Transient free radicals

Smaller B, Remko J R and Avery E C 1968 Electron paramagnetic resonance studies of transient free radicals produced by pulse radiolysis J. Chem. Rhys. 48 5174-81... 

Deactivation of the Mediator Deactivation of the mediator is a commonly encountered event in the practice of homogeneous catalysis. Among the various ways of deactivating the mediator, the version sketched in Scheme 2.10 is particularly important in view of its application to the determination of the redox characteristics of transient free radicals (see Section 2.7.2).14 The current-potential responses are governed by three dimensionless parameters, 2ei = /F)(ke Cjl/v), which measures the effect of the rate-determining... 

The sulfate and nitrate content of atmospheric particles comes primarily from the conversion of sulfur dioxide and nitrogen dioxide. Photochemi-cally initiated atmospheric reactions and transient free radicals are... 

For imaging purposes an activator is also required to produce transient free radicals which react with the stable free radicals to form colourless products. 

However, the chemist is often interested in transient free-radicals in the gas-phase or fluid solution. These may be trapped by rapid freezing or matrix isolation, but the advantages of single crystal studies are thereby lost. Fortunately the results derived from studies of radicals in single crystals have stimulated several groups to return to the problem of interpreting spectra from amorphous solids (Adrian et... 

Emission spectroscopy and, to a lesser degree, absorption spectroscopy have provided considerable information on and insight into the chemistry occurring during the process of combustion. In particular, many of the transient free-radical molecules important in the chain reactions were identified and characterized through their emission spectra in flames. Now, new laser spectroscopic techniques offer the promise of obtaining more detailed and precise information, especially for the ground electronic states of many of the molecules involved in combustion. 

The same conclusions on the structure and configuration of primary and secondary radicals can be achieved by SS ESR. TR ESR allows the relatively simple observation of highly reactive transient free radicals. The method is especially convenient in the case of transient radicals with a few magnetic nuclei, that is, with a simple ESR spectmm. 

Persson, A. L., Salin, M., and Sj berg, B.-M., 1999, Transient free radicals in the reaction witii mutant E441Q Rl, wild-type R2 and CDP of Escherichia coli class la ribonucleotide reductase. Manuscript in preparation. 

Sahlin, M., Lassmann, G., Putsch, S., Sj berg, B.-M., and Gr%oslund, A., 1995, Transient free radicals in iron/oxygen reconstitution of mutant protein R2 Y122F6Possible participants in electron transfer chains in ribonucleotide reductase. J. Biol. Chem. 270 12361nl2372. 

These short pulses induce a non-equilibrium situation in a very short time scale, such that a sufficiently high concentration of transient free radical species is formed. These short-lived free radical species are detected in their lifetimes, by following the changes in their characteristic properties such as optical absorption, electrical conductivity, spin density, Raman spectroscopy, etc. Pulse radiolysis has been found to be extremely useful in studying several of these free radical reactions. Although modern pulse radiolysis techniques are capable of producing much shorter pulses seconds), most of the relevant... 

Fischer, H., and G. Giacometti ESR-studies of transient free radicals... 

According to Mrzewinski [30] this was due to the fomiation of a free radical of diphenylamine (I) a transient free radical of diphenylamine A-oxidc (II). Free radical I is known to the literature (31 ]. It yielded A -nitrosodiphenylarninc (which, as is known possesses stabilizing properties),. A -nitrosonitro. dinitro-and higher nitrated diphenylarnines. According to Mrzewinski free radical 1 is... 

As depicted in Figure 33.28, A" VPA is not formed by dehydration of 4- or 5-hydroxy valproic acids, which are, with the glucuronide conjugate, the major metabolites of valproic acid. The mechanism is proposed to involve an initial hydrogen abstraction to generate a transient free radical intermediate. It has been demonstrated that the carbon-centred radical was localized at the C4 position. The radical undergoes both recombination (which yields 4-hydroxy valproic acid) and elimination (which produces... 

This table lists the fundamental vibrational frequencies of selected three-, four-, and five-atom molecules. Both stable molecules and transient free radicals are included. The data have been taken from evaluated sources. In general, the selected values are based on gas-phase infrared, Raman, or ultraviolet spectra when these were not available, liquid-phase or matrix-isolation spectra were used. 

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