Diphenyl picryl hydrazyl

Antioxidant activity. Aqueous extract of the husk fiber, in cell culture, was active vs 2,2-diphenyl-1-picryl-hydrazyl-hydrate radicals . Juice, in cell culture, was active vs l,l-diphenyl-2-picrylhydrazyl, 2,2 -azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) and superoxide radicals but promoted the production of hydroxyl radicals and increased lipid peroxidation. The activity... 

A radical mechanism can be excluded, since 2,2-diphenyl-1-picryl-hydrazyl, which is a free radical inhibitor, does not inhibit the polymerization initiated by nitrogen dioxide. 

Stable Free Radicals. Stable free radicals are a small minority of the more than 6 million chemical compounds known by 2005. The oxygen molecule is paramagnetic (S = 1). In 1896, Ostwald stated that "free radicals cannot be isolated." Only four years later, Gomberg123 made triphenylmethyl (Fig. 11.63), the first proven stable and persistent free radical [48] An infinitely stable free radical used as a reference in EPR is diphenyl-picryl hydrazyl (DPPH). Other persistent free radicals are Fremy s124 salt (dipotassium nitrosodisulfonate K+ O3S-NO-SO3- K+) 2,2-diphenyl-l-picrylhydrazy (DPPH)l, Galvinoxyl (2,6-di-tert-butyl-a-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-l-ylidene)-p-... 

Secondly there are direct techniques, notably electron spin resonance spectroscopy (ESR), in which the free radicals produced by the fracture of covalent bonds are directly observed, both in respect of their chemical nature and their number. Much of this review is orncemed with the results of ESR studies and this technique is therefore treated at some length below. One little used technique for the direct assessment of free radicals produced by n chanical means is that of Pazonyi et al and Salloum and Eckert They dropped various polymers in an ethanolic solution of diphenyl picryl hydrazyl, a chemical indicator, and determined the free radical concentration in the cut surfaces by colorimetrie measurements of the colour change. This method is subject to soixm uncertainty on account of possible side reactions. 

Turkevich and Selwood (68) have examined the conversion on the solid free radical a, a-diphenyl- -picryl hydrazyl. This substance did not show a very strong van der Waals adsorption of hydrogen, and its efficiency as a catalyst was much increased by mixing it with zinc oxide, which by itself was a powerful adsorbent but a weak catalyst. 

An excellent inhibitor is the resonance stabilized radical diphenyl picryl hydrazyl (DPPH), used extensively as a radical scavenger because the stoichiometry of the reaction is 1 1. 

Certain polymerizations can be stopped by additives. Diphenyl picryl-hydrazyl, for example, is a free radical scavenger, and stops free radical polymerizations. Ionic mechanisms are not affected. Benzoquinone, on the other hand, is also an inhibitor for free radical polymerizations. Because it is strongly basic, it reacts with cations, however, so that it is impossible to employ this additive to distinguish between free radical and cationic polymerizations. 

Phenolic antioxidants (i) 2,6-Dichlorobenzoquinone chlorimine (1-2% in ethanol followed 15 min later by 2% borax in 40% aqueous ethanol). (ii) a,a -Diphenyl picryl hydrazyl (0-1% in 95% aqueous ethanol). (hi) Palladium chloride. Mix 150 ml palladium chloride with 100 ml of 2 N hydrochloric acid. (iv) Diazotised p-nitroaniline. Mix 5 ml 0.5% p-nitroaniline in 2 N hydrochloric acid with 0.5 ml 5% sodium nitrite until colourless and 15 min later add 15 ml 20% sodium acetate. [6,8] [11, 17] [17] [11]... 

Herve J, Pescia J. 1963a. Resonance Magnetique Electroitique — theorie phenomenologique de la mesure du temps de relaxation T], utilisant un champ radiofrequence module en amphtude verification experimental sur le diphenyl-picryl-hydrazyl. Compt Rend 255 2926-2928. 

Stable radicals such as diphenyl picryl hydrazyl, which are reactive enough to terminate propagating radicals but not to initiate polymerization. 

Alpha, alpha -diphenyl picryl hydrazyl (0.1% in 95% aqueous ethanol) 77... 

Catechin-immobilizing polymer particles were prepared by laccase-catalyzed oxidation of catechin in the presence of amine-containing porous polymer particles. The resulting particles showed good scavenging activity toward stable free l,l-diphenyl-2-picryl-hydrazyl radical and 2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonate) radical cation. These particles may be applied for packed column systems to remove radical species such as reactive oxygen closely related to various diseases. 

Radical scavenging activity. Green tea, evaluated using the l,l-diphenyl-2-picryl-hydrazyl radical, indicated that the galloyl... 

Xanthosoma violaceum, Araceae, widely distributed in Dominican Republic, Puerto Rico, Guatemala, and Equator, was investigated for in vitro antioxidant and free-radical scavenger activities. The fraction rich in C-glycosylflavones showed with l,l-diphenyl-2-picryl-hydrazyl radical (DPPH) test an EC50 of 11.6 pg/ml, compared with quercetin (2.3 pg/ml) and a-tocopherol (10.1 pg/ml). 

Harrison and McDowell 138) observed that while neither zinc oxide nor a, o-dip enyl-/3-picryl hydrazyl (a solid free radical) alone, catalyze hydrogen-deuterium exchange measurably at 77° K, a mixture of the two solids possesses considerable catalytic activity. They suggested that the effective catalyst in this mixture is the zinc oxide and that its catalytic activity is enhanced by electron transfer to the a,a-diphenyl-/3-picryl hydrazyl. It should be noted, however, that this implies a dependence of catalytic activity on electron concentration which is opposite to that observed by Molinari and Parravano 134). To bring the results for this system into line with those obtained by the latter workers, it would be necessary to postulate electron transfer in the opposite direction, i.e., from the a, a-diphenyl-/8-picryl hydrazyl to the zinc oxide. ... 

Eley and Inokuchi (168) have recently reported that the deposition of a,a-diphenyl-j3-picryl hydrazyl on a film of A1 or Pd raises the D.C. resistance of the latter suggesting electron transfer from the a,a-diphenyl-i3-picryl hydrazyl to the metal. The suggestion that this may be the case also with ZnO thus appears plausible. 

One of the earliest studies addressing the antioxidant activity of various procyanidins in vitro reported strong scavenging activity against free radicals such as the stable radical 1,1-diphenyl-2-picryl-hydrazyl (DPPH) and the oxygen free radicals O-2 and HO, as assessed by ESR spectroscopy. 

The three bioactive carbazole alkaloids, e.g. mahanimbine, murrayanol and maha-nine, were found to be mosquitocidal and antimicrobial. The antioxidant activity of carbazoles (l,l-diphenyl-2-picryl hydrazyl DPH) from M. koenigii was found to be in order ascorbic acid > bismurraya foline E > euchestine B, mahanine and a-tocopherol... 

The method described by Benington involves the reaction of the free radicals produced in a gas stream with a thin film of organic solution containing triphcnyl methyl radicals. The stream impinges upon the solution-covered surface, and the products of the reaction are measured spectroscopically. The work of Bartlett is more directly concerned with free radicals in solution. A fairly stable but nonetheless reactive free radical l,l-diphenyl-2-picryl hydrazyl (DPPH), 2-N-N-C6H2(N02)3, is capa-... 

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