Radical-trapping agent

The half life for NO in cellular systems ranges from 5—30 seconds. Superoxide, hemoglobin, and other radical trapping agents remove NO after it has been formed. 

Tabic 3,11 Radical Trapping Agents for Studying Initiation... 

The (a-sulfanylalkyl)phosphonates and their difluorinated derivatives are also, by easy radical cleavage of the C-S bond, useful precursors of phospho-nomethyl or phosphonodifluoromethyl radicals, which can be added to double bonds and so, introduced in a variety of structures. Besides, the use of phospho-nodithioformates as radical trapping agents and their use as RAFT reagent for controlled polymerization open a new interesting field of appHcation for these dithioesters. 

Pharmacologic neuroprotection, which might be expected to prevent tissue necrosis or apoptosis until tissue reperfusion can be achieved with rt-PA, is a theoretically attractive adjunct to rt-PA treatment. Despite positive studies in animals, all evaluations of neuroprotective agents in humans have failed. Most recently, the promising initial results for intravenous NXY-059, a ffee-radical-trapping agent, were not replicated in a confirmatory phase III trial (unpublished data). 

Activation rate constants (k) in ATRP/ATRA are typically determined from model studies in which copper complex is reacted with alkyl halide in the presence of radical trapping agents such as TEMPO [127,128,129], Rates are determined by monitoring the rate of disappearance of alkyl halide in the presence of large excess of the activator (Cu X/L) and TEMPO. Under such pseudo-first order conditions, the activation rate constant can be calculated ln([RX]0/[RX]() vs.t plots (slope =-k) Cu C/... 

Stable radicals such as 1 are commonly used as the radical trapping agents and inhibitors or modifiers for polymerization. In the reaction of 1 with vinyl monomers, such as St, VAc, and BD, the adducts 20 are isolated (Eq. 23) ... 

The radical addition products are nitroxyl radicals which are readily characterized by means of their EPR spectra. We used both radical trapping agents to carry out some of the studies. The PBN system is less diagnostic because it is not as sensitive to trapping all the radical species as DMPO. The data in Table II are for the DMPO trap. We also generated hydroxyl... 

As can be seen, the isolation of l-halobicyclo[l.l.l]pentanes offered an opportunity for further molecular manipulation. To illustrate this, the adduct generated from 3-iodo-4,5-dihy-drofuran-2(3//)-one and [1.1.IJpropellane was reacted with tributyltin hydride in the presence of the radical trapping agent methyl acrylate to afford the 1,3-disubstituted biey-clo[l.l.l]pentane 27 in a total yield of 39%.43... 

The uncatalyzed or uninitiated reaction takes place at higher temperatures, i.e. >160 °C. The reaction is not affected by radical trapping agents and is characterized by a low degree of gelation and essentially no loss of unsaturation. The structure of the adduct (179) is completely different and results from an ene reaction with maleic anhydride functioning as enophile (Scheme 86). Presence of the vinylidene double bond has been confirmed by IR and NMR spectroscopy. 

Tabic III-3. Rale Constants of Reactions of Some Radical Trapping Agents with II and C, 11 , at Room Temperature... 

MI-6 Determination of the Primary Photochemical Process by Radical Trapping Agents, 1.35 III 6.1 Examples, 136... 

The use of iodoacetic acid as an aryl radical trapping agent has confirmed the intermediacy of aryl radicals in some hydrodediazoniation reactions, whether these are initiated or not.4 Spontaneous hydrodediazoniation of aryldiazonium fluoroborates occurs in warm dimethylformamide (DMF). Detailed study5 of the conversion of the 4-nitro derivative into nitrobenzene indicates a homolytic mechanism in which H-atom abstraction occurs from both sites in DMF with a formyl methyl preference of 3.5 1.0. High yields of mixed perfluorinated biaryls may be obtained by the catalytic dediazoniation of pentafluorobenzenediazonium ions in acetonitrile containing aromatic substrates and small amounts of iodide salts. The catalytic role of iodide and the isomeric product distributions indicate that arylation proceeds through the pentafluorophenyl radical in an efficient homolytic chain process.6... 

An alternative possibility is the introduction of a substituent by reaction with a suitable radical trapping agent ... 

If an excess of a suitable radical trapping agent is present in the reaction medium, substitution will occur otherwise, radical recombination takes place to give the pyridyl sulfide ... 

Electron-spin resonance (ESR) indicated free radicals in a brown polymer (mean ca 1 kDa by field-desorption MS) from a glucose-4-chloroaniline model system.185 Such free radicals (see Chapter 2) could be a source of visible colour. Exposure of the melanoidin to nitric oxide, a radical-trapping agent, diminished the ESR signal by 48% and changed the colour to red-brown. 

Table 12. Cyclization of C -2,4-Dinitrophenyloxime 95 in the Presence of Several Radical Trapping Agents...

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