Here, we present a 3D localization-based super-resolution technique providing a slowly varying localization precision over a 1 μm range with precisions down to 15 nm. The axial localization is ...performed through a combination of point spread function (PSF) shaping and supercritical angle fluorescence (SAF), which yields absolute axial information. Using a dual-view scheme, the axial detection is decoupled from the lateral detection and optimized independently to provide a weakly anisotropic 3D resolution over the imaging range. This method can be readily implemented on most homemade PSF shaping setups and provides drift-free, tilt-insensitive and achromatic results. Its insensitivity to these unavoidable experimental biases is especially adapted for multicolor 3D super-resolution microscopy, as we demonstrate by imaging cell cytoskeleton, living bacteria membranes and axon periodic submembrane scaffolds. We further illustrate the interest of the technique for biological multicolor imaging over a several-μm range by direct merging of multiple acquisitions at different depths.
In this paper we report the synthesis of a chromophore-catalyst assembly designed for the photoreduction of carbon dioxide. The chromophore unit is made up of a ruthenium trisbipyridyl-like unit ...covalently attached to a nickel cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) via a triazole ring. The intramolecular electron transfer activation of the catalyst unit by visible light was studied by nanosecond flash photolysis and EPR spectroscopy. In aqueous solutions (pH = 6.5), activation of the Ru(II)-Ni(II) modular assembly with 450 nm visible light in the presence of a sacrificial electron donor accomplishes the reduction of CO2 into CO and H2 in a ratio of 2.7 to 1.
The direct and chemoselective N‐transacylation of peracetylated chitooligosaccharides (COSs), readily obtained from chitin, to give per‐N‐trifluoroacetyl derivatives offers an attractive route to ...size‐defined COSs and derived glycoconjugates. It involves the use of various acceptor building blocks and trifluoromethyl oxazoline dimer donors prepared with efficiency and highly reactive in 1,2‐trans glycosylation reactions. This method was applied to the preparation of the important symbiotic glycolipids which are highly active on plants and to the TMG‐chitotriomycin, a potent and specific inhibitor of insect, fungal, and bacterial N‐acetylglucosaminidases.
Short cuts from chitin: Deconstruction of chitin and selective reconstruction to give well‐defined oligosaccharides provide an effective approach to bioactive glycoconjugates. This method was applied to the preparation of the important symbiotic glycolipids.
Currently, identification of pathogenic bacteria present at very low concentration requires a preliminary culture-based enrichment step. Many research efforts focus on the possibility to shorten this ...pre-enrichment step which is needed to reach the minimal number of cells that allows efficient identification. Rapid microbiological controls are a real public health issue and are required in food processing, water quality assessment or clinical pathology. Thus, the development of new methods for faster detection and isolation of pathogenic culturable bacteria is necessary. Here we describe a specific enrichment technique for culturable Gram negative bacteria, based on non-lethal click chemistry and the use of magnetic beads that allows fast detection and isolation. The assimilation and incorporation of an analog of Kdo, an essential component of lipopolysaccharides, possessing a bio-orthogonal azido function (Kdo-N3), allow functionalization of almost all Gram negative bacteria at the membrane level. Detection can be realized through strain-promoted azide-cyclooctyne cycloaddition, an example of click chemistry, which interestingly does not affect bacterial growth. Using E. coli as an example of Gram negative bacterium, we demonstrate the excellent specificity of the technique to detect culturable E. coli among bacterial mixtures also containing either dead E. coli, or live B. subtilis (as a model of microorganism not containing Kdo). Finally, in order to specifically isolate and concentrate culturable E. coli cells, we performed separation using magnetic beads in combination with click chemistry. This work highlights the efficiency of our technique to rapidly enrich and concentrate culturable Gram negative bacteria among other microorganisms that do not possess Kdo within their cell envelope.
In this Communication, we present the synthesis and use of Ru(bpy)2(bpy-CCH)2+, a versatile synthon for the construction of more sophisticated dyads by means of click chemistry. The resulting ...chromophore–acceptor or −donor complexes have been studied by flash photolysis and are shown to undergo efficient electron transfer to/from the chromophore. Additionally, the photophysical and chemical properties of the original chromophore remain intact, making it a very useful component for the preparation of visible-light-active dyads.
Screening of commercially available fluoro monosaccharides as putative growth inhibitors in Arabidopsis thaliana revealed that 2‐fluoro 2‐l‐fucose (2F‐Fuc) reduces root growth at micromolar ...concentrations. The inability of 2F‐Fuc to affect an Atfkgp mutant that is defective in the fucose salvage pathway indicates that 2F‐Fuc must be converted to its cognate GDP nucleotide sugar in order to inhibit root growth. Chemical analysis of cell wall polysaccharides and glycoproteins demonstrated that fucosylation of xyloglucans and of N‐linked glycans is fully inhibited by 10 μm 2F‐Fuc in Arabidopsis seedling roots, but genetic evidence indicates that these alterations are not responsible for the inhibition of root development by 2F‐Fuc. Inhibition of fucosylation of cell wall polysaccharides also affected pectic rhamnogalacturonan‐II (RG‐II). At low concentrations, 2F‐Fuc induced a decrease in RG‐II dimerization. Both RG‐II dimerization and root growth were partially restored in 2F‐Fuc‐treated seedlings by addition of boric acid, suggesting that the growth phenotype caused by 2F‐Fuc was due to a deficiency of RG‐II dimerization. Closer investigation of the 2F‐Fuc‐induced growth phenotype demonstrated that cell division is not affected by 2F‐Fuc treatments. In contrast, the inhibitor suppressed elongation of root cells and promoted the emergence of adventitious roots. This study further emphasizes the importance of RG‐II in cell elongation and the utility of glycosyltransferase inhibitors as new tools for studying the functions of cell wall polysaccharides in plant development. Moreover, supplementation experiments with borate suggest that the function of boron in plants might not be restricted to RG‐II cross‐linking, but that it might also be a signal molecule in the cell wall integrity‐sensing mechanism.
The Re(bpy)(CO)3Cl catalyst pioneered by Lehn for the two‐electron reduction of CO2 has constantly revealed unique facets in the mechanistic understanding of the selective transformation of CO2. A ...novel triazole‐linked ruthenium photosensitizer and a rhenium catalyst dyad was synthesized and investigated for photo‐induced charge accumulation using time‐resolved absorption spectroscopy. The triazole bridging ligand promoted weak electronic communication between the two units, resulting in an anodic shift of the reduction potentials of the Re moiety. Upon excitation of the photosensitizer, the first reduction of the catalyst occurred with a fast apparent rate of >5×107 s−1. Using a double‐excitation nanosecond pump‐pump‐probe setup to track the second electron accumulation on the catalytic unit was not conclusive as no observable absorption changes occurred upon the second excitation, suggesting a pathway for an efficient intramolecular reverse electron transfer preventing the two‐electron accumulation at the catalyst under our experimental conditions. Nevertheless, under continuous irradiation and with the use of sacrificial electron donors, photocatalytic CO2 reduction assays showed good turnover numbers, hinting at the non‐innocent role of byproducts in solution.
Puzzle pieces: A dyad consisting of a ruthenium photosensitizer linked to a rhenium catalyst by a triazole bridge was studied for photo‐induced charge accumulation. A singly reduced catalyst was formed upon first excitation and intramolecular electron transfer, but second excitation did not allow charge accumulation. Regardless, the dyad showed good photocatalytic activity towards CO2 reduction, hinting at the non‐innocent role of byproducts in solution.
Lipochitin oligosaccharides (LCOs) are signaling molecules required by ecologically and agronomically important bacteria and fungi to establish symbioses with diverse land plants. In plants, ...oligo-chitins and LCOs can differentially interact with different lysin motif (LysM) receptors and affect innate immunity responses or symbiosis-related pathways. In animals, oligo-chitins also induce innate immunity and other physiological responses but LCO recognition has not been demonstrated. Here LCO and LCO-like compounds are shown to be biologically active in mammals in a structure dependent way through the modulation of angiogenesis, a tightly-regulated process involving the induction and growth of new blood vessels from existing vessels. The testing of 24 LCO, LCO-like or oligo-chitin compounds resulted in structure-dependent effects on angiogenesis in vitro leading to promotion, or inhibition or nil effects. Like plants, the mammalian LCO biological activity depended upon the presence and type of terminal substitutions. Un-substituted oligo-chitins of similar chain lengths were unable to modulate angiogenesis indicating that mammalian cells, like plant cells, can distinguish between LCOs and un-substituted oligo-chitins. The cellular mode-of-action of the biologically active LCOs in mammals was determined. The stimulation or inhibition of endothelial cell adhesion to vitronectin or fibronectin correlated with their pro- or anti-angiogenic activity. Importantly, novel and more easily synthesised LCO-like disaccharide molecules were also biologically active and de-acetylated chitobiose was shown to be the primary structural basis of recognition. Given this, simpler chitin disaccharides derivatives based on the structure of biologically active LCOs were synthesised and purified and these showed biological activity in mammalian cells. Since important chronic disease states are linked to either insufficient or excessive angiogenesis, LCO and LCO-like molecules may have the potential to be a new, carbohydrate-based class of therapeutics for modulating angiogenesis.
Phenylenediamine-catalyzed click chemistry leads to the efficient, practical, and column-free preparation of neoglycoconjugates from unprotected glucosyl azide, in pure water when aglycon solubility ...permits.
A series of neoglycoconjugates derived from deoxynojirimycin has been prepared by click connection with functionalised adamantanes. They have been assayed as glycosidase inhibitors, as inhibitors of ...the glycoenzymes relevant to the treatment of Gaucher disease, as well as correctors of the defective ion-transport protein involved in cystic fibrosis. We have demonstrated that it is possible to selectively either strongly inhibit ER-α-glucosidases and ceramide glucosyltransferase or restore the activity of CFTR in CF-KM4 cells by varying the length of the alkyl chain linking DNJ and adamantane.
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