New innovations in ionic liquid–based miniaturised amperometric gas sensors

Gas detection is an essential part of everyday life; for some applications, using sensors for toxic and hazardous gases can literally mean the difference between life and death. In this minireview, recent progress in amperometric gas sensing using miniaturised electrodes and devices is described. The focus is on the use of nonvolatile room-temperature ionic liquids (RTILs) as electrolytes, which possess inherent advantages such as wide electrochemical windows, high thermal and chemical stability, intrinsic conductivity and good solvating properties. Various different gases, electrodes and RTILs have been investigated in the strive towards new materials for improved gas sensors. The most recent developments using porous membrane electrodes, planar devices (e.g. screen-printed, thin-film, microarray and interdigitated electrodes) and the modification of these surfaces for improved sensitivity are described. RTILs have great potential to be used as electrolytes in amperometric gas sensors, with improved lifespan of the sensor in hot/dry environments and allowing miniaturisation of devices. However, it is clear that more understanding of their long-term operation and utility in real environments (e.g. background air, varying temperatures and humidity levels) is needed before their realisation in successful commercial devices.     

Interaction of pyridine‐ and 4‐hydroxypyridine‐2,6‐dicarboxylic acids with heavy metal ions in aqueous solutions

Interactions between pyridine‐2,6‐dicarboxylic acid and 4‐hydroxypyridine‐2,6‐dicarboxylic acid with Cu(II), Pb(II), and Cd(II) ions were characterized in aqueous solutions (20°C; I = 0.4 (KNO₃)) by means of dc‐polarography. In solutions with excess of ligand, Cu(II), Pb(II), and Cd(II) form 1:2 complexes with the tridentate dianion of pyridine‐2,6‐dicarboxylic acid (dipic²⁻) from weak acid to alkaline solutions. The values of log β₂ for Cu(II), Pb(II), and Cd(II) are 16.1, 11.8, and 11.0, respectively. The complexing ability of pyridine‐2,6‐dicarboxylic acid is higher in acid solutions and lower in alkaline solutions than that of 4‐hydroxypyridine‐2,6‐dicarboxylic acid. This difference is attributed to the OH‐group, which can deprotonate in basic pH. In acid solutions the OH‐group acts as an electron acceptor and reduces the electron donation available to the nitrogen atom in 4‐hydroxypyridine‐2,6‐dicarboxylic acid, whereas in alkaline solutions the OH‐group is deprotonated, and the deprotonated O₋ group acts as an electron donor and increases the coordination ability of the ligand. The triple‐deprotonated anion of 4‐hydroxypyridine‐2,6‐dicarboxylic acid (chel^3‐) forms a stable diligand complex with Cu(II), the stability constant logarithm being 21.5 ± 0.2.© 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:625–632, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10203     

Diverse morphologies of zinc oxide nanoparticles and their electrocatalytic performance in hydrogen production

Hydrogen is considered an attractive alternative to fossil fuels,but only a small amount of it is produced from renewable energy,making it not such a clean energy carrier after all.Producing hydrogen through water electrolysis is promising,but using a cost-effective and high-performing catalyst that has longterm stability is still a challenge.This study exploits,for the first time,the potential of zinc oxide nanoparticles with diverse morphologies as catalysts for the electrocatalytic production of hydrogen from water.The morphology of the nanoparticles(wires,cuboids,spheres)was easily regulated by changing the concentration of sodium hydroxide,used as the shape controlling agent,during the synthesis.The spherical morphology exhibited the highest electrocatalytic activity at the lowest potential voltage.These spherical nanoparticles had the highest number of oxygen vacancies and lowest particle size compared to the other two morphologies,features directly linked to high catalytic activity.However,the nanowires were much more stable with repeated scans.Density-functional theory showed that the presence of oxygen vacancies in all three morphologies led to diminished band gaps,which is of catalytic interest.     

高速A/D转换器的选择--在选择A/D变换器时,其应用场合是一条重要的依据

模数转换器是连接模拟和数字世界的一个重要接口.A/D转换器将现实世界的模拟信号变换成数字位流以进行处理、传输及其他操作.     

Microchip separations of protein biotoxins using an integrated hand-held device

We report the development of a hand-held instrument capable of performing two simultaneous microchip separations (gel and zone electrophoresis), and demonstrate this instrument for the detection of protein biotoxins. Two orthogonal analysis methods are chosen over a single method in order to improve the probability of positive identification of the biotoxin in an unknown mixture. Separations are performed on a single fused-silica wafer containing two separation channels. The chip is housed in a microfluidic manifold that utilizes o-ring sealed fittings to enable facile and reproducible fluidic connection to the chip. Sample is introduced by syringe injection into a septum-sealed port on the device exterior that connects to a sample loop etched onto the chip. Detection of low nanomolar concentrations of fluorescamine-labeled proteins is achieved using a miniaturized laser-induced fluorescence detection module employing two diode lasers, one per separation channel. Independently controlled miniature high-voltage power supplies enable fully programmable electrokinetic sample injection and analysis. As a demonstration of the portability of this instrument, we evaluated its performance in a laboratory field test at the Defence Science and Technology Laboratory with a series of biotoxin variants. The two separation methods cleanly distinguish between members of a biotoxin test set. Analysis of naturally occurring variants of ricin and two closely related staphylococcal enterotoxins indicates the two methods can be used to readily identify ricin in its different forms and can discriminate between two enterotoxin isoforms.     

4-Hydroxypyridine-2,6-dicarboxylatodioxovanadate(V) complexes: solid state and aqueous chemistry

The aqueous solution and solid state properties of (4-hydroxypyridine-2,6-dicarboxylato)dioxovanadate(V) (also referred to as (4-hydroxydipicolinato)dioxovanadate(V) or (chelidamato)dioxovanadate(V) and abbreviated [VO(2)(dipic-OH)](-)) were investigated. By using (1)H, (13)C, (17)O, and (51)V NMR 1D and 2D spectroscopy, the species present in solution, together with pK(a) values, equilibrium constants, and labilities, were characterized. The complex is most stable at acidic pH down to pH 1 where it is protonated. The stability of this complex is higher than that of the parent dipicolinatodioxovanadate(V) complex. The dipic-OH ligand is coordinated in a tridentate manner throughout the pH range studied, and the vanadium(V) atom is five-coordinate. Solid state structures of (NMe(4))[VO(2)(dipic-OH)].H(2)O (monoclinic, P2(1)/n) and Na[VO(2)(dipic-OH)].2H(2)O (triclinic, P1) were determined. The discrete complex anions in (NMe(4))[VO(2)(dipic-OH)].H(2)O are connected by hydrogen bonding between the hydroxyl group, a water molecule, and a carboxylate oxygen atom. Changing the counterion from NMe(4)(+) to sodium ion in Na[VO(2)(dipic-OH)].2H(2)O leads to the formation of a polymeric structure. Dynamic processes in solution were explored by using (1)H and (13)C EXSY NMR spectroscopy; exchange between complex and free ligand below pH 4 was observed. The differences between the dipicolinatodioxovanadate(V) parent complex and the [VO(2)(dipic-OH)](-) complex in the solid state and in solution demonstrate the subtle consequences of the one substitutional difference between the two ligands. The insulin-mimetic properties of this compound are likely to be of mechanistic interest in developing an understanding of the mode of action of the few known insulin-mimetic vanadium(V) complexes.     

The 17O hyperfine interaction in V17O(H217O)52+ and Mn(H217O)62+ determined by high field ENDOR aided by DFT calculations

The 17O hyperfine interaction of the water ligands and the V=O oxygen in the vanadyl aquo complex and of the water ligands in the Mn2+ aquo complex in a frozen solution were determined by W-band (95 GHz) electron-nuclear double resonance (ENDOR). Orientation selective ENDOR spectra of the vanadyl complex exhibited two distinct signals assigned to the vanadyl oxygen and the water ligands. The assignment of the signals was done based on the orientation of the principal axis system of the hyperfine interaction and through comparison with the hyperfine interaction predicted by DFT calculations. The latter showed good agreement with the experimental values thus providing clear evidence that the vanadyl oxygen is exchangeable. The interaction of the vanadyl oxygen, especially its anisotropic part, was significantly larger than that of the water oxygens due to a relatively large negative spin density on the oxygen p orbitals. The 17O hyperfine interaction of the water ligand in the Mn2+ complex was found to be similar to that of the water ligand in the vanadyl complex and was in good agreement with earlier single-crystal data. Here, due to the large thermal polarization, it was also possible to determine the absolute sign of the hyperfine coupling by selecting different EPR transitions.