1H and 13C solution- and solid-state NMR investigation into wax products from the Fischer-Tropsch process

(1)H and (13)C solid- and solution-state NMR have been used to characterise waxes produced in the Fischer-Tropsch reaction, using Co-based catalysts either unpromoted or promoted with approximately 1 wt% of either cerium or rhenium. The aim was to measure average structural information at the submolecular level of the hydrocarbon waxes produced, along with identification of the minor products, such as oxygenates and olefins, which are typically observed in these waxes. A parameter of key interest is the average number of carbon atoms within the hydrocarbon chain (N(C)). A wax prepared using an unpromoted Co/Al(2)O(3) catalyst had N(C)～20, whilst waxes made using rhenium- or cerium-promoted Co/Al(2)O(3) catalysts were found to have N(C)～21. All three samples contained small amounts of oxygenates and alkenes. The subtle differences found in the waxes, in particular the minor species produced, demonstrate that the different promoters have different effects during the reaction, with the Re-promoted catalyst producing the fewest by-products. It is shown in (13)C solid-state NMR spectra that for that for longer chain (compared to the lengths of chain in previous studies) waxes that the lack of resolution and the complexities added by the differential cross-polarisation (CP) dynamics mean that it is difficult to accurately determine N(C) from this approach. However the N(C) determined by (13)C CP magic angle spinning NMR is broadly consistent with the more accurate solution approaches used and suggest that the wax characteristics do not change in solution. On this basis an alternative approach for determining N(C) is suggested based on (1)H solution state NMR that provides a higher degree of accuracy of the chain length as well as information on the minor constituents.     

Polarization and angular correlation studies of X-rays emitted in relativistic ion-atom collisions

Particle and photon polarization phenomena occurring in collisions of relativistic ions with matter have recently attracted particular interest. Investigations of the emitted characteristic x-ray and radiative electron capture radiation has been found to be a versatile tool for probing our present understanding of the dynamics of particles in extreme electromagnetic fields. Owing to the progress in x-ray detector technology, in addition, accurate measurements of the linear polarization for hard x-ray photons as well as the determination of the polarization plane became possible. This new diagnostic tool enables one today to derive information about the polarization of the ion beams from the photon polarization features of the radiative electron capture process.     

Equivariant Configuration Spaces

The compression theorem is used to prove results for equivariantconfiguration spaces that are analogous to the well-known non-equivariantresults of May, Milgram and Segal.     

Sediment flow in inclined vessels calculated using a multiphase particle-in-cell model for dense particle flows

Sedimentation of particles in an inclined vessel is predicted using a two-dimensional, incompressible, multiphase particle-in-cell (MP-PIC) method. The numerical technique solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Mapping particle properties to an Eulerian grid and then mapping back computed stress tensors to particle positions allows a complete solution of sedimentation from a dilute mixture to close-pack. The solution scheme allows for distributions of types, sizes and density of particles, with no numerical diffusion from the Lagrangian particle calculations. The MP-PIC solution method captures the physics of inclined sedimentation which includes the clarified fluid layer under the upper wall, a dense mixture layer above the bottom wall, and instabilities which produce waves at the clarified fluid and suspension interface. Measured and calculated sedimentation rates are in good agreement.     

Gaussian Fluctuations of Eigenvalues in Wigner Random Matrices

We study the fluctuations of eigenvalues from a class of Wigner random matrices that generalize the Gaussian orthogonal ensemble. We begin by considering an n×n matrix from the Gaussian orthogonal ensemble (GOE) or Gaussian symplectic ensemble (GSE) and let x _k denote eigenvalue number k. Under the condition that both k and n?k tend to infinity as n→∞, we show that x _k is normally distributed in the limit. We also consider the joint limit distribution of eigenvalues $(x_{k_{1}},\ldots,x_{k_{m}})$ from the GOE or GSE where k ₁, n?k _m and k _i+1?k _i , 1≤i≤m?1, tend to infinity with n. The result in each case is an m-dimensional normal distribution. Using a recent universality result by Tao and Vu, we extend our results to a class of Wigner real symmetric matrices with non-Gaussian entries that have an exponentially decaying distribution and whose first four moments match the Gaussian moments.     

Exploring the functionalisation of the thieno[2,3-d]pyrimidinedione core: Late stage access to highly substituted 5-carboxamide-6-aryl scaffolds

The thieno[2,3-d]pyrimidinedione core is found as a component in a range of pharmaceutically active compounds, however, synthetic approaches to these scaffolds rely on access to functionalised, highly substituted thiophenes. Here we describe a new approach for the preparation of 5-carboxamide-6-aryl analogues that involves a two-step synthesis of the thieno[2,3-d]pyrimidinedione core from a readily available mercaptouracil derivative. Thio-alkylation with ethyl 3-bromopyruvate, followed by cyclisation and dehydration mediated by polyphosphoric acid allowed the scalable synthesis of the thieno[2,3-d]pyrimidinedione unit. The late-stage functionalisation of this core motif via bromination of the thiophene ring and a subsequent Suzuki-Miyaura reaction as the key steps permitted access to a novel library of 5-carboxamide-6-aryl analogues. The physicochemical properties of these compounds were determined, generating an insight into the potential bioavailability of these scaffolds. Based on these results, a selection of the novel 5-carboxamide-6-aryl analogues were tested as lactate uptake inhibitors of monocarboxylate transporters 1, 2 and 4 in Xenopus oocytes.     

Liquid chromatography post-column oxidation (PCOX) method for the determination of paralytic shellfish toxins in mussels, clams, oysters, and scallops: collaborative study

Sixteen laboratories participated in a collaborative study to evaluate method performance parameters of a liquid chromatographic method of analysis for paralytic shellfish toxins (PST) in blue mussels (Mytilus edulis), soft shell clams (Mya arenaria), sea scallops (Placopectin magellanicus), and American oysters (Crassostrea virginicus). The specific analogs tested included saxitoxin, neosaxitoxin, gonyautoxins-1 to -5, decarbamoyl-gonyautoxins-2 and -3, decarbamoyl-saxitoxin, and N-sulfocarbamoyl-gonyautoxin-2 and -3. This instrumental technique has been developed as a replacement for the current AOAC biological method (AOAC Official Method 959.08) and an alternative to the pre-column oxidation LC method (AOAC Official Method 2005.06). The method is based on reversed-phase liquid chromatography with post-column oxidation and fluorescence detection (excitation 330 nm and emission 390 nm). The shellfish samples used in the study were prepared from the edible tissues of clams, mussels, oysters, and scallops to contain concentrations of PST representative of low, medium, and high toxicities and with varying profiles of individual toxins. These concentrations are approximately equivalent to 1/2 maximum level (ML), ML, or 2xML established by regulatory authorities (0.40, 0.80, and 1.60 mg STX diHCl eq/kg, respectively). Recovery for the individual toxins ranged from 104 to 127%, and recovery of total toxin averaged 116%. Horwitz Ratio (HorRat) values for individual toxins in the materials included in the study were generally within the desired range of 0.3 to 2.0. For the estimation of total toxicity in the test materials, the reproducibility relative standard deviation ranged from 4.6 to 20%. A bridging study comparing the results from the study participants using the post-column oxidation (PCOX) method with the results obtained in the study director's laboratory on the same test materials using the accepted reference method, the mouse bioassay (MBA; AOAC Official Method 959.08), showed that the average ratio of results obtained from the two methods was 1.0. A good match of values was also achieved with a new certified reference material. The results from this study demonstrated that the PCOX method is a suitable method of analysis for PST in shellfish tissue and provides both an estimate of total toxicity, equivalent to that determined using the MBAAOAC Official Method 959.08, and a detailed profile of the individual toxin present in the sample.     

Selective rotation pulses calculated with an inverse scattering algorithm

Selective rotation pulses cause magnetization within a given frequency range (or slice) to undergo a specified rotation, about a specified axis. Magnetization outside this slice remains unaffected if it is initially along the z axis. It has previously been shown that the design of such pulses can be reduced to the design of selective "point-to-point" pulses, which rotate magnetization within the slice from the y axis. By decomposing the point-to-point pulses into two sub-pulses, it is shown that an inverse scattering algorithm for selective pulse design can be used to calculate selective rotation pulses with any desired spinor response, subject to the constraint that the second spinor component have constant phase across the slice. The design of selective refocusing pulses can be treated specially, requiring the calculation, by the same inverse scattering algorithm, of a single sub-pulse.