DNA damage inhibition was calculated using the formula 1[% N/% B]100, where % N is the percentage of nicked DNA in the sulfur-containing lanes (lanes 5–9) and % B is the percentage of nicked DNA in the CuI/H2O2 or FeII/H2O2 lane (lane 4). Both % N and % B were normalized for residual nicking (lane 2) prior to calculation, and results are the average of at least three trials with standard deviations indicated by error bars. Statistical significance was determined by calculating p values at 95% confidence (p < 0.05 indicates significance) as described by Perkowski et al. [61]; these values can be found in the supplementary material.