Synthesis and Characterization of Ru(II)–DMSO–Cl–Chalcone Complexes: DNA Binding, Nuclease, and Topoisomerase II Inhibitory Activity

The complexes of type cis-[Ru­(S-DMSO)3(RCOCHCHR′)­Cl]
(R = 2-hydroxyphenyl for all, R′ = phenyl 1, naphthyl 2, anthracenyl 3, thiophene 4, 3-methyl
thiophene 5) are synthesized and characterized using
spectroscopic (IR, 1H and 13C NMR, and UV–vis)
and single crystal X-ray diffraction techniques. Their crystal structures
show the formation of both intermolecular and intramolecular H-bonding.
The molecular assembly of complex 5 using secondary interactions
provides a butterfly structure. The binding of complexes with calf
thymus DNA is monitored using UV–vis spectral titrations. The
binding interaction of complexes 1, 2, and 3 with DNA increases with increasing conjugation of aromatic
rings. However, complexes 4 and 5 interact
with DNA strongly. The emission from ethidium bromide (EB) bound DNA
recorded in phosphate buffer solution (pH = 7.2) decreases by incremental
addition of solution of the complexes. The complexes 4 and 5 (100 μM) bind with the minor groove of
DNA and cleave double-stranded pBR322 DNA significantly even in the
absence of an activator. In the presence of H2O2, they cleave supercoiled DNA via oxidative pathway even at lower
concentration (20 μM). Both complexes 4 and 5 inhibit topoisomerase II activity with IC50 values
of 18 and 13. These values suggest that 4 and 5 are potential topoisomerase II inhibitors as compared to some of
known inhibitors like novobiocin and etoposide.