Journal
STRUCTURAL CHEMISTRY
Volume 32, Issue 5, Pages 2051-2059Publisher
SPRINGER/PLENUM PUBLISHERS
DOI: 10.1007/s11224-021-01780-4
Keywords
Structure-antioxidant activity relationship; Density functional theory; Prenylated flavonoids; Bond dissociation enthalpy; Hop
Funding
- Ministry of Education, Science and Technological Development of Serbia [451-03-68/202014/200168]
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Using density functional theory (DFT) method, this study found that desdimethyl-octahydro-iso-cohumulone is the most potent antioxidant in beer, with its enolic -OH being the most reactive site for antioxidant activity. The presence of a beta-keto group weakens the HAT potency and affects the antioxidant performance.
Humulones and iso-humulones are potent natural antioxidants found in beer. In this study, density functional theory (DFT) method was applied for elucidating the structure-antioxidant activity relationship and molecular mechanism of antioxidant activity of eight bioactive humulones previously identified in different beer samples: isoxanthohumol, (R)- and (S)-adhumulone, cis- and trans-iso-adhumulone, cis- and trans-iso-n-humulone, and desdimethyl-octahydro-iso-cohumulone. The calculated bond dissociation enthalpies (BDEs) suggest that desdimethyl-octahydro-iso-cohumulone was the most potent compound with BDEs 5.1 and 23.9 kJ/mol lower compared to the values for resveratrol in gas phase and water, respectively. The enolic -OH is the most reactive site for hydrogen atom transfer (HAT). The presence of beta-keto group with respect to enolic -OH diminishes the HAT potency via the formation of a strong intramolecular hydrogen bond. Another common antioxidant mechanism, single electron transfer followed by proton transfer (SET-PT), is only feasible for isoxanthohumol. The results of this study indicate a strong correlation between the increased antioxidant activity of beer products and the higher content of reduced iso-alpha-acids.
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