Vibrational Dephasing in Ionic Liquids as a Signature of Hydrogen Bonding

Understanding both structure and dynamics is crucial for producing tailor‐made ionic liquids (ILs). We studied the vibrational and structural dynamics of medium versus weakly hydrogen‐bonded C?H groups of the imidazolium ring in ILs of the type [1‐alkyl‐3‐methylimidazolium][bis(trifluoromethanesulfonyl)imide] ([C_nmim][NTf₂]), with n=1, 2, and 8, by time‐resolved coherent anti‐Stokes Raman scattering (CARS) and quantum‐classical hybrid (QCH) simulations. From the time series of the CARS spectra, dephasing times were extracted by modeling the full nonlinear response. From the QCH calculations, pure dephasing times were obtained by analyzing the distribution of transition frequencies. Experiments and calculations reveal larger dephasing rates for the vibrational stretching modes of C(2)?H compared with the more weakly hydrogen‐bonded C(4,5)?H. This finding can be understood in terms of different H‐bonding motifs and the fast interconversion between them. Differences in population relaxation rates are attributed to Fermi resonance interactions.     

Characterisation of exosomes derived from human cells by nanoparticle tracking analysis and scanning electron microscopy

Exosomes from three different cell types (HEK 293T, ECFC, MSC) were characterised by scanning electron microscopy (SEM), dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA). The diameter was around 110 nm for the three cell types. The stability of exosomes was examined during storage at -20°C, 4°C, and 37°C. The size of the exosomes decreased at 4°C and 37°C, indicating a structural change or degradation. Multiple freezing to -20°C and thawing did not affect the exosome size. Multiple ultracentrifugation also did not change the exosome size.     

Synthesis and characterization of tetramethylammonium trifluorosulfate

[Me₄N]⁺[SO₂F₃]^?, the first example of a [SO₂F₃]^? salt, has been prepared from Me₄NF and SO₂F₂. The colorless, microcrystalline solid was characterized by its infrared and Raman spectra. The trigonal bipyramidal structure of C_2v symmetry of the [SO₂F₃]^? anion is predicted by ab initio calculations. Two oxygen atoms with d(SO)=143.2 pm and one fluorine atom with d(SF)=157.9 pm occupy the equatorial plane. The two fluorine atoms in the axial position with d(SF)=168.5 pm are repulsed by the two oxygen atoms forming a bent axis with ?(F_axSF_ax)=165.2°.     

Deciphering the molecular details for the binding of the prion protein to main ganglioside GM1 of neuronal membranes

The prion protein (PrP) resides in lipid rafts in?vivo, and lipids modulate misfolding of the protein to infectious isoforms. Here we demonstrate that binding of recombinant PrP to model raft membranes requires the presence of ganglioside GM1. A combination of liquid- and solid-state NMR revealed the binding sites of PrP to the saccharide head group of GM1. The binding epitope for GM1 was mapped to the folded C-terminal domain of PrP, and docking simulations identified key residues in the C-terminal region of helix C and the loop between strand S2 and helix B. Crucially, this region of PrP is linked to prion resistance in?vivo, and structural changes caused by lipid binding in this region may explain the requirement for lipids in the generation of infectious prions in?vitro.     

Clay‐supported 2‐phenyl‐1H‐imidazole derivatives for heterogeneous catalysis of Henry reaction

Six derivatives ( 1 , 2 , 3 , 4 , 5 , 6 ) of 2‐phenyl‐1H‐imidazole were tested as catalysts of Henry reaction. Three new ( 4 , 5 , 6 ) 2‐phenyl‐1H‐imidazole derivatives, differently substituted (thio)ureas, were synthesized and determined by ¹H NMR and IR spectroscopy and elemental analysis. Two types of catalysis, homogeneous and heterogeneous, were examined and compared. Clay minerals Ca‐MMT and Cu‐MMT were used as solid supports for heterogeneous catalysis. The best results were obtained using compound 2 under conditions of heterogeneous method D from the point of view of yield and reaction time. J. Heterocyclic Chem., (2011)     

Fisher information and matrix-valued valuations

All continuous and affinely contravariant matrix-valued valuations on the Sobolev space W1,2(Rn) are completely classified. It is shown that there is a unique such valuation. This valuation turns out to be the Fisher information matrix.