Employment of the monoanion of 2,6-diacetylpyridine dioxime
(dapdoH2) as a tridentate chelate in palladium(II) and
platinum(II)
chemistry is reported. The syntheses, crystal structures, spectroscopic
and physicochemical characterization, and biological evaluation are
described of [PdCl(dapdoH)] (1) and [PtCl(dapdoH)] (2). Reaction of PdCl2 with 2 equivs of dapdoH2 in MeOH under reflux gave 1, whereas the same
reaction with PtCl2 in place of PdCl2 gave 2 in comparable yields (70–80%). The divalent metal
center in both compounds is coordinated by a terminal chloro group
and a N,N′,N″-tridentate chelating (η3) dapdoH– ligand. Thus, each metal ion is four coordinate with a distorted
square planar geometry. Characterization of both complexes with 1H and 13C NMR and UV–vis and electrospray
ionization mass spectroscopies confirmed their integrity in DMSO solutions.
Interaction of the complexes with human and bovine serum albumin has
been studied with fluorescence spectroscopy, revealing their affinity
for these proteins with relatively high values of binding constants.
UV study of the interaction of the complexes with calf-thymus DNA
(CT DNA) has shown that they can bind to CT DNA, and the corresponding
DNA binding constants have been evaluated. Cyclic voltammograms of
the complexes in the presence of CT DNA solution have shown that the
interaction of the complexes with CT DNA is mainly through intercalation,
which has been also shown by DNA solution viscosity measurements.
Competitive studies with ethidium bromide (EB) have revealed the ability
of the complexes to displace the DNA-bound EB, suggesting competition
with EB. The combined work demonstrates the ability of pyridyl–dioxime
chelates not only to lead to polynuclear 3d-metal complexes with impressive
structural motifs and interesting magnetic properties but also to
yield new, mononuclear 4d- and 5d-metal complexes with biological
implications.