5-Hydroxy-6-methyluracil, an Efficient Scavenger of Peroxyl Radical in Water (original) (raw)
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5-Hydroxy-6-methyluracil as an efficient scavenger of peroxy radicals
Russian Chemical …, 2008
The reaction of 5 hydroxy 6 methyluracil with peroxy radicals generated by the thermal decomposition of azodiisobutyronitrile was studied at 75°С in ethanol, propan 2 ol, and dimethyl sulfoxide. The stoichiometry of the reaction is 1 : 1. The reaction product is dihydro 6 hydroxy 6 methylpyrimidine 2,4,5 trione in an anhydrous solvent or dihydro 5,5,6 trihy droxy 6 methylpyrimidine 2,4 dione in the presence of water. The rate constant for the reac tion of 5 hydroxy 6 methyluracil with the peroxy radicals is ~10 8 L mol-1 s-1 .
5-Aminouracil as Effective Inhibitor of Peroxyl Radicals. Experimental and Theoretical Studies
Current Organic Chemistry, 2012
The reaction of 5-aminouracil with peroxyl radicals generated by the thermal decomposition of 2,2-azo-bis(2methylpropionitrile) (AIBN) and 2,2-azo-bis(2-amidinopropane) dihydrochloride was studied at 50° in ethanol and water (pH 7.0) solution respectively. The oxidation product of 5-aminouracil formed by peroxyl radicals was dihydro-5,5,6-trihydroxypyrimidine-2,4-dione. The relative rate constant of 5-aminouracil vs. quercetin and 2,6-di-tert-butyl-4-methylphenol by peroxyl radicals generated from AIBN was measured in ethanol and found to be 0.19 (50°C) and 3.6 (70°C) respectively. Theoretical data of the redox potential and the bound dissociation energy oppose against single electron/proton transfer mechanism and provide support for a hydrogen atom abstraction mechanism. Transition structures and activation barriers of the hydrogen abstraction from 5-aminouracil, 5-hydroxy-6-methyluracil and 2,6-di-tert-butyl-4-methylphenol by methyl peroxyl radical were determined with the BB1K/6-31+G(d,p) level of theory. The relative theoretical reactivity was found to be in a good agreement with the experimental results and also supported the hydrogen abstraction mechanism.
Application of HPLC to Study the Reaction of Free Radicals with Antioxidants and/or Toxins
Journal of Chemistry, 2014
The application of HPLC in the antioxidative (antiradical) properties studies of various samples is discussed in this paper. The assay is based on the reaction of, characterized by strong oxidizing properties, hydroxyl radicals (generated in the Fenton-like reaction) with the sample and with the, so-called, sensor. The product of the sensor reaction with the radicals is analyzed using RP-HPLC with fluorescence detection. It is well known that antioxidants, which are healthy for living organisms, have a negative environmental effect. Therefore, the goal of the paper is to discuss if the same setup can be used to get rid of unwanted compounds (toxins) from the environment. It was found that the phenols and PAHs are degraded by hydroxyl radicals. The optimal (maximum degree of the degradation) conditions were obtained forpH=3.0and 0.1 mM Fe2+.
Interaction and reactivity of urocanic acid towards peroxyl radicals
Redox Report, 2005
The capacity of urocanic acid to interact with peroxyl radicals has been evaluated in several systems: oxidation in the presence of a free radical source (2,2′-azobis(2-amidinopropane; AAPH), protection of phycocyanin bleaching elicited by peroxyl radicals, and Cu(II)-and AAPH-promoted LDL oxidation. The results indicate that both isomers (cis and trans) are mild peroxyl radical scavengers. For example, trans-urocanic acid is nearly 400 times less efficient than Trolox in the protection of the peroxyl radical promoted bleaching of phycocyanin. Regarding the removal of urocanic acid by peroxyl radicals, nearly 100 µM trans-urocanic acid is required to trap half of the produced radicals under the employed conditions (10 mM AAPH, 37°C). Competitive experiments show that the cis-isomer traps peroxyl radicals ~30% less efficiently than the trans-isomer. Given the high concentrations that trans-urocanic acid reaches in skin, its capacity to trap peroxyl radicals could contribute to the protection of the tissue towards ROS-mediated processes. Furthermore, both isomers, and particularly the cis-isomer, protect LDL from Cu(II)-induced oxidation.
Journal of agricultural and …, 2002
Four oxidized flavonoid derivatives generated from reacting quercetin (a pentahydroxylated flavone) with the peroxyl radical generator 2,2′-azobis-isobutyronitrile (AIBN) were isolated by chromatographic methods and identified by NMR and MS analyses. Compounds included 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (2); 1,3,11a-trihydroxy-9-(3,5,7-trihydroxy-4H-1-benzopyran-4-on-2-yl)-5a-(3,4-dihydroxyphenyl)-5,6,11-hexahydro-5,6,11-trioxanaphthacene-12-one (3); 2-(3,4dihydroxybenzoyloxy)-4,6-dihydroxybenzoic acid (4); and methyl 3,4-dihydroxyphenylglyoxylate (5). Product ratios under different hydrogen ion concentrations and external nucleophiles revealed that two of the products, namely the substituted benzofuranone (2) and the depside (4), are generated from a common carbocation intermediate. Indirect evidence for the operation of a cyclic concerted mechanism in the formation of the dimeric product is provided. The identification of these products supports the model that the principal site of scavenging reactive oxygen species (ROS) in quercetin is the o-dihydroxyl substituent in the B-ring, as well as the C-ring olefinic linkage.
The Scientific World Journal, 2014
We have described a modified method for evaluating inhibitor of peroxyl radicals, a well-recognized and -documented radical involved in cancer initiation and promotion as well as diseases related to oxidative stress and ageing. We are reporting hydrophilic and lipophilic as well as natural and synthetic forms of antioxidants revealing a diversified behaviour to peroxyl radical in a dosedependent manner (1 nM-10 M). A simple kinetic model for the competitive oxidation of an indicator molecule (ABTS) and a various antioxidant by a radical (ROO • ) is described. The influences of both the concentration of antioxidant and duration of reaction (70 min) on the inhibition of the radical cation absorption are taken into account while determining the activity. The induction time of the reaction was also proposed as a parameter enabling determination of antioxidant content by optimizing and introducing other kinetic parameters in 96-well plate assays. The test evidently improves the original PRTC (peroxyl radical trapping capacity) assay in terms of the amount of chemical used, simultaneous tracking, that is, the generation of the radical taking place continually and the kinetic reduction technique (area under curve, peak value, slope, and max ).
Biochemical and Biophysical Research Communications, 2000
The production of hydroxyl radicals by tetrachlorohydroquinone (TCHQ, a major metabolite of the widely used biocide pentachlorophenol) in the presence of H 2 O 2 was studied by salicylate hydroxylation method. HPLC with electrochemical detection was used to measure the levels of 2,3-and 2,5-dihydroxybenzoic acid (DHBA) formed when the hydroxyl radicals react with salicylate. We found that TCHQ and H 2 O 2 could produce both 2,3and 2,5-DHBA when incubated with salicylate. Their production was markedly inhibited by hydroxyl radical scavenging agents dimethyl sulfoxide and ethanol, as well as by tetrachlorosemiquinone radical scavengers desferrioxamine and other hydroxamic acids. In contrast, their production was not affected by the nonhydroxamate iron chelators diethylenetriaminepentaacetic acid (DTPA), bathophenanthroline disulfonic acid, and phytic acid, as well as the copper-specific chelator bathocuprione disulfonic acid. A comparison of product formation and distribution from the reaction of ferrous iron with hydrogen peroxide (the classic Fenton system) strongly suggests that the same hydroxyl radical adducts are formed as in the TCHQ/H 2 O 2 experiments. Taken together, we propose that hydroxyl radicals were produced by TCHQ in the presence of H 2 O 2 , probably through a metal-independent organic Fenton reaction.
Reactivity of 5‐aminouracil derivatives towards peroxyl radicals
Journal of Physical Organic Chemistry, 2020
The reactivity of 5-aminouracil derivatives in the model reaction of autoxidation of styrene initiated by 2,2 0-azobis(2-methylpropionitrile) was studied. Alkyl substituents at the 6-position of the uracil ring have a significant effect on the kinetic parameters of inhibition. The N-H bond dissociation energy calculated at the M06-2X/MG3S and G4 levels of the theory does not agree with the experimental values of the rate constants. The transition state was calculated at the M05/MG3S level of theory for 1,3-dimethyl-5-aminouracil, 1,3,6-trimethyl-5-aminouracil, 1,3-dimethyl-6-ethyl-5-aminouracil, 1,3-dimethyl-6-isopropyl-5-aminouracil and 3-butyl-6-methyl-5-aminouracil. The enthalpy of the transition state is in agreement with the experimental data and it can be used to evaluate the reactivity of the 5-aminouracil derivatives with peroxyl radicals.
Archives of Biochemistry and Biophysics, 2007
In this paper, we report on a method to evaluate the activity of water soluble and H-atom donor antioxidants as peroxyl radical scavengers in a micelle system reproducing the conditions occurring in the upper small intestine in humans, during digestion and absorption of lipids. This method, which overcomes some of the problems of the total radical trapping antioxidant parameter (TRAP) assays, measures the peroxyl radical trapping capacity (n) and the peroxyl radical trapping efficiency IC 50 À1 of antioxidants, that is the number ''n'' of peroxyl radicals trapped by one molecule of the studied antioxidant and the reciprocal of the antioxidant concentration that halves the steady-state concentration of peroxyl radicals, respectively. These two fundamental parameters characterizing the radical chain breaking of many water soluble antioxidants, among which dietary polyphenols, can be obtained with relatively good precision from a single experiment, on the basis of a rigorous treatment of the kinetic data.
The inactivation of lipid peroxide radical by quercetin. A theoretical insight
Physical Chemistry Chemical Physics, 2010
The effectiveness of naturally occurring antioxidant quercetin in the inactivation of the damaging lipid peroxide radical was investigated by means of hybrid density functional based approach, using the direct dynamics method, where the thermal rate constants were calculated using variational transition-state theory with multidimensional tunneling. H-atom abstraction in quercetin by CH 3 OO peroxide occurs preferentially at the 4 0 OH phenolic site, from both kinetic and thermodynamic points of view. In principle, the narrowness of the obtained adiabatic potential-energy profile makes the occurrence of a significant tunnelling contribution possible. In fact, this contribution enhances the value of the computed rate constant at 300 K from 1.94 Â 10 1 to 9.63 Â 10 3 M À1 s À1 indicating that quercetin is a potent natural antioxidant in trapping and scavenging free radicals.