Interaction of oleic acid with dipalmitoylphosphatidylcholine (DPPC) bilayers simulated by molecular dynamics

The fatty acid oleic acid (OA) is known to modulate the structure of membranes, which forms the basis for a number of its important applications including its use as a therapeutic supplement to reduce the risk of cardiovascular disease, in molecule delivery systems such as liposomes, and as a skin permeability enhancer. While a number of studies have investigated the effect of OA on lipid membranes, our understanding of its mechanisms of action at the molecular level remains rudimentary. We have carried out molecular dynamics simulations using coarse-grained models to investigate the interactions of OA at a range of concentrations with a dipalmitoylphosphatidylcholine (DPPC) bilayer in the liquid-crystalline phase. We have also investigated the relative permeability of the bilayers to model hydrophilic and hydrophobic penetrants by means of chemical potential calculations. The results indicate that OA is able to disperse homogeneously into the bilayer at all concentrations without much perturbation. OA appears to slightly weaken the lateral forces between lipid headgroups, and as the concentration of OA increases this manifests itself as a slight decrease in the area compressibility modulus and a minor increase in the diffusion rate of the OA molecules. While the chemical potential profiles showed little or no variation as a function of OA concentration, the frequency of water permeation events was found to double, indicating some OA-induced permeability enhancement. The study suggests that physiological effects of OA are probably more subtle rather than via gross perturbation of the structure, or that its significant effects are restricted to more condensed membrane structures such as the gel phase.     

A simple and efficient approach to the synthesis of endo and exo bicyclo[6.1.0]nona-3,5-diene-9-carboxaldehyde

Monobromination of 1,5-cyclooctadiene, followed by cyclopropanation with ethyl diazoacetate, led to the formation of endo and exo ethyl 4,5-dibromobicyclo[6.1.0]nonane-9-carboxylates 3a and 3b. Bis-dehydrobromination of 3a and 3b using 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) afforded the endo and exo ethyl bicyclo[6.1.0]nona-3,5-diene-9-carboxylates 4a and 4b. Reduction of these compounds to the corresponding alcohols 5a and 5b and subsequent oxidation with pyridinium chlorochromate (PCC) resulted in the formation of the target compounds endo and exo bicyclo[6.1.0]nona-3,5-diene-9-carboxaldehydes 6a and 6b.     

新的金属氧化物纳米催化剂CuO-ZnO高效催化醇化学选择性乙酰化（英文）

A new method has been developed for the chemoselective acetylation of alcohols with acetic anhy‐dride in the presence of phenols using a novel,recyclable Cu O‐Zn O nanocatalyst.The catalyst was synthesized using the co‐precipitation method and characterized by N2 adsorption‐desorption,X‐ray diffraction,scanning electron microscopy,transmission electron microscopy and energy dis‐persion scanning analyses.Furthermore,this catalyst could be recycled up to six times without significant loss in its activity.     

Diastereoselective Synthesis of Novel Pyrrolidine or Pyrrolizine‐Fused Benzo‐δ‐sultams via 1,3‐Dipolar Cycloadditions

The synthesis of novel pyrrolidine or pyrrolizine‐fused benzosultams is described. A number of (E)‐N‐(2‐formylphenyl)‐N‐alkyl‐2‐phenylethenesulfonamides derivatives were synthesized and subjected to intramolecular [3 + 2] cycloaddition with azomethine ylides derived in situ from the reaction with sarcosine, phenylglycine, and L‐proline.     

Ultra-trace arsenic and mercury speciation and determination in blood samples by ionic liquid-based dispersive liquid-liquid microextraction combined with flow injection-hydride generation/cold vapor atomic absorption spectroscopy

A simple, fast, and sensitive method for speciation and determination of As (III, V) and Hg (II, R) in human blood samples based on ionic liquid-dispersive liquid-liquid microextraction (IL-DLLME) and flow injection hydride generation/cold vapor atomic absorption spectrometry (FI-HG/CV-AAS) has been developed. Tetraethylthiuram disulfide, mixed ionic liquids (hydrophobic and hydrophilic ILs) and acetone were used in the DLLME step as the chelating agent, extraction and dispersive solvents, respectively. Using a microwave assisted-UV system, organic mercury (R-Hg) was converted to Hg(II) and total mercury amount was measured in blood samples by the presented method. Total arsenic content was determined by reducing As(V) to As(III) with potassium iodide and ascorbic acid in a hydrochloric acid solution. Finally, As(V) and R-Hg were determined by mathematically subtracting the As(III) and Hg(II) content from the total arsenic and mercury, respectively. Under optimum conditions, linear range and detection limit (3σ) of 0.1–5.0 µg L^?1 and 0.02 µg L^?1 for As(III) and 0.15–8.50 µg L^?1 and 0.03 µg L^?1 for Hg(II) were achieved, respectively, at low RSD values of < 4% (N = 10). The developed method was successfully applied to determine the ultra-trace amounts of arsenic and mercury species in blood samples; the validation of the method was performed using standard reference materials.     

Secondary Crystal Nucleation: Nuclei Breeding Factory Uncovered

Secondary nucleation, wherein crystal seeds are used to induce crystallization, is widely employed in industrial crystallizations. Despite its significance, our understanding of the process, particularly at the molecular level, remains rudimentary. An outstanding question is why do a few seeds give rise to a many‐fold increase in new crystals? Using molecular simulation coupled with experiments we have uncovered the molecular processes that give rise to this autocatalytic behavior. The simulations reveal formation of molecular aggregates in solution, which on coming in contact with the surface of the seed undergo nucleation to form new crystallites. These crystallites are weakly bound to the crystal surface and can be readily sheared by fluid, making the seed surfaces available again to repeat the process. Further, the new crystallites on development can in turn serve as seeds. This mechanistic insight will enable better control in engineering crystalline products to design.     

Cobalt Single-Atom Catalysts with High Stability for Selective Dehydrogenation of Formic Acid

Metal–organic framework (MOF)-derived Co-N-C catalysts with isolated single cobalt atoms have been synthesized and compared with cobalt nanoparticles for formic acid dehydrogenation. The atomically dispersed Co-N-C catalyst achieves superior activity, better acid resistance, and improved long-term stability compared with nanoparticles synthesized by a similar route. High-angle annular dark-field–scanning transmission electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, and X-ray absorption fine structure characterizations reveal the formation of Co^IIN_x centers as active sites. The optimal low-cost catalyst is a promising candidate for liquid H₂ generation.     

Irradiation effects on copper

Copper, one of the most significant metals, is exposed to IR radiation. A Nd:YAG laser (1064 nm, 1.1 MW, 12 ns) has been used to irradiate fine polished and annealed samples (4 N, 1×1×0.3 cm³) with 100 laser shots under a vacuum of ～10^?6 torr. The laser focal spot size and power density on the target were 12 μm and 3×10¹² Wm^?2 respectively. The surface and structural studies were performed by analyzing scanning electron micrographs and X-ray diffractograms (XRDs), respectively. Laser ablation results in boiling, splashing, hydrodynamical sputtering and exfoliation along with other relevant phenomena. The XRD patterns of the exposed sample indicate a change in diffraction intensity and grain sizes. The atomic planes remain undisturbed for the irradiated target. The information collected is useful for investigating the complexities found in radiation–metal interactions.     

A Fast Adaptive Salt and Pepper Noise Reduction Method in Images

In this paper, an effective filtering method is proposed to remove impulse noise from images. In this two-stage method, detected noise-free pixels remain unchanged. Afterwards, a Gaussian filter with adaptive variances according to the image noise level is applied on the noisy pixels. Experimental results show that the proposed method outperforms recent impulse denoising methods in terms of PSNR, MAE, IEF, and SSIM. Moreover, the speed of the method is comparable with them, and it can be used effectively in real-time applications.