Synthesis and characterization of hybrid borosiloxane gels as precursors for Si–B–O–C fibers

The sol–gel method has been used for the synthesis of borosilicate gels from mixtures of methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES) and boric acid. The use of boric acid, B(OH)₃ allows the hydrolysis and condensation of hybrid silicon alkoxides without further addition of water or catalyst. The use of difunctional silicon units, –(CH₃)₂SiO– promote the formation, during the sol–gel process, of linear oligomers which facilitate fiber drawing before gelation. Gel characterization performed by FT-IR, XRD, TG-DTA and DCS analysis indicates the formation of a mixed network with incorporation of the boron units via =B-O-Si≡ bridges. The formation of borosiloxane bonds seems favored by the presence of DMDES. SiBOC glasses were obtained after pyrolysis of the borosilicate gels in argon atmosphere at 1000 °C. TG-DTA study indicates that the ceramic yield decreases by increasing the amount of DMDES. Gel fibers were successfully prepared from convenient partially-aged solutions by hand drawing. Pyrolysis of the obtained gel fibers under argon atmosphere at 1000 °C open the possibility to produce SiBOC homogeneous glass fibers with diameter as low as 10 μm.     

Surface modification of surface sol-gel derived titanium oxide films by self-assembled monolayers (SAMs) and non-specific protein adsorption studies

Biological events occurring at the implant-host interface, including protein adsorption are mainly influenced by surface properties of the implant. Titanium alloys, one of the most widely used implants, has shown good biocompatibility primarily through its surface oxide. In this study, a surface sol-gel process based on the surface reaction of metal alkoxides with a hydroxylated surface was used to prepare ultrathin titanium oxide (TiOx) coatings on silicon wafers. The oxide deposited on the surface was then modified by self-assembled monolayers (SAMs) of silanes with different functional groups. Interesting surface morphology trends and protein adhesion properties of the modified titanium oxide surfaces were observed as studied by non-specific protein binding of serum albumin. The surface properties were investigated systematically using water contact angle, ellipsometry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) measurements. Results showed that the surface sol-gel process predominantly formed homogeneous, but rough and porous titanium oxide layers. The protein adsorption was dependent primarily on the silane chemistry, packing of the alkyl chains (extent of van der Waals interaction), morphology (porosity and roughness), and wettability of the sol-gel oxide. Comparison was made with a thermally evaporated TiOx-Ti/Si-wafer substrate (control). This method further extends the functionalization of surface sol-gel derived TiOx layers for possible titanium alloy bioimplant surface modification.     

The aqueous cationic system sodium undecenoate-dodecyltrimethylammonium bromide at low concentration

The aqueous sodium undecenoate (SUD) –dodecyltrimethylammonium bromide (DTAB) catanionic system was studied at low concentration. The system did not precipitate, even at a 1:1 SUD:DTAB proportion, but showed the formation of a coacervate in a range of surfactant mixture compositions. Micelles have a preferential composition of 0.37 mole fraction of SUD. This behavior is attributed to the presence of the double bond at the distal extreme of the SUD molecule, which can form hydrogen bonds with water. Consequently, the –CH=CH₂ group is situated at the interface between the hydrocarbon micelle core and water, reducing the interfacial free energy. Structural computations demonstrate that the mentioned SUD proportion produces complete coverage of the micelle surface by the double bonds.     

Synthesis of 2-amino-3-hydroxy- and of 2,3-diamino-3H-1,4-benzodiazepines

A new synthesis of 7-chloro-2,3-diamino-5-phenyl-3H-1,4-benzodiazepines is described, which allows for the preparation of compounds bearing the same or different substituents at the 2 and 3 positions, starting from 2-amino-7-chloro-3-hydroxy-5-phenyl-3H-1,4-benzodiazepines.     

Application of the DFT Theory to Study Cobalamin Complexes

The aim of present study is to select the best methodology in the frame of the Density Functional Theory (DFT), which may be employed to study the cobalamin complexes. Our discussion is limited to two approaches, one in which hybrid B3LYP and UB3LYP functionals are used, and the second in which geometry parameters are calculated within LDA-VWN functional, and energies of the investigated systems are computed within RPBE functional. Results of performed calculations show that both methodologies can be successfully applied to study cobalamin derivatives. Probably because of the small ligand binding energies in the studied complexes, the B3LYP and UB3LYP functionals may be used only to predict the pattern of changes in the binding energies. The use of the RPBE functional, originally parameterized to reproduce in a proper way the chemisorption energies of the small molecules on the metallic surfaces, allows to improve their values so as they fit into experimental data. Geometry parameters of the investigated complexes computed within both approaches are in good agreement with the experimental values. Interatomic distances are a little overestimated while calculated within both hybrid functionals, what is in contrast to VWN functional results. The latter, in general, gives shorter distances as observed experimentally.     

Behavior of Humic Acid as a Micellar Phase in Micellar Electrokinetic Chromatography (MEKC)

The possibility of humic acids acting as micellar phase in micellar electrokinetic chromatography was evaluated. We investigated the separation of naphthalene in capillary electrophoresis using various samples of humic acids as micellar phase under different pH conditions, concentrations of humic acid, and temperature. The humic acid samples studied were from different origins including peat, vermicompost and a commercial sample acquired from Aldrich. Methanol was used as a marker for the electroosmotic flow. The results indicate that the formation of micelle depends on the number and nature of the hydrophobic association sites in an aqueous humic acid solution and on the origin and concentration of the humic acid at a defined pH. At lower pH values, the possibility of the humic acid molecule forming pseudomicelles increases due to a combination of neutralized and dissociated charged sites.     

Metabonomics: the use of electrospray mass spectrometry coupled to reversed-phase liquid chromatography shows potential for the screening of rat urine in drug development

The application of liquid chromatography/mass spectrometry (LC/MS) followed by principal components analysis (PCA) has been successfully applied to the screening of rat urine following the administration of three candidate pharmaceuticals. With this methodology it was possible to differentiate the control samples from the dosed samples and to identify the components of the mass spectrum responsible for the separation. These data clearly show that LC/MS is a viable alternative, or complementary, technique to proton NMR for metabonomics applications in drug discovery and development.     

Rank-1 approximation to the van der Waals interaction

We present and discuss a variational single-product approximation to the van der Waals dispersion interaction leading to a simple formula for C ₆ that seems capable to give more than 99% of the ‘exact’ value. The formula is derived from Hylleraas’ variational principle in the tensor product space of the interacting molecules and therefore enjoys bounding properties. The formula has been tested by computing the C ₆ dispersion constants of H–H, and, at Full CI level, of the following systems: He–He, He–Li, Li–Li, LiH–LiH, HF–HF. Connections with the London formula are discussed. Contribution to the Fernando Bernardi Memorial Issue.     

Comparison of liquid chromatography-mass spectrometry interfaces for the analysis of polar metabolites of benz[a]pyrene

 The performance of two liquid chromatography-mass spectrometry (LC/MS) interfacing techniques, thermospray (TSP) and atmospheric pressure chemical ionization (APCI), for the analysis of benzo[a]pyrene (BaP) metabolites (hydroxy, epoxy and quinone derivatives) was compared. Interface and detection parameters such as source temperature, eluent composition or flow rate were optimized using negative ion mode. In TSP, the main ions are mostly [M]^-, [M−H₂O]^- or [M+CH₃COO]^-, whereas APCI gives mainly the [M]^- and [M−H]^- ions. Quantification was carried out by flow injection. Calibration graphs were linear in the range of 10 ng to 1000 ng in TSP and 0.1 ng to 10 ng in APCI. Detection limits were in the range of 1 ng to 20 ng in TSP and 0.002 ng to 0.2 ng in APCI. The presence of BaP-1,6-dione, BaP-3,6-dione, and BaP-6,12-dione was confirmed in environmental samples of air particulate matter. Received: 6 January 1997/Accepted: 18 April 1997     

VISIBLE CHEMILUMINESCENCE ASSOCIATED WITH THE REACTION BETWEEN METHEMOGLOBIN OR OXYHEMOGLOBIN WITH HYDROGEN PEROXIDE

Abstract Visible chemiluminescence is emitted in the irreversible deactivation of hemoglobin or methemoglobin with excess H₂O₂. The emission takes place in two phases. The most intense one lasts a few seconds and is followed by a second phase of lower intensity that remains for longer periods. This second phase presents chaotic or sustained oscillations. Free radicals are implicated in the luminescent process since the emission can be reduced by free radical scavengers such as 6-hydroxy-2,5,7,8,-tetramethylchroman-2-carboxylic acid (Trolox) or ascorbic acid. These additives lead to a delay in reaching the maximum intensity, which can be related to their consumption, implying substantial recycling of the hemoprotein. Chemiluminescence is also observed in the oxidation of hemin by H₂O₂, suggesting a role for the heme group in the processes leading to the excited state production. The lower intensity observed in the presence of hemin can be related to the contribution of the globin chains.