Salting-out effect induced by temperature cycling on a water/nonionic surfactant/oil system

This paper presents original effects induced by temperature cycling on the transitional phase inversion of emulsions, stabilized by a nonionic polyethoxylated C18E6 surfactant model. The phase inversion follow-up is performed by electrical conductivity measurements, which involves focusing the study on the shape and location of the emulsion inversion region. In that way, new observations are brought out as a gradual evolution of the emulsion inversion along the cycling process. Two alternative approaches are considered for tackling these results: (i) first, a molecular approach regarding the particular organization and rearrangement of water clusters surrounding the surfactant polymer polar head, and (ii) second, a thermodynamic approach only considering the whole Gibbs free energy of the system. The volumic approaches are transposed, here, to the water/oil interface, and disclose that the phase inversion zone is included in a metastable region, able to stabilize for a given temperature, either metastable O/W emulsions or stable W/O ones. In that way, this study proposes novel and complementary insights into the phenomena governing the emulsion phase inversion.     

Mechanistic aspects of the solid-state transformation of ammonium cyanate to urea at high pressure

The chemical transformation of ammonium cyanate into urea has been of interest to many generations of scientists since its discovery by Friedrich W?hler in 1828. Although widely studied both experimentally and theoretically, several mechanistic aspects of this reaction remain to be understood. In this paper, we apply computational methods to investigate the behavior of ammonium cyanate in the solid state under high pressure, employing a theoretical approach based on the self-consistent-charges density-functional tight-binding method (SCC-DFTB). The ammonium cyanate crystal structure was relaxed under external pressure ranging from 0 to 700 GPa, leading to the identification of five structural phases. Significantly, the phase at highest pressure (above 535 GPa) corresponds to the formation of urea molecules. At ca. 25 GPa, there is a phase transition of ammonium cyanate (from tetragonal P4/nmm to monoclinic P21/m) involving a rearrangement of the ammonium cyanate molecules. This transformation is critical for the subsequent transformation to urea. The crystalline phase of urea obtained above 535 GPa also has P21/m symmetry (Z = 2). This polymorph of urea has never been reported previously. Comparisons to the known (tetragonal) polymorph of urea found experimentally at ambient pressure suggests that the new polymorph is more stable above ca. 8 GPa. Our computational studies show that the transformation of ammonium cyanate into urea is strongly exothermic (enthalpy change -170 kJ mol-1 per formula unit between 530 and 535 GPa). The proposed mechanism for this transformation involves the transfer of two hydrogen atoms of the ammonium cation toward nitrogen atoms of neighboring cyanate anions, and the remaining NH2 group creates a C-NH2 bond with the cyanate unit.     

Chiral discrimination in host-guest supramolecular complexes. Understanding enantioselectivity and solid solution behaviors by using spectroscopic methods and chemical sensors

Diastereomeric host-guest associations formed between permethylated-beta-cyclodextrin (TMbeta-Cd) and the two enantiomers of p-bromophenylethanol (pBrPE) were characterized in aqueous solution by NMR spectroscopy, revealing similar inclusion geometries and weak binding constants, whatever the guest configuration. These features were confirmed by hydrogenation experiments, and do not allow to account for the ability of TMbeta-Cd to resolve racemic pBrPE by successive crystallizations [Grandeury, A.; Petit, S.; Gouhier, G.; Agasse, V.; Coquerel, G. Tetrahedron: Asymmetry 2003, 14, 2143-2152]. The analysis, by means of solid-state NMR, oxidation experiments, and solubility measurements, of the two crystalline phases containing known proportions of guest enantiomers revealed identical inclusion geometries in a given phase, irrespective of the enantiomeric composition. The corresponding solid solutions were further characterized by the determination of an isothermal section (40 degrees C) in the relevant ternary phase diagram. It appears from all these data that chiral resolution mechanisms in this system can only be envisaged in terms of nucleation conditions of each crystal form (with its specific inclusion geometry) and enantiomeric recognition at crystal solution interfaces during the growth of each crystal packing.     

The stimulating adventure of KRN 7000

Associated with the CD1d protein, KRN 7000, a potent synthetic α-galactosylceramide, is known to activate the invariant NKT immune cells. This stimulation then leads to the production of different cytokines modulating a T(H)1/T(H)2 immune response balance involved in protection against several pathologies such as autoimmune diseases and cancers. Various efforts have been made toward the synthesis of simple and more functionalized analogues in order to selectively induce T(H)1 or T(H)2-type cytokine production. Since the discovery of KRN 7000, structure-activity relationships, crystallographic and modelling studies have pointed to the potential of several GalCer analogues in term of selective bioactivity, and have highlighted interesting elements in order to better understand the recognition and activation mechanisms of immune iNKT cells. By presenting an up-to-date library of analogues, collecting recent breakthroughs done in crystallography and molecular modelling, and relating them to the available biological results, we hope that this review will highlight and help the scientific community in their KRN research.     

1D quintic nonlinear Schrödinger equation with white noise dispersion

In this article, we improve the Strichartz estimates obtained in A. de Bouard, A. Debussche (2010) [12] for the Schrödinger equation with white noise dispersion in one dimension. This allows us to prove global well posedness when a quintic critical nonlinearity is added to the equation. We finally show that the white noise dispersion is the limit of smooth random dispersion.     

Relatively compact Siegel disks with non-locally connected boundaries

We construct holomorphic maps f with a Siegel disk whose boundary is not locally connected (and is an indecomposable continuum), yet compactly contained in the domain of definition of the map. Our examples are injective and defined on a subset of \mathbb C{\mathbb C}.     

Development of a general time-dependent absorbing potential for the constrained adiabatic trajectory method

The constrained adiabatic trajectory method (CATM) allows us to compute solutions of the time-dependent Schro?dinger equation using the Floquet formalism and Fourier decomposition, using matrix manipulation within a non-orthogonal basis set, provided that suitable constraints can be applied to the initial conditions for the Floquet eigenstate. A general form is derived for the inherent absorbing potential, which can reproduce any dispersed boundary conditions. This new artificial potential acting over an additional time interval transforms any wavefunction into a desired state, with an error involving exponentially decreasing factors. Thus, a CATM propagation can be separated into several steps to limit the size of the required Fourier basis. This approach is illustrated by some calculations for the H(2)(+) molecular ion illuminated by a laser pulse.     

Manganese(III)-containing Wells-Dawson sandwich-type polyoxometalates: comparison with their manganese(II) counterparts

We present the synthesis and structural characterization, assessed by various techniques (FTIR, TGA, UV-vis, elemental analysis, single-crystal X-ray diffraction for three compounds, magnetic susceptibility, and electrochemistry) of five manganese-containing Wells-Dawson sandwich-type (WDST) complexes. The dimanganese(II)-containing complex, [Na(2)(H(2)O)(2)Mn(II)(2)(As(2)W(15)O(56))(2)](18-) (1), was obtained by reaction of MnCl(2) with 1 equiv of [As(2)W(15)O(56)](12-) in acetate medium (pH 4.7). Oxidation of 1 by Na(2)S(2)O(8) in aqueous solution led to the dimanganese(III) complex [Na(2)(H(2)O)(2)Mn(III)(2)(As(2)W(15)O(56))(2)](16-) (2), while its trimanganese(II) homologue, [Na(H(2)O)(2)Mn(II)(H(2)O)Mn(II)(2)(As(2)W(15)O(56))(2)](17-) (3), was obtained by addition of ca. 1 equiv of MnCl(2) to a solution of 1 in 1 M NaCl. The trimanganese(III) and tetramanganese(III) counterparts, [Mn(III)(H(2)O)Mn(III)(2)(As(2)W(15)O(56))(2)](15-) (4) and [Mn(III)(2)(H(2)O)(2)Mn(III)(2)(As(2)W(15)O(56))(2)](12-) (6), are, respectively, obtained by oxidation of aqueous solutions of 3 and [Mn(II)(2)(H(2)O)(2)Mn(II)(2)(As(2)W(15)O(56))(2)](16-) (5) by Na(2)S(2)O(8). Single-crystal X-ray analyses were carried out on 2, 3, and 4. BVS calculations and XPS confirmed that the oxidation state of Mn centers is +II for complexes 1, 3, and 5 and +III for 2, 4, and 6. A complete comparative electrochemical study was carried out on the six compounds cited above, and it was possible to observe the distinct redox steps Mn(IV/III) and Mn(III/II). Magnetization measurements, as a function of temperature, confirm the presence of antiferromagnetic interactions between the Mn ions in these compounds in all cases with the exception of compound 2.     

Strong improvement of interfacial properties can result from slight structural modifications of proteins: the case of native and dry-heated lysozyme

Identification of the key physicochemical parameters of proteins that determine their interfacial properties is still incomplete and represents a real stake challenge, especially for food proteins. Many studies have thus consisted in comparing the interfacial behavior of different proteins, but it is difficult to draw clear conclusions when the molecules are completely different on several levels. Here the adsorption process of a model protein, the hen egg-white lysozyme, and the same protein that underwent a thermal treatment in the dry state, was characterized. The consequences of this treatment have been previously studied: net charge and hydrophobicity increase and lesser protein stability, but no secondary and tertiary structure modification (Desfougères, Y.; Jardin, J.; Lechevalier, V.; Pezennec, S.; Nau, F. Biomacromolecules 2011, 12, 156-166). The present study shows that these slight modifications dramatically increase the interfacial properties of the protein, since the adsorption to the air-water interface is much faster and more efficient (higher surface pressure). Moreover, a thick and strongly viscoelastic multilayer film is created, while native lysozyme adsorbs in a fragile monolayer film. Another striking result is that completely different behaviors were observed between two molecular species, i.e., native and native-like lysozyme, even though these species could not be distinguished by usual spectroscopic methods. This suggests that the air-water interface could be considered as a useful tool to reveal very subtle differences between protein molecules.     

Photo-SRM: laser-induced dissociation improves detection selectivity of Selected Reaction Monitoring mode

Selected Reaction Monitoring (SRM) carried out on triple‐quadrupole mass spectrometers coupled to liquid chromatography has been a reference method to develop quantitative analysis of small molecules in biological or environmental matrices for years and is currently emerging as a promising tool in clinical proteomic. However, sensitive assays in complex matrices are often hampered by the presence of co‐eluted compounds that share redundant transitions with the target species. On‐the‐fly better selection of the precursor ion by high‐field asymmetric waveform ion mobility spectrometry (FAIMS) or increased quadrupole resolution is one way to escape from interferences. In the present work we document the potential interest of substituting classical gas‐collision activation mode by laser‐induced dissociation in the visible wavelength range to improve the specificity of the fragmentation step. Optimization of the laser beam pathway across the different quadrupoles to ensure high photo‐dissociation yield in Q2 without detectable fragmentation in Q1 was assessed with sucrose tagged with a push‐pull chromophore. Next, the proof of concept that photo‐SRM ensures more specific detection than does conventional collision‐induced dissociation (CID)‐based SRM was carried out with oxytocin peptide. Oxytocin was derivatized by the thiol‐reactive QSY® 7 C₅‐maleimide quencher on cysteine residues to shift its absorption property into the visible range. Photo‐SRM chromatograms of tagged oxytocin spiked in whole human plasma digest showed better detection specificity and sensitivity than CID, that resulted in extended calibration curve linearity. We anticipate that photo‐SRM might significantly improve the limit of quantification of classical SRM‐based assays targeting cysteine‐containing peptides. Copyright © 2011 John Wiley & Sons, Ltd.