Effet inhibiteur à la longues chaînes et de dérivés thiazolés sur la corrosion du laiton Amirauté.optimale des petites stations d'épuration à boues activées

Dans cette étude, des mesures électrochimiques ont été réalisées pour caractériser le comportement du laiton Amirauté dans une solution de chlorure de sodium 0,5 M en l'absence d'inhibiteur et en présence d'un mélange d'amines à longue chaîne et de dérivés thiazolés. Cette formulation est utilisée pour le traitement des eaux des circuits de refroidissement. Les courbes courant-tension stationnaires et les diagrammes d'impédance électrochimique ont été obtenus avec une electrode tournante.La première partie de cette étude présente les résultats obtenus pour deux concentrations du mélange et deux temps d'immersion préalable au potentiel de corrosion. Les essais électrochimiques montrent que l'effet inhibiteur est d'autant plus marqué que la concentration augmente. Une légère diminution de la protection de la surface du laiton Amirauté est observée avec l'augmentation du temps de maintien au potentiel de corrosion.La deuxième partie de l'étude compare les effets inhibiteurs de chacun des constituants du mélange, d'une part, pour les valeurs de concentration utilisées lors du traitement des eaux des circuits de refroidissement (0,1 mg/l de solution contenant les dérivés thiazolés et 1 mg/l de solution contenant les alkylamines) et, d'autre part, pour des valeurs de concentration comparables (5 mg/l).Pour la concentration de 0,1 mg/l l'action inhibitrice des dérivés thiazolés n'a pas été clairement mise en évidence. Ainsi, la protection contre la corrosion des circuits de refroidissement en laiton Amirauté avec le mélange est apportée principalement par les alkylamines. Celles-ci forment un film compact très protecteur à la surface de l'électrode.Pour des valeurs de concentration plus importantes, l'addition de 0,5 mg/l de dérivés thiazolés à 5 mg/l d'alkylamines améliore la protection du matériau.In this study, electrochemical measurements were carriet out to characterize the behaviour of Admiralty Brass in a 0.5 M sodium chloride solution in the absence of inhibitors and in the presence of a mixture of alkylamines and thiazol-derived products. This formulation is employed for water treatment in cooling circuits.The steady-state current voltage curves and the impedance diagrams were obtained with a rotating disc electrode in order to control the hydrodynamic conditions.The first part of this study deals with the results obtained for two concentrations of the mixture and for two immersion times at the corrosion potential. It has been shown that the inhibitive effect is more marked when the concentration increases from 10 to 50 mg/l. A slight decrease of the protection of the brass surface is observed when the immersion time increasesThe second part of this study is a comparison of the inhibitive effects of each compound of the mixture, on one hand, for concentration values used in the water treatment (0.1 mg/l of tbe solution containing the thiazol-derived products and 1 mg/l of the solution containing the alkylamines) and on the other hand, for identical concentration values (5 mg/l ). For 0.1 mg/l, no inhibitive action of thiazol-derived products could be detected. Thus, the corrosion protection of cooling circuits in Admiralty brass is attributed essentially to the alkylamines. They form a thick, protective film at the electrode surface. For higher concentration values, the addition of 0.5 mg/l of thiazol-derived products to 5 mg/l of alkylamines improves the corrosion resistance of brass

2-C-Hydro­xymethyl-2,3-O-iso­propyl­idene-d-ribono-1,5-lactam. Corrigendum

Corrigendum to Acta Cryst. (2004), E60, o909–o910

Glycosyl Oxocarbenium Ions: Structure, Conformation, Reactivity, and Interactions

Conspectus We also highlight that, from a chemical perspective, the glycosylation reaction can be described as a continuum, from unimolecular SN1 with naked oxocarbenium cations as intermediates to bimolecular SN2-type mechanisms, which involve the key role of counterions and donors. All these factors should be considered and are discussed herein. The importance of dissociative mechanisms (involving contact ion pairs, solvent-separated ion pairs, solvent-equilibrated ion pairs) with bimolecular features in most reactions is also highlighted. The role of theoretical calculations to predict the conformation, dynamics, and reactivity of the oxocarbenium ion is also discussed, highlighting the advances in this field that now allow access to the conformational preferences of a variety of oxocarbenium ions and their reactivities under SN1-like conditions. Specifically, the ground-breaking use of superacids to generate these cations is emphasized, since it has permitted characterization of the structure and conformation of a variety of glycosyl oxocarbenium ions in superacid solution by NMR spectroscopy. We also pay special attention to the reactivity of these glycosyl ions, which depends on the conditions, including the counterions, the possible intra- or intermolecular participation of functional groups that may stabilize the cation and the chemical nature of the acceptor, either weak or strong nucleophile. We discuss recent investigations from different experimental perspectives, which identified the involved ionic intermediates, estimating their lifetimes and reactivities and studying their interactions with other molecules. In this context, we also emphasize the relationship between the chemical methods that can be employed to modulate the sensitivity of glycosyl cations and the way in which glycosyl modifying enzymes (glycosyl hydrolases and transferases) build and cleave glycosidic linkages in nature. This comparison provides inspiration on the use of molecules that regulate the stability and reactivity of glycosyl cations

Burkholderia pseudomallei Capsular Polysaccharide Recognition by a Monoclonal Antibody Reveals Key Details toward a Biodefense Vaccine and Diagnostics against Melioidosis.

Burkholderia pseudomallei is the bacterium responsible for melioidosis, an infectious disease with high mortality rates. Since melioidosis is a significant public health concern in endemic regions and the organism is currently classified as a potential biothreat agent, the development of effective vaccines and rapid diagnostics is a priority. The capsular polysaccharide (CPS) expressed by B. pseudomallei is a highly conserved virulence factor and a protective antigen. Because of this, CPS is considered an attractive antigen for use in the development of both vaccines and diagnostics. In the present study, we describe the interactions of CPS with the murine monoclonal antibody (mAb) 4C4 using a multidisciplinary approach including organic synthesis, molecular biology techniques, surface plasmon resonance, and nuclear magnetic spectroscopy. Using these methods, we determined the mode of binding between mAb 4C4 and native CPS or ad hoc synthesized capsular polysaccharide fragments. Interestingly, we demonstrated that the O-acetyl moiety of CPS is essential for the interaction of the CPS epitope with mAb 4C4. Collectively, our results provide important insights into the structural features of B. pseudomallei CPS that enable antibody recognition that may help the rational design of CPS-based vaccine candidates. In addition, our findings confirm that the mAb 4C4 is suitable for use in an antibody-based detection assay for diagnosis of B. pseudomallei infections

Synthesis of novel purine nucleosides towards a selective inhibition of human butyrylcholinesterase

The search for new and potent cholinesterase inhibitors is an ongoing quest mobilizing many organic chemistry groups around the world as these molecules have been shown to treat the late symptoms of Alzheimer's disease as well as to act as neuroprotecting agents. In this work, we disclose the synthesis of novel 2-acetamidopurine nucleosides and, for the first time, regioselective N 7-glycosylation with 2-acetamido-6-chloropurine, promoted by trimethylsilyl triflate, was accomplished by tuning the reaction conditions (acetonitrile as solvent, 65 oC, 5h) starting from 1-acetoxy bicyclic glycosyl donors, or by direct coupling of a methyl glucopyranoside with the nucleobase to obtain only N 7 nucleosides in reasonable yield (55-60%). The nucleosides as well as their sugar precursors were screened for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition. While none of the compounds tested inhibited AChE, remarkably, some of the N 7 nucleosides and sugar bicyclic derivatives showed potent inhibition towards BChE. Nanomolar inhibition was obtained for one compound competing well with rivastigmine, a drug currently in use for the treatment of Alzheimer's disease. Experimental results showed that the presence of benzyl groups on the carbohydrate scaffold and the N 7-linked purine nucleobase were necessary for strong BChE inactivation. A preliminary evaluation of the acute cytotoxicity of the elongated bicyclic sugar precursors and nucleosides was performed indicating low values, in the same order of magnitude as those of rivastigmine

4′-Methoxyphenacyl-assisted synthesis of β-Kdo glycosides

3-Deoxy-β-d-manno-oct-2-ulosonic acid (β-Kdo) glycosides are mainly found in capsular polysaccharides and extracellular exopolysaccharides from Gram-negative bacteria. These compounds have profound biological implications in immune response and act as virulence factors. We have developed a novel methodology for the stereoselective synthesis of β-Kdo glycosides via the use of a 4′-methoxyphenacyl (Phen) auxiliary group at the C1 position of a peracetylated β-Kdo thioglycoside. Under the promotion of NIS/AgOTf in acetonitrile, a series of Kdo glycosides was synthesized in good yield and β-selectivity while minimizing the formation of undesirable glycals. Stereoselectivity of the glycosylation was shown to be modulated by various factors such as promotor, solvent, anomeric ratio of donor, nature of acceptor, and Phen substitution. Chemoselective cleavage of the Phen group was performed under the action of Zn/HOAc. DFT calculations together with experimental results suggested that α-triflate and a six-membered α-spiroPhen are plausible intermediates of the reaction, accounting for the enhanced formation of β-Kdo glycosides. The developed methodology could be applied to the synthesis of β-Kdo-containing glycans from pathogenic bacteria

Molecular Basis for Inhibition of GH84 Glycoside Hydrolases by Substituted Azepanes: Conformational Flexibility Enables Probing of Substrate Distortion

Here we report the synthesis of a series of polyhydroxylated 3- and 5-acetamido azepanes and detail the molecular basis of their inhibition of family 84 glycoside hydrolases. These family 84 enzymes include human O-GlcNAcase, an enzyme involved in post-translational processing of intracellular proteins modified by O-linked β-N-acetylglucosamine residues. Detailed structural analysis of the binding of these azepanes to BtGH84, a bacterial homologue of O-GlcNAcase, highlights their conformational flexibility. Molecular mechanics and molecular dynamics calculations reveal that binding to the enzyme involves significant conformational distortion of these inhibitors from their preferred solution conformations. The binding of these azepanes provides structural insight into substrate distortion that likely occurs along the reaction coordinate followed by O-GlcNAcase during glycoside hydrolysis. This class of inhibitors may prove to be useful probes for evaluating the conformational itineraries of glycosidases and aid the development of more potent and specific glycosidase inhibitors

Lactation-associated macrophages exist in murine mammary tissue and human milk

Macrophages are involved in immune defense, organogenesis and tissue homeostasis. Macrophages contribute to the different phases of mammary gland remodeling during development, pregnancy and involution postlactation. Less is known about the dynamics of mammary gland macrophages in the lactation stage. Here, we describe a macrophage population present during lactation in mice. By multiparameter flow cytometry and single-cell RNA sequencing, we identified a lactation-induced CD11c$^{+}$CX3CR1$^{+}$Dectin-1$^{+}$ macrophage population (liMac) that was distinct from the two resident F4/80$^{hi}$ and F4/80$^{lo}$ macrophage subsets present pregestationally. LiMacs were predominantly monocyte-derived and expanded by proliferation in situ concomitant with nursing. LiMacs developed independently of IL-34, but required CSF-1 signaling and were partly microbiota-dependent. Locally, they resided adjacent to the basal cells of the alveoli and extravasated into the milk. We found several macrophage subsets in human milk that resembled liMacs. Collectively, these findings reveal the emergence of unique macrophages in the mammary gland and milk during lactation

Functional and expression analysis of the metal-inducible dmeRF system from Rhizobium legumionosarum bv. viciae

A gene encoding a homolog to the cation diffusion facilitator protein DmeF from Cupriavidus metallidurans has been identified in the genome of Rhizobium leguminosarum UPM791. The R. leguminosarum dmeF gene is located downstream of an open reading frame (designated dmeR) encoding a protein homologous to the nickel- and cobalt-responsive transcriptional regulator RcnR from Escherichia coli. Analysis of gene expression showed that the R. leguminosarum dmeRF genes are organized as a transcriptional unit whose expression is strongly induced by nickel and cobalt ions, likely by alleviating the repressor activity of DmeR on dmeRF transcription. An R. leguminosarum dmeRF mutant strain displayed increased sensitivity to Co(II) and Ni(II), whereas no alterations of its resistance to Cd(II), Cu(II), or Zn(II) were observed. A decrease of symbiotic performance was observed when pea plants inoculated with an R. leguminosarum dmeRF deletion mutant strain were grown in the presence of high concentrations of nickel and cobalt. The same mutant induced significantly lower activity levels of NiFe hydrogenase in microaerobic cultures. These results indicate that the R. leguminosarum DmeRF system is a metal-responsive efflux mechanism acting as a key element for metal homeostasis in R. leguminosarum under free-living and symbiotic conditions. The presence of similar dmeRF gene clusters in other Rhizobiaceae suggests that the dmeRF system is a conserved mechanism for metal tolerance in legume endosymbiotic bacteria

Non-Glycosidically Linked Pseudodisaccharides: Thioethers, Sulfoxides, Sulfones, Ethers, Selenoethers, and Their Binding to Lectins

Hydrolytically stable non-glycosidically linked tail-to-tail pseudodisaccharides are linked by a single bridging atom remote from the anomeric centre of the constituent monosaccharides. Some such pseudodisaccharides with sulfur or oxygen bridges were found to act as disaccharide mimetics in their binding to the Banana Lectin and to Concanavalin A. A versatile synthetic route to a small library of such compounds is described.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69166/1/1951_ftp.pd