Kinetic Study of the Thermopolymerization of Furfuryl Methacrylate in Bulk by Mathematical Modeling. Part A: Simulation of Experimental Data and Sensitivity Analysis of Kinetic Parameters

Mathematical modeling of the thermopolymerization of FM and CMFMA was carried out using a cross‐linked kinetic model proposed for the photo‐initiated polymerization of acryl‐furanic compounds. In this model, the photochemical initiation step was substituted by a thermal one and it was assumed that the constant of radical termination was time‐dependent, which allowed the gel effect (Trommsdorff) at high monomer conversion to be simulated. Optimization of all kinetic constants was achieved and the results of simulation suitably fitted the experimental data of the monomer conversion. The contribution of each step in the mechanism and its dependence on the experimental conditions were estimated by a sensitivity analysis technique.

     

Resolving stoichiometries and oligomeric states of glutamate synthase protein complexes with curve fitting and simulation of electrospray mass spectra

A complicating factor in analyzing electrospray ionization mass spectra of intact macromolecular heterogeneous protein complexes is the potential overlap of ions from different species present in solution. Therefore, it is often not possible to assign all ion signals. With the aim of allowing the more efficient and comprehensive analysis of very complex mass spectra of intact heterogeneous protein complexes we developed a software program: SOMMS. The program uses simple user input parameters together with Gaussian curve fitting to simulate putative mass spectra of protein (sub)complexes within a specified charge state window. In addition, the program can simulate spectra for heterogeneous protein complexes using bi- and multinomial distributions and it can calculate zero-charge spectra and relatively quantify the abundance of each component in a mixture. As a proof of concept we analyzed the complex mass spectra of alpha-glutamate synthase and alphabeta-glutamate synthase from Azosprillum brasilense. Using our program we could determine that alpha-glutamate synthase is in equilibrium between its dimeric, tetrameric, hexameric and dodecameric conformation, whereas alphabeta-glutamate synthase forms up to 15 different heterooligomeric assemblies composed of alpha- and beta-subunits. Thus, SOMMS allows resolving stoichiometries and oligomeric states of protein complexes even from very complicated mass spectra. These complexes could not be assigned by using maximum entropy calculations. We compared our mass spectrometry data on glutamate synthases with available X-ray, small-angle X-ray scattering and size-exclusion chromatography data.     

Aldol condensation reactions of [Co(η-C4Ph4){η-C5H4C(O)CH3}]

The aldol condensation reaction between [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₃}] and a range of aromatic aldehydes [RCHO] and [RCHCH-CHO] gives a series of α,β-unsaturated ketones [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CHCH-R}] and [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CHCH-CHCH-R}] (3). The reaction is promoted by various bases: NaH proved to be the most effective whilst ⁿBuLi gave [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(OH)(ⁿBu)CH₃}] as the major product. NaOH was ineffective, perhaps indicating that that the methyl protons in [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₃}] are less acidic than those in [Fe(η⁵-C₅H₅){η⁵-C₅H₄C(O)CH₃}]. Compounds 3 were characterised spectroscopically. Their ¹H NMR spectra are consistent with a trans configuration about their CC bond, and this was confirmed by X-ray crystallography in five cases, which showed that all have the same basic structure with parallel cyclobutadiene and cyclopentadienyl ligands, but they are not identical. The C₅H₄C(O)(CHCH)_n-R (n = 1 or 2) moieties show little evidence for delocalisation and often deviate from planarity. The UV/Vis spectra of those 3 with smaller aromatic rings (R = C₆H₅, 4-C₆H₄NMe₂, 2-C₄H₃S and 1-C₁₀H₇) suggest that these are donor-π-acceptor systems, but as the annellation of R increases (R = 9-C₁₄H₉, 1-C₁₆H₉ and 1-C₂₀H₁₁) the spectra increasingly resemble those of the parent polycyclic aromatic hydrocarbon, RH. Reduction of [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CHCH-C₁₀H₇-1}] with DIBAL gives a mixture of [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₂CH₂-C₁₀H₇-1}] and [Co(η⁴-C₄Ph₄){η⁵-C₅H₄CH(OH)CHCH-C₁₀H₇-1}]. A minor product from the preparation of [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₃}] was shown by X-ray crystallography to be the η⁴-butadiene complex [Co{η⁴-Ph(H)CC(Ph)-C(Ph)C(H)Ph}{η⁵-C₅H₄C(O)CH₃}].     

Landau-Level Quantization of the Yellow Excitons in Cuprous Oxide

Lately, the yellow series of P-excitons in cuprous oxide could be resolved up to the principal quantum number n = 25. Adding a magnetic field, leads to additional confinement normal to the field. Thereby, the transition associated with the exciton n is transformed into the transition between the electron and hole Landau levels with quantum number n, once the associated magnetic length becomes smaller than the related exciton Bohr radius. The magnetic field of this transition scales roughly as n^–3. As a consequence of the extended exciton series, we are able to observe Landau level transitions with unprecedented high quantum numbers of more than 75.     

Design and characterization of arrayed waveguide gratings using ultra-low loss Si3N4 waveguides

Planar waveguides with ultra-low propagation loss are necessary for integrating optoelectronic systems that require long optical time delay or narrowband optical filters. In this paper, we review an ultra-low loss planar waveguide platform that uses thin (<150 nm) Si₃N₄ cores and thick (>8 μm) SiO₂ cladding layers. In particular, we discuss the performance of arrayed waveguide gratings (AWGs) fabricated with the platform. We propose the use of a practical design method that takes the statistical nature of worst-case crosstalk into account. We also demonstrate the measurement of amplitude and phase error distributions in an AWG using an optical backscatter reflectometer. We show that the waveguides have phase errors small enough to achieve AWG crosstalk below ?30 dB, while crosstalk below ?40 dB should also be possible with optimization of the component design.     

Does double electron capture lead to the formation of biradicals? An ECD-SORI-CID study on lacticin 481

We studied lacticin 481, a small lantibiotic with three lanthionine bridges, by electron capture dissociation (ECD) in a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Following electron capture, very little fragmentation was observed, but species formed by nondissociative single and multiple electron capture were abundant. Ions formed by double electron capture were subjected to sustained off resonance irradiation collision induced dissociation (SORI-CID) to determine whether stable biradicals were formed. In the SORI-CID spectra of the ions formed by double electron capture, some, but minor, H* radical loss was observed, which was not observed at all for regularly protonated ions. A small part of the ions formed by double electron capture are thus long-lived biradicals. Apart from the observed H* loss, the SORI-CID spectra of ions that captured two electrons was similar to that of regularly protonated ions and quite different from the SORI-CID spectra of radical ions formed by single electron capture. This implies that recombination of the two radical sites is the dominant process in biradical lacticin 481 ions, at least on the time scale of our SORI-CID experiments.     

Capillary electrophoretic bioanalysis of therapeutically active peptides with UV and mass spectrometric detection after on-capillary preconcentration.

An earlier developed capillary electrophoresis (CE) system with an on-capillary adsorptive phase is investigated for its suitability to quantitate low concentrations of angiotensin II and gonadorelin in plasma. An off-line solid-phase extraction is used for sample preparation. The on-line preconcentration CE system allows multiple capillary volumes of sample solution to be injected, increasing the concentration sensitivity of CE with 3-4 orders of magnitude. Furthermore, possible influence of matrix salts can be ruled out by employing a rinsing step after sample application. Using short-wavelength UV detection, reproducibility and linearity in the low nanomolar range were satisfactory. The capillary could be efficiently regenerated using a programmed between-run rinsing procedure, allowing 20-30 large injections of sample extracts. Coating of the capillary improved the robustness of the method. Mass spectrometric detection via a previously reported sheathless interface increased the selectivity and sensitivity substantially. Recommendations are provided for the sample preparation process, the most critical part of the system. Further purification of the sample is required to allow the loading of larger sample volumes and to optimize the system's robustness.     

Segregation of iron inCuAuFe alloys

TheCuAuFe system has been studied by room temperature Mössbauer spectroscopy in order to examine the influence of varying both iron (Cu_94?yAu₆Fe_y; y=0.2–1.0 at%) and gold (Cu_99?xAu_xFe₁; x=6–50.7 at%) concentrations on the clustering of iron atoms. Samples were examined in different metallurgical states, as rolled, fast quenched and melt spun with similar degrees of clustering being observed. The isomer shift is found to vary inversely with atomic volume for the Cu_99?xAu_xFe₁ alloys.     

Phase synchronization of chaotic oscillations in terms of periodic orbits

We consider phase synchronization of chaotic continuous-time oscillator by periodic external force. Phase-locking regions are defined for unstable periodic cycles embedded in chaos, and synchronization is described in terms of these regions. A special flow construction is used to derive a simple discrete-time model of the phenomenon. It allows to describe quantitatively the intermittency at the transition to phase synchronization. (c) 1997 American Institute of Physics.