Catalase mimics

The Mn complexes of dicarboxylic acids are efficient catalase mimics. The crystal structure of [MnII(ri1ri1-L4)(phen)2] 28, (L4 = cA-5-norbomene-e cfo-2,3,-dicarboxylic acid and phen = 1,10-phenanthroline) (Figure 13) shows that this complex is a water linked dinuclear compound in solid state [100n],... 

Similar to enzymes, the biomimetic catalysts mentioned operate in liquids. Their activity depends on the diluter origin, reaction mixture pH and cell effects. Gas-phase oxidation is free from these effects, which can be considered in the first approximation as oxidation under quasi-ideal conditions [53], The study of resonance Raman spectra [54] of PPFe3+ 0H/A1203 catalase mimic indicated its clear analogy with the fifth coordinate high-spin heme Fe3+ ion, bonded to tyrosine in catalase. 

A catalase mimic, similar to that described above, was synthesized on five forms of aluminum oxide a-, [3-, acidic, basic and neutral. The neutral and basic forms of A1203 were found to be the most active sorbents. Prior to adsorption, hemin was dissolved on an aqueous alcohol solution (pH 9), where it transformed to hematin, and then applied on A1203 forming catalase mimic PPFe3+0H/Al203. According to this technique, iron protoporphyrin was applied on Si02. 

For the purpose of determining low hydrogen peroxide concentrations, the authors have designed the most cost-effective and simple to use potentiometric-biomimetic sensors based on immobilized catalase mimics. These sensors possess high hydrodynamic properties and the fastest speed of response. Figure 8.3 shows experimental data on catalase activity of biomimetic electrode in 0.03% aqueous H202. For the sake of comparison, catalase activities of aluminum electrode and aluminum electrode with applied adhesive are also shown. 

The TON for O2 production by dimanganese(III) chloride complexes of both DPX (11) and DPD (19) are graphically represented in Fig. 20. Both systems are poor catalase mimics, displaying turnover numbers (TONs) for O2 evolution that are <40 (139). Given that the etioporphyrin-type substitution patterns of the parent DPX and DPD systems are generally imstable to oxidizing conditions. 

OAc) core with a Mn-Mn separation of 3.55 A. The catalase mimic Mn2I(2-OHbenzimpn)(OAc) (Fig. 54), has the same core in the lower oxidation state (291) with a nearly identical Mn-Mn separation, 3.54 A. 

Okawa and co-workers have published several papers in recent years on binuclear catalase mimics based on the pentadentate or sep-tadentate binucleating ligands, an example of which is shown in Scheme 21 (441, 442). These ligands have been used to prepare a variety of binuclear Mn" complexes. Their ability to catalyze the dis-porportionation of hydrogen peroxide varies, but is generally low, on the order of 0.79 s 1. A functional scheme for the disproportionation of hydrogen peroxide has been proposed for these complexes that invokes a MnIV=0 intermediate (Scheme 21). 

The most efficient catalase mimic to date is the [Mn salpnC/t-OUa complex (Fig. 50) (244, 446). This complex cycles between Mn v and MnniMnni. The latter oxidation state is represented by two monomeric units, as exhibited by ligand-scrambling experiments. This was determined in catalase mimicry experiments by utilizing two complexes with differing ligand derivatization. When they were reacted with hy-... 

Fig. 75. Representation of the linked porphyrin catalyst utilized for water oxidation. Replacement of the o-phenylene linker with an anthracene linker generates the catalase mimic reported in the catalase segment (443). The authors have noted that reactivity can be altered by the nature of the linker (444). [Reproduced with permission from (455). Copyright 1994 Wiley-VCH Verlag.]...

In 1992, Wieghardt and co-workers reported two manganese catalase mimics based on triazacyclononane ligands 294). These were asymmetric complexes, with one half bearing an A(,A(, iV -trimethyl-... 

Stractures of EUK-8 and EUK-134 K. Baker, C. Bucay Maicus, K. Huffman, H. Kmk, B. Malfroy, S. R. Doctrow, Synthetic combined superoxide dismutase/catalase mimics are protective as a delayed treatment in a rat stroke model a key role for reactive oxygen species in ischemic brain injury. Journal ( Pharmacology and Experimental Therapeutics, 284 (1998), 215-221. 

Figure 11.1 Ligand sets developed for manganese complexes as catalase mimics.

Sakiyama explored various dinuclear manganese complexes as catalase mimics derived from 2,6-bis N-[(2-dimethylamino)ethyl]iminomethyl-4-methylphenolate (2, Figure 10.1) and related ligands. Employing UV- ds and MS techniques both mono-and di-Mn -oxo intermediates could be detected [30]. Notably, the proposed mechanism (Scheme 10.2) is different from that reported for the manganese catalases and model compounds containing ligand 1 [30]. 

Antioxidant activities of other Mn SOD and catalase mimics for inflammation, ischemia, stroke, myocardial infarction, and neurodegenerative diseases... 

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