Heme iron and nonheme dimanganese catalases protect biological systems against oxidative damage caused by hydrogen peroxide. Rubrerythrins are ferritine-like nonheme diiron proteins, which are structurally and mechanistically distinct from the heme-type catalase but similar to a dimanganese KatB enzyme. In order to gain more insight into the mechanism of this curious enzyme reaction, non-heme structural and functional models were carried out by the use of mononuclear [FeII(L1–4)(solvent)3](ClO4)2 (1–4) (L1 = 1,3-bis(2-pyridyl-imino)isoindoline, L2 = 1,3-bis(4′-methyl-2-pyridyl-imino)isoindoline, L3 = 1,3-bis(4′-Chloro-2-pyridyl-imino)isoindoline, L4 = 1,3-bis(5′-chloro-2-pyridyl-imino)isoindoline) complexes as catalysts, where the possible reactive intermediates, diiron-perroxo [FeIII2(μ-O)(μ-1,2-O2)(L1-L4)2(Solv)2]2+ (5–8) complexes are known and well-characterized. All the complexes displayed catalase-like activity, which provided clear evidence for the formation of diiron-peroxo species during the catalytic cycle. We also found that the fine-tuning of iron redox states is a critical issue, both the formation rate and the reactivity of the diiron-peroxo species showed linear correlation with the FeIII/FeII redox potentials. Their stability and reactivity towards H2O2 was also investigated and based on kinetic and mechanistic studies a plausible mechanism, including a rate-determining hydrogen atom transfer between the H2O2 and diiron-peroxo species, was proposed. The present results provide one of the first examples of a nonheme diiron-peroxo complex, which shows a catalase-like reaction.

Bleach catalysis in aqueous medium by iron(III)-isoindoline complexes and hydrogen peroxide

No abstract

The properties of a ferrocenyl ureidopyrimidine derivative, a potential electrochemical sensor for trifluoromethanesulfonic acid and trifluoroacetic acid, were investigated using UV/Vis, NMR, and CV measurements. Upon protonation, a structural change was found to take place leading to the formation of a proper binding site for the anion of the acid. Anion binding has been proved for both CF3SO3– and CF3CO2–as well as for the BF4– anion by 1H NMR measurements. Moreover, titration experiments carried out with CF3SO3H and CF3CO2H resulted in different responses in the NMR spectra of the pyrimidine host. Cyclic voltammetry was found to be suitable to follow the addition of the acids to the host molecule. DFT calculations and X‐ray diffraction were used to explore the properties of anion binding.

No abstract