Analysis of free radicals

Suematsu, M., Suzuki, M., Kitahora, T. et al. (1987a). Increased respiratory burst of leukocytes in inflammatory bowel disease - the analysis of free radical generation by using chemiluminescence probe. J. Clin. Lab. Immunol. 24, 125-128. 

Garrel, C. Fontecave, M. Nitric oxide chemistry and biology, Analysis of Free Radicals in Biological Systems Eds. Favier, A. E. Cadet, J. Kalyanaraman, B. Fontecave, M. Pierre, J.-L. Birkhauser Verlag Basel, 1995, pp. 21-35. 

Buettner GR (1988) In the absence of catalytic metals ascorbate does not autoxidize at pH 7 ascorbate as a test for catalytic metals. J Biochem Biophys Methods 16 27-40 Buettner GR, Jurkiewicz BA (1995) Ascorbate radical a valuable marker of oxidative stress. In Favier AE, Cadet J, Kalyanaraman B, Fontecave M, Piere JL (eds) Analysis of free radicals in biological systems. Birkhauser, Basel, pp 145-164... 

Zhu J, Sevilla MD (1990) Kinetic analysis of free-radical reactions in the low-temperature autoxida-tion of triglycerides. J Phys Chem 94 1447-1452... 

We pause here to note that the steady-state a.ssumption that is so helpful in simplifying the analysis of free-radical kinetics (Section 6.3.4) will not apply to many cationic polymerizations of vinyl monomers, because propagation through free carbenium ions is so much faster than any of the other reactions in the kinetic chain. 

The steady-state assumption that is helpful in simplifying the analysis of free-radical kinetics is not valid in many, if not most, cationic polymerizations, which proceed so rapidly that steady-state is not achieved. Some of these reactions (e.g., isobutylene polymerization by AICI3 at -100°C) are essentially complete in a matter of seconds or minutes. Even in slower polymerizations, the steady-state may not be achieved if > Rt- The expressions given above can only be employed if there is assurance that steady-state conditions exist, at least during some portion of the overall reaction. Steady state is implied if Rp is constant with conversion, except for changes due to decreased monomer and initiator concentrations. A more rapid decline in Rp with time than what is expected or an increase in Rp with time would signify a nonsteady state. Thus many of the experimental expressions reported in the literature to describe the kinetics of specific cationic polymerizations are not valid since they are based on data where steady-state conditions do not apply. 

They confirmed that conversions from I to II and from II to free peroxidase correspond to single-equivalent reductions. Since II was observable as an intermediate in the steady state of the ordinary peroxidase reactions, it was suggested that organic molecules are oxidized to semi-oxidized free radicals. We have confirmed the mechanism by titrating the radicals with suitable electron acceptors (26) and finally by using ESR spectroscopy (29). Kinetic analysis of free radical formation during the peroxidase reaction made it possible to conclude that most of the free radicals formed in Reactions 9 and 10 dismutate with each other rather than react further with the enzyme in the oxidized state (30). 

Scranton, A.B., Klier, J., Peppas, N.A. Statistical analysis of free-radical copolymeriza-tion/crosslinking reactions using probability generating functions Reaction directionality and general termination. Macromolecules 24, 1412-1415 (1991)... 

The book starts with an introductory overview, which is intended to refresh the reader s memory on key aspects of free radicals and reactions thereof. Subsequent sections cover free radicals and food chemistry, natural antioxidants, and nutritional biochemistry and health. In the food chemistry section, topics range from analysis of free radicals within food matrices to Maillard reactions, emulsions, dairy, and meat products. In the antioxidant section, results are presented on the efficacy of antioxidants from tea, seeds, and selected naturally occurring compounds. Finally, in the nutritional biochemistry and health section, free radical inhibition is discussed in relationship to biochemical paths and cancerous cell cultures. 

Takechi K, Tamura H, Yamaoka K, Sakurai H. 1997. Pharmacokinetic analysis of free radicals by in vivo BCM (blood circulation monitoring) ESR method. Free Rad Res 26 483 96. 

Scavengers such as diphenylpicrylhydrazyl radicals [II] react with other radicals and thus provide an indirect method for analysis of the number of free radicals in a system ... 

Well before the advent of modern analytical instruments, it was demonstrated by chemical techniques that shear-induced polymer degradation occurred by homoly-tic bond scission. The presence of free radicals was detected photometrically after chemical reaction with a strong UV-absorbing radical scavenger like DPPH, or by analysis of the stable products formed from subsequent reactions of the generated radicals. The apparition of time-resolved ESR spectroscopy in the 1950s permitted identification of the structure of the macroradicals and elucidation of the kinetics and mechanisms of its formation and decay [15]. 

The reactions of free radicals in ethylene are well known (5, 24), and the applicability of this information to radiation chemistry has been demonstrated (32). Kinetic analysis of radical reactions revealed that the formation of methyl radicals and methane cannot be ascribed to excited precursors alone (32, 37). 

The mechanism of free-radical addition follows the pattern discussed in Chapter 14 (pp. 894-895). The method of principal component analysis has been used to analyze polar and enthalpic effect in radical addition reactions. A radical is generated by... 

Another powerful tool for the structural elucidation of free radicals is X-ray diffraction analysis, which provides unique and reliable information about the structures of the radical species in the crystalline form. Needless to say, the use of such an informative method is limited to the case of stable (isolable) radicals only. 

When using a semiconductor sensor for analysis of the flux of free radicals and atoms produced on the filament, one should rewrite expression (4.1) as... 

All these reactions are exothermic, and the AH values are negative. All these reactions should seemingly occur equally rapidly. The question to how easily the aminyl radicals react with the H—O and H—C bonds of the peroxyl radicals can be answered by analyzing these reactions in terms of the IPM model of free radical reaction (see Chapter 6). This model gives a tool to perform the calculation of the activation energy for a thermally neutral reaction of each class. Analysis of experimental data has shown (see Chapter 15) that, when aminyl... 

As is usually the case in the study of complicated reactions that involve a great many different species, more attention has been given to the analysis of reaction products and intermediates than to the problems of the investigation of the kinetics of possible elementary reaction steps. Analytical studies of the systems have been advanced by the development of techniques such as gas chromatography for the analysis of multicomponent systems and mass spectrometry for the detection of free radicals and other highly unstable species. Furthermore, since most... 

Balaban (1971 Balaban et aL, 1977) investigated radicals of type [1] by esr spectroscopy and noted their long lifetime, which he attributed to the push-pull character of the substituents involved and their mutual conjugation. Katritzky (Baldock et al., 1973, 1974 Katritzky and Soti, 1974) recognized in an analysis of merocyanines that there should be a related class of free radicals [2] which, in accordance with the stability of merocyanines. 

The obvious way to obtain this information is to carry out reactions with various Z groups and to analyze the products for percent ortho, meta, and para isomers, as has so often been done for electrophilic substitution. However, this procedure is much less accurate in the case of free-radical substitutions because of the many side reactions. It may be, for example, that in a given case the ortho position is more reactive than the para, but the intermediate from the para attack may go on to product while that from ortho attack gives a side reaction. In such a case, analysis of the three products does not give a true picture of which position... 

In addition to heat transfer with the wall there may also be chemical effects such as free-radical quenching. Discuss ways in which the analysis could be further extended to include such behavior. Consider the essential role of free radicals, such as atomic H, in sustaining the flame. 

A number of studies of simple reactions using DSC have given values for rate constants and activation energy in good agreement with those determined by methods utilising chemical analysis. An example of this is the work of Barrett18) on the thermal decomposition of free radical initiators. 

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