Molecular Threading: Mechanical Extraction, Stretching and Placement of DNA Molecules from a Liquid-Air Interface

We present “molecular threading”, a surface independent tip-based method for stretching and depositing single and double-stranded DNA molecules. DNA is stretched into air at a liquid-air interface, and can be subsequently deposited onto a dry substrate isolated from solution. The design of an apparatus used for molecular threading is presented, and fluorescence and electron microscopies are used to characterize the angular distribution, straightness, and reproducibility of stretched DNA deposited in arrays onto elastomeric surfaces and thin membranes. Molecular threading demonstrates high straightness and uniformity over length scales from nanometers to micrometers, and represents an alternative to existing DNA deposition and linearization methods. These results point towards scalable and high-throughput precision manipulation of single-molecule polymers

Smart acquisition EELS

We have developed a novel acquisition methodology for the recording of electron energy loss spectra (EELS) using a scanning transmission electron microscope (STEM): “Smart Acquisition”. Smart Acquisition allows the independent control of probe scanning procedures and the simultaneous acquisition of analytical signals such as EELS. The original motivation for this work arose from the need to control the electron dose experienced by beam-sensitive specimens whilst maintaining a sufficiently high signal-to-noise ratio in the EEL signal for the extraction of useful analytical information (such as energy loss near edge spectral features) from relatively undamaged areas. We have developed a flexible acquisition framework which separates beam position data input, beam positioning, and EELS acquisition. In this paper we demonstrate the effectiveness of this technique on beam-sensitive thin films of amorphous aluminium trifluoride. Smart Acquisition has been used to expose lines to the electron beam, followed by analysis of the structures created by line-integrating EELS acquisitions, and the results are compared to those derived from a standard EELS linescan. High angle annular dark-field images show clear reductions in damage for the Smart Acquisition areas compared to the conventional linescan, and the Smart Acquisition low loss EEL spectra are more representative of the undamaged material than those derived using a conventional linescan. Atomically resolved EELS of all four elements of CaNdTiO show the high resolution capabilities of Smart Acquisition

How to model it : problem solving for the computer age /

Comprend des bibliogr.Index: p. 205-20

Recent Studies of Near-Edge Structure

The extent to which near-edge structure depends upon long-range order is explored using polymeric systems, where one can vary the disposition of side-groups and the degree of crystallinity and compare the resulting spectra. Carbon K-edges for polystyrene in atactic and isotactic forms are compared; the former is amorphous and the latter crystalline. Differences between the spectra are very slight but observable, and are attributed to bond orientation effects and to interaction between closely-spaced hydrogens bonded to neighbouring benzene rings and to the backbone. The quality of the spectra collected at doses of less than 300 $\rm e^- nm^{-2}$ from a few square microns compares favourably with previously published EXAFS data. Another example of near-edge structure is provided by segregated species. The case of iron segregated to boundaries in Zr-Nb alloys is of intense interest to the nuclear industry. An attempt has been made to interpret observed fine structure in terms of structure from reference intermetallic compounds. It seems that the fine structure displayed by the segregated iron is different from that displayed by pure metallic iron or by known compounds with Zr, but more akin to ZrNbFe

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

Additional file 1 of Fabry App: the value of a portable technology in recording day-to-day patient monitored information in patients with Fabry disease

Additional file 1: Appendix S1 List of symptoms available on the Fabry App for patients to choose from and submit to the Lysosomal Storage Disorders team; and Appendix S2 Use of Phone App: Screening Questionnaire