Formation of lanthanide(III) texaphyrin complexes with DNA controlled by the size of the central metal cation

Interaction of lanthanide(III) texaphyrins (LnTEX) with calf thymus DNA was studied by UV-Vis, CD, resonance light scattering spectroscopy and by laser flash photolysis. The thermal stability of the LnTEX/DNA complexes decreases with the increasing lanthanide ion radius: LuTEX > DyTEX > GdTEX > EuTEX > CeTEX ⩾ LaTEX. Texaphyrins LaTEX, LuTEX and GdTEX produce O2(1Δg) in methanol solutions. In a phosphate buffer, the concentration of O2(1Δg) produced by these texaphyrins bound to DNA is affected by the formation of aggregates on the DNA backbone.