5-Pyrimidinols:  Novel Chain-Breaking Antioxidants More Effective than Phenols

Pratt, Derek A.; DiLabio, Gino A.; Brigati, Giovanni; Pedulli, Gian Franco; Valgimigli, Luca

doi:10.1021/ja005679l

Cited by 156 publications

(156 citation statements)

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“…Most importantly, they can predict the thermodynamic properties of molecules prior to their experimental study, representing an invaluable aid for their rational design. For instance, DFT methods have been successfully used to predict the O-H BDEs of new classes of antioxidants, such as pyrimidinols 106 and pyridinols, 107 and to rationalize the role of remote H bonding on the para-substituted phenols. 108 The absolute O-H BDEs of phenols in the gas phase can be obtained by calculating the enthalpy change for the reaction (50).…”

Section: Methodsmentioning

confidence: 99%

“…The contribution of strongly electron-donating (ED) and electron-withdrawing (EW) substituents on the phenolic O-H BDE, calculated by using the popular B3LYP functional, have been found larger by about 1-2 kcal mol −1 than the experimental ones. 106 For instance, the BDE of phenol substituted with para-OMe and -NO 2 groups have been calculated as −5.5 and +4.4 kcal mol −1 , respectively, 109 whereas the experimental values in benzene are −4.5 and +2.5 kcal mol −1 , respectively. 100 Furthermore, B3LYP has difficulties in reproducing results obtained with -CMe 3 substituents, so these are normally replaced by -Me for the purpose of calculations (considering that alkyl substituents bring very similar ED contribution into the phenolic ring).…”

Section: Methodsmentioning

confidence: 99%

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Antioxidants in Chemistry and Biology

Valgimigli

Pratt

2012

Encyclopedia of Radicals in Chemistry, Biology and Materials

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109

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Antioxidants are omnipresent in nature and industry; they are used to slow down the autoxidative degradation of both organic tissues and petroleum‐derived products. Various mechanisms by which antioxidants can act are known, the most common of which are introduced here. Since autoxidation is a radical chain reaction, radical‐trapping antioxidants play a particularly important role; therefore, we will discuss these compounds in most detail. To introduce and develop central concepts relating to this topic, we present kinetic and thermodynamic data obtained for the reactions of phenols, the archetypical radical‐trapping antioxidants, with chain‐carrying peroxyl radicals, and describe the means to obtain these data. We then extend our discussion to other important classes of radical‐trapping antioxidants, beginning with the closely related polyphenols and newly developed pyridinol and pyrimidinol antioxidants, and then further to aromatic amines, organosulfur compounds, and their derivatives. We go on to touch upon the synergistic behavior in antioxidant combinations, and the effects of the medium on these interactions, and finally round things up with a few more important biological examples: ascorbate and β‐carotene. A few comments on the state of the field and areas requiring further research and development are included.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Antioxidants in Chemistry and Biology

Valgimigli

Pratt

2012

Encyclopedia of Radicals in Chemistry, Biology and Materials

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109

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“…39,42,83,93 DiLabio et al 16,88,95 found that BDE and ΔBDE values of para-substituted phenols, 6-substituted-3-pyridinols, 2-substituted-5-pyrimidinols, and anilines are linearly dependent on Hammett constants σ p . Klein et al 37,48 found that BDE and ΔBDE values of para-substituted and meta-substituted phenols are linearly dependent on Hammett constants σ p and σ m .…”

Section: 36mentioning

confidence: 99%

DFT/B3LYP Study of the Substituent Effects on the Reaction Enthalpies of the Antioxidant Mechanisms of Magnolol Derivatives in the Gas-Phase and Water

Najafi¹,

Najafi²,

Najafi³

2012

Bulletin of the Korean Chemical Society

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In this paper, the study of various ortho-and meta-substituted Magnolol derivatives is presented. The reaction enthalpies related to three antioxidant action mechanisms HAT, SET-PT and SPLET for substituted Magnolols have been calculated using DFT/B3LYP method in gas-phase and water. Calculated results show that electronwithdrawing substituents increase the bond dissociation enthalpy (BDE), ionization potential (IP) and oxidation/ reduction enthalpy (O/RE), while electron-donating ones cause a rise in the proton dissociation enthalpy (PDE) and proton affinity (PA). In ortho-position, substituents show larger effect on reaction enthalpies than in metaposition. In comparison to gas-phase, water attenuates the substituent effect on all reaction enthalpies. In gasphase, BDEs are lower than PAs and IPs, i.e. HAT represents the thermodynamically preferred pathway. On the other hand, SPLET mechanism represents the thermodynamically favored process in water. Results show that calculated enthalpies can be successfully correlated with Hammett constants (σ m ) of the substituted Magnolols. Furthermore, calculated IP and PA values for substituted Magnolols show linear dependence on the energy of the highest occupied molecular orbital (E HOMO ).

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“…However, low IP values also enhance the probability of superoxide radical anion formation through the direct electron transfer to present O2 (Pratt et al 2001, Wright et al 2001). …”

Section: Introductionmentioning

confidence: 99%