1,721,024 research outputs found
The Structure of MLn(hfbc)4 and a Key to High Circularly Polarized Luminescence
No full texthe heterobimetallic complex CsEu[(+))-hfbc](4) (hfbc = 3-heptafluorobutyryl camphorate), prepared by Kaizaki and co-workers, displays the highest ratio of polarization versus total luminescence (measured by the glum factor), i.e., similar to 85% of the emitted photons at 595 nm are left-circularly polarized. We present a detailed structural analysis in solution, based on paramagnetic nuclear magnetic resonance (NMR), and discuss the possible dynamic processes, where its analogues are involved. We demonstrate that the first coordination sphere is very close to the achiral regular square antiprism (SAPR) with D-4d symmetry, which rules out the intrinsic dissymmetry of the Eu environment for rationalizing the g(lum). In contrast, the dynamic coupling between the f-f transitions, responsible for the emission, to the ligand-centered pi-pi* transition at 310 nm displays almost ideal geometry to justify glum and discloses a key to high circularly polarized emission
Coumarin-based fluorescent biosensor with large linear range for ratiometric measurement of intracellular pH
No full textIntracellular pH is a critical parameter involved in cell machinery, and its dysregulation can either cause or signal pathologic states. Currently described fluorescent pH probes are based on single acid-base equilibria, and for this reason are intrinsically unable to capture the wide range of cell pH, usually spanning over more than four units. Here we describe a fluorescent pH biosensor based on a conjugated coumarin-triazine scaffold that is excitable in the visible range, shows pseudo-linear ratiometric response over more than 6 pH units with a single fluorogenic unit, and allows imaging of the whole endo-lysosomal pH landscape of living cells with a single acquisition. The probe can discriminate, on the basis of intracellular acidity, between physiologic and tumor cells, being potentially suitable in perspective as diagnostic tool
Uranium-free X solution: a new generation contrast agent for biological samples ultrastructure
Full text linkBiological samples are mainly composed of elements with a low atomic number which show a relatively low electron scattering power. For Transmission Electron Microscopy analysis, biological samples are generally embedded in resins, which allow thin sectioning of the specimen. Embedding resins are also composed by light atoms, thus the contrast difference between the biological sample and the surrounding resin is minimal. Due to that reason in the last decades, several staining solutions and approaches, performed with heavy metal salts, have been developed with the purpose of enhancing both the intrinsic sample contrast and the differences between the sample and resin. The best staining was achieved with the uranyl acetate (UA) solution, which has been the election method for the study of morphology in biological samples. More recently several alternatives for UA have been proposed to get rid of its radiogenic issues, but to date none of these solutions has achieved efficiencies comparable to UA. In this work, we propose a different staining solution (X Solution or X SOL), characterized by lanthanide polyoxometalates (LnPOMs) as heavy atoms source, which could be used alternatively to UA in negative staining (NS), in en bloc staining, and post sectioning staining (PSS) of biological samples. Furthermore, we show an extensive chemical characterization of the LnPOM species present in the solution and the detailed work for its final formulation, which brought remarkable results, and even better performances than UA
Recommended from our members
Shape-conserving enhancement of vibrational circular dichroism in lanthanide complexes
No full textThe VCD spectra of lanthanide chelates with two chiral ligands display conserved sequences of bands throughout the Ln series. Some compounds (Tm, Yb) feature increased bands and strongly improved signal-to-noise ratios, an effect we dub Lanthanide Induced VCD Enhancement (LIVE)
Stereoselective synthesis of new pyran-dioxane based polycycles from glycal derived vinyl epoxide
No full textChiral heteropolycyclic structures are widespread in compounds of high pharmaceutical relevance. In particular, linear fused pyran-dioxane based polycycles can be found in several naturally occurring molecules, and among them, cardiac glycosides and antibiotic spectinomycin are characterized by a cis-cisoid-trans geometry. Then, the stereocontrol in the synthesis of this type of polycyclic scaffold is of primary importance. Herein, we present two novel linear fused pyran-dioxane based bi- and tricycles, synthesized with total stereoselectivity from a glycal derived vinyl epoxide. The straightforward methodology described involves a substrate-dependent stereospecific glycosylation step followed by an intramolecular S(N)2 ' conjugate addition process, leading to a pyran-dioxane-cyclohexane tricycle with a cis-cisoid-trans stereochemistry, in agreement with the geometry of many natural products. The stereochemical analysis of these compounds, which was realized by a combined NMR/computational approach, is also reported
Glycoconjugate Vaccine Quantification: An Overview on Present and Future Trends in Analytical Development
No full textPhomopsinones A-D: Four New Pyrenocines from Endophytic Fungus Phomopsis sp.
No full textThe structural elucidation of the compounds isolated from the endophytic Phomopsis sp. revealed phomopsinones A-D (1-4), four new α-pyrone derivatives. Three known compounds were also isolated, namely two phomosines, phomosine A (5) and phomosine C (6), and ergosterol (7). The structures of these compounds were determined by spectroscopic analysis ( 1H, 13C, 1H- 1H COSY, HMQC, HMBC, and ROESY NMR, and mass spectrometry), supported by molecular modeling. The absolute configurations of the new compounds 1-4 were determined by circular dichroism spectroscopy and TDDFT calculations. Preliminary studies indicated that compounds 1 and 4 show strong and good antifungal activity, respectively. Similarly, compounds 2 and 3 showed good antifungal and moderate antibacterial activities as well as antialgal activities
Structure and absolute configuration of toxic polyketide pigments from the fruiting bodies of the fungus Cortinarius rufo-olivaceus
No full textTwo new polyketide-derived pigments, named rufoolivacins B (2), and D (4), with a 4',10-coupled aryl linkage between polysubstituted 1-naphthol and 1,4- or 1,2-anthraquinone, together with nine known metabolites including rufoolivacins A (1) and C (3), have been isolated from the fruiting bodies of the Chinese toadstool Cortinarius rufo-olivaceus (basidiomycetes). Their structures were characterized on the basis of spectroscopic methods, including 2D-NMR experiments (COSY, NOESY, HSQC, and HMBC). The axial chirality of 1 and 2 was assigned through analysis of their CD spectra and ZINDO and TDDFT calculations. Compounds 3 and 4 were found to be unusual natural products incorporating an ortho-anthraquinone chromophore. All the metabolites were shown to be toxic toward the brine shrimp
Consequences of Chirality on the Aggregation Behavior of Poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV)
No full textPoly[2-methoxy-5(2'-ethylhexoxy)-p-phenylenevinylene] (MEH-PPV) has been for the first time prepared and fully characterized in enantiopure (R) form. If the polymer molecular weight is sufficiently low, (R)-MEH-PPV assumes a helical supramolecular structure in the solution aggregates, with consequences on the tendency to aggregation and on the fluorescence quenching, both of which are reduced with respect to the racemic analogue
- …
