UV–vis spectra of NADH in the presence of 1a or 2a (1.5 mL methanol was added to 1.5 mL reaction mixture to quench the reaction). Conditions: w0 7, pH 12, [NADH] 2.1 × 10−4 M, [total iron] = 2.0 × 10−4 M. (a, b: spectra of NADH reacted with 1a or 2a in the absence of O2; c, d: spectra of NADH reacted with 1a or 2a after exposure to air for 15 min; e: spectrum of NADH alone).