Die schirmwirkung zylindersymmetrischer nichtferromagnetischer körper gegen magnetische wechselfelder

The screening effect of a finite nonferromagnetic symmetric cylinder is investigated theoretically and experimentally. The work is based on the definitions for the screening effect with respect to frequency and phase response. A mathematical solution is obtained by solving the integral equation for the magnetic vector potential. Experimental tests support the theoretical results. It is shown that the short cylinder with certain design parameters provides a far better screening effect (in particular for attenuation peaks) than does a cylinder of infinite length. This applies to certain regions at the cylinder openings. This effect is caused by current displacement in the axial direction.     

Mass spectrometric characterization of 4-oxopentanoic acid and gas-phase ion fragmentation mechanisms studied using a triple quadrupole and time-of-flight analyzer hybrid system and density functional theory

4-Oxopentanoic acid was characterized experimentally by electrospray ionization using a triple quadrupole and time-of-flight analyzer hybrid system. This compound was chosen as a model substance for small organic compounds bearing an acetyl and a carboxyl group. Collision-induced dissociation experiments at different activation energies were performed to elucidate possible fragmentation pathways. These pathways were also studied on the theoretical level using density functional theory (DFT) B3LYP/6-311++G(3df,3pd)//B3LYP/6-31+G(d)+ZPVE calculations. CO2 ejection from the [M-H](-) anion of 4-oxopentanoic acid was observed and the fragmentation pathway studied by DFT reveals a new concerted mechanism for CO2 elimination accompanied by an intramolecular proton transfer within a pentagonal transition state structure. Successive elimination of water and CO from the [M-H](-) anion of 4-oxopentanoic acid was also observed. A rearrangement in the primary deprotonated ketene anion produced after water elimination was found on the theoretical level and leads to CO elimination from the primary product anion [M-H-H2O](-). Energy diagrams along the reaction coordinates of the fragmentation pathways are presented and discussed in detail. Mulliken charge distributions of some important structures are presented.     

Determination of higher carboxylic acids in snow samples using solid-phase extraction and LC/MS-TOF

The objective of this work was to develop a method to determine the concentrations of higher organic acids in snow samples. The target species are the homologous aliphatic alpha,omega-dicarboxylic acids from C(5) to C(13), pinonic acid, pinic acid and phthalic acid. A preconcentration procedure utilizing solid phase extraction was developed and optimized using solutions of authentic standards. The influences of different parameters such as flow rate during extraction and the concentration of the eluent on the efficiency of the extraction procedure were investigated. The compounds of interest were separated by HPLC and detected by a quadrupole time-of-flight mass spectrometer (qTOF-MS). The recovery rate (extraction efficiency) of the extraction procedure was found to vary between 41% for tridecanedioic acid and 102% for adipic acid. The limits of detection were determined for all compounds and were between 0.9 nmol/L (dodecanedioic acid) and 29.5 nmol/L (pinonic acid). An exception is pinic acid, for which a considerably higher detection limit of 103.9 nmol/L was calculated. Snow samples were collected in December 2006 and January 2007 at the Fee glacier (Switzerland) from locations at heights from 3056 to 3580 m asl and from different depths within the snow layer. In total, the analysis of 61 single snow samples was performed, and the following compounds could be quantified: homologous aliphatic alpha,omega-dicarboxylic acids with 5-12 carbon atoms and phthalic acid. Tridecanedioic acid, pinonic and pinic acid were identified in the samples but were not quantified due to their low concentrations. The three most abundant acids found in the molten snow samples were glutaric acid (C(5)-di; 3.90 nmol/L), adipic acid (C(6)-di; 3.35 nmol/L) and phthalic acid (Ph; 3.04 nmol/L).     

On-line size exclusion chromatography-pyrolysis-gas chromatography-mass spectrometry for copolymer characterization and additive analysis

On-line coupled size exclusion chromatography-pyrolysis gas chromatography mass spectrometry (SEC-Py-GC-MS) is studied as a novel tool for the characterization of complex polymer samples. An automated system for on-line SEC-Py-GC-MS allowing transfer of multiple fractions was developed based on stop-flow operation of the SEC dimension, syringe-based transfer of the SEC fraction to the GC instrument and solvent elimination with subsequent pyrolysis in a programmed temperature vaporization (PTV) injector. After optimization the system was applied to the characterization of a complex terpolymer composed of very similar monomers. The use of the system for combined pyrolysis and additive analyses in polycarbonate was also demonstrated. Results obtained with the new method indicate the interesting potentials of the method for detailed characterization of polymeric materials.     

Plumbonacrite Identified by X‐ray Powder Diffraction Tomography as a Missing Link during Degradation of Red Lead in a Van Gogh Painting

Red lead, a semiconductor pigment used by artists since antiquity, is known to undergo several discoloration phenomena. These transformations are either described as darkening of the pigment caused by the formation of either plattnerite (β‐PbO₂) or galena (PbS) or as whitening by which red lead is converted into anglesite (PbSO₄) or (hydro)cerussite (2 PbCO₃?Pb(OH)₂; PbCO₃). X‐ray powder diffraction tomography, a powerful analytical method that allows visualization of the internal distribution of different crystalline compounds in complex samples, was used to investigate a microscopic paint sample from a Van Gogh painting. A very rare lead mineral, plumbonacrite (3 PbCO₃? Pb(OH)₂?PbO), was revealed to be present. This is the first reported occurrence of this compound in a painting dating from before the mid 20th century. It constitutes the missing link between on the one hand the photoinduced reduction of red lead and on the other hand (hydro)cerussite, and thus sheds new light on the whitening of red lead.     

Solid state NMR study of nanodiamond surface chemistry

Solid state NMR measurements using 13C, 1H and 19F nuclei (MAS, CP-MAS) underline the surface chemistry of nanodiamonds from different synthesis (detonation, high pressure high temperature and shock compression). The comparison of the spin-lattice relaxation times T1 and physicochemical characterization (spin densities of dangling bonds, specific surface area and Raman and infrared spectroscopies) for the various samples, as synthesized, chemically purified and fluorinated allows the nature and the location of the various groups, mainly C-OH, C-H and C-F to be investigated. C-OH groups are located only on the surface whereas C-H and dangling bonds seem to be distributed in the whole volume. Fluorination was studied as a chemical treatment for purification and change of the hydrophobicity through the conversion of the C-OH groups into covalent C-F bonds.     

A heterobimetallic ruthenium-gadolinium complex as a potential agent for bimodal imaging

Trinuclear heterobimetallic Ln(III)-Ru(II) complexes (Ln = Eu, Gd) based on a 1,10-phenanthroline ligand bearing a diethylenetriaminepentaacetic acid (DTPA) core have been synthesized and fully characterized by a range of experimental techniques. The (17)O NMR and proton nuclear magnetic relaxation dispersion (NMRD) measurements of Gd(III)-Ru(II) show that, in comparison to the parent Gd-DTPA, this complex exhibits improved relaxivity, which is the result of an increase of the rotational correlation time. Relaxometry and ultrafiltration experiments indicate that the 1,10-phenanthroline ligand has a high affinity for noncovalent binding to human serum albumin, which results in a high relaxivity r(1) of 14.3 s(-1) mM(-1) at 20 MHz and 37 °C. Furthermore, the Ln(III)-Ru(II) complexes (Ln = Eu, Gd) show an intense light absorption in the visible spectral region due to metal-to-ligand charge transfer (MLCT) transitions. Upon excitation into the MLCT band at 440 nm, the complexes exhibit a bright-red luminescence centered at 610 nm, with a quantum yield of 4.7%. The luminescence lifetime equals 540 ns and is therefore long enough to exceed the fluorescent background. Monometallic lanthanide complexes have also been synthesized, and the Eu(III) analogue shows a characteristic red luminescence with a quantum yield of 0.8%. Taking into account the relaxometric and luminescent properties, the developed Gd(III)-Ru(II) complex can be considered as a potential in vitro bimodal imaging agent.