Introduction Of Oxygen Atom Research Articles

Exploration of red and deep red Thermally activated delayed fluorescence molecules constructed via intramolecular locking strategy

Red and deep red (DR) organic light-emitting diodes (OLEDs) have garnered increasing attention due to their widespread applications in display technology and lighting devices. However, most red OLEDs exhibit low luminescence efficiency, severely limiting their practical applications. To address this challenge, we theoretically design four novel TADF molecules with red and DR luminescence using intramolecular locking strategies building upon the experimental findings of DCN-DLB and DCN-DSP, and their crystal structures are predicted with the lower energy and higher packing density. The photophysical properties and luminescence mechanism of six molecules in toluene and crystal are clarified using the first principles calculation and thermal vibration correlation function (TVCF) method. The proposed design strategy is anticipated to offer several advantages: enhanced electron-donating capabilities, more rigid structures, longer emission wavelengths and higher luminescence efficiency. Specifically, we introduce oxygen atoms and nitrogen atoms as intramolecular locks, and the newly developed DCN-DBF and DCN-PHC have redshifted emission, narrow singlet–triplet energy gap (ΔEST), fast reverse intersystem crossing rate and enhanced photoluminescence quantum yield (PLQY). Notably, DCN-DBF achieves both long wavelength emission and high efficiency, with emission peaks at 598 nm and 587 nm corresponding to PLQY of 52.13 % and 43.42 % in toluene and crystal, respectively. Our work not only elucidates the relationship between molecular structures and photophysical properties, but also proposes feasible intramolecular locking design strategies and four promising red and DR TADF molecules, which could provide a valuable reference for the design of more efficient red and DR TADF emitters.

(Invited) Development of Leuco Ethyl Violet as Self-Activating Prodrug Photooxygenation Catalyst of Amyloid-β

Abnormal aggregation of amyloid-β (Aβ) and tau protein (tau), called amyloid, is characteristic of Alzheimer's disease (AD). Reducing amyloid levels in AD patients is expected to be an effective approach to AD treatment. To inhibit the hydrophobic interaction of amyloid, which is the cause of toxic aggregates, we planed to generate singlet oxygen by activating oxygen in vivo through photocatalysis, thereby introducing oxygen atoms to amyloid protein and inhibiting aggregation. In accordance with this concept, we are developing photooxygenation catalysts with a switch function that generates singlet oxygen only in the presence of amyloids. We have succeeded in reducing amyloid in AD model mouse brain non-invasively with this photo-oxygenation catalyst. However, moderate catalytic activity and the side effect of scalp damage have been problematic. This time, we identified leucoethyl violet (LEV) as a highly active, amyloid-selective, blood-brain barrier (BBB)-permeable photooxygenation catalyst. LEV is a self-activating procatalyst by external redox stimuli. Autoxidation of LEV by a hydrogen atom transfer process under light irradiation produced active catalyst species Ethyl Violet (EV) only in the presence of amyloids. LEV showed higher catalytic activity than the previously developed photooxygenation catalyst and realized oxygenation of human Aβ and tau. Taking advantage of LEV's high activity and amyloid selectivity, improved BBB permeability, and low cytotoxicity, photooxygenation of Aβ was achieved in an AD model without scalp injury. Figure 1

Modulating band structure of g-C3N4 by doping oxygen to transform FeCo2O4/g-C3N4 heterojunction from type-II to S-scheme for enhancing photo-Fenton-like reaction

Constructing S-scheme heterojunctions is a highly prevalent approach in enhancing the activation efficiency of peroxymonosulfate (PMS). However, the two semiconductors that have the potential to form S-scheme heterojunction (such as FeCo2O4 and carbon nitride) typically tend to form type-II heterojunction. In this study, through oxalic acid assisted oxygen atom doping in carbon nitride, followed by the utilization of oxygen-doped carbon nitride (O-CN) as precursors in combination with cobalt chloride and iron chloride, the final synthesis of a novel composite catalyst is achieved. The introduction of oxygen atoms into the graphite carbon nitride can lead to an overall reduction in the band structure, facilitating the controlled transformation of a type-II heterojunction to an S-scheme heterojunction. This transformation is confirmed through density functional theory (DFT) calculations and electron spin resonance (ESR) tests. In the photo-Fenton-like system, the 15 % FeCo2O4/Oxygen doped-C3N4 (FCOCN) catalyst demonstrated a remarkable degradation efficiency of 93.5 % for tetracycline hydrochloride (TCH). This efficiency surpassed that of O-CN (47.8 %) and FeCo2O4 (60.3 %). Furthermore, the degradation efficiency of the 15 % FCOCN catalyst was significantly higher than that of photocatalysis (2.04 times greater) and Fenton-like treatment (1.11 times greater). Remarkably, within a short period of 14 min, the emerging contaminants, including sulfamethoxazole (SMX), bisphenol A (BPA), and carbamazepine (CBZ), were completely degraded. Atrazine (ATZ) showed a remarkable degradation rate of 77.1 %. This study offers valuable insights into the construction of S-scheme heterojunction through the manipulation of band structure in type-II heterojunction by oxygen doping.

Mechanism of directed activation of peroxymonosulfate by Fe-N/O unsymmetrical coordination-modulated polarized electric field

Iron-nitrogen co-doped carbon materials as heterogeneous catalysts have attracted much attention in advanced oxidation processes involving peroxymonosulfate (PMS) due to their unique structure and enormous catalytic potential. However, there is limited research on the influence of different coordination structures on the central iron atoms. Through simple pyrolysis, we introduced oxygen atoms into the Fe-N coordination structure, constructing Fe-N/O@C catalysts with Fe-N2O2 coordination structure, and achieved efficient degradation of bisphenol A (BPA). Quenching experiments, electron paramagnetic resonance, and electrochemical analysis indicate that compared to the free radical activation pathway of Fe-N@C, high-valent iron-oxo species (≡Fe(Ⅳ) = O) are the main reactive oxygen species (ROS) in the Fe-N/O@C/PMS system. Meanwhile, we compared the differences in the oxidation states of Fe atoms and electron density in different coordination structures, revealing the formation of high-valent iron-oxo species and the mechanism of interfacial electron transfer. Therefore, this study provides new insights into the design and development of Fe-N co-doped catalysts for resource-efficient and environmentally friendly catalytic oxidation systems.

Pitch-based 3D tremella-like porous carbon with cavitary structures: Applications in symmetric capacitors and zinc ion capacitors

The application of porous carbon in electrochemical energy storage devices (e.g., symmetrical capacitors, SCs, zinc ion capacitors, ZICs) is of great value, while pitch is one of the excellent precursors of porous carbon. Herein, the pitch-based 3D tremella-like porous carbons with heteroatoms (N and O) and cavitary structures have been synthesized via one-step oxidation activation. This strategy can introduce oxygen atoms to effectively inhibit the conjugation effect of the pitch and improve the convenience of preparation. The melting and crystallizing effect of NaCl can help the creation of cavitary structures and hierarchical pores. Gases released from the pyrolysis of pitches and decomposition of K2C2O4 contribute to the distortion of the carbon structure, resulting in the tremella-like morphology. The best sample, PC-825, has a specific capacitance of 338.5 F g−1 in a three-electrode system and an energy density of 12.2 Wh kg−1 in SCs. More importantly, PC-825 as cathodes in ZICs has a specific capacitance of up to 193.1 mAh g−1 and an energy density of up to 154.5 Wh kg−1, realizing an outstanding zinc storage capacity. This work realizes the conversion of cheap pitch to high-value-added electrochemical materials.

Oxalamide ligands with additional coordinating groups for Cu-catalyzed arylation of alcohols and phenols.

A novel class of chain-like multidentate oxalamide ligands with additional coordinating groups was developed for the coupling of (hetero)aryl bromides with both alcohols and phenols under mild conditions. Introduction of oxygen atoms in N-alkyl chains is pivotal for the high catalytic efficiency and broad substrate versatility.

Realization of efficient and selective NO and NO2 detection via surface functionalized h-B2S2 monolayer.

In the ever-growing field of two-dimensional (2D) materials, the boron-sulfide (B2S2) monolayer is a promising new addition to MoS2-like 2D materials, with the boron (a lighter element) pair (B2 pair) having similar valence electrons to Mo. Herein, we have functionalized the h-phase boron sulfide monolayer by introducing oxygen atoms (Oh-B2S2) to widen its application scope as a gas sensor. The charge carrier mobilities of this system were found to be 790 × 102 cm2 V-1 s-1 and 32 × 102 cm2 V-1 s-1 for electrons and holes, respectively, which are much higher than the mobilities of the MoS2 monolayer. The potential application of the 2D Oh-B2S2 monolayer in the realm of gas sensing was evaluated using a combination of density functional theory (DFT), ab initio molecular dynamics (AIMD), and non-equilibrium Green's function (NEGF) based simulations. Our results imply that the Oh-B2S2 monolayer outperforms graphene and MoS2 in NO and NO2 selective sensing with higher adsorption energies (-0.56 and -0.16 eV) and charge transfer values (0.34 and 0.13e). Furthermore, the current-voltage characteristics show that the Oh-B2S2 monolayer may selectively detect NO and NO2 gases after bias 1.4 V, providing a greater possibility for the development of boron-based gas-sensing devices for future nanoelectronics.

The effects of side chain engineering on the morphology and charge transport of the A-DA1D-A type of non-fullerene acceptor: a multiscale study.

The appearance of the A-DA1D-A type of non-fullerene acceptor Y6 and its derivatives significantly improves the power conversion efficiency of organic solar cells. However, the effects of the modulation of the side chains of Y6 on its morphology and charge transport in organic thin films are still not well understood. In this work, we have systematically studied the effects of symmetric modifications of the length of alkyl side chains and the types, such as branched or straight alkyl chains, and the introduction of heteroatoms to side chains on these properties. A multiscale study, including density functional theory and classical molecular dynamics simulations, has been used to answer this open question. We find that face-on configurations are generally dominant for the AA, A1A1, and DD stacking of molecular pairs. With respect to prototype Y6, the introduction of oxygen atoms to outer alkyl side chains could enhance AA stacking but worsen the electrical network and enlarge the reorganization energy during electron transfer, and changing outer side straight alkyl chains to branched chains ruins π-π stacking of all units significantly. Finally, we discover that shortening outer alkyl side chains appropriately or changing inner branched chains to straight chains with the same number of carbon atoms is a good strategy to improve the molecular π-π stacking and electron mobility of Y6 while changing outer straight side chains to branched chains or introducing oxygen atoms to outer straight chains is the opposite. This study provides a new insight into the relationship between morphology and electron mobility and will be helpful for the design of future high-performance non-fullerene acceptors.

Self‐integration exactly constructing oxygen‐modified MoNi alloys for efficient hydrogen evolution

AbstractIntroducing oxygen atoms into nickel‐based alloys is an effective strategy for constructing water dissociation sites for hydrogen evolution reaction (HER). However, controlling oxygen content to realize the best match of water dissociation and hydrogen adsorption is challenging. Herein, we exploit the self‐integration process of MoNi alloy in molten salts to introduce oxygen atoms, which ultimately leads to the localized generation of robust NiOxHy around the MoNi alloys. Interestingly, Mo is further doped into NiOxHy (Mo‐NiOxHy) to construct an effective active center for water dissociation due to the high mobility in ionic solutions. Owing to the covering and space confinement of molten salt, MoNi alloy is exactly decorated with Mo‐NiOxHy nanosheets. Both physical characterization and density functional theory calculation prove that the electron transport, water dissociation capability, and hydrogen adsorption of MoNi are finely tuned and benefited from the O and Mo doping, thus greatly expediting HER kinetics. Mo‐NiOxHy exhibits a much lower overpotential of 33 mV at 10 mV cm−2 in alkaline electrolyte, even superior to the Pt/C benchmark. Moreover, the final Mo‐NiOxHy requires a low overpotential of 57 mV at 10 mV cm−2 in acidic media. This enhancement is ascribed to the successful assembly of MoNi foam elicited by molten salt.

Improving the electrical properties of transparent ZnO-based thin- film transistors using MgO gate dielectric with various oxygen concentrations

Zinc oxide (ZnO)-based thin-film transistors (TFTs) have attracted increasing attention towards flat-panel displays as alternatives to silicon-based TFTs due to their transparency to visible light. Magnesium oxide (MgO) has a wide bandgap (7.8 eV) and high dielectric constant (k). This leads to the development of TFTs using MgO as a gate oxide layer, which can significantly reduce the operating voltage. However, the electrical properties and dielectric constant of MgO are determined from the percentage of oxygen in MgO. In this study, a MgO gate-oxide was deposited on ZnO by magnetron sputtering at various oxygen concentrations (0%, 66%, and 100%) to fabricate TFTs. With an increase in the oxygen concentration, the oxygen vacancies of MgO were compensated, thereby improving the crystallinity and enhancing the dielectric constant from 6.53 to 12.9 for the oxygen concentrations of 0% and 100%. No pinch-off (saturation) behavior was observed in the TFTs with 0% oxygen; however, the pinch-off voltages were significantly reduced to 17 and 2 V in the TFTs with 66% and 100% oxygen, respectively; hence, the TFT-100 could be operated at a low operating voltage (2 V). With an increase in oxygen from 0% to 100%, the threshold voltage and trap-state density significantly decreased from −159 V and 1.6 × 1018 cm−3 to −31.4 V and 6.5 × 1016 cm−3, respectively. The TFTs with 0% oxygen exhibited a higher field-effect mobility of 12 cm2 V−1 s−1 due to the uncompensated oxygen vacancy in ZnO, which had a higher electron concentration. After introducing oxygen atoms, the field-effect mobility decreased to 0.16 cm2 V−1 s−1 in the TFTs with 66% oxygen, which can be attributed to the compensated oxygen vacancy and lower electron concentration. In contrast, the field-effect mobility increased to 1.88 cm2 V−1 s−1 for the TFTs with 100% oxygen due to the enhanced dielectric constant and crystallinity of MgO.

A simple surface engineering to develop the potential of carbon nitride nanosheets in high-performance polymer nanocomposites conducted by first-principles calculations

The incompatible interface between carbon nitride (CN) nanosheets and polymer resin is a huge challenge to develop high-performance polymer/CN nanocomposites. Recently, the complicated surface functionalization methods reported severely hinder the commercial production and practical application of polymer/CN nanocomposites. Herein, conducted by the first-principles calculations, a simple surface engineering is put forward to change the surface characteristic of CN nanosheets by rapidly introducing oxygen atoms with a chemical oxidation method. Presented by the first-principles calculations, it is found that the introduction of oxygen atoms can enhance the adsorption energy between oxygen-doping carbon nitride nanosheets (OCN) and waterborne polyurethane (WPU) resin. As a result, a stronger interfacial interaction and better dispersion state are presented in WPU/OCN nanocomposites, thus laying the foundation for the properties enhancement. Further, effective suppression effects for thermal pyrolysis and fire hazards of WPU resin are demonstrated by OCN nanosheets. As presented by cone calorimeter results, the peak values of heat release rate and total heat release in WPU/OCN-2 are decreased to 806 kW/m2 and 43.3 MJ/m2, significantly less than those of pure WPU (1028 kW/m2 and 55.9 MJ/m2). Meanwhile, more char residue, lower signal intensity of pyrolysis gas, and a prolonged time for signal peak also confirm that the addition of 2.0 wt% OCN nanosheets can hinder the thermal degradation behavior of WPU resin. In addition, the introduction of oxygen atoms promotes the formation of hydrogen bond interactions between OCN nanosheets and WPU matrix, thus enhancing interfacial compatibility and overcoming the re-stack problem. As a result, break strength and elongation at break of WPU/OCN-2 are up to 621% and 24.4 MPa, respectively. The combination of first-principles calculations and surface engineering opens a new approach for designing and developing high-performance polymer nanocomposites.

Effects of oxygen contents on the physical properties of MgO films and carrier transport of Au/MgO/ZnO MIS diodes

MgO films with various oxygen contents were deposited on ZnO using radio-frequency magnetron sputtering, and Au/MgO/ZnO metal-insulator-semiconductor (MIS) diodes were fabricated. The effects of various oxygen contents on the physical properties of MgO and the carrier transport in MIS diodes were studied. The crystallinity of MgO films improved with increased oxygen content up to 66%; however, the crystallinity degraded upon further increase of oxygen content up to 100%. X-ray photoelectron spectroscopy showed that the oxygen vacancies were compensated by the introduced oxygen atoms; however, the excess oxygen atoms could not fill the lattice sites and were instead absorbed on the MgO surface. The optical bandgaps of MgO films increased from 5.16 to 5.22 eV for 0 and 100% oxygen content, respectively, resulted by the suppressed oxygen vacancies. The average roughness of MgO films increased from 4.02 to 6.86 nm for 0 and 100% oxygen content, respectively. As compared to MIS diodes without oxygen content, the leakage current was reduced by approximately 300 times in MIS diodes with 66% oxygen content. At a high bias voltage (V ≥ 0.4V), MIS diodes without oxygen exhibited ohmic conduction. In contrast, MIS diodes with oxygen exhibited Fowler-Nordheim tunnelling at high bias voltages. With increasing oxygen content, the tunnelling barrier height increased to its maximum of 0.46 eV in MIS diodes with 66% oxygen content. Nevertheless, the barrier height reduced to 0.29 eV for the excess oxygen content up to 100%. However, at low-bias voltages, all MIS diodes demonstrated a direct tunnelling mechanism owing to their rectangular barriers.

Unraveling the unique role of brown graphitic carbon nitride in robust CO2 photoreduction

Photocatalytic CO2 reduction is one of the important means to alleviate the energy crisis. In this work, an oxygen-linked and brown graphitic carbon nitride (GACN) was successfully prepared by thermal polymerization after oil bath method. GACN introduced oxygen atoms on surface of BulkCN. Various characterizations of the material show that the prepared GACN has a different structure and higher photoelectronic activity compared to BulkCN. GACN possessed strong photocatalytic CO2 reduction capacity, and the photocatalytic activity was significantly improved compared with BulkCN. In view of density functional theory calculations, it is proved that the oxygen atoms introduced by GACN increase CO2 photoreaction reactivity, enhance electronic activity and reduce the reaction energy barrier. This work can have a positive effect on the photocatalytic application of g-C3N4 with the existence of oxygen atoms.

Oxygen-doped biochar for the activation of ferrate for the highly efficient degradation of sulfadiazine with a distinct pathway

Oxygen-containing functional groups in functionalized biochar (BC) play an important role in its environmental applications. Herein, we introduced oxygen atoms into BC by copyrolysis of sawdust and magnesium carbonate basic pentahydrate (MgCO3)4·Mg(OH)2·5 H2O for the preparation of O-enriched porous BC (OPBC). OPBC800 (OPBC pyrolyzed at 800 °C) exhibited ultrahigh activity to activate ferrate (K2FeO4) for the oxidation of sulfadiazine (SDZ, 100% removal of SDZ in 2 min at pH = 5). We found that SDZ molecules can be rapidly adsorbed by the hierarchical porous structure of OPBC and were expediently oxidized by in situ generated Fe(IV) and Fe(V) active species on the surface of OPBC. The degradation mechanism of SDZ involved is quite different from the well-confirmed mechanism in which only active species in the solution play a role. Electrochemical impedance spectroscopy showed that O-doping in OPBC improved the electron-donating ability and expedited the electron transfer to ferrate, thus enhancing the catalytic activity of OPBC. This provides a new functionalization method for BC and provides more information about the activation of ferrate.

Nano-Graphite Prepared by Rapid Pulverization as Anode for Lithium-Ion Batteries.

Reducing the particle size of active material is an effective solution to the poor rate performance of the lithium-ion battery. In this study, we proposed a facile strategy for the preparation of nano-graphite as an anode for a lithium-ion battery via the rapid mechanical pulverization method. It is the first time that diamond particle was selected as the medium to achieve high preparation efficiency and low energy consumption. The as-prepared nano-graphite with the size from 10 to 300 nm displays an intact structure and high specific surface area. The introduced oxygen atoms increased the wettability of nano-graphite electrode and lowered its polarization. The nano-graphite prepared from three hours of grinding shows an excellent reversible capacity of 191 mAh g−1, at a rate of 5 C, after 480 cycles, along with an increase of 86% in capacity, at 1 C, in comparison with pristine graphite. The highlight of this strategy is to optimize the current preparation method. The good electrochemical performance comes from the combined effect of nano-scale particle size, large specific surface area, and continuous mesopores.

Using MgO capping layer to enhance the performance of ZnO based metal-semiconductor-metal photodetectors

Magnesium oxide (MgO) was deposited on zinc oxide (ZnO) surface to achieve a visible-blind ultraviolet (UV) metal-semiconductor-metal photodetectors (MSM-PDs). ZnO and MgO were prepared using a radio-frequency (RF) magnetron sputtering system. As compared to the MSM-PDs without the MgO capping layer, the dark current is greatly subdued by approximately four orders of magnitude in the MSM-PDs with MgO capping layer, which in turn largely increases the photo/dark current ratio from 102 to 105 by three orders in the MSM-PDs. The MgO capping layer enhances the ultraviolet/visible rejection ratio and largely raised the detectivity from 8.3 × 1010 to 1.03 × 1012 Jones in the prepared MSM-PDs. X-ray photoelectron spectroscopy shows that the oxygen vacancies on ZnO surface were compensated by the introduced oxygen atoms from MgO, forming a stable film that passivated the ZnO surface. The MgO capping layer greatly increases the Schottky barrier height (SBH) of an Au/ZnO Schottky barrier diode (SBD) from 0.58 to 0.93 eV for the Au/MgO/ZnO SBD. The raised SBH and suppressed surface defects drastically reduced the dark current and visible response of the prepared MSM-PDs.

Oxygen-doped MoS2 nanoflowers with sulfur vacancies as electrocatalyst for efficient hydrazine oxidation

Direct hydrazine fuel cells (DHFCs) fuel has drawn significant attention due to its characteristics of high energy density. Substantial effort is still needed to explore sustainable and efficient catalysts for hydrazine oxidation reaction (HzOR). Herein, inspired by reducing solvents that can protect the precursors of nanomaterials from oxidation, oxygen-doped MoS2 nanoflowers with sulfur vacancies (O-rich MoS2) were prepared via a simple synthesis method using the readily available ethanol/water as the solvent and applied as electrocatalyst for HzOR. It is found that the ratio of ethanol to water has a significant influence on the morphology of MoS2 and the catalytic performance of hydrazine oxidation. Moreover, the concept of O-doping is proposed by introducing oxygen atoms to mostly replace bulk S atoms in the oxidation process of nanomaterials. The sulfur vacancy and doping were regarded as the main active site for the HzOR. Accordingly, the onset potential of the prepared electrocatalyst is 0.5 V vs. RHE in a 1 M KOH/0.1 M hydrazine electrolyte. This doping method can provide new ideas for improving the construction of hydrazine oxidation catalysts in the future.

Interfacial bonding of CuZr metallic glass via oxide: A molecular dynamics study

A layer of oxygen is introduced into a Cu64Zr36 MG to achieve interfacial bonding. The oxidation kinetics, diffusion behavior, local structure, and mechanical performance of the oxide-bonded MG were investigated via molecular dynamics simulations. The growth of the oxide layer follows the inverse-logarithmic law, indicating that this process is controlled by the ionic drift through the oxide in response to electric fields. The introduction of oxygen atoms seriously deteriorates the short-range ordering of MG by suppressing the formation of icosahedral clusters. Uniaxial tensile tests indicate that the oxide-bonded MG has favorable ductility, while its ultimate tensile strength is reduced.

Effects of Oxygen Atoms Introduced at Different Positions of Non-Fullerene Acceptors in the Performance of Organic Solar Cells with Poly(3-hexylthiophene).

With the development of large-area fabrication technologies for organic solar cells (OSCs), poly(3-hexylthiophene) (P3HT) is the best choice as a photovoltaic donor polymer because it can be easily synthesized in the scale of kilograms at low cost. However, non-fullerene acceptors (NFAs) matching with P3HT for high performance OSCs are very rare. Herein, by introducing oxygen atoms into the side chains or the fused-ring core of indaceno[1,2-b:5,6-b']dithiophene, we synthesized two new A2-A1-D-A1-A2 type NFAs, where benzotriazole (BTA) and 2-(1,1-dicyanomethylene)rhodanine were used as the bridged A1 and terminal A2, respectively. The final NFAs, named BTA43 and BTA53, show wider absorption spectra and enhanced intermolecular/intramolecular interaction in comparison with their analogue BTA3 without oxygen atoms. The photovoltaic devices based on P3HT:BTA43 and P3HT:BTA53 can achieve a high power conversion efficiency of 6.56 and 6.31%, respectively, which are obviously higher than that of BTA3 (5.64%). Our results provide a simple and effective strategy to design promising NFAs to pair with the classic photovoltaic polymer P3HT.

Hydroxylation of Steroids by a Microbial Substrate-Promiscuous P450 Cytochrome (CYP105D7): Key Arginine Residues for Rational Design.

Our previous study showed that CYP105D7, a substrate-promiscuous P450, catalyzes the hydroxylation of 1-deoxypentalenic acid, diclofenac, naringenin, and compactin. In this study, 14 steroid compounds were screened using recombinant Escherichia coli cells harboring genes encoding CYP105D7 and redox partners (Pdx/Pdr, RhFRED, and FdxH/FprD), and the screening identified steroid A-ring 2β- and D-ring 16β-hydroxylation activity. Wild-type CYP105D7 was able to catalyze the hydroxylation of five steroids (testosterone, progesterone, 4-androstene-3,17-dione, adrenosterone, and cortisone) with low (<10%) conversion rates. Structure-guided site-directed mutagenesis of arginine residues around the substrate entrance and active site showed that the R70A and R190A single mutants and an R70A/R190A double mutant exhibited greatly enhanced conversion rates for steroid hydroxylation. For the conversion of testosterone in particular, the R70A/R190A mutant's kcat/Km values increased 1.35-fold and the in vivo conversion rates increased significantly by almost 9-fold with high regio- and stereoselectivity. Molecular docking analysis revealed that when Arg70 and Arg190 were replaced with alanine, the volume of the substrate access and binding pocket increased 1.08-fold, which might facilitate improvement of the hydroxylation efficiency of steroids.IMPORTANCE Cytochrome P450 monooxygenases (P450s) are able to introduce oxygen atoms into nonreactive hydrocarbon compounds under mild conditions, thereby offering significant advantages compared to chemical catalysts. Promiscuous P450s with broad substrate specificity and reaction diversity have significant potential for applications in various fields, including synthetic biology. The study of the function, molecular mechanisms, and rational engineering of substrate-promiscuous P450s from microbial sources is important to fulfill this potential. Here, we present a microbial substrate-promiscuous P450, CYP105D7, which can catalyze hydroxylation of steroids. The loss of the bulky side chains of Arg70 and Arg190 in the active site and substrate entrance resulted in an up to 9-fold increase in the substrate conversion rate. These findings will support future rational and semirational engineering of P450s for applications as biocatalysts.