Oxygen-deficient AgIO3 for efficiently photodegrading organic contaminants under natural sunlight.

Defect engineering is regarded as an effective strategy to boost the photo-activity of photocatalysts for organic contaminants removal. In this work, abundant surface oxygen vacancies (Ov) are created on AgIO3 microsheets (AgIO3-OV) by a facile and controllable hydrogen chemical reduction approach. The introduction of surface Ov on AgIO3 broadens the photo-absorption region from ultraviolet to visible light, accelerates the photoinduced charges separation and migration, and also activates the formation of superoxide radicals (•O2-). The AgIO3-OV possesses an outstanding degradation rate constant of 0.035 min-1, for photocatalytic degrading methyl orange (MO) under illumination of natural sunlight with a light intensity is 50 mW/cm2, which is 7 and 3.5 times that of the pristine AgIO3 and C-AgIO3 (AgIO3 is calcined in air without generating Ov). In addition, the AgIO3-OV also exhibit considerable photoactivity for degrading other diverse organic contaminants, including azo dye (rhodamine B (RhB)), antibiotics (sulflsoxazole (SOX), norfloxacin (NOR), chlortetracycline hydrochloride (CTC), tetracycline hydrochloride (TC) and ofloxacin (OFX)), and even the mixture of organic contaminants (MO-RhB and CTC-OFX). After natural sunlight illumination for 50 min, 41.4% of total organic carbon (TOC) for MO-RhB mixed solution can be decreased over AgIO3-OV. In a broad range of solution pH from 3 to 11 or diverse water bodies of MO solution, AgIO3-OV exhibits attractive activity for decomposing MO. The MO photo-degradation process and mechanism over AgIO3-OV under natural sunlight irradiation has been systemically investigated and proposed. The toxicities of MO and its degradation intermediates over AgIO3-OV are compared using Toxicity Estimation Software (T.E.S.T.). Moreover, the non-toxicity of both AgIO3-OV catalyst and treated antibiotic solution (CTC-OFX mixture) are confirmed by E. coli DH5a cultivation test, supporting the feasibility of AgIO3-OV catalyst to treat organic contaminants in real water under natural sunlight illumination.

Genome-directed discovery of antiproliferative bafilomycins from a deepsea-derived Streptomyces samsunensis.

Genomic bioinformatics analysis identified a bafilomycin biosynthetic gene cluster (named bfl) in the deepsea-derived S. samsunensis OUCT16-12, from which two new (1 and 2, named bafilomycins R and S) along with four known (3-6) bafilomycins were targetly obtained. The structure of 3 was clearly identified for the first time, thus named bafilomycin T herein. Differ from the fumarate substitution at C-21 of known bafilomycins, its location on C-23 is a unique feature of 1 and 2. The stereochemistry of the compounds was established based on NOE correlations, ketoreductase (KR)-types in PKS modules of bfl, and ECD calculations. Moreover, a detailed biosynthetic model of 1-6 in S. samsunensis OUCT16-12 was provided based on the gene function prediction and sequence identity. Compared with the positive control doxorubicin, 1-6 showed more potent antiproliferative activities against drug-resistant lung cancer cell line A549-Taxol, with IC50 values ranging from 0.07 µM to 1.79 µM, which arrested cell cycle in G0/G1 phase to hinder proliferation.

Elucidation of the Late Steps during Hexacosalactone A Biosynthesis in Streptomyces samsunensis OUCT16-12.

Hexacosalactone A (1) is a polyene macrolide compound featuring a 2-amino-3-hydroxycyclopent-2-enone (C5N)-fumaryl moiety. While compound 1 has been proposed to be assembled via a type I modular polyketide synthase (PKS) system, most of the putative biosynthetic steps lack experimental evidence. In this study, we elucidated the post-PKS tailoring steps of compound 1 through in vivo gene inactivation and in vitro biochemical assays. We demonstrated that the amide synthetase HexB and O-methyltransferase HexF are responsible for the installations of the C5N moiety and the methyl group at 15-OH of compound 1, respectively; two new hexacosalactone analogs, named hexacosalactones B (4) and C (5), were purified and structurally characterized, followed by anti-multidrug resistance (anti-MDR) bacterial assays, revealing that the C5N ring and the methyl group are necessary for the antibacterial bioactivities. Through database mining of C5N-forming proteins HexABC, six uncharacterized biosynthetic gene clusters (BGCs), putatively encoding compounds with different types of backbones, were identified, providing potentials to discover novel bioactive compounds with C5N moiety. IMPORTANCE In this study, we elucidate the post-PKS tailoring steps during the biosynthesis of compound 1 and demonstrate that both C5N and 15-OMe groups are critical for the antibacterial activities of compound 1, paving the way for generation of hexacosalactone derivatives via synthetic biology strategy. In addition, mining of HexABC homologs from the GenBank database revealed their wide distribution across the bacterial world, facilitating the discovery of other bioactive natural products with C5N moiety.

Study on the long time aging behavior of MAPbI3: from experiment to first-principles simulation.

As the core functional layer of perovskite solar cells, the serious issues of the CH3NH3PbI3 film related to the long-term stability and its rapid degradation when exposed to the environment should be investigated deeply. In this study, the variation of phase construction, light absorption ability and fluorescence quenching ability during the long time aging process have been monitored. The results show that the degradation process is composed of the original serious fluorescence quenching and the lag behind phase decomposition. Then, the intrinsic physical mechanism has been obtained by the first-principles simulation of defect properties, which shows that the original serious fluorescence emission quenching is attributed to the deep level defects with low formation energies (such as VPb and IPb); meanwhile, the lag behind phase decomposition is caused by the easy ionic diffusion; for example, the diffusion activation energy of the iodine ion is 0.286 eV. The results illustrate that both the defect passivation and prevention of the ion diffusion are necessary for achieving a stable perovskite film.

Increasing electron density by surface plasmon resonance for enhanced photocatalytic CO2 reduction.

The photocatalytic CO2 reduction reaction is a multi-electron process, which is greatly affected by the surface electron density. In this work, we synthesize Ag clusters supported on In2O3 plasmonic photocatalysts. The Ag-In2O3 compounds show remarkedly enhanced photocatalytic activity for CO2 conversion to CO compared to pristine In2O3. In the absence of any co-catalyst or sacrificial agent, the CO evolution rate of optimal Ag-In2O3-10 is 1.56 µmol/g/h, achieving 5.38-folds higher than that of In2O3 (0.29 µmol/g/h). Experimental verification and DFT calculation demonstrate that electrons transfer from Ag clusters to In2O3 on Ag-In2O3 compounds. In Ag-In2O3 compounds, Ag clusters serving as electron donators owing to the SPR behaviour are not helpful to decline photo-induced charge recomnation rate, but can provide more electron for photocatalytic reaction. Overall, the Ag clusters promote visible-light absorption and accelerate photocatalytic reaction kinetic for In2O3, resulting in the photocatalytic activity enhancement of Ag-In2O3 compounds. This work puts insight into the function of plasmonic metal on enhancing photocatalysis performance, and provides a feasible strategy to design and fabricate efficient plasmonic photocatalysts.

Controllable Schottky barriers and contact types of BN intercalation layers in graphene/MoSi2As4 vdW heterostructures via applying an external electrical field.

Graphene-based van der Waals (vdW) heterostructures have opened unprecedented opportunities for various device applications due to their rich functionalities and novel physical properties. Motivated by the successful synthesis of a MoSi2N4 monolayer (Science, 2020, 369, 670), in this work by means of first-principles calculations we construct and investigate the interfacial electronic properties of the graphene/MoSi2As4 vdW heterostructure, which is expected to be energetically favorable and stable. Our results show that the graphene/MoSi2As4 heterostructure forms an n-type Schottky contact with a low barrier of 0.12 eV, which is sensitive to the external electric field and the transformation from an n-type Schottky contact to a p-type one can be achieved at 0.2 V Å-1. The small effective masses and strong optical absorption intensity indicate that the graphene/MoSi2As4 heterostructure will have a high carrier mobility and can be applied to high-speed FET. Importantly, we also show that the opening band gap can be achieved in the graphene/BN/MoSi2As4 heterostructure and the type-I band alignment can transform into type-II under an external electric field of -0.2 V Å-1. These findings demonstrate that the graphene/MoSi2As4 heterostructure can be considered as a promising candidate for high-efficiency Schottky nanodevices.

Designing Multifunctional Donor-Acceptor-Type Molecules to Passivate Surface Defects Efficiently and Enhance Charge Transfer of CsPbI2Br Perovskite for High Power Conversion Efficiency.

High-density and multitype surface defects of CsPbI2Br perovskite induce charge recombination and accumulation, hindering its device efficiency and stability. However, the surface defect types of CsPbI2Br perovskite are still unclear, and conventional organic molecules only passivate one specific defect and cannot achieve good overall passivation. Here, density functional theory is used to explore surface defect types and properties of CsPbI2Br with calculating the defect formation energy and electronic structure. Results show that the dominant deep-level defects are cationic defects (PbBr) under Br-poor conditions and anionic defects (Ii and Bri) under moderate and Br-rich conditions, originating from Pb-Pb bonding and I-I bonding. Multifunctional organic molecules containing donor and acceptor groups are used to passivate both cationic and anionic defects simultaneously. It turns out that the deep-level defects are effectively decreased by forming strong interaction of N-Pb, O-Pb, and halide-Pb bonds. Moreover, the electron and hole transfers from perovskite to molecules increase dramatically to -9.06 × 1012 and 2.60 × 1012 e/cm2 and maybe improve the efficiency of power conversion. Our findings not only reveal the surface defect properties of CsPbI2Br, but also offer an approach for designing new multifunctional passivators for perovskite solar cells with high conversion efficiency.

Genome-Guided Discovery of Antifungal Filipins from a Deep-Sea-Derived Streptomyces antibioticus.

Nine new (1-3, 5-8, 11, and 12; named filipins VI-XIV) and three known (4, 9, and 10) filipin-type polyene macrolides were isolated from the deep-sea-derived Streptomyces antibioticus OUCT16-23 using a genome-guided strategy coupled with bioassay. Their structures were elucidated based on the extensive MS and NMR spectroscopic analyses together with ECD calculations. In an antifungal assay, compounds 4, 5, and 7-10 showed different degrees of growth inhibition against Candida albicans with minimum inhibitory concentrations (MICs) of 1.56-12.5 µg/mL, by which the alkyl side-chain substitution affecting the activity was preliminarily studied. A biosynthetic pathway to 1-12 in S. antibioticus OUCT16-23 is also proposed.

Optimizing the Electronic Structure of ZnS via Cobalt Surface Doping for Promoted Photocatalytic Hydrogen Production.

Developing highly efficient semiconductor photocatalysts for H2 evolution is intriguing, but their efficiency is subjected to the following three critical issues: limited light absorption, low carrier separation efficiency, and sluggish H2 evolution kinetics. Element surface doping is a feasible strategy to synchronously break through the above limitations. In this study, we prepared a series of Co-surface-doped ZnS photocatalysts to systematically investigate the effects of Co surface doping on photocatalytic activity and electronic structure. The implantation of Co results in the emergence of the impurity level above the valence band (VB) and the upshifted conduction band (CB) and enhances its visible light absorption. Co gradient doping inhibits the combination and facilitates the migration of carriers. S atoms are proven to be reactive active sites for photocatalytic H2 evolution over both ZnS and Co-doped ZnS. Co doping alters the surface electronic structure and decreases the absolute value for the hydrogen binding free energy (ΔGH) of the adsorbed hydrogen atom on the catalyst. As a consequence, Co-surface-doped ZnS shows boosted photocatalytic H2 evolution activity relative to the undoped material. This work provides insights into the mechanistic understanding of the surface element doping modification strategy to developing efficient photocatalysts.

The effects of flipped classroom characterized by situational and collaborative learning in a community nursing course: A quasi-experimental design.

BACKGROUND: Since traditional teaching could not help to develop competences, flipped classroom has caught the sight of researchers. Despite the uptake of flipped classroom in other disciplines, there is a dearth of evidence available about the use in nursing curricula. In addition, there is no consensus on how to best implement a flipped classroom. OBJECTIVE: This study aimed to (1) develop a flipped classroom underpinned by constructivism theory and (2) to verify its effectiveness. DESIGN: This study adopted a quasi-experimental design. SETTING AND PARTICIPANTS: This study was conducted in 2018 spring semester at a University in East China with 6th semester undergraduate nursing students in four parallel classes in Community Nursing Course. METHODS: A flipped classroom characterized by situational and collaborative learning was developed and carried out with two classes (intervention group, n = 98). In-class lectures was applied for the other two classes (control group, n = 90). Course examination score, experience (course experience questionnaire, CEQ), and students' appraisal were used to verify the effectiveness of flipped classroom. RESULTS: Compared to control group, the examination score was higher for intervention group. As for the four domains of CEQ, good teaching domain rating was lower, learning burden domain rating was higher for the intervention group. There was no statistical difference in classroom quality and harvest domains. More students in intervention group chose the course helped them in developing "critical thinking" and "self-cognition and evaluation" abilities. Satisfaction rating of groups was not statistically different. CONCLUSIONS: Flipped classroom was efficient in improving students' academic performance and promoting development of higher-level thinking abilities; however, it failed in improving students' satisfaction and course experience. These findings suggest that active learning strategies such as situational and collaborative learning of group problem solving and discussion should be integrated into nursing curriculum and refinement to flipped classroom are needed to create students' buy-in.

Bacillaenes: Decomposition Trigger Point and Biofilm Enhancement in Bacillus.

Bacillaenes are a class of poly-unsaturated enamines produced by Bacillus strains that are notoriously unstable toward light, oxygen, and normal temperature. Herein, in an in-depth study of this highly unstable chemotype, the stability and biological function of bacillaenes were investigated. The structure change of the bacillaene scaffold was tracked by time-course 1H NMR data analysis coupled with the differential analysis of 2D-NMR spectra method, which was demonstrated to be a "domino" effect triggered by 4',5'-cis (2 and 3) configuration rearranged to trans (2a and 3a). These findings provide the possibility for stabilizing the bacillaene scaffold by chemical modification of its trigger points. In the biofilm assay, compounds 1 and 2 accelerated self-biofilm formation in Bacillus methylotrophicus B-9987 at low concentrations of 1.0 and 0.1 µg/mL. Interestingly, bacillaenes play dual roles as antibiotic and biofilm enhancers in a dose-dependent manner, both of which serve in the self-protection of Bacillus.

An Unusual Type II Polyketide Synthase System Involved in Cinnamoyl Lipid Biosynthesis.

As a unique structural moiety in natural products, cinnamoyl lipids (CLs), are proposed to be assembled by unusual type II polyketide synthases (PKSs). Herein, we demonstrate that the assembly of the CL compounds youssoufenes is accomplished by a PKS system that uniquely harbors three phylogenetically different ketosynthase/chain length factor (KS/CLF) complexes (YsfB/C, YsfD/E, and YsfJ/K). Through in vivo gene inactivation and in vitro reconstitution, as well as an intracellular tagged carrier-protein tracking (ITCT) strategy developed in this study, we successfully elucidated the isomerase-dependent ACP-tethered polyunsaturated chain elongation process. The three KS/CLFs were revealed to modularly assemble different parts of the youssoufene skeleton, during which benzene ring closure happens right after the formation of an ACP-tethered C18 polyene. Of note, the ITCT strategy could significantly contribute to the elucidation of other carrier-protein-dependent biosynthetic machineries.

An Effective Strategy for Identification of Highly Unstable Bacillaenes.

Exploration of unstable compounds is a rarely explored area of natural product research. We describe the integration of genomic and metabolomic analyses with bioassay-guided compound mining to effectively explore unstable bacillaenes. New bacillaene structures (2, 4, and 5) were identified from compound mixtures using the DANS-SVI (differential analysis of 2D NMR spectrum-single spectrum with variable intensities) method, which were further verified by the isolation of the pure compounds under strictly controlled conditions. Compound 1 exhibited antibacterial activity against multi-drug-resistant bacterial strains, while glycosylation decreased the activity of the bacillaene scaffold.

Strategy for chemotherapeutic delivery using a nanosized porous metal-organic framework with a central composite design.

BACKGROUND: Enhancing drug delivery is an ongoing endeavor in pharmaceutics, especially when the efficacy of chemotherapy for cancer is concerned. In this study, we prepared and evaluated nanosized HKUST-1 (nanoHKUST-1), nanosized metal-organic drug delivery framework, loaded with 5-fluorouracil (5-FU) for potential use in cancer treatment. MATERIALS AND METHODS: NanoHKUST-1 was prepared by reacting copper (II) acetate [Cu(OAc)2] and benzene-1,3,5-tricarboxylic acid (H3BTC) with benzoic acid (C6H5COOH) at room temperature (23.7°C±2.4°C). A central composite design was used to optimize 5-FU-loaded nanoHKUST-1. Contact time, ethanol concentration, and 5-FU:material ratios were the independent variables, and the entrapment efficiency of 5-FU was the response parameter measured. Powder X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption were used to determine the morphology of nanoHKUST-1. In addition, 5-FU release studies were conducted, and the in vitro cytotoxicity was evaluated. RESULTS: Entrapment efficiency and drug loading were 9.96% and 40.22%, respectively, while the small-angle X-ray diffraction patterns confirmed a regular porous structure. The SEM and TEM images of the nanoHKUST-1 confirmed the presence of round particles (diameter: approximately 100 nm) and regular polygon arrays of mesoporous channels of approximately 2-5 nm. The half-maximal lethal concentration (LC50) of the 5-FU-loaded nanoHKUST-1 was approximately 10 µg/mL. CONCLUSION: The results indicated that nanoHKUST-1 is a potential vector worth developing as a cancer chemotherapeutic drug delivery system.

Differences in rheological and fractal properties of conditioned and raw sewage sludge.

Rheological tests for raw and conditioned activated sludge (AS) or anaerobic digested sludge (ADS) show that power-law relationships can be used to describe the evolution of several theological parameters, i.e., limiting viscosity (eta(infinity)), yield stress (tau(y)), cohesion energy of the sludge network (Ec), and storage modulus (G'), with total suspended solid (TSS) content in raw and conditioned sludge. A gel-like structure that behaves similar to weak-link flocs/aggregates was observed in AS and ADS. As derived from the double-logarithmic plots of G'-TSS content, the mass fractal dimensions of the raw and conditioned AS or ADS flocs/aggregates were 2.70 and 2.53 or 2.85 and 2.79, respectively. The rheological tests also indicate that both polymer conditioning and increased TSS content led to improved elastic behavior, cohesion energy, and yield stress of the sludge network, as well as expanded the corresponding linear viscoelastic range. The porosity of AS or ADS flocs/aggregates will be improved by polymer conditioning.

Effect of solid contents on the controlled shear stress rheological properties of different types of sludge.

Controlled shear stress (CSS) test was used to study the effect of solid contents on the corresponding rheological parameters for sludge. Three types of sludge with or without conditioning, including activated sludge (AS), anaerobic digested sludge (ADS), and water treatment residuals (WTRs), were collected for the CSS test. Results showed that the yield stress and the cohesion energy of the sludge networks were improved with increased total suspending solid (TSS) contents in most cases. For the conditioned AS/ADS and the raw WTRs, exponential law was observed in the relationships between cohesion energy of material networks or yield stress and the TSS contents, whereas for the conditioned WTRs, only exponential law dependence was found between the parameters of shear modulus or critical strain and the TSS contents.