Association constants of guanine oligomers with alkali-metal ions studied using atmospheric pressure droplet IR-laser ablation mass spectrometry

Guanine (G) molecules form a stable tetramer with a metal ion called a G-quartet. We observed G-quartets by using atmospheric pressure droplet Infrared-laser ablation mass spectrometry, which enables us to analyze the abundance of chemical species in solutions. We estimated the association constants of Gn and M+ (M+ = Li+, Na+, and K+) from the intensities of G1–5H+ and G1–4M+ in the obtained mass spectra. The larger association constants of G4 than those of Gn (n ≠ 4) indicate the stability of G-quartets.