Structural Characterisation study of FeCo alloy nanoparticles in a highly porous aerogel silica matrix

A series of FeCo-SiO2 nanocomposite aerogels having different FeCo loadings of 3, 5, and 8 wt % were prepared using a novel urea-assisted sol-gel route. The size of the nanoparticles, which was estimated using Scherrer analysis of the main peak of the x-ray diffraction pattern, varies from 3 to 8 nm. X-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) techniques at both Fe and Co K edges were used to investigate the structure of the FeCo nanoparticles. EXAFS and XANES show that FeCo nanoparticles have the typical bcc structure. Evidence of oxidation was observed in low FeCo content aerogels. Spatially resolved electron energy loss spectroscopy analysis suggests the formation of a passivation layer of predominantly iron oxide

Biochemical and Structural Insights into Bacterial Organelle Form and Biogenesis

Many heterotrophic bacteria have the ability to make polyhedral structures containing metabolic enzymes that are bounded by a unilamellar protein shell (metabolosomes or enterosomes). These bacterial organelles contain enzymes associated with a specific metabolic process (e.g. 1,2-propanediol or ethanolamine utilization). We show that the 21 gene regulon specifying the pdu organelle and propanediol utilization enzymes from Citrobacter freundii is fully functional when cloned in Escherichia coli, both producing metabolosomes and allowing propanediol utilization. Genetic manipulation of the level of specific shell proteins resulted in the formation of aberrantly shaped metabolosomes, providing evidence for their involvement as delimiting entities in the organelle. This is the first demonstration of complete recombinant metabolosome activity transferred in a single step and supports phylogenetic evidence that the pdu genes are readily horizontally transmissible. One of the predicted shell proteins (PduT) was found to have a novel Fe-S center formed between four protein subunits. The recombinant model will facilitate future experiments establishing the structure and assembly of these multiprotein assemblages and their fate when the specific metabolic function is no longer required

Evaporation and deposition of alkyl-capped silicon nanocrystals in ultrahigh vacuum

Nanocrystals are under active investigation because of their interesting size- dependent properties(1,2) and potential applications(3-5). Silicon nanocrystals have been studied for possible uses in optoelectronics(6), and may be relevant to the understanding of natural processes such as lightning strikes(7). Gas-phase methods can be used to prepare nanocrystals, and mass spectrometric techniques have been used to analyse Au-8,(9) and CdSe clusters(10). However, it is difficult to study nanocrystals by such methods unless they are synthesized in the gas phase(11). In particular, pre-prepared nanocrystals are generally difficult to sublime without decomposition. Here we report the observation that films of alkyl-capped silicon nanocrystals evaporate upon heating in ultrahigh vacuum at 200 degrees C, and the vapour of intact nanocrystals can be collected on a variety of solid substrates. This effect may be useful for the controlled preparation of new quantum-confined silicon structures and could facilitate their mass spectroscopic study and size- selection(12)