4,253 research outputs found
Cha-Cha-Cha: Variable Adhesive Activity of the <italic>Haemophilus</Italic> Cryptic Genospecies Trimeric Autotransporter Cha
No full textDisease caused by the Gram-negative Haemophilus cryptic genospecies begins with colonization of the maternal genital or neonatal respiratory tract. The primary goal of this work was to identify and characterize the molecular determinant(s) of Haemophilus cryptic genospecies adherence as a means to better understand the specific adaptation of this species to the urogenital tract and neonatal respiratory tract. Using transposon mutagenesis of prototype strain 1595, we identified a locus that is essential for Haemophilus cryptic genospecies adherence to a variety of epithelial cell lines of both genital and respiratory origin. This locus encodes a protein called Cha that shares homology with trimeric autotransporters. Trimeric autotransporters are composed of an N-terminal signal peptide, an internal passenger domain that harbors adhesive activity, and a short C-terminal membrane anchor domain and are classically characterized by head-stalk-anchor domain architecture. By generating chimeric proteins, we demonstrated that the C-terminus of Cha trimerizes in the bacterial outer membrane and is capable presenting a heterologous passenger domain (Hia) in a functional form, thus confirming that Cha is a trimeric autotransporter. Southern analysis revealed that cha is unique to the Haemophilus cryptic genospecies and is ubiquitous among these strains. Similar to a number of trimeric autotransporters, the passenger domain of Cha contains scattered clusters of YadA-like head domains associated with head-to-stalk neck adaptor motifs, predicted coiled-coil stalks and a series of identical tandem coding repeats which are not required for adherence. By evaluating the adherence capacity of H. influenzae expressing Cha deletion derivatives, we established that the N-terminal 473 residues of Cha harbor the binding domains responsible for Cha-mediated adherence to epithelial cells. In additional studies, we demonstrated that this same N-terminal region mediates bacterial aggregation through inter-bacterial Cha-Cha binding. Further analysis revealed that variable Cha-mediated adherence is linked to spontaneous changes in the number of identical tandem repeats predicted to comprise a coiled-coil stalk domain. Variation in repeat copy number has a direct effect on Cha adhesive and aggregative activity, independent of an impact on transcription of the cha locus or surface localization of Cha protein. Moreover, length of Cha surface fibers correlates with repeat copy number expansion. We propose two hypotheses to explain how repeat expansion inhibits bacterial aggregation and host cell binding: 1) Variation in the number of 28-amino acid repeats may influence the conformation of Cha, thus changing the surface accessibility of the Cha binding pocket. 2) Repeat expansion results in the formation of long, flexible Cha fibers on the bacterial cell surface that may have a greater propensity to interact with neighboring Cha trimers at the N-terminus, thereby precluding adherence to other bacteria or host epithelial cells. In additional studies screening adherent cryptic genospecies isolates for expression of Cha protein, we identified an additional, antigenically-divergent Cha variant that we refer to as Cha2. Amino acid sequence and domain comparison of Cha2 with Cha (now Cha1) revealed that the structurally undefined N-terminal sequences (encompassing the Cha1 adhesive and aggregative domain) are strikingly divergent. Inspite of this, Cha2 mediates efficient adherence to human epithelial cells, similar to Cha1.Identification of Cha offers insight into the apparent tissue tropism associated with the Haemophilus cryptic genospecies. We speculate that the unique regulation of Cha adhesive activity enhances the adaptive capability of this pathogenic organism in the human host.</p
Colloidal graphite-assisted laser desorption/ionization MS and MSn of small molecules. 2. Direct profiling and MS imaging of small metabolites from fruits
No full textGraphene‐based Oxygen Reduction Electrodes for Low Temperature Solid Oxide Fuel Cells
No full textIn this report, we present a study of using nitrogen-doped graphene as the air electrode of low temperature solid oxide fuel cells (LT-SOFCs) operating at 350 degrees C or lower. Three graphene derivatives were prepared through hydrothermal reactions and their electrochemical performance and material properties were characterized in the temperature range of 225-350 degrees C in atmospheric air. Nitrogen-doped graphene was found to exhibit a decent air electrode performance comparable to a porous Pt electrode aged for 8 h at 350 degrees C, but only for a limited time. After similar to 10 h of operation at 350 degrees C, the electrode performance degraded significantly due to carbon oxidation. However, alternative routes of synthesizing/doping graphene derivatives are expected to improve the viability of using these materials as a practical high temperature air electrode.OAIID:RECH_ACHV_DSTSH_NO:T201703089RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A076710CITE_RATE:2.149FILENAME:차석원_국제논문_201704online_지상훈(타).pdfDEPT_NM:기계항공공학부EMAIL:[email protected]_YN:YFILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/ce17dce0-3c2f-48b3-aee4-bccc10e5a4bc/linkN
Measurement of Hepatitis B Surface Antigen Concentrations Using a Piezoelectric Microcantilever as a Mass Sensor
No full textHepatitis B surface antigen (HBsAg) concentrations weremeasured using a piezoelectric microcantilever sensor (PEMS) developed by the authors. The developed PEMS is label-free and detects the sensing signal electrically. It was designed to measure the mass of biomolecules attached to it using an accurate mass-microbalancing technique; its probe area is confined to the end of the cantilever, and its equivalent spring constant is relatively high to minimize the effect of changes in the surface stress when the biomolecules are attached to it. The "dip-and-dry" technique was used to enable the probe area of the sensor to react with reagents in controlled environmental conditions. HBsAg was detected by an immunoreaction whereas the reaction time, antibody density, and its area on the probe were kept at a constant level. The mass of the detected HBsAg was measured in the range of 0.1-100 ng/mL.open1125sciescopu
Partial linear and SQRD-based DF detections for DSTTD-OFDM systems in severely time-varying multipath channels
No full textEx-situ NMR and Raman studies of H3PO4 and H2O uptake of polybenzimidazole membrane for PEMFC
No full text: Polybenzimidazole (PBI) doped with H3PO4 is the most commonly used membrane mate-rial for high-temperature polymer fuel cells. Despite this fact, only less is known on the chemical equilibria of all species inside the membrane as a function of the com¬position of the ternary system PBI - H3PO4 - H2O. This in¬clu¬des details on the proton transfer pro¬ces-ses, on the dominant conduc¬tion me¬cha¬nisms and on the con¬densation equilibria, lea-ding to the formation of di¬phos¬pho¬ric acid and higher homo¬logues species.
In this study Raman and NMR spectroscopy is used to in¬vestigate the chemical inter¬ac-tions between H3PO4, H2O and PBI vs. the H3PO4 doping level. We could ob¬tain in¬forma-tion on the H-bond formation between H3PO4 and the polymer chains, on tauto¬me¬ric pro-ces¬ses as well as on the presence of not directly bounded H3PO4 at high do¬ping levels [1,2]. Investigations were performed with uncrosslinked and cross¬linked m-PBI and AB-PBI. [1] F. Conti, A. Majerus, V. Di Noto, C. Korte, W. Lehnert, and D. Stolten, Phys. Chem. Chem. Phys. 14, 10022-10026 (2012) [2] F. Conti, S. Willbold, S. Mammi, C. Korte, W. Lehnert, and D. Stolten, New J. Chem. 37, 152-156 (2013)
1-Azetines, 1,2-Thiazetin-1,1-dioxides and Isothiazol-1,1-dioxides as Building Blocks in Heterocyclic Synthesis: the Attempted Synthesis of Bicyclic β-Sultams
No full textThis thesis is concerned with the synthesis of β-sultams and the development of new routes for the synthesis of bicyclic versions of these molecules as potential anti-bacterials. The synthesis of 1-azetines, 1,2-thiazetin-1,1-dioxides and isothiazol-1,1-dioxides as precursors of bicyclic heterocycles is described.
1-Azetines were synthesised from azetidin-2-ones prepared via the [2+2] cycloaddition of alkenes with N-chlorosulfonyl isocyanate (CSI). They reacted with diphenylcyclopropenone or nitrile oxides to afford bicyclic systems whose reactivity was explored and afforded a range of heterocycles such as 1,2,4-oxadiazoles, pyridines or pyrimidines via novel reaction pathways.
The synthesis of 1,2-thiazetin-1,1-dioxide through two routes will be discussed: the alkylation of 3-oxo-β-sultams to afford 3-ethoxy-1,2-thiazetin-1,1-dioxides, and the ring contraction of an isothiazol-1,1-dioxide to afford a 3-diethylamino-1,2-thiazetin 1,1-dioxide. The reactivity of these 1,2-thiazetin-1,1-dioxides towards diphenylcyclopropenone, 1,3-dipoles and dienes was studied and is fully described.
In the course of chemistry mentioned above, a series of isothiazol-1,1-dioxides was synthesised. Their reaction with 1,3-dipoles to yield the corresponding bicyclic heterocycles is described
Detecting Fake News in Social Media: An Asia-Pacific Perspective
No full textSocial media is ideal for spreading rumors, because it lacks censorship. Confirmation bias and filter-bubble effects further amplify the spread of unconfirmed information. Upon public outcry, independent fact-checking organizations have emerged globally, and many platforms are making efforts to fight against fake news. For example, the state-run Factually website in Singapore has been known to clarify falsehoods since its inception in May 2012, which was followed recently by the implementation of the Protection from Online Falsehoods and Manipulation Act (POFMA) in October 2019. In Taiwan, the government officially created a feature on the website of the Executive Yuan (the executive branch of Taiwan's government) to identify erroneous reporting and combat the spread of fake news. Taiwan's Open Culture Foundation has also developed and introduced the well-known anti-fake fact-checking chatbot Cofacts in May 2018. The Indonesia government since 2018 has held weekly briefings on hoax news; that same year, the country revised its Criminal Code to permit the imprisonment for up to six years of anyone spreading fake news. Governments in the Asia and Oceania region, including South Korea, Singapore, Japan, Taiwan, Philippines, Cambodia, Malaysia, have enacted relevant laws to prevent fake news from spreading. Nonetheless, fact-checking of fake news remains daunting, and requires tremendous time and effort in terms of human investigation. Moreover, it is prone to low efficiency and inadequate coverage due to the complexity of the topics being checked, and is incapable of keeping up with the fast production and diffusion of falsehoods online. This article will review some of the latest techniques to automatically debunk fake news, many of which were initiated in the Asia and Oceania region.11Nsciescopu
Transient Kinetic Analysis of Low-Temperature NH3-SCR over Cu-CHA Catalysts Reveals a Quadratic Dependence of Cu Reduction Rates on CuII
No full textWe combine gas phase Transient Response Methods with Transient Kinetic Analysis to investigate the reduction half-cycle (RHC: CuII → CuI) of the Standard SCR redox mechanism over Cu-CHA (chabazite) catalysts. The results confirm that NO + NH3 can readily reduce CuII at low temperatures (150-220 °C) according to a Cu:NO:NH3:N2 = 1:1:1:1 stoichiometry. The observed CuII reduction dynamics are invariant with the CuII speciation. Unexpectedly, the CuII reduction rates show a quadratic dependence on CuII, which is hardly compatible with the so far proposed single-site RHC mechanisms. The second order kinetics are found to apply under both dry and wet conditions (0% and 2% H2O v/v in the feed gas, respectively) across different temperatures, space velocities, and NO feed concentrations over two powdered Cu-CHA catalysts with different Cu loadings as well as over a commercial Cu-CHA washcoated honeycomb monolith catalyst. Another unprecedented finding is that H2O significantly inhibits the CuII reduction rate and lowers the RHC apparent activation energy. These findings provide for the first time a complete kinetic description of the low-temperature RHC reaction cascade and, from a mechanistic perspective, strongly suggest a dinuclear-CuII mediated RHC pathway, which may renew interrogations on the current mechanistic understanding of the CuII reduction pathway in the low-temperature NH3-SCR redox chemistry over Cu-CHA
- …
