Ultraviolet relaxation dynamics in uracil: Time-resolved photoion yield studies using a laser-based thermal desorption source

Wavelength-dependent measurements of the RNA base uracil, undertaken with nanosecond ultraviolet laser pulses, have previously identified a fragment at m/z = 84 (corresponding to the C3H4N2O+ ion) at excitation wavelengths ≤232 nm. This has been interpreted as a possible signature of a theoretically predicted ultrafast ring-opening occurring on a neutral excited state potential energy surface. To further investigate the dynamics of this mechanism, and also the non-adiabatic dynamics operating more generally in uracil, we have used a newly built ultra-high vacuum spectrometer incorporating a laser-based thermal desorption source to perform time-resolved ion-yield measurements at pump wavelengths of 267 nm, 220 nm, and 200 nm. We also report complementary data obtained for the related species 2-thiouracil following 267 nm excitation. Where direct comparisons can be made (267 nm), our findings are in good agreement with the previously reported measurements conducted on these systems using cold molecular beams, demonstrating that the role of initial internal energy on the excited state dynamics is negligible. Our 220 nm and 200 nm data also represent the first reported ultrafast study of uracil at pump wavelengths 3(1ππ*) state. These measurements do not, however, provide any evidence for the appearance of the m/z = 84 fragment within the first few hundred picoseconds following excitation. This key finding indicates that the detection of this specific species in previous nanosecond work is not directly related to an ultrafast ring-opening process. An alternative excited state process, operating on a more extended time scale, remains an open possibility

Mass Spectral Signatures of Complex Post-Translational Modifications in Proteins: A Proof-of-Principle Based on X-ray Irradiated Vancomycin

Characterizing post-translational modifications (PTM) of proteins is of key relevance for the understanding of many biological processes, as these covalent modifications strongly influence or even determine protein function. Among the different analytical techniques available, mass spectrometry is attracting growing attention because recent instrumental and computational improvements have led to a massive rise of the number of PTM sites that can be identified and quantified. However, multiple PTM occurring at adjacent amino acid residues can lead to complex and dense chemical patterns that are a challenge to characterize. By means of X-ray synchrotron radiation coupled to mass spectrometry, and through the test-case of the glycopeptide antibiotic vancomycin, we show that such a pattern has a unique and robust signature in terms of photon energy and molecular environment. This highlights the potential of this technique in proteomics and its value as a tool to understand the biological roles of PTM

Multiplex PCR for detection of plasmid-mediated colistin resistance determinants, mcr-1, mcr-2, mcr-3, mcr-4 and mcr-5 for surveillance purposes

International audiencePlasmid-mediated colistin resistance mechanisms have been identified worldwide in the past years. A multiplex polymerase chain reaction (PCR) protocol for detection of all currently known transferable colistin resistance genes (mcr-1 to mcr-5, and variants) in Enterobacteriaceae was developed for surveillance or research purposes. Methods: We designed four new primer pairs to amplify mcr-1, mcr-2, mcr-3 and mcr-4 gene products and used the originally described primers for mcr-5 to obtain a stepwise separation of ca 200 bp between amplicons. The primer pairs and amplification conditions allow for single or multiple detection of all currently described mcr genes and their variants present in Enterobacteriaceae. The protocol was validated testing 49 European Escherichia coli and Salmonella isolates of animal origin. Results: Multiplex PCR results in bovine and porcine isolates from Spain, Germany, France and Italy showed full concordance with whole genome sequence data. The method was able to detect mcr-1, mcr-3 and mcr-4 as singletons or in different combinations as they were present in the test isolates. One new mcr-4 variant, mcr-4.3, was also identified. Conclusions: This method allows rapid identification of mcr-positive bacteria and overcomes the challenges of phenotypic detection of colistin resistance. The multiplex PCR should be particularly interesting in settings or laboratories with limited resources for performing genetic analysis as it provides information on the mechanism of colistin resistance without requiring genome sequencing

The complete genome sequence of Chromobacterium violaceum reveals remarkable and exploitable bacterial adaptability

Chromobacterium violaceum is one of millions of species of free-living microorganisms that populate the soil and water in the extant areas of tropical biodiversity around the world. Its complete genome sequence reveals (i) extensive alternative pathways for energy generation, (ii) ≈500 ORFs for transport-related proteins, (iii) complex and extensive systems for stress adaptation and motility, and (iv) wide-spread utilization of quorum sensing for control of inducible systems, all of which underpin the versatility and adaptability of the organism. The genome also contains extensive but incomplete arrays of ORFs coding for proteins associated with mammalian pathogenicity, possibly involved in the occasional but often fatal cases of human C. violaceum infection. There is, in addition, a series of previously unknown but important enzymes and secondary metabolites including paraquat-inducible proteins, drug and heavy-metal-resistance proteins, multiple chitinases, and proteins for the detoxification of xenobiotics that may have biotechnological applications

Dívida pública brasileira: uma análise comparativa dos três principais indicadores de esforço fiscal do governo

Este artigo busca comparar os três indicadores da dívida pública brasileira mais utilizados como medidores de condição fiscal do país: a Dívida Líquida do Setor Público (DLSP) e a Dívida Bruta do Governo Geral (DBGG), calculadas pelo Banco Central do Brasil, e a Dívida Bruta do Governo Geral, calculada pelo Fundo Monetário Internacional (FMI). O objetivo deste trabalho é responder qual deles seria, atualmente, o que melhor expressa o esforço fiscal do governo. Para tanto, foram feitos exercícios de correlação entre esses indicadores e dois parâmetros econômicos relacionados à capacidade e à disposição do governo em honrar seus compromissos fiscais: crescimento econômico e superávit primário. Os mesmos exercícios foram repetidos para um período de maior volatilidade nos mercados financeiros internacionais, como forma de averiguar como tais indicadores reagem em momentos em que o governo, em geral, necessita se financiar a custos maiores. Os resultados sugerem que a Dívida Bruta do Governo Geral, calculada pelo Banco Central do Brasil, é o melhor indicador, dentre os três pesquisados, para a medição do desempenho fiscal brasileiro nos últimos anos

Mapping the complex metastable fragmentation pathways of excited 3-aminophenol+

This work applies the technique of mapping ion detection using a reflectron mass spectrometer against flight-time and reflection voltage to elucidate the complex metastable fragmentation pattern of the biomolecular ion 3-aminophenol+ (3-AP+, C6H7NO+). Multiphoton ionization experiments revealed the excited ion's fragmentation routes for the first time and comparisons with calculated flight-times enabled 18 μs-timescale dissociations to be assigned. These included the rare observation of a double hydrogen loss channel from a fragment ion. Ab initio calculations provided further insights into the most prominent apparent fragmentation sequence: 3-AP+ (m/z 109) → HCO + C5H6N+ (m/z 80) → CNH + C4H5+ (m/z 53) → C2H2 + C2H3+ (m/z 27)

High strength steel in chevron concentrically braced frames designed according to Eurocode 8

The use of high strength (HS) steel is becoming very popular thanks to their economical and mechanical benefits. Seismic applications represent the rational field to exploit the high performance of HS steel, by means of the ‘‘dual-steel” concept that combines the HS with Mild Carbon (MC) steel in order to increase the strength of non-dissipative elements, thus enforcing a ductile overall failure mode. In this paper, a comprehensive parametric study devoted to investigate the seismic performance of EC8-compliant dual-steel chevron Concentrically Braced Frames (CBF) is presented and discussed. Both static and dynamic nonlinear analyses were carried out to investigate the seismic performance for three limit states: damage limitation (DL), severe damage (SL) and near collapse (NC). The investigated parameters cover both geometric and mechanical variables, as the type of columns, span length, number of stories and spectral shape. The analyses showed that the use of HS steel in EC8-compliant CBFs is effective to avoid the damage in the brace-intercepted beams. However, due to the flexibility of the brace-intercepted beams made of HS steel, the bracing members are characterized by severe deformation demand in compression and elastic response in tension. Also, the behavior factors evaluated by means of dynamic analyses are smaller than those recommended by Eurocode 8. The comparison between dual steel CBFs with those entirely made of MC steel showed that in the second case the use of heavier profiles for braced-intercepted beams can be beneficial to reduce the brace ductility demand in compression and to activate their yielding in tension. Thereby, numerical results show that for chevron CBFs it seems more efficient to guarantee adequate stiffness than increasing the material strength for beams. On the contrary, the use of HS steel is effective for columns of the braced spans, reducing the material consumptions while providing satisfactory structural efficiency

LHC Vacuum Supervisory Application for Run 3

The LHC Vacuum Supervisory Control and Data Acquisition application has been upgraded to fulfil the new requirements of Long Shutdown 2 and Run 3. The number of datapoint elements has been increased from 700k to 1.5M, which constitutes a challenge in terms of scalability. The new configuration of pumping station control hardware has led to an increase in the number of permanently connected PLCs from 150 to almost 300. A new concept has been developed and deployed, in which the PLC configuration is updated online. The goals were to automate, and to speed up periodic updates of the control system. Integrating of the wireless mobile equipment had led to the acquisition of expertise in dealing with temporary connections and dynamic insertion of device representation in the synoptic. Other new features include: the introduction of an innovative remote control and representation in synoptic panel of hardware interlocks, the development of a pre-configured notification system, and the integration of asset management into the user interface