Quality of resolution of black multicomponent systems

In this work, we define the quality of selective regions in a data matrix acquired by two-way instrumental methods. We name the quality parameter as the accumulated analytical signal (AAS) and link this quality measure to the resolution quality. The AAS is calculated as the first singular value divided by the second from a singular value decomposition of the selective region. We also extend this measure to systems containing more than two analytes and define the quality of zero-concentration windows (ZCWs). These regions are crucial in the resolution step. The quality parameter of this region is named as the net accumulated analytical signal (NAAS). It is calculated as the last significant singular value divided by the first non-significant singular value from a singular value decomposition of the ZCW. Since it is sometimes difficult to decide the elution regions by local rank analysis, we introduce a shifting procedure. The different elution regions are shifted and the system is resolved using the new elution windows. Indication of a good resolution is found when a stable solution appears.     

Diradical Organic One‐Dimensional Polymers Synthesized on a Metallic Surface

We report on the synthesis and characterization of atomically precise one‐dimensional diradical peripentacene polymers on a Au(111) surface. By means of high‐resolution scanning probe microscopy complemented by theoretical simulations, we provide evidence of their magnetic properties, which arise from the presence of two unpaired spins at their termini. Additionally, we probe a transition of their magnetic properties related to the length of the polymer. Peripentacene dimers exhibit an antiferromagnetic (S=0) singlet ground state. They are characterized by singlet–triplet spin‐flip inelastic excitations with an effective exchange coupling (J_eff) of 2.5 meV, whereas trimers and longer peripentacene polymers reveal a paramagnetic nature and feature Kondo fingerprints at each terminus due to the unpaired spin. Our work provides access to the precise fabrication of polymers featuring diradical character which are potentially useful in carbon‐based optoelectronics and spintronics.     

Fast Gas Chromatographic Assessment of Polychlorobiphenyl Levels in Wall Plaster Coats

Abstract

Sampling (“scrape test”) and analytical procedures were defined to determine PCBs in sorbing solid surfaces such as wall plaster. After sampling, samples were extracted by means of a mechanical device. Following steps included clean-up on a multilayer chromatographic column and assessment with macrobore capillary gas chromatography equipped with an electron capture detector. Mean recovery yields were ≧75% for PCB levels from 2.00 to 7000μg/m² (0.550–1940 μg/kg). Intralaboratory tests performed by two independent operators yielded: (a) maximum deviation from expected value, 25%; (b) maximum deviation between operators, 17%; and (c) maximum variation coefficient, 20%. Background PCB levels in wall surface layer samples were ≧2.9μg/m² (≧0.81 μg/kg). The analytical procedure tested with agricultural topsoil samples provided mean recovery yields >65% for PCB levels ≧500 μg/ kg (≧ 50 mg/m²).     

Amphiphilic silicone architectures via anaerobic thiol-ene chemistry

Despite broad application, few silicone-based surfactants of known structure or, therefore, surfactancy have been prepared because of an absence of selective routes and instability of silicones to acid and base. Herein the synthesis of a library of explicit silicone-poly(ethylene glycol) (PEG) materials is reported. Pure silicone fragments were generated by the B(C(6)F(5))(3)-catalyzed condensation of alkoxysilanes and vinyl-functionalized hydrosilanes. The resulting pure products were coupled to thiol-terminated PEG materials using photogenerated radicals under anaerobic conditions.     

Cooperative use of cytochrome cd1 nitrite reductase and its redox partner cytochrome c552 to improve the selectivity of nitrite biosensing

In this work, a novel enzymatic biosensor for determination of nitrites constructed on an electrochemical transducing platform is proposed. The sensor is based on cytochrome-cd(1) (cyt-cd(1)) nitrite reductase from Marinobacter hydrocarbonoclasticus strain 617 as biological recognition element, and its putative physiological redox partner cytochrome-c(552) (cyt-c(552)), as electron mediator. The proteins were co-immobilized using a photopolymerizable polyvinyl alcohol (PVA) derivative, onto carbon paste screen printed electrodes (CPSPEs); the optimal modification conditions were 100 μM cyt-cd(1)/100 μM cyt-c(552) and 50% PVA, after a 48 h polymerization time. Electrochemical characterization of the mediator was carried out by cyclic voltammetry. The one-electron exchange between cyt-c(552) and the working electrode is a quasi-reversible process, without mass transport limitations. The formal potential of the mediator is 254±2 mV vs NHE and the intermolecular electron transfer rate constant between cytochromes c(552) and cd(1) is 9.9×10(3)M(-1)s(-1). The analytical parameters of the biosensor response to nitrite as assessed by amperometric measurements were: linear range from 10 to 200 μM; detection and quantification limits of 7 and 24 μM, respectively; sensitivity of 2.49±0.08 Amol(-1)cm(2) μM(-1). Catalytic profiles in the presence of possible interfering species were also investigated. The interference from competitive enzymatic reduction of dissolved oxygen could be overcome by tuning the cyclic voltammograms for faster sweep rates.     

Capture of CO<Subscript>2</Subscript> from flue gas by vacuum pressure swing adsorption using activated carbon beads

Vacuum pressure swing adsorption (VPSA) for CO₂ capture has attracted much research effort with the development of the novel CO₂ adsorbent materials. In this work, a new adsorbent, that is, pitch-based activated carbon bead (AC bead), was used to capture CO₂ by VPSA process from flue gas. Adsorption equilibrium and kinetics data had been reported in a previous work. Fixed-bed breakthrough experiments were carried out in order to evaluate the effect of feed flowrate, composition as well as the operating pressure and temperature in the adsorption process. A four-step Skarstrom-type cycle, including co-current pressurization with feed stream, feed, counter-current blowdown, and counter-current purge with N₂ was employed for CO₂ capture to evaluate the performance of AC beads for CO₂ capture with the feed compositions from 15–50% CO₂ balanced with N₂. Various operating conditions such as total feed flowrate, feed composition, feed pressure, temperature and vacuum pressure were studied experimentally. The simulation of the VPSA unit taking into account mass balance, Ergun relation for pressure drop and energy balance was performed in the gPROMS using a bi-LDF approximation for mass transfer and Virial equation for equilibrium. The simulation and experimental results were in good agreement. Furthermore, two-stage VPSA process was adopted and high CO₂ purity and recovery were obtained for post-combustion CO₂ capture using AC beads.     

On the Factors behind the Photocatalytic Activity of Graphene Quantum Dots for Organic Dye Degradation

Graphene quantum dots (GQD) are promising visible-light photocatalysts for organic dye degradation. Besides having improved visible-light activity compared with commercial TiO₂, GQD are versatile photocatalysts as their chemical composition and, consequently, optical properties can be tuned synthetically, with a direct impact on photoactivity. However, there is a lack of systematic comparative studies to benchmark GQD photocatalytic performance and relate it to their intrinsic properties. This is undertaken in this work for three types of GQD, which are prepared using well-established synthetic methods representative of top-down and bottom-up approaches using different precursors. Resulting GQD are similar in size but differ in chemical composition, crystallinity, bandgap (ranging from 2.63 to 3.63 eV) and visible-light absorptivity. Photoactivity measurements under comparable experimental conditions (visible-light illumination) reveal enormous activity differences for rhodamine B (RhB) degradation, with up to tenfold higher degradation yields at the same time for certain GQD types. The enormous influence of intrinsic and tunable GQD factors, like visible-light absorptivity and surface charge, on their photoactivity for the degradation of organic dyes is demonstrated, highlighting the importance of tailoring such parameters for enhanced photocatalytic performance. A plausible mechanism for GQD-catalyzed photodegradation of RhB is also proposed.     

Controlled Growth of SrxBa1−xNb2O6 Hopper- and Cube-Shaped Nanostructures by Hydrothermal Synthesis

Controlling the shape and size of nanostructured materials has been a topic of interest in the field of material science for decades. In this work, the ferroelectric material Sr_xBa_1−xNb₂O₆ (x=0.32–0.82, SBN) was prepared by hydrothermal synthesis, and the morphology is controllably changed from cube-shaped to hollow-ended structures based on a fundamental understanding of the precursor chemistry. Synchrotron X-ray total scattering and PDF analysis was used to reveal the structure of the Nb-acid precursor, showing Lindqvist-like motifs. The changing growth mechanism, from layer-by-layer growth forming cubes to hopper-growth giving hollow-ended structures, is attributed to differences in supersaturation. Transmission electron microscopy revealed an inhomogeneous composition along the length of the hollow-ended particles, which is explained by preferential formation of the high entropy composition, SBN33, at the initial stages of particle nucleation and growth.     

Enantioselective, chemoenzymatic synthesis, and absolute configuration of the antioxidant (−)-gloeosporiol

The natural antioxidant (−)-gloeosporiol, isolated as a peracetylated derivative from a culture of the fungus Colletotrichum gloeosporioides, has been enantioselectively prepared from 3,4-dihydroxybenzaldehyde by means of a chemoenzymatic synthesis. The key intermediate was obtained by resolution with a lipase from Pseudomonas cepacia. Its stereochemistry, initially assigned as R, according to the Kazlaukas empirical rule for secondary alcohols, was independently confirmed by NMR and chirooptic methods. This, in turn, allowed the assignment of compound (−)-1 as (−)-(2S,3R,4R)-2-(3′,4′dihydroxyphenyl)tetrahydrofuran-3,4-diol.     

Insight into the binary mixture of ethyl lactate+acetonitrile from density,speed of sound and refractive index measurements

Density, sound velocity and refractive index of ethyl lactate + acetonitrile mixtures were measured at five temperatures from 283.15 to 323.15 K. Excess molar volumes, partial molar volumes, thermal expansion coefficients, isentropic compressibility and molar refraction values were calculated. It is concluded that deviations from ideality in this system should be assigned to the ability of the smaller acetonitrile molecules to occupy free volume space of ethyl lactate.