2,2-diphenyl-1 -picrylhydrazyl DPPH

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-... 

Several studies described the interaction of flavonoids with the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical [76, 79, 107-108] (Fig. (3)). DPPH is a stable free radical and is frequently used in ESR studies [109]. The DPPH assay provides information on the reactivity of flavonoids with a stable free radical [79]. Because of its odd electron, DPPH gives a strong absorption band in ethanol at 517 nm. As this... 

Electron spin resonance (ESR) spectrometry measures the presence of unpaired electrons and is a widely accepted method for investigating antioxidant-radical reactions. A few ESR studies have been conducted to investigate the CLA reactions with 1,1-diphenyl-2-picrylhydrazyl (DPPH ) free radical in toluene (7,8). DPPH is... 

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. 

Radical Generation. The ESR spectrometer, flow system, and general procedure have been described (46). The apparatus was calibrated with freshly prepared diphenyl picrylhydrazyl (DPPH) solutions. The peroxy radical concentrations were determined by double integration of derivative spectra. A standard coal sample in the dual cavity allowed corrections to be made for changes in cavity Q. The rates of decay of the less reactive radicals were determined by stopped-flow techniques with manually or electrically operated valves. The decay was recorded... 

Measurement of the g values [relative to polycrystalline diphenyl-picrylhydrazyl (DPPH)] and the a proton [o(H)] or nitrogen [o(N)] couplings, was straightforward, but determination of the central atom hyperfine coupling was not, and requires further comment. 

The intensity (or area) of a spectrum is calibrated with standards such as a, a -diphenyl-//-picrylhydrazyl (DPPH), potassium peroxylamine disulfonate [Fremy s salt K2NO(SO,)2], or carbon One gram of DPPH contains 1 5 X 1021 unpaired spins, and the strong pitch standard (0 1% powdered coal in KC1) has 3 x 1015 spins/cm of length A computer is useful for integrating the spectral area Alternatively, techniques have been developed m which the absorption line is cut out from the paper trace, weighed, and compared with that of a standard sample... 

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- -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 Held [2]. 

Ozgen M, Reese RN, Tulio AZ Jr, Scheerens JC, Miller 7VR. 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 (DPPH) methods. Journal of Agricultural and Food Chemistry. 2006 54(4) 1151-1157. 

Many EOs also exhibit antioxidant activity and therefore several studies have been carried out in order to elucidate the activity of the components [139,153]. For instance, y-terpinene retarded the peroxidation of linoleic acid [139, 154-156], sabinene showed strong radical-scavenging capacity [139, 157], a-pinene [158] and limonene [146] showed low antioxidant activity in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) test, while terpinene and terpinolene showed high hydrogen-donating capacity against the DPPH radical [146, 150, 155, 158],... 

As described in Chapter III, morusin (3) has been found to be anti-tumor promoter in a two-stage carcinogenesis experiment with teleocidin. Considering the similarity of the structures between morusin (3) and artonin E (7), artonin E (7) was expected to be an anti-tumor promoter. Furthermore we found a novel photo-oxidative cyclization of artonin E (7) as follow photo-reaction of artonin E (7) in CHCI3 containing 4% ethanol solution with high-pressure mercury lamp produced artobiloxanthone (8) and cycloartobiloxanthone (9), and the treatment of artonin E (7) with radical reagent (2,2-diphenyl-1-picrylhydrazyl DPPH) resulted in the same products, Fig. (15), [84]. 

To determine the magnetic field at which resonance occurs and the spacings between lines of a spectrum, the ESR spectrum of a standard sample is superimposed on the spectrum being observed. A commonly used standard is the stable solid radical 1, l-diphenyl-2-picrylhydrazyl (DPPH)—the last radical in Fig. 8.15. 

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%. 

One of the earliest applications of electron spin resonance to organic problems was the study of the now well-known radical a,a-diphenyl-jS-picrylhydrazyl (DPPH) (Holden et al., 1950 Townes and Turkevich, 1950). 

Hristea EN, Covaci-Cimpeanu IC, Ionita G, Ionita P, Draghici C, Caproiu MT, Hillebrand M, Constantinescu T, Balaban AT (2009) Reactions of 2,2-diphenyl-1-picrylhydrazyl (DPPH) with two syringylic phenols or one aroxide derivative. Eur J Org Chem 626-634... 

Recently Eley and Parfitt [77] discovered that a,a -diphenyl- p -picrylhydrazyl (DPPH) (III) is one of the best organic semiconductors with an energy gap of only 0.26 eV. 

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. 

The electrochemical and antioxidant properties of delphinidin, cyani-din, pelargonidin, kuromanin and callistephin were studied [60]. Antioxidant activities of the anthocyanins were evaluated using the l,l-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging method. The order of antioxidant activity of the five anthocyanins was delphinidin > cyanidin > pelargonidin > kuromanin > callistephin. 

Details of the operation of the spectrometer will be provided by the instructor. Familiarity with the instrument can be gained by some preliminary experimentation with a stable radical sample such as solid o ,Q -diphenyl-j8-picrylhydrazyl (DPPH), which is often used as an ESR calibration standard. 

A radical reacting with a molecule must produce a particle with an unpaired electron. For the reacting molecule to be called an inhibitor, these secondary radicals should have negligible tendency to propagation. They can have various fates. They either dimerize or react with a further radical that is able to propagate. The initiation rate can be determined by means of an ideal inhibitor. The most important inhibitors are some quinones, nitro and nitroso aromatics, polycyclic aromatic hydrocarbons, some metal chlorides, and stable radicals (e.g. I,l-diphenyl-2-picrylhydrazyl-DPPH, etc.). 

---