The europium (III)‐induced conformational transitions of poly(dG‐dC) · poly(dG‐dC) and poly(dG‐m5dC) · poly(dG‐m5dC) as studied by europium(III) luminescence, UV, and CD spectroscopy

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Abstract
The Eu3+ ion induces a B to Z transition in poly(dG‐dC) · poly(dG‐dC) and poly(dG‐m5dC) · poly(dG‐m5dC). Other conformations were also elicited by this ion. The conformational changes of these polynucleotides were followed by CD and uv spectroscopy. Eu3+ excitation spectra and Eu3+ excited‐state lifetimes were measured for the Eu3+ ion bound to the duplexes in various conformations. B‐form poly(dG‐dC) and poly(dG‐m5dC) appear to have a single class of the Eu3+ binding site while the Z‐form observed conformation exhibits two. The numbers of H2O molecules coordinated to the Eu3+ ion bound to the various conformations of the duplexes were determined by measuring Eu3+ excited‐state lifetimes in H2O and D2O. The first‐order rate constants for the Eu3− and [Co(NH3)6]3+ induced B to Z transitions were measured. The Eu3+ mediated conversion is much faster than the [Co(NH3)6]3+ induced conversion in both polynucleotides.