Uranyl Photofootprinting of DNA-Protein Complexes

It has long been known that the uranyl(V1) ion (UO₂ ²⁺ ) forms strong complexes with various inorganic and organic anions, including phosphates, and that the photochemically excited state of this ion is a very strong oxidant (1 ). For instance, uranyl-mediated photooxidation of alcohols has been studied in detail (2 ,3 ). It is also widely recognized that uranyl chemistry and photophysics/photochemistry are very complex. Thus monomeric UO₂ ²⁺ is only present at low pH (pH ∼ 2.0), whereas polynuclear species and various “hydroxides,” which often precipitate, form at higher pH (4 ).