Final answer:
The main reactions of the guanine radical cation are the oxidation to 8-oxoG due to ROS and the formation of C8-aryl adducts.
Step-by-step explanation:
The main chemical reactions of the guanine radical cation involve the oxidation of bases, specifically the formation of 8-oxo-7,8-dihydroguanine (8-oxoG) and the generation of DNA strand interruptions by reactive oxygen species (ROS). Another significant reaction includes the formation of C8-aryl adducts through the reaction of radical cation metabolites of polycyclic aromatic hydrocarbons with guanine in DNA. The efficiency of these reactions can be influenced by the presence of reactive nitrogen oxide species (RNOS), which can lead to the formation of nitrated guanosine derivatives that have signaling roles within the cell.
Guanine can also participate in self-assembly to form G-tetrads and G-quadruplexes, which is facilitated by structural modifications that provide additional intra-molecular and inter-molecular hydrogen bonding. In the presence of catalytic amounts of metal ions such as Cu, direct C-H activation and intramolecular amination of guanine nucleosides can occur, leading to the synthesis of various functionalized compounds, including fluorescent polycyclic purine nucleosides. However, guanine nucleosides tend to be poor substrates for direct C8 arylation, a challenge that can often be attributed to the binding of catalytic metals at sites distant from C8 or due to the presence of ionizable protons, which affect reactivity.