In-Situ Synthesis and Characterization of Nanocomposites in the Si-Ti-N and Si-Ti-C Systems

The pyrolysis (1000 °C) of a liquid poly(vinylmethyl-co-methyl)silazane modified by tetrakis(dimethylamido)titanium in flowing ammonia, nitrogen and argon followed by the annealing (1000–1800 °C) of as-pyrolyzed ceramic powders have been investigated in detail. We first provide a comprehensive mechanistic study of the polymer-to-ceramic conversion based on TG experiments coupled with in-situ mass spectrometry and ex-situ solid-state NMR and FTIR spectroscopies of both the chemically modified polymer and the pyrolysis intermediates. The pyrolysis leads to X-ray amorphous materials with chemical bonding and ceramic yields controlled by the nature of the atmosphere. Then, the structural evolution of the amorphous network of ammonia-, nitrogen- and argon-treated ceramics has been studied above 1000 °C under nitrogen and argon by X-ray diffraction and electron microscopy. HRTEM images coupled with XRD confirm the formation of nanocomposites after annealing at 1400 °C. Their unique nanostructural feature appears to be the result of both the molecular origin of the materials and the nature of the atmosphere used during pyrolysis. Samples are composed of an amorphous Si-based ceramic matrix in which TiN_xC_y nanocrystals (x + y = 1) are homogeneously formed “in situ” in the matrix during the process and evolve toward fully crystallized compounds as TiN/Si₃N₄, TiN_xC_y (x + y = 1)/SiC and TiC/SiC nanocomposites after annealing to 1800 °C as a function of the atmosphere.     

Reversible Dehalogenation in On‐Surface Aryl–Aryl Coupling

In the emerging field of on‐surface synthesis, dehalogenative aryl–aryl coupling is unarguably the most prominent tool for the fabrication of covalently bonded carbon‐based nanomaterials. Despite its importance, the reaction kinetics are still poorly understood. Here we present a comprehensive temperature‐programmed x‐ray photoelectron spectroscopy investigation of reaction kinetics and energetics in the prototypical on‐surface dehalogenative polymerization of 4,4′′‐dibromo‐p‐terphenyl into poly(para‐phenylene) on two coinage metal surfaces, Cu(111) and Au(111). We find clear evidence for reversible dehalogenation on Au(111), which is inhibited on Cu(111) owing to the formation of organometallic intermediates. The incorporation of reversible dehalogenation in the reaction rate equations leads to excellent agreement with experimental data and allows extracting the relevant energy barriers. Our findings deepen the mechanistic understanding and call for its reassessment for surface‐confined aryl–aryl coupling on the most frequently used metal substrates.     

Framework Effects on Activation and Functionalisation of Methane in Zinc-Exchanged Zeolites

The first selective oxidation of methane to methanol is reported herein for zinc-exchanged MOR (Zn/MOR). Under identical conditions, Zn/FER and Zn/ZSM-5 both form zinc formate and methanol. Selective methane activation to form [Zn-CH₃]⁺ species was confirmed by ¹³C MAS NMR spectroscopy for all three frameworks. The percentage of active zinc sites, measured through quantitative NMR spectroscopy studies, varied with the zeolite framework and was found to be ZSM-5 (5.7 %), MOR (1.2 %) and FER (0.5 %). For Zn/MOR, two signals were observed in the ¹³C MAS NMR spectrum, resulting from two distinct [Zn-CH₃]⁺ species present in the 12 MR and 8 MR side pockets, as supported by additional NMR experiments. The observed products of oxidation of the [Zn-CH₃]⁺ species are shown to depend on the zeolite framework type and the oxidative conditions used. These results lay the foundation for developing structure–function correlations for methane conversion over zinc-exchanged zeolites.     

Kinetic Isotope Effect as a Tool To Investigate the Oxygen Reduction Reaction on Pt-based Electrocatalysts – Part II: Effect of Platinum Dispersion

We investigated the oxygen reduction reaction (ORR) mechanism on Pt nanoparticles (NPs) dispersed on several carbon blacks with various physicochemical properties (i. e. specific surface ranging from 80 to 900 m² g⁻¹, different graphitization degree, etc.). Using the kinetic isotope effect (KIE) along with various electrochemical characterizations, we determined that the rate determining step (RDS) of the ORR is a proton-independent step when the density of Pt NPs on the surface of the carbon support is high. Upon decrease of the density of Pt NPs on the surface, the RDS of the ORR starts involving a proton, as denoted by an increase of the KIE >1. This underlined the critical role played by the carbon support in the oxygen reduction reaction electrocatalysis by Pt supported on high surface area carbon.     

Portable capillary liquid chromatography for pharmaceutical and illicit drug analysis

A newly developed portable capillary liquid chromatograph was investigated for the separation of various pharmaceutical and illicit drug compounds. The system consists of two high‐pressure syringe pumps capable of delivering capillary‐scale flow rates at pressures up to 10 000 psi. Capillary liquid chromatography columns packed with sub‐2 μm particles are housed in cartridges that can be inserted into the system and easily connected through high‐pressure fluidic contact points by simply applying a specific, predetermined torque rather than using standard fittings and less precise sealing protocols. Several over‐the‐counter analgesic drug separations are demonstrated, along with a simple online measurement of tablet dissolution. Twenty illicit drug compounds were also separated across six targeted drug panels. The results described in this study demonstrate the capability of this compact liquid chromatography instrument to address several important drug‐related applications while simplifying system operation, and greatly reducing solvent usage and waste generation essential for onsite analysis.     

Optimization of Biocompatibility for a Hydrophilic Biological Molecule Encapsulation System

Despite considerable advances in recent years, challenges in delivery and storage of biological drugs persist and may delay or prohibit their clinical application. Though nanoparticle-based approaches for small molecule drug encapsulation are mature, encapsulation of proteins remains problematic due to destabilization of the protein. Reverse micelles composed of decylmonoacyl glycerol (10MAG) and lauryldimethylamino-N-oxide (LDAO) in low-viscosity alkanes have been shown to preserve the structure and stability of a wide range of biological macromolecules. Here, we present a first step on developing this system as a future platform for storage and delivery of biological drugs by replacing the non-biocompatible alkane solvent with solvents currently used in small molecule delivery systems. Using a novel screening approach, we performed a comprehensive evaluation of the 10MAG/LDAO system using two preparation methods across seven biocompatible solvents with analysis of toxicity and encapsulation efficiency for each solvent. By using an inexpensive hydrophilic small molecule to test a wide range of conditions, we identify optimal solvent properties for further development. We validate the predictions from this screen with preliminary protein encapsulation tests. The insight provided lays the foundation for further development of this system toward long-term room-temperature storage of biologics or toward water-in-oil-in-water biologic delivery systems.     

Development of Phenothiazine Hybrids with Potential Medicinal Interest: A Review

The molecular hybridization approach has been used to develop compounds with improved efficacy by combining two or more pharmacophores of bioactive scaffolds. In this context, hybridization of various relevant pharmacophores with phenothiazine derivatives has resulted in pertinent compounds with diverse biological activities, interacting with specific or multiple targets. In fact, the development of new drugs or drug candidates based on phenothiazine system has been a promising approach due to the diverse activities associated with this tricyclic system, traditionally present in compounds with antipsychotic, antihistaminic and antimuscarinic effects. Actually, the pharmacological actions of phenothiazine hybrids include promising antibacterial, antifungal, anticancer, anti-inflammatory, antimalarial, analgesic and multi-drug resistance reversal properties. The present review summarizes the progress in the development of phenothiazine hybrids and their biological activity.     

Chain elastic modulus of polyethylene: A spectroscopically determined force field (SDFF) study

Our SDFF for linear saturated hydrocarbon chains has been used to calculate the chain modulus of isolated and crystalline chains of n-alkanes of varying lengths. This has been done for static deformations and for the dynamic deformation in the longitudinal acoustic mode (LAM). Extrapolation to infinite chain length gives a common value of the room-temperature crystal modulus of 303 GPa (also obtained in an infinite chain calculation). Experimental Raman LAM measurements, corrected for chain-end interactions, give a modulus of 305 GPa, in excellent agreement. Problems with the experimental values obtained by inelastic neutron scattering and x-ray diffraction are discussed. © 1996 John Wiley & Sons, Inc.     

Strong,Thermally Superinsulating Biopolymer–Silica Aerogel Hybrids by Cogelation of Silicic Acid with Pectin

Silica aerogels are excellent thermal insulators, but their brittle nature has prevented widespread application. To overcome these mechanical limitations, silica–biopolymer hybrids are a promising alternative. A one‐pot process to monolithic, superinsulating pectin–silica hybrid aerogels is presented. Their structural and physical properties can be tuned by adjusting the gelation pH and pectin concentration. Hybrid aerogels made at pH 1.5 exhibit minimal dust release and vastly improved mechanical properties while remaining excellent thermal insulators. The change in the mechanical properties is directly linked to the observed “neck‐free” nanoscale network structure with thicker struts. Such a design is superior to “neck‐limited”, classical inorganic aerogels. This new class of materials opens up new perspectives for novel silica–biopolymer nanocomposite aerogels.