Generation of a macrocyclic Cr(V) complex and its reactivity toward organic and inorganic reductants and DNA

The complex L1Cr(H2O)2 2+ (L1=1,4,8,11-tetraazacyclotetradecane) reacts with molecular oxygen to yield an end-on superoxo complex, L1(H2O)CrOO2+, with a rate constant kon=(1.80±0.06)×108 M−1 s−1 in acidic aqueous solutions. The reduction of L1(H2O)CrOO2+ with one-electron reductants generates a transient species, believed to be L1CrOOH2+, which undergoes a first-order transformation to an oxochromium(V) complex, L1CrO3+, k=0.19 s−1 in 0.02 M HClO4. The ion L1CrO3+ reacts rapidly with a number of inorganic and organic reductants, H2O2, and DNA. The extent and nature of the DNA damage depend on the reductant used to generate L1CrO3+, suggesting that different reductants have different scavenging abilities toward the intermediates responsible for DNA damage. In the absence of oxidizable substrates, L1CrO3+ decays in a first-order process, k=0.39±0.05 s−1.