Assignment of the 13C chemical shifts of ethidium bromide and analogs in D2O solution

The ¹³C resonances of ethidum bromide (1), dimidium bromide (2) and 3,8-diamino-5-methylphenanthridinium chloride (3) in D₂O solution have been assigned. Assignments were made using fully coupled spectra, spectra obtained from a selected 180°-τ-90° pulse sequence in conjunction with gated irradiation to obtain NOE intensification, selective proton decoupling, chemical shift arguments and by noting the effect of pD on the ¹³C chemical shifts of 1 and 3.