Abstract
This study compares the ability to scavenge different peroxyl radicals and to act as chain-breaking antioxidants of monomers related to curcumin (1): dehydrozingerone (2), zingerone (3), (2Z,5E)-ethyl 2-hydroxy-6-(4-hydroxy-3-methoxyphenyl)-4-oxohexa-2,5-dienoate (4), ferulic acid (5) and their corresponding C2-symmetric dimers 6–9. Four models were applied: model 1 – chemiluminescence (CL) of a hydrocarbon substrate used for determination of the rate constants (kA) of the reactions of the antioxidants with peroxyl radicals; model 2 – lipid autoxidation (lipidAO) used for assessing the chain-breaking antioxidant efficiency and reactivity; model 3 – oxygen radical absorbance capacity (ORAC), which yields the activity against peroxyl radicals generated by an azoinitiator; model 4 – density functional theory (DFT) calculations at UB3LYP/6-31+G(d,p) level, applied to explain the structure–activity relationship. Dimers showed 2–2.5-fold higher values of kA than their monomers. Model 2 gives information about the effects of the side chains and revealed much higher antioxidant activity for monomers and dimers with α,β-unsaturated side chains. Curcumin and 6 in fact are dimers of the same monomer 2. We conclude that the type of linkage between the two “halves” by which the molecule is made up does not exert influence on the antioxidant efficiency and reactivity of these two dimers. The dimers and the monomers demonstrated higher activity than Trolox (10) in aqueous medium (model 3). A comparison of the studied compounds with DL-α-tocopherol (11), Trolox and curcumin is made. All dimers are characterized through lower bond dissociation enthalpies (BDEs) than their monomers (model 4), which qualitatively supports the experimental results.
Highlights
Bioantioxidants have played an important role throughout the last decade in the protection of human health (as food additives) and in treatment of various human diseases (in a monotherapy at high concentrations or in a combination therapy with other drugs at low concentrations) [1,2]
Bioantioxidants have played an important role throughout the last decade in the protection of human health and in treatment of various human diseases [1,2]
The present study demonstrates experimental and theoretical models for assessing radical scavenging and antioxidant activity of curcumin-related hydroxylated biphenyls and their corresponding monomers
Summary
Bioantioxidants have played an important role throughout the last decade in the protection of human health (as food additives) and in treatment of various human diseases (in a monotherapy at high concentrations or in a combination therapy with other drugs at low concentrations) [1,2]. The present study compares the capacity of curcumin-related compounds to scavenge different free radicals and to act as chain-breaking antioxidants. The present study demonstrates experimental and theoretical models for assessing radical scavenging and antioxidant activity of curcumin-related hydroxylated biphenyls (dimers) and their corresponding monomers.
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