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MnO2@PCs (porous carbons) exhibiting high energy and power density are utilized as supercapacitor electrodes and prepared by impregnating porous carbons (PCs) derived from coal tar pitch (CTP) with KMnO4 as the manganese source. This study systematically investigates the impact of MnO2 loading on the microstructure and electrochemical performance in sample. It is found that the specific surface areas (SSA) of all MnO2@PCs significantly reduced compared to that of the PCs 2789 m2 g−1. The suggested mechanism might be a combination of the energy storage mechanism of dual layer capacitors with pseudo‐capacitance due to redox reactions of MnO2. Notably, MnO2@PCs‐0.0075 exhibits a maximum SSA of 1454.62 m2 g−1. Its specific capacitance reached 561 F g−1 at 0.5 A g−1, while the capacitance of the PCs increased by 81.5% to 309 F g−1. Remarkably, the Coulombic efficiency remained at 100%. The power density and energy density are determined in a two‐electrode test system to be 0.5 kW kg−1 and 58.01 Wh kg−1, respectively, at 0.5 A g−1. Concluding from these results and related literature, the MnO2 content significantly influences the electrochemical performance, suggesting that MnO2@PCs‐0.0075 could be a promising supercapacitor (SC) electrode material, provided its capacitance retention is enhanced.

This work prepared porous carbon with excellent electrochemical performance using hydrothermal and carbonization methods. Specifically, caragana was used as carbon precursor, hydrazine hydrate as nitrogen source, and nickel acetate as nickel source during this preparation process. The results showed that porous carbon carbonized at 700 °C has excellent surface area (1779 m2 g−1), moderate oxygen content (7.88 at%), and nitrogen content (1.64 at%), which are conducive to improving pseudocapacitance. The N4NiPC180-3 has specific capacitance of 427 F g−1 at 0.5 A g−1, and high capacitance retention of 74.3% even at 20 A g−1. The retention rate after 10,000 cycles is 97.4%, verifying its excellent cycling stability. In addition, the N4NiPC180-3 in the two-electrode system test can achieve an energy density of 35.8 W h kg−1 at a power density of 500.1 W kg−1. This work extends high value-added utilization of biomass derivatives in energy storage applications.

A green and effective nitrogen and nickel in-situ doping strategy was designed to prepare cellulose-based N/Ni co-doped porous carbon (PC). The co-hydrothermal pretreatment induced by hydrazine hydrate and nickel acetate effectively modifies the physico-chemical structure of PC and further improves its electrochemical performance. The efficient N-supply and unique heteroatom regulation performance of hydrazine hydrate is related to its strong reducibility. The specific surface area and total pore volume of the synthesized N4NiPC220-3 are 1383.66 m2 g−1 and 0.59 cm3 g−1, while the N and O contents are 1.35 and 10.41%, respectively. At current densities of 0.5 and 20 A g−1, N4NiPC220-3 exhibits a high specific capacitance of 415 F g−1 and a good capacitance retention of 72.22%, respectively. After 10,000 charge/discharge cycles, the retention rate is as high as 96.06%, confirming its excellent cycling stability. The two-electrode system test results further show that the energy density of N4NiPC220-3 is as high as 35.6 W h kg−1 at a power density of 500.1 W kg−1, while a high retention rate of 87.87% is still obtained after 10,000 cycles. This green and efficient synthesis method based on in-situ co-doping of hydrazine hydrate and nickel acetate is a promising alternative strategy for producing carbon-based supercapacitors.

ABSTRACT Cytochrome P450 2E1 is widely known for its ability to oxidize both low molecular weight xenobiotics and endogenous fatty acids (e.g., arachidonic acid (AA)). In this study, we investigated the structural features of the AA-bound CYP2E1 complex utilizing molecular dynamics (MD) and found that the distinct binding modes for both AA and fatty acid analog are conserved. Moreover, multiple random acceleration MD simulations and steered MD simulations uncovered the most possible tunnel for fatty acids. The main attractions are derived from three key residues, His107, Ala108, and His109, whose side chains reorient to keep ligands bound via hydrogen bonds during the initial unbinding process. More importantly, based on the calculated binding free energy results, we hypothesize that the hydrogen bonds between the receptor and the ligand are the most important contributors involved in the binding affinity. Thus, it is inferred that the hydrogen bonds between these three residues and the ligand may help offer insights into the structural basis of the different ligand egress mechanisms for fatty acids and small weight compounds. Our investigation provides detailed atomistic insights into the structural features of human CYP2E1-fatty acid complex structures. Furthermore, the ligand-binding characteristics obtained in the present study are helpful for both experimental and computational studies of CYPs and may allow future researchers to achieve desirable changes in enzymatic activities. © 2014 Wiley Periodicals, Inc. Biopolymers 103: 53-66, 2015. [ABSTRACT FROM AUTHOR]

Cytosolic insect theta class glutathione S-transferases (GSTs) have not been studied completely and their physiological roles are unknown. A detailed understanding of Anopheles gambiae GST (Aggst1-2) requires an accurate structure, which has not yet been determined. A high quality model structure of Aggst1-2 was constructed using homology modeling and the ligand–protein complex was obtained by the docking method. Molecular dynamics (MD) simulations were carried out to study conformational changes and to calculate binding free energy. The results of MD simulation indicate that Aggst1-2 undergoes small conformational changes after ligands dock to the protein, which facilitate the catalytic reaction. An essential hydrogen bond was found between the sulfur atom of glutathione (GSH) and the hydrogen atom of hydroxyl group in Ser9, which was in good agreement with experimental data. A π–π interaction between Phe204 and CDNB ligand was also found. This interaction seems to be important in stabilization of the ligand. Further study of binding free energy decomposition revealed a van der Waals interaction between two ligands that may play a key role in nucleophilic addition reaction. This work will be a good starting point for further determination of the biological role of cytosolic insect theta class GSTs and will aid the design of structure-based inhibitors. [ABSTRACT FROM AUTHOR]

Experiments revealed that cytochrome P450 2C8 enzyme (CYP2C8) has two distinct substrate binding sites to the physiologically important molecules, retinoic acids, and the main difference between these two binding sites is whether there is a salt bridge interaction between the anionic carboxylate tail of retinoic acids and the surrounding protein environment. However, the influence of such salt bridge interaction toward catalysis is still elusive. In the present paper, density functional theory (DFT) calculations were employed to research the reaction mechanism of all- trans-retinoic acid (atRA) 4-hydroxylation mediated by CYP2C8. Our DFT calculations revealed that such salt bridge interaction has obvious effects on the reaction mechanism of atRA 4-hydroxylation. In the binding site containing a salt bridge interaction between the anionic carboxylate tail of atRA and the cationic guanidine group of Arg241, - bond activation proceeds via a normal hydrogen atom transfer (HAT) mechanism; in the other site without this salt bridge interaction, however, - bond activation is achieved via a stepwise electron transfer and hydrogen atom transfer, thus, a novel ET/HAT mechanism. These findings enrich the mechanism patterns of - bond activation catalyzed by metalloenzymes and their biomimetics. Meanwhile, the self-interaction error (SIE) problem encountered during our calculations in vacuum was affected and removed by the inclusion of an external electric field in the calculations. The salt bridge interaction between the carboxylate end of atRA and the guanidine group of Arg241 dramatically affects the reaction process. Without this salt bridge interaction, an electron transfers from atRA to Cpd I before the hydrogen atom transfer (HAT); with this salt bridge interaction, however, no electron transfer occurs before the HAT process. In other words, such salt bridge interaction controls the reaction channel. [ABSTRACT FROM AUTHOR]

Cytochrome P450 (CYP) 7B1 is a steroid cytochrome P450 7α-hydroxylase that has been linked directly with bile salt synthesis and hereditary spastic paraplegia type 5 (SPG5). The enzyme provides the primary metabolic route for neurosteroids dehydroepiandrosterone (DHEA), cholesterol derivatives 25-hydroxycholesterol (25-HOChol), and other steroids such as 5α-androstane-3β,17β-diol (anediol), and 5α-androstene-3β,17β-diol (enediol). A series of investigations including homology modeling, molecular dynamics (MD), and automatic docking, combined with the results of previous experimental site-directed mutagenesis studies and access channels analysis, have identified the structural features relevant to the substrate selectivity of CYP7B1. The results clearly identify the dominant access channels and critical residues responsible for ligand binding. Both binding free energy analysis and total interaction energy analysis are consistent with the experimental conclusion that 25-HOChol is the best substrate. According to 20 ns MD simulations, the Phe cluster residues that lie above the active site, particularly Phe489, are proposed to merge the active site with the adjacent channel to the surface and accommodate substrate binding in a reasonable orientation. The investigation of CYP7B1-substrate binding modes provides detailed insights into the poorly understood structural features of human CYP7B1 at the atomic level, and will be valuable information for drug development and protein engineering. [ABSTRACT FROM AUTHOR]