DPPH trapping

DPPH trapping a, a-Diphenyl-j8-picrylhydrazyl. Useful under lipophilic conditions Brand and Eichner454... 

Stable radicals can show selectivity for particular radicals. For example, nitroxides do not trap oxygcn-ecntcrcd radicals yet react with carbon-ccntcrcd radicals by coupling at or near diffusion controlled rates.179,184 This capability was utilized by Rizzardo and Solomon181 to develop a technique for characterizing radical reactions and has been extensively used in the examination of initiation of radical polymerization (Section 3.5.2.4). In contrast DPPH, w hile an efficient... 

The ability of the stable free radical diphenylpicrylhydrazyl (DPPH) to act as an efficient trap for reactive radicals such as 804 and OH- has been utilised by Bawn and Margerison in their examination of the Ag -S20g couple. The disappearance of the intensely coloured DPPH gave excellent zero-order kinetics the rate as a whole was identical with that found by Fronaeus and Ostman and 2 was given by 3.1 x 10 exp(—17.9x lO /RT) l.mole sec A Sengar and Gupta have also determined Arrhenius parameters for this reduction and have compared them with those for some redox processes (Table 23). 

A-max = 525 run) has allowed both a determination of the depolymerisation rate and the number of break points (i. e. 2 DPPH molecules per bond breakage). Evidence for the formation of macroradicals in the degradation of polymethyl methacrylate, polystyrene and polyvinylacetate has also been provided by Tabata [63] using spin trapping and esr techniques. Taranukha [64] has also used spin traps to study the degradation of aqueous polyacrylamide. 

The interaction of acrolein with a catalyst was investigated using a DPPH method (27), in which an acyl radical formed by the initiation was trapped by DPPH, and the rate of consumption of DPPH, corresponding to the rate of formation of the radical, was determined by visible light spectra. The rate equation for acyl radical formation is... 

Popular EPR-based assays of antioxidant activity include the DPPH assay, in which the ability of compounds to quench (by H-atom transfer) the 1,1-diphenyl-2-picrylhydrazyl radical is used to rank their antioxidant activity. This method has been applied widely to the analysis of dietary antioxidants and extracts from medicinal plants.213 219 Extensive use has also been made of assays based on the competition between spin traps and test compounds for reaction with enzymatically-generated 02 and, in the presence of a metal catalyst, the OH rad-... 

The concentration of trapped radicals and the degree of occlusion (how deeply they are buried) have been studied extensively by Bamford and Jenkins (9). They determined the approximate radical concentration by swelling or dissolving polymer in solutions of diphenylpicryl hydrazyl (DPPH), a violet substance that becomes colorless on reaction with radicals. Nitrobenzene was generally used as the medium to dissolve the hydrazyl and to swell the polymer /3-propiolactone, a solvent for the polymer, was used also. 

Use of Electron Spin Resonance Techniques. Electron spin resonance (ESR) studies have been used to examine both activity of antioxidants " and their location within the Uposome . Studies of antioxidant radicals via ESR provide data on the electron delocalization within the antioxidant, which can be correlated with antioxidant activity, although not always with very good agreement with inhibition studies . Spin traps have been themselves examined as potential antioxidants, and have been used to attempt to trap peroxyl species for study . However, trapped peroxyl species are not very stable and carbon-centered radicals have been preferentially trapped, even though in some studies other techniques (e.g. malondialdehyde/thiobarbituric acid, MDA/TEARS-technique) indicate the presence of peroxide species in the sample . Eremy s salt ((K+S03 )2N0 ) has been used in micellar systems to determine rate constants quantitatively for the antioxidants a-Toc and ascorbic acid and their derivatives, because it reacts with them in a way similar to peroxyl radicals and can be used as a spin probe in stop-flow ESR studies . ESR has also been used to monitor the loss of dPPH and galvinoxyl signal intensity... 

Electrons generated by the plasma are quantitatively trapped by DPPH. The... 

Radical traps like galvinoxyl, TEMPO, and DPPH (Q ) are sometimes used a.s a test for the presence of radicals, R , in solution in such a case the adduct Q-R is expected as product. Unfortunately, this procedure can be misleading in organometallic chemistry becase typical Q abstract H from some palladium hydrides at rates competitive with those of typical organometallic reactions [PdHCl(PPh3)2] reacts in this way but [PdH(PEt3)3]BPh4 is stable. ... 

The cathodic solution exerted a radical scavenging effect on aqueous 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical (4), so that the antioxidant effect of the cathodic solution on AAPH-induced oxidation would be in part due to the trapping of aqueous AAPH radicals by the cathodic solution. The radical scavenging effect of the cathodic solution may be derived from the reduction in activity caused by dissolved hydrogen formed just after preparation. The cathodic solution also had an inhibitory effect on AMVN-induced oxidation, although this effect was weaker than that on AAPH-induced oxidation Figure 4). AMVN is a fat-soluble radical initiator and induces the oxidation of lipids in emulsion from the lipid droplet interior, but it was reported that AMVN also induced oxidation from the interface of water and the lipid phase (P). Therefore, the antioxidant action of tiie cathodic solution on AMVN-induced oxidation would be derived from its scavenging effect on the AMVN radical at the interface. 

Com oil phenols have been studied with respect to their potential to scavenge the free radicals, the peroxyl radicals, the superoxide radicals, etc. The free radical scavenging activity of the phenolic acids using model free radicals such as l,7-diphenyl-2-picrylhydrazyl radical (DPPH ), or ABTS (2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt cation radical) is often measured. TEAC (Trolox equivalent antioxidant capacity), FRAP (Ferric-reducing antioxidant capacity) and TRAP (total-radical-trapping antioxidant parameter) of the com oil are also used in order to obtain additional information, necessary to investigate the relation between the antioxidant intake and the oxidative stress related diseases (Stratil et al., 2008 Ceto et al., 2014 Apak et al., 2007). 

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