Electrocatalytic reduction of COsub.2 to valuable chemicals can alleviate the energy crisis, and solve the greenhouse effect. The key is to develop non-noble metal electrocatalysts with high ...activity, selectivity, and stability. Herein, bimetallic metal organic frameworks (MOFs) materials (BiZn-MOF, BiSn-MOF, and BiIn-MOF) were constructed by coordinating the metals Zn, In, Sn, and Bi with the organic ligand 3-amino-1H-1,2,4-triazole-5-carboxylic acid (Hsub.2atzc) through a rapid microwave synthesis approach. The coordination centers in bimetallic MOF catalyst were regulated to optimize the catalytic performance for electrochemical COsub.2 reduction reaction (COsub.2RR). The optimized catalyst BiZn-MOF exhibited higher catalytic activity than those of Bi-MOF, BiSn-MOF, and BiIn-MOF. BiZn-MOF exhibited a higher selectivity for formate production with a Faradic efficiency (FE = 92%) at a potential of −0.9 V (vs. RHE, reversible hydrogen electrode) with a current density of 13 mA cmsup.−2. The current density maintained continuous electrolysis for 13 h. The electrochemical conversion of COsub.2 to formate mainly follows the *OCHO pathway. The good catalytic performance of BiZn-MOF may be attributed to the Bi-Zn bimetallic coordination centers in the MOF, which can reduce the binding energies of the reaction intermediates by tuning the electronic structure and atomic arrangement. This study provides a feasible strategy for performance optimization of bismuth-based catalysts.
Besides acidic environments, pyrite oxidation also occurs in circumneutral environments, such as well-buffered marine and estuarine sediments and salt marshes where low-molecular-weight organic acids ...(LMWOAs) (e.g., citrate and oxalate) prevail. However, the production of hydroxyl radicals (OH) from pyrite oxidation by oxygen (O2) in these circumneutral environments is poorly understood. In this study, OH production was measured during the abiotic oxidation of pyrite by O2 under circumneutral conditions. A pyrite suspension (50g/L pyrite) that was buffered at pH 6–8 was exposed to air for oxygenation in the dark. Benzoate (20mM) was added into the suspension to trap OH. At pH 7, the cumulative OH reached 7.5μM within 420min in the absence of LMWOAs, whereas it increased to 14.8, 12 and 11.2μM in the presence of 1mM ethylenediaminotetraacetate, citrate and oxalate, respectively. When the citrate concentration, which serves as a LMWOAs model, was increased from 0.5 to 5mM, the cumulative OH increased from 10.3 to 27.3μM within 420min at pH 7. With the decrease in pH from 8 to 6, the cumulative OH increased from 2.1 to 23.3μM in the absence of LMWOAs, but it increased from 8.8 to 134.9μM in the presence of 3mM citrate. The presence of LMWOAs enhanced the OH production from pyrite oxidation under circumneutral conditions.
In the absence of LMOWAs, OH is produced mostly from the oxidation of adsorbed Fe(II) by O2. In the presence of citrate, OH production is attributed mainly to the oxidation of Fe(II)-citrate− by O2 and secondarily to the oxidation of H2O on surface-sulfur defects. The acceleration of pyrite oxidation by Fe(III)-citrate increases OH production. Fe(II)-citrate− is generated mainly from the complexation of adsorbed Fe(II) by citrate and the reduction of Fe(III)-citrate, and the generation is suppressed by the oxidation of adsorbed Fe(II). Fe(III)-citrate is generated predominantly from Fe(II)-citrate− oxidation. Most soluble Fe3+ that is produced from pyrite oxidation hydrolyzes to Fe(III) hydroxide. Kinetic models that were developed according to the proposed mechanisms identified the relative importance of each reaction for OH production. Using the kinetic model, the oxidation efficiencies of the redox-active substances that react with OH at different reaction-rate constants were estimated in the presence of 1mM citrate. This study presents on the overlooked role of LMWOAs in enhancing OH production from pyrite oxidation by O2 in pyrite-rich circumneutral environments, such as marine and estuarine sediments and salt marshes.
Six new polyene carboxylic acids named serpentemycins E-J (1-6), together with three known analogs (7-9), were isolated from the fermentation medium of Streptomyces sp. TB060207, which was isolated ...from arid soil collected from Tibet, China. The structures of the new compounds were elucidated mainly on the basis of HR-ESI-MS and NMR spectroscopic analyses. The inhibitory activities of compounds 1-9 against NO production in LPS-activated RAW264.7 cells were evaluated. Compound 9 has an inhibition rate of 87.09% to 60.53% at concentrations ranging from 5.0 to 40.0 µM.
Testing a number of N-omega-(purin-6-yl)aminoalkanoyl derivatives of 7,8-difluoro-3,4-dihydro-3-methyl-2H-1,4benzoxazine in a panel of nine tumor cell lines has shown that the studied compounds ...exhibit high cytotoxic activity, especially against 4T1 murine mammary carcinoma, COLO201 human colorectal adenocarcinoma, SNU-1 human gastric carcinoma, and HepG2 human hepatocellular carcinoma cells. Synthesis and study of structural analogs of these compounds made it possible to find that the presence of both a difluorobenzoxazine fragment and a purine residue bound via a linker of a certain length is crucial for the manifestation of the cytotoxic activity of this group of compounds. The study of the effect of the most promising compound on the cell cycle of the human tumor cell lines, the most sensitive and least sensitive to cytotoxic action (MDA-MB-231 breast adenocarcinoma and COLO201 colorectal adenocarcinoma, respectively), allows us to conclude that this compound is an inhibitor of DNA biosynthesis. The found group of purine conjugates may be of interest in the design of new antitumor agents.
A sensitive colorimetric method is described for the determination of the activity of alkaline phosphatase (ALP). It is based on the regulation of the oxidase-mimicking activity of MnO.sub.2 ...nanosheets. In the absence of ALP, MnO.sub.2 nanosheets are capable of catalyzing the oxidation of the colorless substrate 3,3',5,5'-tetramethylbenzidine (TMB) by oxygen to form a blue oxidized product (TMB Ox) with an absorption peak at 652 nm. In the presence of ALP and its substrate ascorbic acid-2-phosphate, the latter is hydrolyzed to form ascorbic acid (AA). AA triggers the decomposition of MnO.sub.2 nanosheets by reducing MnO.sub.2 to Mn.sup.2+, thereby weakening the enzyme mimicking activity of the MnO.sub.2 nanosheets and causing a drop in absorbance. The drop in absorbance at 652 nm is related to the ALP activity in the range from 0.05-10 m-units per mL (mU·mL.sup.-1), and the detection limit is 0.05 mU·mL.sup.-1. The method was applied to the determination of ALP in spiked calf serum samples and gave satisfactory results.
The identification of unstable metabolites of ellagitannins having ortho-quinone structures or reactive carbonyl groups is important to clarify the biosynthesis and degradation of ellagitannins. Our ...previous studies on the degradation of vescalagin, a major ellagitannin of oak young leaves, suggested that the initial step of the degradation is regioselective oxidation to generate a putative quinone intermediate. However, this intermediate has not been identified yet. In this study, young leaves of Quercus dentata were extracted with 80% acetonitrile containing 1,2-phenylenediamine to trap unstable ortho-quinone metabolites, and subsequent chromatographic separation afforded a phenazine derivative of the elusive quinone intermediate of vescalagin. In addition, phenylenediamine adducts of liquidambin and dehydroascorbic acid were obtained, which is significant because liquidambin is a possible biogenetic precursor of C-glycosidic ellagitannins and ascorbic acid participates in the production of another C-glycosidic ellagitannin in matured oak leaves.
Submerged macrophytes have important impacts on the denitrification and anaerobic ammonia-oxidizing (anammox) processes. Leaf damage in these plants probably changes the rhizosphere environment, ...affecting organic acid release and denitrifying bacteria. However, there is a lack of comprehensive understanding of the specific changes. This study investigated these changes in the rhizosphere of Potamogeton crispus with four degrees of leaf excision. When 0 %, 30 %, 50 % and 70 % of leaves were excised, the concentrations of total organic acid were 31.45, 32.67, 38.26, and 35.16 mg/L, respectively. The abundances of nirS-type denitrifying bacteria were 2.10 × 1010, 1.59 × 1010, 2.54 × 1010, and 4.67 × 1010 copies/g dry sediment, respectively. The abundances of anammox bacteria were 7.58 × 109, 4.59 × 109, 3.81 × 109, and 3.90 × 109 copies/g dry sediment, respectively. The concentration of total organic acids and the abundance of two denitrification microorganisms in the rhizosphere zone were higher than those in the root zone and non-rhizosphere zone. With increasing leaf damage, the number of OTUs in the Pseudomonas genus of nirS-type denitrifying bacteria first increased and then decreased, while that of the Thauera genus was relatively stable. The overall increase in the OTU number of anammox bacteria indicated that leaf damage promotes root exudates release, thereby leading to an increase in their diversity. The co-occurrence network revealed that the two denitrification microorganisms had about 60.52 % positive connections in rhizosphere while 64.73 % negative connections in non-rhizosphere. The abundance and community composition of both denitrification microorganisms were positively correlated with the concentrations of various substances such as oxalic acid, succinic acid, total organic acids and NO2--N. These findings demonstrate that submerged plant damage has significantly impacts on the structure of denitrification microbial community in the rhizosphere, which may alter the nitrogen cycling process in the deposit sediment.
This study reveals leaf damage of macrophyte changed the rhizosphere denitrification microbial community, which is helpful to further understand the process of nitrogen cycle in water.
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•Plant damage increased the release of organic acids.•Abundance of denitrifying bacteria increased while anammox bacteria decreased.•Different denitrifying bacteria exhibited diverse response to rhizosphere organic acids.•Increase of rhizosphere organic acids enhanced diversity of anammox bacteria.
Aesculus hippocastanum L., also known as horse chestnut, is an ornamental tree whose seeds are mostly discarded in landfills in the regions where they are grown. However, recent studies have shown ...that these seeds can be a source of interesting compounds for several industries. This work aimed to chemically characterize horse chestnut seeds at the level of compounds recognized for their wide bioactivity, i.e., organic acids, including phenolic compounds, using chromatographic methodologies (UFLC-DAD and LC-DAD-ESI/MSn). In addition, the bioactivity of these seeds was evaluated by in vitro methodologies, seeking to relate the respective (bio)activity to the compounds present in the endocarp (husk), seed coat (skin), and peeled seed (pulp). The antioxidant activity (lipid peroxidation inhibition and oxidative haemolysis inhibition), antibacterial potential (against Gram-positive and Gram-negative bacteria) and cytotoxicity (in human tumour cell lines and porcine liver primary cells) were evaluated. Kaempferol-O-pentoside-O-hexoside-O-hexoside was the main phenolic identified in the pulp. At the same time, (-)-epicatechin and β-type (epi)catechin dimer were the major phenolics present in husk and skin, respectively. In general, A. hippocastanum extracts presented antioxidant and antibacterial potential, without toxicity up to the maximal tested dose. Overall, these findings anticipate potential applications of A. hippocastanum seeds in food- or pharmaceutical-related uses.
This study investigated B. cereus presence in 122 samples belonging to 34 typologies of fresh or short-ripened cheeses made from cow, sheep, goat, or buffalo pasteurized milk, and sold on the Italian ...market. B. cereus was isolated at a prevalence of 9.8%, with a marked variability among cheese categories, and at low counts (always below 2.26 Log CFU/g). Twelve isolates were identified by MALDI-TOF analysis and typified by RAPD PCR as belonging to different B. cereus strains. All the strains were tested for the production of hemolysin BL, phosphatidylcholine-specific phospholipase C, proteases, and biofilm formation, and for the presence of chromosomal toxin-encoding genes (sph, plcA, cytK, entFM, bcet, nheA, nheB, nheC). Overall, 92% of strains harbored bcet, 75% the three genes nheA, nheB, and nheC, as well as plcA and sph, 67% entFM, and 33% cytK. All strains showed biofilm-forming ability. A chemical-physical characterization of the cheeses was also performed to show their suitability as substrates for B. cereus growth, showing high heterogeneity in terms of pH, aw, salt content, and concentration of organic acids. Finally, the ability to support spore germination and vegetative cell growth of a selected cheese was investigated in spores-inoculated samples maintained at 10 °C and 15 °C, showing the inhibitory effect of low storage temperatures.
Higher secondary porosity was observed in the centre of a sandstone unit in the Eocene Shahejie Formation fan delta front sandstones from the Bozhong Depression, Bohai Bay Basin. This differs from ...past studies showing secondary porosity mainly in the marginal parts of sandstones adjacent to shales. This study utilized reactive transport models involving low‐molecular‐weight organic acids (LMWOA) to discuss potential processes resulting in the contrary distribution of secondary porosity. An interface model simulating LMWOA diffusion from adjacent shales to the sandstone resulted in secondary porosity in sandstones adjacent to shales. In contrast, an advection model simulating advective transport of LMWOA parallel to the sandstone bedding successfully generated higher secondary porosity in the central part. The central part of the sandstone exhibited better grain sorting (greater depositional porosity) and significantly less early carbonate cements compared to the marginal sandstone parts. Consequently, the central part had greater porosity prior to the dissolution through LMWOA. The initially higher porosity in the central part allowed for a higher advective flux of LMWOA‐rich water and associated lower pH, resulting in decreased oligoclase saturation, higher oligoclase dissolution rates and ultimately higher secondary porosity. This study indicates that grain sorting during sediment deposition, early carbonate cementation, LMWOA production in adjacent shales, and advection processes collectively control the diagenetic reactions and the distribution of secondary porosity in sandstones.
The caption of this graphical is as follows: Schematic representation of the reconstructed diagenetic evolution model showing the stepwise mechanisms resulting in the higher secondary porosity in the central part of a sandstone unit. The middle interval B has a better grain sorting, resulting in a greater depositional porosity. Although the interval B experienced a stronger mechanical compaction, it had significantly less early carbonate cements. These resulted in a greater preserved porosity in the interval B prior to the dissolution phase. During the dissolution phase, LMWOA produced in the adjacent top and bottom shales were limited, resulting in minor secondary porosity in marginal sandstones. However, the higher preserved porosity in interval B facilitated higher advection flux of LMWOA‐rich water and ultimately resulted in higher secondary porosity. COPL, compactional porosity loss; LMWOA, low‐molecular‐weight organic acids.
