‘Chimie douce’ synthesis, crystal and electronic structures of the novel Hg~4.2Mo15X19 (X = S, Se) compounds containing Hg3, Mo6 and Mo9 clusters

The new compounds Hg_~4.2Mo₁₅X₁₉ (X = S, Se) were obtained by inserting mercury into the metastable Mo₁₅X₁₉ compounds at low temperature. Their crystal structures, determined from single-crystal X-ray diffraction data, show that the molybdenum–chalcogenide network is maintained through the synthesis. It consists of an equal mixture of Mo₆X₈X₆ and Mo₉X₁₁X₆ cluster units interconnected through Mo–X bonds as in the parent compounds. In both compounds, the mercury is present either as Hg²⁺ cations or forming linear clusters Hg₃²⁺. It is the first time that the latter cluster is observed in a chalcogen environment. To cite this article: D. Salloum et al., C. R. Chimie 8 (2005).     

Mechanical reliability of silica optical fibers

Dynamic and static mechanical tests were implemented using a tensile test bench and a static fatigue test under uniform curve. The incidence of aging treatments at 65 and 85 °C was investigated on two standard silica optical fibers (with polyacrylate and fluorinated coatings). Microscopic observations helped the understanding of the failure mechanism. It appears that the cyclic variations of the failure stress phenomenon, with respect to the aging time, are the result of the silicate gel which migrates towards the polymer coating.     

Real meromorphic functions and linear differential polynomials

We determine all real meromorphic functions f in the plane such that f has finitely many zeros, the poles of f have bounded multiplicities, and f and F have finitely many non-real zeros, where F is a linear differential polynomial given by F = f (k) +Σk-1j=0ajf(j) , in which k≥2 and the coefficients aj are real numbers with a0≠0.     

Ag2.54Tl2Mo12Se15: a new structure type containing Mo6 and Mo9 clusters

The novel structure‐type Ag_2.54Tl₂Mo₁₂Se₁₅ (silver thallium molybdenum selenide) is built up of Mo₆Seⁱ₈Se^a₆ and Mo₉Seⁱ₁₁Se^a₆ cluster units in a 1:2 ratio, which are three‐dimensionally connected to form the Mo–Se network. The Ag and Tl cations are distributed in several voids within the cluster network. Three of the seven independent Se atoms and one Tl atom lie on sites with 3.. symmetry (Wyckoff sites 2c or 2d).     

Attachment of Chloride Anion to Sugars: Mechanistic Investigation and Discovery of a New Dopant for Efficient Sugar Ionization/Detection in Mass Spectrometers

A new method for efficient ionization of sugars in the negative‐ion mode of electrospray mass spectrometry is presented. Instead of using strongly hydrophobic dopants such as dichloromethane or chloroform, efficient ionization of sugars has been achieved by using aqueous HCl solution for the first time. This methodology makes it possible to use hydrophilic dopants, which are more appropriate for chromatographic separation techniques with efficient sugar ionization and detection in mass spectrometry. The interaction between chloride anions and monosaccharides (glucose and galactose) was studied by DFT in the gas phase and by implementing the polarizable continuum model (PCM) for calculations in solution at the high B3LYP/6‐31+G(d,p)//B3LYP/6‐311+G(2d,p) level of theory. In all optimized geometries of identified [M+Cl]^? anions, a non‐covalent interaction exists. Differences were revealed between monodentate and bidentate complex anions, with the latter having noticeably higher binding energies. The calculated affinity of glucose and galactose toward the chloride anion in the gas phase and their chloride anion binding energies in solution are in excellent agreement with glucose and galactose [M+Cl]^? experimental intensity profiles that are represented as a function of the chloride ion concentration. Density functional calculations of gas‐phase affinities toward chloride anion were also performed for the studied disaccharides sucrose and gentiobiose. All calculations are in excellent agreement with the experimental data. An example is introduced wherein HCl was used to effectively ionize sugars and form chlorinated adduct anions to detect sugars and glycosylated metabolites (anthocyanins) in real biological systems (Vitis vinifera grape extracts and wines), whereas they would not have been easily detectable under standard infusion electrospray mass spectrometry conditions as deprotonated species.     

Capillary electrokinetic fractionation mass spectrometry (CEkF/MS): Technology setup and application to metabolite fractionation from complex samples coupled at‐line with ultrahigh‐resolution mass spectrometry

Capillary electrokinetic fractionation (CEkF) is investigated as a new, simple, and robust approach for semipreparative and analytical sample analysis based on pK_a‐dependant pH‐driven electrophoretic mobility. CEkF was optimized with contactless conductivity detection and conducted with 10 kV reverse voltage for 10 min, then coupled on/at‐line to ESI/MS. We propose a semi‐empirical model with 14 representative compounds based on the correlation between sample/medium pH regulating the partial charge, the electrokinetic loading of the capillary and intensity (I) of analytes. According to the model, an empirical function (I = f (pH)) could be derived to calculate the acid dissociation constant (pK_a) of various model compounds based on their pH‐dependant MS intensity profiles with the RSD < 4.05. Using the ultrahigh‐resolution of ion cyclotron resonance Fourier transform MS, the pK_a model was further illustrated in real samples into the structure prediction of important compounds in wine over two vintages. The established CEkF was successfully used to selectively fractionate sulfur compounds from the complex wine samples at pH 1.66. The proposed CEkF approach should allow in the future the simultaneous pK_a evaluation of multiple constituents without complicated separation out of a complex mixture in metabolomics or environmental chemistry.