Negative electron transfer dissociation Fourier transform mass spectrometry of glycosaminoglycan carbohydrates

Electron transfer through gas phase ion-ion reactions has led to the widespread application of electron- based techniques once only capable in ion trapping mass spectrometers. Although any mass analyzer can in theory be coupled to an ion-ion reaction device (typically a 3-D ion trap), some systems of interest exceed the capabilities of most mass spectrometers. This case is particularly true in the structural characterization of glycosaminoglycan (GAG) oligosaccharides. To adequately characterize highly sulfated GAGs or oligosaccharides above the tetrasaccharide level, a high resolution mass analyzer is required. To extend previous efforts on an ion trap mass spectrometer, negative electron transfer dissociation coupled with a Fourier transform ion cyclotron resonance mass spectrometer has been applied to increasingly sulfated heparan sulfate and heparin tetrasaccharides as well as a dermatan sulfate octasaccharide. Results similar to those obtained by electron detachment dissociation are observed.     

A chemo-mechanical tweezer for single-molecular characterization of soft materials

A new atomic force microscopy (AFM)-based chemo-mechanical tweezer has been developed that can measure mechanical properties of individual macromolecules in supramolecular assembly and reveal positions of azide-containing polymers. A key feature of the new technology is the use of an AFM tip densely modified with 4-dibenzocyclooctynols (chemo-mechanical tweezer) that can react with multiple azide containing macromolecules of micelles to give triazole "clicked" compounds, which during retracting phases of AFM imaging are removed from the macromolecular assembly thereby providing a surface topographical image and positions of azide-containing polymers. The force-distance curves gave mechanical properties of removal of individual molecules from a supramolecular assembly. The new chemo-mechanical tweezer will make it possible to characterize molecular details of macromolecular assemblies thereby offering new avenues to tailor properties of such assemblies.     

Phase equilibria of mixed carbon dioxide and tetrahydrofuran hydrates in sodium chloride aqueous solutions

In this work, the competing effects of sodium chloride (NaCl) and tetrahydrofuran (THF) on carbon dioxide hydrate formation are investigated through phase equilibrium measurements. The phase behaviour in the hydrate forming region for the binary system carbon dioxide–water, the ternary systems carbon dioxide–tetrahydrofuran–water and ternary carbon dioxide–sodium chloride–water and, in addition, the quaternary system carbon dioxide–tetrahydrofuran–water–sodium chloride are determined experimentally, using a Cailletet apparatus. All measurements are made in a temperature and pressure region of 275–290 K and 0.5–7.0 MPa, respectively. In these ranges, three different hydrate equilibrium curves are measured namely: H-L_W-V, H-L_W-L_V-V and H-L_W-L_V. The formation of an organic-rich liquid phase in the systems due to a liquid–liquid two-phase split between water and tetrahydrofuran when pressurized with carbon dioxide causes the occurrence of an upper quadruple point (Q₂) to evolve into a four-phase H-L_W-L_V-V equilibrium line. The presence of sodium chloride in the quaternary system enhances the split between the two liquids due to the salting-out effect. It was found that the hydrate promoting effect of tetrahydrofuran is able to suppress the inhibiting effect of sodium chloride especially at lower concentration of sodium chloride.     

Assessing Density Functionals for Describing Methane Dissociative Chemisorption on Pt(110)-(2×1) Surface

In this work, we explore the suitability of several density functionals with the generalized gradient approximation (GGA) and beyond for describing the dissociative chemisorption of methane on the reconstructed Pt(110)-(2\begin{document}$ \times $\end{document}1) surface. The bulk and surface structures of the metal, methane adsorption energy, and dissociation barrier are used to assess the functionals. A van der Waals corrected GGA functional (optPBE-vdW) and a meta-GGA functional with van der Waals correction (MS PBEl-rVV10) are selected for ab initio molecular dynamics calculations of the sticking probability. Our results suggest that the use of these two functionals may lead to a better agreement with existing experimental results, thus serving as a good starting point for future development of reliable machine-learned potential energy surfaces for the dissociation of methane on the Pt(110)-(2\begin{document}$ \times $\end{document}1) surface.     

Sticking of CO to crystalline and amorphous ice surfaces

We present results of classical trajectory calculations on the sticking of hyperthermal CO to the basal plane (0001) face of crystalline ice Ih and to the surface of amorphous ice Ia. The calculations were performed for normal incidence at a surface temperature Ts = 90 K for ice Ia, and at Ts = 90 and 150 K for ice Ih. For both surfaces, the sticking probability can be fitted to a simple exponentially decaying function of the incidence energy, Ei: Ps = 1.0e(-Ei(kJ/mol)/90(kJ/mol)) at Ts = 90 K. The energy transfer from the impinging molecule to the crystalline and the amorphous surface is found to be quite efficient, in agreement with the results of molecular beam experiments on the scattering of the similar molecule, N2, from crystalline and amorphous ice. However, the energy transfer is less efficient for amorphous than for crystalline ice. Our calculations predict that the sticking probability decreases with Ts for CO scattering from crystalline ice, as the energy transfer from the impinging molecule to the warmer surfaces becomes less efficient. At high Ei (up to 193 kJ/mol), no surface penetration occurs in the case of crystalline ice. However, for CO colliding with the amorphous surface, a penetrating trajectory was observed to occur into a large water pore. The molecular dynamics calculations predict that the average potential energy of CO adsorbed to ice Ih is -10.1 +/- 0.2 and -8.4 +/- 0.2 kJ/mol for CO adsorbed to ice Ia. These values are in agreement with previous experimental and theoretical data. The distribution of the potential energy of CO adsorbed to ice Ia was found to be wider (with a standard deviation sigma of 2.4 kJ/mol) than that of CO interacting with ice Ih (sigma = 2.0 kJ/mol). In collisions with ice Ia, the CO molecules scatter at larger angles and over a wider distribution of angles than in collisions with ice Ih.     

Synthesis and biological evaluation of a lipid A derivative that contains an aminogluconate moiety

A highly convergent strategy for the synthesis of several derivatives of the lipid A of Rhizobium sin-1 has been developed. The synthetic derivatives are 2-aminogluconate 3 and 2-aminogluconolactone 4, both of which lack C-3 acylation. These derivatives were obtained by the preparation of disaccharides in which the two amino groups and the C-3' hydroxy group could be modified individually with acyl or beta-hydroxy fatty acyl groups. Detailed NMR spectroscopy and MS analysis of 3 and 4 revealed that, even under neutral conditions, the two compounds equilibrate. The synthetic compounds lack the proinflammatory effects of Escherichia coli lipopolysaccharide (LPS), as indicated by an absence of tumor necrosis factor production. Although 3 and 4 were able to antagonize E. coli LPS, they were significantly less potent than the synthetic compound 2, which is acylated at C-3, and R. sin-1 LPS; these results indicate that the beta-hydroxy fatty acyl group at C-3 contributes to the antagonistic properties of R. sin-1 LPS. Based on a comparison of the biological responses of the synthetic lipid A derivatives with those of the R. sin-1 LPS and lipid A, the 3-deoxy-D-manno-octulosonic moieties appear to be important for the optimal antagonization of enteric LPS-induced cytokine production.     

Preparation of a lipid a derivative that contains a 27-hydroxyoctacosanoic acid moiety

[structure: see text] A general synthetic strategy for long-chain omega-1 hydroxy fatty acids has been developed, which employs as a key reaction step a cross metathesis between omega-unsaturated ester and 3-butene-2-ol. The resulting lipids were used for the preparation of lipid A derivatives of Rhizobium sin-1, which have the ability to inhibit the E. coli LPS-dependent synthesis of tumor necrosis factor by human monocytes.     

Equation of state modeling of the phase equilibria of ionic liquid mixtures at low and high pressure

Accurate design of processes based on ionic liquids (ILs) requires knowledge of the phase behavior of the systems involved. In this work, the truncated perturbed chain polar statistical associating fluid theory (tPC-PSAFT) is used to correlate the phase behavior of binary and ternary IL mixtures. Both non-polar and polar solvents are examined, while methyl imidazolium ILs are used in all cases. tPC-PSAFT accounts explicitly for weak dispersion interactions, highly directive polar interactions between permanent dipolar and quadrupolar molecules and association between hydrogen bonding molecules. For mixtures of non-polar solvents, tPC-PSAFT predicts accurately the binary mixture data. For the case of polar solvents, a binary interaction parameter is fitted to the experimental data and the agreement between experiment and correlation is very good in all cases.     

One-pot synthesis of oligosaccharides by combining reductive openings of benzylidene acetals and glycosylations

Combining triflic acid-promoted glycosylations of trichloroacetimidates with reductive opening of benzylidene acetals with triflic acid and triethylsilane as one-pot procedures provides access to a wide range of disaccharides and 2,4- and 3,4-branched trisaccharides.