The europium (III)‐induced conformational transitions of poly(dG‐dC) · poly(dG‐dC) and poly(dG‐m 5 dC) · poly(dG‐m 5 dC) as studied by europium(III) luminescence, UV, and CD spectroscopy

The Eu 3+ ion induces a B to Z transition in poly(dG‐dC) · poly(dG‐dC) and poly(dG‐m 5 dC) · poly(dG‐m 5 dC). Other conformations were also elicited by this ion. The conformational changes of these polynucleotides were followed by CD and uv spectroscopy. Eu 3+ excitation spectra and Eu 3+ excited‐state lifetimes were measured for the Eu 3+ ion bound to the duplexes in various conformations. B‐form poly(dG‐dC) and poly(dG‐m 5 dC) appear to have a single class of the Eu 3+ binding site while the Z‐form observed conformation exhibits two. The numbers of H 2 O molecules coordinated to the Eu 3+ ion bound to the various conformations of the duplexes were determined by measuring Eu 3+ excited‐state lifetimes in H 2 O and D 2 O. The first‐order rate constants for the Eu 3− and [Co(NH 3 ) 6 ] 3+ induced B to Z transitions were measured. The Eu 3+ mediated conversion is much faster than the [Co(NH 3 ) 6 ] 3+ induced conversion in both polynucleotides.