High mobility of dithiophene-tetrathiafulvalene single-crystal organic field effect transistors

Single-crystal field effect transistors of the organic semiconductor dithiophene-tetrathiafulvalene (DT-TTF) were prepared by drop casting. Long, thin crystals connected two microfabricated gold electrodes, and a silicon substrate was used as a back gate. The highest hole mobility observed was 1.4 cm2/Vs, which is the highest reported for an organic semiconductor not based on pentacene. A high ON/OFF ratio of at least 7 x 105 was obtained for this device.     

Nanogel nanosecond photonic crystal optical switching

We developed a robust nanosecond photonic crystal switching material by using poly(N-isopropylacrylamide) (PNIPAM) nanogel colloidal particles that self-assemble into crystalline colloidal arrays (CCAs). The CCA was polymerized into a loose-knit hydrogel which permits the individual embedded nanogel PNIPAM particles to coherently and synchronously undergo their thermally induced volume phase transitions. A laser T-jump from 30 to 35 degrees C actuates the nanogel particle shrinkage; the resulting increased diffraction decreases light transmission within 900 ns. Additional transmission decreases occur with characteristic times of 19 and 130 ns. Individual NIPAM sphere volume switching occurs in the approximately 100 ns time regime. These nanogel nanosecond phenomena may be useful in the design of fast photonic crystal switches and optical limiting materials. Smaller nanogels will show even faster volume phase transitions.     

Highly conjugated p-quinonoid pi-extended tetrathiafulvalene derivatives: a class of highly distorted electron donors

A new class of pi-extended TTF-type electron donors (11 a-c) has been synthesized by Wittig-Horner olefination of bianthrone (9) with 1,3-dithiole phosphonate esters (10 a-c). In cyclic voltammetry experiments, donors 11 a-c reveal a single, electrochemically irreversible oxidation-yielding the corresponding dicationic products-at relatively low oxidation potentials (approximately 0.7-0.8 V). Theoretical calculations, performed at the DFT level (B3 P86/6-31 G*), predict a highly-folded C(2h) structure for 11 a. In the ground state, the molecule adopts a double saddle-like conformation to compensate the steric hindrance. The calculations suggest that the intramolecular charge transfer associated with the HOMO-->LUMO transition is responsible for an absorption band observed above 400 nm. While the radical cation 11 a*+ retains the folded C(2h) structure predicted for the neutral molecule as the most stable conformation, the dication 11 a(2+) has a fully aromatic D(2) structure, formed by an orthogonal 9,9'-bianthryl central unit to which two singly-charged dithiole rings are attached. The drastic conformational changes that compounds 11 undergo upon oxidation account for their electrochemical properties. By means of pulse radiolysis measurements, radical-induced one-electron oxidation of 11 a-c was shown to lead to the radical cation species (11 a-c*+), which were found to disproportionate with generation of the respective dication species (11 a-c(2+)) and the neutral molecules (11 a-c).     

Structure of colloid silica determined by viscosity measurements

The viscosity of nanosized colloid silica suspensions, used as binders in the investment casting, was determined as a function of their weight fraction reaching 52%. A new capillary viscometer was used whose construction eliminated sedimentation effects. The experiments have been carried out at fixed pH 10.0 and controlled ionic strength. It was found that for a low silica concentration range (weight fraction below 5%) the suspension viscosity increased more rapidly than the Einstein theory predicts. This anomalous behavior could not be explained in terms of the primary electroviscous effect predicted to be a few orders of magnitude smaller as observed. This discrepancy was accounted for by postulating a fuzzy, gel-like structure of colloid silicas used in our experiments. Hence, the apparent hydrodynamic radius of silica particles in aqueous suspensions was found to be larger than the primary particle size in accordance with previous observations. Based on this postulate, an apparent density of the silica sols was found to be 1.32-1.37 g/cm(3) instead of 2.2-2.32 g/cm(3) as determined from the suspension dilution method. This behavior was interpreted in terms of the core/shell model with high shell porosity, reaching 85%. Similarly, for higher concentration ranges, silica viscosity increased more rapidly with increased sol concentration than predicted by the Batchelor model derived for hard particles. The deviation was attributed to the secondary electroviscous effect stemming from the electrostatic interactions among silica particles in sheared suspensions. This effect has quantitatively been interpreted in terms of Russel's theory. On the other hand, for the high concentration range the experimental results were well accounted for by the Dougherty-Krieger model. By exploiting our experimental findings a sensitive method of determining the structure and apparent density of silica sols in aqueous media was proposed.     

Global ab initio potential energy surfaces for the O2(3Σg-)+O2(3Σg-) interaction

Completely ab initio global potential energy surfaces (PESs) for the singlet and triplet spin multiplicities of rigid O(2)((3)Σ(g)(-))+O(2)((3)Σ(g)(-)) are reported for the first time. They have been obtained by combining an accurate restricted coupled cluster theory with singles, doubles, and perturbative triple excitations [RCCSD(T)] quintet potential [Bartolomei et al., J. Chem. Phys. 128, 214304 (2008)] with complete active space second order perturbation theory (CASPT2) or, alternatively, multireference configuration interaction (MRCI) calculations of the singlet-quintet and triplet-quintet splittings. Spherical harmonic expansions, containing a large number of terms due to the high anisotropy of the interaction, have been built from the ab initio data. The radial coefficients of these expansions are matched at long range distances with analytical functions based on recent ab initio calculations of the electric properties of the monomers [M. Bartolomei, E. Carmona-Novillo, M. I. Hernández, J. Campos-Martínez, and R. Hernández-Lamoneda, J. Comput. Chem. (2010) (in press)]. The singlet and triplet PESs obtained from either RCCSD(T)-CASPT2 or RCCSD(T)-MRCI calculations are quite similar, although quantitative differences appear in specific terms of the expansion. CASPT2 calculations are the ones giving rise to larger splittings and more attractive interactions, particularly in the region of the absolute minima (in the rectangular D(2h) geometry). The new singlet, triplet, and quintet PESs are tested against second virial coefficient B(T) data and, their spherically averaged components, against integral cross sections measured with rotationally hot effusive beams. Both types of multiconfigurational approaches provide quite similar results, which, in turn, are in good agreement with the measurements. It is found that discrepancies with the experiments could be removed if the PESs were slightly more attractive. In this regard, the most attractive RCCSD(T)-CASPT2 PESs perform slightly better than the RCCSD(T)-MRCI counterpart.     

Comparison of protein precipitation methods for various rat brain structures prior to proteomic analysis

Sample preparation is a fundamental step in proteomic methodologies. The quality of the results from a proteomic experiment is dependent on the nature of the sample and the properties of the proteins. In this study, various pre-treatment methods were compared by proteomic analysis; we analysed various rat brain structures after chloroform/methanol, acetone, TCA/acetone and TCA protein precipitation procedures. The protein content of the supernatant was also examined by 2-DE. We found that for four of the rat brain structures, precipitation with chloroform/methanol and acetone delivered the highest protein recovery for top-down proteomic analysis; however, TCA precipitation resulted in good protein separation and the highest number of protein spots in 2-DE. Moreover, TCA precipitation also gave high efficiency of protein recovery if prior sonication procedure was performed.     

Comparative performance of extraction strategies for polycyclic aromatic hydrocarbons in peats

The assessment of historical trends in atmospheric deposition of organic contaminants by using peat samples has been reported on several occasions because these samples represent an almost ideal medium for recording temporal changes in organic contaminant deposition rates. The determination of polycyclic aromatic hydrocarbons (PAHs) in peat samples is complicated due to the high content of organic matter in peat, which affects both extraction efficiency and analytical quality. A rapid and simple method is proposed for the determination of 10 US Environmental Protection Agency indicator PAHs in complex matrices such as peat. This article reviews and addresses the most relevant analytical methods for determining PAHs in peat. We discuss and critically evaluate three different extraction procedures, such as ultrasound-assisted solvent extraction (UASE), shaking and pressurized liquid extraction (PLE). Clean-up of extracts was performed by solid-phase extraction using silica cartridges. Detection of the selected PAHs was carried out by high-performance liquid chromatography coupled with fluorescence detection for determination. Optimization of the variables affecting extraction by the selected extraction techniques was conducted, concluding that the UASE extraction method using hexane:dichloromethane (80:20) as extractant was robust enough to determine the selected PAHs in peat samples with estimated quantification limits between 0.050 and 3.5 μg/kg depending on the PAH. UASE did not demand sophisticated equipment and long extraction times. PLE involved sophisticated equipment and showed important variations in the results. The method proposed was applied to the determination of PAHs in peat samples from Xistral Mountains (Galicia, Spain).     

One-step in-syringe ionic liquid-based dispersive liquid–liquid microextraction

Dispersive liquid–liquid microextraction (DLLME) has been proved to be a powerful tool for the rapid sample treatment of liquid samples providing at the same time high enrichment factors and extraction recoveries. A new, simple and easy to handle one step in-syringe set-up for DLLME is presented and critically discussed in this paper. The novel approach avoids the centrifugation step, typically off-line and time consuming, opening-up a new horizon on DLLME automation. The suitability of the proposal is evaluated by means of the determination of non-steroidal anti-inflammatory drugs in urine by liquid chromatography/ultraviolet detection. In the presented approach an ionic liquid is used as extractant. The target drugs can be determined in urine within the concentration range 0.02–10 μg mL⁻¹, allowing their determination at therapeutic and toxic levels. Limits of detection were in the range from 8.3 ng mL⁻¹ (indomethacin) to 32 ng mL⁻¹ (ketoprofen). The repeatability of the proposed method expressed as RSD (n = 5) varied between 2.5% (for ketoprofen) and 8.6% (for indomethacin).     

Copper(II) and lanthanoid(III) complexes of a new β-diketonate ligand with an appended non-coordinating phenol group

New mononuclear compounds of the ligand 1-(2-hydroxyphenyl)-3-phenylpropane-1,3-dione (H₂L) with Cu(II) and several lanthanoid(III) ions, where Ln(III) = Pr, Nd, Eu, Gd, have been synthesized and characterized by spectroscopic methods and X-ray crystal structure determinations. In all compounds, the ligand coordinates in a bidentate chelating manner, using the diketone function. In the [Cu(HL)₂], the coordination geometry of Cu(II) ion is slightly distorted square-planar; two strong intramolecular (OH?O) hydrogen-bonding interactions are established between the phenolate group and the neighboring ketone function. The lanthanoid(III) compounds have the general formula [Ln(HL)₃(CH₃OH)₂] · CH₃OH · 2H₂O; the lanthanoid(III) ion (Ln) is eight-coordinated and the coordination geometry is based on a distorted square-antiprism. In addition to the intramolecular hydrogen bonding (OH?O), intermolecular hydrogen-bonding interactions are also present between the coordinated methanol molecule and the non-coordinated methanol molecule giving rise to a three-dimensional network.