DNA binding and unwinding by self-assembled supramolecular hetero-bimetallacycles

Abstract

Two new tetracationic hetero-bimetallacycles were prepared from a bis-pyridine amide ligand and metal (Pd and Pt) acceptors. We found that both self-assembled hetero-bimetallacycles bind and unwind supercoiled DNA as established by photophysical and gel electrophoresis analyses, respectively.

Figure 1

Calculated (top) and experimental (bottom) ESI- MS spectra of 4 (a) and 5 (b).

Figure 2

X-ray crystal structure of HBMCs 4 (a) and 5 (b) showing the encapsulation of a triflate anion through H- bonding interactions.

Figure 3

UV/Vis absorption spectra (left) 4 (a) and 5 (b) upon incremental addition of DNA. Arrows show the absorbance changes upon increasing amount of DNA (Inset in figure: binding constant plot for the supercoiled DNA-HBMCs). Emission spectra (right) of 4 (a) and 5 (b) upon gradual addition of DNA (EB bound) (Inset in figure: Stern- volmer plot for the supercoiled DNA- HBMCs).

Figure 4

Agarose gel electrophoresis showing the interaction of supercoiled DNA with HBMC 4 (A) and 5 (B). Plasmids at a concentration of 2×10⁻⁴ M were mixed with increasing concentrations of the HBMCs in 10 mM Tris-HCl (pH 7.4), incubated for 1 hr at 37 °C, and analyzed on 1% agarose gels (Lanes 1 and 11, molecular weight markers; Lane 2, control (non-modified DNA); Lanes 3–10, DNA with HBMCs concentrations of 1, 2, 3, 4, 5, 10, 15, and 20 μM respectively). The SC and OC (open circular) indicate supercoiled and relaxed forms of plasmid DNA.

Scheme 1

Synthesis of hetero- metallacycles 4 and 5.