The kinetic behavior of cinnamic acids, their methyl esters, and two catechols 1−10 (ArOH) in the reaction with DPPH• methanol ethanol is not compatible a mechanism that involves hydrogen atom abstraction from hydroxyl group by DPPH•. rate this at 25°C is, fact, comparatively fast despite phenolic OH ArOH bonded to solvent molecules. observed constants (k1) relative + are 3−5 times larger for esters than corresponding free acids and, latter, decrease as concentration increased according...

The antioxidant activity of selected representatives flavonoids, coumarins, and cinnamic acids was examined by measuring their protective action toward linoleic acid peroxidation in micelles sodium dodecyl sulfate buffer solution, pH 7.4. Results are expressed as relative efficiency (RAE), defined the ratio (AE) tested compound to that α-tocopherol. best RAE values were observed for followed coumarins acids. From results, within each class compounds a structure−activity relationship can be...

The formal H-atom abstraction by the 2,2-diphenyl-1-picrylhydrazyl (dpph•) radical from 27 phenols and two unsaturated hydrocarbons has been investigated a combination of kinetic measurements in apolar solvents density functional theory (DFT). computed minimum energy structure dpph• shows that access to its divalent N is strongly hindered an ortho H atom on each phenyl rings o-NO2 groups picryl ring. Remarkably small Arrhenius pre-exponential factors for [range (1.3−19) × 105 M−1 s−1] are...

gamma-Terpinene (TH), a monoterpene hydrocarbon present in essential oils, retards the peroxidation of linoleic acid (LH). The TH has been shown to yield p-cymene as only organic product chain reaction which carrier is hydroperoxyl radical, HOO(.). LH well-known be chains are carried by linoleylperoxyl radicals, LOO., and products linoleyl hydroperoxides. retardation found due rapid termination via very fast cross-reaction between HOO. LOO. radicals. This antioxidant mechanism completely...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe Surprisingly High Reactivity of Phenoxyl RadicalsM. Foti, K. U. Ingold, and J. LusztykCite this: Am. Chem. Soc. 1994, 116, 21, 9440–9447Publication Date (Print):October 1, 1994Publication History Published online1 May 2002Published inissue 1 October 1994https://pubs.acs.org/doi/10.1021/ja00100a005https://doi.org/10.1021/ja00100a005research-articleACS PublicationsRequest reuse permissionsArticle Views1472Altmetric-Citations153LEARN ABOUT THESE...

1,8-Naphthalenediol, 5, and its 4-methoxy derivative, 6, were found to be potent H-atom transfer (HAT) compounds on the basis of their rate constants for 2,2-di(4-t-octylphenyl)-1-picrylhydrazyl radical (DOPPH•), kArOH/DOPPH•, or as antioxidants during inhibited styrene autoxidation, kArOH/ROO•, initiated with AIBN. The showed that 5 6 are more active HAT than ortho-diols, catechol, 1, 2,3-naphthalenediol, 2, 3,5-di-tert-butylcatechol, 3. Compound has almost twice antioxidant activity,...

The effects of polar (acetonitrile and tert-butyl alcohol) apolar (cyclohexane) solvents on the peroxyl-radical-trapping antioxidant activity some flavonoids, catechol derivatives, hydroquinone, monophenols have been studied. inhibition rate constants k(inh) antioxidants determined by following increase in absorbance at 234 nm a dilute solution linoleic acid 50 degrees C containing small amounts radical initiator. Despite low concentration acid, peroxidation process has confirmed to be free...

Catechols and 1,8-naphthalene diols contain one "free" hydroxyl intramolecularly H-bonded group. The hydroxyls are strong hydrogen-bond donors (HBDs) with alpha2H values (Abraham et al. J. Chem. Soc., Perkin Trans. 2 1989, 699) ranging from 0.685 to 0.775, indicating that these compounds have similar HBD properties those of strongly acidic phenols such as 4-chlorophenol (alpha2H = 0.670) 3, 5-dichlorophenol 0.774). Kinetic effects on H-atom abstractions the in HB acceptor (HBA) solvents can...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFunctionalization of calix[4]arenes by alkylation with 2-(chloromethyl)pyridine hydrochlorideSebastiano Pappalardo, Luigi Giunta, Mario Foti, George Ferguson, John F. Gallagher, and Branko KaitnerCite this: J. Org. Chem. 1992, 57, 9, 2611–2624Publication Date (Print):April 1, 1992Publication History Published online1 May 2002Published inissue 1 April...

Abstract Objectives The aim of this review article is to introduce the reader mechanisms, rates and thermodynamic aspects processes involving most biologically relevant non-phenolic radical-trapping antioxidants. Key findings Antioxidant defences in living organisms rely on a complex interplay between small molecules enzymes, which cooperate regulating concentrations potentially harmful oxidizing species within physiological limits. noxious effects an uncontrolled production oxygen-...

In methanol/water, dpph• bleaching (519 nm) by quercetin, QH2, exhibits biphasic kinetics. The reacts completely with the quercetin anion within 100 ms. Subsequent slower involves solvent and QH2 addition to quinoid products. fast reaction is first-order in but only ca. 0.38 order [QH2]. This extraordinary nonintegral attributed reversible formation of π-stacked {QH–/dpph•} complexes which electron transfer products, {QH•/dpph–}, slow (kET ≈ 105 s–1).

Abstract Angiogenesis is involved in many pathological states such as progression of tumours, retinopathy prematurity and diabetic retinopathy. The latter a more complex complication which neurodegeneration plays significant role leading cause blindness. vascular endothelial growth factor (VEGF) powerful pro‐angiogenic that acts through three tyrosine kinase receptors (VEGFR‐1, VEGFR‐2 VEGFR‐3). In this work we studied the anti‐angiogenic effect quercetin (Q) some its derivates human...

Remote intramolecular hydrogen bonds (HBs) in phenols and benzylammonium cations influence the dissociation enthalpies of their O−H C−N bonds, respectively. The direction these HBs, para → meta or para, determines sign variation with respect to molecules lacking remote HBs. For example, bond enthalpy 3-methoxy-4-hydroxyphenol, 4, is about 2.5 kcal/mol lower than that its isomer 3-hydroxy-4-methoxyphenol, 5, although group additivity rules would predict nearly identical values. In case...

The kinetics and energetics of the reversible reaction phenols with dpph˙ radical have been studied; steric shielding divalent N by o-NO2 in seems to be main cause entropic barriers this reaction.

The kinetics of the reaction peroxyl and dpph˙ radicals with phenols H-bonded to N-bases have been studied for first time. Electron-transfer processes are observed in MeCN but only radical.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTp-tert-Butylcalix[6]arene symmetrically tetrasubstituted with pyridine pendant groups: synthesis, x-ray crystal structure, and conformational analysis by dynamic NMR spectroscopy molecular mechanics calculationsPlacido Neri, Mario Foti, George Ferguson, John F. Gallagher, Branko Kaitner, Miquel Pons, M. Antonia Molins, Luigi Giunta, Sebastiano PappalardoCite this: J. Am. Chem. Soc. 1992, 114, 20, 7814–7821Publication Date (Print):September 1,...

The 2,2'-azobis(isobutyronitrile)(AIBN)-induced autoxidation of gamma-terpinene (TH) at 50 degrees C produces p-cymene and hydrogen peroxide in a radical-chain reaction having HOO* as one the chain-carrying radicals. kinetics this cyclohexane tert-butyl alcohol show that chain termination involves formal HOO. + self-reaction over wide range gamma-terpinene, AIBN, O2 concentrations. However, acetonitrile process is accompanied by via cross-reaction terpinenyl radical, T., with radical under...