Positron implantation profile in nickel

A method for measurement of the positron implantation profile in the geometry employed in most positron annihilation experiments is described. The method is applied to the case of Ni as absorber and²²Na as positron emitter. The experimental accuracy is discussed and a proposal for its improvement is outlined. Since absorption studies of positrons is usually performed in geometries quite different from the present, we give a short discussion on the impact of these differences on the transmission curves obtained.     

Observations of the use of o-phthalaldehyde condensation for the measurement of histamine

The in vitro study of mast cell degranulation utilises the measurement of histamine as a quantitative marker of this process. Histamine is most commonly assayed, following organic extraction, by condensing it with o-phthalaldehyde (OPT) and thereby obtaining a highly fluorescent adduct. A number of variables that might affect the performance of this assay, including assay conditions, stability and purity, were evaluated during the course of developing this assay for use in our laboratory. We observed the stability of OPT-histamine and found it to be very stable at 0 and 25 degrees C, following acidification. Derivatisation conditions and the purity of the leukocyte histamine extract were also assessed, and indicated that derivatisation at low temperatures slows down decay, providing a greater over-all fluorescence intensity. Extraction procedures are necessary, prior to condensation with OPT, to eliminate both positive and negative interfering substances from leukocyte preparations.     

Pulsed reagent introduction through a membrane reactor for flow-injection systems

A method of intermittent reagent introduction, functionally equivalent to stop-go pumping, is described. A pneumatically pressurized reagent reservoir is used to deliver liquid through a high-speed on/off valve to the outer channel of an annular tube assembly. Except for this single entry point, the outer channel is otherwise sealed. The inner flow channel bearing the principal flow stream contains a short microporous membrane tube. When the reagent delivery valve is activated, reagent flows radially inward through the membrane into the principal flow stream.     

119Sn Mössbauer study of the implantation behaviour of119In,119Sn,119mSn,119Sb and119mTe ions in SiC

The implantation behaviour of stable¹¹⁹Sn⁺ ions and radioactive¹¹⁹In⁺,^119mSn⁺,¹¹⁹Sb⁺ and^119mTe⁺ ions in SiC has been investigated by, respectively, conversion-electron Mössbauer spectroscopy on the 24 keV transition of¹¹⁹Sn, and by Mössbauer emission spectroscopy on the 24 keV radiation emitted by the¹¹⁹Sn daughter after the decays of the radioactive isotopes. The Mössbauer spectra could be decomposed in most cases into two groups of lines, one originating from¹¹⁹Sn atoms on substitutional Si sites, the other from various Sn-vacancy complexes distinguished by their Mössbauer parameters. Annealing experiments reveal a strong dependence of the structure of the defects and the formation and annealing kinetics on the chemical nature of the impurities. Defects formed in 297 K implantations with^119mSn and¹¹⁹Sb anneal above 500 C, resulting in a preferential location of the impurities on substitutional Si sites, whereas^119mTe atoms are efficient defect-trapping centres and no stable, substitutional fraction is observed on either lattice site. Possible structures for the Sn-vacancy complexes are discussed and comparison is made to similar defect complexes in group IV and in III–V semiconductors.     

Apparatus and method for interfacing capillary electrophoresis and chemiluminescence nitrogen detection for the analysis of nitrogen-containing compounds

We have developed an interface that allows the specific detection of nitrogen-containing compounds by using a chemiluminescence nitrogen detector. The feasibility of using this interface was demonstrated by separating and detecting two nitrogen-containing compounds, p-aminosalicylic acid and L-phenylalanine. Although baseline separation was achieved, the theoretical plates were lower when compared to UV detection (25000 vs. approximately 85000). A sensitivity of 75 ng (approximately 500 pmol) per injection was achieved with this system which is adequate for pharmaceutical and biotech applications.     

Optically pumped submillimetre laser action in formaldoxime and ammonia

Strong submillimetre laser action has been obtained on five lines of a new laser gas, formaldoxime. Several new emission lines have also been produced by isotopic CO₂ laser pumping of¹⁴NH₃ and¹⁵NH₃. One of these lines at 102.9 m is a rotation-inversion transition in the 2v ₂ state, and is the first example of cw laser action in such a highly excited state.     

Analytical and preparative native polyacrylamide gel electrophoresis: Investigation of the recombinant and natural major grass pollen allergen Phl p 2

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot are amongst the most popular methods for allergen characterization, such as comparison of recombinant allergens with their natural counterparts. Native PAGE was evaluated as a possible robust and simple method offering high-resolution capacity for characterization of the major grass pollen allergen Phl p 2. Analytical separation of recombinant Phl p 2 provided a superior quality control in terms of homogeneity and, after Western blotting, immunoglobulin E (IgE) reactivity. Separation of natural Phl p 2 identified two major isoforms which were shown to have different N-terminal sequences and IgE-binding properties. After isolation using preparative native PAGE in combination with electrodialysis, both isoforms were investigated by specific proteolysis and reversed-phase high-performance liquid chromatography (RP-HPLC). The results demonstrate differences in the primary structures and that the recombinant counterpart corresponds exactly to one isoform. Analytical and preparative native PAGE thus proved to be powerful tools for the investigation of allergen isoforms and quality control of recombinant counterparts.     

Analysis of membrane protein cluster densities and sizes in situ by image correlation spectroscopy

Communication between cells invariably involves interactions of a signalling molecule with a receptor at the surface of the cell. Typically, the receptor is imbedded in the membrane and it is hypothesized that the binding of the signalling molecule causes a change in the state of aggregation of the receptor which, in turn, initiates a biochemical signal within the cell. Subsequently, many of the occupied receptors bind to membrane-associated structures, called coated pits, which invaginate and pinch off to form coated vesicles, thereby removing the receptors from the cell surface. The state of aggregation of membrane receptors is obviously in constant flux. Any useful approach to measuring the state of aggregation must, therefore, allow for dynamic measurements in living cells. It is possible to use fluorescently labelled signalling molecules or antibodies directed at the receptor of interest to visualize the receptor on the cell surface with a fluorescence microscope. By employing a laser confocal microscope, high resolution images can be produced in which the fluorescence intensity is quantitatively imaged as a function of position across the surface of the cell. Calculations of autocorrelation functions of these images provide direct and accurate measures of the density of fluorescent particles on the surface. Combined with the average intensity in the image, which reflects the total average number of molecules, it is possible to estimate the degree of aggregation of the receptor molecules. We refer to this analysis as image correlation spectroscopy (ICS). We show how ICS can be used to measure the density of several receptors on a variety of cells and how it can be used to measure the density of coated pits and the number of molecules per coated pit. We also show how the technique can be used to monitor fusion of virus particles to cell membranes. Further, we illustrate that, by calculating cross-correlation functions between pairs of images, we can extend the analysis to measurements of the distributions as a function of time, on the second timescale, as well as to measurements of the movement of the receptor aggregates on the surface. Finally, we illustrate that, by this approach, we can measure the extent of interaction between two different receptors as a function of time. This represents the most quantitative measurement of the extent of co-localization of receptors available and is independent of the spatial resolution of the confocal microscope. The theory of ICS and image cross-correlation spectroscopy (ICCS), focussing on the interpretation of the data in terms of the biological phenomenon being probed, is discussed.