Chain-extending of Hydroxytelechelic Polybutadiene: Synthesis and Characterization

Extension of hydroxytelechelic polybutadiene oligomers ( 3200 g/mol) is performed in mild conditions, in order to avoid backbone modifications, using succinic anhydride or methylenedicyclohexyl diisocyanate. The two routes present significative extension of the initial oligomers. Extension through the anhydride route, in the presence of DCC and DMAP, leads to new hydroxytelechelic oligomers ( 8000 g/mol). Extension through the diisocyanate route, catalyzed by DBTL at 65°C leads to hydroxytelechelic oligomers of higher average molecular weight ( 20000 g/mol). New materials are characterized by FTIR/¹H-NMR and changes in their Tg according to , are discussed. The influence of reaction time on the length of the macromolecular chains is also studied.     

Differentiation of Linear and Cyclic Polymer Architectures by MALDI Tandem Mass Spectrometry (MALDI-MS2)

[M + Ag]⁺ ions from cyclic and linear polystyrenes and polybutadienes, formed by matrix-assisted laser desorption ionization (MALDI), give rise to significantly different fragmentation patterns in tandem mass spectrometry (MS²) experiments. In both cases, fragmentation starts with homolytic cleavage at the weakest bond, usually a C–C bond, to generate two radicals. From linear structures, the separated radicals depolymerize extensively by monomer losses and backbiting rearrangements, leading to low-mass radical ions and much less abundant medium- and high-mass closed-shell fragments that contain one of the original end groups, along with internal fragments. With cyclic structures, depolymerization is less efficient, as it can readily be terminated by intramolecular H-atom transfer between the still interconnected radical sites (disproportionation). These differences in fragmentation reactivity result in substantially different fragment ion distributions in the MS² spectra. Simple inspection of the relative intensities of low- versus high-mass fragments permits conclusive determination of the macromolecular architecture, while full spectral interpretation reveals the individual end groups of linear polymers or the identity of the linker used to form the cyclic polymer.

Small Changes Have Consequences: Lessons from Tetrabenzyltitanium and ‐zirconium Surface Organometallic Chemistry

Homoleptic benzyl derivatives of titanium and zirconium have been grafted onto silica that was dehydroxylated at 200 and 700 °C, thereby affording bi‐grafted and mono‐grafted single‐site species, respectively, as shown by a combination of experimental techniques (IR, MAS NMR, EXAFS, and elemental analysis) and theoretical calculations. Marked differences between these compounds and their neopentyl analogues are discussed and rationalized by using DFT. These differences were assigned to the selectivity of the grafting process, which, depending on the structure of the molecular precursors, led to different outcomes in terms of the mono‐ versus bi‐grafted species for the same surface concentration of silanol species. The benzylzirconium derivatives were active towards ethylene polymerization in the absence of an activator and the bi‐grafted species displayed higher activity than their mono‐grafted analogues. In contrast, the benzyltitanium and neopentylzirconium counterparts were not active under similar reaction conditions.     

Iα → Iβ transition of cellulose under ultrasonic radiation

Aqueous suspensions of dispersed Glaucocystis cellulose microfibrils were sonicated at 4 °C for 3 h, using 24 kHz ultrasonic waves. This treatment induced a variety of ultrastructural defects, as the microfibrils became not only shortened, but also presented substantial damage materialized by kinks and subfibrillation. Upon analysis by X-ray diffraction and ¹³C solid-state NMR spectroscopy, it was found that the initial sample that contained 90 % of cellulose I_α allomorph became, to a large extent, unexpectedly converted into the I_β phase, while the loss of crystallinity was only moderate during the sonication treatment.     

Characteristics of polyurethane-based sustained release membranes for drug delivery

This paper is focused on the preparation and physicochemical characterization of two poly(ester ether urethane)s with rifampicin in their matrix and different molar concentrations of urethane groups. The polyurethanes with rifampicin were processed as asymmetrical microporous membranes by a phase inversion method and characterized by attenuated total reflection — Fourier transform infrared (ATR-FTIR) spectroscopy and differential scanning calorimetry (DSC). The influence of the surface morphology in the release of drug compounds was analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle, and water uptake. The release of rifampicin depends on the molar concentration of urethane groups and also on the surface morphology of the polyurethane membranes. The antibacterial activity was evaluated with S. Epidermidis RP 62 A and P. Aeruginosa ATCC 1544. Finally, the biocompatibility of the polyurethane membranes was studied with human dermal fibroblasts (HDF) to evaluate the potential biomedical applications.      

Ultra‐fast heralded single photon source based on telecom technology

The realization of an ultra‐fast source of heralded single photons emitted at the wavelength of 1540 nm is reported. The presented strategy is based on state‐of‐the‐art telecom technology, combined with off‐the‐shelf fiber components and waveguide non‐linear stages pumped by a 10 GHz repetition rate laser. The single photons are heralded at a rate as high as 2.1 MHz with a heralding efficiency of 42%. Single‐photon character of the source is inferred by measuring the second‐order autocorrelation function. For the highest heralding rate, a value as low as 0.023 is found. This not only proves negligible multi‐photon contributions but also represents one of the best measured values reported to date for heralding rates in the MHz regime. These performances, associated with a device‐like configuration, are key ingredients for both fast and secure quantum communication protocols.

     

Phospholipid-based nonlamellar mesophases for delivery systems: Bridging the gap between empirical and rational design

Phospholipids are ubiquitous cell membrane components and relatively well-accepted ingredients due to their natural origin. Phosphatidylcholine (PC) in particular offers a promising alternative to monoglycerides for lyotropic liquid crystalline (LLC) delivery system applications in the food, cosmetics and pharmaceutical industries, provided its strong tendency to form zero-mean curvature lamellar mesophases in water can be overcome. Higher negative curvatures are usually reached through the addition of a third lipid component, forming a ternary diagram phospholipid/water/oil.     

Toward the understanding of the environmental effects on core ionizations

Experimental X‐ray absorption spectra are extensively used to determine electronic structure of small molecules but remain difficult to exploit for proteins due to the large number of peaks within their spectra. For such complex systems, theoretical tools like quantum mechanics/molecular mechanics methodology can greatly ease the assignment of the spectra. This study presents a systematic methodology to evaluate core‐ionization energies (E_ion) in proteins with the help of the asymptotic projection approach (Glushkov and Tsaune, Z. Vichislit. Matem. Mat. Fiz. 1985, 25, 298; Glushkov, Chem. Phys. Lett. 1997, 273, 122; Glushkov, Chem. Phys. Lett. 1998, 287, 189; Glushkov, J. Math. Chem. 2002, 31, 91; Glushkov, Opt. Spectrosc. 2002, 93, 15). An in‐depth inspection of E_ion of systems of increasing complexity is considered, going from amino acids to polyglycine and to glycine in human serum albumin (HSA). Computational analysis can help to better understand experimental data and to discriminate environmental effects by tracing them back to individual and collective electrostatic contributions. In the present work, it was found that E_ion of alpha carbon of glycine residues in HSA ranges from 285 to 295 eV depending on their surroundings. © 2014 Wiley Periodicals, Inc.     

Isolated boundary singularities of semilinear elliptic equations

Given a smooth domain ${\Omega\subset\mathbb{R}^N}$ such that ${0 \in \partial\Omega}$ and given a nonnegative smooth function ?? on ???, we study the behavior near 0 of positive solutions of ???u?=?u ^q in ?? such that u =? ?? on ???\{0}. We prove that if ${\frac{N+1}{N-1} < q < \frac{N+2}{N-2}}$ , then ${u(x)\leq C |x|^{-\frac{2}{q-1}}}$ and we compute the limit of ${|x|^{\frac{2}{q-1}} u(x)}$ as x ?? 0. We also investigate the case ${q= \frac{N+1}{N-1}}$ . The proofs rely on the existence and uniqueness of solutions of related equations on spherical domains.