Development of Dipolar Proton Transfer Reaction Mass Spectrometer for Real-time Monitoring of Volatile Organic Compounds in Ambient Air

Volatile organic compounds (VOCs) in ambient air can participate in photochemical reactions, which lead to the generation of secondary pollutants such as ozone and aerosol. So real-time and accurate monitoring of atmospheric VOCs plays an important role in the study of the causes of air pollution. On the basis of proton transfer reaction mass spectrometry (PTR-MS) research, a novel dipolar proton transfer reaction mass spectrometer (DP-PTR-MS) for real-time and on-line monitoring of atmospheric VOCs was developed. Compared with conventional PTR-MS with one kind of reagent ion H₃O⁺, DP-PTR-MS had three kinds of reagent ions H₃O⁺, OH^?, (CH₃)₂COH⁺, which could be switched according to the actual detection need. So DP-PTR-MS can improve the qualitative ability and expand the detection range effectively. The reagent ion H₃O⁺ can be used for detecting VOCs whose proton affinities are greater than that of H₂O. The reagent ion OH^? can be used to identify VOCs cooperating with the reagent ion H₃O⁺, and can also be used for detecting some inorganic substances such as CO₂. The reagent ion (CH₃)₂COH⁺ can be used for accurately detecting NH₃ under interference elimination circumstances. The limit of detection (LOD) and sensitivity of DP-PTR-MS were measured by using six kinds of standard gases. The results showed that the LOD for detecting toluene was 7 × 10^?12 (V/V) and the sensitivity for detecting ammonia reached 126 cps/10^?9 (V/V). The ambient air in Hefei city was on-line and real-time monitored for continuous 78 h with DP-PTR-MS. The results showed that the newly developed DP-PTR-MS could be used for long-term and real-time monitoring atmospheric VOCs at the concentration of 10^?12 (V/V) level. DP-PTR-MS is an important tool to the study of the causes of atmospheric pollution and the monitoring of trace VOCs emissions.     

Fast determination of β-endosulfan, α-hexachlorocyclohexane and pentachlorobenzene in the river water from northeast of China

A magnetic solid-phase extraction method for the preconcentration of three organochlorine pesticides (OCPs) from water samples has been proposed, based on magnetic phosphatidylcholine (MPC) as adsorbents. The extraction procedure was carried out in a single step by stirring the mixture of MPC and water samples. Subsequently, the MPC was collected by an external magnetic field without additional centrifugation or filtration. The analytes were desorbed from the MPC and finally analysed by gas chromatography–tandem mass spectrometry. The influence of various parameters on OCPs recoveries was studied. Results show that phosphatidylcholine amount and extraction time were critical in enhancing extraction performance, and the presence of humic acid was shown to significantly reduce the extraction efficiency. The limits of detection obtained were in the range of 0.1–0.15 ng L^?1. Recoveries of spiked water samples ranged from 76.2% to 101.5% with relative standard deviations varying from 3.8% to 7.7%. The proposed method was employed for analysis of pentachlorobenzene, α-hexachlorocyclohexane and β-endosulfan in the surface water from two rivers in northeast China.     

A comparative study on in vitro cytotoxicity,cellular uptake,localization and apoptosis-inducing mechanism of two ruthenium(II) complexes

Two ruthenium complexes [Ru(MeIm)₄(bpy)]²⁺ (Ru1, MeIm = 1-methylimidazole, bpy = 2,2′-bipyridine) and [Ru(Im)₄(bpy)]²⁺ (Ru2, Im = imidazole) with the same PF ₆ ^? counter-ion but different lipophilicities were synthesized and characterized and as potent anticancer agents. The relationships between cellular uptake, localization and molecular action mechanisms of these complexes were elucidated. The results showed that Ru1 with higher logP_o/w exhibited faster cellular uptake rates, but lower anticancer activity than Ru2. In addition, Ru1 predominantly accumulated in the mitochondria and cytoplasm, and induced G0/G1 cell cycle arrest, whereas the more hydrophilic Ru2 tended to localize and accumulate in the cell nucleus and mitochondria. Further mechanism studies indicated that Ru2 caused cell cycle arrest at S phase by regulating cell cycle related proteins and induced apoptosis in A549 cells through DNA damage, cellular ROS accumulation, activation of the caspase pathway and mitochondrial dysfunction.     

pH-responsive Micelles from a Blend of PEG-<Emphasis Type="Italic">b</Emphasis>-PLA and PLA-<Emphasis Type="Italic">b</Emphasis>-PDPA Block Copolymers: Core Protection Against Enzymatic Degradation

pH-responsive micelles with a biodegradable PLA core and a mixed PEG/PDPA shell were prepared by self-assembly of poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) and poly(2-(diisopropylamino)ethyl methacrylate)-b-poly(lactic acid) (PDPA-b-PLA). The micellization status with different pH and the enzyme degradation behavior were characterized by ¹H-NMR spectroscopy, dynamic light scattering measurement and zeta potential test. The pH turning point of PDPA block was determined to be in the range of 5.5?7.0. While the pH was above 7.0, the PDPA block collapsed onto the PLA core and could protect the PLA core from invasion of enzyme, as a result, the micelle exhibited a resistance to the enzymatic degradation.     

Molecular dynamics study of salt effects on micellization of N-dodecyl-N,N-dimethyl-3-ammonio-1-propane-sulfonate

In this paper, molecular dynamics simulation methods were used to investigate salt effects on micellization of N-Dodecyl-N,N-Dimethyl-3-Ammonio-1-Propane-sulfonate (SB12-3) in aqueous solution. It is proved that micelle shapes transform from spherical to prolate spherical shape after 30.0?ns simulation with different NaCl and CaCl₂ concentration. By comparison with the eccentricity value without salt addition, SB12-3 shows salt tolerance behaviors due to its unique “inner salt” structure of amphiphilic surfactant. Radial distribution function (RDF), hydrophobic groups solvent accessible surface area (SASA), hydrogen bond, and the deuterium order parameter (S_CD) are to elucidate salt effects on SB12-3 micelle formation. The radius of micelle is achieved by the related RDF value and in accordance with other researches. The addition of NaCl and CaCl₂ didn’t change the structure of micelle significantly and have little effects on the interactions between SB12-3 and water molecule. By comparison with the results without salt system, SASA of hydrophobic groups is almost the same, and SASA of hydrophilic groups and total molecule fluctuates only slightly. This further indicates that the surface of micelles is more hydrophilic due to the strong interactions between SB12-3 and water molecules. The existence of NaCl and CaCl₂ will enhance the hydrophilic interactions.     

The role of RGO in TiO<Subscript>2</Subscript>–RGO composites for the transesterification of dimethyl carbonate with phenol to diphenyl carbonate

TiO₂–RGO composites were prepared and used as efficient heterogeneous catalysts for the transesterification of dimethyl carbonate with phenol. Transmission electron microscopy images demonstrated that the RGO could remarkablely improve the dispersion of TiO₂. X‐ray photoelectron spectroscopy showed that RGO could change the chemical states of Ti species. Py-IR and Py-TPD results indicated the addition of RGO led to the increase of medium Lewis acid sites of TiO₂, which are positive for the transesterification reaction. The TiO₂–RGO composite with 50 wt% RGO exhibited a remarkable catalytic performance for the transesterification of dimethyl carbonate with phenol to diphenyl carbonate. Under the optimized conditions, the 53.5% phenol conversion and 99.9% transesterification selectivity were achieved. This phonel conversion of 53.5% could be compared with the result of homogeneous catalysts. RGO has been an excellent structural and electronic promoter in TiO₂–RGO composites.     

Promoting infrared light driven photocatalytic activity of W18O49 nanorods by coupling polypyrrole

Research on Chemical Intermediates - It is essential to promote the infrared light driven photocatalytic activity of W18O49. To do this, W18O49 nanorods coupled with polypyrrole (PPY) have been...     

Spinnability of Polyacrylonitrile Gel Dope in the Mixed Solvent of Dimethyl Sulfoxide/Dimethylacetamide and Characterization of the Nascent Fibers

In this work, acrylonitrile copolymers were prepared via precipitation polymerization. The copolymer solutions prepared at various ratio of dimethyl sulfoxide and dimethylacetamide were tested to prepare the nascent fibers by one-step wet-spun method. The effect of temperature, solvent ratio, molecular weight and the solid content on the rheological properties of polyacrylonitrile gel solution in different mixed solvent were studied. It was shown that the viscosity decreased with the increase of the temperature and fluctuated with the different solvent ratio reaching the minimal value at the ratio of dimethyl sulfoxide to dimethylacetamide equal to 1.25. The crystallinity of copolymers and the structure of the nascent fiber surface also depended from the solvent ratio in polymerization. The optimum conditions for spinnability of copolymers were determined. The high-quality polyacrylonitrile precursor was achieved with the controllable range of 0.5–0.8 dtex and the toughness of polyacrylonitrile precursor was greater than 6.0 cN/dtex after the wet spinning process, while the tensile strength of carbon fiber is up to 6.25 GPa after their pre-oxidation and carbonization process.     

Effect of Compatibilizer and Nucleation Agent on the Properties of Poly(lactic acid)/Polycarbonate (PLA/PC) Blends

Poly(lactic acid) (PLA) and polycarbonate (PC) blends were prepared by melt processing with a twin-screw extruder. Ethylene-maleic anhydride-glycidyl methacrylate terpolymer (EMG) as compatibilizer and talc as nucleation agent were added in PLA/PC blends. The effect of EMG and talc on the mechanical properties including tensile, flexural, Izod notched impact properties and heat deflection temperature (HDT) of PLA/PC blends were investigated. The morphologies were observed by scanning electron microscopy (SEM). The crystalline behavior of PLA/PC blends was analyzed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The nanoscale mechanical properties of PLA/PC blends were investigated by atomic force microscope (AFM). The results showed that the addition of EMG and talc simultaneously with annealing treatment is the most effective process.     

Self-Nucleation Efficiency of PDLA in PLAs: Crystallization Behavior and Morphology

Crystallization behavior and morphology of PLA blended with 0.05–1.00 wt % loadings of poly(D-lactic acid) (PDLA) forming stereocomplex crystallites as in-situ nucleating agents, were studied using wideangle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and polarizing-light optical microscopy (POM). Blending PLA with small amount of PDLA does lead to formation of PLA stereocomplex (SC), although the PLA is a random copolymer. The in-situ formed SC crystal acted as nucleation sites in blends and accelerated the crystallization of PLA by decreasing the half-time (t_1/2). The nucleation efficiency of PDLA obviously increased and the crystallization induction time decreased while the content of PDLA reached up to 0.20 wt %. While the content of PDLA is 0.2 wt %, the nucleation efficiency of PDLA is up to 43.8%, and the induction time decreased from 430 to 88 s. In addition, compared with pure PLA, t_1/2 decreases from 15.1 to 3.5 min at T_c = 127.5°C while the amount PDLA is 1.0 wt %. The equilibrium melting temperature of PLA decreased from 187.2 to 181.2°C with the increase of PDLA content.