Metal carbonyl vapor generation coupled with dielectric barrier discharge to avoid plasma quench for optical emission spectrometry.

The scope of dielectric barrier discharge (DBD) microplasma as a radiation source for optical emission spectrometry (OES) is extended by nickel carbonyl vapor generation. We proved that metal carbonyl completely avoids the extinguishing of plasma, and it is much more suitable for matching the DBD excitation and OES detection with respect to significant DBD quenching by concomitant hydrogen when hydride generation is used. A concentric quartz UV reactor allows sample solution to flow through the central channel wherein to efficiently receive the uniformly distributed UV irradiation in the confined cylindrical space between the concentric tubes, which facilitates effective carbonyl generation in a nickel solution. The carbonyl is transferred into the DBD excitation chamber by an argon stream for nickel excitation, and the characteristic emission of nickel at 232.0 nm is detected by a charge-coupled device (CCD) spectrometer. A 1.0 mL sample solution results in a linear range of 5-100 µg L(-1) along with a detection limit of 1.3 µg L(-1) and a precision of 2.4% RSD at 50 µg L(-1). The present DBD-OES system is validated by nickel in certified reference materials.

Crystal structures of Pseudomonas putida esterase reveal the functional role of residues 187 and 287 in substrate binding and chiral recognition.

A recombinant carboxylesterase (rPPE) from Pseudomonas putida ECU1011 was previously cloned and engineered to give a potential application for resolving chiral α-hydroxy acids including mandelic acids and derivatives. Two variants rPPEW187H and rPPED287A showed a ∼100-fold increase in activity towards rac-2-acetoxy-2-(2'-chlorophenyl) acetate (rac-AcO-CPA), but rPPED287A had a significant decrease in enantioselectivity (E=8.7) compared to rPPEW187H and the wild-type rPPE (rPPEWT) (E>200). Here we report the crystal structures of rPPEWT and rPPEW187H, both by themselves and in complex with the substrate, to elucidate the structural basis of this phenomenon. An inactive mutation of nucleophile residue S159A was introduced to obtain the structure of rPPES159A/W187H complexed with (S)-AcO-CPA. The structural analysis reveals that the side chain of residue Asp287 in rPPEWT would have a potential steric conflict with (S)-AcO-CPA when the substrate binds at the active site of the enzyme. However, the mutation W187H could facilitate the relocation of Asp287, while D287A directly eliminates the hindrance of Asp287, both of which offer sufficient space for the binding and hydrolysis of substrate. Moreover, Asp287 generates one site of the "three-point attachment model" as a hydrogen-bond donor that determines the excellent enantioselectivity of rPPE in chiral recognition, and D287A would obviously destroy the hydrogen bond and result in the low enantioselectivity of rPPED287A.

Boosting H2O2 generation by shortening the charge migration distance in BiPO4 nanocrystals.

The photocatalytic production of H2O2 has gained recognition as an economical and eco-friendly technology, but it suffers from limitations such as low production rates and difficulty in achieving high concentrations. This study was designed to overcome these limitations by preparing BiPO4 nanocrystals (BIP NCs) via high-temperature hydrolysis, and X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that BIP NCs with particle sizes of 8.5 ± 3 nm were synthesized. In a photocatalytic performance test, only H2O and O2 were used to produce H2O2, resulting in an accumulation of H2O2 of up to 30.44 mM·g-1, as measured with the potassium titanium oxalate method; this value was 3.13 times greater than that of bulk BiPO4 (BIP-B). The resulting nanocrystals demonstrated superior electron-hole transport and separation efficiency compared to those of BIP-B, and H2O2 was formed in a one-step two-electron process. Furthermore, a film composed of a gas diffusion layer (GDL) and BIP NCs provided continuous accumulation of H2O2; a concentration of 7.23 mM was achieved after 96 h of reaction, and the stability of the film was confirmed by comparing scanning electron microscopy (SEM) images obtained before and after the reaction. Construction of a nanocrystalline structure to enhance the activities of photocatalysts and films and achieve continuous accumulation of H2O2 will provide insights into the photocatalytic production of highly concentrated H2O2.

Iodine excitation in a dielectric barrier discharge micro-plasma and its determination by optical emission spectrometry.

A low temperature micro-plasma generated in a dielectric barrier discharge (DBD) was used as a radiation source for the excitation of iodine and its determination by vapor generation-optical emission spectrometry. A piece of ceramic tube served as an excitation chamber to provide a small gas path for introducing a helium stream to generate a DBD micro-plasma by using a neon power supply. Iodine was on-line vaporized by reaction of iodide in sample solution (or iodate pre-reduced to iodide by ascorbic acid) with H(2)O(2). The vapor was subsequently separated and transferred into the DBD excitation chamber by a helium stream for performing optical emission and detection at a 905 nm emission line. The emission spectra were measured with a QE65000 charge-coupled device spectrometer. A few important issues governing the performance of the entire system, e.g., selection of the analytical emission line, elimination of the DBD micro-plasma background variation and optimization of the experimental parameters, were investigated. With a sampling volume of 1.0 mL, a linear range of 0.1-10.0 mg L(-1) was obtained along with a detection limit of 0.03 mg L(-1). A precision of 2.1% RSD was achieved at the concentration level of 2 mg L(-1) iodine. The present system was applied in the determination of trace iodine in real samples, i.e., GBW10023 laver, table salt and cydiodine buccal tablets, giving rise to satisfactory results.

Sago cycas-based hierarchical-structured porous carbon for adsorption of acetone vapour: preparation, characterization and performance.

The porous structure and oxygen-containing functional groups of carbon materials play important roles in the adsorption of volatile organic compounds (VOCs). In this study, hierarchical-structured porous carbons (HSPCs) with a large specific surface area and abundant oxygen-containing functional groups were prepared from sago cycas without a template or post-processing for acetone (one of the most common VOCs) adsorption. The micropore volume (0.41-1.15 cm3 g-1) and oxygen-containing functional groups (0.3-1.92 mmol g-1) of HSPCs were manipulated by adjusting the activation temperature. Static adsorption data showed that the HSPC activated at 600 °C (HSPC-600) was superior for acetone adsorption, and a maximum adsorption capacity of 3.75 mmol g-1 was achieved at 25 °C and 0.1 kPa. Breakthrough curves and cyclic adsorption-desorption tests demonstrated the dynamic adsorption capacity and regeneration performance of HSPC-600 were excellent as well. The adsorption isotherms were well described by Langmuir and Langmuir-Freundlich models, indicating the adsorption of acetone on HSPCs is a monolayer adsorption process. Due to electrostatic interaction, hydrogen bond and van der Waals forces between acetone molecules and oxygen-containing functional groups, the adsorption capacity of HSPCs for acetone was significantly improved at low relative pressure. This study may provide a peculiar insight into the development of high-performance acetone adsorbent.

Fish scale-based biochar with defined pore size and ultrahigh specific surface area for highly efficient adsorption of ciprofloxacin.

A fish scale-based porous activated biochar with defined pore size (DPBC) was fabricated by a one-step calcination and activation method. The DPBC possessed an ultrahigh specific surface area of 3370 m2 g-1 and its pore diameter centered at 1.49 nm which fits into the ciprofloxacin (CIP) molecular dimension, making it an ideal adsorbent for CIP adsorption due to the molecular pore-filling effect. The maximum Langmuir monolayer adsorption capacity of DPBC for CIP was higher than 1000 mg g-1 and the equilibrium time was less than 4 h, superior to most adsorbents reported in literature. Thermodynamic analysis indicated the adsorption process was spontaneous and endothermic. Notably, fixed-bed experiments showed an encouraging adsorption performance towards CIP, with a high saturated dynamic adsorption capacity of 880.3 mg g-1. Both Thomas and Yoon-Nelson models predict the fixed-bed column adsorption performance well. Hydrophobic effect, π-π interaction, π-π EDA, cation exchange, hydrogen bonding formation, pore filling effect, electrostatic and cation-π interaction involved in the CIP adsorption on the DPBC.

Nicotinamide mononucleotide adenylyltransferase uses its NAD+ substrate-binding site to chaperone phosphorylated Tau.

Tau hyper-phosphorylation and deposition into neurofibrillary tangles have been found in brains of patients with Alzheimer's disease (AD) and other tauopathies. Molecular chaperones are involved in regulating the pathological aggregation of phosphorylated Tau (pTau) and modulating disease progression. Here, we report that nicotinamide mononucleotide adenylyltransferase (NMNAT), a well-known NAD+ synthase, serves as a chaperone of pTau to prevent its amyloid aggregation in vitro as well as mitigate its pathology in a fly tauopathy model. By combining NMR spectroscopy, crystallography, single-molecule and computational approaches, we revealed that NMNAT adopts its enzymatic pocket to specifically bind the phosphorylated sites of pTau, which can be competitively disrupted by the enzymatic substrates of NMNAT. Moreover, we found that NMNAT serves as a co-chaperone of Hsp90 for the specific recognition of pTau over Tau. Our work uncovers a dedicated chaperone of pTau and suggests NMNAT as a key node between NAD+ metabolism and Tau homeostasis in aging and neurodegeneration.

Facile synthesis of electrospun carbon nanofiber/graphene oxide composite aerogels for high efficiency oils absorption.

Oil contamination will seriously affect the health of water environment, so it is necessary to design ideal oil absorbents with large absorption capacity and high selectivity for effectively purify the oil contaminated water. Preparing high performance carbon aerogel for oil absorption has attracted growing attention, but challenges remain. Here we report a facile approach to fabricate mechanical strength enhanced three-dimensional (3D) nanofibrous aerogel principally through supporting agent liquid assisted collection-electrospinning technology, in which the immersion work was applied to measure the immersion capacity of nanofibers according to liquid-solid interfaces theory. Particularly, electrospun polyacrylonitrile (PAN) nanofibers (NFs) were collected directly in graphene oxide (GO) aqueous dispersion, and the continuous fibrous skeleton assembled with two-dimensional (2D) GO sheets to form open porous networks during the electrospinning process, which basically avoided the tedious preparation steps (nanofiber membrane cutting and re-crosslinking) that have been used previously. Due to the open porous networks promising structure stability of the aerogel, the GO sheets content required in the aerogel stacking process was largely reduced, and there was no strict requirement on the pre-freezing temperature and manner in the subsequent freeze-drying process. Furthermore, followed by thermal treating the PAN NFs/GO composite aerogel, fluffy carbon nanofibers/GO aerogels (CNF/GOAs) were obtained, which exhibited ultra-low density (2-3 mg/mL) and great compressibility (80%). After hydrophobic modification of polydimethylsiloxane by vapor deposition, the CNF/GOAs performed high absorption capacity (120-286 wt/wt) toward diverse oils. Owing to the fire-resistance and great elasticity, the CNF/GOAs could be recycled simply by combustion or mechanical squeeze, and still showed great absorption capacity after 10 cycles, which were feasible for large scale application.

The protective effect of Luteolin on myocardial ischemia/reperfusion (I/R) injury through TLR4/NF-κB/NLRP3 inflammasome pathway.

The purpose of the present study was to investigate the effect of Luteolin(Lut) on myocardial ischemia reperfusion injury and explore the underlying mechanism. Myocardial ischemia reperfusion injury (I/R) model was induced with 30min of left anterior descending (LAD) occlusion followed by 24h of reperfusion. In vivo, the rats were randomly divided into 5 groups: (1)Sham, (2)I/R, (3)I/R+Lut(40mg/kg), (4)I/R+Lut(80mg/kg) and (5)I/R+Lut(160mg/kg). In vitro, the H9c2 cells were assigned to five groups: (1)control, (2)hypoxia-reoxygenation(H/R), (3)H/R+Lut(5µM), (4)H/R+Lut(10µM) and (5)H/R+Lut(20µM). The H9c2 cells were stimulated with H/R protocol in the presence or absence of TAK-242, a TLR4 inhibitor. As a result, Lut ameliorated myocardial ischemia reperfusion injury and hypoxia-reoxygenation as evidenced by triphenyl tetrazolium chloride (TTC) staining and MTT assay, respectively. Lut was founded to decrease the levels of aspartate transaminase(AST), creatine phosphokinase-isoenzyme (CK-MB) and lactate dehydrogenase (LDH) in serum. Moreover, Lut could reduce the contents of interleukin-1ß(IL-1ß), interleukin-18 (IL-18) and tumor necrosis factor-α (TNF-α) in serum of rats and supernant of H9c2 cells. In addition, Lut remarkably downregulated the expressions of toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88) and nuclear factor kappa B (NF-κB). Lut also inhibited the upregulations of inflammasome components, such as NOD-like receptor 3(NLRP3), apoptosis-associated speck-like protein containing CARD(ASC) in I/R-induced rats and H/R-induced H9c2 cells. In conclusion, Lut exhibited strong favorable cardioprotective effect on myocardial I/R injury which might be related to the down-regulation of the TLR4-meidated NF-κB/NLRP3 inflammasome in vivo and in vitro.