8 research outputs found
Three-Dimensional Field-Emission Scanning Electron Microscopy as a Tool for Structural Biology
No full textSynthesis of Polyols for the preparation of biodegradable polyurethanes
No full textNatural oils such as rapeseed oil do not contain the necessary chemical functionality (hydroxyl groups) required for the synthesis of the target biodegradable Polyurethane. The main aim of this work was to find an appropriate dihydroxylation reaction route to convert natural oils containing double bonds into polyols that can be used to produce biodegradable polyurethanes. We were particularly aiming for a low-cost process which could also be scaled up. Initial experiments were performed on model substrates containing double bonds (hexene and decatriene) to allow complete characterization of the compounds and consequently gain a more thorough understanding of the chemistry taking place. Several methods were investigated to find a suitable process to dihydroxylate alkenes and also to convert the unsaturated oils into polyols suitable for the preparation of polyurethanes. The permanganate and water system was suitable for the model compounds, but requiring a stoichiometriс amount of catalyst was a disadvantage for scale-up. The results of hydroxylation reaction of alkenes using hydrogen peroxide and formic acid were not encouraging. The results of hydroxylation reactions using phosphoric acid and hydrogen peroxide were quite encouraging. The reactions using natural oils were quite successful producing polyols with the hydroxide numbers of 187 and 164 for soyabean and rapeseed samples respectively. The method using organic peroxide, meta-сhlого perbenzoic acid (m-СРВА) was also encouraging. The (^1)Ή NMR analysis of the reaction of m-CPBA with the decatriene model compound revealed that m-CPBA selectively hydroxylates the internal double bonds. However, when natural oils, water and m-CPBA powder were mixed and stirred the reaction mixtures became dough like and were therefore difficult to manipulate
Simultaneous Correlative Scanning Electron and High-NA Fluorescence Microscopy
No full textCorrelative light and electron microscopy (CLEM) is a unique method for investigating biological structure-function relations. With CLEM protein distributions visualized in fluorescence can be mapped onto the cellular ultrastructure measured with electron microscopy. Widespread application of correlative microscopy is hampered by elaborate experimental procedures related foremost to retrieving regions of interest in both modalities and/or compromises in integrated approaches. We present a novel approach to correlative microscopy, in which a high numerical aperture epifluorescence microscope and a scanning electron microscope illuminate the same area of a sample at the same time. This removes the need for retrieval of regions of interest leading to a drastic reduction of inspection times and the possibility for quantitative investigations of large areas and datasets with correlative microscopy. We demonstrate Simultaneous CLEM (SCLEM) analyzing cell-cell connections and membrane protrusions in whole uncoated colon adenocarcinoma cell line cells stained for actin and cortactin with AlexaFluor488. SCLEM imaging of coverglass-mounted tissue sections with both electron-dense and fluorescence staining is also shown.IST/Imaging Science and TechnologyApplied Science
OMNY PIN-A versatile sample holder for tomographic measurements at room and cryogenic temperatures
No full textNowadays ptychographic tomography in the hard x-ray regime, i.e., at energies above about 2 keV, is a well-established measurement technique. At the Paul Scherrer Institut, currently two instruments are available: one is measuring at room temperature and atmospheric pressure, and the other, the socalled OMNY (tOMography Nano crYo) instrument, is operating at ultra-high vacuum and offering cryogenic sample temperatures down to 10 K. In this manuscript, we present the sample mounts that were developed for these instruments. Aside from excellent mechanical stability and thermal conductivity, they also offer highly reproducible mounting. Various types were developed for different kinds of samples and are presented in detail, including examples of how specimens can be mounted on these holders. We also show the first hard x-ray ptychographic tomography measurements of high-pressure frozen biological samples, in the present case Chlamydomonas cells, the related sample pins and preparation steps. For completeness, we present accessories such as transportation containers for both room temperature and cryogenic samples and a gripper mechanism for automatic sample changing. The sample mounts are not limited to x-ray tomography or hard x-ray energies, and we believe that they can be very useful for other instrumentation projects. (C) 2017 Author(s)
NDC1 : a crucial membrane-integral nucleoporin of metazoan nuclear pore complexes
No full textPOM121 and gp210 were, until this point, the only known membrane-integral nucleoporins (Nups) of vertebrates and, thus, the only candidate anchors for nuclear pore complexes (NPCs) within the nuclear membrane. In an accompanying study (Stavru et al.), we provided evidence that NPCs can exist independently of POM121 and gp210, and we predicted that vertebrate NPCs contain additional membrane-integral constituents. We identify such an additional membrane protein in the NPCs of mammals, frogs, insects, and nematodes as the orthologue to yeast Ndc1p/Cut11p. Human NDC1 (hNDC1) likely possesses six transmembrane segments, and it is located at the nuclear pore wall. Depletion of hNDC1 from human HeLa cells interferes with the assembly of phenylalanine-glycine repeat Nups into NPCs. The loss of NDC1 function in Caenorhabditis elegans also causes severe NPC defects and very high larval and embryonic mortality. However, it is not ultimately lethal. Instead, homozygous NDC1-deficient worms can be propagated. This indicates that none of the membrane-integral Nups is universally essential for NPC assembly, and suggests that NPC biogenesis is an extremely fault-tolerant process
OMNY-A tOMography Nano crYo stage
No full textFor many scientific questions gaining three-dimensional insight into a specimen can provide valuable information. We here present an instrument called "tOMography Nano crYo (OMNY)," dedicated to high resolution 3D scanning x-ray microscopy at cryogenic conditions via hard X-ray ptychography. Ptychography is a lens-less imaging method requiring accurate sample positioning. In OMNY, this in achieved via dedicated laser interferometry and closed-loop position control reaching sub-10 nm positioning accuracy. Cryogenic sample conditions are maintained via conductive cooling. 90 K can be reached when using liquid nitrogen as coolant, and 10 K is possible with liquid helium. A cryogenic sample-change mechanism permits measurements of cryogenically fixed specimens. We compare images obtained with OMNY with older measurements performed using a nitrogen gas cryo-jet of stained, epoxy-embedded retina tissue and of frozen-hydrated Chlamydomonas cells. (C) 2018 Author(s)
Direct observation of individual hydrogen atoms at trapping sites in a ferritic steel.
No full textThe design of atomic-scale microstructural traps to limit the diffusion of hydrogen is one key strategy in the development of hydrogen-embrittlement-resistant materials. In the case of bearing steels, an effective trapping mechanism may be the incorporation of finely dispersed V-Mo-Nb carbides in a ferrite matrix. First, we charged a ferritic steel with deuterium by means of electrolytic loading to achieve a high hydrogen concentration. We then immobilized it in the microstructure with a cryogenic transfer protocol before atom probe tomography (APT) analysis. Using APT, we show trapping of hydrogen within the core of these carbides with quantitative composition profiles. Furthermore, with this method the experiment can be feasibly replicated in any APT-equipped laboratory by using a simple cold chain
Test and treat-impact of microbiological testing on antibiotic prescribing for Legionnaires' disease in Switzerland: results of the multicentre SwissLEGIO study
No full textLegionnaires' disease (LD) is a severe form of primarily community-acquired pneumonia (CAP). To confirm a Legionella infection, microbiological testing is required. The Swiss and European guidelines recommend LD testing for all hospitalised CAP patients. However, the low positivity rate of such routine testing (1.5-3%) raises concerns about its cost-effectiveness and clinical utility. In a setting where routine testing is recommended, this multicentre study evaluated the impact of LD testing on the clinical management of the infection and antimicrobial prescribing.
Data from medical records of 195 community-acquired LD (CALD) patients from 20 Swiss hospitals (August 2022-March 2024) were analysed. We assessed the clinical management of CALD, focusing on the impact of microbiological testing on antibiotic prescribing. The appropriateness of antibiotic choice and duration of treatment was assessed using a standardised pathway analysis approach. Factors associated with unsupported antibiotic prescribing were assessed using mixed-effects logistic regression analysis.
Microbiological testing was initiated promptly, with results available within 24 h after presenting to the hospital for 85.1% and within 48 h for 92.3% of patients. Antibiotics with Legionella coverage were initiated in 88.2% of patients within 24 h of admission. A positive Legionella test influenced antibiotic prescribing: 97.9% of patients received antibiotics active against Legionella spp., and 79.6% were prescribed appropriate and targeted monotherapy within 24 h of receiving the test result. Overall, 35.4% of patients were treated with antibiotics for a median of 4 days (IQR 3-4 days) longer than guidelines recommend (defined as > 10 days for immunocompetent or > 21 days for immunocompromised patients). Prolonged treatment was associated with CALD severity and antibiotic use > 2 days postdischarge (proxy for clinical stability reached). 38.5% of patients with impaired renal function received a suboptimal loading dose of levofloxacin.
Routine aetiological testing for LD has improved the clinical management of CALD by facilitating rapid detection of CALD cases and timely initiation of appropriate and targeted antibiotic therapy. Future antimicrobial stewardship efforts should sensitise physicians that a shorter duration of antibiotic treatment for CALD of 5 to 7 days according to the latest Swiss CAP guidelines is sufficient and safe.
© 2025. The Author(s)
