Relative quantification of cellular sections with molecular depth profiling ToF-SIMS imaging

We report the use of secondary ion mass spectrometry (SIMS) imaging to quantify the relative difference in the amount of lipid between two sections, the plasma membrane and the cytoplasm, of single cells from two different populations. Cells were each labeled with lipophillic dyes, frozen, fractured and analyzed in a ToF-SIMS mass spectrometer equipped with a 40 keV C₆₀⁺ ion source. In addition to identifying cells from separate populations, the lipophilic dyes can be used as a marker for the outer leaflet of the cell membrane and therefore as a depth finder. Here, we show that it is possible to compare the amount of lipids with particular headgroups in the cell membrane of a treated cell to the membrane of a control cell. Following erosion of the cell membranes, the amount of the two specific lipid head groups in the cytoplasm of the treated cell can be compared to those lipids in a control cell. Here we take the first step in this experimental design and display the ability to analyze multiple sections of frozen cells following a single fracture.     

Preconditioned conjugate gradient methods for large-scale fluid flow applications

The simulation of large-scale fluid flow applications often requires the efficient solution of extremely large nonsymmetric linear and nonlinear sparse systems of equations arising from the discretization of systems of partial differential equations. While preconditioned conjugate gradient methods work well for symmetric, positive-definite matrices, other methods are necessary to treat large, nonsymmetric matrices. The applications may also involve highly localized phenomena which can be addressed via local and adaptive grid refinement techniques. These local refinement methods usually cause non-standard grid connections which destroy the bandedness of the matrices and the associated ease of solution and vectorization of the algorithms. The use of preconditioned conjugate gradient or conjugate-gradient-like iterative methods in large-scale reservoir simulation applications is briefly surveyed. Then, some block preconditioning methods for adaptive grid refinement via domain decomposition techniques are presented and compared. These techniques are being used efficiently in existing large-scale simulation codes.     

Anoxia followed by hyperoxia: In vivo 31-P NMR of cat brain

In vivo ³¹P NMR spectroscopy was performed on a cat brain subjected to an extended period of anoxia followed by restoration of oxygen. High energy phosphate spectra were continuously obtained and pH measured. Following the onset of anoxia, phosphocreatine and ATP peaks decreased with a concomitant increase in inorganic phosphate. Following 34 min ventilation on 100% N₂, the animal was ventilated on 100% O₂. The spectral content progressively changed, inorganic phosphate decreased and ATP increased with the spectrum closely resembling that of control. Our results suggest that the absence of NMR detectable ATP signal cannot be interpreted as an irreversable change in cellular metabolic function.     

NMR parameters of sulphur heterocycles: Solvent and concentration effects for thiophen and related systems

Infinite dilution data for six sulphur heterocycles have been obtained from second order analyses of their NMR spectra in CS₂, CDCl₃, CD₃COCD₃, or C₆D₆. Use of LAOCOON3 leads to accurate chemical shifts, but substantial errors remain in some of the coupling constants. Evidence is presented of specific association of chloroform with the sulphur heterocycles and of the interaction of acetone with the sulphur atom. An apparently anomalous geometry for the complex of benzene with thiophen and with other solutes is discussed. Dilution effects are considered in relation to the formation of solute dimers.     

Electronic properties of Bi2O3 and MoO3 and relationships to oxidation catalysis

A semiempirical atom superposition and electron delocalization molecular orbital analysis of the bonding and electronic structure of MoO₃, oxygen deficient MoO₃, and the α, β, and δ phases of Bi₂O₃ has been made. It is found that both small — e.g. MoO₆ — and large — e.g. Mo₆O₂₄ — clusters are useful models for cation electronic structure within the theory used. From the calculations, an interpretation is given for all available optical and photoemission data for the oxides. The color, conductivity, and new photoemission peak of oxygen-deficient MoO₃ conducting bronzes are found to be due to the addition of electrons to the lowest of three Mo 5d bands which are empty in MoO₃. Weakly allowed d ← d transitions in the red are responsible for the color. Strongly allowed Mo 5d ← O 2p charge transfer excitations are responsible for the optical absorption above 3.2 eV. For the bismuth oxides, three occupied bands are found showing strong Bi 6s, 6p, 6d and O 2p hybridization. These bands have been seen experimentally. The highest band surprisingly has Bi 6p lone-pair character which is explained in terms of the relative Bi 6s and 6p and O 2p ionization potentials using perturbation theory. Rather similar electronic structures are found for the three phases despite their varying cation coordinations and structures. A charge transfer optical absorption edge at ～ 2.6 eV for the β form agrees well with observations reported in the literature, and similar edges should occur for the other phases. The cubic δ form has an unusual low-lying band suggesting absorption in the infrared. Our results provide insight into the surface properties of these oxides.     

NMR studies of sulphur heterocycles: III—13C spectra of benzo[b]thiophene and the methylbenzo[b]thiophenes

All carbon resonances in the title compounds have been unequivocably assigned. Steric effects in the peri substituted compounds have been compared with analogous effects in naphthalene and benzo[b]furan. The observed effects are not explained by current theory. Unusual deshielding steric shifts are observed at some carbons. Methyl substituent effects are not additive at any position in the sterically crowded 2,3-disubstituted compounds.     

DNA separations in microfabricated devices with automated capillary sample introduction

A novel method is presented for automated injection of DNA samples into microfabricated separation devices via capillary electrophoresis. A single capillary is used to electrokinetically inject discrete plugs of DNA into an array of separation lanes on a glass chip. A computer-controlled micromanipulator is used to automate this injection process and to repeat injections into five parallel lanes several times over the course of the experiment. After separation, labeled DNA samples are detected by laser-induced fluorescence. Five serial separations of 6-carboxyfluorescein (FAM)-labeled oligonucleotides in five parallel lanes are shown, resulting in the analysis of 25 samples in 25 min. It is estimated that approximately 550 separations of these same oligonucleotides could be performed in one hour by increasing the number of lanes to 37 and optimizing the rate of the manipulator movement. Capillary sample introduction into chips allows parallel separations to be continuously performed in serial, yielding high throughput and minimal need for operator intervention.     

Monitoring the absorption of organic vapors to a solid phase extraction medium applications to detection of trace volatile organic compounds by integration of solid phase absorbents with fiber optic Raman spectroscopy

By combining fiber optic Raman spectroscopy with a C-18 solid phase extraction medium, real time in situ detection of organic vapors is demonstrated. The response of the probe is fully reversible for benzene, trichloroethylene and carbon tetrachloride vapors. Because of the high degree of selectivity afforded by Raman spectroscopy, the composition of mixtures of the vapors can also be determined using the C-18 probe. The detection of ppm levels of benzene in water via headspace analysis using the C-18 probe is demonstrated.