Surface-Ligand Tuned Reversible Transformations in Aqueous Environments Between CdSe Magic-Size Clusters and Their Precursor Compounds.

That magic-size clusters (MSCs) have their counterpart precursor compounds (PCs) has not been generally accepted by expertise circles. Here, experimental evidence to support this new concept is presented. With aqueous-phase CdSe MSCs as a model system, it is shown that when the MSCs are dispersed in water containing a certain amount of L-cysteine (Cys), the MSCs disappear slowly. Upon the addition of CdCl2 , the MSCs recover. It is proposed that after dispersing, the MSCs transform to their quasi-isomeric, non-absorbing PCs upon Cys addition. In the presence of CdCl2 , the PCs transform back to the MSCs due to Cys elimination. The surface ligand Cys of the MSCs plays a significant role in the reversible transformations. The present study provides compelling evidence that absorbing MSCs have their non-absorbing PCs. The study findings suggest that the transformation between two MSCs that display absorption spectral shifts in a stepwise pattern is assisted by their PCs.

Thermal Decomposition of Anionic, Zwitterionic, and Cationic Polyfluoroalkyl Substances in Aqueous Film-Forming Foams.

In this study, we investigated thermal decomposition mechanisms of cationic, zwitterionic, and anionic polyfluoroalkyl substances, including those present in aqueous film-forming foam (AFFF) samples. We present novel evidence that polyfluoroalkyl substances gave quantitative yields of perfluoroalkyl substances of different chain lengths during thermal treatment. The results support a radical-mediated transformation mechanism involving random-chain scission and end-chain scission, leading to the formation of perfluoroalkyl carboxylic acids such as perfluorooctanoic acid (PFOA) from certain polyfluoroalkyl amides and sulfonamides. Our results also support a direct thermal decomposition mechanism (chain stripping) on the nonfluorinated moiety of polyfluoroalkyl sulfonamides, resulting in the formation of perfluorooctanesulfonic acid (PFOS) and other structurally related polyfluoroalkyl compounds. Thermal decomposition of 8:2 fluorotelomer sulfonate occurred through end-chain scission and recombination reactions, successively yielding PFOS. All of the studied polyfluoroalkyl substances began to degrade at 200-300 °C, exhibiting near-complete decomposition at ≥400 °C. Using a high-resolution parent ion search method, we demonstrated for the first time that low-temperature thermal treatments of AFFF samples led to the generation of anionic fluoroalkyl substances, including perfluoroheptanesulfonamide, 8:2 fluorotelomer sulfonic acid, N-methyl perfluorooctane sulfonamide, and a previously unreported compound N-2-propenyl-perfluorohexylsulfonamide. This study provides key insights into the fate of polyfluoroalkyl substances in thermal processes.

HPLC-MS/MS methods for the determination of 52 perfluoroalkyl and polyfluoroalkyl substances in aqueous samples.

Two quantitative methods using high-performance liquid chromatography (HPLC) combined with triple quadrupole tandem mass spectrometry (MS/MS) were developed to determine perfluoroalkyl and polyfluoroalkyl substances (PFASs) in aqueous samples. The first HPLC-MS/MS method was applied to 47 PFASs of 12 different substance classes with acidic characteristics such as perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkane sulfonic acids (PFSAs), as well as precursor substances and biotransformation intermediates (e.g., unsaturated fluorotelomer carboxylic acids). In addition, 25 13C-, 18O-, and 2H-labeled PFASs were used as internal standards in this method. The second HPLC-MS/MS method was applied to fluorotelomer alcohols (FTOHs) and perfluorooctane sulfonamidoethanols as these compounds have physicochemical properties different from those of the previous ones. Accuracy between 82% and 110% and a standard deviation in the range from 2% to 22% depending on the substances were determined during the evaluation of repeatability and precision. The method quantification limit after solid-phase extraction ranged from 0.3 to 199 ng/L depending on the analyte and matrix. The HPLC-MS/MS methods developed were suitable for the determination of PFASs in aqueous samples (e.g., wastewater treatment plant effluents or influents after solid-phase extraction). These methods will be helpful in monitoring campaigns to evaluate the relevance of precursor substances as indirect sources of perfluorinated substances in the environment. In one exemplary application in an industrial wastewater treatment plant, FTOHs were found to be the major substance class in the influent; in particular, 6:2-FTOH was the predominant compound in the industrial samples and accounted for 74% of the total PFAS concentration. The increase in the concentration of the transformation products of FTOHs in the corresponding effluent, such as fluorotelomer carboxylic acids, unsaturated fluorotelomer carboxylic acids, n:3 polyfluorinated saturated carboxylic acids (n indicates the number of nonfluorinated carbon atoms), and PFCAs, indicated biotransformation of FTOHs or their derivatives during wastewater treatment. However, only 33 mol% of the total amount of PFASs present in the influent was quantified in the corresponding effluent. Graphical abstract Method development of an HPLC-MS/MS multi-method for the determination of PFASs in aqueos samples.

Discovery of Ten Anti-HIV Hit Compounds and Preliminary Pharmacological Mechanisms Studies

BACKGROUND: The research and development of HIV drugs is very important, but at the same time it is a long cycle and expensive system project. High-throughput drug screening systems and molecular libraries of potential hit compounds remain the main ways for the discovery of hit compounds with anti-HIV activity. OBJECTIVE: The aim of this study was to screen out the hit compounds against HIV-1 in the natural product molecule library and the antiviral molecule library, and elucidate the molecular mechanism of their inhibition of HIV-1, so as to provide a new choice for AIDS drug research. METHODS: In this study, a drug screening system using HIV Rev-dependent indicator cell line (Rev-A3R5-GFP reporter cells) with pseudoviruses (pNL4-3) was used. The natural drug molecule library and antiviral molecule library were screened, and preliminary drug mechanism studies were performed. RESULTS: Ten promising hit compounds were screened. These ten molecules and their drug inhibitory IC50 were as follows: Cephaeline (0.50 µM), Yadanziolide A (8.82 µM), Bruceine D (2.48 µM), Astragaloside IV (4.30 µM), RX-3117 (1.32 µM), Harringtonine (0.63 µM), Tubercidin (0.41 µM), Theaflavine-3, 3'-digallate (0.41 µM), Ginkgetin (10.76 µM), ZK756326 (5.97 µM). The results of the Time of additions showed that except for Astragaloside IV and Theaflavine-3, 3'-digallate had a weak entry inhibition effect, and it was speculated that all ten compounds had an intracellular inhibition effect. Cephaeline, Harringtonine, Astragaloside IV, Bruceine D, and Tubercidin may have pre-reverse transcriptional inhibition. Yadanziolide A, Theaflavine-3, 3'-digallate, Ginkgetin and RX-3117 may be in the post-reverse transcriptional inhibition. The inhibitory effect of ZK 75632 may be in the reverse transcriptional process. CONCLUSION: A drug screening system using Rev-A3R5-GFP reporter cells with pseudoviruses (pNL4-3) is highly efficient. This study provided potential hit compounds for new HIV drug research.

A Two-Pathway Model for the Evolution of Colloidal Compound Semiconductor Quantum Dots and Magic-Size Clusters.

A fundamental understanding of formation pathways is critical to the controlled synthesis of colloidal semiconductor nanocrystals. As ultrasmall-size quantum dots (QDs) sometimes emerge in reactions along with magic-size clusters (MSCs), distinguishing their individual pathway of evolution is important, but has proven difficult. To decouple the evolution of QDs and MSCs, an unconventional, selective approach has been developed, along with a two-pathway model that provides a fundamental understanding of production selectivity. For on-demand production of either ultrasmall QDs or MSCs, the key enabler is in how to allow a reaction to proceed in the time prior to nucleation and growth of QDs. In this prenucleation stage, an intermediate compound forms, which is the precursor compound (PC) to the MSC. Here, the two-pathway model and the manipulation of such PCs to synthesize either ultrasmall QDs or binary and ternary MSCs are highlighted. The two-pathway model will assist the development of nucleation theory as well as provide a basis for a mechanism-enabled design and predictive synthesis of functional nanomaterials.

Focused Electron Beam-Induced Deposition and Post-Growth Purification Using the Heteroleptic Ru Complex (η3-C3H5)Ru(CO)3Br.

Focused electron beam-induced deposition using the heteroleptic complex (η3-C3H5)Ru(CO)3Br as a precursor resulted in deposition of material with Ru content of 23 at. %. Transmission electron microscopy images indicated a nanogranular structure of pure Ru nanocrystals, embedded into a matrix containing carbon, oxygen, and bromine. The deposits were purified by annealing in a reactive 98% N2/2% H2 atmosphere at 300 °C, resulting in a reduction of contaminants and an increase of the Ru content to 83 at. %. Although a significant volume loss of 79% was found, the shrinkage was observed mostly for vertical thickness (around 75%). The lateral dimensions decreased much less significantly (around 9%). Deposition results, in conjunction with previous gas-phase and condensed-phase surface studies on the electron-induced reactions of (η3-C3H5)Ru(CO)3Br, provide insights into the behavior of allyl, carbonyl, and bromide ligands under identical electron beam irradiation.

Tentative characterization of precursor compounds and co-factors of pigment formation in production of 'wu mi' from Vaccinium bracteatum Thunb. Leaves.

Vaccinium bracteatum leaves (VBTL) are traditionally used in China to dye rice grains, which assume a deep blue color, named 'Wu mi'. Information on the mechanism of pigment formation is limited. In this study, CIELAB color space parameters were used to represent the color of 'Wu mi'. Precursor compounds of pigments formed during the dyeing process were identified by UPLC Q-TOF MS analysis. The changes in co-factors for pigment formation in VBTL were measured at different growth stages. The L∗ and b∗ values of dyed rice increased as the leaves aged, whereas a∗ values showed irregular changes. Six compounds were tentatively identified as pigment precursors by UPLC Q-TOF MS analysis. The pH and ß-glucosidase activity at different growth stages of VBTL were indicated to be crucial co-factors for pigment formation. A tentative hypothesis is presented that iridoid glycosides are hydrolyzed by acids and ß-glucosidases to form a dialdehyde structure that binds covalently with amino residues of lysine side chains in rice protein molecules.

Direct Electron Beam Writing of Silver-Based Nanostructures.

Direct writing utilizing a focused electron beam constitutes an interesting alternative to resist-based techniques, as it allows for precise and flexible growth onto any conductive substrate in a single-step process. One important challenge, however, is the identification of appropriate precursors which allow for deposition of the material of choice, e.g., for envisaged applications in nano-optics. In this regard the coinage metal silver is of particular interest since it shows a relatively high plasma frequency and, thus, excellent plasmonic properties in the visible range. By utilizing the precursor compound AgO2Me2Bu, direct writing of silver-based nanostructures via local electron beam induced deposition could be realized for the first time. Interestingly, the silver deposition was strongly dependent on electron dose; at low doses of 30 nC/µm2 a dominant formation of pure silver crystals was observed, while at higher electron doses around 104 nC/µm2 large carbon contents were measured. A scheme for the enhanced silver deposition under low electron fluxes by an electronic activation of precursor dissociation below thermal CVD temperature is proposed and validated using material characterization techniques. Finally, the knowledge gained was employed to fabricate well-defined two-dimensional deposits with maximized silver content approaching 75 at. %, which was achieved by proper adjustment of the deposition parameters. The corresponding deposits consist of plasmonically active silver crystallites and demonstrate a pronounced Raman signal enhancement of the carbonaceous matrix.

Uneven distribution of inorganic pollutants in marine air originating from ocean-going ships.

The distribution of mass, water-soluble inorganic salts and mineral elements of size-segregated aerosols (PM1, PM2.5-1 and PM10-2.5), precursor gaseous pollutants, black carbon, and nanoparticles (10-300 nm size range) at the Southern Bight of the North Sea has been studied. The concentrations of air pollutants peaked over shipping lanes, open-water anchorage areas and frequently navigated waters, due to the presence of mobile emission sources. A considerable decrease in air pollutant levels was seen when diverting from these marine areas towards remote or coastal banks. These findings showed the rapid dispersion of pollutants in the marine air. The nano-aerosol count, originating from ocean-going ships, peaked at lower average aerodynamic diameters (e.g., ≈28 nm) than those, observed from low-displacement vessels (45-50 nm, e.g., for fishing boats). The average diameter of nano-PM depended also on weather conditions, e.g., it was higher (≈50 nm) in air of higher humidity.