Resonance and nonresonant laser ionization of sputtered uranium atoms from thin films and single microparticles: evaluation of a combined system for particle trace analysis

The resonance and nonresonant laser ionization of uranium atoms sputtered from thin metal films and individual micrometer-size uranium oxide particles, respectively, was studied to evaluate a new setup for the analysis of actinide-containing micrometer-size particles. Experiments using nonresonant (193-nm) ionization of atoms and molecules sputtered from micrometer-size uranium oxide particles have shown that the uranium detection efficiencies for sputtered neutral atoms are approximately 2 orders of magnitude higher than for secondary ions. In uranium particles of 0.5-microm diameter, 6 x 10(6) atoms of 235U were easily detected and the isotopic ratio of 235U/238U = 0.0048 +/- 4.6% is in excellent agreement with the certified value. The use of two-color, two-step resonance ionization of the sputtered neutral uranium atoms from thin films was investigated. Several excitation schemes were tested, and a significant population of several low-lying metastable states after ion sputtering was observed. Autoionizing states for double-resonant ionization were determined, and the high selectivity of ionization schemes involving these autoionizing states was illustrated by comparing the flight-time distributions of different sputtered species obtained both by resonance and nonresonant multiphoton (355-nm) laser postionization. Ideally, the options for resonance as well as nonresonant ionization would be combined in a single setup, to obtain a large gain in sensitivity and selectivity. Thus, information about the main components as well as specific isotopic information of a trace element could be obtained from the same single particle.     

Elution-extrusion countercurrent chromatography. Use of the liquid nature of the stationary phase to extend the hydrophobicity window

Countercurrent chromatography (CCC) is a liquid chromatography technique with a liquid stationary phase. Taking advantage of the liquid nature of the stationary phase, it is possible to perform unique operations not possible in classical liquid chromatography with a solid stationary phase. It is easy to avoid any solute-irreversible absorption in the CCC column. If the retention volumes of solutes become too high, the dual mode will be used. The roles of the phases are reversed. The stationary phase becomes the mobile phase, and the CCC column is started again. The solutes elute rapidly in what was previously the stationary phase. The theoretical basis of the dual-mode method is recalled. The dual-mode method is a discontinuous method. The separation should be stopped when the phase switch is performed. The elution-extrusion procedure is another way to avoid any irreversible adsorption of solutes in the column. The method uses the fact that the liquid volumes occupied by the solutes highly retained inside the column can be orders of magnitude lower than the mobile-phase volume that would be needed to elute them. The elution-extrusion method also has two steps: the first step is a regular CCC chromatogram. Next, the stationary phase containing the partially separated hydrophobic solutes is extruded out of the column in a continuous way using the liquid stationary phase. The theory of the process is developed and compared to the dual-mode theory. Alkylbenzene homologues are experimentally used as model compounds with the heptane/methanol/water biphasic liquid system to establish the theoretical treatment and compare the performance of two types, hydrodynamic and hydrostatic, of CCC columns. It is shown that the method can dramatically boost the separation power of the CCC technique. An apparent efficiency higher than 20 000 plates was obtained for extruded octylbenzene and a 160-mL hydrodynamic CCC column with less than 500 plates when conventionally used.     

Chip-based analysis of protein-protein interactions by fluorescence detection and on-chip immunoprecipitation combined with microLC-MS/MS analysis

A new chip-based method to identify protein-protein interactions was developed using the guanine nucleotide exchange factor GRF2 and two interacting proteins, Ras and calmodulin, as model proteins. A generic immobilization strategy for FLAG-tagged bait proteins on a protein-repellent streptavidin chip surface was implemented by presentation of an oriented anti-FLAG antibody. A flow cell device, integrating different chip surfaces, was developed, and the interaction of immobilized GRF2 with the two analytes was verified by fluorescence assays. On-chip tryptic digest assays were then performed on the capture surface and analyzed by microLC-MS/MS. The interaction of GRF2 with calmodulin and Ras was demonstrated, and the lower limit of detection was determined. We also implemented an on-chip immunoprecipitation assay to identify GRF2-binding partners from complex protein mixtures. Cells overexpressing FLAG-GRF2 were lysed and then incubated with the anti-FLAG chip. In addition to detecting GRF2, we also identified calmodulin, demonstrating that this technique can successfully identify endogenous levels of proteins, bound to recombinant bait proteins. This chip-based method has the advantage that no subsequent gel separations of protein complexes prior to LC-MS analysis are required and is therefore amenable to miniaturized high-throughput determination of protein-protein interactions.     

Physiological functions of FMRFamide-like peptides (FLPs) in crustaceans

Neuropeptides play important roles in chemical signalling in the central and peripheral nervous systems. One of the largest families of neuropeptides is that of the FMRFamide-like peptides (FLPs). This paper reviews what is known about the physiological functions of FLPs in crustaceans, focussing on the cardiovascular, digestive and neuromuscular systems.     

Induced maturation of frog mast cells by nerve growth factor during ontogenesis

The effect of nerve growth factor (NGF) on ontogenesis of frog mast cells was investigated in vivo by histochemical, morphometric, and ultrastructural analysis. Three groups of tadpoles at various stages of development were used. In the first group, the larvae received i.p. injections of 1 ng NGF/g; the second group received 10 ng NGF/g, while the control group received only the vehicle. The first recognizable mast cells arose symmetrically in the tongue at stage 26 of Witschi's standard table. At stages 26 and 29, the mast cell number in the NGF-injected tadpoles was significantly higher than the control group. From stage 29 onward, the mast cell number rapidly increased in all groups. No significant differences in mast cell number were observed between the control group and the NGF-injected groups at stages 31 and 33. Electron microscopy revealed that at metamorphic climax (stage 33), the mast cells in the NGF-treated groups were more mature than those in the control group. Therefore, nerve growth factor at early stages of tadpole development is likely to induce differentiation of mast cell precursors, while at later stages it is likely to induce maturation of immature mast cells. The close anatomical association between mast cells and perineurium, observed during nerve development, is intriguing. Already in the early stages of nerve development, the mast cells form a network around Schwann cell-axon complexes, together with the perineurial cells. At climax, the mast cells are located between the perineurial layers, suggesting that they may play a role in the tissue-nerve barrier of the perineurium. Nerve growth factor also seems to induce perineurial cell maturation.     

“Smart” polymeric nanospheres as new materials for possible biomedical applications

Novel random terpolymers of N-isopropylacrylamide (NIPAM), sodium 2-acrylamido-2-methyl-1-propanesulfonate (AMPS), and cinnamoyloxyethylmethacrylate (CEMA) were synthesized by free radical copolymerization using AIBN as an initiator. Five terpolymers were obtained by copolymerization of the monomer mixtures containing a fixed amount of 10 mol % of AMPS while the content of CEMA ranged from 5 to 25 mol % and was changed in 5 mol % increments. The terpolymers obtained are water-soluble. Because of their amphiphilic nature they undergo self-organization in the aqueous solution with the formation of micelles capable of solubilizing sparingly water soluble organic compounds, such as drugs. The terpolymers are susceptible to three external stimuli, i.e. temperature, ionic strength and UV light. Due to the presence of NIPAM in the terpolymers they display the lower critical solution temperature (LCST), the presence of AMPS makes them sensitive to the ionic strength of the solution, while the light-responsiveness of the terpolymers is due to the presence of cinnamoyl chromophores, which undergo photodimerization when irradiated with UV light at about 280 nm. Application of any of these stimuli alone or in combination with other stimuli allows changing the copolymer properties in a controlled way.     

Study of electron beam curing process using epoxy resin system

Polymeric matrix composite (PMC) has been used in engineering applications instead of metal in the last few years, due to its corrosion resistance and excellent relation between tensile strength/density and elastic modulus/density. However, PMC materials cured by thermal process require high temperature and are time-consuming. The electron beam (EB) curing technology allows its use at room temperature and reduced curing times, and this is one of the main advantages over thermal technology. The aim of this work is to investigate electron beam curable epoxy formulations to use in filament winding processes to produce composite material with similar or better properties than thermal curable composites. The study has been made with commercial epoxy resins and cationic initiators. The epoxy resin samples were irradiated for few minutes with total dose of 150 kGy. The glass transition temperatures (T_g) were determined by dynamic mechanical analyzer (DMA) and the result was 137 °C. The thermal process was carried out in a furnace following three steps: 4 h at 90 °C, increasing temperature from 90 °C to 130 °C during 4 h and 12 h at 130 °C. The total process time was 20 h. The T_g of this sample was 102 °C.