Mechanisms of air oxidation of ethoxylated surfactants--computational estimations of energies and reaction behaviors

Pathways for formation of previously observed autoxidation products of ethoxylated surfactants have been studied by DFT (B3LYP). In addition to the established radical-chain reaction, several mechanistic possibilities for intramolecular fragmentation of the intermediate radicals have been characterized concerning reaction barriers and energies of transition states. The results can rationalize the formation of previously observed autoxidation products, including several, which have been implicated as strongly allergenic.     

A Series of Low-Coordinate Iron Selenido Complexes: Reactivity of a Linear Iron(I) Silylamide towards Selenium

A variety of different low-coordinate iron selenide complexes is reported. These are obtained by reaction of the linear iron(I) silylamide K{18c6}[Fe(N(Dipp)SiMe₃)₂] (Dipp=2,6-diisopropylphenyl) with red selenium. Careful adjustment of the reaction conditions results in the formation of unique low-coordinate selenido iron complexes, namely a monoselenide bridged [2Fe−1Se]²⁺ complex, as well as mononuclear iron per- and triselenides. Further, C−H bond activation of one of the silylamide ligands by a putative terminal iron monoselenide is observed.     

Hermiticity of Hamiltonian Matrix using the Fourier Basis Sets in Bond-Bond-Angle and Radau Coordinates

In quantum calculations a transformed Hamiltonian is often used to avoid singularities in a certain basis set or to reduce computation time. We demonstrate for the Fourier basis set that the Hamiltonian can not be arbitrarily transformed. Otherwise, the Hamiltonian matrix becomes non-hermitian, which may lead to numerical problems. Methods for correctly constructing the Hamiltonian operators are discussed. Specific examples involving the Fourier basis functions for a triatomic molecular Hamiltonian (J=0) in bond-bond angle and Radau coordinates are presented. For illustration, absorption spectra are calculated for the OClO molecule using the time-dependent wavepacket method. Numerical results indicate that the non-hermiticity of the Hamiltonian matrix may also result from integration errors. The conclusion drawn here is generally useful for quantum calculation using basis expansion method using quadrature scheme.     

Pressure-adjusted continual flow heart-cutting for the high throughput determination of amphetamine-type stimulant drugs in whole blood by fast multidimensional gas chromatography-mass spectrometry

Innovative features and technical improvements in modern bench-top quadrupole gas chromatograph-mass spectrometer (GC-MS) have prepared the way for faster and more cost-effective applications while still maintaining sufficient chromatographic resolution, speed of MS data acquisition and reliability of analytical methodology. In this paper, a short wide-bore capillary column with low film thickness (5 m x 0.32 mm i.d., 0.1 microm) was used a pre-fractionating column and only chosen heart-cuts were transferred to the second chromatographic dimension (15 m x 0.25 mm i.d., 0.25 microm) by means of a pressure-adjusted continual flow type switching device for quantification of five common amphetamine-type stimulant drugs. The instrumental setting used, in combination with carefully optimized operational fast GC and MS parameters, markedly decreased the retention times of the targeted analytes, e.g., amphetamine 0.891 min and methamphetamine 1.037 min, and the total chromatographic runtime (1.700 min), as well as reducing the need for continuous cleaning of the MS ion source and increasing column life compared with conventional GC-MS approaches. The performance of the instrumental configuration and analytical method was evaluated in validation experiments and the method was also applied to authentic samples. The method demonstrates the potential of fast GC-MS in combination with a gas-phase microfluidic Deans switch device for analysing of (semi)volatile compounds, such as amphetamine-type stimulant (ATS) drugs. This should be particularly useful in modern laboratories aiming at cost-efficient analysis as well as the optimum use of available laboratory capacity and instrumentation.     

Determination of the Nanostructure of Polymer Materials by Electron Paramagnetic Resonance Spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy is one the few methods that can characterize structural features in the range between 0.5 and 5 nm in systems that lack long‐range order. Approaches based on EPR spectroscopy provide good structural contrast even in complex materials, as the sites of interest can be selectively labeled or addressed by suitably functionalized spin probes using well established techniques. This article assesses the EPR experiments available for distance measurements on nanoscales in terms of the accessible distance range, precision, and sensitivity. Recommendations are derived for the proper choice of experiment for a given problem. Both simple and sophisticated methods for data analysis are described and their limitations are evaluated. It is discussed which assumptions must be made to extract a pair correlation function from EPR data. Finally, applications to the study of polymer chain conformation and the structure of ionically functionalized diblock copolymers are highlighted.     

Serial MR imaging of intracranial metastases after radiosurgery

Purpose: To evaluate the spatiotemporal evolution of radiosurgical induced changes both in metastases and in normal brain tissue adjacent to the lesions by serial magnetic resonance (MR) imaging. Methods and Materials: Thirty-five intracranial metastases of different primaries were treated in 25 patients by single high-dose radiosurgery. MR images acquired before radiosurgery were available in all patients. Sixty-three follow-up MR studies were performed in these patients including T₂- and contrast-enhanced T₁-weighted MR images. The average follow-up time was 9 ± 5 months (mean ± standard deviation [SD]). Based on contrast-enhanced T₁-weighted MR images, tumor response was radiologically classified in the following four groups: stable disease was assumed if the average tumor diameter after treatment did not show a tumor shrinkage of more than 50% and an increase of more than 25%, partial remission as a shrinkage of tumor size of more than 50%, a disappearance of contrast-enhancing tumor as a complete remission, and an increase of tumor diameter of more than 25% as tumor progress. Moreover, we analysed signal changes on T₂-weighted images in brain parenchyma adjacent to the enhancing metastases. Results: The overall mean survival time was 10.5 ± 7 months, with a 1-year actuarial survival rate of 40%. Stable disease, partial or complete remission of the metastatic tumor was observed in 22 patients (88%). Central or homogeneous loss of contrast enhancement appeared to be a good prognostic sign for stable disease or partial remission. This association was statistically significant (p < 0.05). Three patients (12%) suffered from tumor progression. In eight patients (32%) with stable disease or partial remission, signal changes on T₂-weighted images were observed in tissue adjacent to the contrast enhancing lesions. A progression of the high signal on T₂-weighted images was seen in seven of the eight patients between 3 and 6 months after therapy, followed by a signal regression 6–18 months after irradiation. Conclusion: MR imaging is a sensitive imaging tool to evaluate tumor response as well as the presence or absence of adjacent parenchymal changes following radiosurgery. Loss of homogeneous or central contrast enhancement on Gd-enhanced MR images appeared to be a good prognostic sign for tumor response. Tumor shrinkage seems not to be dependent on time. In addition, most cases of radiation induced changes in normal brain parenchyma observed on T₂-weighted images seem to be self limited.     

Crystal Structure of BaNb6.3(1)Ti3.6(1)O16 containing Nb6O12, fused Ti3O13 Clusters and Ti3O10 Units

A new phase, BaNb_6.3(1)Ti_3.6(1)O₁₆, has been synthesised. Electron diffraction studies indicate an hexagonal substructure with unit cell parameters a ≈ 8.9 Å and c ≈ 9.5 Å. In some of the ED patterns superstructure reflections are present, indicating a supercell with a = √3 · a_sub and c = c_sub. However, X‐ray single‐crystal diffraction studies of a crystallite yielding reflections corresponding to the supercell revealed it to be monoclinic, with the unit cell parameters a = 26.811(2) Å, b = 15.4798(2) Å, c = 9.414(2) Å, β = γ = 90° and α = 90.0(3)°. The average crystal structure was refined, using the subcell with a = 8.937(2) Å, b = 15.479(2) Å, c = 9.414(2) Å, β = γ = 90° and α = 90.0(3)°, space group Cm11, and Z = 4, to R_I = 3.24% and R_wI = 3.44%. The structure can be described as an hexagonal close packing layers of Nb₆ octahedra, Ba, and O atoms (A1, A2) and layers of O atoms (B1, B2), appearing in the packing sequence: A1B1A2B2. The Nb₆ octahedra are found in isolated Nb₆O₁₂O₆ clusters, and the Ti atoms in Ti₃O₁₃ and Ti₃O₁₀ units in octahedral and tetrahedral voids formed by O atoms, respectively. The Ti positions were found to be only partly occupied. Microanalysis indicates that some Nb atoms are located in the Ti₃ triangles. A model is presented that interprets these not fully occupied Ti₃ triangles as a result of a superimposing of three different structures. Two of these consist of two fused Ti₃O₁₃ units, forming an Ti₆O₁₉ unit, and a Ti₃O₁₀ unit, while the third consists of alternating Ti₃O₁₃ units.