The heme in the active center of peroxidases reacts with hydrogen peroxide to form highly reactive intermediates, which then oxidize simple substances called peroxidase substrates. Human peroxidases can be divided into two groups: (1) True peroxidases are enzymes whose main function is to generate free radicals in the peroxidase cycle and (pseudo)hypohalous acids in the halogenation cycle. The major true peroxidases are myeloperoxidase, eosinophil peroxidase and lactoperoxidase. (2) Pseudo-peroxidases perform various important functions in the body, but under the influence of external conditions they can display peroxidase-like activity. As oxidative intermediates, these peroxidases produce not only active heme compounds, but also protein-based tyrosyl radicals. Hemoglobin, myoglobin, cytochrome c/cardiolipin complexes and cytoglobin are considered as pseudo-peroxidases. Рeroxidases play an important role in innate immunity and in a number of physiologically important processes like apoptosis and cell signaling. Unfavorable excessive peroxidase activity is implicated in oxidative damage of cells and tissues, thereby initiating the variety of human diseases. Hence, regulation of peroxidase activity is of considerable importance. Since peroxidases differ in structure, properties and location, the mechanisms controlling peroxidase activity and the biological effects of peroxidase products are specific for each hemoprotein. This review summarizes the knowledge about the properties, activities, regulations and biological effects of true and pseudo-peroxidases in order to better understand the mechanisms underlying beneficial and adverse effects of this class of enzymes.

https://www.mdpi.com/1420-3049/23/10/2561/pdf

Peroxidase Activity of Human Hemoproteins: Keeping the Fire under Control.

Selective etching of C-N bonds for preparation of porous carbon with ultrahigh specific surface area and superior capacitive performance

Density functional theory was used to study the mechanism and kinetics of benzoic acid with hydroxyl radicals in both gas and aqueous phases as well as benzoate with hydroxyl radicals in the aqueous phase at the M06-2X/6-311+G(d,p) level of theory. The results show that all reaction pathways involved the formation of pre-reactive complexes which in turn alter reaction energy barriers. The reaction rate constants, calculated based on classical transitional theory, followed the order of meta addition > para addition > ortho addition for the reaction of benzoic acid and hydroxyl radicals in both gas and aqueous media. The energy barrier analysis reveals that the ortho adducts were also less vulnerable to subsequent reaction. In addition, the rate constants for the addition reactions were highest for benzoate in the aqueous phase, followed by benzoic acid in the aqueous phase, then by benzoic acid in the gas phase, consistent with electrostatic potential analysis. However, the rate constants of hydrogen abstraction in the aqueous phase were much lower than that in the gas phase and thus, gas phase reactions are preferred. The incorporation of one explicit water molecule, for addition reactions between benzoic acid and hydroxyl radicals, lowered reaction rates in the aqueous phase by increasing the bond length between the oxygen and reacting carbon in the benzene ring.

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Reactions of hydroxyl radicals with benzoic acid and benzoate

Visible-light photocatalyzed (VLPC) late-stage C–H functionalization is a powerful addition to the chemical synthesis toolkit. VLPC has a demonstrated potential for discovery of elusive and valuable transformations, particularly in functionalization of bioactive heterocycles. In order to fully harvest the potential of VLPC in the context of complex molecule synthesis, a thorough understanding of the elementary processes involved is crucial. This would enable more rational design of suitable reagents and catalysts, as well as prediction of activated C–H sites for functionalization. Such knowledge is essential when VLPC is to be employed in retrosynthetic analysis of complex molecules. Herein, we present a density functional theory (DFT) study of mechanistic details in the C–H functionalization of bioactive heterocycles exemplified by the methylation of the antifungal agent voriconazole. Moreover, we show that readily computed atomic charges can predict major site-selectivity in good agreement with experime...

Mechanism and Site Selectivity in Visible-Light Photocatalyzed C-H Functionalization: Insights from DFT Calculations.

Using Pt6 clusters as model catalysts in this paper, by means of the B3LYP functional in DFT at the 6-31+G(d) level (the LanL2DZ extra basis set was used for Pt atoms) we studied separately the microreaction mechanism of the selective hydrogenation of cinnamaldehyde catalyzed by pure Pt clusters and co-doped Pt clusters. The rationality of the transition state can be proved by vibration frequency analysis and IRC computations. Moreover, atoms-in-molecules (AIM) theory and natural bond orbital (NBO) theory were applied for discussing the interaction among orbitals and the bonding characteristics. The calculating results indicate that Pt6 clusters are favored for catalyzing the activation and hydrogenation of the CO bond in cinnamaldehyde molecules, eventually producing cinnamyl alcohol, which proved that Pt6 clusters have a strong reaction selectivity for catalyzing the hydrogenation of cinnamaldehyde. Compared with Co-doped Pt clusters, Pt6 clusters are more likely to catalyze the activation and hydrogenation of the CO bond. Using Co-doped Pt clusters to catalyze the selective hydrogenation reaction of cinnamaldehyde to produce cinnamyl alcohol, the activation energy is lower than that of the reaction catalyzed by pure Pt clusters. The doped catalyst has a synergetic catalytic effect. Our findings have explained the mechanism of action of the doped catalyst and the experimental phenomena.

Selective hydrogenation of cinnamaldehyde catalyzed by Co-doped Pt clusters: a density functional theoretical study

Four different possible reaction pathways of phenol and hydroxyl radical reaction were investigated theoretically by density functional theory (DFT) B3LYP with the 6-31+G(d,p) calculations under th...

NanayakkaraNadeeshani

Papers

Theoretical study of phenol and hydroxyl radical reaction mechanism in aqueous medium by the DFT/B3LYP/6-31+G(d,p)/CPCM model