Evaluation of porous graphitic carbon stationary phase for simultaneous preconcentration and separation of organic and inorganic selenium species in "clean" water systems

A high performance liquid chromatography procedure, based on porous graphitic carbon stationary phase, was evaluated for simultaneous on-line preconcentration and separation of organic and inorganic selenium species. Detection was achieved by inductively coupled plasma mass spectrometry with collision/reaction cell (ICP-CRC-MS). Different concentrations of formic acid were tested as mobile phase. A 240 mmol L(-1) concentration with pH adjusted to 2.6, allowed the separation of five species, i.e. selenite, selenate, selenomethionine, selenocystine and selenoethionine. On-line preconcentration of these five species was achieved when heptafluorobutyric acid was used as injection medium, inducing an enrichment of solutes at the top of the column which allowed large volumes (up to 1 mL) to be injected. Combining these injection conditions and 80Se monitoring with ICP-CRC-MS, detection limits between 2 and 8 ng (Se)L(-1), depending on the species, were obtained. Because of the extremely low detection limits obtained, the method was successfully applied to mineral waters.     

Osmotic compression and expansion of highly ordered clay dispersions

Aqueous dispersions of nanometric clay platelets (Laponite) have been dewatered through different techniques: centrifugation, mechanical compression, and osmotic stress (dialysis against a polymer solution). The positional and orientational correlations of the particles have been determined through small-angle neutron scattering. Uniaxial compression experiments produce concentrated dispersions (volume fraction > 0.03) in which the platelets have strong orientational and positional correlations. The orientational correlations cause the platelets to align with their normal along a common axis, which is the axis of compression. The positional correlations cause the platelets to be regularly spaced along this direction, with a spacing that matches the average volume per particle in the dispersion. The swelling law (volume fraction versus separation distance) is one-dimensional, as in a layered system. Changes in the applied osmotic pressure cause the water content of the dispersion to either rise or decrease, with time scales that are controlled by interparticle friction forces and by hydrodynamic drag. At long times, the dispersions approach osmotic equilibrium, which can be defined as the common limit of swelling and deswelling processes. The variation of the equilibrium water content with the applied osmotic pressure has been determined over 1 decade in volume fractions (0.03 < phi < 0.3) and 3 decades in pressures. This equation of state matches the predictions made from the knowledge of the forces and thermal agitation for all components in the dispersion (particles, ions, and water).     

The acylation state of mycobacterial lipomannans modulates innate immunity response through toll-like receptor 2

Detection of Mycobacterium tuberculosis antigens by professional phagocytes via toll-like receptors (TLR) contributes to controlling chronic M. tuberculosis infection. Lipomannans (LM), which are major lipoglycans of the mycobacterial envelope, were recently described as agonists of TLR2 with potent activity on proinflammatory cytokine regulation. LM correspond to a heterogeneous population of acyl- and glyco-forms. We report here the purification and the complete structural characterization of four LM acyl-forms from Mycobacterium bovis BCG using MALDI MS and 2D (1)H-(31)P NMR analyses. All this biochemical work provided the tools to investigate the implication of LM acylation degree on its proinflammatory activity. The latter was ascribed to the triacylated LM form, essentially an agonist of TLR2, using TLR2/TLR1 heterodimers for signaling. Altogether, these findings shed more light on the molecular basis of LM recognition by TLR.     

Effect of the surface free energy on the behaviour of surface and guided waves

The aim of this paper is to evaluate the influence of the surface free energy upon the propagation of the eigenmodes of structures, by studying successively (a) the Rayleigh wave for an elastic half-space, (b) the Lamb waves for an elastic layer, and (c) the guided modes for a tri-layer structure (e.g., metal/adhesive/metal). The surface free energy is a parameter which appears in the jump conditions of stresses and displacements at each interface, and which consequently modifies the eigenmodes, solutions of the boundary conditions system. As expected, the Rayleigh wave is dispersive and its velocity increases when the surface free energy increases. In the same way, the velocity of Lamb waves also increases except at normal angle of propagation where the surface free energy does not arise. Moreover, near the Rayleigh angle, the behaviour of the A₀ and S₀ Lamb modes varies strongly according to the surface free energy. Similar results are observed for the tri-layer structure.     

SSPaQ: A Subtractive Segmentation Approach for the Exhaustive Parallel Quantification of the Extent of Protein Modification at Every Possible Site

Protein modifications, whether chemically induced or post-translational (PTMs), play an essential role for the biological activity of proteins. Understanding biological processes and alterations thereof will rely on the quantification of these modifications on individual residues. Here we present SSPaQ, a subtractive method for the parallel quantification of the extent of modification at each possible site of a protein. The method combines uniform isotopic labeling and proteolysis with MS, followed by a segmentation approach, a powerful tool to refine the quantification of the degree of modification of a peptide to a segment containing a single modifiable amino acid. The strength of this strategy resides in: (1) quantification of all modifiable sites in a protein without prior knowledge of the type(s) of modified residues; (2) insensitivity to changes in the solubility and ionization efficiency of peptides upon modification; and (3) detection of missed cleavages caused by the modification for mitigation. The SSPaQ method was applied to quantify modifications resulting from the interaction of human phosphatidyl ethanolamine binding protein 1 (hPEBP1), a metastasis suppressor gene product, with locostatin, a covalent ligand and antimigratory compound with demonstrated activity towards hPEBP1. Locostatin is shown to react with several residues of the protein. SSPaQ can more generally be applied to induced modification in the context of drugs that covalently bind their target protein. With an alternate front-end protocol, it could also be applied to the quantification of protein PTMs, provided a removal tool is available for that PTM.

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Graphical Abstract ?

     

Access to L- and D-iminosugar C-glycosides from a D-gluco-derived 6-azidolactol exploiting a ring isomerization/alkylation strategy

A flexible synthetic access to six-membered L- and D-iminosugar C-glycosides is reported starting from the easily available 6-azido-6-deoxy-2,3,4-tri-O-benzyl-D-glucopyranose precursor. This methodology involves a highly diastereoselective tandem ring enlargement/alkylation and a stereocontrolled ring contraction. It allows an efficient synthesis of iminosugar C-glycosides displaying structural diversity at both C-1 and C-6.     

A polymer surfactant corona dynamically replaces water in solvent-free protein liquids and ensures macromolecular flexibility and activity

The observation of biological activity in solvent-free protein-polymer surfactant hybrids challenges the view of aqueous and nonaqueous solvents being unique promoters of protein dynamics linked to function. Here, we combine elastic incoherent neutron scattering and specific deuterium labeling to separately study protein and polymer motions in solvent-free hybrids. Myoglobin motions within the hybrid are found to closely resemble those of a hydrated protein, and motions of the polymer surfactant coating are similar to those of the hydration water, leading to the conclusion that the polymer surfactant coating plasticizes protein structures in a way similar to hydration water.     

Interplay between Cationic and Neutral Species in the Rhodium‐Catalyzed Hydroaminomethylation Reaction

The reactivity of [Rh(CO)₂{(R,R)‐Ph? BPE}]BF₄ ( 2 ) toward amine, CO and/or H₂ was examined by high‐pressure NMR and IR spectroscopy. The two cationic pentacoordinated species [Rh(CO)₃{(R,R)‐Ph? BPE}]BF₄ ( 4 ) and [Rh(CO)₂(NHC₅H₁₀){(R,R)‐Ph‐BPE}]BF₄ ( 8 ) were identified. The transformation of 2 into the neutral complex [RhH(CO)₂{(R,R)‐Ph? BPE}] ( 3 ) under hydroaminomethylation conditions (CO/H₂, amine) was investigated. The full mechanisms related to the formation of 3 , 4 and 8 starting from 2 are supported by DFT calculations. In particular, the pathway from 2 to 3 revealed the deprotonation by the amine of the dihydride species [Rh(H)₂(CO)₂{(R,R)‐Ph? BPE}]BF₄ ( 6 ), resulting from the oxidative addition of H₂ on 2 .