Laser-induced europium(III) luminescence spectroscopy as a probe of DNA structur

Laser-induced Eu$sp{3+}$ luminescence spectroscopy is used to probe the interaction of Eu$sp{3+}$ ion with nucleotides, single-stranded oligomers, and several families of DNA double helix. By using time-resolved and non-time resolved Eu$sp{3+}$ luminescence techniques, two classes of Eu$sp{3+}$ binding sites are observed in oligo(dG)$sb{10}$, oligo(dG)$sb8$, oligo(dG)$sb6$, oligo(dG)$sb4$, and d-GMP. One class of Eu$sp{3+}$ ion binds more strongly to the oligomers than the other. The tight class of Eu$sp{3+}$ binding site is attributed to an interstrand association of Eu$sp{3+}$ with the oligomers forming a polymeric or dimeric structure. The dissociation constants (K$sb{rm d}$) for the 1:1 complexes of Eu(d-GMP)$sp+$; EU(ATP)-, and Eu(d-GTP)$sp-$ are determined as well as the K$sb{rm d}$ for the dimerization reaction of Eu(d-GMP)$sp+$. The Tb$sp{3+}$ luminescence enhancement properties of these various molecules are examined in relation to their Eu$sp{3+}$ binding characteristics.;Oligo(dC)$sb8$, oligo(dA)$sb8$, and oligo(dT)$sb8$ along with d-CMP, d-AMP, and d-TMP also possess two classes of Eu$sp{3+}$ binding site. By analogy to the guanine-containing oligomers, it is assumed that the tight class of Eu$sp{3+}$ ion observed with these oligomers and nucleotides corresponds to a dimeric or polymeric structure. Comparisons of the results between the guanine and non-guanine containing oligomers implies Eu$sp{3+}$ possibly coordinates base nitrogen atoms in an outer sphere mode (hydrogen bonding via the H$sb2$O molecules coordinated to Eu$sp{3+}$).;Specific bonds are formed between the Eu$sp{3+}$ ion and the atoms of Poly(dG)$cdot$Poly(dC), Poly(dA-dC)$cdot$Poly(dG-dT), and calf thymus DNA. This proves that the interaction between Eu$sp{3+}$ ion and the double helix is more than an "ionic atmosphere" type association. Two classes of Eu$sp{3+}$ binding site are seen with the B-form families of double helix, while one class is observed with Poly(dG)$cdot$Poly(dC) (A-form).;The Eu$sp{3+}$ ion induces a B to Z transition in Poly(dG-dC)$cdot$Poly(dG-dC) and Poly(dG-m$sp5$dC)$cdot$Poly(dG-m$sp5$dC). Other conformations were also elicited by this ion. The conformational changes of these polynucleotides were followed by circular dichroism (CD) and UV spectroscopy. Eu$sp{3+}$ excitation spectra and Eu$sp{3+}$ excited-state lifetimes were measured for the Eu$sp{3+}$ ion bound to the duplexes in various conformations. B-form Poly(dG-dC) and Poly(dG-m$sp5$dC) appear to have a single class of Eu$sp{3+}$ binding site while the Z-form observed conformation exhibits two.