Schultze P, Hud NV, Smith FW, Feigon J (1999) The effect of sodium, potassium and ammonium ions on the conformation of the dimeric quadruplex formed by the Oxytricha nova telomere repeat oligonucleotide d(G(4)T(4)G(4)). <i>Nucleic acids research</i> 27(15):3018-28