Bibliografie tematiche / Free radicals (Chemistry)

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Letteratura scientifica selezionata sul tema "Free radicals (Chemistry)"

Autore: Grafiati
Pubblicato: 4 giugno 2021
Ultima modifica: 29 luglio 2024

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Articoli di riviste sul tema "Free radicals (Chemistry)"

1

Ionita, Petre. "The Chemistry of DPPH· Free Radical and Congeners". International Journal of Molecular Sciences 22, n. 4 (3 febbraio 2021): 1545. http://dx.doi.org/10.3390/ijms22041545.

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Since the discovery in 1922 of 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl stable free radical (DPPH·), the chemistry of such open-shell compounds has developed continuously, allowing for both theoretical and practical advances in the free radical chemistry area. This review presents the important, general and modern aspects of the chemistry of hydrazyl free radicals and the science behind it.
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Nagendrappa, G. "An appreciation of free radical chemistry Part 4. Free radicals in atmospheric chemistry". Resonance 10, n. 7 (luglio 2005): 61–72. http://dx.doi.org/10.1007/bf02867108.

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Nagendrappa, G. "An appreciation of free radical chemistry 6. Experiments involving free radicals". Resonance 10, n. 9 (settembre 2005): 79–84. http://dx.doi.org/10.1007/bf02896323.

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4

[Sbreve]imkovic, Ivan. "FREE RADICALS IN WOOD CHEMISTRY". Journal of Macromolecular Science, Part C: Polymer Reviews 26, n. 1 (febbraio 1986): 67–80. http://dx.doi.org/10.1080/07366578608081969.

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5

Halliwell, Barry. "The Chemistry of Free Radicals". Toxicology and Industrial Health 9, n. 1-2 (gennaio 1993): 1–21. http://dx.doi.org/10.1177/0748233793009001-203.

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6

Pryor, W. A. "Free radicals in organic chemistry". Free Radical Biology and Medicine 21, n. 2 (gennaio 1996): 253–54. http://dx.doi.org/10.1016/0891-5849(96)90038-6.

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Murphy, John A. "Free radicals in synthesis. Clean reagents affording oxidative or reductive termination". Pure and Applied Chemistry 72, n. 7 (1 gennaio 2000): 1327–34. http://dx.doi.org/10.1351/pac200072071327.

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Abstract (sommario):
Neurotoxic organotin reagents currently play a key role in radical chemistry. As a result, this is an important area for development of new clean replacement reactions. The pharmaceutical industry in particular has had to avoid use of radical methodology for the formation of carbon_carbon bonds for this reason. With the current dawn in green chemistry, a host of new clean radical methods is beginning to flourish. Our aim has been to develop new nontoxic methodology for carbon_carbon bond formation by radical chemistry, which would provide either reductive termination (giving a hydrogen atom to the ultimate radical, as happens with tributyltin hydride), or oxidative functionalization, installing a useful polar group at the site of the ultimate radical. Two methods for effecting radical reactions in an environmentally friendly way are presented: (i) The tetrathiafulvalene (TTF)-mediated radical-polar crossover reaction converts arenediazonium salts to aryl radicals, which have sufficient lifetime to cyclize onto alkenes—the resulting alkyl radicals couple with TTF+• to afford sulfonium salts which, in turn, undergo solvolysis to alcohols, ethers or amides. The method provides the key step in a synthesis of (±)-aspidospermidine. (ii) Hypophosphite salts and hypophosphorous acid, on the other hand, form C_C bonds with reductive termination. These economical reagents afford radicals efficiently, starting from aryl iodides, alkyl bromides, and alkyl iodides, and give very easy separation of products from by-products.
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Lemaire, M. T. "Recent developments in the coordination chemistry of stable free radicals". Pure and Applied Chemistry 76, n. 2 (1 gennaio 2004): 277–93. http://dx.doi.org/10.1351/pac200476020277.

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Several advances in the coordination chemistry of stable free-radical species over the past six years are documented in this review article. Specifically, a number of recent reports focused on the coordination chemistry of chelating nitroxide ligands are highlighted, with an emphasis on enhanced magnetic or optical properties in these complexes. Furthermore, very intriguing recent magnetic and optical studies with one-dimensional nitroxide chain complexes (new "Glauber" chains and chiral magnets) are also discussed. The verdazyls are another family of stable radicals whose coordination chemistry was literally unexplored prior to 1997. A summary of recent reports discussing metal-verdazyl coordination complexes is also presented, followed by an eye to the future of stable radical design and the coordination chemistry of these interesting molecules.
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Yañez Jaramillo, Lina M., Joy H. Tannous e Arno de Klerk. "Persistent Free Radicals in Petroleum". Processes 11, n. 7 (11 luglio 2023): 2067. http://dx.doi.org/10.3390/pr11072067.

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The persistent free radical content in petroleum is of the order 1018 spins/g (1 μmol/g), with higher and lower values found depending on origin and in different distillation fractions. The field of persistent free radicals in petroleum was reviewed with the aim of addressing and explaining apparent inconsistencies between free radical persistence and reactivity. The macroscopic average free radical concentration in petroleum is persistent over geological time, but individual free radical species in petroleum are short-lived and reactive. The persistent free radical concentration in petroleum can be explained in terms of a dynamic reaction equilibrium of free radical dissociation and association that causes a finite number of species at any given time to be present as free radicals. Evidence to support this description are observed changes in free radical concentration related to change in Gibbs free energy when the bulk liquid properties are changed and responsiveness of free radical concentration to dynamic changes in temperature. Cage effects, solvent effects, steric protection, and radical stabilization affect free radical reaction rate but do not explain the persistent free radical concentration in petroleum. The difference between persistent free radicals in straight-run petroleum and converted petroleum is that straight-run petroleum is an equilibrated mixture, but converted petroleum is not at equilibrium and the free radical concentration can change over time. Based on the limited data available, free radicals in straight-run petroleum appear to be part of the compositional continuum proposed by Altgelt and Boduszynski. Persistent free radical species are partitioned during solvent classification of whole oil, with the asphaltenes (n-alkane insoluble) fraction having a higher concentration of persistent free radicals than maltenes (n-alkane soluble) fraction. Attempts to relate persistent free radical concentration to petroleum composition were inconclusive.
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Van Lente, Frederick. "Free Radicals". Analytical Chemistry 65, n. 12 (15 giugno 1993): 374–77. http://dx.doi.org/10.1021/ac00060a601.

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Tesi sul tema "Free radicals (Chemistry)"

1

Qureshi, Tariq. "Spin chemistry". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365292.

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Mills, Tim. "Studies in free radical chemistry". Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342465.

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Imrie, Christopher. "The chemistry of free radicals containing a ferrocenyl moiety". Thesis, University of Strathclyde, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390393.

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梁韻詩 e Wan-sze Leung. "High resolution spectroscopy of free radicals". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31237319.

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Leung, Wan-sze. "High resolution spectroscopy of free radicals /". Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19737610.

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Crockett, Rowena. "Generation of free radicals from heterocyclic compounds". Thesis, University of Aberdeen, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290239.

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Tetrazolinones, thiatriazole 1-oxides and meso-ionic oxatriazoles were investigated as sources of free radicals. Mono-substituted tetrazolinones decomposed at their melting points. Nitrosation and nitration of the tetrazolinone ring was unsuccessful, although alkoxyalkylation of the ring took place in ether in the presence of nitrosomium and nitronium tetrafluoroborate. The tetrazolinone ring was photolytically unstable, and both eliminated nitrogen and cycloreverted. γ-irradiation of the naphthyl deivative caused cleavage of the nitrogen-hydrogen bond to give a radical which was identified by spin trapping and esr spectroscopy. Thiatriazolyl radicals were generated from thiatriazol-1-ium salts by reduction over sodium metal. Deuterium and nitrogen-15 labelled diphenylthiatriazolium salts were prepared in the reaction between thiatriazole 1-oxides and phosphorus pentachloride or pentabromide. This allowed an unambiguous assignment of the nitrogen and hydrogen hyperfine coupling constants in the esr spectrum of the unlabelled thiatriazolyl radical. X-ray crystallographic analysis was carried out on single crystals of 2,4-diphenyl-2,5-dihydro-1,2,3,5-thiatriazol 1-oxide and 2,4-diphenyl-2H-1,2,3,5-thiatriazol-1-ium bromide. Meso-ionic oxatriazolones were relatively stable to thermolysis, whereas oxatriazolimines decomposed at their melting points. The oxatriazolones decomposed on photolysis via two mechanistic pathways, while the oxatriazol-imines were resistant to photolysis. Radicals were generated by γ-irradiation and oxidation via decomposition of the heterocyclic ring. Electrochemical reduction of nitrophenyl derivatives allowed an investigation of radicals in which the heterocyclic ring was remote from the radical centre. Photochemical reaction between the nitrophenyl derivatives of the oxatriazole and tetrahydrofuran produced oxy-nitroxide radicals which were realatively long-lived and in which the heterocyclic ring was intact. The rates of hydrolysis and crystal structures of three diacetylazolinones, including diacetyltetrazolinone were investigated with the aim of determining whether a correlation existed between bond lengths and reactivity. The relative rates of hydrolysis were found to be independent of the bond lengths. However a correlation was found between the rates of hydrolysis and the acidity of the unsubstituted azolinones.
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Robles, Eric San Jose. "Electronic spectroscopy of jet-cooled organometallic free radicals /". The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487776801323524.

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Towle, Jonathan Peter. "The LMR spectra of free radicals". Thesis, University of Oxford, 1992. http://ora.ox.ac.uk/objects/uuid:7ac8e9e4-33e8-428b-962d-943bf07d5f94.

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Laser Magnetic Resonance (LMR) is a very sensitive, accurate and high resolution spectroscopic technique. Transitions of paramagnetic species are brought into coincidence with a fixed frequency laser using Zeeman tuning. Three different LMR spectrometers are described, two of which use the CO laser as a radiation source and the other used optically pumped far-infrared lasers. These LMR spectrometers have been used to study four radicals, germanium hydride (GeH), tellurium deuteride (TeD), iron hydride (FeH) and iron deuteride (FeD). Transitions in the fundamental and first hot bands of the GeH radical have been detected by CO LMR. The transitions occur within both 2Π1andfrasl;2 and 2Π3andfrasl;2 manifolds. These data have been fitted with previously published data for GeH and GeD to determine the parameters of a single model effective Hamiltonian which describes all naturally occurring isotopomers. Details of the Hamiltonian are given. The same Hamiltonian was used to model transitions in the fundamental and first two hot bands of the TeD radical that were also recorded using CO LMR. Resonances from the seven most abundant isotopomers, including the two with I = ½, have been identified. Seven transitions in the fundamental band of FeH have been observed using Faraday CO LMR. Due to the complicated electronic structure for FeH it is not possible to model these data using a single model effective Hamiltonian. It has been possible to fit the parameters of a second order Zeeman expression to these FeH data and so determine accurate zerofield transition wavenumbers for six of these transitions. Pure rotational transitions in the ground state of FeD have been observed using FIR LMR. As for FeH the parameters of second order Zeeman expressions can be fitted to these transitions and zero field wavenumbers determined.
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Hon, Nyok-Sai. "Formation, characterization, and chemical reactions of free radicals in lignin". Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/54437.

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Free radicals are produced in lignin during mechanical treatment and irradiation with light of various wavelengths. During mechanical treatment, the lignin macromolecule is degraded severely as revealed by ESR and viscosity measurements. Several types of mechano-radicals are produced in lignin during the mechanical process. Among these the phenoxy radicals are rather stable, where carbon-radicals are labile at ambient conditions. Transient mechano-radicals reacted readily with oxygen molecules to produce peroxy radicals even at 77°K, but they decayed rapidly at ambient temperature. Photodegradation of lignin was observed when macromolecule was irradiated with light of λ<3500 Å as revealed by ESR, viscosity, and weight loss. Phenoxy radicals are the predominant intermediates in the photoirradiated lignin as shown by ESR studies. Elimination of side chains of lignin phenyl propane units took effect in α-carbonyl group bearing molecules. By contrast, β aryl ether substituents adjacent to α-carbonyl groups caused ether cleavage under identical conditions of photoirradiation. This is attributed to energy transferred from excited α-carbonyl groups to the ether bonds. The α-carbonyl groups also functioned as photosensitizers accelerating photochemical reactions of lignin. Termination and decomposition reactions of mechano-radicals and photoinduced free radicals in lignin ultimately lead to the formation of para- and ortho-quinones, carbonyl groups, and double bonds which cause the color of lignin. These potential choromophoric groups can be partially removed from lignin by using ultraviolet light of λ> 4000 Å; and they can be completely removed by irradiation of lignin in the presence of dioxane-water with light of λ>3500 Å. Experimental findings suggest chat chromophoric groups in lignin were being trapped or blocked by dioxanyl radicals resulting in brightening. However, the photoreduced lignin-adduct suffered color reversion. This adverse effect can be prevented by using 2-hydroxy-4-methoxy-benzophenone as a photostabilizer. The feasibility of applying photoreduction techniques to high- yield pulps was demonstrated. However, optimal experimental conditions for photoreduction of lignin in high-yield pulps have not been established yet.
Ph. D.
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Wood, Geoffrey Paul Farra. "Theoretical Investigations of Radical-Mediated Protein Oxidation". Thesis, The University of Sydney, 2006. http://hdl.handle.net/2123/1413.

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This thesis primarily details the application of high-level ab initio quantum chemistry techniques in order to understand aspects of free-radical mediated protein oxidation. Traditionally, product analysis and electron paramagnetic resonance (EPR) spectroscopy are the primary means for elucidating the chemistry of protein oxidation. However, in experiments involving relatively small proteins reacting with a controlled radical-flux, a vast array of compounds can be produced, which are often difficult to analyse. Quantum chemical techniques on the other hand, can calculate the properties of any particular species directly, without suffering from the problems associated with experiment, such as side-reactions and chain processes. The results presented in this thesis are aimed at elucidating mechanistic details of protein oxidation, which might otherwise be difficult to probe experimentally. Chapter 1 gives an overview of the free-radical hypothesis of disease and ageing. Protein-derived radicals can undergo a variety of reactions, with the particular reaction that occurs depending on numerous aspects. Many types of reactions have been identified through radiolysis experiments of amino acids, and these are detailed in this chapter. In addition, the key reactive species are characterized and their different chemistries explained. Chapter 2 details the theoretical tools used throughout this thesis. Species with unpaired electrons (radicals) present unique problems for quantum chemistry to handle, thus an appropriate choice of theoretical technique is needed. The approach taken in this thesis is to use high-level compound methods, many of which have been directly formulated to give improved results for radical species, to provide benchmark quality results by which other less demanding techniques can be assessed. During the course of this study, it became apparent there was a void in the armoury of tools that could be used for the theoretical chemistry calculations. Chapter 3 details the formulation of a new tool in an attempt to fill this gap. Historically, the formulation of this new procedure came after much of the work in this thesis had been carried out. Thus, for the study of many of the reactions of this thesis the new method has not been used. However, it is most appropriate to place its formulation after summarizing the current status of techniques in common use today. Chapters 4 and 5 detail computations carried out on models of peptides containing backbone carbon- and nitrogen-centered radicals. A number of different theoretical techniques are used in these chapters, ranging from the highly accurate and computationally intensive to the less reliable and less demanding. The highly accurate techniques are used to gauge the accuracy of the other less demanding theoretical techniques so that the latter can be used with confidence in larger systems. Not only is the choice of theoretical technique important but also the judicious choice of model is essential. With this in mind, models are incrementally built until convergence of the particular property of interest is reached. Chapters 6 and 7 detail the calculations of β-scission reactions of alkoxyl radicals, which are a particular class of reaction known to occur on peptide backbones. Alkoxyl radicals are particularly difficult for theory to describe correctly. Therefore, Chapter 6 extensively assesses and then identifies the theoretical methods needed to portray them. Chapter 7 uses the techniques identified in the previous chapter in order to predict how the preference for a particular type of β-scission reaction changes.
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Libri sul tema "Free radicals (Chemistry)"

1

Perkins, M. John. Radical chemistry. New York: Ellis Horwood, 1994.

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Walling, Cheves. Fifty years of free radicals. Washington, DC: American Chemical Society, 1995.

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Paulauskas, Irena O. Radical polymerization: New developments. Hauppauge, N.Y: Nova Science Publishers, 2011.

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A, Lund, e Rhodes Christopher J, a cura di. Radicals on surfaces. Dordrecht: Kluwer Academic Publishers, 1995.

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Francesco, Minisci, North Atlantic Treaty Organization. Scientific Affairs Division. e NATO Advanced Research Workshop on Free Radicals in Biology and Environment (1996 : Bardolino, Italy), a cura di. Free radicals in biology and environment. Dordrecht: Kluwer, 1997.

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6

Leffler, John E. An introduction to free radicals. New York: Wiley, 1993.

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7

Postigo, J. Alberto. Organic radical reactions in water and alternative media. Hauppauge, N.Y: Nova Science Publishers, 2011.

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A, Punchard Neville, e Kelly Frank J, a cura di. Free radicals: A practical approach. Oxford: IRL Press at Oxford University Press, 1996.

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P, Yu Byung, a cura di. Free radicals in aging. Boca Raton: CRC Press, 1993.

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Catherine, Rice-Evans, a cura di. Free radicals: Chemistry, pathology and medicine. London: Richelieu Press, 1988.

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Capitoli di libri sul tema "Free radicals (Chemistry)"

1

Dolbier, William R. "Fluorinated free radicals". In Organofluorine Chemistry, 97–163. Berlin, Heidelberg: Springer Berlin Heidelberg, 1997. http://dx.doi.org/10.1007/bfb0119266.

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Lappert, M. F. "Aspects of Organometallic Free Radical Chemistry". In Organic Free Radicals, 101–2. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-73963-7_50.

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Scaiano, J. C. "Two Photon Processes in Free Radical Chemistry". In Organic Free Radicals, 183–84. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-73963-7_91.

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de Montellano, Paul R. Ortiz. "Free Radicals in the Catalytic Chemistry of Hemoproteins". In Organic Free Radicals, 151. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-73963-7_75.

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Baumann, U., e M. Schmittel. "Solution Chemistry of Keto and Enol Cation Radicals". In Organic Free Radicals, 189. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-73963-7_94.

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Mattay, J. "Radical Ions and Photochemical Charge Transfer Phenomena in Organic Chemistry". In Organic Free Radicals, 119–20. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-73963-7_59.

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Niki, Etsuo. "Free Radicals in Chemistry and Biochemistry". In Food and Free Radicals, 1–10. Boston, MA: Springer US, 1997. http://dx.doi.org/10.1007/978-1-4899-1837-6_1.

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Joseph, Jomy, e Andrey P. Antonchick. "Free Radicals in Heterocycle Functionalization". In Topics in Heterocyclic Chemistry, 93–149. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/7081_2017_8.

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Stein, Stephen E. "Free Radicals in Coal Conversion". In Chemistry of Coal Conversion, 13–44. Boston, MA: Springer US, 1985. http://dx.doi.org/10.1007/978-1-4899-3632-5_2.

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Platt, U., B. Alicke, R. Dubois, A. Geyer, A. Hofzumahaus, F. Holland, M. Martinez et al. "Free Radicals and Fast Photochemistry during BERLIOZ". In Tropospheric Chemistry, 359–94. Dordrecht: Springer Netherlands, 2002. http://dx.doi.org/10.1007/978-94-010-0399-5_15.

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Atti di convegni sul tema "Free radicals (Chemistry)"

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Pfaendtner, Jim, Linda J. Broadbelt e Q. Jane Wang. "Quantum Chemical Studies of Free-Radical, Hindered Phenol Stabilizers". In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-64007.

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Quantum chemical investigations of the action of hindered phenol radical stabilizers in lubricant degradation chemistry have been completed. We are currently developing the first mechanistic models of lubricant degradation with the aim of including the chemistry of additives such as radical stabilizers that are found in commercial lubricant formulations. A key component of development of these models is obtaining reliable estimates of the kinetic parameters for all reactions. Specifically, rate constants and structure-reactivity correlations for the interaction of hindered phenol radical stabilizers with small peroxy radicals have been sought using quantum chemistry and transition state theory. Accurate thermodynamic properties of hindered phenol radical stabilizers and structure-reactivity relationships have been obtained. Such relationships provide researchers the ability to quickly estimate reactivity of hindered phenol stabilizers using their thermodynamic properties and therefore may be useful in additive design.
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Hudgens, Jeffrey W., e David S. Green. "Degenerate Four Wave Mixing Spectroscopy of Free Radicals in Low-Pressure Plasmas". In Modern Spectroscopy of Solids, Liquids, and Gases. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/msslg.1995.ssab2.

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Four wave mixing spectroscopies offer new ways to measure chemical species in extremely hostile environments. Among the most demanding of these applications is the measurement of radical chemistry within plasmas. Most plasmas are highly luminous and are characterized by steep gradients in temperature and concentration. These hostile properties thwart fluorescence and absorption diagnostics. In addition, in many useful plasma reactors the electrodes and associated electronics impose cumbersome optical geometries. We are using degenerate four-wave mixing (DFWM) spectroscopy to sidestep these impediments and to provide sensitive and spatially resolved measurements of concentration and temperature. In conjunction with computer simulations this data will lead to a better understanding of fundamental chemistry within plasma environments. In this paper we describe proof-of-principal experiments that use NH radical spectra to profile the evolution of gas mixtures containing ammonia, hydrogen (or fluorine) and argon passed through a microwave discharge. We will also present data from similar experiments in which hydrocarbon radicals are the important reaction intermediates produced by the plasma chemistry.
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Moore, C. B., R. G. Bergman, I.-C. Chen, D. C. Darwin, H. S. Johnston, Y. Guo, E. P. Wasserman e A. T. Young. "Infrared flash kinetic spectroscopy of free radicals". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.thr1.

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Two IR flash kinetic spectrometers are described. Both use nanosecond pulsed UV lasers to produce high concentrations of reactive species. These are then probed by tunable cw IR lasers. High-resolution spectra of singlet and triplet states of CH2 and of HCO are presented. Measurements of reaction rates and of product quantum yields are described for several reactions important in atmospheric and combustion chemistry with particular emphasis on the dynamics of radical-radical reactions. The reactivity of the coordinatively unsaturated organometallic intermediate cyclopentadienylcobaltmonocarbonyl (CpCoCO) to a variety of ligands is studied in both gas and liquid phases.
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Gámez-Montaño, Rocío, Pedro A. Cano e Alejandro Islas-Jácome. "Synthesis of spiro-cyclohexendienone-gamma-lactams via free-radicals and study of thermal regioselective spirocyclization". In The 21st International Electronic Conference on Synthetic Organic Chemistry. Basel, Switzerland: MDPI, 2017. http://dx.doi.org/10.3390/ecsoc-21-04779.

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Mulyani, Hani, Yati Maryati, Euis Filailla, Agustine Susilowati, Puspa D. N. Lotulung e Aspiyanto Aspiyanto. "Benefits of fermented beet (Beta vulgaris L.) against digestive infection Escherichia coli and free radicals prevention". In PROCEEDINGS OF THE 5TH INTERNATIONAL SYMPOSIUM ON APPLIED CHEMISTRY 2019. AIP Publishing, 2019. http://dx.doi.org/10.1063/1.5134589.

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Wu, Hanqing. "Organic and Drug Molecules Spin Traps and Free Radicals Multi-frequency EPR Spectra Simulation by Fast Fourier Transform (FFT)". In The 1st International Electronic Conference on Synthetic Organic Chemistry. Basel, Switzerland: MDPI, 1997. http://dx.doi.org/10.3390/ecsoc-1-02058.

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7

Wylde, Jonathan J. "The Challenges Associated with Reaction Products Left in Scale Inhibitor Species after Radical Polymerization". In SPE International Oilfield Scale Conference and Exhibition. SPE, 2014. http://dx.doi.org/10.2118/spe-169778-ms.

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Abstract (sommario):
Abstract The use of polymeric scale inhibitors has been ubiquitously accepted by the oil and gas industry for many years. There are many benefits to the use of this type of chemistry that include aspects such as high performance, scale species selectivity, enhanced brine compatibility, favorable environmental properties and high thermal stability. A very common way to manufacture polymeric scale inhibitors is via free radical polymerization. Here an initiator is used to propagate the generation of free radicals from a species, such as hydrogen peroxide. The initiator chemistry can be very varied and usually comprises different types of transition metal salts, hypophosphite or persulfate species. Different monomer units can be polymerized using different initiator and free radical species to yield the same polymer. However, subtle differences can result, including poly-dispersity, average molecular weight and different residual composition. The implications for the end user of the chemistry can be profound regarding performance differences in aspects such as detectability, compatibility, thermal stability and sometimes even scale inhibition and adsorption efficacy. A case study has been presented where a very commonly used sulfonated copolymer species from four different sources was evaluated in a whole host of compatibility and performance tests. The different routes used different combinations of hydrogen peroxide and transition metal initiator or persulfate/hypophosphite combinations as the free radical source. There were major differences seen in the compatibility of these products with different scale inhibitors and then in performance. The tests performed highlighted the differences that can occur between the different radical polymerization synthetic routes mentioned above. The conclusions show that there are many benefits to being able to control the manufacturing process of scale inhibitor species in order to ensure the full composition is understood and can be quantified. The benefits to owning the supply chain are highlighted and lead to not only better control of quality and cost but, more importantly, to the overall risk reduction for the end user in the end use application.
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8

Werle, Peter. "Fast sub-ppb Trace Gas Detection by Infrared Diode-Laser FM-Spectroscopy". In Modern Spectroscopy of Solids, Liquids, and Gases. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/msslg.1995.ssaa5.

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Sensitivity, specifity, high time resolution and cost effective simultaneous measurements of several components using operational systems are the main requirements for atmospheric research and air pollution monitoring1 Tunable diode lasers absorption spectroscopy (TDLAS) is increasingly being used to measure atmospheric trace gas concentrations down to low ppb-levels (10-9 volume mixing ratio). Semiconductor lead salt diode lasers give access to the mid infrared spectral region, where the most important atmospheric constituents have strong rotational vibrational absorption bands. The application of high frequency modulation (FM) schemes can further improve sensitivity and detection speed of modern instrumentation. Operational instruments are needed for fast airborne measurements and sensitive and reliable field measurements. The great number of gaseous pollutants and their generally low variable concentrations with large local differences pose challenging requirements to analytical techniques. Research in atmospheric chemistry requires highly sensitive techniques for measurement of concentrations of free radicals which determine the rate of photochemical destruction of most atmospheric pollutants.
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9

Fackler, K. Boyd, Megan Karalus, Igor Novosselov, John Kramlich e Philip Malte. "NOx Behavior for Lean-Premixed Combustion of Alternative Gaseous Fuels". In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42069.

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Gaseous fuels other than pipeline natural gas are of interest in high-intensity premixed combustors (e.g., lean-premixed gas turbine combustors) as a means of broadening the range of potential fuel resources and increasing the utilization of alternative fuel gases. An area of key interest is the change in emissions that accompanies the replacement of a fuel. The work reported here is an experimental and modeling effort aimed at determining the changes in NOx emission that accompany the use of alternative fuels. Controlling oxides of nitrogen (NOx) from combustion sources is essential in non-attainment areas. Lean-premixed combustion eliminates most of the thermal NOx emission, but is still subject to small, though significant amounts of NOx formed by the complexities of free radical chemistry in the turbulent flames of most combustion systems. Understanding these small amounts of NOx, and how their formation is altered by fuel composition, is the objective of this paper. We explore how NOx is formed in high-intensity, lean-premixed flames of alternative gaseous fuels. This is based on laboratory experiments and interpretation by chemical reactor modeling. Methane is used as the reference fuel. Combustion temperature is maintained the same for all fuels so that the effect of fuel composition on NOx can be studied without the complicating influence of changing temperature. Also, the combustion reactor residence time is maintained nearly constant. When methane containing nitrogen and carbon dioxide (e.g., landfill gas) is burned, NOx increases since the fuel/air ratio is enriched in order to maintain combustion temperature. When fuels of increasing C/H ratio are burned leading to higher levels of carbon monoxide (CO) in the flame, or when the fuel contains CO, the free radicals made as the CO oxidizes cause the NOx to increase. In these cases, the change from high-methane natural gas to alternative gaseous fuel causes the NOx to increase. However, when hydrogen is added to the methane, the NOx may increase or decrease, depending on the combustor wall heat loss. In our work, in which combustor wall heat loss is present, hydrogen addition deceases the NOx. This observation is compared to the literature. Additionally, minimum NOx emission is examined by comparing the present results to the findings of Leonard and Stegmaier.
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10

Lulan, Theodore Y. K., Sri Fatmawati, Mardi Santoso e Taslim Ersam. "Free radical scavenging activity of Artocarpus champeden extracts". In THE 3RD INTERNATIONAL SEMINAR ON CHEMISTRY: Green Chemistry and its Role for Sustainability. Author(s), 2018. http://dx.doi.org/10.1063/1.5082460.

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Rapporti di organizzazioni sul tema "Free radicals (Chemistry)"

1

Lampe, F. W. The free-radical and ion chemistry of volatile silanes, germanes and phosphines. Office of Scientific and Technical Information (OSTI), gennaio 1990. http://dx.doi.org/10.2172/6290400.

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2

Lampe, F. W. The free-radical and ion chemistry of silanes, germanes, phosphines, and related compounds. Final report, 1965--1994. Office of Scientific and Technical Information (OSTI), dicembre 1995. http://dx.doi.org/10.2172/135060.

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