Bulk modes in complex layer structures

Normal modes, dispersions and spectral densities were calculated for macroscopic layer structures with an arbitrary number of layers per periodicity unit. The influence of the arrangement of layers on the band structure is discussed.     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of lipids: ionization and prompt fragmentation patterns

Ionization and prompt fragmentation patterns of triacylglycerols, phospholipids (PLs) and galactolipids were investigated using matrix-assisted laser desorption/ionization (MALDI). Positive ions of non-nitrogen-containing lipids appeared only in the sodiated form, while nitrogen-containing lipids were detected as both sodiated and protonated adducts. Lipids containing acidic hydroxyls were detected as multiple sodium adducts or deprotonated ions in the positive and negative modes, respectively, with the exception of phosphatidylcholines. The positive MALDI spectra of triacylglycerols contained prompt fragments equivalent to the loss of RCOO(-) from the neutral molecules. Prompt fragment ions [PL-polar head](+) were observed in the positive MALDI spectra of all phospholipids except phosphatidylcholines. The phosphatidylcholines produced only a minor positive fragment corresponding to the head group itself (m/z 184). Galactolipids did not undergo prompt fragmentation. Post-source decay (PSD) was used to examine the source of prompt fragments. PSD fragment patterns indicated that the lipid prompt fragment ions did not originate from the observed molecular ions (sodiated or protonated), and suggested that the prompt fragmentation followed the formation of highly unstable, probably protonated, precursor ions. Pathways leading to the formation of prompt fragment ions are proposed.     

Analysis of plant phosphatidylcholines by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The use of matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) for the quantitative determination of phospholipid (PL) molecular species has been problematic, due primarily to the formation of multiple signals (corresponding to the molecular ion and other adducts) for some classes of PL. For example, analysis of phosphatidylcholine (PC) yielded signals that corresponded to protonated and sodiated molecules in the MALDI spectrum. The resulting spectral overlap among various molecular species (e.g. [PC(16:0/18:2) + Na] and [PC(18:2/18:3)]) made it impossible to ascertain their relative amounts using this technique. Other spectral ambiguities existed among different structural isomers, such as PC(18:1/18:1) and PC(18:0/18:2). We determined that molecular species could be resolved by MALDI-TOFMS by first removing the polar head (e.g. phosphocholine) from the phospholipid to effect production of only the sodiated molecules of the corresponding diacylglycerols (DAGs). Analysis of the resulting spectrum allowed unequivocal determination of the molecular species profile of PC from potato tuber and soybean. Estimation of fatty acid composition based on the molecular species determined by MALDI-TOFMS analysis agreed with that from GC-FID analysis. Post-source decay (PSD) was used to resolve standard isomers of PC (e.g. 18:1/18:1 vs. 18:0/18:2). Our results indicated that PSD is a useful approach for resolving structural isomers of PL molecular species.     

Brillouin scattering in layered structures

Theoretical and experimental results on Brillouin scattering in inhomogeneous materials are presented: Normal elastic modes and Brillouin intensities have been calculated for a periodic layer system. Measurements on semicrystalline polybutene-1 are discussed in terms of the theoretical results. Both theory and experiment yield several Brillouin lines in VV scattering instead of the one peak characteristic for homogeneous specimens.     

Anion-exchange and size-exclusion chromatography of proteins in mouse ascites fluid: Changes in the protein pattern during tumour growthIn vivo

Summary During the transition of Ehrlich mouse ascites tumour cells from the proliferating to the resting state of growth a large loss of purine and pyrimidine compounds occurs. This decrease is accompanied by a change in the amount of protein in the supernate of ascites fluid, which is known from the study of the ATP-consumption during protein synthesis. The ascites fluid was investigated by anion-exchange and size-exclusion chromatography (SEC). SDS-PAGE (sodium, dodecyl sulfate-polyacrylamide gel electrophoresis) data were compared with SEC data. The total amount of protein increased by 50% between day 5 and 12 of growth. At least 5 new peaks are observed in the chromatograms of an ion-exchange separation of Ehrlich ascites fluid at day 12 postinoculation. The amounts of transferrin, albumin and IgG (immunoglobulin G) were increased to 132, 134, 157%, respectively duringin vivo growth.     

Infrared and Raman spectroscopy at high pressures

Pressure is accepted theoretically as a useful variable. However in a studies on liquid or solid samples, it is still relatively unusual for pressure to be used as an experimental variable. The reluctance of experimentalists to use this theoretically attractive variable is caused mainly by the technical difficulties associated with the use of sufficiently high pressures. In this talk I will try to show that in many cases the experimental limitations are no longer those introduced by the use of high pressures. High pressure spectroscopic studies clearly imply the use of high pressure spectroscopic cells. A brief account will therefore be given of the various types of high pressure optical cells which are currently being used for spectroscopic studies. Each individual high pressure spectroscopic study has its own special justification. However there are a few quite general observations that can be made which cover many of the specific objectives of individual high pressure spectroscopic studies. For example:(i) pressure induced frequency shifts carry unambiguous information about anharmonic terms in the relevant potential function (i.e. the potential V is a function of distance d. therefore pressure can be used to change d and study V.)(ii) all known materials undergo structural phase transitions if the form which is thermodynamically stable under ambient conditions is compressed to high enough pressures: these high pressure phases should be studied.(iii) as the application of pressure forces a material towards a phase transition, the spectroscopic study can be used to gain information about the approaching structural instability.(iv) virtually all infrared and Raman spectra contain examples of Fermi resonance which confuse the interpretation of the spectra and the effects of pressure are valuable aids to the correct assignment of the resonating levels.(v) pressure induced frequency shifts can often give extra information to help with the more reliable assignment of features within a spectrum.The above points will be discussed and illustrated by examples chosen mainly from recent work by members of the spectroscopy group at King's College London.     

Deformation charge distribution and total energy for perowskites

A microscopic theory of solids is presented which allows the calculation of lattice properties from first principles. The method is based on the Density-Functional-Theory and a new version of the Linear-Muffin-Tin-Orbital method, which includes nonspherical charge distributions in the total energy calculations. Explicit results for BaTiO₃ and SrTiO₃ are reported. The deformations of the charge density due to a homogeneous volume change and due to a soft mode deformation were determined. Differences between BaTiO and SrTiO₃ and the nature of the chemical bonding are discussed. Calculated cohesive energies and lattice constants agree well with experimental data.Dedicated to Prof. Dr. H.E. Müser on the occasion of his 60th birthday     

A detection method for unified chromatography: Ion mobility monitoring

Ion mobility monitoring has been used for detection in gas, supercritical fluid, and liquid chromatography, illustrating its potential as a method of detection for unified chromatography. Applications presented include GC-IMD of dioxins in fly ash, SFC-IMD of vitamin E, and HPLC-IMD of alkylamines. Ion mobility spectra of several mixed supercritical fluid mobile phases are also presented. Use of methanol, acetonitrile, and dichloromethane as modifiers of supercritical carbon dioxide, and use of supercritical dichlorodifluoromethane and chlorodifluoromethane as mobile phases had little effect on the reactant ion pattern at the flow rates and concentrations used in this study. Only when acetone was used as a modifier of carbon dioxide did the positive reactant ions change significantly. No effect of modifiers or mobile phase was observed for the negative reactant ions.     

Evaluation of direct axial sample introduction for ion mobility detection after capillary gas chromatography

An ion mobility detector has been designed and constructed for direct axial interfacing with capillary gas chromatography. The principle advantages of this detector were the following: (1) Direct concentric introduction of the capillary column into the ionization region, eliminating peak broadening in the transfer line and improving the efficiency with which neutral molecules were swept from the detector. (2) A variable capillary insertion distance, providing a sensitivity/resolution interplay that could be modified in response to the needs of the assay. (3) An inert gas flow external to the drift cylinder, preventing atmospheric impurities from infiltrating the ultratrace detector. Qualitative and quantitative capabilities of the detector were evaluated using standard preparations of n-hexyl ether.