A density functional theory study on the intramolecular proton transfer in 6-thioguanine and alkali metal cations substituted derivatives (M-TG, MÂ =Â Li+, Na+, K+)

► Metal cations play a crucial role in many different biochemical and physiological pathways. ► 6-Thioguanine is used widely for its cytotoxic and immunosuppressive properties. ► The influence of metal cations on the tautomerization of 6-thioguanine was studied. ► The study can help to further explore the pharmacological properties of 6-thioguanine.