“…Of particular interest were their interactions with amino acids (Fan et al, 2010;Samijlenko et al, 2001Samijlenko et al, , 2004Stepanyugin et al, 2002aStepanyugin et al, , 2002b and protons or alkali metal cations (Lippert et al, 1986;Lippert & Gupta, 2009;Samijlenko et al, 2010;Šponer et al, 2001), as the extra positive charge could stabilize the structure of rare tautomers through an intramolecular salt bridge. Moreover, the coordination of metal ions to nucleobases is known to lead frequently to the stabilization of rare tautomeric forms (Burda et al, 2000;Lippert et al, 1986;Lippert & Gupta, 2009;Samijlenko et al, 2010), with numerous examples reported for various nucleobases (Lippert & Gupta, 2009;Lippert et al, 1986;Schoellhorn et al, 1989;Renn et al, 1991;Zamora et al, 1997).…”