LANTHANIDE ION LUMINESCENCE AS A PROBE OF DNA-STRUCTURE .1. GUANINE-CONTAINING OLIGOMERS AND NUCLEOTIDES

Laser-induced Eu3+ luminescence spectroscopy is used to probe the interaction of EU3+ ion with guanine-containing nucleotides and single-stranded oligomers. By using time-resolved and non-time-resolved Eu3+ luminescence techniques, two classes of EU3, binding site are observed in oligo(dG)10, oligo(dG)8, oligo(dG)6, oligo(dG)4, and d-GMP. One class of site binds EU3+ ions more strongly than the other. Since the "tight" class of bound Eu3+ ions have two coordinated water molecules, it is inferred that six or seven atoms from the oligomers are coordinating the EU3+. The "weaker" class of EU3+ ion sites involve the coordination of six or seven water molecules and, therefore, are coordinated by one or two atoms from the oligomer. The tight class of EU3+ binding site is attributed to an interstrand association of Eu3+ with the oligomers forming dimeric or polymeric structures. The dissociation constants (K(d)) for the 1:1 complexes Eu(d-GMP)+ and Eu(d-GTP)- have been determined as well as the K(d) for the dimerization reaction of Eu(d-GMP)+. The Tb3+ luminescence enhancement properties of these molecules are also examined in relation to their Eu3+ binding characteristics.