2-picrylhydrazyl free radical

Ratty AK, Sunamoto J, Das NP. 1988. Interaction of flavonoids with l,l-diphenyl-2-picrylhydrazyl free radical, liposomal membranes and soybean lipoxygenase-1. Biochem Pharmacol 37 989-995. 

A multisyringe spectroscopic flow injection analysis (FIA) system was proposed for evaluating the antioxidant capacity of solutions, as a function of the solvent and the pH. The method is based on UVD at 517 nm of the scavenging capacity of the test solution in the presence of the 2,2-diphenyl-1-picrylhydrazyl free radical (14) during 3 min after stopping the flow. The method was validated for ascorbic acid and a series of phenolic antioxidants. ... 

Hausser [13] reports that such a reaction occurs between diphenyl-picrylhydrazyl free radicals and AT.AT -tetramethyl-p-phenylenediamine with a heat of reaction in toluene at —40°C equal to —20 5 kcal mole-1, but this is a system which would be expected to favour electron transfer. The position with kinetic isotope effects is equally complex, both positive... 

Several phenolic diterpenoids with antioxidant activities were isolated from rosemary leaves. These include camosol, camosic acid, rosmanol, isorosmanol, and epirosmanol. Camosol showed potent antioxidative activity as revealed by scavenging a,a-diphenyl-(3-picrylhydrazyl free radicals and protection of oxidative DNA damage. In chronic inflammation, cytokines induce the production of nitric oxide, which is converted to DNA-damaging and carcinogenic peroxynitrite. Peroxynitrite is a cytotoxicant with... 

Rosemary (Rosmarinus officinalis) contains flavonoids, phenols, volatile oil and terpenoids. Topical application of rosemary extract, carnosol or ursolic acid to mouse skin inhibited the covalent binding of benzo[a]pyrene to epidermal DNA (Huang et al. 1994), tumour initiation by 7,12-dimethylbenz [ajanthracene (Singletary and Nelshoppen 1991), 12-0-tetradecano)dphorbol-13-acetate-induc-ed tumour promotion, ornithine decarboxylase (EC 4.1.1.17) activity and inflammation. Carnosol showed potent antioxidative activity in a,a-diphe-nyl-P-picrylhydrazyl free radicals scavenge and DNA protection from Fenton reaction (Lo et al. 2002). 

Jimenez-Escrig A, Jimenez-Jimenez I, Sanchez-Moreno C and Saura-Calixto F. 2000. Evaluation of free radical scavenging of dietary carotenoids by the stable radical 2,2-diphenyl-l-picrylhydrazyl. J Sci Food Agric 80(11) 1686—1690. 

The retarder may be a free radical which is too unreactive to initiate a Polymer chain (e.g. triphenyl methyl or diphenyl-picrylhydrazyl). The mechanism of retardation is simply the combination or disproportionation of radicals. 

Free radical scavenging activity was assessed using the DPPH (1, 1-di-phenyl-2-picrylhydrazyl) assay as described by Harbilas et al. [22] with incubation time increased to 65 min. Briefly, 250 tiL of 100 timol/L DPPH dissolved in methanol was added to 40 p.L of extract (tested at 5 concentrations) in a microplate well. A standard curve of ascorbic acid (positive control) was included as a reference and all data were blanked against a treatment with only methanol. Absorbance was read with a microplate reader at 517 nm. The inhibitory concentration for 50% scavenging (IC50) of each extract was calculated and compared to the IC50 of the ascorbic acid standard curve. 

Pure crystals of 2,2-diphenyl-l-picrylhydrazyl, the stable, low-molecular-weight free radical, contain about 2 x 10 radicals/g. (Adapted from Dellinger et ah, 2001)... 

Glavind J, Holmer G. Thin-layer chromatographic determination of antioxidants by the stable free radical a, a -diphenyl-(3-picrylhydrazyl. Journal of the /American Oil Chemists Society. 1967 44(9) 539 - 542. 

Yamaguchi T, Takamura H, Matoba T, Terao J. HPFC method for evaluahon of the free radical-scavenging achvity of foods by using l,l-diphenyl-2-picryLhydrazyl. Bioscience, Biotechnology, and Biochemistry. 1998 62(6) 1201-1204. 

Evidence for such stable free radicals has been obtained from electron spin resonance measurements. A sample of the 77-23 PVC-styrene, which had been exposed to 0.8 megarad of gamma-radiation at room temperature, displayed resonance peaks comparable to 3 X 10 8 mole per gram of free radicals (compared with a diphenyl picrylhydrazyl standard). When an identical sample was heated for 10 minutes at 75°C. following irradiation, the free radical population had fallen below detection limits. Heating evidently destroyed or decreased the free radical content by reaction or termination. 

A more fruitful approach to the irradiation of pure liquids would appear to be that being undertaken by Schuler (S2) in this country and Chapiro (C2) in France. In these studies solutes (iodine and diphenyl-picrylhydrazyl) are added to organic liquids prior to irradiation and the disappearance of these solutes is taken as a measure of the number of free radicals produced by the radiation. The experimental results using the two scavengers mentioned yield values in good agreement for the number of free radicals produced in the radiolysis of organic liquids. 

Because of the affinity of their unpaired electrons, free radicals have short lives, lend to dimerize and thus lose their reactivity. Because of their generally short half-lives (1-100 milliseconds), detection and identification of these entities is essentially through spectrophoiometric methods. However, in solid systems, free radicals can he trapped for appreciable lengths of time and at least one of these, 2,2-diphenyl-l-picrylhydrazyl. has such a long half-life that it is sold as such for the photometric determination of tocophcml. 

Nanjo F, Goto K, Seto R, Suzuki M, Sakai M, Hara Y. 1996. Scavenging effects of tea catechins and their derivatives on l,l-diphenyl-2-picrylhydrazyl radical. Free Radic Biol Med 21 895-902. 

Different model systems and different methods are used to evaluate the antioxidant properties of flavonoids. The stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH), which changes color after being reduced by an antiradical compound, was employed to study the antioxidant properties of isoflavones genistein (42) and daidzein (40), flavones apigenin (23) and lute-... 

Y2. Yamaguchi, T., Takamura, H., Matoba, T., and Terao, J., HPLC method for evalution of the free radical-scavenging activity of foods by using 1, l-diphenyl-2-picrylhydrazyl. Biosci. Biotechnol. Biochem. 62, 1201-1204 (1998). 

Some stable free radicals (top left) triphenylmethyl (top right) 2,2-diphenyl-1-picrylhydrazyl (DPPH) (bottom left) TEMPO (bottom right) Galvinoxyl. 

The early experiments of Goldschmidt clearly indicated that phenols are sensitive to radical attack. Not only were fairly stable radicals found in oxidation processes of phenols (Goldschmidt and Schmidt, 1922 Goldschmidt and Stiegerwald, 1924), but the oxidation of hydroquinone to quinone could also be brought about by the stable free radical 2,2-diphenyl-l-picrylhydrazyl (DPPH, Goldschmidt and Renn, 1922). The mechanism of the radical attaok remained unknown for a long time. The kinetic isotope effect played a very important role in its elucidation. 

A number of oxazine dye salts, on dissolving in aqueus alkali, precipitated the free radical thus the dye Meldola s blue, which precipitates even in almost neutral solution, yields a very stable solid free radical which can be kept in air and can be used as standard like 2,2-diphenyl-1 -picrylhydrazyl. 

The enthalpy of activation for the decomposition of perlauric acid is given in Table 128 the Arrhenius activation energy, determined with the use of diphenyl-picrylhydrazyl, was found to be 19 + 2 kcal.mole . In the aromatic series, the activation energy for perbenzoic acid decomposition is reported to be 30 kcal. mole in benzene solvent . The measurements were made by following the rate of disappearance of the free radical scavenger, diphenylpicrylhydrazyl. The activation energies appear to be low and the difficulty may be due to induced decomposition. Additional rate data are given in Table 129 for various aliphatic peracids. 

As is generally known, electron spin resonance reveals the presence of unpaired electrons. This is of course characteristic of free radicals and the most well known stable free radical is a, a-diphenyl-0-picrylhydrazyl(DPPH) (1,213). In the ESR spectrum it gives a narrow signal close to free spin value g 2.0036 and is used for calibrating the magnetic field (2). 

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