A Comparative Study of Fe(II) and Fe(III) Interactions with DNA Duplex: Major and Minor Grooves Bindings

The involvement of the Fe cations in autoxidation in cells and tissues is well documented. DNA is a major target in such reaction, and can chelate Fe cation in many ways. The present study was designed to examine the interaction of calf-thymus DNA with Fe(II) and Fe(III), in aqueous solution at pH 6.5 with cation/DNA (P) (P = phosphate) molar ratios (r) of 1:160 to 1:2. Capillary electrophoresis and Fourier transform infrared (FTIR) difference spectroscopic methods were used to determine the cation binding site, the binding constant, helix stability and DNA conformation in Fe–DNA complexes. Structural analysis showed that at low cation concentration (r = 1/80 and 1/40), Fe(II) binds DNA through guanine N-7 and the backbone PO2 group with specific binding constants of KG = 5.40 × 104 M–1 and KP = 2.40 × 104 M–1. At higher cation content, Fe(II) bindings to adenine N-7 and thymine O-2 are included. The Fe(III) cation shows stronger interaction with DNA bases and the backbone phosphate group. At low cation concentration (r = 1:80), Fe(III) binds mainly to the backbone phosphate group, while at higher metal ion content, cation binding to both guanine N-7 atom and the backbone phosphate group is prevailing with specific binding constants of KG = 1.36 × 105 M–1 and KP = 5.50 × 104 M–1. At r = 1:10, Fe(II) binding causes a minor helix destabilization, whereas Fe(III) induces DNA condensation. No major DNA conformational changes occurred upon iron complexation and DNA remains in the B-family structure.