Physical and electrochemical characterizations of microwave-assisted polyol preparation of carbon-supported PtRu nanoparticles

PtRu nanoparticles supported on Vulcan XC-72 carbon and carbon nanotubes were prepared by a microwave-assisted polyol process. The catalysts were characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). The PtRu nanoparticles, which were uniformly dispersed on carbon, were 2-6 nm in diameter. All PtRu/C catalysts prepared as such displayed the characteristic diffraction peaks of a Pt face-centered cubic structure, excepting that the 2theta values were shifted to slightly higher values. XPS analysis revealed that the catalysts contained mostly Pt(0) and Ru(0), with traces of Pt(II), Pt(IV), and Ru(IV). The electro-oxidation of methanol was studied by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry. It was found that both PtRu/C catalysts had high and more durable electrocatalytic activities for methanol oxidation than a comparative Pt/C catalyst. Preliminary data from a direct methanol fuel cell single stack test cell using the Vulcan-carbon-supported PtRu alloy as the anode catalyst showed high power density.     

Influence of the heating rate on the temperature profiles and on the conversion rate of powdery cellulose and pine sawdust

An experimental study of the thermal decomposition of powdered cellulose and pine sawdust has been performed. The influence of the heating rate on the temperature profiles in the sample and on the solid conversion rate has been studied. A mathematical model without adjustable parameters has been used to calculate the temperature at different points in the solid bed and the average total solid conversion. The experimental results have been compared with those calculated by the model. A good agreement has been obtained for sawdust. Some differences are observed for cellulose at high heating rates, and the influence of the thermal conductivity and the reaction heat on the results has been analysed.     

Phase transfer and its applications in nanotechnology

As nanoparticle syntheses in aqueous and organic systems have their own merits and drawbacks, specific applications may call for the transfer of newly formed nanoparticles from a polar to a non-polar environment (or vice versa) after synthesis. This critical review focuses on the application of phase transfer in nanoparticle synthesis, and features core-shell structures in bimetallic nanoparticles, replacement reactions in organic media, and catalytic properties of various nanostructures. It also describes the reversible organic and aqueous phase transfer of semiconductor and metallic nanoparticles for biological applications, and the use of phase transfer in depositing noble metals on semiconductor nanoparticles (258 references).     

Targeted quantitative bioanalysis in plasma using liquid chromatography/high-resolution accurate mass spectrometry: an evaluation of global selectivity as a function of mass resolving power and extraction window, with comparison of centroid and profile modes

There is a growing interest in exploring the use of liquid chromatography coupled with full-scan high resolution accurate mass spectrometry (LC/HRMS) in bioanalytical laboratories as an alternative to the current practice of using LC coupled with tandem mass spectrometry (LC/MS/MS). Therefore, we have investigated the theoretical and practical aspects of LC/HRMS as it relates to the quantitation of drugs in plasma, which is the most commonly used matrix in pharmacokinetics studies. In order to assess the overall selectivity of HRMS, we evaluated the potential interferences from endogenous plasma components by analyzing acetonitrile-precipitated blank human plasma extract using an LC/HRMS system under chromatographic conditions typically used for LC/MS/MS bioanalysis with the acquisition of total ion chromatograms (TICs) using 10 k and 20 k resolving power in both profile and centroid modes. From each TIC, we generated extracted ion chromatograms (EICs) of the exact masses of the [M + H](+) ions of 153 model drugs using different mass extraction windows (MEWs) and determined the number of plasma endogenous peaks detected in each EIC. Fewer endogenous peaks are detected using higher resolving power, narrower MEW, and centroid mode. A 20 k resolving power can be considered adequate for the selective determination of drugs in plasma. To achieve desired analyte EIC selectivity and simultaneously avoid missing data points in the analyte EIC peak, the MEW used should not be too wide or too narrow and should be a small fraction of the full width at half maximum (FWHM) of the profile mass peak. It is recommended that the optimum MEW be established during method development under the specified chromatographic and sample preparation conditions. In general, the optimum MEW, typically ≤ ±20 ppm for 20 k resolving power, is smaller for the profile mode when compared with the centroid mode.     

Naturally-occurring nitro compounds

Naturally-occurring nitro compounds display great structural diversity, and a wide range of biological activities. This review summarizes current information on the structures of naturally-occurring nitro compounds and on the biosynthesis of the nitro group.     

Rational design of a Tn antigen mimic

A novel Tn antigen mimic, in which the natural underlying amino acid has been replaced by the non-natural α-methylserine analogue, is reported. This derivative exhibits a similar affinity for a natural lectin as for the natural Tn and retains the bioactive conformation observed in the Tn-containing glycopeptides with anti-MUC1 antibodies.     

Spectroscopic, structural, and conformational properties of (Z)-4,4,4-trifluoro-3-(2-hydroxyethylamino)-1-(2-hydroxyphenyl)-2-buten-1-one, C12H12F3NO3: a trifluoromethyl-substituted β-aminoenone

The (Z)-4,4,4-trifluoro-3-(2-hydroxyethylamino)-1-(2-hydroxyphenyl)-2-buten-1-one (C(12)H(12)F(3)NO(3)) compound was thoroughly studied by IR, Raman, UV-visible, and (13)C and (19)F NMR spectroscopies. The solid-state molecular structure was determined by X-ray diffraction methods. It crystallizes in the P2(1)/c space group with a = 12.1420(4) ?, b = 7.8210(3) ?, c = 13.8970(5) ?, β = 116.162(2)°, and Z = 4 molecules per unit cell. The molecule shows a nearly planar molecular skeleton, favored by intramolecular OH···O and NH···O bonds, which are arranged in the lattice as an OH···O bonded polymer coiled around crystallographic 2-fold screw-axes. The three postulated tautomers were evaluated using quantum chemical calculations. The lowest energy tautomer (I) calculated with density functional theory methods agrees with the observed crystal structure. The structural and conformational properties are discussed considering the effect of the intra- and intermolecular hydrogen bond interactions.     

Anisotropy on the collective dynamics of water confined in swelling clay minerals

Collective excitations of water confined in the interlayer space of swelling clay minerals were studied by means of inelastic neutron scattering. The effect of bidimensional confinement on the dynamics of the interlayer water was investigated by using a synthetic Na-saponite sample with a general formula of Si(7.3)Al(0.7)Mg(6)O(20)(OH)(4)Na(0.7) in a bilayer hydration state. Experimental results reveal two inelastic signals, different from those described for bulk water with a clear anisotropy on the low-energy excitation of the collective dynamics of interlayer water, this difference being stronger in the perpendicular direction. Results obtained for the parallel direction follow the same trend as bulk water, and the effect of the confinement is mainly manifested from the fact that clay interlayer water is more structured than bulk water. Data obtained in the perpendicular direction display a nondispersive behavior below a cutoff wavenumber value, Q(c), indicating a nonpropagative excitation below that value. Molecular dynamics simulations results agree qualitatively with the experimental results.     

Laboratory studies of CHF2CF2CH2OH and CF3CF2CH2OH: UV and IR absorption cross sections and OH rate coefficients between 263 and 358 K

Fluorinated alcohols, such as 2,2,3,3-tetrafluoropropanol (TFPO, CHF(2)CF(2)CH(2)OH) and 2,2,3,3,3-pentafluoropropanol (PFPO, CF(3)CF(2)CH(2)OH), can be potential replacements of hydrofluorocarbons with large global warming potentials, GWPs. IR absorption cross sections for TFPO and PFPO were determined between 4000 and 500 cm(-1) at 298 K. Integrated absorption cross sections (S(int), base e) in the 4000-600 cm(-1) range are (1.92 ± 0.34) × 10(-16) cm(2) molecule(-1) cm(-1) and (2.05 ± 0.50) × 10(-16) cm(2) molecule(-1) cm(-1) for TFPO and PFPO, respectively. Uncertainties are at a 95% confidence level. Ultraviolet absorption spectra were also recorded between 195 and 360 nm at 298 K. In the actinic region (λ > 290 nm), an upper limit of 10(-23) cm(2) molecule(-1) for the absorption cross sections (σ(λ)) was reported. Photolysis in the troposphere is therefore expected to be a negligible loss for these fluoropropanols. In addition, absolute rate coefficients for the reaction of OH radicals with CHF(2)CF(2)CH(2)OH (k(1)) and CF(3)CF(2)CH(2)OH (k(2)) were determined as a function of temperature (T = 263-358 K) by the pulsed laser photolysis/laser induced fluorescence (PLP-LIF) technique. At room temperature, the average values obtained were k(1) = (1.85 ± 0.07) × 10(-13) cm(3) molecule(-1) s(-1) and k(2) = (1.19 ± 0.03) × 10(-13) cm(3) molecule(-1) s(-1). The observed temperature dependence of k(1)(T) and k(2)(T) is described by the following expressions: (1.35 ± 0.23) × 10(-12) exp{-(605 ± 54)/T} and (1.36 ± 0.19) × 10(-12) exp{-(730 ± 43)/T} cm(3) molecule(-1) s(-1), respectively. Since photolysis of TFPO and PFPO in the actinic region is negligible, the tropospheric lifetime (τ) of these species can be approximated by the lifetime due to the homogeneous reaction with OH radicals. Global values of τ(OH) were estimated to be of 3 and 4 months for TFPO and PFPO, respectively. GWPs relative to CO(2) at a time horizon of 500 years were calculated to be 8 and 12 for TFPO and PFPO, respectively. Despite the higher GWP relative to CO(2), these species are not expected to significantly contribute to the greenhouse effect in the next decades since they are short-lived species and will not accumulate in the troposphere even as their emissions grow up.     

Integration of gold nanoparticles in optical resonators

The optical absorption of one-dimensional photonic crystal based resonators containing different types of gold nanoparticles is controllably modified by means of the interplay between planar optical cavity modes and localized surface plasmons. Spin-casting of metal oxide nanoparticle suspensions was used to build multilayered photonic structures that host (silica-coated) gold nanorods and spheres. Strong reinforcement and depletion of the absorptance was observed at designed wavelength ranges, thus proving that our method provides a reliable means to modify the optical absorption originated at plasmonic resonances of particles of arbitrary shape and within a wide range of sizes. These observations are discussed on the basis of calculations of the spatial and spectral dependence of the optical field intensity within the multilayers.