Fig. 2.

Structures of a variety of chemicals that serve as ROS generators and modifying agents in the environment. The ROS generators in pink circle are redox active and thus cause redox cycle reaction associated with ROS production. The modifying agents cause covalent binding to nucleophiles such as protein cysteine residues. 1,2-Naphthoquinone and 1,4-naphthoquinone, however, can generate ROS by both redox cycling and direct protein modification.