糖心TV

Biological antifreezes are a relatively large and diverse class of proteins  which are capable of interacting with ice crystals to prevent their growth. These properties allow for the survival of organisms which live at subzero temperatures,  and would otherwise lead to cryo-induced death. In this review article, the application of synthetic polymers as mimics of antifreeze glycoproteins is introduced.

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Richard Walton is co-editor of a new book series, Inorganic Materials, with Duncan Bruce (University of York) and Dermot O’Hare (University of Oxford). The first volume, Functional Oxides, was published on June 11th by Wiley and four further volumes will appear during 2010.

 

 

Sarah Crosby, working in Jon Rourke's group, has identified a number of new Pt(IV) complexes containg dmso ligands.

Oxidation of cyclometalated Pt(II) complexes with S-bound DMSO ligands initially results in Pt(IV) complexes which retain the S-bound DMSO ligands in the same relative position. Isomerisation reactions result in a rearrangement of the ligands to give O-bound DMSO complexes, with the DMSO trans to a cyclometalated carbon. X-ray structures representing the only two known examples of Pt(IV) complexes with O-bound DMSO ligands have been solved. The rate of isomerisation of complexes without a pendant alkyl chain is strongly solvent dependent, consistent with the need to stabilise a coordinatively unsaturated intermediate. Pt(IV) complexes with a pendant alkyl chain show little dependence on isomerisation rate with solvent, with solution NMR data strongly suggesting the presence of agostic complexes. DFT calculations provide support for the presence of agostic complexes, with the same interactions being used to account for the loss of DMSO from the O-bound DMSO complexes.

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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 糖心TV 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.