Effect of conformational changes on a one-electron reduction process: evidence of a one-electron P-P bond formation in a bis(phosphinine)

EPR spectra show that one-electron reduction of bis(3-phenyl-6,6-(trimethylsilyl)phosphinine-2-yl)dimethylsilane (1) on an alkali mirror leads to a radical anion that is localized on a single phosphinine ring, whereas the radical anion formed from the same reaction in the presence of cryptand or from an electron transfer with sodium naphthalenide is delocalized on the two phosphinine rings. Density functional theory (DFT) calculations show that in the last species the unpaired electron is mainly confined in a loose P-P bond (3.479 A), which results from the overlap of two phosphorus p orbitals. In contrast, as attested by X-ray spectroscopy, the P-P distance in neutral 1 is large (5.8 A). As shown by crystal structure analysis, addition of a second electron leads to the formation of a classical P-P single bond (P-P 2.389 A). Spectral modifications induced by the presence of cryptand or by a change in the reaction temperature are consistent with the formation of a tight ion pair that stabilizes the radical structure localized on a single phosphinine ring. It is suggested that the structure of this pair hinders internal rotation around the C-Si bonds and prevents 1 from adopting a conformation that shortens the intramolecular P-P distance. The ability of the phosphinine radical anion to reversibly form weak P-P bonds with neutral phosphinines in the absence of steric hindrance is confirmed by EPR spectra obtained for 2,6-bis(trimethylsilyl)-3-phenylphosphinine (2). Moreover, as shown by NMR spectroscopy, in this system, which contains only one phosphinine ring, further reduction leads to an intermolecular reaction with the formation of a classical P-P bond.     

Characterization of lactosylated proteins of infant formula powders using two-dimensional gel electrophoresis and nanoelectrospray mass spectrometry

Infant formula powders were analyzed by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) to assess the whey proteins quality, which may be altered by the heat treatment used during the processing conditions. Lactosylation was found to be the major chemical modification occurring in whey proteins. In parallel, a two-dimensional (2-D) gel electrophoresis was performed on the milk sample and the entire protein patterns were analyzed by nano-ESI-MS after cutting the different gel spots and in-gel trypsin digestion. A highly selective and specific tandem MS technique has been developed to characterize and localize up to ten lactosylation sites in beta-lactoglobulin (beta-Lg) and alpha(S2)-casein. alpha-Lactalbumin (alpha-La), with five lactosylated peptides, was found to be an interesting protein marker in the milk powder sample to detect chemical modification induced by the processing/storage conditions.     

Organometallic reactions of α-haloimines as a useful tool in organic synthesis

The reaction of organometallic reagents, e.g. alkyllithiums, cuprates and alkylcoppers, with α-haloimines gave selectively a variety of synthetically useful reactions, including coupling to 1,4-diimines, homologation, and production of heterocycles.     

The occupation measure of super-Brownian motion conditioned to nonextinction

We study super-Brownian motion inR ^d starting from a nontrivial finite measure and conditioned to nonextinction as defined by Evans. If (Y _t ) _t0 denotes this process, we provide a new approach to the immortal particle representation of (Y _t ) _t0 . We then show that the measureZ onR ^d defined byZ(B)= _o ¹ Y _t (B) dt is almost surely finite on compact sets whend5 and almost surely infinite on every ball whend4.     

Isolated singularities of some semilinear elliptic equations

Let Ω be an open subset of $\text{R}{}^{\mathrm{<mi\; mathvariant="italic"\; is="true">N</mi>}}$, N ? 3, containing 0. We consider the solutions of ?Δu(x) + g(u(x)) = f(x) in Ω-{0}, where g is nondecreasing and f is bounded and we study the possible singularities at 0: when u(x) = o(|x|^{1 ? N}) we prove that u is isotropic near 0 and show that either it is a C¹ function in Ω (removable singularity) or |x|^{N ? 2}u(x) → c, c ≠ 0 (weak singularity) or |x|^{N ? 2} |u(x) |→ + ∞ (strong singularity). We also characterize the g's for which solutions with a weak singularity exist and improve a previous removability result of H. Brézis and L. Véron (Arch. Rational Mech. Anal.23 (1979), 153–166).     

Oxidative dearomatization of phenols and anilines via lambda(3)- and lambda(5)-iodane-mediated phenylation and oxygenation

Treatment of 2-methylphenols with chloro(diphenyl)-lambda(3)-iodane led to their regioselective dearomatizing 2-phenylation into cyclohexa-2,4-dienone derivatives via a proposed ligand coupling reaction. In the same vein of investigation, treatment of 2-methylanilines with the lambda(5)-iodane 2-iodoxybenzoic acid IBX reagent led to their regioselective dearomatization into previously undescribed ortho-quinol imines.     

Emulsified microemulsions and oil-containing liquid crystalline phases

Self-assembled nanostructures, such as inverted type mesophases of the cubic or hexagonal geometry or reverse microemulsion phases, can be dispersed using a polymeric stabilizer, such as the PEO-PPO-PEO triblock copolymer Pluronic F127. The particles, which are described in the present study, are based on monolinolein (MLO)-water mixtures. When adding tetradecane (TC) to the MLO-water-F127 system at constant temperature, the internal nanostructure of the kinetically stabilized particles transforms from a Pn3m (cubosomes) to a H2 (hexosomes) and to a water-in-oil (W/O, L2) microemulsion phase (emulsified microemulsion (EME)). To our knowledge, this is the first time that the formation of stable emulsified microemulsion (EME) systems has been described and proven to exist even at room temperature. The same structural transitions can also be induced by increasing temperature at constant tetradecane content. The internal nanostructure of the emulsified particles is probed using small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). At each investigated composition and temperature, the internal structure of the dispersions is observed to be identical to the corresponding structure of the nondispersed, fully hydrated bulk phase. This is clear evidence for the fact that the self-assembled inner particle nanostructure is preserved during the dispersion procedure. In addition, the internal structure of the particles is in thermodynamic equilibrium with the surrounding water phase. The internal structure of the dispersed, kinetically stabilized particles is a "real" and stable self-assembled nanostructure. To emphasize this fact, we denoted this new family of colloidal particles (cubosomes, hexosomes, and EMEs) as "ISASOMES" (internally self-assembled particles or "somes").     

Near-IR luminescence of monolayer-protected metal clusters

Visible-near-IR luminescence spectra of gold MPCs that are similar, irrespective of the number of core atoms (all <2 nm diameter) and different monolayers, are reported. The luminescence can be quantitatively invoked by introducing polar ligands into nonpolar MPC monolayers and by galvanic exchange of metal atoms on the MPC core surface with different metals. The observed emissions are believed to result from surface-localized states that depend on both the core metal of the nanoparticle and the ligands attached to the metal surface.     

Relaxometric study of copper [15]metallacrown-5 gadolinium complexes derived from alpha-aminohydroxamic acids

Proton nuclear magnetic relaxation dispersion (NMRD) profiles were recorded between 0.24 mT and 1.4 T for lanthanum(III)- and gadolinium(III)-containing [15]metallacrown-5 complexes derived from alpha-aminohydroxamic acids and with copper(II) as the ring metal. The influence of the different R-groups on the proton relaxivity was investigated, and a linear relationship between the relaxivity and the molecular mass of the metallacrown complex was found. The selectivity of the metallacrown complexes was tested by transmetalation experiments with zinc(II) ions. The crystal structure of the copper [15]metallacrown-5 gadolinium complex with glycine hydroximate ligands is reported.     

IR and theoretical studies of monocarbonyl Ni complexes formed by adsorption of CO at low pressure on silica-supported Ni(II) ions

This work reports on the reactivity of coordination vacancies of Ni(II) ions grafted onto the tridentate silica support (Ni(II)(3c) ions) with respect to CO used as a probe molecule. The adsorption of CO at 77 K in the 0.3 to 3.5 Pa CO pressure range is studied by FTIR on two samples differing in the dispersion of nickel. Quantum chemical calculations by the DFT method are performed to investigate, using a cluster approach, the binding of Ni to silica and, after CO adsorption, the geometry of the resulting carbonyl Ni complexes. Silica is modeled by using clusters composed of three types of monodentate ligands, SiO(-), SiOSi and/or SiOH, found on the surface of silica. This work is devoted to the monocarbonyl complexes. Whatever the sample, only one type of monocarbonyl is formed from Ni(II)(3c) ions. It is shown that the charge of the silica cluster is the major parameter influencing the CO IR frequency whereas the nature and the size of the silica cluster do not affect the CO bond length, confirming that local electrostatic interactions predominate. Only the 1- charged silica cluster Si(5)O(3)(-), composed of SiO(-), 2SiOSi fragments, respectively, reproduces the Ni[bond]O distances derived from EXAFS for the Ni(II)(3c) grafted site and gives CO frequencies in good agreement with the experimental values. It is shown that CO is stabilized by a magnetic transition from the (3)Ni(2+) triplet to the (1)Ni(2+) singlet state occurring upon adsorption.