Reactions of Tetraazamacrocyclic FeIII Complexes with Hydrogen Peroxide − Putative Catalase Mimics?

Catalase-Like Activity of a Non-Heme Dibenzotetraaza[14]annulene−Fe(III) Complex under Physiological Conditions

“…Catalase models that were built around iron(III) centers were mostly based on heme-type structures; , non-heme iron complexes have been much less investigated for their catalase activity or, more general, “oxygen-activation” properties. − However, although these compounds decompose H 2 O 2 , − the notation “catalase mimic” in our view often appears to be rather euphemistic. Most of the published models have inherent serious deficiences with respect to the preferred characteristics of a “good” catalase mimic, that is, water-solubility, quantitative O 2 production obeying the stoichiometry of eq 1, catalytic activity at physiological pH values (pH 7 ± 1) and micromolar catalyst and H 2 O 2 concentrations, and low activity as oxygenating (peroxidase-like) agent . We now find that the non-heme iron(III)-tetraaza[14]annulene complex 1 provides a promising starting point for the development of useful catalase mimics in that it catalyzes, at micromolar concentrations, the release of O 2 in high yield from low concentrations of H 2 O 2 in buffer solution at pH 7.2.…”

“…The question remains why complex 1 is more effective in its catalase-like activity under physiological conditions than other non-porphyrin Fe(III) complexes reported thus far. ,,,− , Apart from pH dependencies this might tentatively be attributed to the presence of the electron-donating alkoxy substituents at the benzene rings. In the catalase cycle of H 2 O 2 dismutation, a ferryl iron−porphyrin radical cation species, Por •+ Fe(IV)O, plays a central role. , As a first hypothesis one might argue that the electron-donor properties of the alkoxy substituents in 1 would facilitate a similar formation of a radical cation of the aza[14]annulene ligand .…”

Synthesis of 12-Membered Tetra-aza Macrocyclic Pyridinophanes Bearing Electron-Withdrawing Groups

“…Tetra-aza macrocycles were of immediate interest to chemists due to the structural similarities to porphyrin and corrin compounds as found in nature. Additional studies have examined the properties of these systems as analogues of the widely known crown ether family. , Today, tetra-aza macrocycles are ubiquitous across all disciplines of the core sciences and are readily modified using well-established organic methods. − The overwhelming and consistent prevalence of these systems in the literature can largely be attributed to the promiscuous metal-binding nature of the cyclic tetra-aza backbone. For example, lanthanide complexes, particularly those derived from the 12-membered tetra-aza macrocycle cyclen (1,4,7,10-tetraazacyclododecane), are commonly explored and used as biological imaging agents (PET and MRI). − Cyclen has further been explored as a ligand for transition metal-catalyzed C–C coupling and oxidation reactions, to name a few. − Importantly, the use of tetra-aza macrocycles (such as cyclen) provides a tool for modeling the function of biological systems, , synthesis of biomimetics, , and therapeutics, amongst others. , This diverse set of applications for the use of tetra-aza macrocycles is largely due to the ease at which (i) modifications can be made to the C-C bridges between N-atoms and (ii) added functionalities to the N-atoms can be accomplished.…”

Morphology-Controlled Synthesis and Characterization of Magnetic Iron Oxide Nanocrystals and Their Potential Applications in Selective Oxidation of Alcohols and Olefins

“…Iron-based catalysts have been extensively used because they are easily accessible, inexpensive, environmentally benign, and relatively nontoxic in comparison with other transition metals. Different iron (II) [21][22][23] and iron (III) compounds [24][25][26][27][28] have been used as for the oxidation reactions. Herein, we report the synthesis and characterization of iron oxide nanomaterials of two different morphologies (namely, nanorod and octahedron) and their successful applications in the selective oxidation of aryl-methanol and vinyl-arene with H 2 O 2 under organic solvent-free condition.…”