Phenols as Antioxidants

Ross, L. J. N.; Barclay, C.; Vinqvist, Melinda R.

doi:10.1002/9780470682531.pat0288

Cited by 21 publications

(43 citation statements)

References 264 publications

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“…The mean of the results obtained for each cresol by the higher level theoretical methods (CBS-QB3 and CCSD/cc-pVDZ//B3LYP/cc-pVTZ), with the larger uncertainty of the corresponding individual values, were selected in this work as ∆ f H m°( C 6 Table 4 with corresponding results from experimental and theoretical methods reported in the literature. 4,[26][27][28][29][30][31][32][33][34][35][36][37][38] As noted in the Introduction, much better agreement is observed when the DH°(C 6 situation is unlikely to improve until a general consensus is reached about the value of DH°(C 6 H 5 O-H). The relative stabilities of the cresols and of the corresponding methylphenoxyl radicals in the gas phase, as measured by the differences in their Gibbs energies of formation at 298.15 K, can be analyzed by using the standard enthalpies of formation (or their differences relative to phenol in the case of the radicals) recommended in this work and the following entropy values:…”

Section: Enthalpies Of Formation Of Methylphenoxyl Radicals and O-h Bmentioning

confidence: 99%

Energetics of Cresols and of Methylphenoxyl Radicals

et al. 2007

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Combustion calorimetry studies were used to determine the standard molar enthalpies of formation of o-, m-, and p-cresols, at 298.15 K, in the condensed state as Delta(f)H(m) degrees (o-CH(3)C(6)H(4)OH,cr) = -204.2 +/- 2.7 kJ.mol(-1), Delta(f)H(m) degrees (m-CH(3)C(6)H(4)OH,l) = -196.6 +/- 2.1 kJ.mol(-1), and Delta(f)H(m) degrees (p-CH(3)C(6)H(4)OH,cr) = -202.2 +/- 3.0 kJ.mol(-1). Calvet drop calorimetric measurements led to the following enthalpy of sublimation and vaporization values at 298.15 K: Delta(sub)H(m) degrees (o-CH(3)C(6)H(4)OH) = 73.74 +/- 0.46 kJ.mol(-1), Delta(vap)H(m) degrees (m-CH(3)C(6)H(4)OH) = 64.96 +/- 0.69 kJ.mol(-1), and Delta(sub)H(m) degrees (p-CH(3)C(6)H(4)OH) = 73.13 +/- 0.56 kJ.mol(-1). From the obtained Delta(f)H(m) degrees (l/cr) and Delta(vap)H(m) degrees /Delta(sub)H(m) degrees values, it was possible to derive Delta(f)H(m) degrees (o-CH(3)C(6)H(4)OH,g) = -130.5 +/- 2.7 kJ.mol(-1), Delta(f)H(m) degrees (m-CH(3)C(6)H(4)OH,g) = -131.6 +/- 2.2 kJ.mol(-1), and Delta(f)H(m) degrees (p-CH(3)C(6)H(4)OH,g) = -129.1 +/- 3.1 kJ.mol(-1). These values, together with the enthalpies of isodesmic and isogyric gas-phase reactions predicted by the B3LYP/cc-pVDZ, B3LYP/cc-pVTZ, B3P86/cc-pVDZ, B3P86/cc-pVTZ, MPW1PW91/cc-pVTZ, CBS-QB3, and CCSD/cc-pVDZ//B3LYP/cc-pVTZ methods, were used to obtain the differences between the enthalpy of formation of the phenoxyl radical and the enthalpies of formation of the three methylphenoxyl radicals: Delta(f)H(m) degrees (C(6)H(5)O*,g) - Delta(f)H(m) degrees (o-CH(3)C(6)H(4)O*,g) = 42.2 +/- 2.8 kJ.mol(-1), Delta(f)H(m) degrees (C(6)H(5)O*,g) - Delta(f)H(m) degrees (m-CH(3)C(6)H(4)O*,g) = 36.1 +/- 2.4 kJ.mol(-1), and Delta(f)H(m) degrees (C(6)H(5)O*,g) - Delta(f)H(m) degrees (p-CH(3)C(6)H(4)O*,g) = 38.6 +/- 3.2 kJ.mol(-1). The corresponding differences in O-H bond dissociation enthalpies were also derived as DH degrees (C(6)H(5)O-H) - DH degrees (o-CH(3)C(6)H(4)O-H) = 8.1 +/- 4.0 kJ.mol(-1), DH degrees (C(6)H(5)O-H) - DH degrees (m-CH(3)C(6)H(4)O-H) = 0.9 +/- 3.4 kJ.mol(-1), and DH degrees (C(6)H(5)O-H) - DH degrees (p-CH(3)C(6)H(4)O-H) = 5.9 +/- 4.5 kJ.mol(-1). Based on the differences in Gibbs energies of formation obtained from the enthalpic data mentioned above and from published or calculated entropy values, it is concluded that the relative stability of the cresols varies according to p-cresol < m-cresol < o-cresol, and that of the radicals follows the trend m-methylphenoxyl < p-methylphenoxyl < o-methylphenoxyl. It is also found that these tendencies are enthalpically controlled.

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Section: Enthalpies Of Formation Of Methylphenoxyl Radicals and O-h Bmentioning

confidence: 99%

Energetics of Cresols and of Methylphenoxyl Radicals

et al. 2007

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“…They can also act synergistically, increasing the effect of other antioxidants. Thanks to their diverse hydrophobic–lipophilic nature, coming from structural differences, they can be present in environment of different polarities (Ross et al ., ).…”

Section: Introductionmentioning

confidence: 97%

A review of methods used for investigation of protein–phenolic compound interactions

Czubiński

Dwiecki

2016

Int J of Food Sci Tech

152

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Interactions between the different compounds present in foods are common and have influence on the nutritional and functional properties of food products. Among a wide range of these interactions, the formation of complexes between proteins and phenolic compounds seems to be the most important issue. Complexation of the phenolic compounds with proteins can be analysed considering several aspects. These complexes might strongly affect nutritional potential of polyphenols by masking their antioxidant capacity, and on the other hand might have influence on the structure of proteins which may cause their precipitation or decrease susceptibility to digestion. The complexity of protein–phenolic compound interactions is a challenge for food analysts and forced researchers to establish a wide range of analytical methods, allowing determination of complexes formation. The main aim of this review is to give researchers an overview of the currently used methods that can be applied to study the interactions between proteins and phenolic compounds.

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“…The number of electrons participating in oxidation is 2.0 AE 0.2 for 2,2 0 -thiobis(6-tert-butyl-4-methylphenol), 2,6-di-tertbutyl-4-a,b-diacetylethylphenol, 2,6-di-isobornyl-4-methylphenol, and a-tocopherol; and 1.00 AE 0.05 for amino derivatives of BHT. The number of electrons is calculated by comparison of oxidation currents of compounds under investigation with standard compound (BHT) that undergoes two-electronic oxidation (Medeiros et al 2010;Ross, Barclay, and Vinqvist 2003). The hydroxyl group of phenol participates in oxidation with formation of corresponding quinoid derivatives in accordance to Scheme 1.…”

Section: Cyclic Voltammetry Of Phenolic Antioxidantsmentioning

confidence: 99%

Determination of Sterically Hindered Phenols and α-Tocopherol by Cyclic Voltammetry

Ziyatdinova¹,

Khuzina²,

Budnikov³

2012

Analytical Letters

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Sterically hindered phenols (2,6-di-tert-butyl-4-methylphenol (BHT) and its derivatives) are irreversibly oxidized at þ0.96-1.30 V on glassy carbon electrode (GCE) in 0.1 M LiCIO 4 in acetonitrile in accordance to cyclic voltammetry data. a-Tocopherol gives oxidation step at þ0.4 V on voltammograms under the same conditions. Oxidation process leads to formation of corresponding quinoid derivatives. Calibration graphs linearity is 1.5-2 order for all compounds under investigation. Limits of detection are in the range 9.6-44.3 lM. The approach has been applied for determination of BHT and a-tocopherol in vegetable and lubricating oils as well as pharmaceuticals and cosmetics using preliminary single extraction of analytes with acetonitrile for 15 min at oil/extractant ratio of 1:2.5.

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Phenols as Antioxidants

Abstract: Introduction Kinetics and Mechanism Efficiencies of Phenolic Antioxidants Chemical Calculations on Phenols Future Prospects for Antioxidants

Cited by 21 publications

References 264 publications

Energetics of Cresols and of Methylphenoxyl Radicals

Energetics of Cresols and of Methylphenoxyl Radicals

A review of methods used for investigation of protein–phenolic compound interactions

Determination of Sterically Hindered Phenols and α-Tocopherol by Cyclic Voltammetry

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