Scheme 1: UVA-induced excitation of thioguanosine (TG) and its Type I/Type II ROS-generating Pathways. | Communications Chemistry

Scheme 1: UVA-induced excitation of thioguanosine (TG) and its Type I/Type II ROS-generating Pathways.

From: Chemical and photoinduced interstrand crosslinking of oligo DNA duplexes containing 2′-deoxythioguanosines

Scheme 1

Eq. (1) Upon UVA irradiation, ground-state thioguanosine (0TG) is excited to the singlet state (1TG), which undergoes an intersystem crossing (ISC) to the excited triplet state (3TG). Two possible pathways of 3TG to generate ROS in the presence of 3O2, Eq. (2) 3TG can transfer energy to 3O2, generating 1O2 via a type II reaction. Eq. (3) Alternatively, electron transfer from 3TG to 3O2 can produce O2•− in a type I reaction, a process that is favored in the presence of electron donors.

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