Latest ArticlesAmphichoterpenoids A–C (1–3), unprecedented picoline-derived meroterpenoids possessing a pyrano[3, 2-c]pyridinyl-γ-pyranone scaffold, were characterized from the ascidian-derived fungus Amphichorda felina SYSU-MS7908. Their structures were elucidated by spectroscopic methods, X-ray diffraction and electronic circular dichroism (ECD) calculations. A plausible biosynthetic pathway was proposed. The isolated compounds displayed moderate inhibitory activity against acetylcholinesterase with 50% inhibiting concentration (IC50) values of 18.8–53.2 μmol/L.
The electrocatalysis of nitrate reduction reaction (NRR) has been considered to be a promising nitrate removal technology. Developing a highly effective iron-based electrocatalyst is an essential challenge for NRR. Herein, boron-iron nanochains (B-Fe NCs) as efficient NRR catalysts were prepared via a facile low-cost and scalable method. The Fe/B ratio of the B-Fe NCs-x can be elaborately adjusted to optimize the NRR catalytic performance. Due to the electron transfer from boron to metal, the metal-metal bonds are weakened and the electron density near the metal atom centers are rearranged, which are favor of the conversion from NO3- into N2. Moreover, the well-crosslinked chain-like architectures benefit the mass/electron transport to boost the exposure of abundant catalytic active sites. Laboratory experiments demonstrated that the optimized B-Fe NCs catalyst exhibits superior intrinsic electrocatalytic NRR activity of high nitrate conversion (~80%), ultrahigh nitrogen selectivity (~99%) and excellent long-term reactivity in the mixed electrolyte system (0.02 mol/L NaCl and 0.02 mol/L Na2SO4 mixed electrolyte), and the electrocatalytic activity of the material shows poor performance at low chloride ion concentration (Nitrate conversion of ~61% and nitrogen selectivity of ~57% in 0.005 mol/L NaCl and 0.035 mol/L Na2SO4 mixed electrolyte). This study provides a broad application prospect for further exploring the high-efficiency and low-cost iron-based functional nanostructures for electrocatalytic nitrate reduction.
The remarkable development of nanotechnology and nanoscience has greatly promoted the vigorous development of the field of nanomaterials. This study explores a porous cuboid Ni/NiO composite nanomaterial obtained by calcining NiC2O4·2H2O under a N2 environment. The composite affords direct electrochemical activity and good electrocatalytic properties. Compared to uncalcined precursor, the porous Ni/NiO obtained after calcination exhibited higher catalytic activity for glucose oxidation with higher sensitivity. Moreover, because of its regular cube structure the as-synthesized Ni/NiO exhibited improved electrochemical stability. Such porous Ni/NiO nanocubes represent promising glucose catalyst with high sensitivity and selectivity, improved stability and fast amperometric response.
An enzyme-responsive polysaccharide supramolecular targeted nanoassembly was successfully constructed by the host-guest complexation of positively charged mono-(6-(tetraethylenepentamine)-6-deoxy)-β-cyclodextrin (TEPA-CD) with adamantane-grafted hyaluronic acid (HA-ADA). Possessing a series of positively charged polyamine chains, the obtained polysaccharide nanoassembly could serve as a biocompatible plasmid DNA (pDNA) container. More interestingly, the pDNA could be released from the nanoassembly through the enzymatic degradation of HA skeleton, which realized the controlled pDNA binding and release. Besides, the polysaccharide nanoassembly exhibited lower cytotoxicity than the commercial transfection reagents 25kDa bPEI (PEI25k), accompanied by similar gene delivery effect. We believe that this work might present a convenient method for targeted, controlled gene delivery.
The methanol oxidation reaction (MOR) is the limiting half-reaction in direct methanol fuel cell (DMFC). Although Pt is the most active single-metal electrocatalyst for MOR, it is hampered by high cost and CO poisoning. Constructing a Pt or Ru monolayer on a second metal substrate by means of galvanic replacement of underpotentially deposited (UPD) Cu monolayer has been shown as an efficient catalyst design strategy for the electrocatalysis of MOR because of the presumed 100% utilization of atoms and resistance to CO poisoning. Herein, we prepared one-dimensional surface-alloyed electrocatalyst from predominantly (111) faceted Au nanowires with high aspect ratio as the substrate of under-potential deposition. The electrocatalyst comprises a core of the Au nanowire and a shell of catalytically active Pt coated by Ru. Coverage-dependent electro-catalytic activity and stability is demonstrated on the Pt/Ru submonolayers on Au wires for MOR. Among all these catalysts, Au@PtML@RuML exhibits the best electrocatalytic activity and poisoning tolerance to CO. This presents a viable method for the rational catalyst design for achieving high noble-metal utilization efficiency and high catalytic performance.
4-Hydroxyphenylpyruvate dioxygenase (HPPD) is an important target for both drug and pesticide discovery. As a typical Fe(Ⅱ)-dependent dioxygenase, HPPD catalyzes the complicated transformation of 4-hydroxyphenylpyruvic acid (HPPA) to homogentisic acid (HGA). The binding mode of HPPA in the catalytic pocket of HPPD is a focus of research interests. Recently, we reported the crystal structure of Arabidopsis thaliana HPPD (AtHPPD) complexed with HPPA and a cobalt ion, which was supposed to mimic the pre-reactive structure of AtHPPD-HPPA-Fe(Ⅱ). Unexpectedly, the present study shows that the restored AtHPPD-HPPA-Fe(Ⅱ) complex is still nonreactive toward the bound dioxygen. QM/MM and QM calculations reveal that the HPPA resists the electrophilic attacking of the bound dioxygen by the trim of its phenyl ring, and the residue Phe381 plays a key role in orienting the phenyl ring. Kinetic study on the F381A mutant reveals that the HPPD-HPPA complex observed in the crystal structure should be an intermediate of the substrate transportation instead of the pre-reactive complex. More importantly, the binding mode of the HPPA in this complex is shared with several well-known HPPD inhibitors, suggesting that these inhibitors resist the association of dioxygen (and exert their inhibitory roles) in the same way as the HPPA. The present study provides insights into the inhibition mechanism of HPPD inhibitors.
Tyrosinase (TYR) is an important polyphenolic oxidase enzyme and usually regards as a biomarker of melanoma cancer. Highly effective tracking TYR activity in vivo will help to study the mechanism of TYR in living organisms and forecasts related diseases. In this study, we present a novel TYR-activatable fluorescent probe (CHMC-DOPA) for tracking TYR activity in vitro and in vivo. CHMC-DOPA is constructed by incorporating dopamine (DOPA) moiety into a fluorescent chloro-hydroxyl-merocyanine (CHMC) scaffold. Upon exposure to TYR, the dopamine unit in CHMC-DOPA is oxidized to a dopaquinone derivative, and an intramolecular photo-induced electron transfer (PET) process between CHMC fluorophore and o-dopaquinone will take place, the fluorescence of CHMC-DOPA is quenched rapidly. Therefore, the evaluation of TYR activity is established in terms of the relationship between fluorescence quenching efficiency and TYR activity. In our experiments, CHMC-DOPA shows various advantages, such as fast response (8 min), low concentration of TYR activation (0.5 U/mL), good water-solubility, as well as the lowest detection limit (0.003 U/mL) compared with previously reported works. Furthermore, CHMC-DOPA also exhibits excellent cell membrane permeability and low cytotoxicity, which is successfully used to monitor endogenous TYR activity in living cancer cells and zebrafish models. CHMC-DOPA performs well, and we anticipate that this newly designed novel platform will provide an alternative for high effective monitoring TYR activity in biosystems.
Herein, we designed and constructed two metallacycles, 1 and 2, to illustrate the conformational effect of isomeric AIE fluorophores on the platform of supramolecular coordination complexes (SCCs). Specifically, the dangling phenyl rings in TPE units of the metallacycle 1 align completely outside the main cyclic structure, while in the metallacycle 2, these phenyl rings align half inside and half outside. The experimental results showed that two metallacycles exhibited different behaviors in terms of AIE fluorescence and chemical sensing, which could be attributed to the subtle structural difference of the TPE units. This work represents the unification of topics such as self-assembly, AIE, and chemical sensing, and further promotes the understanding for the structure-property relationship of isomeric AIE fluorophores.
Rhodium(Ⅲ)-catalyzed [4 + 1] cyclization of azobenzenes with α-Cl ketones has been developed. 3-Acyl-2H-indazoles could be easily afforded in up to 97% yields for more than 30 examples. The obtained products are potentially valuable in organic synthesis and drug discovery. This protocol featured with high efficiency, extensive functional group tolerance and mild reaction conditions. The one-step efficient construction of an anti-inflammatory agent confirms the practicability of this procedure.
The improvement in accuracy of in vitro diagnosis has always been the focus of early screening of thyroid dysfunction. We constructed a microfluidic chip based on a polystyrene polymer substrate. Total triiodothyronine (TT3), total thyroxine (TT4), free triiodothyronine (FT3), free thyroxine (FT4), and thyrotropin (TSH) in human whole blood samples were analysed by fluorescence immunoassay to evaluate thyroid function. The results indicate that the microfluidic chip shows a good linear relationship in the detection of TT3, TT4, FT3, FT4, and TSH standards, and the correlation coefficient (r) is not less than 0.9900. In addition, the chip also has strong anti-interference (RSD% ≤ 5%) and good repeatability (CV ≤ 8%), and its inter-batch differences are small (CV ≤ 15%). The results of practical application in clinical thyroid function measurement indicated its high accuracy (r ≥ 0.9900). It provides a new method for the determination of thyroid function and lays a foundation for subsequent clinical application.
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