Showing papers on "DPPH published in 1989"

Effects of the Interaction of Tannins with Co-existing Substances. VI. : Effects of Tannins and Related Polyphenols on Superoxide Anion Radical, and on 1, 1-Diphenyl-2-picrylhydrazyl Radical

Abstract: The scavenging effects of twenty-five tannins including low-molecular polyphenols on the superoxide anion radical (O2-) generated in the hypoxanthine-xanthine oxidase system were estimated by electron spin resonance (ESR) measurements of the adducts formed by 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) and the radical. The scavenging effects of tannins and related polyphenols having ortho-trihydroxyl (pyrogallol) structure [galloyl, hexahydroxydiphenoyl (HHDP) groups in hydrolyzable tannins, galloyl group in acylated proanthocyanidins, and the B-ring of some flavan-3-ols] were stronger than the effects of unacylated proanthocyanidins. The effects of tannins and related polyphenols on the superoxide anion radical were also compared with those on the 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical. Each tannin in an ethanol solution of DPPH radical reduced the intensity of the signal of the DPPH radical, and gave a weak signal assignable to a radical derived from that tannin, in a similar way to the appearance of the signal of dl-α-tocopherol radical, accompanied with reduction of the signal of DPPH radical, in a mixture of dl-α-tocopherol and the DPPH radical. In contrast to the case of the superoxide anion radical, the effects of unacylated proanthocyanidins on DPPH radical were comparable with those of the other types of tannins. The scavenging effects of all of the tannins and related polyphenols tested in the experiments on DPPH radical were stronger than that of dl-α-tocopherol.

Studies on Inhibition Mechanism of Autoxidation by Tannins and Flavonoids. V. Radical-Scavenging Effects of Tannins and Related Polyphenols on 1, 1-Diphenyl-2-picrylhydrazyl Radical

Abstract: Radical scavenging effects of tannins and related polyphenols on 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical were evaluated by colorimetry. All of the polyphenols examined showed effects much stronger than that of α-tocopherol.The hydrolyzable tannins having galloyl groups in the molecule exhibited stronger effects than those having modified galloyl groups, such as hexahydroxydiphenoyl (HHDP), dehydrohexahydroxydiphenoyl (DHHDP) and chebuloyl groups. (-)-Epigallocatechin gallate, (-)-epigallocatechin, (-)-epicatechin gallate and methyl gallate also showed fairly significant effects, even though they are small molecules. The predominant reaction products upon the treatment of various alkyl gallates with DPPH radical on a preparative scale were dialkyl hexahydroxydiphenates, which should be formed by mutual coupling of C-centered galloyl radicals. Evidence for the formation of the alkyl gallate radicals was also obtained by the electron spin resonance spectroscopy.

Emulsion copolymerization of acrylonitrile and butyl acrylate, 10. Effect of 1,1-diphenyl-2-picrylhydrazyl on the polymerization process†

Abstract: The emulsion copolymerization of acrylonitrile with butyl acrylate, initiated by ammonium persulfate in the presence of disodium dodecylphenoxybenzenedisulfonate and 1,1-diphenyl-2-picrylhydrazyl (DPPH), was kinetically investigated at 70°C by conventional GLC and gravimetric methods. The copolymerization under batch conditions was conducted to both low and high conversion. In the presence of a small amount of DPPH the molecular weight of the copolymer is little decreased when compared with that prepared without DPPH. In addition, the rate of copolymerization unexpectedly decreases with increasing emulsifier concentration. The radical scavenger was found to decrease the average particle size. In the interval 2 the rate of polymerization is approximately proportional to the 0,35th power of the emulsifier concentration and to the 0,5th power of the initiator concentration (without DPPH). The dependence of the rate of polymerization on the final particle number and of the final particle number on the emulsifier concentration also deviates from the simple micellar theory predictions. The results can be explained by a coagulative nucleation mechanism.

Selective Spectrophotometric Determination of Vanadium (II) in the Presence of 35 Common Cations by Means of Di-2-Pyridyl Ketone 2-Pyridylhydrazone (DPPH)

Abstract: DPPH was tested with 36 cations in slightly acidic medium, in the presence, of EDTA but only vanadium(II) formed a stable red complex. Based on these effects a method was worked out for the selective spectrophotometric determination of vanadium(II) in the presence of the remaining tested cations. A comparison of the sensitivity and selectivity of this method with recently reported methods is presented.

Isolation of Phenolic Antioxidant Components from Panax ginseng

Abstract: To isolate new antioxidants from Panax ginseng, methanol extract of Panax ginseng was fractionated into several subfractions and their antioxidant activities were measured by using , (DPPH). Four compounds were isolated from two subfractions that showed high DPPH quenching activities by silica gel, Bondapak or Sephadex LH-20 column chromatography. The four compounds were confirmed to be phenolic substances by color reaction and UV spectral analysis.