Sites for Methane Activation on Lithium‐Doped Magnesium Oxide Surfaces

Density functional calculations yield energy barriers for H abstraction by oxygen radical sites in Li‐doped MgO that are much smaller (12±6 kJ mol^?1) than the barriers inferred from different experimental studies (80–160 kJ mol^?1). This raises further doubts that the Li⁺O^.? site is the active site as postulated by Lunsford. From temperature‐programmed oxidative coupling reactions of methane (OCM), we conclude that the same sites are responsible for the activation of CH₄ on both Li‐doped MgO and pure MgO catalysts. For a MgO catalyst prepared by sol–gel synthesis, the activity proved to be very different in the initial phase of the OCM reaction and in the steady state. This was accompanied by substantial morphological changes and restructuring of the terminations as transmission electron microscopy revealed. Further calculations on cluster models showed that CH₄ binds heterolytically on Mg²⁺O^2? sites at steps and corners, and that the homolytic release of methyl radicals into the gas phase will happen only in the presence of O₂.     

Silica/lignosulfonate hybrid materials: Preparation and characterization

The research reported here concerns the synthesis, characterization and potential applications of silica/lignosulfonate hybrid materials. Three types of silica were used (Aerosil®200, Syloid®244 and hydrated silica), along with magnesium lignosulfonate. The effectiveness of the hybrid material synthesis methodology was confirmed indirectly, using Fourier transform infrared spectroscopy, elemental and colorimetric analysis. Dispersive-morphological analysis indicates that the products with the best properties were obtained using 10 parts by weight of magnesium lignosulfonate per 100 parts of Syloid®244 silica. The relatively high thermal stability recorded for the majority of the synthesized products indicates the potential use of this kind of a material as a polymer filler. Results indicating the high electrokinetic stability of the materials are also of great importance. Additionally, the very good porous structure properties indicate the potential use of silica/lignosulfonate systems as biosorbents of hazardous metal ions and harmful organic compounds.      

Determination of pipecuronium bromide and its impurities in pharmaceutical preparation by high-performance liquid chromatography with coulometric electrode array detection

A sensitive and selective HPLC method with coulometric electrode array detection for the determination of pipecuronium bromide and its four impurities has been developed. The coulometric electrode array detection at increasing potentials from +300 to +900mV of the porous graphite electrode versus the palladium reference electrode was used. The limit of detection and quantitation for pipecuronium bromide was 8 and 25ngml(-1), respectively. This elaborate method for the simultaneous analysis of pipecuronium bromide and its impurities proved to be fast, precise, accurate, sensitive, and could be applied to analysis in substances and in pharmaceutical preparations.     

QCM-D analysis of the performance of blocking agents on gold and polystyrene surfaces

With today's developments of biosensors and medical implants comes the need for efficient reduction of nonspecific binding. We report on a comparison of the ability of traditionally used blocking agents and poly(ethylene glycol) (PEG) derivatives to prevent protein adsorption on both gold and polystyrene surfaces. The adsorption kinetics of blocking molecules and proteins was monitored gravimetrically using quartz crystal microbalance with dissipation (QCM-D). The resistance to nonspecific adsorption was evaluated on gold and polystyrene surfaces coated with bovine serum albumin (BSA) or casein, gold coated with three different 6-11 ethylene glycol (EG) long hydroxyl- or methoxy-terminated PEG-thiolates and polystyrene blocked with a PLL-g-PEG or three different 12 EG long benzyl-PEG-derivatives. The prevention of protein adsorption on the coated surfaces was evaluated by monitoring the mass uptake at the addition of both pure prostate specific antigen (PSA) and seminal plasma. We demonstrate that on pure gold the PEG-thiols are superior to the other blocking molecules tested, with the end group and length of the PEG-thiols used being of minor importance. On polystyrene surfaces blocking with PLL-g-PEG, BSA and casein gave the best results. These results have an impact on further development of an optimized immunoassay protocol.     

Versatile synthesis of isocoumarins and α-pyrones by ruthenium-catalyzed oxidative C-H/O-H bond cleavages

An inexpensive cationic ruthenium(II) catalyst enabled the expedient synthesis of isocoumarins through oxidative annulations of alkynes by benzoic acids. This C-H/O-H bond functionalization process also proved applicable to the preparation of α-pyrones and was shown to proceed by rate-limiting C-H bond ruthenation.     

Preparation of Pseudo‐Peptide Building Blocks with retro‐Thioamide Bond Mediated via Thiocarbamoyl Meldrum's Acid

An easy and efficient synthesis of pseudo‐tripeptide containing a thiomalonamide moiety was developed. Isothiocyanate derivatives of amino acids react smoothly with 2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione (Meldrum's acid) to yield new thiocarbamoyl derivatives of Meldrum's acids. Thermal decomposition of these new derivatives leads to thiocarbamoyl ketenes, which acylate amino acid esters to give pseudo‐tripeptides.     

Studies of the hydrolytic stability of poly(urethane-urea) elastomers synthesized from oligocarbonate diols

Polyurethane and poly(urethane-urea) elastomers synthesized from oligocarbonate diols are characterized by very good mechanical properties, biocompatibility and excellent resistance to both oxidation and hydrolysis and therefore are widely used in medical applications. In this paper the results of studies on hydrolytic stability of poly(urethane-urea) elastomers (PURC) obtained by moisture-curing of corresponding urethane prepolymers synthesized from isophorone diisocyanate (IPDI) and four different oligocarbonate diols (OCD) are presented. OCD were synthesized from dimethyl carbonate and 1,6-hexanediol, from cyclic ethylene carbonate and 1,6-hexanediol as well as from trimethylene carbonate. The changes of the sample weight, mechanical properties and surface properties after immersion in a standard phosphate buffer solution (pH = 7.4) for up to 3 months at 70 °C were monitored. It was shown that neither sample weight nor mechanical properties changed significantly for PURC obtained from OCDs synthesized from 1,6-hexanediol and dimethyl carbonate or ethylene carbonate what confirms good resistance to hydrolysis of those PURC. Also SEM studies of those samples before and after immersion did not reveal any surface degradation effects. However, PURC sample obtained from OCD synthesized from trimethylene carbonate showed significant changes in mechanical properties and distinct change of appearance and surface erosion after 3 months immersion. The initial decrease and later increase of stress at break observed for PURC samples during immersion, was explained by the reaction of residual NCO groups present in PURC with water leading to molecular weight increase which proceeded during immersion period in parallel to hydrolysis of carbonate bond.