratios were also significantly higher than measured at night. Addition of RO2 + RO2 accretion reactions for terpene-derived RO2 radicals to the model can partially explain the discrepancy between measurements and modeled peroxy radical concentrations at night but cannot explain the daytime discrepancies when OH reactivity is dominated by isoprene. The models also overestimated measured concentrations of isoprene-derived hydroxyhydroperoxides (ISOPOOH) by a factor of 10 during the daytime, consistent with the model overestimation of peroxy radical concentrations. Constraining the model to the measured concentration of peroxy radicals improves the agreement with the measured ISOPOOH concentrations, suggesting that the measured radical concentrations are more consistent with the measured ISOPOOH concentrations. These results suggest that the models may be missing an important daytime radical sink and could be overestimating the rate of ozone and secondary product formation in this forest.
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Ito, Takeo, Susumu Kuno, Tsukasa Uchida, Shin-ichi Fujita y Sei-ichi Nishimoto. "Properties and Reactivity of the Adenosine Radical Generated by Radiation-Induced Oxidation in Aqueous Solution". Journal of Physical Chemistry B 113, n.º 1 (8 de enero de 2009): 389–94. http://dx.doi.org/10.1021/jp801976t.
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Jiang, Yihuang, Zaifa Shi, Qingjie Zeng, Jiangle Zhang, Zefeng Deng, Qiaolin Wang, Jing Yang, Jingxiong Yu, Zhengbo Qin y Zichao Tang. "Investigation on the Edge Doping Process of Nitrogen-Doped Carbon Materials by In Situ Pyrolysis Mass Spectrometry and Laser-Induced Acoustic Desorption Mass Spectrometry". Catalysts 13, n.º 5 (30 de abril de 2023): 830. http://dx.doi.org/10.3390/catal13050830.
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Nitrogen-doped carbon materials demonstrate high performance as electrodes in fuel cells and higher oxygen reduction reactivity than traditional Pt-based electrodes. However, the formation process of nitrogen-doped carbon materials has long been a mystery. In this study, the formation mechanism of nitrogen-doped carbon materials from polyaniline (PANI) pyrolysis was studied by the combination of in situ pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry (Py-VUVPI-TOF MS) and substrate-enhanced, laser-induced acoustic desorption source time-of-flight mass spectrometry (SE-LIAD-TOF MS). The initial pyrolysis species, including free radicals and intermediates, were investigated via in situ Py-VUVPI-TOF MS during the temperature-programmed desorption process (within tens of microseconds). The pyrolysis residues were collected and further investigated via SE-LIAD-TOF MS, revealing the product information of the initial pyrolysis products. The results show that the edge doping of carbon materials depends on free radical reactions rather than the direct substitution of carbon atoms by nitrogen atoms. Meanwhile, pyrrole nitrogen and pyridine nitrogen are formed by the free radical cyclization reaction and the amino aromatization reaction at the initial stage of pyrolysis, while the formation of graphitic nitrogen depends on the further polymerization reaction of pyrrole nitrogen and pyridine nitrogen.
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Gildikov, Dmitriy. "Hepatoprotective and antioxidant effects of Mexidol-Vet® in an experiment on rats". Russian veterinary journal 2020, n.º 5 (25 de noviembre de 2020): 38–42. http://dx.doi.org/10.32416/2500-4379-2020-5-38-42.
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The aim of the work was to establish the hepatoprotective and antioxidant effect of Mexidol-Vet® in rats with toxic hepatitis. We have reproduced the toxic hepatitis in sexually mature male rats (n = 90) by a single intragastric injection of carbon tetrachloride. For 30 days, we studied reactivity, variations in blood biochemical parameters, the intensity of iron-induced chemiluminescence of homogenates and histological changes in the liver. The experiment confirmed the antioxidant effect and for the first time established the hepatoprotective effect of Mexidol-Vet®. The use of Mexidol-Vet® in rats with tetrachloromethane hepatitis increases reactivity and adaptive capabilities, correction of carbohydrate (lactate dehydrogenase) and protein metabolism (total protein, aspartate aminotransferase and alanine aminotransferase), inhibition of free radical oxidation and the development of oxidative stress.
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Romero, Ana I., Fredrik B. Thorén, Mats Brune y Kristoffer Hellstrand. "Histamine Dihydrochloride Maintains Cytotoxic Effector T Lymphocyte Function and Viability under Conditions of Oxidative Stress." Blood 110, n.º 11 (16 de noviembre de 2007): 2309. http://dx.doi.org/10.1182/blood.v110.11.2309.2309.
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Abstract BACKGROUND: Malignant diseases are frequently accompanied by suppression of cytotoxic lymphocyte function, and a large body of circumstantial evidence suggests that lymphocyte suppression may have implications for disease-free survival in several hematopoietic cancers. In AML, a plethora of immunosuppressive mechanisms have been described including the production of T- and NK-cell-inhibitory factors by AML blasts, a deficient expression of activating receptors on natural killer (NK) cells, and an impaired stimulatory interaction between the CD28 antigen expressed by T cells and contact antigens on AML blasts. We and others have proposed that the production of oxygen radicals (including hydrogen peroxide and its derivatives) by normal and leukemic phagocytic cells may significantly contribute to the state of immunosuppression in AML. The phagocyte-derived oxygen radicals strongly suppress the anti-leukemic cytotoxicity of natural killer (NK) cells with ensuing NK cell death by apoptosis, and inhibitors of oxygen radical formation efficiently rescue NK cells from inhibition and apoptosis. These mechanisms may have implications for AML treatment, as exemplified by the use of the T and NK cell activator interleukin-2 (IL-2) in conjunction with the oxygen radical inhibitor histamine dihydrochloride (HDC) as relapse-protective therapy in AML (Blood108: 88–96). METHODS and RESULTS: The question whether oxygen radical-induced activation apply to CD8+ T cells with spontaneous reactivity against human primary AML blasts has remained unresolved. Autoreactive T cells in AML were recently phenotypically defined as CD3+/8+/45RA+/CCR7 cells (CD8+/45RA+ cells; Blood 100:2132–7). We recovered these cells from human peripheral blood by FACS sorting (FACSAria) with high purity (>98%) and exposed them to exogenous hydrogen peroxide or oxygen radical-producing mononuclear phagocytes. CD8+/45RA+ T cells acquired features of apoptosis at low concentrations of hydrogen peroxide. Also, more than 60% of the CD8+/45RA+ cells acquired features of apoptosis when admixed with autologous mononuclear phagocytes (at a 1:1 phagocyte to T cell ratio, n=11, p<0.0001). HDC, an inhibitor of oxygen radical formation in phagocytes, completely prevented apoptosis in the CD8+/45RA+ T cell subset (n=8, p<0.0001). In the presence of mononuclear phagocytes, HDC synergized with IL-2 in promoting cell cycle proliferation (n=4, p=0.004) and activation (as measured by the acquisition of membrane CD69; n=9, p=0.017) in CD8+/45RA+ cells. CONCLUSIONS: The phenotype of T cells with spontaneous reactivity against AML blasts is highly sensitive to oxidants. By inhibiting oxygen radical formation, HDC efficiently protects these cytotoxic lymphocytes from apoptosis in an environment of oxidative stress. In addition, HDC synergizes with IL-2 to activate and expand CD8+/45RA+ T cells. These mechanisms of T cell activation may be relevant to the prevention of leukemic relapse reported for post-consolidation treatment with HDC/IL-2 in AML.
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Guan, Jiwen, Roshan Daljeet y Yang Song. "Pressure-selected reactivity between 2-butyne and water induced by two-photon excitation". Canadian Journal of Chemistry 95, n.º 11 (noviembre de 2017): 1212–19. http://dx.doi.org/10.1139/cjc-2017-0155.
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High-pressure photochemistry between 2-butyne (H3CC≡CCH3) and trace amount of H2O was investigated at room temperature using multiline UV radiation at λ ≈ 350 nm and monitored by FTIR spectroscopy. Instead of the expected polymerization of 2-butyne, the IR spectral analysis suggests the formation of cis- and trans-2-butene, as well as 2-butanone, as the primary products. The possible reaction mechanisms and production pathways of these products were examined, where the dissociation of water molecule as the other reactant is believed as the essential step of the photochemical reaction. We further found that initial loading pressure of the mixture can not only substantially influence the reaction kinetics, but also regulate the accessibilities to some reaction channels, which was evidenced by quantitative analysis of the characteristic IR bands of 2-butene and 2-butanone. The relative abundance of two products is found to be highly dependent on pressure and radiation time. This study provides attractive physical routes in the absence of solvents, catalysts, and radical initiators, to synthesis the relevant products with a great selectivity and feasibility.
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Hashimoto, Ryoko, Shoko Narita, Yasuko Yamada, Kyoko Tanaka y Shosuke Kojo. "Unusually high reactivity of apolipoprotein B-100 among proteins to radical reactions induced in human plasma". Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids 1483, n.º 2 (enero de 2000): 236–40. http://dx.doi.org/10.1016/s1388-1981(99)00167-5.
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Zannoni, N., S. Dusanter, V. Gros, R. Sarda Esteve, V. Michoud, V. Sinha, N. Locoge y B. Bonsang. "Intercomparison of two Comparative Reactivity Method instruments in the Mediterranean basin during summer 2013". Atmospheric Measurement Techniques Discussions 8, n.º 5 (18 de mayo de 2015): 5065–104. http://dx.doi.org/10.5194/amtd-8-5065-2015.
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Abstract. The hydroxyl radical (OH) plays a key role in the atmosphere, as it initiates most of the oxidation processes of Volatile Organic Compounds (VOCs), and can ultimately lead to the formation of ozone and Secondary Organic Aerosols (SOA). There are still uncertainties associated with the OH budget assessed using current models of atmospheric chemistry and direct measurements of OH sources and sinks have proved to be valuable tools to improve our understanding of the OH chemistry. The total first order loss rate of OH, or total OH reactivity, can be directly measured using three different methods, such as: total OH Loss rate Measurement, Laser Induced Pump and Probe Technique and Comparative Reactivity Method. Observations of total OH reactivity are usually coupled to individual measurements of reactive compounds in the gas phase, which are used to calculate the OH reactivity. Studies using the three methods have highlighted that a significant fraction of OH reactivity is often not explained by individually measured reactive compounds and could be associated to unmeasured or unknown chemical species. Therefore accurate and reproducible measurements of OH reactivity are required. The Comparative Reactivity Method (CRM) has demonstrated to be an advantageous technique with an extensive range of applications, and for this reason it has been adopted by several research groups since its development. However, this method also requires careful corrections to derive ambient OH reactivity. Herein we present an intercomparison exercise of two CRM instruments (CRM-LSCE and CRM-MD), conducted during July 2013 at the Mediterranean site of Ersa, Cape Corsica, France. We discuss in detail the experimental approach adopted and how the data sets were processed for both instruments. Corrections required for the two instruments lead to higher values of reactivity in ambient air; overall 20% increase for CRM-MD and 49% for CRM-LSCE compared to the raw data. We show that ambient OH reactivity measured by the two instruments agrees very well (correlation described by a linear least squares fit with a slope of 1 and R2 of 0.75). This study highlights that ambient measurements of OH reactivity with differently configured CRM instruments yield consistent results in a low NOx, terpene rich environment, despite differential corrections relevant to each instrument. Conducting more intercomparison exercises, involving more CRM instruments operated under different ambient and instrumental settings will help in assessing the variability induced due to instrument specific corrections further.
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Novelli, A., K. Hens, C. Tatum Ernest, D. Kubistin, E. Regelin, T. Elste, C. Plass-Dülmer, M. Martinez, J. Lelieveld y H. Harder. "Characterisation of an inlet pre-injector laser induced fluorescence instrument for the measurement of ambient hydroxyl radicals". Atmospheric Measurement Techniques Discussions 7, n.º 1 (28 de enero de 2014): 819–58. http://dx.doi.org/10.5194/amtd-7-819-2014.
Texto completoResumen
Abstract. Ambient measurements of hydroxyl radicals (OH) are challenging due to a high reactivity and consequently low concentration. The importance of OH as an atmospheric oxidant has resulted in a sustained effort leading to the development of a number of analytical techniques. Recent work has indicated that the laser-induced fluorescence of the OH molecules method based on the fluorescence assay by gas expansion technique (LIF-FAGE) for the measurement of atmospheric OH in some environments may be influenced by artificial OH generated within the instrument, and a chemical method to remove this interference was implemented in a LIF-FAGE system by Mao et al. (2012). We have applied this method to our LIF-FAGE HORUS (HydrOxyl Radical Measurement Unit based on fluorescence Spectroscopy) system, and developed and deployed an inlet pre-injector (IPI) to determine the chemical zero level in the instrument via scavenging the ambient OH radical. We describe and characterise this technique in addition to its application at field sites in forested locations in Finland, Spain, and Germany. Ambient measurements show that OH generated within the HORUS instrument is a non-negligible fraction of the total OH signal, which can comprise 30% to 80% during the day and 60% to 100% during the night. The contribution of the background OH varied greatly between measurement sites and was likely related to the type and concentration of volatile organic compounds (VOCs) present at each particular location. Two inter-comparisons in contrasting environments between the HORUS instrument and two different chemical ionisation mass spectrometers (CIMS) are described to demonstrate the efficacy of the inlet-pre-injector and the necessity of the chemical zeroing method in such environments.
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Xie, Hanyun, Runhua Chen, Yuxia Song, Yan Shen, Fengming Song, Bo He, Xiaomei Jiang, Yifan Yin y Wenming Wang. "Myriophyllum Biochar-Supported Mn/Mg Nano-Composites as Efficient Periodate Activators to Enhance Triphenyl Phosphate Removal from Wastewater". Materials 17, n.º 5 (29 de febrero de 2024): 1118. http://dx.doi.org/10.3390/ma17051118.
Texto completoResumen
Transition metals and their oxide compounds exhibit excellent chemical reactivity; however, their easy agglomeration and high cost limit their catalysis applications. In this study, an interpolation structure of a Myriophyllum verticillatum L. biochar-supported Mn/Mg composite (Mn/Mg@MV) was prepared to degrade triphenyl phosphate (TPhP) from wastewater through the activating periodate (PI) process. Interestingly, the Mn/Mg@MV composite showed strong radical self-producing capacities. The Mn/Mg@MV system degraded 93.34% TPhP (pH 5, 10 μM) within 150 min. The experimental results confirmed that the predominant role of IO3· and the auxiliary ·OH jointly contributed to the TPhP degradation. In addition, the TPhP pollutants were degraded to various intermediates and subsequent Mg mineral phase mineralization via mechanisms like interfacial processes and radical oxidation. DFT theoretical calculations further indicated that the synergy between Mn and Mg induced the charge transfer of the carbon-based surface, leading to the formation of an ·OH radical-enriched surface and enhancing the multivariate interface process of ·OH, IO3, and Mn(VII) to TPhP degradation, resulting in the further formation of Mg PO4 mineralization.
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Tsai, Tung-Lung, Shyue-Yih Chang, Chin-Yin Ho y Yu Ru Kou. "Neural and hydroxyl radical mechanisms underlying laryngeal airway hyperreactivity induced by laryngeal acid-pepsin insult in anesthetized rats". Journal of Applied Physiology 101, n.º 1 (julio de 2006): 328–38. http://dx.doi.org/10.1152/japplphysiol.00064.2006.
Texto completoResumen
Laryngopharyngeal or gastroesophageal reflux is associated with laryngeal airway hyperreactivity (LAH), but neither the cause-effect relationship nor the underlying mechanism has been elucidated. Here we established a rat model with enhanced laryngeal reflex reactivity induced by laryngeal acid-pepsin insult and investigated the neural and hydroxyl radical (·OH) mechanisms involved. The laryngeal segments of 103 anesthetized rats were functionally isolated while animals breathed spontaneously. Ammonia vapor was delivered into the laryngeal segment to measure laryngeal reflex reactivity. We found that the laryngeal pH 5-pepsin treatment doubled the reflex apneic response to ammonia, whereas laryngeal pH 7.4-pepsin, pH 2-pepsin, and pH 5-denatured pepsin treatment had no effect. Histological examination revealed limited laryngeal inflammation and epithelial damage after pH 5-pepsin treatment and more severe damage after pH 2-pepsin treatment. In rats that had received the laryngeal pH 5-pepsin treatment, the apneic response to ammonia was abolished by either denervation or perineural capsaicin treatment (PCT; a procedure that selectively blocks capsaicin-sensitive afferent fibers) of the superior laryngeal nerves, but was unaffected by perineural sham treatment. LAH was prevented by laryngeal application of either dimethylthiourea (DMTU; a ·OH scavenger) or deferoxamine (DEF; an antioxidant for ·OH), but was unaltered by the DMTU vehicle or iron-saturated DEF (ineffective DEF). LAH reappeared after recovery from PCT, DMTU, or DEF treatment. We conclude that 1) laryngeal insult by pepsin at a weakly acidic pH, but not at acidic pH, can produce LAH; and 2) LAH is probably mediated through sensitization of the capsaicin-sensitive laryngeal afferent fibers by a ·OH mechanism.
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Grjol, Blaž y Marjan Jereb. "Reactivity of substrates with multiple competitive reactive sites toward NBS under neat reaction conditions promoted by visible light". Chemical Papers 75, n.º 10 (3 de junio de 2021): 5235–48. http://dx.doi.org/10.1007/s11696-021-01711-x.
Texto completoResumen
AbstractRegioselectivity of visible-light-induced transformations of a range of (hetero)aryl alkyl-substituted ketones bearing several competitive reactive sites (α-carbonyl, benzyl and aromatic ring) with N-bromosuccinimide (NBS) was studied under solvent-free reaction conditions (SFRC) and in the absence of inert-gas atmosphere, radical initiators and catalysts. An 8-W energy-saving household lamp was used for irradiation. Heterogeneous reaction conditions were dealt with throughout the study. All substrates were mono- or dibrominated at the α-carbonyl position, and additionally, some benzylic or aromatic bromination was observed in substrates with benzylic carbon atoms or electron-donating methoxy groups, respectively. Surprisingly, ipso-substitution of the acyl group with a bromine atom took place with (4-methoxynaphthyl) alkyl ketones. While the addition of the radical scavenger TEMPO (2,2,6,6-tetramethylpiperidin-1-yloxy) decreased the extent of α- and ring bromination, it completely suppressed the benzylic bromination and α,α-dibromination with NBS under SFRC.
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Abou-Seif, M. A. M. "Oxidative Stress of Vanadium-Mediated Oxygen Free Radical Generation Stimulated by Aluminium on Human Erythrocytes". Annals of Clinical Biochemistry: International Journal of Laboratory Medicine 35, n.º 2 (marzo de 1998): 254–60. http://dx.doi.org/10.1177/000456329803500209.
Texto completoResumen
It has been suggested that aluminium stimulates vanadium-mediated superoxide radical generation. The oxidative stress of generated superoxide radicals on antioxidant enzyme activity, oxidation of NADH and NADPH, membrane lipid peroxidation and osmotic fragility in human red blood cells (RBC) was investigated. RBC were incubated with varying concentrations of vanadium and aluminium ions at 37°C for 2 h. RBC incubated with vanadium ions showed significantly increased superoxide dismutase and catalase activities, and oxidized NADH and NADPH concentrations compared with control RBC preparations. Erythrocyte lipid peroxidation was assessed by measuring thiobarbituric acid reactivity. RBC incubated with elevated levels of vanadium showed significantly increased membrane lipid peroxidation when compared with control RBC; it increased further on addition of aluminium. A significant positive correlation was observed between the extent of vanadium induced membrane lipid peroxidation and the osmotic fragility of treated RBC. In the presence of vanadium, aluminium stimulates superoxide dismutase and catalase activities, NADH and NADPH oxidation and membrane lipid peroxidation, as well as increasing osmotic fragility of human erythrocytes. The stimulatory effect of aluminium was dependent on concentration. These results may have implications for the mechanism of toxicity of aluminium and vanadium in haemodialysis patients.
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Hung, Sheng-Kai, Chia-Chi Yeh, Pei-Chi Ting, Cay-Huyen Chen y Ming-Chang Kao. "Successful management of rocuronium-induced anaphylaxis with sugammadex: A case report". Journal of International Medical Research 50, n.º 7 (julio de 2022): 030006052211139. http://dx.doi.org/10.1177/03000605221113913.
Texto completoResumen
Although anaphylaxis during anaesthesia is a rare event, neuromuscular blocking drugs are responsible for 62% of anaesthesia-related anaphylaxis. However, sugammadex, a modified gamma-cyclodextrin, can encapsulate rocuronium molecules and cause the rapid reversal of the neuromuscular blockade. A 68-year-old man who presented for a radical prostatectomy was induced with IV fentanyl/propofol/rocuronium. He had not received rocuronium previously but had received cisatracurium. Shortly after anaesthesia, the patient’s heart rate abruptly increased, and systolic blood pressure (SBP) dropped to 40 mm Hg. Despite cardiopulmonary resuscitation and intensive management, his haemodynamic stability did not improve until he received IV sugammadex, 200 mg. Intradermal skin tests showed he was positive for cisatracurium, rocuronium and succinylcholine. The patient was suspected to have cross-reactivity of rocuronium with cisatracurium. This case highlights the potential benefit of sugammadex as an adjunct to conventional measures during rocuronium-induced anaphylaxis.
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Novelli, A., K. Hens, C. Tatum Ernest, D. Kubistin, E. Regelin, T. Elste, C. Plass-Dülmer, M. Martinez, J. Lelieveld y H. Harder. "Characterisation of an inlet pre-injector laser-induced fluorescence instrument for the measurement of atmospheric hydroxyl radicals". Atmospheric Measurement Techniques 7, n.º 10 (8 de octubre de 2014): 3413–30. http://dx.doi.org/10.5194/amt-7-3413-2014.
Texto completoResumen
Abstract. Atmospheric measurements of hydroxyl radicals (OH) are challenging due to a high reactivity and consequently low concentration. The importance of OH as an atmospheric oxidant has motivated a sustained effort leading to the development of a number of highly sensitive analytical techniques. Recent work has indicated that the laser-induced fluorescence of the OH molecules method based on the fluorescence assay by gas expansion technique (LIF-FAGE) for the measurement of atmospheric OH in some environments may be influenced by artificial OH generated within the instrument, and a chemical method to remove this interference was implemented in a LIF-FAGE system by Mao et al. (2012). While it is not clear whether other LIF-FAGE instruments suffer from the same interference, we have applied this method to our LIF-FAGE HORUS (Hydroxyl Radical Measurement Unit based on fluorescence Spectroscopy) system, and developed and deployed an inlet pre-injector (IPI) to determine the chemical zero level in the instrument via scavenging the ambient OH radical. We describe and characterise this technique in addition to its application at field sites in forested locations in Finland, Spain and Germany. Ambient measurements show that OH generated within the HORUS instrument is a non-negligible fraction of the total OH signal, which can comprise 30 to 80% during daytime and 60 to 100% during the night. The contribution of the background OH varied greatly between measurement sites and was likely related to the type and concentration of volatile organic compounds (VOCs) present at each particular location. Two inter-comparisons in contrasting environments between the HORUS instrument and two different chemical ionisation mass spectrometers (CIMS) are described to demonstrate the efficacy of IPI and the necessity of the chemical zeroing method for our LIF-FAGE instrument in such environments.
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Nölscher, A. C., V. Sinha, S. Bockisch, T. Klüpfel y J. Williams. "A new method for total OH reactivity measurements using a fast Gas Chromatographic Photo-Ionization Detector (GC-PID)". Atmospheric Measurement Techniques Discussions 5, n.º 3 (15 de mayo de 2012): 3575–609. http://dx.doi.org/10.5194/amtd-5-3575-2012.
Texto completoResumen
Abstract. The primary and most important oxidant in the atmosphere is the hydroxyl radical (OH). Currently OH sinks, particularly gas phase reactions, are poorly constrained. One way to characterize the overall sink of OH is to measure directly the ambient loss rate of OH, the total OH reactivity. To date direct measurements of total OH reactivity have been either performed using a Laser Induced Fluorescence (LIF) system ("pump-and-probe" or "flow reactor") or the Comparative Reactivity Method (CRM) with a Proton Transfer Reaction Mass Spectrometer (PTR-MS). Both techniques require large, complex and expensive detection systems. This study presents a feasibility assessment for CRM total OH reactivity measurements using a new detector, a Gas Chromatographic Photo-Ionization Detector (GC-PID). Such a system is smaller, more portable, less power consuming and less expensive than other total OH reactivity measurement techniques. Total OH reactivity is measured by the CRM using a competitive reaction between a reagent (here pyrrole) with OH alone and in the presence of atmospheric reactive molecules. The new CRM method for total OH reactivity has been tested with parallel measurements of the GC-PID and the previously validated PTR-MS as detector for the reagent pyrrole during laboratory experiments, plant chamber and boreal field studies. Excellent agreement of both detectors was found when the GC-PID was operated under optimum conditions. Time resolution (60–70 s), sensitivity (LOD 3–6 s−1) and overall uncertainty (25% in optimum conditions) for total OH reactivity were equivalent to PTR-MS based total OH reactivity measurements. One drawback of the GC-PID system was the steady loss of sensitivity and accuracy during intensive measurements lasting several weeks, and a possible toluene interference. Generally, the GC-PID system has been shown to produce closely comparable results to the PTR-MS and thus in suitable environments (e.g. forests) it presents a viably economical alternative for groups interested in total OH reactivity observations.
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Nölscher, A. C., V. Sinha, S. Bockisch, T. Klüpfel y J. Williams. "Total OH reactivity measurements using a new fast Gas Chromatographic Photo-Ionization Detector (GC-PID)". Atmospheric Measurement Techniques 5, n.º 12 (4 de diciembre de 2012): 2981–92. http://dx.doi.org/10.5194/amt-5-2981-2012.
Texto completoResumen
Abstract. The primary and most important oxidant in the atmosphere is the hydroxyl radical (OH). Currently OH sinks, particularly gas phase reactions, are poorly constrained. One way to characterize the overall sink of OH is to measure directly the ambient loss rate of OH, the total OH reactivity. To date, direct measurements of total OH reactivity have been either performed using a Laser-Induced Fluorescence (LIF) system ("pump-and-probe" or "flow reactor") or the Comparative Reactivity Method (CRM) with a Proton-Transfer-Reaction Mass Spectrometer (PTR-MS). Both techniques require large, complex and expensive detection systems. This study presents a feasibility assessment for CRM total OH reactivity measurements using a new detector, a Gas Chromatographic Photoionization Detector (GC-PID). Such a system is smaller, more portable, less power consuming and less expensive than other total OH reactivity measurement techniques. Total OH reactivity is measured by the CRM using a competitive reaction between a reagent (here pyrrole) with OH alone and in the presence of atmospheric reactive molecules. The new CRM method for total OH reactivity has been tested with parallel measurements of the GC-PID and the previously validated PTR-MS as detector for the reagent pyrrole during laboratory experiments, plant chamber and boreal field studies. Excellent agreement of both detectors was found when the GC-PID was operated under optimum conditions. Time resolution (60–70 s), sensitivity (LOD 3–6 s−1) and overall uncertainty (25% in optimum conditions) for total OH reactivity were similar to PTR-MS based total OH reactivity measurements. One drawback of the GC-PID system was the steady loss of sensitivity and accuracy during intensive measurements lasting several weeks, and a possible toluene interference. Generally, the GC-PID system has been shown to produce closely comparable results to the PTR-MS and thus in suitable environments (e.g. forests) it presents a viably economical alternative for groups interested in total OH reactivity observations.
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Sahini, Victor y Gabriela Ionita. "Evidence of changes in hydrophilic/hydrophobic balance and in chemical activity of HSA induced by thermal treatments". Open Chemistry 9, n.º 2 (1 de abril de 2011): 245–52. http://dx.doi.org/10.2478/s11532-010-0148-2.
Texto completoResumen
AbstractSamples of human serum albumin (HSA) obtained as a result of heat denaturation followed by refolding controlled by a cooling of the protein solution were studied by several methods: chromatographic measurements, kinetic of the reaction with a water soluble free radical and by electron paramagnetic resonance (EPR) spectroscopy. In this context the interaction of this protein with β-cyclodextrin (β-CD) and sodium dodecyl sulfate (SDS) was also investigated. Reversed phase thin layer chromatography (RP-TLC) showed changes in lipophylicity of HSA, which are related with the existence of different ensembles of conformers. The UV-Vis absorption spectra had shown the broadening of absorption band of the protein and a hyperchrom effect in the presence of SDS; β-CD reduces the effect of SDS on protein UV-Vis spectra.Kinetic measurements related to the reaction of HSA with a water soluble DPPH type free radical provided evidence that reactivity of the HSA denaturated conformers is higher compared with the natural conformer. The affinity of SDS to the albumins surface and the effect of β-CD on the SDS/protein aggregates were also evident by changes in the EPR spectra of the spin probe CAT16.
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Olas, B., H. M. Zbikowska, B. Wachowicz, T. Krajewski, A. Buczyński y A. Magnuszewska. "Inhibitory effect of resveratrol on free radical generation in blood platelets." Acta Biochimica Polonica 46, n.º 4 (31 de diciembre de 1999): 961–66. http://dx.doi.org/10.18388/abp.1999_4119.
Texto completoResumen
Resveratrol (3,4',5-trihydroxystilbene), a compound found in many plants, has been shown to prevent coronary heart diseases and to exert a variety of antiinflammatory and anticancerogenic effects. It is effective in lowering the level of serum lipids and in inhibiting platelet aggregation. We evaluated the effect of trans-resveratrol on the production of free radicals in pig blood platelets and showed that resveratrol inhibited the production of different reactive oxygen species (O2*-, H2O2, singlet oxygen and organic radicals) measured by the luminol-dependent chemiluminescence in resting platelets (P < 0.05). Resveratrol inhibited also the generation of radicals in platelets activated by thrombin (P < 0.05). Treatment of platelets with resveratrol at concentrations of 6.25 and 12.5 microg/ml caused a statistically insignificant increase in the production of O2*- in these cells, as measured by reduction of cytochrome c; however, at higher doses (25, 50 and 100 microg/ml) resveratrol distinctly reduced the generation of O2*- in platelets (P < 0.05). We suggest that free radicals play an important role in the reduced reactivity of blood platelets induced by resveratrol.
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Zannoni, N., S. Dusanter, V. Gros, R. Sarda Esteve, V. Michoud, V. Sinha, N. Locoge y B. Bonsang. "Intercomparison of two comparative reactivity method instruments inf the Mediterranean basin during summer 2013". Atmospheric Measurement Techniques 8, n.º 9 (21 de septiembre de 2015): 3851–65. http://dx.doi.org/10.5194/amt-8-3851-2015.
Texto completoResumen
Abstract. The hydroxyl radical (OH) plays a key role in the atmosphere, as it initiates most of the oxidation processes of volatile organic compounds (VOCs), and can ultimately lead to the formation of ozone and secondary organic aerosols (SOAs). There are still uncertainties associated with the OH budget assessed using current models of atmospheric chemistry and direct measurements of OH sources and sinks have proved to be valuable tools to improve our understanding of the OH chemistry. The total first order loss rate of OH, or total OH reactivity, can be directly measured using three different methods, such as the following: total OH loss rate measurement, laser-induced pump and probe technique and comparative reactivity method. Observations of total OH reactivity are usually coupled to individual measurements of reactive compounds in the gas phase, which are used to calculate the OH reactivity. Studies using the three methods have highlighted that a significant fraction of OH reactivity is often not explained by individually measured reactive compounds and could be associated to unmeasured or unknown chemical species. Therefore accurate and reproducible measurements of OH reactivity are required. The comparative reactivity method (CRM) has demonstrated to be an advantageous technique with an extensive range of applications, and for this reason it has been adopted by several research groups since its development. However, this method also requires careful corrections to derive ambient OH reactivity. Herein we present an intercomparison exercise of two CRM instruments, CRM-LSCE (Laboratoire des Sciences du Climat et de l'Environnement) and CRM-MD (Mines Douai), conducted during July 2013 at the Mediterranean site of Ersa, Cape Corsica, France. The intercomparison exercise included tests to assess the corrections needed by the two instruments to process the raw data sets as well as OH reactivity observations. The observation was divided in three parts: 2 days of plant emissions (8–9 July), 2 days of ambient measurements (10–11 July) and 2 days (12–13 July) of plant emissions. We discuss in detail the experimental approach adopted and how the data sets were processed for both instruments. Corrections required for the two instruments lead to higher values of reactivity in ambient air; overall 20 % increase for CRM-MD and 49 % for CRM-LSCE compared to the raw data. We show that ambient OH reactivity measured by the two instruments agrees very well (correlation described by a linear least squares fit with a slope of 1 and R2 of 0.75). This study highlights that ambient measurements of OH reactivity with differently configured CRM instruments yield consistent results in a low NOx (NO + NO2), terpene rich environment, despite differential corrections relevant to each instrument. Conducting more intercomparison exercises, involving more CRM instruments operated under different ambient and instrumental settings will help in assessing the variability induced due to instrument-specific corrections further.