The complex L 1 Cr(H 2 O) 2 2 + (L 1 =1,4,8,11-tetraazacyclotetradecane) reacts with molecular oxygen to yield an end-on superoxo complex, L 1 (H 2 O)CrOO 2 + , with a rate constant k o n =(1.80+/-0.06)x10 8 M - 1 s - 1 in acidic aqueous solutions. The reduction of L 1 (H 2 O)CrOO 2 + with one-electron reductants generates a transient species, believed to be L 1 CrOOH 2 + , which undergoes a first-order transformation to an oxochromium(V) complex, L 1 CrO 3 + , k=0.19 s - 1 in 0.02 M HClO 4 . The ion L 1 CrO 3 + reacts rapidly with a number of inorganic and organic reductants, H 2 O 2 , and DNA. The extent and nature of the DNA damage depend on the reductant used to generate L 1 CrO 3 + , suggesting that different reductants have different scavenging abilities toward the intermediates responsible for DNA damage. In the absence of oxidizable substrates, L 1 CrO 3 + decays in a first-order process, k=0.39+/-0.05 s - 1 .