2, 2-Diphenyl-l-picrylhydrazyl

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. 

Ozgen M, Reese RN, Tulio AZ Jr., Scheerens JC and Miller AR. 2006. Modified 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) method to measure antioxidant capacity of selected small fruits and comparison to ferric reducing antioxidant power (FRAP) and 2,2 -diphenyl-l-picrylhydrazyl (DPPJf) methods. J Agric Food Chem 54(4) 1151-1157. 

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)... 

The EPR spectra, recorded at — 196°C or at 25°C, were taken with Varian E6S and V4502 spectrometers for X-band (9.1 GHz), and Q-band (35 GHz) measurements, respectively. The g values were evaluated by using a 2,2-diphenyl-l-picrylhydrazyl (DPPH) standard, with a g value of 2.0036. Spin concentrations were obtained by using a single crystal of freshly recrystallized CuS04-5H20 as a standard. The estimated error in spin concentration is 30%. 

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. 

Antioxidant activity values measured with the proposed potentio-metric method correlate with antioxidant activity determined by RANDOX methods and photometric method with the use of stable radical 2.2-diphenyl-l-picrylhydrazyl. Correlations are linear. 

Figure 27.15 displays the results of potentiometric and photometric AOA determination of water and alcohol herb extracts with the use of 2.2-diphenyl-l-picrylhydrazyl stable radical. Correlation coefficients are 94% for water and 99% for alcohol extracts. 

This model describes the observed behaviour when 2,2 -methylene-bis(4-methyl-6-terf-butylphenol) (ArOH in Fig. 4.7) reacts with 2,2-diphenyl-l-picrylhydrazyl (Y ), for example, in several solvents including CC14 and 1,4-dioxane [19]. 

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. 

The DPPH (2,2-diphenyl-l-picrylhydrazyl) systan offers a stable radical-generating procedure. It is sensitive enough to detect active principles at low concentrations. The antioxidant process of catechins is thought to be divided into the following two stages ... 

FIGURE 8.12 Proposed scavenging mechanism of epicatechin and catechin to 2,2-diphenyl-l-picrylhydrazyl. (From Sang, S., Cheng, X., Stark, R. E., Rosen, R. T., Yang, C. S., and Ho, C.-T. 2002. Chemical studies on antioxidant mechanism of tea catechins Analysis of radical reaction products of catechin and epicatechin with 2,2-diphenyl-l-picrylhydrazyl. Bioorg. Med. Chem. 10 2233-37. With permission.)... 

DPPH = 2,2-diphenyl-l-picrylhydrazyl ENDOR= electron-nuclear double resonance EPR = electron paramagnetic resonance ESE = electron spin echoes ESEEM = electron spin echo envelope modulation FFT = fast fourier transformations FWHM = full width at half maximum HYSCORE = hyperline sublevel correlation nqi = nuclear quadrupole interaction TauD = taurine/aKG dioxygenase TWTA = traveling wave tube amplifier ZFS = zero field splitting. 

Some EPR spectra of solid PM were measured using a Bruker ESP-300 EPR equipped with X-band Klystron and 100 kHz modulator. Hyperfine splitting and g values were determined directly from the spectrometer s field scan, g factors were measured by comparison with aqueous solution of Fremy s salt (g = 2.0055). The majority of EPR spectra were measured using a Varian E-4 EPR spectrometer. Typical parameters 100 kHz, X-band microwave frequency 9.4 GHz attenuation power 20 mW modulation amplitude 1-2 G scan time 8 min receiver gain 2.5 X 10 -5 X 10. The g values of EPR spectra were calculated from the g value of 2.0036 of the stable free radical of 2,2-diphenyl-l-picrylhydrazyl (DPPH). 

Chen, Y., Wang, M., Rosen, R.T., and Ho, C.-T., 2,2-Diphenyl-l-picrylhydrazyl radical-scavenging active components from Polygonum multiflorum Thnnb, J. Agric. Food Chem., 47, 2226-2228, 1999. 

Espfn, J.C., Soler-Rivas, C., and Wichers, H.J., Characterization of the total free radical scavenger capacity of vegetable oils and oil fractions using 2,2-diphenyl-l-picrylhydrazyl radical, J. Agric. Food. Chem., 48, 648-656, 2000. 

To our knowledge, there are no ptrevious reports concerning in vitro antioxidant activities of these plant part extracts. The purposes of this study were to determine the total phenolic and the total flavonoid contents, to evaluate their antioxidant activities using 2, 2 -azino-bis (3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) and 2, 2-diphenyl-l-picrylhydrazyl (DPPH) tests, and finally to identify and to quantify some polyphenolic compounds by using a RP-HPLC coupled to an UV detector. 

A plot of Equation 22.12 as rate versus Py for the bleaching of 2,2-diphenyl-l-picrylhydrazyl (DPPH) in a number of solvents appears in Figure 22.5 (Suslick et al., 1983a). The linearity of the plot validates Equation 22.12 and also brings... 

Saito, J., Teramae, N., Hara, J., Toda, S., and Tanaka, S., Analysis of inhibition reaction of 2,2-diphenyl-l-picrylhydrazyl in polymerization by field desorption mass spectrometry, Kobunshi Ronbunshu, 40, 531, 1983. 

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