Free Radical Scavenging Properties of Guaiacol Oligomers: A Combined Experimental and Quantum Study of the Guaiacyl-Moiety Role

Abstract

Natural polyphenols are known to exhibit a lot of different biological properties, including antioxidant activity. For some polyphenols these activities are attributed to the presence of a guaiacol moiety. In the present paper we focus on the role of this moiety. For this purpose nine different compounds were enzymatically synthesized from guaiacol. To elucidate the structure-activity relationship of these polyphenols, DFT-(PCM)B3P86/6-311+G(2d,3pd)//(PCM)B3P86/6-31+G(d,p) calculations supported the experimental DPPH free radical scavenging activities. The antioxidant activities were correlated to (i) O-H BDEs (bond dissociation enthalpies), (ii) BDE(D) (BDE of a second H atom abstraction from the phenoxyradicals), (iii) spin density, (iv) HOMO (highest occupied molecular orbital) distribution, (v) IPs (ionization potentials), (vi) DeltaG and DeltaG(#) free energies of HAT (H atom transfer), and (vii) HAT rate constants. BDE(D) appeared to be the most important descriptor to understand the free radical scavenging ability of these compounds.

Lipocarbazole, an efficient lipid peroxidation inhibitor anchored in the membrane

“…[12][13][14]29 The O-H BDE obtained for compounds 1 and 2 is very similar to that obtained for the most active OH group of quercetin, a powerful free radical scavenger. A 76.7 kcal mol À1 BDE confirms the efficient free radical scavenging capacity, as already measured for compound 1.…”

“…[11][12][13][14] The O-H bond dissociation enthalpy (BDE) was shown to be the major descriptor to predict free radical scavenging; the lower the BDE, the higher the capacity of H-atom transfer (HAT) from the antioxidant to the free radical, and the higher the antioxidant activity of the corresponding OH group. It perfectly and systematically correlates with DPPH scavenging.…”

“…This parameter has been extensively evaluated and it systematically correlates with the DPPH scavenging activity. [12][13][14] Both O-H and N-H BDEs were calculated for both compounds 1 and 2 ( Table 1). The N-H BDEs of compound 1 (85.9 kcal mol À1 in water) is much higher than that of the corresponding OH group (76.7 kcal mol À1 ).…”

Dimerisation Process of Silybin-Type Flavonolignans: Insights from Theory

“…Such a mechanism usually occurs in the presence of two ortho-OH groups (e.g. a catechol moiety) [16] or at least requires the presence of two highly conjugated OH groups; [17] 2) revert to the original ArOH compound (i.e. regeneration [18] or dismutation); 3) react with anNatural polyphenols are known to be oxidized by free radicals, which partially explains the antioxidant properties of a number of these compounds.…”

Importance of Proton-Coupled Electron Transfer from Natural Phenolic Compounds in Superoxide Scavenging

“…[20][21][22] However, the theoretical aspects of the free radical scavenging mechanism of phenolic antioxidants remains an important subject for the accurate prediction of free radical scavenging activity in physiological environments. [23][24][25][26][27] As a free radical, O 2 ·− is an important biological intermediate in living cells, 28) and is overproduced in tissues subjected to chronic infection and inflammation. 29) O 2 ·− causes oxidative DNA damage in living tissues under inflammatory conditions.…”