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Combined electrochemical and planar waveguide surface plasmon resonance measurements demonstrating the oxidative desorption through cyclic voltammetry in acid of an alkane thiol monolayer from a gold film are presented in this paper. We show that the thiol film can be systematically removed and we investigate the oxidative mechanism using both a gold wire and evaporated gold on Pyrex surfaces. For the latter we use a combined planar waveguide surface plasmon resonance (SPR) and electrochemical sensor, where the gold pad acts as both the sensing area for SPR measurements and the electrode for electrochemical investigations. The results show a linear relationship between the fractional coverage of the gold electrode and the transmission measured using SPR, and these results are compared to the results of a numerical simulation. This sens...
Spectroscopic and vanadium K-edge EXAFS data on VO2Cl suggest a structure based upon a dimeric OClV(-O)2VClO core linked by longer V···Cl interactions into a polymer. The crystal structure of [{Cl2VO(O2PCl2)(POCl3)}2], obtained from VO2Cland POCl3, shows a centrosymmetric dimer with bridgingPO2Cl2 groups, and terminal POCl3 ligands O-coordinated to each vanadium atom. Cl14O8P4V2: Space group P, Z = 1, lattice dimensions at 120 K: a = 8.039(2), b = 8.1641(15), c = 10.308(3) Å, = 92.586(15), = 103.829(10), = 106.963(15)°; R1 = 0.065.
This paper discusses efficient simulation methods for stochastic chemical kinetics. Based on the -leap and midpoint -leap methods of Gillespie [D. T. Gillespie, J. Chem. Phys. 115, 1716 (2001)], binomial random variables are used in these leap methods rather than Poisson random variables. The motivation for this approach is to improve the efficiency of the Poisson leap methods by using larger stepsizes. Unlike Poisson random variables whose range of sample values is from zero to infinity, binomial random variables have a finite range of sample values. This probabilistic property has been used to restrict possible reaction numbers and to avoid negative molecular numbers in stochastic simulations when larger stepsize is used. In this approach a binomial random variable is defined for a single reaction channel in order to keep the reactio...
This paper discusses H2S and OCS measurements in a variety of museums. It addresses several issues of interpretation of those results, such seasonal and spatial variation, effects of sources and sinks local to the measurement. Typical indoor H2S concentrations found vary from 86 to 600 ppt, whereas OCS varies from 400 to 850 ppt. A lowest observed adverse effect dose (LOAED) for H2S and silver is defined (3.85 μg m−3 yr−1~ 2.5 ppb yr−1). All museum H2S concentration data collected by the authors thus far is compared to this LOAED and in the main found to be considerably lower. Therefore tarnishing is not solely a function of H2S, instead is the result of multiple factors.
A personal selection of 27 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as dibelamcandal A from Belamcanda chinensis.
Density functional theory in conjunction with nonequilibrium Green’s functions has been used to explore charge transport through the cobalt-based extended metal atom chain, Co3(dpa)4(NCS)2. The isolated molecule has a doublet ground state, and the singly occupied σ nonbonding orbital proves to be the dominant transport channel, providing spin filtering efficiencies in excess of 90%. The metal chain differs from typical organic conductors in that the π orbitals that form the contact with the gold electrode are orthogonal to the transport channel. As a result, the rehybridization of these π levels by the applied electric field has only a minor impact on the current, allowing spin filtering to persist even at biases in excess of 1 V.
A novel method has been developed for determining the natural decay series radionuclides (NDS), Pb-210, Bi-210, and Po-210, in seawater by way of state-of-the-art liquid scintillation spectrometry. For Pb-210 analysis, the method makes use of a Pb-212 yield tracer, prepared by ion exchange separation from aged Th(NO3)(4). Bi-210 recovery is determined using Bi-207 as the yield tracer, and Po-210 is determined using the conventional Po-208 yield tracer. The limits of detection for this method are 0.32, 0.34, and 0.004 mBq l(-1) for Pb-210, Bi- 210, and Po-210, respectively. The analysis can be completed within 10 days, as compared with up to one year for traditional methods. Results are presented for a preliminary study of Pb- 210, Bi-210, and Po-210 in the dissolved and particle-bound phases of Irish Sea water.
This paper describes the application of a simple chromium reduction furnace which can be interfaced with a dual inlet isotope-ratio mass spectrometer thus providing the capacity for cheap, fast, accurate and precise measurement of deltaD(V-SMOW) by dynamic mass spectrometry. Measurements are precise to the order of less than or equal to0.5%. Mean 95% confidence intervals for the Vienna Standard Mean Ocean Water (V-SMOW) to Standard Light Antarctic Precipitation (SLAP) range are in the order of 2.5 parts per thousand and the system is linear over the range -428 to 23,000 parts per thousand. Memory effects do exist, but are small for natural abundance samples and can be minimised by careful planning of the analytical load.
There is a growing interest in the use of C-13-enriched substrates to investigate metabolic processes in humans. The non-invasive nature of C-13 breath tests makes them attractive to clinicians, particularly because they can be safely used in children. The availability of suitable C-13-enriched substrates can limit the application of this biotechnology. We have used isotope ratio mass spectrometry to assay the chemical purity and isotopic enrichment of substrates that were synthesised to study gut transit and colonic fermentation. Lactose ureide and lactose [C-13]ureide were synthesised by acid-catalysed condensation of lactose and urea or C-13 urea, respectively. Glucose ureide and glucose [C-13]ureide were synthesised by similar methods but required an additional purification step to remove urea. of crystallisation. Substrates were a...
The issue of comparability of measurements (and thus bias, accuracy, and precision of measurement) from diverse laboratories is one which has been the focus of some attention both within the radiocarbon community and the wider user communities. As a result, the C-14 community has undertaken a widescale, far-reaching, and evolving program of inter- comparisons, to the benefit of laboratories and users alike. The benefit to the users is, however, indirect, since the C-14 intercomparisons have not been used to generate "league tables" of performance, but rather to allow individual laboratories to check procedures and modify them as required. The historical progression of C-14 laboratory intercomparisons from the Third (TIRI, completed in 1995, Gulliksen and Scott 1995) and Fourth (FIRI, completed in 2000, Scott 2003; Boaretto et al. 2000;...
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