The use of imidazolium ionic liquids for the formation and stabilization of ir0 and rh0 nanoparticles: efficient catalysts for the hydrogenation of arenes

Stable transition-metal nanoparticles of the type [M(0)](n) are easily accessible through the reduction of Ir(I) or Rh(III) compounds dissolved in "dry" 1-n-butyl-3-methylimidazolium hexafluorophosphate ionic liquid by molecular hydrogen. The formation of these [M(0)](n) nanoparticles is straightforward; they are prepared in dry ionic liquid whereas the presence of the water causes the partial decomposition of ionic liquid with the formation of phosphates, HF and transition-metal fluorides. Transmission electron microscopy (TEM) observations and X-ray diffraction analysis (XRD) show the formation of [Ir(0)](n) and [Rh(0)](n) nanoparticles with 2.0-2.5 nm in diameter. The isolated [M(0)](n) nanoparticles can be redispersed in the ionic liquid, in acetone or used in solventless conditions for the liquid-liquid biphasic, homogeneous or heterogeneous hydrogenation of arenes under mild reaction conditions (75 degrees C and 4 atm). The recovered iridium nanoparticles can be reused several times without any significant loss in catalytic activity. Unprecedented total turnover numbers (TTO) of 3509 in 32 h, for arene hydrogenation by nanoparticles catalysts, have been achieved in the reduction of benzene by the [Ir(0)](n) in solventless conditions. Contrarily, the recovered Rh(0) nanoparticles show significant agglomeration into large particles with a loss of catalytic activity. The hydrogenation of arenes containing functional groups, such as anisole, by the [Ir(0)](n) nanoparticles occurs with concomitant hydrogenolysis of the C-O bond, suggesting that these nanoparticles behave as "heterogeneous catalysts" rather than "homogeneous catalysts".     

Enhanced fluorescence from arrays of nanoholes in a gold film

Arrays of sub-wavelength holes (nanoholes) in gold films were used as a substrate for enhanced fluorescence spectroscopy. Seven arrays of nanoholes with distinct periodicities (distances between the holes) were fabricated. The arrays were then spin-coated with polystyrene films containing different concentrations of the fluorescent dye oxazine 720. The dye was excited via resonant extraordinary transmission of the laser source through the nanoholes. Enhanced fluorescence was observed when the geometric characteristics of the arrays allowed for an enhancement in the transmitted excitation. This enhancement occurred via surface plasmon excitation by the laser and a consequential increase in the local electromagnetic field in a sub-wavelength region at the metal-film interface. It was demonstrated that the sensitivity of the fluorescence measurement (change in signal vs change in dye concentration in the polymer film) is significantly larger at the surface plasmon resonance conditions than that obtained from equivalent films on glass substrates. Enhancement factors for the fluorescence emission were calculated for each array, with a maximum enhancement of close to 2 orders of magnitude as compared to the emission of films on glass. The results presented here indicate that arrays of nanoholes are interesting substrates for the development of fluorescence sensors based on surface plasmon resonance, as they provide a platform that allows both spatial confinement and enhancement of excitation light. Moreover, the collinear characteristics of the present optical setup, due to the resonant extraordinary transmission through the nanohole arrays, are more conducive to miniaturization and chip integration than more traditional experimental geometries.     

Specific influence of univalent cations on the ionization of alumina-coated TiO2 particles and on the adsorption of poly(acrylic)acid

A surface counterion titration method was used to monitor the interaction of monovalents cations (Li(+), Na(+), TMA(+)) with the surface of alumina-coated TiO(2) particles in concentrated media at different pH and electrolyte concentrations. This method allows measuring separately the negative and positive contribution to the surface charge. It showed that Cl(-) and TMA(+) are indifferent ions, but Li(+) and Na(+) specifically adsorb on the non-ionized alumina surface sites. The binding sequence of cations is Li(+)>Na(+)>TMA(+) at all ionic strengths investigated and is consistent with the structure-making and structure-breaking model developed a few decades ago. Polyacrylic acid (PAA) previously neutralized with the corresponding hydroxide (LiOH, NaOH, TMAOH) has been adsorbed on the alumina surface at different pH. The polymer counterion has a significant influence on the polymer adsorption. The sequence of the surface coverage as a function of the polymer counterion follows the order Li-PAA > Na-PAA > TMA-PAA. The much higher surface coverage with Li-PAA and Na-PAA compared to TMA-PAA is explained by the specific adsorption of Li-PAA and Na-PAA on the nonionized alumina surface sites, the same way LiCl and NaCl do.     

Optimization of the design and operation of FAIMS analyzers

Field asymmetric waveform ion mobility spectrometry (FAIMS) holds significant promise for post-ionization separations in conjunction with mass-spectrometric analyses. However, a limited understanding of fundamentals of FAIMS analyzers has made their design and operation largely an empirical exercise. Recently, we developed an a priori simulation of FAIMS that accounts for both ion diffusion (including anisotropic components) and Coulomb repulsion, and validated it by extensive comparisons with FAIMS/MS data. Here it is corroborated further by FAIMS-only measurements, and applied to explore how key instrumental parameters (analytical gap width and length, waveform frequency and profile, the identity and flow speed of buffer gas) affect FAIMS response. We find that the trade-off between resolution and sensitivity can be managed by varying gap width, RF frequency, and (in certain cases) buffer gas, with equivalent outcome. In particular, the resolving power can be approximately doubled compared to "typical" conditions. Throughput may be increased by either accelerating the gas flow (preferable) or shortening the device, but below certain minimum residence times performance deteriorates. Bisinusoidal and clipped-sinusoidal waveforms have comparable merit, but switching to rectangular waveforms would improve resolution and/or sensitivity. For any waveform profile, the ratio of two between voltages in high and low portions of the cycle produces the best performance.     

Synthesis of a Naphthalimide Functionalized Calix[4]arene; A Host Type Fluorophore for Inclusion Compounds in Organic Medium

This article reports the synthesis and the properties of 5,11,17,23-tetra(t-butyl)-25,27-bis-(ethoxy-1,8-naphthalimide)-26,28-hidroxy-calix[4]arene and the formation of an inclusion compound in organic medium. This functionalized calix[4]arene was conceived as the association of a potential host species with a good fluorophore for optical sensoring purposes. Calix[4]-NI as we will call it, maintains its ‘cone-pinched’ configuration and exhibits typical naphthalimide fluorescence bands in non-polar solvents. Its ability to interact with guest species via hydrogen bonding in its endo-hydrophilic cavity to form inclusion compounds was verified with absorption and fluorescence measurements using N-ethanol-1,8-naphthalimide as guest species, which was projected to fit exactly the host cavity and to interact with its naphthalimide π electrons. For this reason, it was possible to follow the formation of the inclusion compound with electronic spectroscopy.     

Practical aspects of carbon content determination in carburized steels by EPMA.

The carbon contents in carburized steels were investigated by electron probe microanalysis (EPMA) for a range of carbon levels in the solid solution less than 1 wt%. This article describes the difficulties encountered with the classic analytical procedure using the k ratio of X-ray intensities and the phi(rhoz) model. Here, a suitable calibration curve method is presented with emphasis on the metallographic study of standard specimens and on the carbon decontamination of samples.     

Aspects of the physical chemistry of polymers, biomaterials and mineralised tissues investigated with atomic force microscopy (AFM)

Beyond being merely a tool for measuring surface topography, atomic force microscopy (AFM) has made significant contributions to various scientific areas dealing with physical chemistry processes. This paper presents aspects of the physical chemistry at surfaces and interfaces of polymers, biomaterials and tissues investigated with AFM. Selected examples presented include surface induced self-assembly of polymer blends, copolymer interfacial reinforcement of immiscible homopolymers, protein adsorption on biomaterials and erosion of mineralised human tissues. In these areas, AFM is a useful and versatile tool to study structural or dynamic sample properties including thermodynamically driven surface evolution of polymer surfaces, lateral surface composition of interfaces, adsorption processes, and the metrology of demineralisation phenomena.     

Copper corrosion in buffered and non-buffered synthetic seawater: a comparative study

The electrochemical behaviour of copper in neutral buffered and non-buffered synthetic seawater and in pure chloride solutions has been studied by cyclic voltammetry, weight loss measurements, open circuit potential and scanning electron microscopy (SEM). Values of the repassivation potentials of Cu in non-buffered and buffered synthetic seawater, at 50 mV s^–1, were 0.12 and 0.46 V vs. SCE, respectively. The sharpness, heights and location of the different peaks as well as their charges were shown to be influenced by the composition of the solution, buffering conditions, deoxygenation, polarization potential and time. High chloride concentrations lead to higher oxidation charges. The anodic and the cathodic charges were shown to increase as the chloride concentration increases. The open circuit potential transients of copper in non-deoxygenated, non-buffered synthetic seawater indicate pitting from the beginning of the exposure, while in buffered solutions the pitting appeared only after a quite long exposure period, i.e. after 40 days. Corrosion rates of Cu samples after 3 months of immersion were higher in solutions of pure chloride (0.5 M) than in synthetic seawater. After six months the differences were even more noticeable. SEM images have showed a somewhat higher density of pits on copper samples immersed in the chloride solution (0.5 M), in comparison with those in synthetic seawater.     

Matrix optimization for matrix-assisted laser desorption/ionization mass spectrometry of oligosaccharides from human milk

Neutral and acidic oligosaccharides from human milk were analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS). These experiments require suitable matrices; their selection and particularly their preparation protocols must be optimized. Important criteria are sensitivity, reproducibility, tolerance against impurities and resolution over a wide mass range. For analytical investigations of these oligosaccharides, containing labile fucosylated and sialylated components, another property of a matrix becomes a significant factor, namely the influence on ion stability and the extent of (metastable) fragmentation. The experience gained with the MALDI/MS of neutral and acidic oligosaccharides is summarized taking into account different intentions of measurement and typical problems, such as impurities after enzymatic treatment. For a rapid screening of an oligosaccharide sample, superior results were obtained with a new preparation technique using 5-chloro-2-mercaptobenzothiazole (CMBT) as the first layer for 2,5-dihydroxybenzoic acid. For structural analysis by post-source decay, CMBT as the first layer for 3-aminoquinoline is a favoured preparation protocol, because extensive fragmentation is achieved. For acidic oligosaccharides, a special preparation protocol makes it possible to determine the number of sialic acids by inducing highly effective cationization. Matrix-assisted laser desorption/ionization mass spectrometry; matrices; oligosaccharides; post-source decay.     

Detailed characterization of (3 x 3) iodine adlayer on Pt(111) by unequal-sphere packing model

A simple unequal-sphere packing model is applied to study the iodine (3x3) adlayer on the Pt(111) surface. By using a newly introduced parameter, defined as the average adsorbate height, three characteristic adlattices, (3x3)-sym, (3x3)-asym, and (3x3)-lin, have been selected and characterized in great detail, including the exact adatom registry. The (3x3)-sym iodine adlattice, observed in many experimental studies, appears to be, on average, the closest one to the substrate surface. A special contour plot of average adsorbate height vs X and Y positions of the (3x3) iodine unit cell indicates the existence of two local minima, which are related to preferential formation of (3x3)-sym and (3x3)-asym iodine adlattices. Our model gives good agreement with experimental findings, and explains the mechanism of preferential appearance of (3x3)-sym and (3x3)-asym structures.