Theoretical investigation on antioxidant activity of bromophenols from the marine red alga Rhodomela confervoides: H-atom vs electron transfer mechanism.

Bromophenols are known as antioxidant radical scavengers for some biomolecules such as those in marine red alga. Full understanding of the role played by bromophenols requires detailed knowledge of the radical scavenging activities in probable pathways, a focus of ongoing research. To gain detailed insight into two suggested pathways, H-atom transfer and electron transfer, theoretical studies employing first principle quantum mechanical calculations have been carried out on selected bromophenols. Detailed investigation of the aforementioned routes revealed that upon H-atom abstraction or the electron transfer process, bromophenols cause an increase in radical species in which the unpaired electron appears to be delocalized as much as possible over the whole aromatic ring, especially in the bromine substituent. The O-H bond dissociation energies (BDEs) and ionization potential energies (IPs) are reported at the B3LYP level of theory, providing the first complete series of BDEs and IPs for bromophenols. The observations are compared to those of other antioxidants for which BDEs and IPs have been previously obtained.