- Use of 2,2-Diphenyl-1-picrylhydrazyl To Investigate the Chemical Behavior of Free Radicals Induced by Ultrasonic Cavitation
-
The sonolysis of 2,2-diphenyl-1-picrylhydrazyl (DPPH) has been studied in methanol-water solutions in the presence of air, oxygen, and argon.It is found that, for a specific solvent composition, 83 percent of the reacted DPPH is reduced to 2,2-diphenyl-1-picrylhydrazine (DPPH2) with all the gases examined.The absolute amount of DPPH converted is greatest with oxygen and it is believed that the latter combines with the primary radicals produced in the cavitation process to give a greater concentration of stable free radicals which can readily diffuse out of the bubble to react with DPPH.The conversion of DPPH DPPH2 decreases with increasing methanol concentration and it is believed to be due to the volatile alcohol inhibiting the cavitation process.
- Sehgal, C.,Yu, T. J.,Sutherland, R. G.,Verall, R. E.
-
-
Read Online
- Spectral analysis allows using the DPPH* UV–Vis assay to estimate antioxidant activity of colored compounds
-
Abstract: An accurate measurement of antiradical activity to samples, such as herbal extract and natural or synthetic pure compounds, is essential to estimate its scope as antioxidant, for example, in functional foods. The 2,2-diphenyl-1-picrylhydrazyl (DPPH*) UV–Vis assay is the most widely used method for this aim. Nevertheless, it can drive to erroneous results if the spectroscopic properties of each substance, in the reaction medium, are not considered. To overcome this limitation, we present a new methodology based on spectral analysis which, instead of reading at fixed wavelength, uses the UV–Vis spectra of selected compounds, as well as simple algebraic operations and fitting by residual sum of squares. The proposed methodology was assayed successfully to determine the antiradical activity of three compounds: naringin, which does not present absorbance in the absorption band of DPPH*, naringin-Cu(II) complex, with moderate absorbance at this range, and naringin-Fe(III) complex, which shows intense absorption at the studied range. The proposed methodology is simple with a broad scope, since it allows to study the free radical scavenging activity on samples with high color that could not be analyzed, by UV–Vis spectrophotometry, up to the moment. Graphic abstract: [Figure not available: see fulltext.].
- Celiz, Gustavo,Renfige, Melisa,Finetti, Mariela
-
-
Read Online
- Abnormal solvent effects on hydrogen atom abstraction. 2. Resolution of the curcumin antioxidant controversy. The role of sequential proton loss electron transfer
-
The rates of reaction of 1,1-diphenyl-2-picrylhydrazyl (dpph.) radicals with curcumin (CU, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3, 5-dione), dehydrozingerone (DHZ, "half-curcumin"), and isoeugenol (IE) have been measured in methanol and ethanol and in two non-hydroxylic solvents, dioxane and ethyl acetate, which have about the same hydrogen-bond-accepting abilities as the alcohols. The reactions of all three substrates are orders of magnitude faster in the alcohols, but these high rates can be suppressed to values essentially equal to those in the two non-hydroxylic solvents by the addition of acetic acid. The fast reactions in alcohols are attributed to the reaction of dpph. with the CU, DHZ, and IE anions (see J. Org. Chem. 2003, 68, 3433), a process which we herein name sequential proton loss electron transfer (SPLET). The most acidic group in CU is the central keto-enol moiety. Following CU's ionization to a monoanion, ET from the [-(O)CCHC(O)-]- moiety to dpph. yields the neutral [-(O)CCHC(O)-]. radical moiety which will be strongly electron withdrawing. Consequently, a phenolic proton is quickly lost into the alcohol solvent. The phenoxide anion so formed undergoes charge migration to produce a neutral phenoxyl radical and the keto-enol anion, i.e., the same product as would be formed by a hydrogen atom transfer (HAT) from the phenolic group of the CU monoanion. The SPLET process cannot occur in a nonionizing solvent. The controversy as to whether the central keto-enol moiety or the peripheral phenolic hydroxyl groups of CU are involved in its radical trapping (antioxidant) activity is therefore resolved. In ionizing solvents, electron-deficient radicals will react with CU by a rapid SPLET process but in nonionizing solvents, or in the presence of acid, they will react by a slower HAT process involving one of the phenolic hydroxyl groups.
- Litwinienko, Grzegorz,Ingold
-
-
Read Online
- Kaempferol Binding to Zinc(II), Efficient Radical Scavenging through Increased Phenol Acidity
-
Zinc(II) enhances radical scavenging of the flavonoid kaempferol (Kaem) most significantly for the 1:1 Zn(II)-Kaem complex in equilibrium with the 1:2 Zn(II)-Kaem complex both with high affinity at 3-hydroxyl and 4-carboxyl coordination. In methanol/chloroform (7/3, v/v), 1:1 Zn(II)-Kaem complex reduces β-carotene radical cation, β-Car?+, with a second-order rate constant, 1.88 × 108 L·mol-1·s-1, while both Kaem and 1:2 Zn(II)-Kaem complex are nonreactive, as determined by laser flash photolysis. In ethanol, 1:1 Zn(II)-Kaem complex reduces the 2,2-diphenyl-1-picrylhydrazyl radical, DPPH?, with a second-order rate constant, 2.48 × 104 L·mol-1·s-1, 16 times and 2 times as efficient as Kaem and 1:2 Zn(II)-Kaem complex, respectively, as determined by stopped-flow spectroscopy. Density functional theory calculation results indicate significantly increased acidity of Kaem as ligand in 1:1 Zn(II)-Kaem complex other than in 1:2 Zn(II)-Kaem complex. Kaem in 1:1 Zn(II)-Kaem complex loses two protons (one from 3-hydroxyl and one from phenolic hydroxyl) forming 1:1 Zn(II)-(Kaem-2H) during binding with Zn(II), while Kaem in 1:2 Zn(II)-Kaem complex loses one proton in each ligand forming Zn(II)-(Kaem-H)2, as confirmed by UV-vis absorption spectroscopy. Zn(II)-(Kaem-2H) is a far stronger reductant than Kaem and Zn(II)-(Kaem-H)2 as determined by cyclic voltammetry. Significant rate increases for the 1:1 complex in both β-Car?+ scavenging by electron transfer and DPPH? scavenging by hydrogen atom transfer were ascribed to decreases of ionization potential and of bond dissociation energy of 4′-OH for deprotonated Zn(II)-(Kaem-2H), respectively. Increased phenol acidity of plant polyphenols by 1:1 coordination with Zn(II) may explain the unique function of Zn(II) as a biological antioxidant and may help to design nontoxic metal-based drugs derived from natural bioactive molecules.
- Xu, Yi,Qian, Ling-Ling,Yang, Jing,Han, Rui-Min,Zhang, Jian-Ping,Skibsted, Leif H.
-
-
Read Online
- Antioxidant activity of hydrazones with sterically hindered phenol fragments
-
Kinetic parameters of the antiradical activity of derivatives of hydrazones of 4-hydroxy-3,5-di-tert-butyl-benzaldehyde are determined photocolorimetrically in their reactions with a stable diphenylpicrylhydrazyl radical, and by chemiluminescence from the capture of peroxide radicals upon the initiated oxidation of ethylbenzene. It is found that during inhibited oxidation, the reactive centers (N-H and O-H) in hetaryl-and acylhydrazone molecules operate in parallel. Regularities of the compounds' inhibiting effect are studied in heterogeneous systems upon the initiated oxidation of ethylbenzene in emulsion, and in a waterlipid model of the oxidation of phosphatidylcholine dispersion. It is established that hydrazone derivatives are antioxidants of combined action in heterophase processes of the oxidation of unsaturated substrates, displaying properties of hydroperoxide deactivators in addition to their antiradical activity. Pleiades Publishing, Ltd., 2012.
- Nikolaevskii,Kniga,Khizhan,Tikhonova,Vinogradov,Khizhan
-
-
Read Online
- Acidity of hydroxyl groups: An overlooked influence on antiradical properties of flavonoids
-
The reactions of 10 flavonoids with 2,2-diphenyl-1-picrylhydrazyl radical (dpph.) carried out in alcohols always occur significantly faster than in acidified alcohols or in dioxane. These fast kinetics benefit from the contribution of the elect
- Musialik, Malgorzata,Kuzmicz, Rafal,Pawlowski, Tomasz S.,Litwinienko, Grzegorz
-
-
Read Online
- Synthesis of luteolin loaded zein nanoparticles for targeted cancer therapy improving bioavailability and efficacy
-
A naturally occurring flavonoid, Luteolin possess wide range of pharmaceutical activities from anti-inflammatory to anticancer effect. Luteolin inhibits cell proliferation by arresting cell cycle pathways and triggers apoptotic cell death. Poor aqueous solubility of luteolin limits its oral bioavailability. Therefore, to improve the oral bioavailability of luteolin by use of biodegradable protein zein and sodium caseinate as nanocarrier. The nanoparticles were prepared by simple precipitation process. The resulting nanoparticles had mean size of 200–300 nm with negative zeta potential with 92% encapsulation efficiency and luteolin release at intestinal pH. Anti-oxidant activity of loaded molecule with respect to parent molecule significantly indicate the free radical scavenging potential of luteolin increases after encapsulation in zein nanoparticles. Luteolin loaded zein nanoparticles showed enhanced cytotoxicity against SW480 colon cancer cells and induces apoptosis. In this paper, we have shown the potential of luteolin loaded zein nanoparticles for treating colon cancer which could serve as promising strategy to develop oral formulation of this water insoluble drug enhancing its bioavailability.
- Shinde, Priyanka,Agraval, Hina,Singh, Ajeet,Yadav, Umesh C.S.,Kumar, Umesh
-
-
Read Online
- (+)-kunstlerone, a new antioxidant neolignan from the leaves of beilschmiedia kunstleri gamble
-
A new neolignan, 3,4-dimethoxy-3',4'-methylenedioxy-2,9-epoxy-6,7-cyclo- 1,8-neolign-11-en-5(5H)-one, which has been named (+)-kunstlerone (1), together with six known alkaloids: (+)-norboldine (2), (+)-N-methylisococlaurine (3), (+)-cassythicine (4), (+)
- Mollataghi, Abbas,Hadi, A. Hamid M.,Awang, Khalijah,Mohamad, Jamaludin,Litaudon, Marc,Mukhtar, Mat Ropi
-
-
Read Online
- Electron-transfer mechanism in radical-scavenging reactions by a vitamin E model in a protic medium
-
The scavenging reaction of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH*) or galvinoxyl radical (GO*) by a vitamin E model, 2,2,5,7,8-pentamethylchroman-6-ol (1H), was significantly accelerated by the presence of Mg(ClO4)2 in de-aerated methanol (MeOH). Such an acceleration indicates that the radical-scavenging reaction of 1H in MeOH proceeds via an electron transfer from 1H to the radical, followed by a proton transfer, rather than the one-step hydrogen atom transfer which has been observed in acetonitrile (MeCN). A significant negative shift of the one-electron oxidation potential of 1H in MeOH (0.63 V vs. SCE), due to strong solvation as compared to that in MeCN (0.97 V vs. SCE), may result in change of the radical-scavenging mechanisms between protic and aprotic media.
- Nakanishi, Ikuo,Kawashima, Tomonori,Ohkubo, Kei,Kanazawa, Hideko,Inami, Keiko,Mochizuki, Masataka,Fukuhara, Kiyoshi,Okuda, Haruhiro,Ozawa, Toshihiko,Itoh, Shinobu,Fukuzumi, Shunichi,Ikota, Nobuo
-
-
Read Online
- Linking an α-tocopherol derivative to cobalt(0) nanomagnets: Magnetically responsive antioxidants with superior radical trapping activity and reduced cytotoxicity
-
Covalent attachment of a phenolic antioxidant analogue of α-tocopherol to graphite-coated magnetic cobalt nanoparticles (CoNPs) provided a novel magnetically responsive antioxidant capable of preventing the autoxidation of organic materials and showing a reduced toxicity toward human cells.
- Viglianisi, Caterina,Di Pilla, Veronica,Menichetti, Stefano,Rotello, Vincent M.,Candiani, Gabriele,Malloggi, Chiara,Amorati, Riccardo
-
-
Read Online
- Kinetics of the reaction between the antioxidant Trolox and the free radical DPPH? in semi-aqueous solution
-
Reaction of the free-radical diphenylpicrylhydrazyl (DPPH) with Trolox (TrOH) was investigated in buffered hydroalcoholic media by using a stopped-flow system. DPPH was reduced to the hydrazine analogue DPPH-H with a measured stoichiometry of about 2. DPPH-H was characterized by an acid-base equilibrium (pKa = 8.6). Time-resolved absorption spectra recorded with an excess of either TrOH or DPPH indicated that no significant amount of the TrO radical was accumulated. The TrO radical formed in a first step further reacted quickly with DPPH. For 1: 1 ethanol-buffer mixtures at pH 7.4, the bimolecular rate constants of the first and second steps were 1.1 × 104 M-1 s-1 and 2 × 106 M -1 s-1, respectively. A significant increase of the measured rate constant was observed for ethanol-buffer solutions as compared to ethanol. The rate was also increased at higher pH. A deuterium isotopic effect of 2.9 was measured. These data are discussed with regards to mechanisms involving either electron or proton exchange as rate determining steps in the reaction of DPPH with Trolox. The importance of solvent acidity control in investigation of antioxidant properties is outlined. The Royal Society of Chemistry 2006.
- Friaa, Ouided,Brault, Daniel
-
-
Read Online
- DPPH·–luminol chemiluminescence system and its application in the determination of scutellarin in pharmaceutical injections and rat plasma with flow injection analysis
-
In this article, a DPPH·–luminol chemiluminescence (CL) system was reported and the CL mechanism was discussed according to the CL kinetic properties after sequence injecting DPPH· into the DPPH·–luminol reaction mixture. It was observed that scutellarin could inhibit the CL response of the DPPH·–luminol system. Based on this observation, a simple and rapid flow injection CL method was developed for the determination of scutellarin using the inhibition effect in alkaline medium. The optimized chemical conditions for the CL reaction were 5?×?10?6?mol/L DPPH· and 1.0?×?10?4?mol/L luminol in 0.01?mol/L NaOH. Under optimized conditions, the CL intensity was inversely proportional to the concentration of scutellarin over the ranges 5–2000 and 40–3200?ng/ml in pharmaceutical injection and rat plasma, respectively. The limits of detection (S/N?=?3) were 5 and 40?ng/ml in preparations and rat plasma, respectively. Furthermore, the precision, recovery and stability of the validated method were acceptable for the determination of scutellarin in both pharmaceutical injections and rat plasma. The presented method was successfully applied in the determination of scutellarin in pharmaceutical injections and real rat plasma samples.
- Yao, Hong,Huang, Xiaomei,Shi, Peiying,Lin, Zhen,Zhu, Meilan,Liu, Ailin,Lin, Xinhua,Tang, Yuhai
-
-
Read Online
- Synthesis and evaluation of the antioxidant and antiinflammatory activities of some benzo[l]khellactone derivatives and analogues
-
Treatment of 3-hydroxy-β-lapachone 4 with ylide 5 gave the coumarin derivative 7a, which was transformed to compounds 10-14. Compound 14 was then transformed to benzo[f]seselin 15 as well as to benzo[l]khellactones 16, 18 from which the title compounds 17, 19I, 19II, 20, 21 I and 21II were prepared. All the tested compounds were found to interact with DPPH in a concentration and time dependent manner. All the tested compounds highly inhibited the soybean lipoxygenase, whereas compounds 12, 17 and 19II highly compete with DMSO for ?OH. Compounds 7a, 7b, 12 and 17 induced at 48.7-58.9% protection against carrageenin induced rat paw edema.
- Nicolaides, Demetrios N.,Gautam, Daman R.,Litinas, Konstantinos E.,Hadjipavlou-Litina, Dimitra J.,Fylaktakidou, Konstantina C.
-
-
Read Online
- Synthesis of water-soluble 2,2′-diphenyl-1-picrylhydrazyl nanoparticles: A new standard for electron paramagnetic resonance spectroscopy
-
(Graph Presented) This communication reports a size-controlled synthesis of water-soluble 2,2′-diphenyl-1-picrylhydrazyl (DPPH) nanoparticles (NPs). These nanoparticles exhibit size-dependent absorption spectra and fast spin exchange-narrowed single-line
- Chen, Ou,Zhuang, Jiaqi,Guzzetta, Fabrizio,Lynch, Jared,Angerhofer, Alexander,Cao, Y. Charles
-
-
Read Online
- Synthesis and characterization of a novel non-symmetrical bidentate Schiff base ligand and its Ni(II) complex: electrochemical and antioxidant studies
-
Abstract: This paper describes the synthesis and properties of a new nitro-substituted bidentate Schiff base ligand (HL) and its nickel complex (Ni(II)-2L). Its ligand was derived from the condensation of 2′-methoxyphenyl-2-ethylamine with 5-nitro-2-hydroxybenzaldehyde. This ligand and its nickel complex were characterized through elemental analysis, UV–Vis, IR, 1H NMR and 13C NMR. The molecular structure of the nickel complex was confirmed using single-crystal X-ray diffraction. This complex crystallizes in dichloromethane in triclinic system, space group of P-1 with a = 6.6803 (2), b = 9.6702 (2), c = 12.1836 (3) and 1 formula unit in the cell. The obtained data revealed that the Ni(II) center is tetra-coordinated by two oxygen and two nitrogen atoms involving two ligands. Cyclic voltammograms of the nickel complex, recorded in DMF solutions, showed one quasi-reversible redox couple related to the Ni(II)/Ni(I) couple, demonstrating its electro-activity. This indicates a slow redox transition and/or electron exchange process, which implies that this electrochemical process is mainly diffusion-controlled. The antioxidant activity of the synthesized compounds was evaluated from the reactivity with the free radical DPPH, showing IC50 values between 0.4 and 4.5?mg/mL. Graphic abstract: [Figure not available: see fulltext.].
- Bougossa, Imène,Aggoun, Djouhra,Ourari, Ali,Berenguer, Raúl,Bouacida, Sofiane,Morallon, Emilia
-
-
Read Online
- Spectral studies and crystal structures of molybdenum(VI) complexes containing pyridine or picoline as auxiliary ligands: interaction energy calculations and free radical scavenging studies
-
Three cis-MoO2 complexes [MoO2(CAB)(py)] (1), [MoO2(CAB)(3-pic)] (2) and [MoO2(CAB)(4-pic)] (3) which vary in?the nature of the?heterocyclic bases in the auxiliary coordination site derived from an ONO donor aroylhydrazone (H2CAB) have been synthesized and characterized by various physicochemical methods. The single-crystal X-ray diffraction studies reveal that the complexes adopt a distorted octahedral N2O4 coordination sphere around the Mo(VI) center in which the ONO donor atoms of hydrazone moiety and one oxido oxygen constitute the NO3 basal plane and the axial position by the other oxido oxygen and nitrogen atom of coordinated pyridine molecule in [MoO2(CAB)(py)] (1) or picoline molecule in [MoO2(CAB)(3-pic)] (2) and [MoO2(CAB)(4-pic)] (3). The hydrogen bonding interaction generates a two-dimensional supramolecular sheet-like architecture in [MoO2(CAB)(py)] (1) and [MoO2(CAB)(3-pic)] (2), whereas a three-dimensional network?was observed in [MoO2(CAB)(4-pic)] (3). The interaction energy calculations reveal that the dispersion energy component dominates over other components and [MoO2(CAB)(3-pic)] (2) is found to be energetically more stable. Furthermore, the aroylhydrazone shows free radical scavenging activity, whereas the complexes are inactive.
- Kuriakose, Daly,Kurup, M. R. Prathapachandra
-
-
Read Online
- Total antioxidant capacity of some commercial fruit juices: Electrochemical and spectrophotometrical approaches
-
The aim of this paper was to assess the total antioxidant capacity of some commercial fruit juices (namely citrus), spectrophotometrically and by the biamperometric method, using the redox couple DPPH· (2,2-diphenyl-1- picrylhydrazyl)/DPPH (2,2-diphenyl-1
- Pisoschi, Aurelia Magdalena,Cheregi, Mihaela Carmen,Danet, Andrei Florin
-
-
Read Online
- Radical-scavenging activities of citrus essential oils and their components: Detection using 1,1-diphenyl-2-picrylhydrazyl
-
Thirty-four kinds of citrus essential oils and their components were investigated for radical-scavenging activities by the HPLC method using 1,1-diphenyl-2-picrylhydrazyl (DPPH). To examine the oils' relative radical-scavenging activities compared with that of a standard antioxidant, Trolox was employed. All of the essential oils were found to have scavenging effects on DPPH in the range of 17.7-64.0%. The radical-scavenging activities of 31 kinds of citrus essential oils were comparable with or stronger than that of Trolox (p 0.05). The oils of Ichang lemon (64.0%, 172.2 mg of Trolox equiv/mL), Tahiti lime (63.2%, 170.2 mg of Trolox equiv/mL), and Eureka lemon (61.8%, 166.2 mg of Trolox equiv/mL) were stronger radical scavengers than other citrus oils. Citrus volatile components such as geraniol (87.7%, 235.9 mg of Trolox equiv/mL), terpinolene (87.4%, 235.2 mg of Trolox equiv/mL), and γ-terpinene (84.7%, 227.9 mg of Trolox equiv/mL) showed marked scavenging activities on DPPH (p 0.05).
- Choi, Hyang-Sook,Sun Song, Hee,Ukeda, Hiroyuki,Sawamura, Masayoshi
-
-
Read Online
- Synthesis-temperature-regulated multi-enzyme-mimicking activities of ceria nanozymes
-
Ceria (CeO2) nanozymes have drawn much attention in recent years due to their unique physiochemical properties and excellent biocompatibility. It is therefore very important to establish a simple and robust guideline to regulate CeO2with desired multi-enzyme-mimicking activities that are ideal for practical bioapplications. In this work, the multi-enzyme-mimicking activities of CeO2were regulated in a facile manner by a wet-chemical method with different synthesis temperatures. Interestingly, a distinct response in multi-enzyme-mimicking activities of CeO2was observed towards different synthesis temperatures. And the regulation was ascribed to the comprehensive effect of the oxygen species, size, and self-restoring abilities of CeO2. This study demonstrates that high-performance CeO2can be rationally designed by a specific synthesis temperature, and the guidelines from radar chart analysis established here can advance the biomedical applications of ceria-based nanozymes.
- An, Xueying,Li, Sirong,Li, Tong,Lin, Anqi,Liu, Quanyi,Liu, Xiaoli,Wang, Quan,Wei, Hui,Wu, Jiangjiexing,Yang, Ming,Zhang, Yihong,Zhou, Zijun
-
supporting information
p. 7238 - 7245
(2021/09/22)
-
- Effects of a Constant Magnetic Field on the Electrochemical Reactions of Quercetin
-
The paper presents a study of the effect of a constant magnetic field (CMF) on the basic processes of quercetin electrochemical reactions. According to the observation made in previous studies, the presence of a double bond in the C-ring of quercetin enhances the antioxidant properties of that compound, whereas the presence of ?OH groups also affects the antioxidant properties. Using cyclic voltammetry it was found that the constant magnetic field improves the efficiency of quercetin electrooxidation, especially of the third stage of the process, i. e. the stage in which the oxidation of the OH groups in the A-ring is the most difficult. The use of HPLC confirmed the electrochemical measurements and the results of cyclic voltammetry studies. The beneficial effect of the magnetic field on the efficiency of quercetin oxidation was confirmed by the results of impedance spectroscopy measurements.
- Zieliński, Marek,Burnat, Barbara,Mi?ko?, Ewa
-
p. 1229 - 1235
(2020/07/13)
-
- Synthesis and spectral comparison of electronic and molecular properties of some hydrazines and hydrazyl free radicals
-
Continuing our work on hydrazyl free radicals, five triphenylhydrazine derivatives, one a new compound, were synthesized to compare the electronic and molecular properties of these compounds, study the influence of substituents on the phenyl rings, and compare their properties with the parent hydrazines and corresponding anions. These hydrazines demonstrate both acid-base and redox properties. The hydrazine proton can be removed by base, yielding the corresponding anion and both the hydrazines and their anions can be oxidized to the corresponding hydrazyl free radicals. ESR spectra confirmed their formation and X-ray crystallography of one compound confirmed their structures.
- Ionita, Petre,Lete, Cecilia,Madalan, Augustin,Matache, Mihaela,Patrascu, Bianca,Paun, Anca,Popescu, Codruta
-
-
- Boosting effect of ortho-propenyl substituent on the antioxidant activity of natural phenols
-
Seven new antioxidants derived from natural or synthetic phenols have been designed as alternatives to BHT and BHA antioxidants. Influence of various substituents at the ortho, meta and para positions of the aromatic core of phenols on the bond dissociation enthalpy of the ArO-H bond was evaluated using a DFT method B3LYP/6-311++G(2d,2p)//B3LYP/6-311G(d,p). This prediction highlighted the ortho-propenyl group as the best substituent to decrease the bond dissociation enthalpy (BDE) value. The rate constants of hydrogen transfer from these phenols to DPPH radical in a non-polar and non-protic solvent have been measured and were found to be in agreement with the BDE calculations. For o-propenyl derivatives from 2-tert-butyl-4-methylphenol, BHA, creosol, isoeugenol and di-o-propenyl p-cresol, fewer radicals were trapped by a single phenol molecule, i.e. a lower stoichiometric number. Reaction mechanisms involving the evolution of the primary phenoxyl radical ArO are proposed to rationalise these effects.
- Marteau, Clémentine,Guitard, Romain,Penverne, Christophe,Favier, Dominique,Nardello-Rataj, Véronique,Aubry, Jean-Marie
-
supporting information
p. 418 - 427
(2015/10/19)
-
- DDQ-promoted dehydrogenation from natural rigid polycyclic acids or flexible alkyl acids to generate lactones by a radical ion mechanism
-
A novel and facile DDQ-mediated dehydrogenation from natural rigid polycyclic acids or flexible alkyl acids to generate lactones is described. The formation of lactones proceeds by a radical ion mechanism, which has been established by DPPH?-mediated chemical identification, ESR spectroscopy and an enol intermediate trapping.
- Ding, Ye,Huang, Zhangjian,Yin, Jian,Lai, Yisheng,Zhang, Shibo,Zhang, Zhiguo,Fang, Lei,Peng, Sixun,Zhang, Yihua
-
supporting information; experimental part
p. 9495 - 9497
(2011/10/31)
-
- Antimicrobial and antioxidant activities of new metal complexes derived from 3-aminocoumarin
-
3-Aminocoumarin (L) has been synthesized and used as a ligand for the formation of Cr(III), Ni(II), and Cu(II) complexes. The chemical structures were characterized using different spectroscopic methods. The elemental analyses revealed that the complexes where M=Ni(II) and Cu(II) have the general formulae [ML2Cl2], while the Cr(III) complex has the formula [CrL2Cl2]Cl. The molar conductance data reveal that all the metal chelates, except the Cr(III) one, are non-electrolytes. From the magnetic and UV-Visible spectra, it is found that these complexes have octahedral structures. The stability for the prepared complexes was studied theoretically using Density Function Theory. The total energy for the complexes was calculated and it was shown that the copper complex is the most stable one. Complexes were tested against selected types of microbial organisms and showed significant activities. The free radical scavenging activity of metal complexes have been determined by measuring their interaction with the stable free radical DPPH and all the compounds have shown encouraging antioxidant activities.
- Kadhum, Abdul Amir H.,Mohamad, Abu Bakar,Al-Amiery, Ahmed A.,Takriff, Mohd S.
-
experimental part
p. 6969 - 6984
(2011/10/11)
-
- Reactivity of dpph in the oxidation of catechol and catechin
-
A kinetic study of the reduction of pyrocatechol and catechin by dpph radical has been carried out in various ratios of CH 3OH/H2O mixed solvent at pH 5.5-7.5, μ = 0.10 M [(n-Bu)4N]ClO4, and T = 25°C. The rate constants of oxidation in aqueous solvent, kH2O, were obtained from the extrapolation of the linear plots of the specific rate constants k vs. % H 2O plots at each pH value. A linear relationship between k H2O and 1/[H+] was observed for both flavonoids with kH2O = k1Ka1/[H+], where K a1 was the first acid dissociation constant on the catechol ring and k1 is the rate constant of the oxidation of the mononegative species HX-. The values of k1 obtained from the slopes of the plots are (8.2 ± 0.2) × - 105 and (6.1 ± 0.1) × - 105 M-1 s-1 for pyrocatechol and catechin, respectively. The analysis of the reaction on the basis of Marcus theory for an outer-sphere electron transfer reaction yielded a value of 3.7 × - 103 M-1 s-1 for the self-exchange rate constant of dpph/dpphH couple.
- Chen, Wei-Lin,Li, Wei-Shuen,Fu, Ping-Jou,Yeh, Andrew
-
supporting information; scheme or table
p. 147 - 153
(2011/10/02)
-
- Synthesis, antioxidant evaluation, and quantitative structure-activity relationship studies of chalcones
-
Synthesis, antioxidant activity, and quantitative structure-activity relationship (QSAR) of 25 of chalcone derivatives is reported here. They were synthesized by Claisen-Schmidt reaction and were characterized by FTIR, NMR, and mass spectroscopy. Antioxidant activity is evaluated through four different methods namely, superoxide radical-scavenging, hydrogen peroxide scavenging, reducing power, and DPPH radical-scavenging assays. Generally, compounds with -SCH3 and -OCH3 in the para position of the A-ring and -OH in the B-ring were more active than others. In few cases some of the compounds were more active than ascorbic acid or butylated hydroxytoluene. QSAR was developed correlating the antioxidant activity with the structural features of the compounds and the predictive capability of the models was estimated using internal and external validation methods. All the predictions were within the 99% confidence level. Spatial, structural, and lipophilic properties of the compounds determine their antioxidant properties.
- Sivakumar,Prabhakar,Doble
-
body text
p. 482 - 492
(2012/04/04)
-
- Reactions of 2,2-diphenyl-1-picrylhydrazyl (DPPH) with two syringylic phenols or one aroxide derivative
-
The reactions between excess 2,2-diphenyl-1-picrylhydrazyl (DPPH) and either 4-hydroxy-3,5-dimethoxybenzaldehyde (syringaldehyde, 1) or methyl 4-hydroxy-3,5-dimethoxyben-zoate (methyl syringate, 2) afford different products from those obtained with the corresponding aroxide (3)of l.In the former case (with the free phenols) the aryloxy (syringyl) group substitutes the 4-nitro group of DPPH, yielding dinitro products 7 and 8 (new stable free radicals) and 9 and 10 (corresponding hydrazines), whereas in the latter case (with the sodium aroxide 3) the aryloxy (syringyl) group substitutes one of the phenyl groups of DPPH in the para position, forming trinitro products 14 (new stable free radical) and 15 (corresponding hydrazine). Accompanying products were isolated by TLC and identified by their 1H NMR, 13C NMR, UV/Vis, and EPR spectra. The reaction mechanisms involving hy-drazyl and aroxyl free radicals are discussed.
- Hristea, Elena N.,Covaci-C?mpeanu, Irina C.,Ioni?ǎ, Gabriela,Ioni?ǎ, Petre,Draghici, Constantin,Cǎproiu, Miron T.,Hillebrand, Mihaela,Constantinescu, Titus,Balaban, Alexandru T.
-
experimental part
p. 626 - 634
(2009/07/17)
-
- Structure and antioxidant activity of brominated flavonols and flavanones
-
Hypobromous acid (HOBr) produced by both eosinophil peroxidase (EPO) and myeloperoxidase (MPO) is a stronger oxidant than HOCl, and is also essential for optimal and efficient microbial killing. Considering the potential cytotoxic effect of HOBr, if it is formed outside the phagosome, it should be useful to scavenge it in order to protect the nearby tissues. In this study the ability of selected flavonoids to protect against HOBr mediated oxidation reactions was performed through a competitive reaction, and the resulting products identified by high performance liquid chromatography (HPLC) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). Several structural features were found to be important to confer high antioxidant activity to flavonoids towards HOBr: the C2=C3 double bond and the 3-OH group in the C-ring, and the presence of both 5-OH and 7-OH groups in the A-ring. TheMS results showed that flavonoids are dibrominated in the A-ring, suggesting that (except for fisetin) bromination occurs at C6 and C8 positions, through an electrophilic aromatic substitution reaction. The chemical modifications achieved by bromination of flavonoids have changed their biological properties, presenting their brominated derivatives higher antioxidant activity, as radical scavengers, and higher lipophilicity, than the parent flavonoids. Brominated flavonoids may then diffuse easily through membranes increasing the intracellular concentration of the compounds. These locally formed metabolites may also interact with signaling cascades involving cytokines and regulatory transcription factors, thus playing a role in inflammation and in the regulation of immune response. Copyright
- Justino, Goncalo C.,Rodrigues, Margarida,Florencio, M. Helena,Mira, Lurdes
-
experimental part
p. 1459 - 1468
(2010/05/18)
-
- A kinetic study of the reaction of N,N-dimethylanilines with 2,2-diphenyl-1-picrylhydrazyl Radical: A Concerted Proton-Electron Transfer?
-
(Chemical Equation Presented) The reactivity of the 2,2-diphenyl-1- picrylhydrazyl radical (dpph?) toward the N-methyl C-H bond of a number of 4-X-substituted-N,N-dimethylanilines (X = OMe, OPh, CH3, H) has been investigated in MeCN, in the absence and in the presence of Mg(ClO4)2, by product, and kinetic analysis. The reaction was found to lead to the N-demethylation of the N,N-dimethylaniline with a rate quite sensitive to the electron donating power of the substituent (ρ+ = -2.03). With appropriately deuterated N,N-dimethylanilines, the intermolecular and intramolecular deuterium kinetic isotope effects (DKIEs) were measured with the following results. Intramolecular DKIE [(k H/kD)intra] was found to always be similar to intermolecular DKIE [(kH/kD)inter]. These results suggest a single-step hydrogen transfer mechanism from the N-C-H bond to dpph? which might take the form of a concerted proton-electron transfer (CPET). An electron transfer (ET) step from the aniline to dpph ? leading to an anilinium radical cation, followed by a proton transfer step that produces an α-amino carbon radical, appears very unlikely. Accordingly, a rate-determining ET step would require no DKIE or at least different inter and intramolecular isotope effects. On the other hand, an equilibrium-controlled ET is not compatible with the small slope value (-0.22 kcal-1 K-1) of the log kH/ΔG° plot. Furthermore, the reactivity increases by changing the solvent to the less polar toluene whereas the reverse would be expected for an ET mechanism. In the presence of Mg2+, a strong rate acceleration was observed, but the pattern of the results remained substantially unchanged: inter and intramolecular DKIEs were again very similar as well as the substituent effects. This suggests that the same mechanism (CPET) is operating in the presence and in the absence of Mg2+. The significant rate accelerating effect by Mg2+ is likely due to a favorable interaction of the Mg2+ ion with the partial negatively charged α-methyl carbon in the polar transition state for the hydrogen transfer process.
- Baciocchi, Enrico,Calcagni, Alessandra,Lanzalunga, Osvaldo
-
p. 4110 - 4115
(2008/09/21)
-
- Hybrid macromolecular antioxidants based on hydrophilic polymers and sterically hindered phenols
-
A novel class of biologically active substances was created. These are hybrid macromolecular antioxidants (HMAO) based on hydrophilic polymers with chemically grafted sterically hindered phenols with different structural parameters. The antiradical activities of HMAO were assessed in reactions with 2,2-diphenyl-1-picrylhydrazyl and the corresponding sodium sulfonate in various solvents. The mechanism that explains the substantially enhanced activities of HMAO in water was proposed. The state of HMAO in solutions was studied by viscosimetry and photon correlation spectroscopy. HMAO were assayed in biological models.
- Aref'ev,Belostotskaya,Vol'Eva,Domnina,Komissarova,Sergeeva,Khrustaleva
-
p. 781 - 790
(2008/04/12)
-
- Abnormal solvent effects on hydrogen atom abstraction. 3. Novel kinetics in sequential proton loss electron transfer chemistry
-
A prolonged search involving several dozen phenols, each in numerous solvents, for an ArOH/2,2-diphenyl-1-picrylhydrazyl (dpph.) reaction that is first-order in ArOH but zero-order in dpph. has reached a successful conclusion. These unusual kinetics are followed by 2,2′-methylene-bis(4-methyl-6-tert-butylphenol), BIS, in five solvents (acetonitrile, benzonitrile, acetone, cyclohexanone, and DMSO). In 15 other solvents the reactions were first-order in both BIS and dpph. (i.e., the reactions followed "normal" kinetics). The zero-order kinetics indicate that in the five named solvents the BIS/dpph. reaction occurs by sequential proton loss electron transfer (SPLET). This mechanism is not uncommon for ArOH/dpph. reactions in solvents that support ionization, and normal kinetics have always been observed previously (see Litwinienko, G.; Ingold, K. U. J. Org. Chem. 2003, 68, 3433 and Litwinienko, G.; Ingold, K. U. J. Org. Chem. 2004, 69, 5888). The zero-order kinetics found for the BIS/dpph. reaction in five solvents, S, imply that BIS ionization has become the rate-determining step (rds, rate constants 0.20-3.3 s -1) in the SPLET reaction sequence: S + HOAr ? S- HOAr →rds SH+ + -OAr →dpph. SH+ + .OAr + dpph- → S + .OAr + dpph-H, where ArOH = BIS. Some properties specific to BIS that may be relevant to its relatively slow ionization in the five solvents are considered.
- Litwinienko, Grzegorz,Ingold
-
p. 8982 - 8990
(2007/10/03)
-
- Antioxidant properties of natural and synthetic chromanol derivatives: Study by fast kinetics and electron spin resonance spectroscopy
-
(Chemical Equation Presented) Chromanol-type compounds act as antioxidants in biological systems by reduction of oxygen-centered radicals. Their efficiency is determined by the reaction rate constants for the primary antioxidative reaction as well as for disproportionation and recycling reactions of the antioxidant-derived radicals. We studied the reaction kinetics of three novel chromanols: cis- and trans-oxachromanol and the dimeric twin-chromanol, as well as ubichromanol and ubichromenol, in comparison to α-tocopherol and pentamethylchromanol. The antioxidant-derived radicals were identified by optical and electron spin resonance spectroscopy (ESR). The kinetics of the primary antioxidative reaction and the disproportionation of the chromanoxyl radicals were assessed by stopped-flow photometry in different organic solvents to simulate the different polarities associated with biomembranes. Furthermore, the reduction of the chromanoxyl radicals by ubiquinol and ascorbate was measured after laser-induced one-electron chromanol oxidation in ethanol and in a micellar system, respectively. The rate constants showed that twin-chromanol had better radical scavenging properties than α-tocopherol and a significantly slower disproportionation rate of its corresponding chromanoxyl radical. In addition, the radical derived from twin-chromanol is reduced by ubiquinol and ascorbate at a faster rate than the tocopheroxyl radical. Finally, twin-chromanol can deliver twice as many reducing equivalents, which makes this compound a promising new candidate as artificial antioxidant in biological systems.
- Gregor, Wolfgang,Grabner, Gottfried,Adelwoehrer, Christian,Rosenau, Thomas,Gille, Lars
-
p. 3472 - 3483
(2007/10/03)
-
- AZOLIDINECARBONITRILES AND THEIR USE AS DPP-IV INHIBITORS
-
The invention discloses a novel heterocyclic compounds that falls within f the ambit of general formula (I), its stereoisomers, pharmaceutically acceptable salts or solvates wherein X, n,k,z, R1, R2, R3, R4, R5 and R6 are as defined in the specification that are useful in (i) normalizing elevated blood pglucose levels in diabetes, (ii) treating disorders related to glucose intolerance and (iii) for scavenging free radicals of mammals. The invention also discloses pharmaceutically acceptable composition comprising these compounds, method for preparation of the compounds as defined bove and method of treating mammals including human beings by administering an effective amount of said compounds to a subject in need thereof. The invention further discloses use of these compounds in the manufacture of a medicament useful for treatment of different disease conditions as stated above.
- -
-
Page/Page column 46-48
(2008/06/13)
-
- Abnormal solvent effects on hydrogen atom abstractions. 1. The reactions of phenols with 2,2-diphenyl-1-picrylhydrazyl (dpph?) in alcohols
-
Rate constants, kArOH/dpph?,s, for hydrogen atom abstraction from 13 hindered and nonhindered phenols by the diphenylpicrylhydrazyl radical, dpph?, have been determined in n-heptane and a number of alcoholic and nonalcoholic, hydrogen-bond accepting solvents. Abnormally enhanced values of kArOH/dpph?,s have been observed in alcohols. It is proposed that this is due to partial ionization of the phenols and a very fast electron transfer from phenoxide anion to dpph?. The popular assessment of the antioxidant activities of phenols with dpph? in alcohol solvents will generally lead to an overestimation of their activities.
- Litwinienko, Grzegorz,Ingold
-
p. 3433 - 3438
(2007/10/03)
-
- 125I-labeled 2-O- and 3-O-m-iodobenzyl, and 6-O-m-iodophenyl derivatives of L-ascorbic acid: Synthesis and preliminary tissue distribution
-
Three 125I-labeled 2-O- and 3-O-m-iodobenzyl, and 6-O-m-iodophenyl derivatives of L-ascorbic acid were prepared by melt exchange procedures in isolated radiochemical yields of 12-60% after HPLC purification. Biodistribution studies in tumor-bearing mice showed very different in vivo tissue uptake properties from previous results obtained with 14C-labeled ascorbic acid and 6-deoxy-6-[18F]fluoro-L-ascorbic acid. None of these seems to be suitable radioiodinated analogs of L-ascorbic acid for imaging study of its in vivo biochemistry. Copyright
- Yamamoto, Fumihiko,Kuwano, Eri,Kaneshiro, Tetsuo,Sasaki, Shigeki,Maeda, Minoru
-
p. 737 - 750
(2007/10/03)
-
- Gallic esters of sucrose as efficient radical scavengers in lipid peroxidation
-
Three tests of increasing complexity were used to assess the antioxidant activity of five synthetic gallic esters of sucrose bearing 3, 6, 7, or 8 galloyl units. In addition, two of these compounds had 1 or 2 hydrocarbon (C10-C12) acyl chains. Reaction with the DPPH radical led to the evaluation of the number of radicals trapped per galloyl unit n (3-4), as well as the apparent second-order rate constant for H atom donation k (1200-1500/M/s). These results indicated similar contribution and reactivity of all the galloyl units. Inhibition of the AAPH-initiated peroxidation of linoleic acid in a micellar medium confirmed the additive contribution of the galloyl units, whereas the presence of the hydrocarbon acyl chains had no influence. These results suggest an inhibition of initiation at high antioxidant levels and an underlying prooxidant effect of the galloyl radicals at low concentrations. Finally, LDL peroxidation was inhibited in proportion to the number of galloyl units, in agreement with the preceding tests.
- Dufour, Claire,Da Silva, Eric,Potier, Pierre,Queneau, Yves,Dangles, Olivier
-
p. 3425 - 3430
(2007/10/03)
-
- Water-soluble flavonol (= 3-hydroxy-2-phenyl-4H-1-benzopyran-4-one) derivatives: Chemical synthesis, colouring, and antioxidant properties
-
Water-soluble derivatives of rutin, a very common glycoside of quercetin (= 3,3',4',5,7-pentahydroxyflavone = 2-(3,4-dihydroxyphenyl)-3,5,7- trihydroxy-4H-1-benzopyran-4-one) and a potent plant antioxidant from the flavonol family, were synthesized by simple chemical procedures aimed at introducing carboxy or sulfo groups at the sugar moiety (Scheme 1). Such derivatives form stable molecular complexes with malvin, a polyphenolic pigment from the anthocyanin family, and thereby prove to be very effective in the enhancement (hyperchromism) and variation (bathochromism) of natural colours. The H2O-solubilizing carboxylate and sulfate groups are shown to deeply modify the enthalpy-entropy balance of the pigment-flavonol complexation (copigmentation). A molecular interpretation of the complexation-induced bathochromic shift in the pigment VIS band is proposed. Finally, the H2O-soluble rutin derivatives are shown to retain the high antioxidant ability of rutin as evidenced by their efficient trapping of the coloured radical DPPH (=2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl).
- Alluis, Bertrand,Perol, Nathalie,Hajji, Hakima El,Dangles, Olivier
-
p. 428 - 443
(2007/10/03)
-
- Stopped-flow and spectrophotometric study on radical scavenging by tea catechins and the model compounds
-
Radical scavenging of four tea catechins, (-)-epicatechin (EC), (-)- epigallocatechin (EGC), (-)-epicatechin gallate (ECg) and (-)- eppigallocatechin gallate (EGCg), and the model compounds of their partial structure was examined against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical using stopped-flow and spectrophotometric methods. The number of DPPH radicals scavenged by a polyphenol molecule was larger than that of phenolic hydroxyl groups, suggesting that hydrogens which bond directly to the aromatic ring can also participate in radical scavenging. A model for the scavenging reaction was proposed in which the reaction proceeded with successive dehydrogenation from a polyphenol molecule. Analysis of the second order reaction rate constants and the activation parameters between DPPH and polyphenol at the early stage of the reaction showed that the values depended on the number of phenolic hydroxyl groups and their mutual position. Contribution of the A ring of catechins to the rate constants was estimated to be far smaller than that from the B ring. In the EGCg molecule, the B ring and the gallate group were not independent, but acted as a single group for DPPH radical scavenging.
- Senba, Yasushi,Nishishita, Tsukasa,Saito, Kieko,Yoshioka, Hiroe,Yoshioka, Hisashi
-
p. 1369 - 1374
(2007/10/03)
-
- One-electron oxidation of quercetin and quercetin derivatives in protic and non protic media
-
Quercetin (3,3′,4′,5,7-pentahydroxyflavone) and quercetin derivatives (3-methylquercetin, rutin) are strong flavonoid antioxidants abundant in plants and in human diet. Their oxidation by DPPH, CAN or dioxygen (autoxidation) is studied in protic and non protic solvents. From kinetic investigations by UV-visible spectroscopy, oxidation rate constants are estimated. Fast disproportionation of flavonoid radicals is shown to give quinones which can be identified by their adducts with methanol (quercetin quinone) or sodium benzenesulfinate (rutin quinone). In strongly alkaline non aqueous conditions, the quercetin quinone can also be evidenced by strong charge transfer absorption bands in the range 700-800 nm. The consequences of these observations for the antioxidant properties of quercetin and quercetin derivatives are discussed.
- Dangles, Olivier,Fargeix, Guillaume,Dufour, Claire
-
p. 1387 - 1395
(2007/10/03)
-
- Novel Water-Soluble Diorganyl Tellurides with Thiol Peroxidase and Antioxidant Activity
-
Novel water-soluble diaryl tellurides, alkyl aryl tellurides, and dialkyl tellurides carrying sulfopropyl groups were prepared and found to possess potent peroxide decomposing and chain-breaking antioxidative capacity. The dilithium, disodium, dipotassium, and bis-tetramethylammonium salts of bis(4-hydroxyphenyl) telluride (4) were treated with 2.3 equiv of 1,3-propanesultone in aqueous tert-butyl alcohol to give the corresponding salts 5 of bis-O-sulfopropylated diaryl telluride. A variety of diaryl ditellurides were reduced with sodium borohydride in ethanol. Upon addition of propanesultone to the resulting sodium arenetellurolates, the corresponding 3-aryltellurenylpropanesulfonic acid sodium salts 8 were precipitated. Diphenyl diselenide and dibutyl ditelluride reacted similarly to afford the sodium salts of 3-benzeneselenenylpropanesulfonic acid (9) and 4-telluraoctanesulfonic acid (10), respectively. The glutathione peroxidase-like activity of the water-soluble compounds was assessed at pH = 7.4 by using the coupled GSSG reductase assay. Dialkyl telluride 10 turned out to be the most efficient catalyst. Several alkyl aryl tellurides 8 were also more efficient than any of the previously tested organotellurium compounds in this model. Bulky and electron-withdrawing aryl substituents seemed to reduce activity, whereas electron-donating groups enhanced it. Alkyl aryl selenide 9 was void of any catalytic activity. The novel compounds were also assessed by 1H NMR spectroscopy for their capacity to catalyze the hydrogen peroxide oxidation of N-acetylcysteine in D2O under acidic conditions. In the presence of 0.01 mol % of the organotellurium catalyst, the thiol concentration was reduced to 50% within 12 min for the most active catalyst (compound 5b). Although many of the compounds showed high catalytic activity, it was not possible to rationalize their relative efficiency. The capacity of the novel organotellurium compounds to act as a scavengers of 1,1-diphenyl-2-picrylhydrazyl (DPPH) was also investigated. The organotelluriums seem to act primarily as electron donors in their reaction with DPPH. Compounds 8d, 10, and 8b were the most effective scavengers. Bulky or electron-withdrawing aryl substituents caused a reduction in activity, whereas electron-donating ones enhanced it. None of the compounds could match vitamin E in their scavanging capacity.
- Kanda, Takahiro,Engman, Lars,Cotgreave, Ian A.,Powis, Garth
-
p. 8161 - 8169
(2007/10/03)
-
- Interphase processes involving hydrazine derivatives. VI: The syntheses of 2-(p-nitrophenyl)-2-phenyl-1-picrylhydrazine, 2,2-bis(p-nitrophenyl)-1-picrylhydrazine and their 15n labelled congeners
-
The stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) dissolved in methylene chloride reacts with solid sodium nitrite in the presence of 15C5 crown ether to yield selectively 2-(p-nitrophenyl)-2-phenyl-1-picrylhydrazine (NO2DPPH2), or its 15N congener if the sodium nitrite used was labelled. When the reaction of DPPH is carried out in liquid-liquid diphasic system with nitrous acid generated in situ, only 2,2-bis(p-nitrophenyl)-1-picrylhydrazine is formed [(NO2)2DPPH2]. Using 15N labelled sodium nitrite the corresponding labelled congeners could be obtained. In both cases the presence of free NO2 species in the reaction mixture was proved by the capture with t-butylphenylnitrone and ESR characterization of species formed. In the case of the labelled derivatives the couplings between 15N with 1H and 13C are presented.
- Luca, Constantin,Ioni?ǎ, Petre,Cǎproiu, Miron Teodor,Cǎldǎraru, Horia,Constantinescu, Titus
-
p. 221 - 224
(2007/10/03)
-
- SULFENAMIDES AND SULFINAMIDES VI. REACTIONS OF ARYL SULFENAMIDES WITH DIPHENYLPICRYLHYDRAZYL FREE RADICAL
-
Hydrogen abstraction may be postulated as the first step in reactions of aryl sulfenamides with the stable diphenylpicrylhydrazyl free radical.Differences in the reactivity of the sulfenamides are controlled by steric and electronic effects of the substituents, with attention drawn to the capacity of the divalent sulfur atom to relay these effects.Origins of decomposition products are discussed.
- Chan, Christopher,Cole, Edward R.,Southwell-Keely, Peter T.
-
p. 261 - 269
(2007/10/02)
-
- 3-O-Alkylascorbic Acids as Free-Radical Quenchers: Synthesis and Inhibitory Effect on Lipid Peroxidation
-
A novel series of 3-O-alkylascorbic acids (3-RASA, 3a-n) was synthesized to act as radical scavengers for active oxygen species and free radicals, and their redox potential and inhibitory effects on lipid peroxidation in rat liver microsomes were evaluated.The redox potentials of the 3-RASA compounds were increased by the substituent group to 90-190 mV above the potential for ascorbic acid (i.e., 3-RASA compounds were harder to oxidize).Although 3-O-dodecylascorbic acid (3c) and 3-O-(decylcarbomethyl)ascorbic acid (3i) differed in their redox potentials, they both markedly inhibited lipid peroxidation in rat liver microsomes to a similar extent (IC50 = 3.1 and 3.3E-6M, respectively).Structure-activity relationship studies demonstrated that the anti lipid peroxidation activity of the 3-RASA compounds was markedly dependent upon their hydrophobicity.
- Nihro, Yasunori,Miyataka, Hideki,Sudo, Tadamitsu,Matsumoto, Hitoshi,Satoh, Toshio
-
p. 2152 - 2157
(2007/10/02)
-
- SULFENAMIDES AND SULFINAMIDES VII. REACTIONS OF ARYL SULFINAMIDES WITH DIPHENYLPICRYLHYDRAZYL FREE RADICAL
-
In common with the sulfenamides, hydrogen abstraction is postulated as the first step in reactions of aryl sulfinamides with the stable diphenylpicrylhydrazyl free radical.However, marked differences between the reations of the two classes are established, with rates and extents of reaction controlled by the oxidation level of the sulfur atom.Reversibility of the sulfinamide reaction is discussed.
- Clarke, Victor,Cole, Edward R.,Southwell-Keely, Peter T.
-
p. 237 - 243
(2007/10/02)
-
- 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
-
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.Keywords - tannin; 1,1-diphenyl-2-picrylhydrazyl; radical scavenger; radical coupling; alkyl gallate; dialkyl hexahydroxydiphenate; hydrolyzable tannin.
- Yoshida, Takashi,Mori, Kazuko,Hatano, Tsutomu,Okumura, Tomoko,Uehara, Ikue,et al.
-
p. 1919 - 1921
(2007/10/02)
-
- MODEL COMPOUND STUDIES RELATED TO PEROXIDASES-II THE CHEMICAL REACTIVITY OF A HIGH VALENT PROTOHEMIN COMPOUND
-
The chemical reactivity of the model analog to compound I of the peroxidases resulting from the reaction of "chelated protohemin" and m-chloroperbenzoic acid is examined.The model intermediate shows no H-atom abstraction or O insertion activity and substrate reactivity depends only on the E1/2 value of the substrate.A Marcus theory treatment of the available kinetic data for HRP suggests that the oxidative pathway for substrate oxidations is an outer-sphere electron transfer.From the results of the model catalyzed oxidation of 1,4-cyclohexadiene to benzene, an alternate mechanism for cytochrome P-450 catalyzed hydroxylations is suggested.
- Traylor, T. G.,Lee, William A.,Stynes, Dennis V.
-
p. 553 - 568
(2007/10/02)
-
- Isotope effects in the diphenylpicrylhydrazyl-inhibited thermal polymerization of 2,6-dideuteriostyrene
-
There is an inverse isotope effect in the reaction between 2,2-diphenyl-1-picrylhydrazyl DPPH and 2,6-dideuteriostyrene of 0.75 +/- 0.07 at 75 deg C in degassed neat styrene.This result is consistent with the proposal that the reaction involves hydrogen transfer to DPPH from a Diels-Alder dimer of styrene.The rate constant for dimerization of styrene to this calculated to be 1.8E-10 L mol-1s-1 at 75 deg C.
- Kopecky, Karl R.,Hall, Michael C.
-
p. 3090 - 3094
(2007/10/02)
-
- Products of reaction between styrene and some radicals with 2,2-diphenyl-1-picrylhydrazyl
-
Addition of 2,2-diphenyl-1-picrylhydrazyl DPPH to styrene at 75 deg C results in little change in the amounts of cis- and trans-1,2-diphenylcyclobutane and 1,2,3,4-tetrahydro-1-phenylnaphthalene, in a slightly smaller amount of 1-phenylnaphthalene, and in a considerable increase in the amount of 1,2-dihydro-1-phenylnaphthalene that are formed.Formation of the styrene trimer 1,2,3,4-tetrahydro-1-phenyl-4-(1-phenylethyl)naphthalene is eliminated completely.Products derived from DPPH are 1-(4-nitrophenyl)-1-phenyl-2-picrylhydrazine 9 and 1--2,2-diphenylhydrazine, 10.DPPH intercepts the thermally formed Diels-Alder dimer of styrene as soon as it is formed to give the 1,2,3,4-tetrahydro-4-phenyl-1-naphthyl radical.Thermolysis of bis(1,2,3,4-tetrahydro-4-phenyl-1-naphthyl)diazene in the presence of DPPH yields 20percent of 10, 10percent of 1--2-(4-nitrophenyl)-2-phenylhydrazine and 9 while thermolysis of 1,2-bis(1-phenylethyl)diazene in the presence of DPPH yields 9 and 44percent of 1--2,2-diphenylhydrazine showing that substituted benzyl radicals efficiently displace the 4-nitro group of DPPH.The nitro group is transferred to an unsubstituted phenyl group of DPPH.
- Kopecky, Karl R.,Hall, Michael C.
-
p. 3095 - 3104
(2007/10/02)
-