Spectral changes of TSC compounds associated with metal complexation. (a) Spectral changes of TSC-NO2 after the addition of ferrous sulfate. The red line corresponds to the initial spectrum before metal addition. The structure of TSC-NO2 complexed with Fe2+ is shown beside the spectrum. (b) A progressive decrease of the band that peaks at 340 nm and increase of the A240 nm/A340 nm ratio are associated with the disaggregation of TSC-NO2 and the formation of metal complexes. Panel (c), black line, shows the spectrum obtained when bathophenanthroline is added to the medium containing ferrous sulfate after 6 h incubation of with TSC-NO2. The red line corresponds to the spectrum of bathophenanthroline added to a fresh solution of ferrous sulfate, and the gray line corresponds to the control, that is, bathophenanthroline added to a solution of ferrous sulphate incubated for 6 h in the absence of TSC-NO2.