Home Publications Research Grants Inventions & Patents Awards Additional Research Activities Faculties & Institutions Research Areas

Combined experimental and theoretical study on the reactivity of Compounds I and II in horseradish peroxidase biomimetics

Ji L, Franke A, Brindell M, Oszajca M, Zahl A, van Eldik R (2014)

---

Publication Type: Journal article

Publication year: 2014

Journal

Book Volume: 20

Pages Range: 14437-14450

Journal Issue: 44

DOI: 10.1002/chem.201402347

Abstract

For the exploration of the intrinsic reactivity of two key active species in the catalytic cycle of horseradish peroxidase (HRP), Compound I (HRP-I) and Compound II (HRP-II), we generated in situ [Fe^IV=O(TMP⁺•)(2-MeIm)] + and [Fe^IV=O(TMP)(2-MeIm)]⁰ (TMP = 5,10,15,20-tetramesitylporphyrin; 2-MeIm = 2-methylimidazole) as biomimetics for HRP-I and HRP-II, respectively. Their catalytic activities in epoxidation, hydrogen abstraction, and heteroatom oxidation reactions were studied in acetonitrile at -15 °C by utilizing rapid-scan UV/Vis spectroscopy. Comparison of the secondorder rate constants measured for the direct reactions of the HRP-I and HRP-II mimics with the selected substrates clearly confirmed the outstanding oxidizing capability of the HRP-I mimic, which is significantly higher than that of HRP-II. The experimental study was supported by computational modeling (DFT calculations) of the oxidation mechanism of the selected substrates with the involvement of quartet and doublet HRP-I mimics (^2,4Cpd I) and the closed-shell triplet spin HRP-II model (³Cpd II) as oxidizing species. The significantly lower activation barriers calculated for the oxidation systems involving ^2,4Cpd I than those found for ³Cpd II are in line with the much higher oxidizing efficiency of the HRP-I mimic proven in the experimental part of the study. In addition, the DFT calculations show that all three reaction types catalyzed by HRP-I occur on the doublet spin surface in an effectively concerted manner, whereas these reactions may proceed in a stepwise mechanism with the HRP-II mimic as oxidant. However, the high desaturation or oxygen rebound barriers during C-H bond activation processes by the HRP-II mimic predict a sufficient lifetime for the substrate radical formed through hydrogen abstraction. Thus, the theoretical calculations suggest that the dissociation of the substrate radical may be a more favorable pathway than desaturation or oxygen rebound processes. Importantly, depending on the electronic nature of the oxidizing species, that is, ^2,4Cpd I or ³Cpd II, an interesting region-selective conversion phenomenon between sulfoxidation and H-atom abstraction was revealed in the course of the oxidation reaction of dimethylsulfide. The combined experimental and theoretical study on the elucidation of the intrinsic reactivity patterns of the HRP-I and HRP-II mimics provides a valuable tool for evaluating the particular role of the HRP active species in biological systems.

Authors with CRIS profile

Involved external institutions

How to cite

APA:

Ji, L., Franke, A., Brindell, M., Oszajca, M., Zahl, A., & van Eldik, R. (2014). Combined experimental and theoretical study on the reactivity of Compounds I and II in horseradish peroxidase biomimetics. Chemistry - A European Journal, 20(44), 14437-14450. https://doi.org/10.1002/chem.201402347

MLA:

Ji, Li, et al. "Combined experimental and theoretical study on the reactivity of Compounds I and II in horseradish peroxidase biomimetics." Chemistry - A European Journal 20.44 (2014): 14437-14450.

BibTeX: Download