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Rational design and facile synthesis of highly active electrocatalysts with low cost for oxygen reduction reaction (ORR) are always of great challenge. Specifically, development of a new type of energy-saving materials with convenient method is regarded as the current bottleneck. Herein, an innovative strategy based on amino trimethylene phosphonic acid (ATMP) as chelating agent for cobalt-metaphosphate coordination polymer is reported to one-pot synthesis of a novel precursor in methanol for ORR electrocatalyst. Carbonization of the precursor at 900 °C at N2 atmosphere results in the feasible formation of cobalt metaphosphate based composite (Co(PO3)2/NC). A further step in the thermal cleavage at 650 °C at air for 4 h, Co(PO3)2/NC can be finally transformed into inorganic Co(PO3)2. Advanced spectroscopic techniques and density function theory (DFT) calculations are applied to confirm the main catalytically active center and the physical properties of Co(PO3)2/NC. This obtained Co(PO3)2/NC nanocomposite exhibits superior electrocatalysis to Co(PO3)2 with an enhanced onset potential (0.906 V vs. RHE) and diffusion limiting current (5.062 mA cm−2), which are roughly close to those of commercial 20% Pt/C (0.916 V, 5.200 mA cm−2).

Cytochrome P450 enzymes (P450 or CYP) are some of the most versatile biocatalysts, and offer advantages for oxidizing unreactive C–H bonds in mild conditions. In this study, we identified a novel cytochrome P450 154C2 from Streptomyces avermitilis and characterized its function in 2α-hydroxylation of testosterone with regio- and stereoselectivity. To investigate the efficiency of electron transfer, we conducted biotransformation using two different P450 redox partners—RhFRED (RhF reductase domain) from Rhodococcus sp. and Pdx (putidaredoxin)/Pdr (putidaredoxin reductase) from Pseudomonas putida and revealed that RhFRED was more effective than Pdx/Pdr, especially in vivo. The Km and kcat values for testosterone were estimated to be 0.16 ± 0.05 mM and 0.13 ± 0.02 min−1, and kcat/Km was 0.81 min−1 mM−1. We also determined the crystal structure of the substrate-free form of CYP154C2 at 1.5 A resolution. The structure has a closed conformation, and the substrate binding pocket is narrow, which can explain the strict substrate specificity of the enzyme.

Tuning the coordination environment between metal centers and organic ligands is a promising way to design of the precursors of electrocatalysts for water splitting or other renewable energy options. In this work, a novel coordinated polymer was prepared feasibly in polyvinyl pyrrolidone (PVP) aqueous solution using aminotrimethylene phosphonic acid (ATMP, L1) and 2-methylimidazole (MeMI, L2) as ligands with the ratio of 2:5, Co2+ and Zn2+ as metal centers. Based on the concept of acid-base neutralization reaction, the proton-transfer induced “deprotonation and protonation” for L1 and L2, respectively. Thus, the coordination was dominated by the deprotonated L1. Owing to also partial of protonated L2 adsorbed as “counter ions”, carbonization of the obtained precursor at 800 °C under N2 atmosphere endows the pyrolysis product with nitrogen-doped carbon supported metal pyrophosphate (M2P2O7@NC). Thus, the resulting M2P2O7@NC exhibits the enhanced and durable ORR and HER performance. For ORR in 0.1 M KOH, an enhanced onset potential (0.925 V vs. RHE), half wave potential (0.793 V vs. RHE) and diffusion limiting current (6.132 mA cm−2) can be obtained comparable to those of Pt/C. For HER in 0.5 M H2SO4, it only needs an over potential of 180 mV to realize a current density of 10 mA cm−2.

The cytochrome P450 enzymes are ubiquitous heme-thiolate proteins performing regioselective and stereoselective oxygenation reactions in cellular metabolism. Due to their broad substrate scope and catalytic versatility, P450 enzymes are also attractive candidates for many industrial and biopharmaceutical applications. For particular uses, enzyme properties of P450s can be further optimized through directed evolution, rational, and semi-rational engineering approaches, all of which introduce mutations within the P450 structures. In this review, we describe the recent applications of these P450 engineering approaches and highlight the key regions and residues that have been identified using such approaches. These “hotspots” lie within critical functional areas of the P450 structure, including the active site, the substrate access channel, and the redox partner interaction interface. Keywords: Cytochrome P450, Protein engineering, Rational design, Crystal structure

Research of highly dispersed transition metal phosphides (TMPs)-based catalysts for electrocatalytic hydrogen evolution is of great significance in the area of renewable energy. Herein, the high dispersion of FeNiP nanoparticles on N, P-doped electrospun carbon fibers was realized via the confinement effect induced by phytic acid (PA) and polyacrylonitrile (PAN), as well as electrospinning technique. PA and PAN were used as ligand for coordinating transition metal (TM) ions and carbon sources, respectively. In addition, the nucleophilic addition reaction between PA and PAN resulted in the cyclization of PAN and the further formation of a supramolecular network. Besides, the chelating ability of PA to TM ions was also modulated. Benefitting from the confinement effect, the optimized FeNiP/NPC800 exhibit good hydrogen evolution reaction (HER) activities for achieving a current density of 10 mA cm−2 at an overpotential of 277 mV in 0.5 M H2SO4.

Flavanones have a wide range of pharmacological activities. Previously, we showed that CYP105D7, a cytochrome P450, from Streptomyces avermitilis can catalyze hydroxylation of diclofenac at the C4′ position. Here, we demonstrated that CYP105D7 also catalyzes hydroxylation of two flavanones, naringenin and pinocembrin. Naringenin was hydroxylated at the 3′-position in a regiospecific manner to yield eriodictyol. Spectroscopic analyses showed that CYP105D7 binds to naringenin and pinocembrin in a weakly cooperative manner with an affinity of 103 μM and 52 μM, and a Hill coefficient of 1.25 and 1.47, respectively. A possible binding model of naringenin was investigated by molecular-docking analyses. The substrate-binding pocket of CYP105D7 is sufficiently wide to accommodate two naringenin molecules simultaneously, and the C3′ atom of the proximal molecule is in the appropriate location for aromatic hydroxylation.

Fe-N catalysts are one of the promising candidates with efficient oxygen reduction reaction (ORR) activities comparable to Pt-based catalysts. Therefore, in this work, a novel Fe-N based electrocatalyst with high activity, porous structure, and durability were prepared. Highly active N,N′-carbonyldiimidazole (CDI) was used to form zinc-based zeolitic imidazole frameworks involved with zinc carbonate (Zn-ZIFs@ZnCO3). Fe-doping can be feasibly achieved by partial substitution Zn by Fe using Fe (NO)3. Owing to the presence of ZnCO3 and Fe3+, carbonization of Fe/Zn-ZIFs@ZnCO3 at 925 °C under N2 atmosphere endows the pyrolysis products with many highly active heterostructures of 3D graphene structure. The obtained Fe-N@ZnO possesses superior ORR performance to commercial 20% Pt/C catalysts, such as positive half-wave potential (0.851 V), good durability and methanol tolerance in 0.1 M KOH.

Reliable and sensitive detection of xanthine has important medical and biological significance. In this work, a novel three-dimensional (3D) conductive polymer hydrogel of polyaniline (PAni) was feasibly prepared using aniline (Ani), amino trimethylene phosphonic acid (ATMP) and ammonium persulfate ((NH4)2S2O8) as monomer, gelatinizing agent and oxidizing agent, respectively. Protonation of aniline can be achieved by ATMP, inducing good conductivity of the obtained hydrogel. ATMP remained the chelating abilities in the conductive hydrogel, enabling further immobilization with silver nanoparticles (AgNPs) functionalized by a luminol derivative, N-(aminobutyl)-N-(ethylisoluminol) (ABEI). ABEI-Ag@PAni-ATMP exhibited an enhanced performance of solid-state electrochemiluminescence (ECL). Integrated with xanthine oxidase (XOD), the proposed biosensor can be applied in the detection of xanthine via in-situ generated hydrogen peroxide (H2O2), and present a low detection limit of 9.6 nM, a wide linear range (from 0.01 to 200 μM) and excellent stability.

The polyene macrolide antibiotic filipin is widely used as a probe for cholesterol and a diagnostic tool for type C Niemann-Pick disease. Two position-specific P450 enzymes are involved in the post-polyketide modification of filipin during its biosynthesis, thereby providing molecular diversity to the "filipin complex." CYP105P1 and CYP105D6 from Streptomyces avermitilis, despite their high sequence similarities, catalyze filipin hydroxylation at different positions, C26 and C1', respectively. Here, we determined the crystal structure of the CYP105P1-filipin I complex. The distal pocket of CYP105P1 has the second largest size among P450 hydroxylases that act on macrolide substrates. Compared with previously determined substrate-free structures, the FG helices showed significant closing motion on substrate binding. The long BC loop region adopts a unique extended conformation without a B' helix. The binding site is essentially hydrophobic, but numerous water molecules are involved in recognizing the polyol side of the substrate. Therefore, the distal pocket of CYP105P1 provides a specific environment for the large filipin substrate to bind with its pro-S side of position C26 directed toward the heme iron. The ligand-free CYP105D6 structure was also determined. A small sub-pocket accommodating the long alkyl side chain of filipin I was observed in the CYP105P1 structure but was absent in the CYP105D6 structure, indicating that filipin cannot bind to CYP105D6 with a similar orientation due to steric hindrance. This observation can explain the strict regiospecificity of these enzymes.