Development of a certified reference material for the determination of perfluorooctanoic acid

A certified reference material (CRM) for the determination of perfluorooctanoic acid (PFOA) has been issued as NMIJ CRM 4056-a by the National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). Purity (kg kg^?1) based on a titration method was determined by subtracting the mass fractions of impurities measured using liquid chromatography/mass spectrometry (LC/MS) from those of acids expressed as PFOA measured by a neutralization potentiometric titration. To validate an obtained result, purity based on a mass balance method was determined by subtracting the mass fractions of impurities, measured using LC/MS, Karl-Fischer titration (KFT), and vacuum evaporation, from 1 kg kg^?1. Results from both titration and mass balance methods were in agreement within the accepted limits of uncertainty. The certified purity of NMIJ CRM 4056-a was determined to be 0.959 kg kg^?1, calculated as the mean of the results obtained with the two methods. The standard uncertainty of the certified purity was evaluated from purity evaluations as well as from sample homogeneity and stability obtained from LC/MS and KFT analyses. Consequently, the expanded uncertainty was estimated to be 0.005 kg kg^?1 with a coverage factor of k = 2.     

Efficient Light-Harvesting Antennae Resulting from the Dense Organization of Dyes into DNA Junctions through d-Threoninol

Herein we report the construction of efficient light-harvesting antennae by hybridization of DNA oligonucleotides containing high densities of fluorophores into DNA junctions through d -threoninol. Six pyrene donors could be incorporated into each arm without self-quenching. A perylene acceptor was located at the center of the junction. Antenna effects of a duplex and three- to eight-way junctions were systematically compared. Six- and eight-way junctions had the highest antenna effects, and their effective absorption coefficients were 8.5 times higher than that of perylene. Interestingly, even-numbered junctions had higher efficiencies than odd-numbered junctions. Nondenaturing gel analyses and fluorescence lifetime measurements demonstrated that the strong odd–even effects were derived from differences in the stability of junctions. The results presented will guide the design of efficient artificial photosynthetic systems.     

Preconcentration and determination of cadmium by GFAAS after solid-phase extraction with synthetic zeolite.

The solid-phase extraction (SPE) method for the preconcentration of trace amounts of cadmium using synthetic zeolite A-4 and its determination by graphite furnace atomic absorption spectrometry (GFAAS) was investigated. The preconcentration conditions, such as the optimum pH range of the sample solution for the adsorption of cadmium and the kind of acid solution for dissolving the cadmium-adsorbed synthetic zeolite A-4, as well as the measurement conditions for the determination of cadmium by GFAAS, e.g., the ashing and atomizing temperature, were investigated. Quantitative recovery of cadmium onto zeolite A-4 from the sample solution over the pH range 2.0 - 9.0 was achieved by the batch method. After the solid-phase (cadmium-adsorbed zeolite A-4) was separated from the sample solution by a membrane filter, it was dissolved in 2.0 cm(3) of 2.0 mol dm(-3) nitric acid. An aliquot of the resulting solution was injected into the graphite furnace. In GFAAS measurements an alternate gas (Ar, 90%; O(2), 10%) was used as a sheath gas, and the ashing temperature and atomizing temperature were 400 degrees C and 1600 degrees C, respectively. The detection limit (3 sigma) for cadmium was 0.002 microg dm(-3). The relative standard deviation at 0.010 microg dm(-3) was 3.5 - 4.5% (n = 5). The proposed method has been successfully applied to the analysis of trace cadmium in environmental water samples.     

Hydrogen Production from a Methanol–Water Solution Catalyzed by an Anionic Iridium Complex Bearing a Functional Bipyridonate Ligand under Weakly Basic Conditions

An efficient catalytic system for the production of hydrogen from a methanol–water solution has been developed using a new anionic iridium complex bearing a functional bipyridonate ligand as a catalyst. This system can be operated under mild conditions [weakly basic solution (0.046 mol L^?1 NaOH) below 100 °C] without the use of an additional organic solvent. Long‐term continuous hydrogen production from a methanol–water solution catalyzed by the anionic iridium complex was also achieved.     

A simultaneous space sampling method for DNA fraction collection using a comb structure in microfluidic devices

Fraction collection of selected components from a complex mixture plays a critical role in biomedical research, environmental analysis, and biotechnology. Here, we introduce a novel electrophoretic chip device based on a signal processing theorem that allows simultaneous space sampling for fractionation of ssDNA target fragments. Ten parallel extraction channels, which covered 1.5-mm-long sampling ranges, were used to facilitate the capturing of fast-moving fragments. Furthermore, the space sampling extraction made it possible to acquire pure collection, even from partly overlapping fragments that had been insufficiently separated after a short electrophoretic run. Fragments of 180, 181, and 182 bases were simultaneously collected, and then the recovered DNA was PCR amplified and assessed by CE analysis. The 181-base target was shown to be isolated in a 70-mm-long separation length within 10 min, in contrast to the >50 min required for the 300-mm-long separation channel in our previous study. This method provides effective combination of time and space, which is a breakthrough in the traditional concept of fraction collection on a chip.     

Redox-controlled, reversible rearrangement of a tris(2-pyridylthio)methyl ligand on nickel to an isomer with an “N,S-confused” 2-pyridylthiolate arm

Interchange between the nickel +2 and +3 oxidation states precisely controls the reversible rearrangement of the tris(2-pyridylthio)methanide (tptm) ligand in the organometallic nickel(II) complex [{Ni(μ-Br)-(tptm)}(2)] (2). Oxidation of 2 first gives the corresponding Ni(III) complex [{Ni(μ-Br)(tptm)}(2)][PF(6)](2) (4). However, in solution the tptm ligand in 4 slowly undergoes a rearrangement, in which the N and S atoms of one of the pyridylthiolate arms exchange Ni and C bonding partners, thereby resulting in an "N,S-confused" isomer of tptm in the product, [NiBr(bpttpm)]PF(6) (5; bpttpm= bis(2-pyridylthio)(2-thiopyridinium)-methyl). Reduction of 5 reverses this ligand rearrangement and 2 is reformed quantitatively. The individual steps involved in these unusual ligand rearrangements were investigated by a number of methods, including voltammetric analysis, and a mechanism for this process is proposed. X-ray crystal structure determinations of the key compounds 2, 4 and 5 have been obtained.     

Disruption of reverse micelles and release of trapped ribonuclease A photochemically induced by Malachite Green leuconitrile derivative

Photoinduced disruption of a sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelle is triggered by a Malachite Green leuconitrile derivative (MGL). UV irradiation of MGL solubilized in an AOT-water-chloroform mixture creates a cationic surfactant that interacts electrostatically with the anionic AOT. We investigated the disruption of the reverse micelle by using proton nuclear magnetic resonance spectroscopy and found that UV irradiation of MGL decreases the number of water molecules solubilized in the interior of the AOT reverse micelles. Furthermore, the photoinduced disruption of the reverse micelle is shown to release ribonuclease A, which is trapped in the water in the interior of the AOT reverse micelle. This photoinduced release may offer a desirable transport system of biopolymers.     

On-chip fraction collection for multiple selected ssDNA fragments using isolated extraction channels

High efficiency and high-purity fraction collection is highly sought in analysis of fragments-of-interest from selective polymerase chain reaction (PCR) products generated by High Coverage Gene Expression Profiling (HiCEP) methods. Here we demonstrate a new electrophoretic chip device enabling automatic high-efficient fractionation of multiple ssDNA target fragments during a run of separation. We used thoroughly isolated extraction channels for each selected target to reduce the risk of cross-contamination between targets due to cross-talk of extraction channels. Fragments of 35, 108 and 138 b, were successfully isolated, then the recovery was PCR-amplified and assessed by capillary electrophoresis (CE) analysis. Total impurity level of the targets due to unwanted fragments of 0.7%, 2% and 6% respectively, was estimated. Difficulties in collecting multiple target factions are due to band diffusion and DNA adsorption to the walls for the fragments in the separation channel, which is generated by transferring the DNA target fraction from the extraction section to the target reservoir. Therefore, we have carefully measured band broadening and analyzed its influence on the separation resolution due to the delay.     

On time-like surfaces of positive constant Gaussian curvature and imaginary principal curvatures

We establish the Bäcklund transformation for the construction of time-like surfaces with positive Gaussian curvature and imaginary principal curvatures. The construction can be realized by algebraic algorithm via Darboux transformations.     

Flat translation invariant surfaces in the 3-dimensional Heisenberg group

Flat translation invariant surfaces in 3-dimensional Heisenberg group are classified.