# Hydroperoxyl Radical Scavenging Activity of Bromophenols from Marine Red Alga Polysiphonia urceolata: Mechanistic Insights, Kinetic Analysis, and Influence of Physiological Media

## TL;DR

This study explores how bromophenols from a marine red alga neutralize harmful radicals, revealing their potential as powerful natural antioxidants.

## Contribution

The study provides novel mechanistic and kinetic insights into the hydroperoxyl radical scavenging activity of bromophenols in different environments.

## Key findings

- BP 2 showed 600-fold greater radical scavenging activity than BP 1 in lipid media.
- Both BPs exhibited comparable activity in aqueous media with high rate constants.
- Formal hydrogen atom transfer is the main pathway for radical scavenging in both environments.

## Abstract

Bromophenols (BPs), particularly those derived from marine sources, are known for their potent radical scavenging activity, effectively neutralizing reactive oxygen species (ROS). However, their exact mechanism of action remains largely unexplored, limiting our understanding of their potential as natural antioxidants. In this study, the antiradical mechanisms of two BP derivatives (1 and 2), previously isolated from the marine red alga Polysiphonia urceolata, were systematically investigated using thermodynamic and kinetic calculations. Both compounds demonstrated potent hydroperoxyl radical (HOO•) scavenging activity in polar and lipid environments, with rate constants surpassing those of the well-known antioxidant standards Trolox and BHT. In lipid media, BP 2 exhibited approximately 600-fold greater activity than BP 1, with rate constants of 9.75 × 105 and 1.64 × 103 M−1 s−1, respectively. In contrast, both BPs showed comparable activity in aqueous media, with rate constants of 3.46 × 108 and 9.67 × 108 M−1 s−1 for 1 and 2, respectively. Mechanistic analysis revealed that formal hydrogen atom transfer (f-HAT) is the predominant pathway for radical scavenging in both lipid and polar environments. These findings provide critical insights into the antiradical mechanisms of natural BPs and underscore the potential of BP 1 and BP 2 as highly effective hydroperoxyl radical scavengers under physiological conditions.