ß-Bi2O3 reduction by laser irradiation in a liquid environment.

This study reports the structural and stoichiometric modifications of bismuth oxide nanoparticles in the ß phase (ß-Bi2O3) by UV pulsed laser irradiation in water or ethanol solutions. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance and high-resolution transmission electron microscopy were used to characterize the synthesized nanomaterials. The various analyses demonstrate that the laser irradiation of ß-Bi2O3 nanospheres is a green, fast and effective method to produce Bi2O2CO3 nanosheets or metallic Bi nanoparticles depending on the liquid environment used. Bi subcarbonate is obtained by laser irradiation in water, whereas metallic Bi is produced by laser irradiation in ethanol, and in particular the relative amount of metallic Bi is found to depend on the laser fluence. These typologies of materials find application in several fields, such as photocatalytic processes, light filters and environmental sensors.

Novel approach to the fabrication of Au/silica core-shell nanostructures based on nanosecond laser irradiation of thin Au films on Si.

We demonstrate the possibility of producing Au/SiO(2) core-shell nanoparticles by nanosecond laser irradiation of thin (5 and 20 nm) Au films on Si. The Au/Si eutectic reaction and dewetting process caused by the fast melting and solidification dynamics induced by the nanosecond laser irradiations are investigated as the origin of the formation of core-shell nanoparticles. Using several microscopic techniques (Rutherford backscattering spectrometry, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and energy filtered transmission electron microscopy) the formation and evolution of the core-shell structures are investigated as a function of the laser fluence in the 500-1500 mJ cm(-2) range for both film thicknesses. In particular, the mean height and diameter and surface density evolution of the core-shell structures are quantified and correlated to the laser fluence and Au film thickness.

Effect of surrounding environment on atomic structure and equilibrium shape of growing nanocrystals: gold in/on SiO2.

We report on the equilibrium shape and atomic structure of thermally-processed Au nanocrystals (NCs) as determined by high resolution transmission electron microscopy (TEM). The NCs were either deposited on SiO2surface or embedded in SiO2layer. Quantitative data on the NCs surface free energy were obtained via the inverse Wulff construction. Nanocrystals inside the SiO2layer are defect-free and maintain a symmetrical equilibrium shape during the growth. Nanocrystals on SiO2surface exhibit asymmetrical equilibrium shape that is characterized by the introduction of twins and more complex atomic defects above a critical size. The observed differences in the equilibrium shape and atomic structure evolution of growing NCs in and on SiO2is explained in terms of evolution in isotropic/anisotropic environment making the surface free energy function angular and/or radial symmetric/asymmetric affecting the rotational/translational invariance of the surface stress tensor.

Agonist-selective regulation of polyphosphoinositide metabolism in pulmonary artery smooth muscle cells.

Using a rat pulmonary artery smooth muscle cell line (PAC1), detailed analysis of polyphosphoinositide (PPI) metabolism reveals receptor type-selective patterns in the formation of inositol phosphates and 3-hydroxyphosphorylated PPIs. Responses to several agonists that stimulate hypertrophy or proliferation were examined, and distinct categories of response profile were observed. Thrombin and angiotensin II stimulated the hydrolysis of phosphatidylinositol (PI) 4,5-bisphosphate and the formation of several cytosolic species of inositol phosphates without the activation of PI 3-hydroxykinase. The response to thrombin was distinctive because a very large production of inositol 1,4-bisphosphate was accompanied by hydrolysis of PI 4-phosphate. The response to platelet-derived growth factor (PDGF) was distinguished by the production of the PI 3-hydroxykinase product, PI 3,4,5-trisphosphate, and the appearance of PI 3-hydroxykinase activity in immunoprecipitates. PDGF treatment of PAC1 cultures did not produce accumulation of detectable amounts of inositol 1,4,5-trisphosphate, although a small sustained elevation in the level of inositol monophosphate and a gradual accumulation of inositol 1,3,4-trisphosphate were observed. Characterization of these distinctive responses permitted us to correlate agonist-regulated PPI metabolism with induction of immediate-early genes and stimulation of hypertrophy or proliferation of PAC1 cultures (Rothman, A., Wolner, B., Button, D., and Taylor, P. (1994) J. Biol. Chem. 269, 6399-6404). Thrombin-stimulated PPI turnover and the production of a high level of inositol bisphosphate may be early signals linked to the induction of fosB and PAC1 cell hypertrophy, whereas the activation of PI 3-hydroxykinase and the accumulation of PI 3,4,5-trisphosphate in response to PDGF appear to be associated with mitogenesis.

Promoter elements and transcriptional control of the mouse acetylcholinesterase gene.

The 5'-untranslated region of the mouse acetylcholinesterase gene has been characterized structurally by RNase protection, primer extension, and sequencing. Evidence has been obtained for the use of two alternative promoters in brain. Tissue-specific splicing to alternative acceptor sites in the 5'-untranslated exons occurs in brain, muscle, and erythropoietic cells. cis elements 5' of the cap site that is predominantly used in these tissues and cells have been analyzed by deletion analysis of promoter-reporter gene constructs and by site-specific mutagenesis. The cap site is found 107 base pairs (bp) 5' of the translation start site. This region is devoid of CAAT or TATA sequences; further in the 5' direction 50 and 70 bp are tandem Egr-1 sites. The putative promoter has been coupled to the open reading frame of a luciferase reporter gene. Deletion analysis shows that this region largely accounts for tissue-specific transcription seen upon transfection of neuronal and muscle cells. Mutagenesis of the Egr-1 sites results in a marked loss of reporter gene activity, further substantiating the importance of this region in the control of transcription. cis elements in the promoter differ from those found for the genes encoding the various subunits of the nicotinic acetylcholine receptor, and distinct differences in control of transcription are evident when the respective reporter genes are transfected into C2 muscle cells.

Expression of recombinant acetylcholinesterase in a baculovirus system: kinetic properties of glutamate 199 mutants.

The glycophospholipid-linked, amphiphilic form of acetylcholinesterase (AChE) from Torpedo californica and the hydrophilic form from mouse were overexpressed in Sf9 insect cells using the baculovirus expression system. Recombinant baculovirus, constructed by inserting AChE cDNA's into the genome of Autographa californica nuclear polyhedrosis virus adjacent to the strong polyhedron promoter, yielded recombinant enzyme varying between 0.5 and 3.8 mg/L. The recombinant enzyme was glycosylated although it migrated slightly more rapidly in SDS gel electrophoresis than enzyme purified from the electric organ of Torpedo. Kinetic properties of the recombinant DNA- and tissue-derived enzymes are identical. The detailed catalytic properties and susceptibility to inhibitors were examined for two enzyme mutations of the glutamate residue N-terminal to the active site serine. The Glu199 to Gln mutation shifted both the Km and Kss to higher substrate concentrations and resulted in a kcat of 28% of the wild type. Mutation of Glu199 to Asp also yielded a reduction in kcat but with no change in Km. Substrate inhibition normally apparent in wild-type AChE was eliminated with the Asp mutation, suggesting that substrate catalysis and substrate inhibition are not directly linked. Both mutations decreased the affinity of reversible inhibitors and reduced the rates of phosphorylation and carbamoylation; these changes were more striking with the Gln199 mutation. Decarbamoylation rates were unaffected by these mutations. Glu199 is the charged residue found deep within the active center gorge close to the site of acetylcholine binding, and our findings indicate it influences, but is not essential for, efficient catalysis.

Appropriate prevention and detection of gastrointestinal neoplasms in the elderly.

The incidence of colorectal carcinoma and gastric cancer is related to environmental factors and lifestyle. Long-term exposure to multiple mutagens is believed to initiate the carcinogenesis of colorectal and gastric cancer. Even though patients older than 65 years of age have developed particular modes of cooking and dietary preferences, these habits can be changed with instruction, patient-doctor rapport, and suggestions of alternative foodstuffs that are palatable to them. Elderly patients can be persuaded to avoid fatty foods; smoked, pickled, and salted fish; and red meat. They should be encouraged to eat chicken, fish, fresh fruit, and vegetables (especially cruciferous vegetables), to ingest vitamin C, and to avoid overcooking, frying, and excessive broiling of meat and fish. Surveillance examinations must be practiced in the elderly to avoid malignant conversion of adenomatous polyps. All patients who have undergone gastric resections for peptic ulcer disease need to be watched carefully, with identification of high-risk individuals who must undergo periodic endoscopy.

Synapses and ephapses in the spiral ganglion.

Spiral ganglion cells and their nerve fibers in Rosenthal's canal of the macaque monkey were studied in serial sections by electron microscopy. There were four types of neurons. In type I myelinated neurons, the first segments of the peripheral processes established direct contact with each other demonstrating asymmetric densities at opposing junctional membranes. The first segments were also in direct contact with the peripheral processes of type II neurons (ephaptic contact). In type II unmyelinated neurons the perikarya and the peripheral and central processes showed synapses, presumably with the efferent fibers. The processes of type II neurons came in direct contact with each other and also with the adrenergic type fibers. In the third type of neuron (IIA), which showed thinly or partly myelinated perikarya with unmyelinated axons, the peripheral and central processes showed synapses similar to those shown in type II neurons. The peripheral process formed a varicosity and made presynaptic contacts (dendrodendritic synapses) on the peripheral processes of type II and IIA neurons. In the fourth type, the perikaryon was unmyelinated but the axons were myelinated. All cytological features and synapses on the perikaryon were similar to those of type II neurons. These findings suggest that nerve fibers of different types communicate with each other, and when sensory cells degenerate, the surviving neurons which have lost their connections to these sensory cells, may still send electrical signals to the cochlear nuclei through the synapses and ephapses of their neurites in Rosenthal's canal.