Journal articles: 'Radical Oligomerization'

1

Renard, P., F. Siekmann, A. Gandolfo, J. Socorro, G. Salque, S. Ravier, E. Quivet, et al. "Radical mechanisms of methyl vinyl ketone oligomerization through aqueous phase OH-oxidation: on the paradoxical role of dissolved molecular oxygen." Atmospheric Chemistry and Physics 13, no. 13 (July 8, 2013): 6473–91. http://dx.doi.org/10.5194/acp-13-6473-2013.

Full text

Abstract:

Abstract. It is now accepted that one of the important pathways of secondary organic aerosol (SOA) formation occurs through aqueous phase chemistry in the atmosphere. However, the chemical mechanisms leading to macromolecules are still not well understood. It was recently shown that oligomer production by OH radical oxidation in the aerosol aqueous phase from α-dicarbonyl precursors, such as methylglyoxal and glyoxal, is irreversible and fast. Methyl vinyl ketone (MVK) was chosen in the present study as it is an α,β-unsaturated carbonyl that can undergo radical oligomerization in the aerosol aqueous phase. We present here experiments on the aqueous phase OH-oxidation of MVK, performed under various conditions. Using NMR and UV absorption spectroscopy, high and ultra-high resolution mass spectrometry, we show that the fast formation of oligomers up to 1800 Da is due to radical oligomerization of MVK, and 13 series of oligomers (out of a total of 26 series) are identified. The influence of atmospherically relevant parameters such as temperature, initial concentrations of MVK and dissolved oxygen are presented and discussed. In agreement with the experimental observations, we propose a chemical mechanism of OH-oxidation of MVK in the aqueous phase that proceeds via radical oligomerization of MVK on the olefin part of the molecule. This mechanism highlights in our experiments the paradoxical role of dissolved O2: while it inhibits oligomerization reactions, it contributes to produce oligomerization initiator radicals, which rapidly consume O2, thus leading to the dominance of oligomerization reactions after several minutes of reaction. These processes, together with the large range of initial concentrations investigated show the fundamental role that radical oligomerization processes likely play in polluted fogs and atmospheric aerosol.

APA, Harvard, Vancouver, ISO, and other styles

2

Renard, P., F. Siekmann, A. Gandolfo, J. Socorro, G. Salque, S. Ravier, E. Quivet, et al. "Radical mechanisms of methyl vinyl ketone oligomerization through aqueous phase OH-oxidation: on the paradoxical role of dissolved molecular oxygen." Atmospheric Chemistry and Physics Discussions 13, no. 1 (January 28, 2013): 2913–54. http://dx.doi.org/10.5194/acpd-13-2913-2013.

Full text

Abstract:

Abstract. It is now accepted that one of the important pathways of Secondary Organic Aerosol (SOA) formation occurs through aqueous phase chemistry in the atmosphere. However, the liquid phase chemical mechanisms leading to macromolecules are still not well understood. For α-dicarbonyl precursors, such as methylglyoxal and glyoxal, radical reactions through OH-oxidation produce oligomers, irreversibly and faster than accretion reactions. Methyl vinyl ketone (MVK) was chosen in the present study as it is an α, β-unsaturated carbonyl that can undergo such reaction pathways in the aqueous phase and forms even high molecular weight oligomers. We present here experiments on the aqueous phase OH-oxidation of MVK, performed under atmospheric relevant conditions. Using NMR and UV absorption spectroscopy, high and ultra-high resolution mass spectrometry, we show that the fast formation of oligomers up to 1800 Da is due to radical oligomerization of MVK, and 13 series of oligomers (out of a total of 26 series) are identified. The influence of atmospherically relevant parameters such as temperature, initial concentrations of MVK and dissolved oxygen are presented and discussed. In agreement with the experimental observations, we propose a chemical mechanism of OH-oxidation of MVK in the aqueous phase that proceeds via radical oligomerization of MVK on the olefin part of the molecule. This mechanism highlights the paradoxical role of dissolved O2: while it inhibits oligomerization reactions, it contributes to produce oligomerization initiator radicals, which rapidly consume O2, thus leading to the supremacy of oligomerization reactions after several minutes of reaction. These processes, together with the large ranges of initial concentrations investigated (60–656 μM of dissolved O2 and 0.2–20 mM of MVK) show the fundamental role that O2 likely plays in atmospheric organic aerosol.

APA, Harvard, Vancouver, ISO, and other styles

3

Bedilo, Alexander F., and Alexander M. Volodin. "Suppression of radical-cationic benzene oligomerization on sulfated zirconia." Reaction Kinetics and Catalysis Letters 67, no. 1 (May 1999): 197–203. http://dx.doi.org/10.1007/bf02475848.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Bizilj, S., DP Kelly, AK Serelis, DH Solomon, and KE White. "The Self-Reactions of 1-Methoxycarbonyl-1-methylethyl and Higher Ester Radicals: Combination vs Disproportionation and Oligomeric Products from Secondary Reactions." Australian Journal of Chemistry 38, no. 11 (1985): 1657. http://dx.doi.org/10.1071/ch9851657.

Full text

Abstract:

The geminate self-reactions of the title methyl, ethyl and butyl ester radicals-(2a-c), formed by decomposition of the corresponding azo precursors (1a-c) in the presence of stable nitroxide radical scavengers, were found on the basis of product analysis to comprise combination and disproportionation in the ratios 56 : 44 (methyl), 58 : 42 (ethyl) and 47 : 53 (butyl). In the absence of radical scavengers, extensive oligomerization is observed. Hydrogenation and degradation were used in conjunction with g.l.c.-m.s . to deduce the identities of the dimeric, trimeric and tetrameric products, which were in most cases subsequently confirmed by isolation and n.m.r . analysis. Of particular interest is the highly regioselective disproportionation of radical (3) to give dimethyl 4-methylpent-1-ene-2,4-dicarboxylate (8), and the further reaction of (8) with (2a) to form branched oligomers (10) and (15).

APA, Harvard, Vancouver, ISO, and other styles

5

Pithawalla, Yezdi B., Michael Meot-Ner, Junling Gao, M. Samy El Shall, Vladimir I. Baranov, and Diethard K. Bohme. "Gas-Phase Oligomerization of Propene Initiated by Benzene Radical Cation." Journal of Physical Chemistry A 105, no. 15 (April 2001): 3908–16. http://dx.doi.org/10.1021/jp003421b.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Yurtsever, M., and E. Yurtsever. "Density functional theory study of the electrochemical oligomerization of thiophene: transition states for radical–radical and radical–neutral pathways." Polymer 45, no. 26 (December 2004): 9039–45. http://dx.doi.org/10.1016/j.polymer.2004.10.050.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Holman, R. W., B. Atkins, Daryl Giblin, Don Rempel, and Michael L. Gross. "Cyclopropane as a propagating reagent in gas-phase radical cation oligomerization." International Journal of Mass Spectrometry 210-211 (September 2001): 569–84. http://dx.doi.org/10.1016/s1387-3806(01)00439-0.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Renard, Pascal, Allison E. Reed Harris, Rebecca J. Rapf, Sylvain Ravier, Carine Demelas, Bruno Coulomb, Etienne Quivet, Veronica Vaida, and Anne Monod. "Aqueous Phase Oligomerization of Methyl Vinyl Ketone by Atmospheric Radical Reactions." Journal of Physical Chemistry C 118, no. 50 (October 29, 2014): 29421–30. http://dx.doi.org/10.1021/jp5065598.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Suzuki, Takayuki, Kazuma Murakami, Naotaka Izuo, Toshiaki Kume, Akinori Akaike, Tetsu Nagata, Tomoyuki Nishizaki, et al. "E22Δ Mutation in Amyloidβ-Protein Promotesβ-Sheet Transformation, Radical Production, and Synaptotoxicity, But Not Neurotoxicity." International Journal of Alzheimer's Disease 2011 (2011): 1–8. http://dx.doi.org/10.4061/2011/431320.

Full text

Abstract:

Oligomers of 40- or 42-mer amyloidβ-protein (Aβ40, Aβ42) cause cognitive decline and synaptic dysfunction in Alzheimer's disease. We proposed the importance of a turn at Glu22 and Asp23 of Aβ42 to induce its neurotoxicity through the formation of radicals. Recently, a novel deletion mutant at Glu22 (E22Δ) of Aβ42 was reported to accelerate oligomerization and synaptotoxicity. To investigate this mechanism, the effects of the E22Δ mutation in Aβ42 and Aβ40 on the transformation ofβ-sheets, radical production, and neurotoxicity were examined. Both mutants promotedβ-sheet transformation and the formation of radicals, while their neurotoxicity was negative. In contrast, E22P-Aβ42 with a turn at Glu22 and Asp23 exhibited potent neurotoxicity along with the ability to form radicals and potent synaptotoxicity. These data suggest that conformational change in E22Δ-Aβis similar to that in E22P-Aβ42 but not the same, since E22Δ-Aβ42 exhibited no cytotoxicity, unlike E22P-Aβ42 and wild-type Aβ42.

APA, Harvard, Vancouver, ISO, and other styles

10

ANDREKOPOULOS, Christopher, Hao ZHANG, Joy JOSEPH, Shasi KALIVENDI, and B. KALYANARAMAN. "Bicarbonate enhances alpha-synuclein oligomerization and nitration: intermediacy of carbonate radical anion and nitrogen dioxide radical." Biochemical Journal 378, no. 2 (March 1, 2004): 435–47. http://dx.doi.org/10.1042/bj20031466.

Full text

Abstract:

α-Synuclein, a neuronal presynaptic protein, has been reported to undergo oligomerization to form toxic Lewy bodies in neurodegenerative disorders. One of the proposed mechanisms for aggregation of α-synuclein involves oxidative and nitrative modifications. In the present study, we show that addition of 3-morpholino-sydnonimine chloride (SIN-1) or slow infusion of pre-formed peroxynitrite (ONOO−) to mixtures containing α-synuclein and HCO3− markedly enhanced both nitration and aggregation of α-synuclein through dityrosine formation. Bicarbonate-dependent peroxidase activity of Cu,Zn-superoxide dismutase (SOD1) also induced covalent aggregation of α-synuclein via a CO3•−-dependent mechanism. Nitrone spin traps completely inhibited CO3•−-mediated oxidation/nitration and aggregation of α-synuclein. Conversely, α-synuclein inhibited CO3•−-induced spin adduct formation. Independent evidence for CO3•−-mediated oxidation and dimerization of α-synuclein was obtained from UV photolysis of [(NH3)5CoCO3]+, which generates authentic CO3•−. Irradiation of [(NH3)5CoCO3]+ and NO2− in the presence of α-synuclein yielded nitration and aggregation products that were similar to those obtained from a SIN-1 (or slowly infused ONOO−) and HCO3− or a myeloperoxidase/H2O2/NO2− system. Hydrophobic membranes greatly influenced α-synuclein aggregation and nitration in these systems. We conclude that both CO3•− and NO2• could play a major role in the nitration/aggregation of α-synuclein.

APA, Harvard, Vancouver, ISO, and other styles

11

Ohkubo, Kei, Ryosuke Iwata, Takahiro Yanagimoto, and Shunichi Fukuzumi. "Enhanced photoinduced oligomerization of fullerene via radical coupling between fullerene radical cation and radical anion using 9-mesityl-10-methylacridinium ion." Chemical Communications, no. 30 (2007): 3139. http://dx.doi.org/10.1039/b705289h.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Liu, Li, Xing Wang, and Chaozhong Li. "Deoligomerization: A New Route to Lactams from Unsaturated Amides via Radical Oligomerization." Organic Letters 5, no. 3 (February 2003): 361–63. http://dx.doi.org/10.1021/ol027428i.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Huang, Zhipeng, Zhitong Zhao, Chaofeng Zhang, Jianmin Lu, Huifang Liu, Nengchao Luo, Jian Zhang, and Feng Wang. "Enhanced photocatalytic alkane production from fatty acid decarboxylation via inhibition of radical oligomerization." Nature Catalysis 3, no. 2 (February 2020): 170–78. http://dx.doi.org/10.1038/s41929-020-0423-3.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Schwarzenbacher, Gerald, Marion S. Gangl, Marian Goriup, Martin Winter, Matthias Grunert, Franz Renz, Wolfgang Linert, and Robert Saf. "Preparation and Radical Oligomerization of anFe(II) Complex without Loss of Spin-Crossover Properties." Monatshefte fuer Chemie/Chemical Monthly 132, no. 4 (April 12, 2001): 519–29. http://dx.doi.org/10.1007/s007060170114.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Berkemeier, Thomas, Masayuki Takeuchi, Gamze Eris, and Nga L. Ng. "Kinetic modeling of formation and evaporation of secondary organic aerosol from NO<sub>3</sub> oxidation of pure and mixed monoterpenes." Atmospheric Chemistry and Physics 20, no. 24 (December 14, 2020): 15513–35. http://dx.doi.org/10.5194/acp-20-15513-2020.

Full text

Abstract:

Abstract. Organic aerosol constitutes a major fraction of the global aerosol burden and is predominantly formed as secondary organic aerosol (SOA). Environmental chambers have been used extensively to study aerosol formation and evolution under controlled conditions similar to the atmosphere, but quantitative prediction of the outcome of these experiments is generally not achieved, which signifies our lack in understanding of these results and limits their portability to large-scale models. In general, kinetic models employing state-of-the-art explicit chemical mechanisms fail to describe the mass concentration and composition of SOA obtained from chamber experiments. Specifically, chemical reactions including the nitrate radical (NO3) are a source of major uncertainty for assessing the chemical and physical properties of oxidation products. Here, we introduce a kinetic model that treats gas-phase chemistry, gas–particle partitioning, particle-phase oligomerization, and chamber vapor wall loss and use it to describe the oxidation of the monoterpenes α-pinene and limonene with NO3. The model can reproduce aerosol mass and nitration degrees in experiments using either pure precursors or their mixtures and infers volatility distributions of products, branching ratios of reactive intermediates and particle-phase reaction rates. The gas-phase chemistry in the model is based on the Master Chemical Mechanism (MCM) but trades speciation of single compounds for the overall ability of quantitatively describing SOA formation by using a lumped chemical mechanism. The complex branching into a multitude of individual products in MCM is replaced in this model with product volatility distributions and detailed peroxy (RO2) and alkoxy (RO) radical chemistry as well as amended by a particle-phase oligomerization scheme. The kinetic parameters obtained in this study are constrained by a set of SOA formation and evaporation experiments conducted in the Georgia Tech Environmental Chamber (GTEC) facility. For both precursors, we present volatility distributions of nitrated and non-nitrated reaction products that are obtained by fitting the kinetic model systematically to the experimental data using a global optimization method, the Monte Carlo genetic algorithm (MCGA). The results presented here provide new mechanistic insight into the processes leading to formation and evaporation of SOA. Most notably, the model suggests that the observed slow evaporation of SOA could be due to reversible oligomerization reactions in the particle phase. However, the observed non-linear behavior of precursor mixtures points towards a complex interplay of reversible oligomerization and kinetic limitations of mass transport in the particle phase, which is explored in a model sensitivity study. The methodologies described in this work provide a basis for quantitative analysis of multi-source data from environmental chamber experiments but also show that a large data pool is needed to fully resolve uncertainties in model parameters.

APA, Harvard, Vancouver, ISO, and other styles

16

Kiselar, Janna, Andrew Nix, Anant Paravastu, Rosenberry L. Terrone, and Alexandra L. Klinger. "Sequence Specific Quantitative Hydroxyl Radical Footprinting Reveals Structural Details of Amyloid-ß (1-42) Peptide Oligomerization." Biophysical Journal 112, no. 3 (February 2017): 363a. http://dx.doi.org/10.1016/j.bpj.2016.11.1970.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Markova, M. V., A. V. Ivanov, and B. A. Trofimov. "Free-Radical Co-Oligomerization of N-Vinylpyrroles with N-Vinylpyrrolidone: A Route to New Bioactive Oligomers." Doklady Chemistry 482, no. 2 (October 2018): 237–41. http://dx.doi.org/10.1134/s0012500818100075.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Lim, Y. B., Y. Tan, and B. J. Turpin. "Chemical insights, explicit chemistry, and yields of secondary organic aerosol from OH radical oxidation of methylglyoxal and glyoxal in the aqueous phase." Atmospheric Chemistry and Physics 13, no. 17 (September 3, 2013): 8651–67. http://dx.doi.org/10.5194/acp-13-8651-2013.

Full text

Abstract:

Abstract. Atmospherically abundant, volatile water-soluble organic compounds formed through gas-phase chemistry (e.g., glyoxal (C2), methylglyoxal (C3), and acetic acid) have great potential to form secondary organic aerosol (SOA) via aqueous chemistry in clouds, fogs, and wet aerosols. This paper (1) provides chemical insights into aqueous-phase OH-radical-initiated reactions leading to SOA formation from methylglyoxal and (2) uses this and a previously published glyoxal mechanism (Lim et al., 2010) to provide SOA yields for use in chemical transport models. Detailed reaction mechanisms including peroxy radical chemistry and a full kinetic model for aqueous photochemistry of acetic acid and methylglyoxal are developed and validated by comparing simulations with the experimental results from previous studies (Tan et al., 2010, 2012). This new methylglyoxal model is then combined with the previous glyoxal model (Lim et al., 2010), and is used to simulate the profiles of products and to estimate SOA yields. At cloud-relevant concentrations (~ 10−6 − ~ 10−3 M; Munger et al., 1995) of glyoxal and methylglyoxal, the major photooxidation products are oxalic acid and pyruvic acid, and simulated SOA yields (by mass) are ~ 120% for glyoxal and ~ 80% for methylglyoxal. During droplet evaporation oligomerization of unreacted methylglyoxal/glyoxal that did not undergo aqueous photooxidation could enhance yields. In wet aerosols, where total dissolved organics are present at much higher concentrations (~ 10 M), the major oxidation products are oligomers formed via organic radical–radical reactions, and simulated SOA yields (by mass) are ~ 90% for both glyoxal and methylglyoxal. Non-radical reactions (e.g., with ammonium) could enhance yields.

APA, Harvard, Vancouver, ISO, and other styles

19

Harrington, Cameron R., William J. Leigh, Bryan K. Chan, Peter P. Gaspar, and Dong Zhou. "Time-resolved spectroscopic studies of the photochemistry of some diphenylgermylene (Ph2Ge:) precursors." Canadian Journal of Chemistry 83, no. 9 (September 1, 2005): 1324–38. http://dx.doi.org/10.1139/v05-148.

Full text

Abstract:

The photochemistry of diphenylbis(trimethylsilyl)germane (2a) and 1,4-dihydro-5-methyl-1,2,3,4,9,9-hexaphenyl-1,4-germanonaphthalene (11) has been studied in solution by steady-state and laser flash photolysis methods with a view to detecting the transient germylene derivative diphenylgermylene (Ph2Ge), which has previously been shown to be the major product of photolysis of 2a and a closely related derivative of 11. Steady-state trapping experiments confirm the formation of Ph2Ge as the major germanium containing primary product in both cases; with 2a, the results indicate that other transient species are also formed in minor yields, including phenyl(trimethylsilyl)germylene (Ph(TMS)Ge, ca. 6%) and diphenyl(trimethylsilyl)germyl radicals (Ph2(TMS)Ge, ≥15%). Laser flash photolysis of 2a in deoxy genated hexane solution yields a complex mixture of overlapping transient absorptions, which is shown to be comprised of Ph2Ge, tetraphenyldigermene (15) and its oligomerization products, and another species with spectral characteristics similar to the Ph2(TMS)Ge radical. The latter has been independently generated by hydrogen abstraction from diphenyl(trimethylsilyl)germane by tert-butoxyl radicals. Compound 11 extrudes Ph2Ge more cleanly and efficiently upon photolysis in solution, yet laser flash photolysis affords excited triplet and triplet-derived species as the only detectable transient products; interpretation of the results for this compound is made difficult by its slow thermal decomposition to 5-methyl-1,2,3,4-tetraphenylnaphthalene. It is concluded that in spite of the fact that both 2a and 11 afford Ph2Ge in high yield upon photolysis, they are poor precursors for study of the species in solution by time-resolved UVvis methods, owing to the formation of other, more strongly absorbing transient products than Ph2Ge, whose lowest energy absorption is characteristically weak.Key words: germylene, germyl radical, flash photolysis, disilylgermane, photochemistry.

APA, Harvard, Vancouver, ISO, and other styles

20

Lim, Y. B., Y. Tan, and B. J. Turpin. "Chemical insights, explicit chemistry and yields of secondary organic aerosol from methylglyoxal and glyoxal." Atmospheric Chemistry and Physics Discussions 13, no. 2 (February 19, 2013): 4687–725. http://dx.doi.org/10.5194/acpd-13-4687-2013.

Full text

Abstract:

Abstract. Atmospherically abundant, volatile water soluble organic compounds formed through gas phase chemistry (e.g., glyoxal (C2), methylglyoxal (C3) and acetic acid) have great potential to form secondary organic aerosol (SOA) via aqueous chemistry in clouds, fogs and wet aerosols. This paper (1) provides chemical insights into aqueous-phase OH radical-initiated reactions leading to SOA formation from methylglyoxal and (2) uses this and a previously published glyoxal mechanism (Lim et al., 2010) to provide SOA yields for use in chemical transport models. Detailed reaction mechanisms including peroxy radical chemistry and a full kinetic model for aqueous photochemistry of acetic acid and methylglyoxal are developed and validated by comparing simulations with the experimental results from previous studies (Tan et al., 2010, 2012). This new methylglyoxal model is then combined with the previous glyoxal model (Lim et al., 2010), and is used to simulate the profiles of products and to estimate SOA yields. At cloud relevant concentrations (∼ 10−6–∼ 10−3 M; Munger et al., 1995) of glyoxal and methylglyoxal, the major photooxidation products are oxalic acid and pyruvic acid, and simulated SOA yields (by mass) are ∼ 120% for glyoxal and ∼ 80% for methylglyoxal. Oligomerization of unreacted aldehydes during droplet evaporation could enhance yields. In wet aerosols, where total dissolved organics are present at much higher concentrations (∼ 10 M), the major products are oligomers formed via organic radical-radical reactions, and simulated SOA yields (by mass) are ∼ 90% for both glyoxal and methylglyoxal.

APA, Harvard, Vancouver, ISO, and other styles

21

Sáfrány, Ágnes, and László Wojnárovits. "First steps in radiation-induced hydrogel synthesis: radical formation and oligomerization in dilute aqueous N-isopropylacrylamide solutions." Radiation Physics and Chemistry 67, no. 6 (August 2003): 707–15. http://dx.doi.org/10.1016/s0969-806x(03)00147-6.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Ito, Tetsuro. "Resveratrol oligomer structure in Dipterocarpaceaeous plants." Journal of Natural Medicines 74, no. 4 (April 30, 2020): 619–37. http://dx.doi.org/10.1007/s11418-020-01412-x.

Full text

Abstract:

Abstract Oligostilbenoids are a group of natural products derived from the oxidative coupling of C6–C2–C6 units found in some plant families. A structurally diverse chemical pool is produced after the successive regioselective and stereoselective oligomerization of resveratrol. This review describes the current status and knowledge of the structure of resveratrol oligomers (ROs) in Dipterocarpaceaeous plants (DPs). Beginning with the recently validated formation of ROs in DPs, each downstream conversion is described from the perspective of the resveratrol coupling mode. Particular emphasis is placed upon the regioselectivity of monomer- and dimer-derived radical–radical coupling processes, which are responsible for producing dimers, trimers, and tetramers with various cyclic frame skeletons, as well as related processes that result in highly condensed scaffolds, such as hexamers and octamers. Trimers in oxidized, dearomatized, and rearranged forms are also summarized, as well as the biogenic relationship between the compounds. Furthermore, emphasis is placed on the O- and C-glucosides of ROs, as well as on the hetero-coupled ROs. In addition, several stereoisomers that originate from asymmetric carbons and the stereochemistry with respect to the conformation due to the chiral axis are described. Besides, NMR spectroscopic properties such as coalescence and anisotropy are briefly described. Approaches to determine absolute configuration are also summarized.

APA, Harvard, Vancouver, ISO, and other styles

23

Coelho, Fernando R., Asif Iqbal, Edlaine Linares, Daniel F. Silva, Filipe S. Lima, Iolanda M. Cuccovia, and Ohara Augusto. "Oxidation of the Tryptophan 32 Residue of Human Superoxide Dismutase 1 Caused by Its Bicarbonate-dependent Peroxidase Activity Triggers the Non-amyloid Aggregation of the Enzyme." Journal of Biological Chemistry 289, no. 44 (September 18, 2014): 30690–701. http://dx.doi.org/10.1074/jbc.m114.586370.

Full text

Abstract:

The role of oxidative post-translational modifications of human superoxide dismutase 1 (hSOD1) in the amyotrophic lateral sclerosis (ALS) pathology is an attractive hypothesis to explore based on several lines of evidence. Among them, the remarkable stability of hSOD1WT and several of its ALS-associated mutants suggests that hSOD1 oxidation may precede its conversion to the unfolded and aggregated forms found in ALS patients. The bicarbonate-dependent peroxidase activity of hSOD1 causes oxidation of its own solvent-exposed Trp32 residue. The resulting products are apparently different from those produced in the absence of bicarbonate and are most likely specific for simian SOD1s, which contain the Trp32 residue. The aims of this work were to examine whether the bicarbonate-dependent peroxidase activity of hSOD1 (hSOD1WT and hSOD1G93A mutant) triggers aggregation of the enzyme and to comprehend the role of the Trp32 residue in the process. The results showed that Trp32 residues of both enzymes are oxidized to a similar extent to hSOD1-derived tryptophanyl radicals. These radicals decayed to hSOD1-N-formylkynurenine and hSOD1-kynurenine or to a hSOD1 covalent dimer cross-linked by a ditryptophan bond, causing hSOD1 unfolding, oligomerization, and non-amyloid aggregation. The latter process was inhibited by tempol, which recombines with the hSOD1-derived tryptophanyl radical, and did not occur in the absence of bicarbonate or with enzymes that lack the Trp32 residue (bovine SOD1 and hSOD1W32F mutant). The results support a role for the oxidation products of the hSOD1-Trp32 residue, particularly the covalent dimer, in triggering the non-amyloid aggregation of hSOD1.

APA, Harvard, Vancouver, ISO, and other styles

24

Chuang, Wayne K., and Neil M. Donahue. "Dynamic consideration of smog chamber experiments." Atmospheric Chemistry and Physics 17, no. 16 (August 28, 2017): 10019–36. http://dx.doi.org/10.5194/acp-17-10019-2017.

Full text

Abstract:

Abstract. Recent studies of the α-pinene + ozone reaction that address particle nucleation show relatively high molar yields of highly oxidized multifunctional organic molecules with very low saturation concentrations that can form and grow new particles on their own. However, numerous smog-chamber experiments addressing secondary organic aerosol (SOA) mass yields, interpreted via equilibrium partitioning theory, suggest that the vast majority of SOA from α-pinene is semivolatile. We explore this paradox by employing a dynamic volatility basis set (VBS) model that reproduces the new-particle growth rates observed in the CLOUD experiment at CERN and then modeling SOA mass yield experiments conducted at Carnegie Mellon University (CMU). We find that the base-case simulations do overpredict observed SOA mass but by much less than an equilibrium analysis would suggest; this is because delayed condensation of vapors suppresses the apparent mass yields early in the chamber experiments. We further find that a second VBS model featuring substantial oligomerization of semivolatile monomers can match the CLOUD growth rates with substantially lower SOA mass yields; this is because the lighter monomers have a higher velocity and thus a higher condensation rate for a given mass concentration. The oligomerization simulations are a closer match to the CMU experiments than the base-case simulations, though they overpredict the observations somewhat. However, we also find that if the chemical conditions in CLOUD and the CMU chamber were identical, substantial nucleation would have occurred in the CMU experiments when in fact none occurred. This suggests that the chemical mechanisms differed in the two experiments, perhaps because the high oxidation rates in the SOA formation experiments led to rapid termination of peroxy radical chemistry.

APA, Harvard, Vancouver, ISO, and other styles

25

Kiselar, Janna, Andrew Nix, Anant Paravastu, Terrone Rosenberry, and Alexandra Klinger. "Quantitative Hydroxyl Radical Footprinting Study Reveals Structural Details of the Disorder-to-Order Transition in Amyloid-Beta (1-42) Oligomerization." Biophysical Journal 114, no. 3 (February 2018): 430a. http://dx.doi.org/10.1016/j.bpj.2017.11.2385.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Chen, Long, Yu Huang, Yonggang Xue, Junji Cao, and Wenliang Wang. "Effect of oligomerization reactions of Criegee intermediate with organic acid/peroxy radical on secondary organic aerosol formation from isoprene ozonolysis." Atmospheric Environment 187 (August 2018): 218–29. http://dx.doi.org/10.1016/j.atmosenv.2018.06.001.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Illsley, Derek R., and Roy S. Lehrle. "Polymerization of dec-1-ene—II. Product analysis shows that the free radical process is an oligomerization, and reveals mechanistic details." European Polymer Journal 27, no. 2 (January 1991): 177–84. http://dx.doi.org/10.1016/0014-3057(91)90219-e.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Grzybowska, Dorota, Przemysław Malinowski, Zoran Mazej, and Wojciech Grochala. "Probing the Reactivity of the Potent AgF2 Oxidizer. Part 1: Organic Compounds." Collection of Czechoslovak Chemical Communications 73, no. 12 (2008): 1729–46. http://dx.doi.org/10.1135/cccc20081729.

Full text

Abstract:

The reactivity of Ag(II)F2 towards a variety of organic compounds of a high degree of fluorination has been investigated. AgF2 readily fluorinates P(C6F5)3 to PF2(C6F5)3, and attacks the isothiocyanate functional group, -NCS, yielding Ag2S. Perfluorinated aliphatic nitriles resist the action of AgF2, but aromatic C6F5CN undergoes a radical-initiated oligomerization; byproducts include C6F6CN• and C6F5N2• (after intramolecular rearrangement following the bimolecular reaction). AgF2 oxidizes higher fluorosulfonic acids (C4F9SO3H, C8F17SO3H) at or close to the room temperature and triflic acid (CF3SO3H) at its boiling point to the corresponding peroxides. CF3COOH and CF3CONH2 are also decomposed in redox reactions, but the gaseous products have not been identified. Surprisingly, AgF2 is kinetically inert to perfluorinated aromatic hydrocarbons and to CCl4, but it decomposes CBr4 with vigorous elimination of Br2. CI4 decomposes explosively in the presence of AgF2. C6F5OH and CF3COOH are readily oxidized with AgF2 but, surprisingly, t-C4F9OH is kinetically resistant under similar conditions. Coordination complexes of perfluorinated aza and oxa Lewis bases (including perfluorinated 15-crown-5 ether) and AgF2 are not formed under the experimental conditions.

APA, Harvard, Vancouver, ISO, and other styles

29

Ervens, B., P. Renard, S. Tlili, S. Ravier, J. L. Clément, and A. Monod. "Aqueous-phase oligomerization of methyl vinyl ketone through photooxidation – Part 2: Development of the chemical mechanism and atmospheric implications." Atmospheric Chemistry and Physics 15, no. 16 (August 17, 2015): 9109–27. http://dx.doi.org/10.5194/acp-15-9109-2015.

Full text

Abstract:

Abstract. Laboratory experiments of efficient oligomerization from methyl vinyl ketone (MVK) in the bulk aqueous phase were simulated in a box model. Kinetic data are applied (if known) or fitted to the observed MVK decay and oligomer mass increase. Upon model sensitivity studies, in which unconstrained rate constants were varied over several orders of magnitude, a set of reaction parameters was found that could reproduce laboratory data over a wide range of experimental conditions. This mechanism is the first that comprehensively describes such radical-initiated oligomer formation. This mechanism was implemented into a multiphase box model that simulates secondary organic aerosol (SOA) formation from isoprene, as a precursor of MVK and methacrolein (MACR) in the aqueous and gas phases. While in laboratory experiments oxygen limitation might occur and lead to accelerated oligomer formation, such conditions are likely not met in the atmosphere. The comparison of predicted oligomer formation shows that MVK and MACR likely do negligibly contribute to total SOA as their solubilities are low and even reduced in aerosol water due to ionic strength effects (Setchenov coefficients). Significant contribution by oligomers to total SOA might only occur if a substantial fraction of particulate carbon acts as oligomer precursors and/or if oxygen solubility in aerosol water is strongly reduced due to salting-out effects.

APA, Harvard, Vancouver, ISO, and other styles

30

Illsley, Derek R., and Roy S. Lehrle. "Polymerization of dec-1-ene—III. Detailed kinetic analysis of total product formation provides reactivities and kinetic parameters for the free radical oligomerization." European Polymer Journal 27, no. 2 (January 1991): 185–88. http://dx.doi.org/10.1016/0014-3057(91)90220-i.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Yu, Lu, Jeremy Smith, Alexander Laskin, Katheryn M. George, Cort Anastasio, Julia Laskin, Ann M. Dillner, and Qi Zhang. "Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: competition among oligomerization, functionalization, and fragmentation." Atmospheric Chemistry and Physics 16, no. 7 (April 13, 2016): 4511–27. http://dx.doi.org/10.5194/acp-16-4511-2016.

Full text

Abstract:

Abstract. Organic aerosol is formed and transformed in atmospheric aqueous phases (e.g., cloud and fog droplets and deliquesced airborne particles containing small amounts of water) through a multitude of chemical reactions. Understanding these reactions is important for a predictive understanding of atmospheric aging of aerosols and their impacts on climate, air quality, and human health. In this study, we investigate the chemical evolution of aqueous secondary organic aerosol (aqSOA) formed during reactions of phenolic compounds with two oxidants – the triplet excited state of an aromatic carbonyl (3C∗) and hydroxyl radical (•OH). Changes in the molecular composition of aqSOA as a function of aging time are characterized using an offline nanospray desorption electrospray ionization mass spectrometer (nano-DESI MS) whereas the real-time evolution of SOA mass, elemental ratios, and average carbon oxidation state (OSC) are monitored using an online aerosol mass spectrometer (AMS). Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation equivalent to ∼ 2 h irradiation under midday winter solstice sunlight in Northern California. At later reaction times functionalization (i.e., adding polar oxygenated functional groups to the molecule) and fragmentation (i.e., breaking of covalent bonds) become more important processes, forming a large variety of functionalized aromatic and open-ring products with higher OSC values. Fragmentation reactions eventually dominate the photochemical evolution of phenolic aqSOA, forming a large number of highly oxygenated ring-opening molecules with carbon numbers (nC) below 6. The average nC of phenolic aqSOA decreases while average OSC increases over the course of photochemical aging. In addition, the saturation vapor pressures (C∗) of dozens of the most abundant phenolic aqSOA molecules are estimated. A wide range of C∗ values is observed, varying from < 10−20 µg m−3 for functionalized phenolic oligomers to > 10 µg m−3 for small open-ring species. The detection of abundant extremely low-volatile organic compounds (ELVOC) indicates that aqueous reactions of phenolic compounds are likely an important source of ELVOC in the atmosphere.

APA, Harvard, Vancouver, ISO, and other styles

32

Yu, L., J. Smith, A. Laskin, K. M. George, C. Anastasio, J. Laskin, A. M. Dillner, and Q. Zhang. "Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: competition among oligomerization, functionalization, and fragmentation." Atmospheric Chemistry and Physics Discussions 15, no. 20 (October 30, 2015): 29673–704. http://dx.doi.org/10.5194/acpd-15-29673-2015.

Full text

Abstract:

Abstract. Organic aerosol is formed and transformed in atmospheric aqueous phases (e.g., cloud and fog droplets and deliquesced airborne particles containing small amounts of water) through a multitude of chemical reactions. Understanding these reactions is important for a predictive understanding of atmospheric aging of aerosols and their impacts on climate, air quality, and human health. In this study, we investigate the chemical evolution of aqueous secondary organic aerosol (aqSOA) formed during reactions of phenolic compounds with two oxidants – the triplet excited state of an aromatic carbonyl (3C&ast;) and hydroxyl radical (•OH). Changes in the molecular composition of aqSOA as a function of aging time are characterized using an offline nanospray desorption electrospray ionization mass spectrometer (nano-DESI MS) whereas the real-time evolution of SOA mass, elemental ratios, and average carbon oxidation state (OSC) are monitored using an online aerosol mass spectrometer (AMS). Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation equivalent to ∼ 2 h irradiation under midday, winter solstice sunlight in northern California. At later reaction times functionalization (i.e., adding polar oxygenated functional groups to the molecule) and fragmentation (i.e., breaking of covalent bonds) become more important processes, forming a large variety of functionalized aromatic and open-ring products with higher OSC values. Fragmentation reactions eventually dominate the photochemical evolution of phenolic aqSOA, forming a large number of highly oxygenated open-ring molecules with carbon numbers (nC) below 6. The average nC of phenolic aqSOA decreases while average OSC increases over the course of photochemical aging. In addition, the saturation vapor pressures C&ast;) of dozens of the most abundant phenolic aqSOA molecules are estimated. A wide range of C&ast; values is observed, varying from < 10-20 μg m-3 for functionalized phenolic oligomers to > 10 μg m-3 for small open-ring species. The detection of abundant extremely low volatile organic compounds (ELVOC) indicates that aqueous reactions of phenolic compounds are likely an important source of ELVOC in the atmosphere.

APA, Harvard, Vancouver, ISO, and other styles

33

Fang, Ming, Joy H. Farnaby, Joseph W. Ziller, Jefferson E. Bates, Filipp Furche, and William J. Evans. "Isolation of (CO)1– and (CO2)1– Radical Complexes of Rare Earths via Ln(NR2)3/K Reduction and [K2(18-crown-6)2]2+ Oligomerization." Journal of the American Chemical Society 134, no. 14 (March 28, 2012): 6064–67. http://dx.doi.org/10.1021/ja211220r.

Full text

APA, Harvard, Vancouver, ISO, and other styles

34

Chumakov, Anton A., Oleg A. Kotelnikov, and Yuriy G. Slizhov. "OXIDATION OF FERRIC XYLENOL ORANGE CHELATES BY HYDROGEN PEROXIDE IN AQUEOUS SOLUTION: CONCEPTION OF OXYGEN SINGLET ATOMS GENERATION FROM HYDROGEN PEROXIDE." IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 61, no. 2 (January 29, 2018): 15. http://dx.doi.org/10.6060/tcct.20186102.5623.

Full text

Abstract:

We observed for the first time the reaction of oxidation of ferric xylenol orange chelates by hydrogen peroxide in aqueous solution. The reaction is accompanied with decoloration of the violet aqueous solution. Based on generally accepted conception, there is a process of free radical chain oxidation of indicator molecule in the solution. However, after investigating the final colorless solution by 1H NMR-spectroscopy we found the modified but not broken structure in which the initial hydrocarbon core remained mainly unchanged. We concluded that kind of reaction was an oxyfunctionalization by hydrogen peroxide versus free radical chain destruction. We argued steps of the reaction such as N-oxidation, Cope’s elimination, and certain rearrangements with possible products oligomerization. There was a need to explain the mechanism of interaction between the ferric iron ion and the hydrogen peroxide molecule and to argue the nature of intermediate reactive oxygen species. There is similarity between the ferric-catalyzed hydroperoxide xylenol orange oxidation and the peroxygenase-catalyzed biochemical oxyfunctionalization reactions. However, based on literature data and molecular orbital modeling, we proposed another mechanism of interaction between the ferric iron ion and the hydrogen peroxide molecule instead the tetravalent iron generation. Concretely, we proposed the hydrogen peroxide zwitter-ionization (isomerization to oxywater molecule) and subsequent intramolecular disproportionation with generation of a water molecule and a singlet oxygen atom as a reactive oxygen species. In this view, the iron ion oxidation state is unchanged during the reaction and remains ferric. An oxyfunctionalization of any organic substrate by hydrogen peroxide in the presence of ferric iron ions is promising approach in organic synthesis. However, the usage of organic ligands for ferric iron ions as components of catalysts is limited and requires only non-oxidizable compounds. On the other hand, one can choose an oxidation substrate as a ligand for ferric iron ions that is the formation of chelate complex of ferric catalyst with an organic substrate.Forcitation:Chumakov A.A., Kotelnikov O.A., Slizhov Yu.G. Oxidation of ferric xylenol orange chelates by hydrogen peroxide in aqueous solution: conception of oxygen singlet atoms generation from hydrogen peroxide. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 2. P. 15-22

APA, Harvard, Vancouver, ISO, and other styles

35

Johnson, Charles H. J., Thomas H. Spurling, and Graeme Moad. "Evolution of Molar Mass Distributions Using a Method of Partial Moments: Initiation of RAFT Polymerization." Polymers 14, no. 22 (November 18, 2022): 5013. http://dx.doi.org/10.3390/polym14225013.

Full text

Abstract:

We describe a method of partial moments devised for accurate simulation of the time/conversion evolution of polymer composition and molar mass. Expressions were derived that enable rigorous evaluation of the complete molar mass and composition distribution for shorter chain lengths (e.g., degree of polymerization, Xn = N < 200 units) while longer chains (Xn ≥ 200 units) are not neglected, rather they are explicitly considered in terms of partial moments of the molar mass distribution, μxN(P)=∑n=N+1∞nx[Pn] (where P is a polymeric species and n is its’ chain length). The methodology provides the exact molar mass distribution for chains Xn < N, allows accurate calculation of the overall molar mass averages, the molar mass dispersity and standard deviations of the distributions, provides closure to what would otherwise be an infinite series of differential equations, and reduces the stiffness of the system. The method also allows for the inclusion of the chain length dependence of the rate coefficients associated with the various reaction steps (in particular, termination and propagation) and the various side reactions that may complicate initiation or initialization. The method is particularly suited for the detailed analysis of the low molar mass portion of molar mass distributions of polymers formed by radical polymerization with reversible addition-fragmentation chain transfer (RAFT) and is relevant to designing the RAFT-synthesis of sequence-defined polymers. In this paper, we successfully apply the method to compare the behavior of thermally initiated (with an added dialkyldiazene initiator) and photo-initiated (with a RAFT agent as a direct photo-iniferter) RAFT-single-unit monomer insertion (RAFT-SUMI) and oligomerization of N,N-dimethylacrylamide (DMAm).

APA, Harvard, Vancouver, ISO, and other styles

36

King, S. M., T. Rosenoern, J. E. Shilling, Q. Chen, Z. Wang, G. Biskos, K. A. McKinney, U. Pöschl, and S. T. Martin. "Cloud droplet activation of mixed organic-sulfate particles produced by the photooxidation of isoprene." Atmospheric Chemistry and Physics Discussions 10, no. 1 (January 7, 2010): 213–44. http://dx.doi.org/10.5194/acpd-10-213-2010.

Full text

Abstract:

Abstract. The cloud condensation nuclei (CCN) properties of ammonium sulfate particles mixed with organic material condensed during the hydroxyl-radical-initiated photooxidation of isoprene (C5H8) were investigated in the continuous-flow Harvard Environmental Chamber. CCN activation curves were measured for organic particle mass concentrations of 0.5 to 10.0 μg m−3, NOx concentrations from under 0.4 ppbv up to 38 ppbv, particle mobility diameters from 70 to 150 nm, and thermodenuder temperatures from 25 to 100 °C. At 25 °C, the observed CCN activation curves were accurately described by a Köhler model having two internally mixed components, namely ammonium sulfate and secondary organic material. The modeled physicochemical parameters of the organic material were equivalent to an effective hygroscopicity parameter κORG of 0.10±0.03, regardless of the C5H8:NOx concentration ratio for the span of >200:0.4 to 50:38 (ppbv:ppbv). The volatilization curves (i.e., plots of the residual organic volume fraction against temperature) were also similar for the span of investigated C5H8:NOx ratios, suggesting a broad similarity of particle chemical composition. This suggestion was supported by limited variance at 25 °C among the particle mass spectra. For example, the signal intensity at m/z 44 (which can result from the fragmentation of oxidized molecules believed to affect hygroscopicity and CCN properties) varied weakly from 6 to 9% across the range of investigated conditions. In contradistinction to the results for 25 °C, conditioning up to 100 °C in the thermodenuder significantly reduced CCN activity. The altered CCN activity might be explained by chemical reactions (e.g., decomposition or oligomerization) of the secondary organic material at elevated temperatures. The study's results at 25 °C, in conjunction with the results of other chamber and field studies for a diverse range of conditions, suggest that a value of 0.10±0.05 for κORG is representative of both anthropogenic and biogenic secondary organic material. This finding supports the use of κORG as a simplified yet accurate general parameter to represent the CCN activation of secondary organic material in large-scale atmospheric and climate models.

APA, Harvard, Vancouver, ISO, and other styles

37

King, S. M., T. Rosenoern, J. E. Shilling, Q. Chen, Z. Wang, G. Biskos, K. A. McKinney, U. Pöschl, and S. T. Martin. "Cloud droplet activation of mixed organic-sulfate particles produced by the photooxidation of isoprene." Atmospheric Chemistry and Physics 10, no. 8 (April 27, 2010): 3953–64. http://dx.doi.org/10.5194/acp-10-3953-2010.

Full text

Abstract:

Abstract. The cloud condensation nuclei (CCN) properties of ammonium sulfate particles mixed with organic material condensed during the hydroxyl-radical-initiated photooxidation of isoprene (C5H8) were investigated in the continuous-flow Harvard Environmental Chamber. CCN activation curves were measured for organic particle mass concentrations of 0.5 to 10.0 μg m−3, NOx concentrations from under 0.4 ppbv up to 38 ppbv, particle mobility diameters from 70 to 150 nm, and thermodenuder temperatures from 25 to 100 °C. At 25 °C, the observed CCN activation curves were accurately described by a Köhler model having two internally mixed components, namely ammonium sulfate and secondary organic material. The modeled physicochemical parameters of the organic material were equivalent to an effective hygroscopicity parameter κORG of 0.10±0.03, regardless of the C5H8:NOx concentration ratio for the span of >200:0.4 to 50:38 (ppbv:ppbv). The volatilization curves (i.e., plots of the residual organic volume fraction against temperature) were also similar for the span of investigated C5H8:NOx ratios, suggesting a broad similarity of particle chemical composition. This suggestion was supported by limited variance at 25 °C among the particle mass spectra. For example, the signal intensity at m/z 44 (which can result from the fragmentation of oxidized molecules believed to affect hygroscopicity and CCN properties) varied weakly from 6 to 9% across the range of investigated conditions. In contradistinction to the results for 25 °C, conditioning up to 100 °C in the thermodenuder significantly reduced CCN activity. The altered CCN activity might be explained by chemical reactions (e.g., decomposition or oligomerization) of the secondary organic material at elevated temperatures. The study's results at 25 °C, in conjunction with the results of other chamber and field studies for a diverse range of conditions, suggest that a value of 0.10±0.05 for κORG is representative of both anthropogenic and biogenic secondary organic material. This finding supports the use of κORG as a simplified yet accurate general parameter to represent the CCN activation of secondary organic material in large-scale atmospheric and climate models.

APA, Harvard, Vancouver, ISO, and other styles

38

Wu, Zi-cong, Qiang Xue, Zhen-ling Zhao, Peng-jun Zhou, Qun Zhou, Zhen Zhang, Jian-ping Deng, et al. "Suppressive Effect of Huzhentongfeng on Experimental Gouty Arthritis: An In Vivo and In Vitro Study." Evidence-Based Complementary and Alternative Medicine 2019 (December 4, 2019): 1–15. http://dx.doi.org/10.1155/2019/2969364.

Full text

Abstract:

Background. Huzhentongfeng (HZTF) is an extract from four Chinese medical herbs for treating gout. This study aims to evaluate its antigout activity and preliminary explore its mechanism in vivo and in vitro. Methods. The rats were intragastrically administered with HZTF for 5 days and then injected 0.1 ml (10 mg) of MSU crystals to their joints for generating a gout model to analyze the paw volume and histopathology of joint synovial tissues of rats with different doses. We also investigated the antioxidant capacity of HZTF in vitro using indication including lipid peroxidation, DPPH·, and ABTS+ radical-scavenging capacity; besides, we used qRT-PCR to measure the effect of HZTF on interleukin (IL)-1β, caspase-1, NLRP3, and NQO1 expression in hydrogen peroxide-stimulated RAW264.7 macrophages and IL-1β, IL-6, and tumor necrosis factor (TNF)-α in MSU crystal-induced THP-1 monocytes. Confocal microscopy analysis was used to observe the dimerization of ASC adapter proteins. In addition, we also established quality standard of HZTF by using the high-performance liquid chromatography (HPLC) method. Results. HZTF could significantly suppress the paw swelling and neutrophil infiltration induced by MSU intra-articular injection in rats compared with the control group. HZTF also showed inhibition effects of inflammatory cytokines (IL-1β, IL-6, and TNF-α) secretion at 25.00 and 50.00 μg/ml in MSU-induced THP-1 cells but showed no effects of IL-1β, IL-6, and TNF-α mRNA expression in MSU-induced THP-1 cells. Furthermore, confocal microscopy analysis showed that HZTF could prevent the oligomerization of ASC. Moreover, HZTF also showed effects in cell-free and cell-base tests of antioxidant capacity. Conclusion. The results prove that HZTF possessed the potential preventive effect against gout arthritis, and the effect may be attributed to its preventing effect on neutrophil infiltration and proinflammatory cytokines secretion such as IL-1β, IL-6, and TNF-α which were caused by the activation of inflammasome.

APA, Harvard, Vancouver, ISO, and other styles

39

Wang, Kunpeng, and David Staack. "Electric production of high-quality fuels via electron beam irradiation under ambient conditions." Green Chemistry 24, no. 3 (2022): 1177–89. http://dx.doi.org/10.1039/d1gc03299b.

Full text

Abstract:

Collisions between high energy electrons and molecules effectively activate molecules (radicals) which may free pair and produce the desired products. Two conversion processes could be initiated by this mechanism: oligomerization and dimerization.

APA, Harvard, Vancouver, ISO, and other styles

40

Breton, Gary W., and James Alexander Bowron. "1-(4-{[3,5-bis({[3,5-Dimethyl-4-(4-methyl-3,5-dioxo-1,2,4-triazolidin-1-yl)-phenoxy]methyl})phenyl]methoxy}-2,6-dimethyl-phenyl)-4-methyl-1,2,4-triazolidine-3,5-dione." Molbank 2023, no. 1 (December 27, 2022): M1535. http://dx.doi.org/10.3390/m1535.

Full text

Abstract:

Appropriately substituted N-centered urazolyl radicals are capable of generating interesting cage-like structures upon forming N-N bonds. The radicals are generated by the oxidation of the corresponding NH urazole precursors. We synthesized a triurazole precursor that we hoped would dimerize through the formation of three N-N bonds to afford a large molecular cage. Unfortunately, the attempts at the oxidation of the urazoles to form urazolyl radicals instead only lead to random oligomerization, forming plastic-like materials rather than the desired cages.

APA, Harvard, Vancouver, ISO, and other styles

41

Ervens, B., and R. Volkamer. "Glyoxal processing outside clouds: towards a kinetic modeling framework of secondary organic aerosol formation in aqueous particles." Atmospheric Chemistry and Physics Discussions 10, no. 5 (May 11, 2010): 12371–431. http://dx.doi.org/10.5194/acpd-10-12371-2010.

Full text

Abstract:

Abstract. This study presents a modeling framework based on laboratory data to describe the kinetics of glyoxal reactions in aqueous aerosol particles that form secondary organic aerosol (SOA). Recent laboratory results on glyoxal reactions are reviewed and a consistent set of reaction rate constants is derived that captures the kinetics of glyoxal hydration and subsequent reversible and irreversible reactions in aqueous inorganic and water-soluble organic aerosol seeds to form (a) oligomers, (b) nitrogen-containing products, (c) photochemical oxidation products with high molecular weight. These additional aqueous phase processes enhance the SOA formation rate in particles compared to cloud droplets and yield two to three orders of magnitude more SOA than predicted based on reaction schemes for dilute aqueous phase (cloud) chemistry. The application of this new module in a chemical box model demonstrates that both the time scale to reach aqueous phase equilibria and the choice of rate constants of irreversible reactions have a pronounced effect on the atmospheric relevance of SOA formation from glyoxal. During day time a photochemical (most likely radical-initiated) process is the major SOA formation pathway forming ~5 μg m−3 SOA over 12 h (assuming a constant glyoxal mixing ratio of 300 ppt). During night time, reactions of nitrogen-containing compounds (ammonium, amines, amino acids) contribute most to the predicted SOA mass; however, the absolute predicted SOA masses are reduced by an order of magnitude as compared to day time production. The contribution of the ammonium reaction significantly increases in moderately acidic or neutral particles (5<pH<7). Reversible glyoxal oligomerization, parameterized by an equilibrium constant Kolig=1000 (in ammonium sulfate solution), contributes <1% to total predicted SOA masses at any time. Sensitivity tests reveal five parameters that strongly affect the predicted SOA mass from glyoxal: (1) time scales to reach equilibrium states (as opposed to assuming instantaneous equilibrium), (2) particle pH, (3) chemical composition of the bulk aerosol, (4) particle surface composition, and (5) particle liquid water content that is mostly determined by the amount and hygroscopicity of aerosol mass and to a lesser extent by the ambient relative humidity. Glyoxal serves as an example molecule, and the conclusions about SOA formation in aqueous particles can serve for comparative studies also of other molecules that form SOA as the result of multiphase chemical processing in aerosol water. This SOA source is currently underrepresented in atmospheric models; if included it is likely to bring SOA predictions (mass and O/C ratio) into better agreement with field observations.

APA, Harvard, Vancouver, ISO, and other styles

42

Eissa, Ahmed Samar Abd Elmoaty, Ossama Rasslan, Lamia Fouad, Fahim Hisham Abdelmajeed, and Amira Esmail Abdel-Hamid. "Nucleotide Oligomerization Domain-like receptor 4 (NLR4) Gene Expression and Interleukin 1-β (IL 1-β) Level in Urine Samples Before and After Intravesical BCG Therapy For Treatment of Bladder Cancer." Medical Immunology (Russia) 22, no. 6 (January 10, 2021): 1141–54. http://dx.doi.org/10.15789/1563-0625-nod-2101.

Full text

Abstract:

Bladder cancer is the 7th most commonly diagnosed cancer in males worldwide and the 11th when both genders are considered. Seventy five per cent of bladder cancer cases are non-muscle invasive bladder cancer (NMIBC). Bacillus Calmette–Gu rin (BCG) immunotherapy remains the standard intravesical agent for NMIBC. The exact mechanism by which BCG prevents recurrence is unknown. The aim of this study was to evaluate NLR4 gene expression and IL-1β as possible prognostic indicators for NMIBC recurrence and BCG treatment failure, and to detect the difference in their levels among muscle invasive bladder cancer (MIBC) and NMIBC that may aid in primary differentiation between cases. This study was conducted in 30 patients who had NMIBC and 17 patients who had MIBC. Urine samples were obtained in sterile cups before operation. From NMIBC cases, four more samples were obtained as mentioned below. Evaluation of NLR4 gene expression was performed in pre-surgical sample for MIBC and in 4 samples for NMIBC: pre-surgical sample, sample collected 4 hours after the 3rd dose of BCG instillation, and samples collected during follow up (3 and 6 months post-surgically). There was statistical significant increase in NLRP4 expression levels in NMIBC (CT=0.87±1.48) compared to MIBC (CT=2.82±2.07). As far as we searched, no published results were found regarding comparative gene expression levels between NMIBC and MIBC cases. Gene expression in recurrent cases was higher in pre-surgical urine samples than in non-recurrent cases. The expression level further increased up to 21 fold than the pre-surgical level in the sample taken after injection of the 3rd dose of BCG. This level decreased distinctly to become 1-fold increase over pre-surgical level at the 3rd month follow up then to only 0.9-fold at the 6th month. In non- recurrent cases, gene expression level started pre-surgically in much lower levels than those encountered in recurrent cases. There were 11-fold increase in expression level after 3rd dose of BCG instillation and then decreased to be 5.6 folds higher in the sample taken at 3rd month follow up than in presurgical samples. Gene expression further decreased to become 4.1 fold higher in samples taken at 6 month follow up than the pre-surgical levels. IL-1β levels were estimated for NMIBC and MIBC cases in urine samples pre-surgically and during BCG therapy in case of NMIBC before and 4 hours after the 3rd dose and during 3rd month follow-up of those cases for searching its possible use of for primary differentiation between NMIBC and MIBC, and also as a prognostic factor for possible recurrence in case of NMIBC cases. The level of IL-1β was generally higher in pre-surgical samples (0.62±0.12 pg/ml) when compared to its level before the 3rd dose of BCG induction therapy (0.53±0.13 pg/ml). Its level was distinctly higher four hours after administration of the 3rd dose BCG (1.96±0.62 pg/ml) than both previous levels. Levels decreased bellow pre-surgical level at 3rd month follow up (0.57±0.099 pg/ml). The levels of IL-1β estimated in samples collected four hours after the 3rd dose BCG was higher in cases that showed recurrence later on than non-recurrent cases. The levels decreased in both cases and became higher in non-recurrent cases (0.64±0.05 pg/ml) than in cases already developed recurrence at the 3rd month diagnosed during follow-up (0.45±0.05 pg/ml). To conclude, on following NLRP4 gene expression and IL-1β levels during BCG administration among recurrent and non-recurrent cases of thirty NMIBC cases, there was a significant statistical difference in both levels for the samples collected after the third dose BCG, being higher in patients who showed subsequent recurrence at the 3rd and 6th month of follow-up. If these preliminary reported findings will be confirmed in upcoming larger cohort’s studies, it could be promising in prognosis of such cases, with the possibility of early manipulation of individualized treatment schedule, keeping patients most probably prone to encounter recurrence safe from possible side effects of BCG therapy. The assessment of NLRP4 expression and IL-1β levels could help predict failure of BCG therapy, playing an appreciable role in early deciding radical surgery. When comparing NLRP4 expression and IL-1β levels between MIBC and NMIBC cases, increased values were noted among non-invasive ones. This finding may serve as a possible diagnostic tool, which represents a challenging issue. Hence, cut-off values for gene expression and cytokine level are to be specified.

APA, Harvard, Vancouver, ISO, and other styles

43

Ervens, B., and R. Volkamer. "Glyoxal processing by aerosol multiphase chemistry: towards a kinetic modeling framework of secondary organic aerosol formation in aqueous particles." Atmospheric Chemistry and Physics 10, no. 17 (September 2, 2010): 8219–44. http://dx.doi.org/10.5194/acp-10-8219-2010.

Full text

Abstract:

Abstract. This study presents a modeling framework based on laboratory data to describe the kinetics of glyoxal reactions that form secondary organic aerosol (SOA) in aqueous aerosol particles. Recent laboratory results on glyoxal reactions are reviewed and a consistent set of empirical reaction rate constants is derived that captures the kinetics of glyoxal hydration and subsequent reversible and irreversible reactions in aqueous inorganic and water-soluble organic aerosol seeds. Products of these processes include (a) oligomers, (b) nitrogen-containing products, (c) photochemical oxidation products with high molecular weight. These additional aqueous phase processes enhance the SOA formation rate in particles and yield two to three orders of magnitude more SOA than predicted based on reaction schemes for dilute aqueous phase (cloud) chemistry for the same conditions (liquid water content, particle size). The application of the new module including detailed chemical processes in a box model demonstrates that both the time scale to reach aqueous phase equilibria and the choice of rate constants of irreversible reactions have a pronounced effect on the predicted atmospheric relevance of SOA formation from glyoxal. During day time, a photochemical (most likely radical-initiated) process is the major SOA formation pathway forming ∼5 μg m−3 SOA over 12 h (assuming a constant glyoxal mixing ratio of 300 ppt). During night time, reactions of nitrogen-containing compounds (ammonium, amines, amino acids) contribute most to the predicted SOA mass; however, the absolute predicted SOA masses are reduced by an order of magnitude as compared to day time production. The contribution of the ammonium reaction significantly increases in moderately acidic or neutral particles (5 < pH < 7). Glyoxal uptake into ammonium sulfate seed under dark conditions can be represented with a single reaction parameter keffupt that does not depend on aerosol loading or water content, which indicates a possibly catalytic role of aerosol water in SOA formation. However, the reversible nature of uptake under dark conditions is not captured by keffupt, and can be parameterized by an effective Henry's law constant including an equilibrium constant Kolig = 1000 (in ammonium sulfate solution). Such reversible glyoxal oligomerization contributes <1% to total predicted SOA masses at any time. Sensitivity tests reveal five parameters that strongly affect the predicted SOA mass from glyoxal: (1) time scales to reach equilibrium states (as opposed to assuming instantaneous equilibrium), (2) particle pH, (3) chemical composition of the bulk aerosol, (4) particle surface composition, and (5) particle liquid water content that is mostly determined by the amount and hygroscopicity of aerosol mass and to a lesser extent by the ambient relative humidity. Glyoxal serves as an example molecule, and the conclusions about SOA formation in aqueous particles can serve for comparative studies of other molecules that form SOA as the result of multiphase chemical processing in aerosol water. This SOA source is currently underrepresented in atmospheric models; if included it is likely to bring SOA predictions (mass and O/C ratio) into better agreement with field observations.

APA, Harvard, Vancouver, ISO, and other styles

44

Wang, Xueli, See-Lok Ho, Chung-Yan Poon, Ting Yan, Hung-Wing Li, and Man Shing Wong. "Amyloid-β Aggregation Inhibitory and Neuroprotective Effects of Xanthohumol and its Derivatives for Alzheimer’s Diseases." Current Alzheimer Research 16, no. 9 (October 29, 2019): 836–42. http://dx.doi.org/10.2174/1567205016666190827123222.

Full text

Abstract:

Background: Xanthohumol has been reported to have cytoprotection through activation of Nrf2−ARE signaling pathway and; it has capability of scavenging free radicals, suggesting its potential for the prevention of neurodegeneration. However, the bio-incompatibility and blood-brain barrier impermeability of xanthohumol hindered its in vivo efficacy potential for treating Alzheimer’s disease (AD). Objective: We designed and prepared a series of xanthohumol derivatives to enhance the desirable physical, biological and pharmacological properties in particular the blood-brain barrier permeability for intervention of AD. Methods: We designed and synthesized a novel series of 9 xanthohumol derivatives. Their inhibitory effect on amyloid-β (1-42), Aβ1-42, oligomerization and fibrillation as well as neuroprotection against amyloid-β induced toxicities, were explored. Results: Among the 9 xanthohumol derivatives, some of them exhibited a moderate to high inhibitory effect on Aβ1-42 oligomerization and fibrillation. They were biocompatible and neuroprotective to the SH-SY5Y cells by reducing the ROS generation and calcium uploading that were induced by the amyloid- β. Importantly, two of the derivatives were found to be blood-brain barrier permeable showing promising potential for AD treatment. Conclusion: Two derivatives have been identified to be biocompatible, non-toxic, neuroprotective against Aβ-induced toxicities and blood-brain barrier permeable highlighting their promising potential as AD drug candidates for future clinical use.

APA, Harvard, Vancouver, ISO, and other styles

45

Ali, Feda E. A., Kevin J. Barnham, Colin J. Barrow, and Frances Separovic. "Metal-Catalyzed Oxidative Damage and Oligomerization of the Amyloid-β Peptide of Alzheimer’s Disease." Australian Journal of Chemistry 57, no. 6 (2004): 511. http://dx.doi.org/10.1071/ch04026.

Full text

Abstract:

The most common form of dementia in old age is Alzheimer’s disease (AD). The presence in the brain of senile plaque is the major pathological marker of AD. The plaques are primarily composed of aggregated amyloid-β peptide (Aβ). Aβ is a 40–42 amino acid peptide that is a proteolytic product derived from the β-amyloid precursor protein. The function of Aβ and the exact mechanism of Aβ aggregation and neurotoxicity are unclear. However, metal coordination by Aβ plays an important role in inducing aggregation and the generation of reactive oxygen species, which appears to be at least partially responsible for Aβ neurotoxicity. In this review we examine the role of copper and zinc ions in Aβ neurotoxicity, especially with regards to the generation of free radicals. We discuss the role of copper or zinc ions in oxidative damage and Aβ conformational changes and the relationship of these metals to AD.

APA, Harvard, Vancouver, ISO, and other styles

46

Gordon, D. A., G. A. Estrina, A. I. Bol’shakov, and A. I. Mikhailov. "Methyl acrylate and methyl methacrylate oligomerization initiated by radicals generated via low-temperature treatment with molecular chlorine." High Energy Chemistry 49, no. 3 (May 2015): 138–42. http://dx.doi.org/10.1134/s001814391503008x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Madhu, Azad, Myoseon Jang, and David Deacon. "Modeling the influence of chain length on secondary organic aerosol (SOA) formation via multiphase reactions of alkanes." Atmospheric Chemistry and Physics 23, no. 2 (January 27, 2023): 1661–75. http://dx.doi.org/10.5194/acp-23-1661-2023.

Full text

Abstract:

Abstract. Secondary organic aerosol (SOA) from diesel fuel is known to be significantly sourced from the atmospheric oxidation of aliphatic hydrocarbons. In this study, the formation of linear alkane SOA was predicted using the Unified Partitioning Aerosol Phase Reaction (UNIPAR) model that simulated multiphase reactions of hydrocarbons. In the model, the formation of oxygenated products from the photooxidation of linear alkanes was simulated using a nearly explicit gas kinetic mechanism. Autoxidation paths integrated with alkyl peroxy radicals were added to the Master Chemical Mechanism v3.3.1 to improve the prediction of low-volatility products in the gas phase and SOA mass. The resulting gas products were then lumped into volatility- and reactivity-based groups that are linked to mass-based stoichiometric coefficients. The SOA mass in the UNIPAR model is produced via three major pathways: partitioning of gaseous oxidized products onto both the organic and wet inorganic phases, oligomerization in the organic phase, and reactions in the wet inorganic phase (acid-catalyzed oligomerization and organosulfate formation). The model performance was demonstrated for SOA data that were produced through the photooxidation of a homologous series of linear alkanes ranging from C9–C15 under varying environments (NOx levels and inorganic seed conditions) in a large outdoor photochemical smog chamber. The product distributions of linear alkanes were mathematically predicted as a function of carbon number using an incremental volatility coefficient (IVC) to cover a wide range of alkane lengths. The prediction of alkane SOA using the incremental volatility-based product distributions, which were obtained with C9–C12 alkanes, was evaluated for C13 and C15 chamber data and further extrapolated to predict the SOA from longer-chain alkanes (≥ C15) that can be found in diesel. The model simulation of linear alkanes in diesel fuel suggests that SOA mass is mainly produced by alkanes C15 and higher. Alkane SOA is insignificantly impacted by the reactions of organic species in the wet inorganic phase due to the hydrophobicity of products but significantly influenced by gas–particle partitioning.

APA, Harvard, Vancouver, ISO, and other styles

48

Syafruddin, Saiful Effendi, Sheen Ling, Teck Yew Low, and M. Aiman Mohtar. "More Than Meets the Eye: Revisiting the Roles of Heat Shock Factor 4 in Health and Diseases." Biomolecules 11, no. 4 (March 31, 2021): 523. http://dx.doi.org/10.3390/biom11040523.

Full text

Abstract:

Cells encounter a myriad of endogenous and exogenous stresses that could perturb cellular physiological processes. Therefore, cells are equipped with several adaptive and stress-response machinery to overcome and survive these insults. One such machinery is the heat shock response (HSR) program that is governed by the heat shock factors (HSFs) family in response towards elevated temperature, free radicals, oxidants, and heavy metals. HSF4 is a member of this HSFs family that could exist in two predominant isoforms, either the transcriptional repressor HSFa or transcriptional activator HSF4b. HSF4 is constitutively active due to the lack of oligomerization negative regulator domain. HSF4 has been demonstrated to play roles in several physiological processes and not only limited to regulating the classical heat shock- or stress-responsive transcriptional programs. In this review, we will revisit and delineate the recent updates on HSF4 molecular properties. We also comprehensively discuss the roles of HSF4 in health and diseases, particularly in lens cell development, cataract formation, and cancer pathogenesis. Finally, we will posit the potential direction of HSF4 future research that could enhance our knowledge on HSF4 molecular networks as well as physiological and pathophysiological functions.

APA, Harvard, Vancouver, ISO, and other styles

49

CHAUHAN, Radha, and Shekhar C. MANDE. "Characterization of the Mycobacterium tuberculosis H37Rv alkyl hydroperoxidase AhpC points to the importance of ionic interactions in oligomerization and activity." Biochemical Journal 354, no. 1 (February 8, 2001): 209–15. http://dx.doi.org/10.1042/bj3540209.

Full text

Abstract:

An alkyl hydroperoxidase (AhpC) has been found frequently to be overexpressed in isoniazid-resistant strains of Mycobacterium tuberculosis. These strains have an inactivated katG gene encoding a catalase peroxidase, which might render mycobacteria susceptible to the toxic peroxide radicals, thus leading to the concomitant overexpression of the AhpC. Although the overexpressed AhpC in isoniazid-resistant strains of M. tuberculosis may not directly participate in isoniazid action, AhpC might still assist M. tuberculosis in combating oxidative damage in the absence of the catalase. Here we have attempted to characterize the AhpC protein biochemically and report its functional and oligomerization properties. The alkyl hydroperoxidase of M. tuberculosis is unique in many ways compared with its well-characterized homologues from enteric bacteria. We show that AhpC is a decameric protein, composed of five identical dimers held together by ionic interactions. Dimerization of individual subunits takes place through an intersubunit disulphide linkage. The ionic interactions play a significant role in enzymic activity of the AhpC protein. The UV absorption spectrum and three-dimensional model of AhpC suggest that interesting conformational changes may take place during oxidation and reduction of the intersubunit disulphide linkage. In the absence of the partner AhpF subunit in M. tuberculosis, the mycobacterial AhpC might use small-molecule reagents, such as mycothiol, for completing its enzymic cycle.

APA, Harvard, Vancouver, ISO, and other styles

50

Tritscher, T., J. Dommen, P. F. DeCarlo, P. B. Barmet, A. P. Praplan, E. Weingartner, M. Gysel, et al. "Volatility and hygroscopicity of aging secondary organic aerosol in a smog chamber." Atmospheric Chemistry and Physics Discussions 11, no. 3 (March 3, 2011): 7423–67. http://dx.doi.org/10.5194/acpd-11-7423-2011.

Full text

Abstract:

Abstract. The evolution of secondary organic aerosols (SOA) during (photo-)chemical aging processes was investigated in a smog chamber. SOA from 10–40 ppb α-pinene was formed during ozonolysis followed by aging with OH radicals. The particles' volatility and hygroscopicity (expressed as volume fraction remaining (VFR) and hygroscopicity parameter κ) were measured with a volatility and hygroscopicity tandem differential mobility analyzer (V/H-TDMA). These measurements were used as sensitive physical parameters to reveal the possible mechanisms responsible for the chemical changes in the SOA composition during aging: A change of VFR and/or κ during processing of atmospheric aerosol may occur either by addition of SOA mass (by condensation) or by an exchange of molecules in the SOA by other molecules with different properties. The former process increases the SOA mass by definition, while the latter keeps the SOA mass roughly constant and may occur either by heterogeneous reactions on the surface of the SOA particles, by homogeneous reactions like oligomerization or by an evaporation – gas-phase oxidation – recondensation cycle. Thus, when there is a substantial change in the aerosol mass with time, the condensation mechanism may be assumed to be dominant, while, when the mass stays roughly constant the exchange mechanism is likely to be dominant, a process termed ripening here. Depending on the phase of the experiment, an O3 mediated condensation, O3 mediated ripening, OH mediated condensation, and OH mediated ripening could be distinguished. During the O3 mediated condensation the particles volatility decreased (increasing VFR) while the hygroscopicity increased. Thereafter, in the course of O3 mediated ripening volatility continued to decrease, but hygroscopicity stayed roughly constant. After exposing the SOA to OH radicals an OH mediated condensation started with a significant increase of SOA mass. Concurrently, hygroscopicity and volatility increased. This phase was then followed by an OH mediated ripening with a decrease of volatility.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Radical Oligomerization'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles