E. Kimura et al., MACROCYCLIC METAL-COMPLEXES FOR SELECTIVE RECOGNITION OF NUCLEIC-ACIDBASES AND MANIPULATION OF GENE-EXPRESSION, Pure and applied chemistry, 69(10), 1997, pp. 2187-2195
Interaction of Zn-II-cyclen complexes 1, 3, 6, and 7 with uracil and t
hymine bases in double-stranded poly(A).poly(U) and poly(dA).poly(dT)
has been investigated. These zinc(II) complexes lowered the melting te
mperatures (T-m) of poly(A).poly(U) and poly(dA).poly(dT) in 5 mM Tris
-HCl buffer (pH 7.6) containing 10 mM NaCl as their concentrations inc
reased, indicating that they destabilized the duplex structure of poly
nucleotides. The comparison of circular dichroism (CD) spectra of poly
(A).poly(U), poly(A), and poly(U) in the presence of zinc(II) complex
3 led us to conclude that the spectral changes of poly(A).poly(U) were
due to a structural change from double to single-strand, caused by zi
nc(II) complex 3 binding exclusively to uracils in poly(U). The destab
ilization effect of zinc(II) complexes was not observed with poly(dG).
poly(dC) in thermal denaturation experiments (50% formamide aqueous so
lution, 2.5 mM Tris-HCl buffer (pH 7.6) and 5 mM NaCl). However, the a
cridine-pendant cyclen complex 3, which associates with guanine at N-7
and O-6, and through pi-pi stacking, interacted with poly(dG) in the
double helix and greatly stabilized the poly(dG).poly(dC) double-stran
d, as was indicated by the higher T-m than those with reference interc
alating agents. Poly(A).poly(U) double-strand was most effectively dis
rupted with a bis(Zn-II-cyclen) bridged by para-xylyl group 6 that was
designed as a host molecule to bind to two neighboring uracils in a 1
:2 complex. Zn-II-cyclen complexes thus may become a prototype of smal
l molecules that can affect the biological properties of nucleic acids
at the molecular level.