Crystal structure,vibrational spectra and thermal decomposition study of a new,dicationic, acidic pyrophosphate: KHMgP<Subscript>2</Subscript>O<Subscript>7</Subscript>⋅2H<Subscript>2</Subscript>O

Colourless crystals of a new, dicationic, hydropyrophosphate dihydrate salt, KHMgP₂O₇⋅ 2H₂O, are formed, when a mixture of aqueous equimolar solutions of MgCl₂⋅4H₂O and K₄P₂O₇, at pH 2.12, are left to stand at ambient temperature for 4 days. The new pyrophosphate salt has been characterized by single-crystal X-ray diffraction, IR and Raman spectra, and DSC-TG thermal analysis. The structure consists of alternating layers of [HP₂O₇]³⁻ groups and MgO₆ octahedra, joined by K⁺ ions and bridging hydrogen bonds. The [P₂O₇]⁴⁻ anions exhibit a bent eclipsed conformation. The absence of coincidences for the majority of the IR and Raman bands is in accord with the centrosymmetric structure of the material. The ³¹P chemical shift tensor components have been determined from the solid-state MAS NMR spectra. The structural changes occurring during thermal decomposition have been examined by TG-DSC, X-ray powder diffraction (XRD) and IR spectroscopy. When the new pyrophosphate salt is heated gradually, it first becomes amorphous and then condenses to chain metaphosphates.     

Separation and quantification by high-performance liquid chromatography with light scattering detection of the main wheat flour phospholipids during dough mixing in the presence of phospholipase

Phospholipids (PL) are minor components of wheat flour involved in baking quality and exogenous phospholipids are used as emulsifiers giving better loaf volume and crumb grain. Few biochemical data are available on the phospholipid evolution during mixing, probably because of the time-consuming methods proposed for their extraction, separation and quantification. In the present study, the extraction, separation and quantification of the main wheat flour phospholipids were carried out. Total lipids (2% dry mass of wheat flour) were extracted from flour or dough by a mixture of chloroform-methanol-water (1:1:1 (v/v)). The phospholipids were separated from the lipid extract on silica cartridge by solid-phase extraction (SPE) procedure under a 1.5-4 mmHg vacuum, at a 0.8 mL min(-1) flow rate (1 mmHg = 133.322 Pa). The recovery of the lipid extract was 100%, whereas the SPE yield for the PLs was 50%. The resulting fraction was then submitted to HPLC with evaporative light scattering detection on a Diol stationary phase allowing the separation and quantification of each class of phospholipids, in less than 16 min. The developed method allowed to quantify the phospholipid amounts from eight wheat flours as well as their evolution during mixing in the presence of phospholipase.     

Symbiotic signaling in actinorhizal symbioses

Actinorhizal symbioses are mutualistic associations between plants belonging to eight angiosperm families and soil bacteria of the genus Frankia. These interactions lead to the formation of new root organs, actinorhizal nodules, where the bacteria are hosted and fix atmospheric nitrogen thus providing the plant with an almost unlimited source of nitrogen for its nutrition. It involves an elaborate signaling between both partners of the symbiosis. In recent years, our knowledge of this signaling pathway has increased tremendously thanks to a series of technical breakthroughs including the sequencing of three Frankia genomes [1] and the implementation of RNA silencing technology for two actinorhizal species. In this review, we describe all these recent advances, current researches on symbiotic signaling in actinorhizal symbioses and give some potential future research directions.     

Nineteenth century roots of quasideterminants

In this expository paper I provide a complete record of the nineteenth century publications that bear on the development of quasideterminants in the twentieth century. Two important recursive feasible algorithms, Sylvester’s from 1851 and Dodgson’s from 1866 are discussed, and the antecedents of both are traced back to work by Jacobi.     

KF/Al2O3 and PEG-400 as a recyclable medium for the selective α-selenation of aldehydes and ketones. Preparation of potential antimicrobial agents

2-Phenylseleno aldehydes and ketones were selectively obtained using solid-supported catalyst (KF/Al₂O₃) and PEG-400 as clean, recyclable medium in good to excellent yields. The method was applied in the preparation of highly functionalized 2-phenylseleno citronellal and citronellol, potential bactericide agents. The catalytic system KF/Al₂O₃ and PEG-400 can be re-used for four times without previous treatment.     

Top-hat cw-laser-induced time-resolved mode-mismatched thermal lens spectroscopy for quantitative analysis of low-absorption materials

Thermal lens spectroscopy is a highly sensitive and versatile photothermal technique for material analysis, providing optical and thermal properties. To use less expensive multimode non-Gaussian lasers for quantitative analysis of low-absorption materials, this Letter presents a theoretical model for time-resolved mode-mismatched thermal lens spectroscopy induced by a cw laser with a top-hat profile. The temperature profile in a sample was calculated, and the intensity of the probe beam center at the detector plane was also derived using the Fresnel diffraction theory. Experimental validation was performed with glass samples, and the results were found well consistent with literature values of the thermo-optical properties of the samples.     

Scattering by a fluid cylinder in a porous medium: application to trabecular bone

In a trabecular bone, considered as a nondissipative porous medium, the scattering of an incident wave by cylindrical pores larger than the wavelength is studied. The goal is to know if scattering alone may cause such a high attenuation as that observed in calcaneus. The porous medium is modelized via Biot's theory and the scattering by a single pore is characterized from the definition of a scattering matrix. An approximation of weakly disordered medium is then discussed to estimate the effective attenuation and dispersion as a function of frequency. These effective properties are shown to be different of those measured on calcaneus, due to the neglect of wave conversions during the scattering process.     

Sorption Mechanisms of Eu(3+) on CSH Phases of Hydrated Cements

The sorption mechanisms of Eu(3+) on calcium silicate hydrate (CSH) phases of hydrated cement were investigated as a tool for the prediction of the behavior of trivalent radionuclides with aged/degraded cements in radioactive waste repositories. Four techniques were used: site-selective and time-resolved luminescence spectroscopy, XPS, high-resolution SEM coupled with EDX, and XRD. Results showed that europium is not precipitated in the solution despite its low solubility limit. It is strongly retained on CSH, resulting in a more than 99.8% sorption rate. Two main sorption sites were characterized by luminescence spectroscopy. One site, with a long lifetime, can be interpreted as Eu included in the framework of CSH. Another one, with a shorter lifetime, can be interpreted as a site with a hydrated environment that is high but is less than that of europium hydroxide. It corresponds to superficial complexation or precipitation. Copyright 2001 Academic Press.