title: Antioxidant potential of curcumin-related compounds studied by chemiluminescence kinetics, chain-breaking efficiencies, scavenging activity (ORAC) and DFT calculations.
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 C 2-symmetric dimers 6-9. Four models were applied: model 1 - chemiluminescence (CL) of a hydrocarbon substrate used for determination of the rate constants (k A) 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 k A 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.
authors.affiliation: Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl. 9, Sofia 1113, Bulgaria.
authors.forename: Adriana K
authors.initials: AK
authors.lastname: Slavova-Kazakova
authors.affiliation: Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl. 9, Sofia 1113, Bulgaria.
authors.forename: Silvia E
authors.initials: SE
authors.lastname: Angelova
authors.affiliation: Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygina str. 4, Moscow 119334, Russian Federation.
authors.forename: Timur L
authors.initials: TL
authors.lastname: Veprintsev
authors.affiliation: Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl. 9, Sofia 1113, Bulgaria.
authors.forename: Petko
authors.initials: P
authors.lastname: Denev
authors.affiliation: CNR-Institute of Biomolecular Chemistry, Traversa La Crucca 3, I-07100 Sassari, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Fabbri
authors.affiliation: CNR-Institute of Biomolecular Chemistry, Traversa La Crucca 3, I-07100 Sassari, Italy.
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: Dettori
authors.affiliation: Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl. 9, Sofia 1113, Bulgaria.
authors.forename: Maria
authors.initials: M
authors.lastname: Kratchanova
authors.affiliation: Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygina str. 4, Moscow 119334, Russian Federation.
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Naumov
authors.affiliation: Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygina str. 4, Moscow 119334, Russian Federation ; Moscow Institute of Physics and Technology, 9 Institutskiy per., Dolgoprudny, Moscow Region, 141700, Russian Federation.
authors.forename: Aleksei V
authors.initials: AV
authors.lastname: Trofimov
authors.affiliation: Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygina str. 4, Moscow 119334, Russian Federation.
authors.forename: Rostislav F
authors.initials: RF
authors.lastname: Vasil'ev
authors.affiliation: CNR-Institute of Biomolecular Chemistry, Traversa La Crucca 3, I-07100 Sassari, Italy.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Delogu
authors.affiliation: Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl. 9, Sofia 1113, Bulgaria.
authors.forename: Vessela D
authors.initials: VD
authors.lastname: Kancheva
keywords: DFT calculations; antioxidant activity; chain-breaking efficiencies; chemiluminescence kinetics; scavenging activity (ORAC)