Comparison of the acid–base properties of purine derivatives in aqueous solution. Determination of intrinsic proton affinities of various basic sitesElectronic supplementary information (ESI) available: Figures S1 (UV absorption spectra of 9-methyladenine), S2 (spectra of 1,9-dimethyladenine), S3 (plot of absorption versus H0/pH for 1,9-dimethyladenine), S4 (spectra of 1-methyladenosine), S5 (absorption versus H0/pH for 1-methyladenosine), S6 (spectra of 7,9-dimethyladenine), S7 (absorption versus H0/pH for 7,9-dimethyladenine), S8 (absorption versus H0/pH for N6′,N6′,N9-trimethyladenine), as well as S9, S10, S11 and S12 with the micro acidity constant schemes for 9-ethylguanine, guanosine, 9-methylhypoxanthine, and inosine, respectively. See http://www.rsc.org/suppdata/p2/b2/b202023h/