Oxidative Catalysis by TAMLs: Obtaining Rate Constants for Non-Absorbing Targets by UV-Vis Spectroscopy

Understanding the catalysis of oxidative reactions by TAML activators of peroxides, i. e. iron(III) complexes of tetraamide macrocyclic ligands, advocated a spectrophotometric procedure for quantifying the catalytic activity of TAMLs for colorless targets (k(II)', M-1 s(-1)), which is incomparably more advantageous in terms of time, cost, energy, and ecology than NMR, HPLC, UPLC, GC-MS and other similar techniques. Dyes Orange II or Safranin O (S) are catalytically bleached by non-excessive amount of H2O2 in the presence of colorless substrates (S-1) according to the rate law: -d[S]/dt=k(I)k(II)[H2O2][S][TAML]/(k(I)[H2O2]+k(II)[S]+k(II)'[S-1]). The bleaching rate is thus a descending hyperbolic function of S-1 : v=ab/(b+[S-1]). Values of k(II)' found from a and b for phenol and propranolol with commonly used TAML [Fe-III{o,o '-C6H4(NCONMe2CO)(2)CMe2}(2)(OH2)](+) are consistent with those for S-1 (phenol, propranolol) obtained directly by UPLC. The study sends vital messages to enzymologists and environmentalists.