Partition relations for Hurewicz-type selection hypotheses

We give a general method to reduce Hurewicz-type selection hypotheses into standard ones. The method covers the known results of this kind and gives some new ones.Building on that, we show how to derive Ramsey theoretic characterizations for these selection hypotheses.     

Universal peptidomimetics

This paper concerns peptidomimetic scaffolds that can present side chains in conformations resembling those of amino acids in secondary structures without incurring excessive entropic or enthalpic penalties. Compounds of this type are referred to here as minimalist mimics. The core hypothesis of this paper is that small sets of such scaffolds can be designed to analogue local pairs of amino acids (including noncontiguous ones) in any secondary structure; i.e., they are universal peptidomimetics. To illustrate this concept, we designed a set of four peptidomimetic scaffolds. Libraries based on them were made bearing side chains corresponding to many of the protein-derived amino acids. Modeling experiments were performed to give an indication of kinetic and thermodynamic accessibilities of conformations that can mimic secondary structures. Together, peptidomimetics based on these four scaffolds can adopt conformations that resemble almost any combination of local amino acid side chains in any secondary structure. Universal peptidomimetics of this kind are likely to be most useful in the design of libraries for high-throughput screening against diverse targets. Consequently, data arising from submission of these molecules to the NIH Molecular Libraries Small Molecule Repository (MLSMR) are outlined.     

Investigating comprehensive two-dimensional gas chromatography conditions to optimize the separation of oxygenated compounds in a direct coal liquefaction middle distillate

Considering the global energetic context, diversifying fuels is of growing importance and many new alternatives are promising. Coal liquefaction products definitely appear among the new generation substitutes. These product's characteristics are very far from fuel specifications as they are mainly composed of naphthenes, aromatics, polycondensed naphthenic and aromatic structures and heteroatomic compounds (nitrogen and oxygen), with a very low paraffin content. Identification and quantification of oxygen-containing species in coal-derived liquids are of considerable importance to understand their behaviors in further processing. However, these species have not been characterized as fully as the predominant hydrocarbon components. Literature shows that these compounds consist mainly in alkylated phenolic and furanic structures. Therefore, comprehensive two-dimensional gas chromatography has been investigated to provide enhanced molecular characterization of these complex samples. Several different configurations involving innovative column configurations were tested. Each of them was optimized by testing different column lengths, modulation periods, and oven conditions. A comparison of the contribution of each column configuration was carried out regarding four main criteria: individual separation of oxygenates, group type separation, resolution, and space occupation. One of them enabled an outstanding separation of paraffins, naphthenes, monoaromatics, diaromatics and targeted O-compounds in a direct coal liquefaction product. It was therefore subjected to further experimentations using a time-of-flight mass spectrometer to validate the identification and unravel more than fifty oxygenated molecular structures. A group-type quantification was also established for four column arrangements and gives the distribution of paraffins, naphthenes and aromatics. It can be concluded from this study that a non-orthogonal arrangement involving a highly polar column in the first dimension was the most adapted one.     

Global approach for the selection of high temperature comprehensive two-dimensional gas chromatography experimental conditions and quantitative analysis in regards to sulfur-containing compounds in heavy petroleum cuts

Extending the knowledge on sulfur-containing compounds is crucial for the petroleum industry because they contribute to atmospheric pollution by combustion. Most of them are concentrated in heavy petroleum cuts, such as vacuum gas oils (VGOs). However, the resolution of the existing analytical methods does not allow a quantitative speciation of S-compounds contained in VGOs. Therefore, a high temperature GC×GC chromatograph hyphenated to a SCD was implemented in this study to obtain a quantitative S-compounds speciation. Firstly, various thermally stable stationary phases, in particular the new ionic liquid IL59 and Mega Wax-HT, were investigated in 1D-GC as a way to reduce the number of columns sets to be used in GC×GC. Consequently, several normal and reversed configurations of these columns were selected and tested in GC×GC. Then, a decision method was applied to facilitate the choice of the best combination of columns. Finally, the most adapted methods led to an innovative group type quantification and to a quantitative distribution of heavy sulfur species contained in a VGO sample. These results represent a major step towards the study of S-compounds in heavy petroleum cuts.     

ChemInform Abstract: Synthesis and Structural Characterization of ACu9Tt4 (A: Ca,Sr, Ba,Eu; Tt: Si,Ge, Sn) — Tetragonally Distorted Ternary Variants of the Cubic NaZn13 Structure Type. Improved Structure Refinement of SrCu2Ge2.

The title compounds are synthesized from the elements using excess Cu and Si, Ge, or Sn as a flux (alumina crucibles, 1100 °C, 2 h).     

Hydrogenation and Fluorination of Graphene Models: Analysis via the Average Local Ionization Energy

We have investigated the use of the average local ionization energy, I?(S)(r), as a means for rapidly predicting the relative reactivities of different sites on two model graphene surfaces toward the successive addition of one, two, and three hydrogen or fluorine atoms. The I?(S)(r) results were compared with directly computed interaction energies, at the B3LYP/6-311G(d,p) level. I?(S)(r) correctly predicts that the edges of graphene sheets are more reactive than the interior portions. It shows that added hydrogens activate the adjoining (ortho) sites and deactivate those that are separated by one site (meta). Overall, I?(S)(r) is effective for rapidly (single calculations) estimating the relative site reactivities of these large systems, although it reflects only the system prior to an interaction and cannot take into account postinteraction factors, e.g., structural distortion.     

Profiling an electrospray plume by laser-induced fluorescence and Fraunhofer diffraction combined to mass spectrometry: influence of size and composition of droplets on charge-state distributions of electrosprayed proteins

We investigated how physico-chemical properties of charged droplets are affected by the electrospray process, using simultaneous in situ measurements by laser-induced fluorescence (LIF), Fraunhofer diffraction and mass spectrometry. For this purpose, we implemented a laser-induced-fluorescence profiling setup in conjunction with a fast, high-resolution particle sizing scheme on a modified Agilent Jet Stream electrospray source coupled to a single quadrupole mass analyser. The optical setup permits us to profile the solvent fractionation and the size of the droplets as they evaporate in an electrospray plume by measuring both the angular scattering pattern and emission spectra of a solvatochromic fluorescent dye. Mass spectra are recorded simultaneously. These mass spectrometry and optical spectroscopy investigations allow us to study the relation between the observed charge-state distributions of protein anions and physico-chemical properties of evaporating droplets in the spray plume. By mixing water with methanol, a refolding of cytochrome C is observed as the water percentage increases in the plume due to the preponderant evaporation of volatile methanol.     

Design, synthesis and evaluation of β-lactam antigenic peptide hybrids; unusual opening of the β-lactam ring in acidic media

β-Lactam peptides were envisioned as conformational constraints in antigenic peptides (APs). Three different β-lactam tripeptides of varying flexibility were prepared in solution and incorporated in place of the central part of the altered melanoma associated antigenic peptide Leu(27)-Melan-A(26-35) using solid phase synthesis techniques. Upon TFA cleavage from the solid support, an unexpected opening of the β-lactam ring occurred with conservation of the amide bond. After adaptation of the solid phase synthesis strategy, β-lactam peptides were successfully obtained and both opened and closed forms were evaluated for their capacity to bind to the antigen-presenting class-I MHC HLA-A2 protein system. None of the closed β-lactam peptides bound to HLA-A2, but their opened variants were shown to be moderate to good HLA-A2 ligands, one of them being even capable of stimulating a Melan-A-specific T cell line.     

Extended characterization of a vacuum gas oil by offline LC‐high‐temperature comprehensive two‐dimensional gas chromatography

In a context of environmental preservation, purification and conversion of heavy petroleum cuts into high‐quality fuel becomes essential. The interest for the characterization of those very complex matrices becomes a trendy analytical challenge, when it comes to get molecular information for the optimization of industrial processes. Among new analytical techniques, high‐temperature 2‐D GC has recently proved its applicability to heavy petroleum matrices, but lacks in selectivity to separate all chemical groups. To gain resolution, heart cutting is demonstrated for LC separation of saturated, aromatic and polar compounds prior to high‐temperature 2‐D GC. Therefore, an extended global resolution was obtained, especially by a better distinction of saturated compounds. This includes iso‐paraffins and biomarker polynaphthenic structures, which are impossible to quantify with MS methods. This new way to analyze heavy petroleum fractions gives innovative opportunities for the construction of global weight distributions by carbon atoms number and by chemical families. This can right now be employed for quantitative analysis of heavy petroleum fractions and for studying conversion processes.