Colorimetric and Electrochemical Methods for the Detection of SARS-CoV-2 Main Protease by Peptide-Triggered Assembly of Gold Nanoparticles.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease (Mpro) has been regarded as one of the ideal targets for the development of antiviral drugs. The currently used methods for the probing of Mpro activity and the screening of its inhibitors require the use of a double-labeled peptide substrate. In this work, we suggested that the label-free peptide substrate could induce the aggregation of AuNPs through the electrostatic interactions, and the cleavage of the peptide by the Mpro inhibited the aggregation of AuNPs. This fact allowed for the visual analysis of Mpro activity by observing the color change of the AuNPs suspension. Furthermore, the co-assembly of AuNPs and peptide was achieved on the peptide-covered electrode surface. Cleavage of the peptide substrate by the Mpro limited the formation of AuNPs/peptide assembles, thus allowing for the development of a simple and sensitive electrochemical method for Mpro detection in serum samples. The change of the electrochemical signal was easily monitored by electrochemical impedance spectroscopy (EIS). The detection limits of the colorimetric and electrochemical methods are 10 and 0.1 pM, respectively. This work should be valuable for the development of effective antiviral drugs and the design of novel optical and electrical biosensors.

Chemistry and Bioactivity of Briaranes from the South China Sea Gorgonian Dichotella gemmacea.

Seven new briarane diterpenoids, gemmacolides AZ-BF (1-7), were isolated together with eight known analogues (8-15) from the South China gorgonian Dichotella gemmacea. Their structures were elucidated based on detailed spectroscopic analysis and a comparison with reported data. In an in vitro bioassay, these compounds exhibited different levels of growth inhibition activity against A549 and MG63 cells, giving continuous evidences about the biological contribution of functional groups at C-2, C-12, C-13, and C-16. These compounds were also evaluated for their antibacterial and antifungal activities. Compound 8 exhibited a potential antibacterial activity against both Gram-positive bacterium Bacillus megaterium and Gram-negative bacterium Escherichia coli.

Briarane diterpenoids from the gorgonian Dichotella gemmacea.

Seven new briarane diterpenoids, gemmacolides AS-AY (1-7), were isolated together with ten known analogues (8-17) from the South China Sea gorgonian Dichotella gemmacea. The structures of the new compounds were elucidated by the detailed analysis of spectroscopic data and comparison with reported data. The absolute configuration of compounds was determined based on electronic circular dichroism (ECD) experiments and genetic correlations as well. Compounds 15 and 16 were reported for the first time for the gorgonian. In the preliminary in vitro bioassays, compound 5 showed potential growth inhibitory activity against MG63 cells.

Optical Bioassays Based on the Signal Amplification of Redox Cycling.

Optical bioassays are challenged by the growing requirements of sensitivity and simplicity. Recent developments in the combination of redox cycling with different optical methods for signal amplification have proven to have tremendous potential for improving analytical performances. In this review, we summarized the advances in optical bioassays based on the signal amplification of redox cycling, including colorimetry, fluorescence, surface-enhanced Raman scattering, chemiluminescence, and electrochemiluminescence. Furthermore, this review highlighted the general principles to effectively couple redox cycling with optical bioassays, and particular attention was focused on current challenges and future opportunities.

Chemistry and tumor cell growth inhibitory activity of 11,20-epoxy-3Z,5(6)E-diene briaranes from the South China Sea gorgonian Dichotella gemmacea.

Eighteen new 11,20-epoxy-3Z,5E-dien briaranes, gemmacolides AA-AR (1-18), were isolated together with three known analogs, dichotellides F (19) and I (20), and juncenolide C (21), from the South China Sea gorgonian Dichotella gemmacea. The structures of the compounds were elucidated by detailed spectroscopic analysis and comparison with reported data. The absolute configuration was determined based on the ECD experiment. In the in vitro bioassay, compounds 1-3, 5, 6, 8-12, and 14-19 exhibited different levels of growth inhibition activity against A549 and MG63 cell lines. Preliminary structure-activity analysis suggests that 12-O-isovalerate may increase the activity whereas 13- or 14-O-isovalerate may decrease the activity. Contribution of substitutions at C-2 and C-16 remains uncertain.

Progress in Electrochemical Immunosensors with Alkaline Phosphatase as the Signal Label.

Electrochemical immunosensors have shown great potential in clinical diagnosis, food safety, environmental protection, and other fields. The feasible and innovative combination of enzyme catalysis and other signal-amplified elements has yielded exciting progress in the development of electrochemical immunosensors. Alkaline phosphatase (ALP) is one of the most popularly used enzyme reporters in bioassays. It has been widely utilized to design electrochemical immunosensors owing to its significant advantages (e.g., high catalytic activity, high turnover number, and excellent substrate specificity). In this work, we summarized the achievements of electrochemical immunosensors with ALP as the signal reporter. We mainly focused on detection principles and signal amplification strategies and briefly discussed the challenges regarding how to further improve the performance of ALP-based immunoassays.

Achieving High Activity and Long-Term Stability towards Oxygen Evolution in Acid by Phase Coupling between CeO2-Ir.

The development of efficient and stable catalysts with high mass activity is crucial for acidic oxygen evolution reaction (OER). In this study, CeO2-Ir heterojunctions supported on carbon nanotubes (CeO2-Ir/CNTs) are synthesized using a solvothermal method based on the heterostructure strategy. CeO2-Ir/CNTs demonstrate remarkable effectiveness as catalysts for acidic OER, achieving 10.0 mA cm-2 at a low overpotential of only 262.9 mV and maintaining stability over 60.0 h. Notably, despite using an Ir dosage 15.3 times lower than that of c-IrO2, CeO2-Ir/CNTs exhibit a very high mass activity (2542.3 A gIr-1@1.53 V), which is 58.8 times higher than that of c-IrO2. When applied to acidic water electrolyzes, CeO2-Ir/CNTs display a prosperous potential for application as anodic catalysts. X-ray photoelectron spectrometer (XPS) analysis reveals that the chemical environment of Ir nanoparticles (NP) can be effectively modulated through coupling with CeO2. This modulation is believed to be the key factor contributing to the excellent OER catalytic activity and stability observed in CeO2-Ir/CNTs.

Magnetically Assisted Immobilization-Free Detection of microRNAs Based on the Signal Amplification of Duplex-Specific Nuclease.

The double specific nuclease (DSN)-based methods for microRNAs (miRNAs) detection usually require the immobilization of DNA probes on a solid surface. However, such strategies have the drawbacks of low hybridization and cleavage efficiency caused by steric hindrance effect and high salt concentration on the solid surface. Herein, we proposed an immobilization-free method for miRNA detection on the basic of DSN-assisted signal amplification. The biotin- and fluorophore-labeled probes were captured by streptavidin-modified magnetic beads through streptavidin-biotin interactions, thus producing a poor fluorescence signal. Once the DNA probes were hybridized with target miRNA in solution to form DNA-miRNA duplexes, DNA stands in the duplexes would be selectively digested by DSN. The released target miRNA could initiate the next hybridization/cleavage recycling in the homogeneous solution, finally resulting in the release of numerous fluorophore-labeled fragments. The released fluorophores remained in solution and emitted strong fluorescence after treatment by the streptavidin-modified magnetic beads. The immobilization-free method achieved the assays of miRNA-21 with a detection limit down to 0.01 pM. It was employed to evaluate the expression levels of miRNA-21 in different cancer cells with satisfactory results.

Bioactive briarane diterpenoids from the South China Sea gorgonian Dichotella gemmacea.

Six new briarane diterpenoids, gemmacolides T-Y (1-6), were isolated together with three known analogs, juncenolide J (7), praelolide (8), and junceellolide C (9), from the South China Sea gorgonian Dichotella gemmacea. The structures of the new compounds were elucidated by detailed spectroscopic analysis and comparison with reported data. The absolute configuration was suggested based on biosynthetic considerations. In an in vitro bioassay, compounds 3 and 6 showed potent growth inhibition towards tumor cell lines of A549 and MG63, being stronger than the positive control of adriamycin. These compounds also exhibited weak antimicrobial activity against the bacterium Escherichia coli and the fungi Microbotryum violaceum and Septoria tritici.

New bioactive sulfated alkenes from the sea cucumber Apostichopus japonicus.

Two new alkene sulfates, (5Z)-dec-5-en-1-yl sulfate (4) and (3E)-dec-3-en-1-yl sulfate (5), together with three known sulfated alkanes, 2,6-dimethylheptyl sulfate (1), octyl sulfate (2), and decyl sulfate (3), were isolated from the sea cucumber Apostichopus japonicus. The structures of the new compounds 4 and 5 were elucidated by spectroscopic analysis, including ¹H-, ¹³C-, and 2D-NMR, ESI-MS, and HR-ESI-MS. Compounds 2 and 3 were isolated from natural sources for the first time. In preliminary bioassays in vitro, compounds 4 and 5 showed antibacterial, antifungal, and cytotoxic activities.

Insight into a Nitrogen-Doping Mechanism in a Hard-Carbon-Microsphere Anode Material for the Long-Term Cycling of Potassium-Ion Batteries.

To investigate the alternatives to lithium-ion batteries, potassium-ion batteries have attracted considerable interest due to the cost-efficiency of potassium resources and the relatively lower standard redox potential of K+/K. Among various alternative anode materials, hard carbon has the advantages of extensive resources, low cost, and environmental protection. In the present study, we synthesize a nitrogen-doping hard-carbon-microsphere (N-SHC) material as an anode for potassium-ion batteries. N-SHC delivers a high reversible capacity of 248 mAh g-1 and a promoted rate performance (93 mAh g-1 at 2 A g-1). Additionally, the nitrogen-doping N-SHC material also exhibits superior cycling long-term stability, where the N-SHC electrode maintains a high reversible capacity at 200 mAh g-1 with a capacity retention of 81% after 600 cycles. DFT calculations assess the change in K ions' absorption energy and diffusion barriers at different N-doping effects. Compared with an original hard-carbon material, pyridinic-N and pyrrolic-N defects introduced by N-doping display a positive effect on both K ions' absorption and diffusion.

O-Doping Configurations Reduce the Adsorption Energy Barrier of K-Ions to Improve the Electrochemical Performance of Biomass-Derived Carbon.

In recent years, atomic-doping has been proven to significantly improve the electrochemical performance of biomass-derived carbon materials, which is a promising modification strategy. Among them, there are relatively few reports about O-doping. Here, porous carbon derived from orange peel was prepared by simple carbonization and airflow-annealing processes. Under the coordination of microstructure and surface groups, the derived carbon had excellent electrochemical performance for the K-ion batteries' anode, including a high reversible specific capacity of 320.8 mAh/g, high rate performance of 134.6 mAh/g at a current density of 2000 mA/g, and a retention rate of 79.5% even after 2000 long-term cycles, which shows great application potential. The K-ion storage mechanisms in different voltage ranges were discussed by using various characterization techniques, that is, the surface adsorbed of K-ionswas in the high-potential slope area, and the intercalation behavior corresponded to the low-potential quasi-plateau area. In addition, the density functional theory calculations further confirmed that O-doping can reduce the adsorption energy barrier of K-ions, change the charge density distribution, and promote the K-ion storage. In particular, the surface Faraday reaction between the C=O group and K-ions plays an important role in improving the electrochemical properties.

A General, Label-Free and Homogeneous Electrochemical Strategy for Probing of Protease Activity and Screening of Inhibitor.

Proteases play a critical role in regulating various physiological processes from protein digestion to wound healing. Monitoring the activity of proteases and screening their inhibitors as potential drug molecules are of great importance for the early diagnosis and treatment of many diseases. In this work, we reported a general, label-free and homogeneous electrochemical method for monitoring protease activity based on the peptide-copper interaction. Cleavage of peptide substrate results in the generation of a copper-binding chelator peptide with a histidine residue in the first or third position (His1 or His3) at the N-terminal. The redox potential and current of copper coordinated with the product are different from the free copper or the copper complex with the substrate, thus allowing for the detection of protease activity. Angiotensin-converting enzyme (ACE) and thrombin were determined as the model analytes. The label-free and homogeneous electrochemical method can be used for screening protease inhibitors with high simplicity and sensitivity.

Bioactive 11,20-epoxy-3,5(16)-diene briarane diterpenoids from the South China Sea gorgonian Dichotella gemmacea.

Seven new briarane diterpenoids, gemmacolides G-M (1-7), were isolated together with two known analogues, juncin O and junceellolide C, from the South China Sea gorgonian Dichotella gemmacea. The structures of the new compounds were elucidated by detailed analysis of spectroscopic data and comparison with reported data. In an in vitro bioassay, these compounds exhibited different levels of growth inhibition activity against A549 and MG63 cells. In particular, compound 4 was more active than the positive control adriamycin against A549 cells. Compounds 4 and 7 also exhibited weak antimicrobial activity against the bacterium Bacillus megaterium and the fungus Septoria tritici, respectively.

Bioactive (3Z,5E)-11,20-epoxybriara-3,5-dien-7,18-olide diterpenoids from the South China Sea gorgonian Dichotella gemmacea.

Six new (3Z,5E)-11,20-epoxybriara-3,5-dien-7,18-olide diterpenoids, gemmacolides N-S (1-6), were isolated together with four known analogues, juncenolide D, and juncins R, S and U (7-10), from the South China Sea gorgonian Dichotella gemmacea. The structures of the new compounds were elucidated by the detailed analysis of spectroscopic data in combination with the comparison with reported data. The absolute configuration of 1 was determined by a TDDFT calculation of its solution ECD spectrum, affording the determination of absolute configuration of other analogues by simply comparing their ECD spectra with that of 1. The cytotoxic and antimicrobial activities of these compounds were evaluated. In preliminary in vitro bioassays, compounds 4, 5, 6, 8 and 9 showed cytotoxicity against A549 and MG63, while compounds 1, 2, 4, 7-10 showed antimicrobial activity against the fungus Septoria tritici and the bacterium Escherichia coli.

Monodentate Transient Directing Group-Assisted Palladium-Catalyzed Direct ortho-C-H Iodination of Benzaldehydes for Total Synthesis of Hernandial.

The first palladium-catalyzed direct o-C-H iodination of benzaldehydes was successfully developed with the assistance of commercially available 2,5-bis(trifluoromethyl)aniline as the optimal monodentate transient directing group (MonoTDG). Moderate to excellent yields and good selectivity were achieved for a broad substrate scope under mild conditions. More importantly, the synthetic application was demonstrated by a concise two-step total synthesis of the natural product hernandial, which was accomplished by merging this new MonoTDG-assisted C-H iodination and subsequent copper-catalyzed cross-coupling.

Antifungal active triterpene glycosides from sea cucumber Holothuria scabra.

To study the new antifungal active triterpene glycosides of sea cucumber Holothuria scabra. Triterpene glycosides from Holothuria scabra were separated and purified by silica gel chromatography, reversed-phase silica gel chromatography and RP-HPLC. Their structures were elucidated on the basis of spectral data and chemical evidence. Three triterpene glycosides were identified as scabraside A (1), echinoidea A (2) and holothurin A1 (3). Scabraside A (1) is a new triterpene glycoside, and compounds 2 and 3 were isolated from Holothuria scabra for the first time. They showed antifungal activities (1 < or = MIC80 < or = 16 microg mL(-1)).

Selective and Sensitive Detection of Cyanide Based on the Displacement Strategy Using a Water-Soluble Fluorescent Probe.

A water-soluble fluorescent probe (C-GGH) was used for the highly sensitive and selective detection of cyanide (CN(-)) in aqueous media based on the displacement strategy. Due to the presence of the recognition unit GGH (Gly-Gly-His), the probe C-GGH can coordinate with Cu(2+) and consequently display ON-OFF type fluorescence response. Furthermore, the in situ formed nonfluorescent C-GGH-Cu(2+) complex can act as an effective OFF-ON type fluorescent probe for sensing CN(-) anion. Due to the strong binding affinity of CN(-) to Cu(2+), CN(-) can extract Cu(2+) from C-GGH-Cu(2+) complex, leading to the release of C-GGH and the recovery of fluorescent emission of the system. The probe C-GGH-Cu(2+) allowed detection of CN(-) in aqueous solution with a LOD (limit of detection) of 0.017 µmol/L which is much lower than the maximum contaminant level (1.9 µmol/L) for CN(-) in drinking water set by the WHO (World Health Organization). The probe also displayed excellent specificity for CN(-) towards other anions, including F(-), Cl(-), Br(-), I(-), SCN(-), PO4 (3-), N3 (-), NO3 (-), AcO(-), SO4 (2-), and CO3 (2-).