Antioxidant properties of phenolic Schiff bases: structure-activity relationship and mechanism of action.
Phenolic Schiff bases are known for their diverse biological activities and ability to scavenge free radicals. To elucidate (1) the structure-antioxidant activity relationship of a series of thirty synthetic derivatives of 2-methoxybezohydrazide phenolic Schiff bases and (2) to determine the major mechanism involved in free radical scavenging, we used density functional theory calculations (B3P86/6-31+(d,p)) within polarizable continuum model. The results showed the importance of the bond dissociation enthalpies (BDEs) related to the first and second (BDEd) hydrogen atom transfer (intrinsic parameters) for rationalizing the antioxidant activity. In addition to the number of OH groups, the presence of a bromine substituent plays an interesting role in modulating the antioxidant activity. Theoretical thermodynamic and kinetic studies demonstrated that the free radical scavenging by these Schiff bases mainly proceeds through proton-coupled electron transfer rather than sequential proton loss electron transfer, the latter mechanism being only feasible at relatively high pH.
Atta-ur-Rahman Institute for Natural Product Discovery (RiND), Universiti Teknologi MARA, Kampus Puncak Alam, 42300 Bandar Puncak Alam, Shah Alam, Selangor DE, Malaysia, anouarelhassane@yahoo.fr.
El Hassane
el H
Anouar
Salwa
S
Raweh
Imene
I
Bayach
Muhammad
M
Taha
Mohd Syukri
MS
Baharudin
Florent
F
Di Meo
Mizaton Hazizul
MH
Hasan
Aishah
A
Adam
Nor Hadiani
NH
Ismail
Jean-Frédéric F
JF
Weber
Patrick
P
Trouillas
D000975:Antioxidants / Q000737:chemistry* / Q000494:pharmacology; D007700:Kinetics; D008958:Models, Molecular; D010636:Phenols / Q000737:chemistry* / Q000494:pharmacology; D011522:Protons; D011789:Quantum Theory; D012545:Schiff Bases / Q000737:chemistry* / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D000975:Antioxidants; D010636:Phenols; D011522:Protons; D012545:Schiff Bases