Investigation on the interaction of newly designed potential antibacterial Zn(II) complexes with CT-DNA and HSA

Abstract

Two Zn(II) complexes of formula [Zn(bpy)(Gly)]NO₃ (I) and [Zn(phen)(Gly)]NO₃ (II) (where bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline and Gly = glycine) were synthesized and characterized by elemental analysis, molar conductance measurements, UV–vis, FT-IR, and ¹H NMR spectra. The interaction ability of these complexes with calf thymus DNA was monitored using spectroscopic methods, including UV–vis absorption spectroscopy, ethidium bromide displacement, Fourier transform infrared, and electrophoretic mobility assay. Further, the human serum albumin interactions of complexes I and II were investigated using UV–vis absorption spectroscopy, fluorescence quenching, circular dichroism, and Fourier transform infrared. The results obtained from these analyses indicated that both complexes interact effectively with CT-DNA and HSA. The binding constant (K_b), the Stern–Volmer constant (K_sv), and the number of binding sites (n) at different temperatures were determined for CT-DNA and HSA. Also, the negative ΔH° and ΔS° values showed that both hydrogen bonds and van der Waals forces played major roles in the association of CT-DNA-Zn(II) and HSA-Zn(II) complex formation. The displacement experiments suggested that Zn(II)-complexes primarily bound to Sudlow’s site II of HSA. The distance between the donor (HSA) and the acceptor (Zn(II) complexes) was estimated on the basis of the Forster resonance energy transfer (FRET) and the alteration of HSA secondary structure induced by the compounds were confirmed by FT-IR spectroscopy. The complexes follow the binding affinity order of I > II with DNA and II > I with HSA. Finally, Antibacterial activity of complexes I and II have been screened against gram positive and gram negative bacteria.

Keywords:

• Zn(II) complexes
• CT-DNA binding
• HSA binding
• fluorescence quenching
• antibacterial activity

Abbreviations:

• bpy; 2,2′-bipyridine
• Phen; 1,10-phenanthroline
• Gly; Glycine
• EB; ethidium bromide
• K_app; apparent of binding constant
• K_sv; stern–Volmer constant
• K_b; binding constant
• N; number of binding sites
• ΔH°; enthalpy changes
• ΔS°; entropy changes
• ΔG°; free energy changes
• SDS; sodium dodecyl sulfate
• EDTA; ethylenediaminetetraacetic acid