桃色视频

In this article in Angewandte Chemie, Rodger and coworkers us metadynamics computer simulations to show that the eggshell protein ovocleidin-17 induces the formation of calcite crystals from amorphous calcium carbonate nanoparticles. Multiple spontaneous crystallization and amorphization events were simulated; these simulations suggest a catalytic cycle that explains the role of ovocleidin-17 in the first stages of eggshell formation (the picture shows one intermediate of this cycle).

Mark Barrow has been interviewed for an article in the May edition of Chemistry World, entitled "A barrel load of compounds."  The article focuses upon researchers studying petroleum using mass spectrometry, which is an area of research often referred to as "petroleomics."  As high quality petroleum becomes increasingly scarce whilst demand continues to grow, there is a growing need to find new ways of producing crude oil and to characterize petroleum-related samples.  With petroleum samples being amongst the world's most complex mixtures, high field FTICR instruments have become the mass spectrometers of choice due to the inherent ultra-high resolving power and mass accuracy.  One of the less conventional sources of petroleum is the Athabasca oil sands in Canada, and Mark's collaboration with Environment Canada is aimed at investigating the environmental impact of this industry.  As large quantities of water are used for processing the oil sands, there are concerns about the potential for components of the bitumen entering the surrounding environment and, ultimately, the food chain.

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In this chapter, we will highlight conceptual physical approaches towards the fabrication of nanocomposite polymer latexes in which each individual latex particle contains one or more “hard” nanoparticles, such as clays, silicates, titanates, or other metal(oxides). By “physical approaches” we mean that the “hard” nanoparticles are added as pre-existing entities, and are not synthesized in situ as part of the nanocomposite polymer latex fabrication process. We will narrow our discussion to focus on physical methods that rely on the assembly of nanoparticles onto the latex particles after the latex particles have been formed, or its reciprocal analogue, the adhesion of polymer onto an inorganic nanoparticle. First, will discuss the phenomenon of heterocoagulation and its various driving forces, such as electrostatic interactions, the hydrophobic effect, and secondary molecular interactions. We will then address methods that involve assembly of nanoparticles onto or around the more liquid precursors (i.e., swollen/growing latex particles or monomer droplets). We will focus on the phenomenon of Pickering stabilization. We will then discuss features of particle interaction with soft interfaces, and see how the adhesion of particles onto emulsion droplets can be applied in suspension, miniemulsion, and emulsion polymerization. Finally, we will very briefly mention some interesting methods that make use of interface-driven templating for making well-defined assembled clusters and supracolloidal structures.

The work published in the latest number of Physical Review B by Giovanni Costantini and co-workers () reports on the shape evolution of epitaxially grown InAs/GaAs(001) quantum dots after the controlled removal of material by in situ etching.  An atomic force and scanning tunnelling microscopy investigation shows that a reversal of the shape transition that occurs during growth takes place. This reversibility impressively confirms that both the growth process and the etching process are dominated by thermodynamic factors. It is further found that the evolution of the quantum dots is not determined by direct etching but is caused by the removal of the wetting layer and the subsequent diffusion of In atoms from the quantum dots onto the bare GaAs.

Rob Deeth reports in JACS on the discovery that new coordination complexes which can support spin crossover (SCO) or light-induced excited spin state trapping (LIESST) could be radically improved by better computational tools. While methods such as density functional theory (DFT) are capable of high accuracy, they are too slow for molecular discovery, where millions of individual calculations may be required. In contrast, empirical ligand-field molecular mechanics (LFMM) captures the d-electron effects implicit in DFT and thus can be as accurate, but LFMM is up to 4 orders of magnitude faster. We demonstrate for simple Fe(II) am(m)ines how LFMM can be used to redesign “old” systems to generate novel, potential SCO and LIESST complexes.

Jon Rourke and collaborators report in ACS nano on the structural analysis of graphene oxide (GO) by transmission electron microscopy (TEM). Electron diffraction shows that on average the underlying carbon lattice maintains the order and lattice-spacings of graphene; a structure that is clearly resolved in 80 kV aberration-corrected atomic resolution TEM images. These results also reveal that single GO sheets are highly electron transparent and stable in the electron beam, and hence ideal support films for the study of nanoparticles and macromolecules by TEM. We demonstrate this through the structural analysis of physiological ferritin, an iron-storage protein.

Proteins age in many ways, but one of them involves deamidation of asparagine and glutamine to aspartic and glutamic acids respectively.  When this occurs, two isomers of the acidic species are generated.  Glutamine deamidation of proteins is specifically studied by the O'Connor group in a new report in Analytical chemistry, with the result that the two isomers can be readily differentiated with a new fragmentation technique called Electron Capture Dissociation. 

 

 

Mark Barrow from 桃色视频 Chemistry in Collaboration with Bruker Daltonic and the Aquatic Ecosystem Protection Research Division of Environment Canada have studied the potential evironmental impact of oil exploration from the Athabasca oil sands in Canada.  There are concerns with particular respect to components in oil sands process water which may enter the aquatic ecosystem. Naphthenic acids have been previously targeted for study, due to their implications in toxicity toward aquatic wildlife, but it is believed that other components, too, contribute toward the potential toxicity of the oil sands process water. When mass spectrometry is used, it is necessary to use instrumentation with a high resolving power and mass accuracy when studying complex mixtures, but the technique has previously been hindered by the range of compounds that have been accessible via common ionization techniques, such as electrospray ionization. The research described here applied Fourier transform ion cyclotron resonance mass spectrometry in conjunction with electrospray ionization and atmospheric pressure photoionization, in both positive-ion and negative-ion modes, to the characterization of oil sands process water for the first time. The results highlight the need for broader characterization when investigating toxic components within oil sands process water.

The fate of nanoparticles used as stabilizers in solids-stabilized, or Pickering, emulsion polymerization for the formation of armored hybrid polymer latexes was studied. We showed that disk centrifugation can be used as a powerful quantitative tool to analyze and determine the concentration of nanoparticles in the water phase throughout solids-stabilized emulsion polymerizations. We performed a series of emulsion polymerizations using vinyl acetate, vinyl pivalate, methyl methacrylate, or butyl acrylate in presence of silica nanoparticles (Ludox TM-40, ca. 25 nm in diameter). The developed method to quantify the number of silica nanoparticles in the water phase proved to be an invaluable tool for determining key features of the polymerization process. The obtained concentration profiles versus monomer conversion explained the existence of limited coalescence of armored particles in the later stages of the solids-stabilized emulsion polymerization process of vinyl acetate, leading to nonspherical structures. Moreover, we demonstrated that the correlation of the measured number of silica nanoparticles present in the water phase with the average particle sizes of the latex particles provided excellent predictions for the coverage of the armored layer of nanoparticles on the surfaces of the polymer particles, corresponding to observed packing patterns.

Ann Dixon and her group report the strong interaction of the platelet-derived growth factor beta-receptor (PDGF beta), which represents an important subclass of receptor tyrosine kinase (RTK) thought to be activated by ligand-induced dimerization. Interestingly, the receptor is also activated by the bovine papillomavirus E5 oncoprotein, an interaction involving the transmembrane domains of both proteins and resulting in constitutive downstream signalling. This unique mode of activation along with emerging data for other RTKs raises important questions about the role of the PDGF beta transmembrane domain in signalling. To address this, we have investigated the murine PDGF beta transmembrane and juxtamembrane domains. We show for the first time the strong oligomerization behavior of PDGF beta transmembrane domain, forming dimers and trimers in natural membranes and detergents; and that these self-interactions are mediated by a leucine-zipper-like motif. The juxtamembrane regions are found to regulate these helix-helix interactions and select specifically for dimer formation. These data provide evidence that PDGF beta is able to form ligand-independent dimers, supporting similar observations in a number of other RTK's. A point mutant in the PDGF beta juxtamembrane domain previously shown to cause receptor activation was studied and yielded no change in oligomerization or folding, suggesting (in-line with observations of the c-Kit receptor) that it may moderate interactions with other regions of PDGF beta. 

Dave Haddleton and collaborators report on the Antibacterial Effects of Poly(2-(dimethylamino ethyl)methacrylate) against Selected Gram-Positive and Gram-Negative Bacteria in Biomacromolecules. Antimicrobial coatings can reduce the occurrence of medical device-related bacterial infections. Poly(2-(dimethylamino ethyl)methacrylate) (pDMAEMA) is one such polymer that is being researched in this regard. The aims of this study were to (1) elucidate pDMAEMA’s antimicrobial activity against a range of Gram-positive and Gram-negative bacteria and (2) to investigate its antimicrobial mode of action. The methods used include determination of minimum inhibitory concentration (MIC) values against various bacteria and the effect of pH and temperature on antimicrobial activity. The ability of pDMAEMA to permeabilise bacterial membranes was determined using the dyes 1-N-phenyl-naphthylamine and calcein-AM. Flow cytometry was used to investigate pDMAEMA’s capacity to be internalized by bacteria and to determine effects on bacterial cell cycling. pDMAEMA was bacteriostatic against Gram-negative bacteria with MIC values between 0.1−1 mg/mL. MIC values against Gram-positive bacteria were variable. pDMAEMA was active against Gram-positive bacteria around its pK_a and at lower pH values, while it was active against Gram-negative bacteria around its pK_a and at higher pH values. pDMAEMA inhibited bacterial growth by binding to the outside of the bacteria, permeabilizing the outer membrane and disrupting the cytoplasmic membrane. By incorporating pDMAEMA with erythromycin, it was found that the efficacy of the latter was increased against Gram-negative bacteria. Together, the results illustrate that pDMAEMA acts in a similar fashion to other cationic biocides.