Lewis acid properties of phosphenium and arsenium cations: Study of their adducts with pyridine

In the growing field of dicoordinated Group 15 cations, the quantitative study of the Lewis acid properties of phosphenium or arsenium cations has not yet been undertaken. Moreover, there are only a few described examples of syntheses of arsenium cations. The aim of this work is to enhance this series and to develop a quantitative comparative study of their complexation with Lewis bases such as pyridine. The observation of the ¹³C NMR C-4 variation in the pyridine ring is a good probe to obtain the apparent equilibrium constant K_c and thus a Lewis acidity scale. Phosphenium cations are more acidic than arsenium cations.     

The Exceptional Jordan Eigenvalue Problem

We discuss the eigenvalue problem for 3 ×3 octonionic Hermitian matrices which is relevant to theJordan formulation of quantum mechanics. In contrast tothe eigenvalue problems considered in our previous work, all eigenvalues are real and solve theusual characteristic equation. We give an elementaryconstruction of the corresponding eigenmatrices, and wefurther speculate on a possible application to particle physics.     

Photomodulable Materials. Synthesis and Properties of Photochromic 3H‐Naphtho[2,1‐b]pyrans Linked to Thiophene Units via an Acetylenic Junction

The synthesis of 3H‐naphtho[2,1‐b]pyrans linked to mono‐, di‐, or terthiophene via an acetylenic junction is described (Schemes 2 and 3). The synthetic approaches involve successive Sonogashira coupling reactions. The photochromic properties in solution of these novel materials were investigated under continuous irradiation.     

Aza-Michael silicone cure is accelerated by β-hydroxyalkyl esters

The aza-Michael reaction is proving to be a practical, catalyst free method by which a variety of polymers, including silicones, can be cured. However, its adoption may be compromised by slow cure rates; for many applications is it not practical to accelerate cure by heating. OH groups on the amine, acrylate partner or solvent are known to lead to accelerated rates of aza-Michael reactions. The impact of the location of OH groups on reaction partners is demonstrated using both small molecules and small molecules plus telechelic silicones. While all OH groups are shown to increase reaction rates, a special enhancement is provided by β-hydroxyalkyl acrylate esters, which have significantly higher rates of reaction than simple acrylates per se, and yet higher reactivities in hydroxylic media. Using this motif, in the absence of solvents, silicone elastomer cure based on the β-hydroxyalkyl acrylate motif is facile and complete in less than 30 min at room temperature.     

Enhancing Potency and Selectivity of a DC-SIGN Glycomimetic Ligand by Fragment-Based Design: Structural Basis

Chemical modification of pseudo-dimannoside ligands guided by fragment-based design allowed for the exploitation of an ammonium-binding region in the vicinity of the mannose-binding site of DC-SIGN, leading to the synthesis of a glycomimetic antagonist (compound 16 ) of unprecedented affinity and selectivity against the related lectin langerin. Here, the computational design of pseudo-dimannoside derivatives as DC-SIGN ligands, their synthesis, their evaluation as DC-SIGN selective antagonists, the biophysical characterization of the DC-SIGN/ 16 complex, and the structural basis for the ligand activity are presented. On the way to the characterization of this ligand, an unusual bridging interaction within the crystals shed light on the plasticity and potential secondary binding sites within the DC-SIGN carbohydrate recognition domain.     

An insight into tapioca and wheat starch gelatinization mechanisms using TD-NMR and complementary techniques

To provide evidence for previously proposed assumptions concerning starch gelatinization sub-mechanisms, a more detailed investigation was carried out using multiscale analysis of a starch type selected for its marked difference. Tapioca starch was chosen due to its cohesive/springy properties and its growing use in the food industry. Time-domain nuclear magnetic resonance (TD-NMR) was used to investigate the leaching of material, water absorption and crystallite melting in hydrated tapioca starch (45%). The interpretation of T2 mass intensity evolutions, especially those of the (intra- and extra-granular) aqueous phases, was discussed drawing on complementary techniques such as microscopy, Rapid Visco Analyser (RVA), differential scanning calorimetry (DSC) and swelling factor (SF) and solubility index (SI) measurements. Results show that the T2 assignments usually proposed in the literature are dependent on starch origin. The differences in T2 evolutions (value and mass intensity) observed between wheat and tapioca starches at intermediate hydration levels could be linked to the different gelatinization behaviour of tapioca starch involving the latter's higher granule rupture level, higher gelatinization temperature and greater swelling power above its gelatinization temperature.