Formation Of Final Reaction Product Research Articles

Production of neutron-rich nuclides in the vicinity ofN= 126 shell closure in multinucleon transfer reactions

Multinucleon transfer in low-energy nucleus-nucleus collisions is widely discussed as a method of production of yet-unknown neutron-rich nuclei hardly accessible (or inaccessible) by other methods. Modeling of complicated dynamics of nuclear reactions induced by heavy ions is done within a multidimensional dynamical model of nucleus-nucleus collisions based on the Langevin equations. The model gives a continuous description of the system evolution starting from the well-separated target and projectile in the entrance channel of the reaction up to the formation of final reaction products. In this paper, rather recent sets of experimental data for the 136 Xe+198 Pt,208 Pb reactions are analyzed together with the production cross sections for neutron-rich nuclei in the vicinity of the N = 126 magic shell.

Emission of heavy clusters in nuclear reactions at low collision energies

A survey of theoretical and experimental investigations of the process involving the emission of heavy clusters from excited nuclear systems produced in heavy-ion reactions at low collision energies is given. The dinuclear system (DNS) model for calculating cross sections for the formation of heavy clusters in complete-fusion and quasifission reactions is described in detail. The results of respective calculations are compared with relevant experimental data and with the results obtained on the basis of different models. The role of the angular momentum, the asymmetry of the entrance channel, the N/Z ratio, and the excitation energy in the formation of final reaction products is studied within the proposed approach. A method is developed for calculating cross sections for evaporation-residue formation. This method takes into account both channels of light-particle emission and channels of heavy-cluster emission. The possibility for the formation of Rn, Fr, and Ra isotopes in channels of heavy-cluster emission from the excited compound nucleus of Pu is demonstrated for the first time. The calculated cross sections and isotopic distributions for residual nuclei arising upon the emission of heavy clusters from an excited compound nucleus of Pu are in good agreement with experimental data. The model developed in the present study permits finding optimum experimental conditions (projectile-target combination and bombarding energy) for studying processes involving the emission of specific complex fragments.

From Experiment to Theory: Molecular Orbital Parameters to Interpret the Skin Sensitization Potential of 5-Chloro-2-methylisothiazol-3-one and 2-Methylisothiazol-3-one

5-Chloro-2-methylisothiazol-3-one (MCI) and 2-methylisothiazol-3-one (MI) are the major constituents of the commercial biocide Kathon CG. These two compounds have both been shown to exhibit skin sensitization potential: MCI is classified as an extreme sensitizer while MI is classified as a moderate sensitizer. The purpose of the present investigation was to provide further insights into the chemistry underlying their skin sensitizing properties. First, a molecular modeling (in silico) study was carried out of the initial reaction pathways of MI and MCI with nucleophiles representative of those involved in the skin sensitization process, and we compared the findings with the reported chemical and allergenic properties of these compounds. These reaction pathways were assessed using molecular orbital calculations. A novel parameter, the activation energy (AE) index, is proposed and is calculated from a knowledge of the energy changes in the frontier molecular orbitals as the electrophile is converted to an anionic intermediate. The AE indices correspond to the reactivity of MCI and MI with nucleophiles and also their skin sensitization potential. Second, the previously unexplained formation of final reaction products from MCI and butylamine is discussed and a reaction mechanism is proposed. A key finding of this analysis is that the reaction produces "positive chlorine" in the form of N-chloro- and/or N,N-dichloro-butylamine, which could contribute to the skin sensitizing properties of MCI.

In situ detection of spontaneous superoxide anion and singlet oxygen production by mitochondria in rat liver and small intestine.

In the present study, the endogenous formation of reactive oxygen species was localized in rat liver and small intestine. The 3,3'-diaminobenzidine (DAB)-Mn2+ technique in which cobalt ions were included in the incubation medium was applied to unfixed cryostat sections of intact tissues. Addition of manganese ions to the DAB-Co(2+)-containing medium greatly increased the amounts of final reaction product formed compared with incubations with only DAB and cobalt ions. In liver, a blue final reaction product was deposited, particularly in hepatocytes surrounding portal tracts. In the small intestine, the DAB-cobalt complex was mainly found at the basal side of enterocytes. Goblet cells remained unstained. Electron microscopical images revealed that an electron-dense reaction product was exclusively present at both inner and outer membranes and at the intermembrane space in mitochondria of liver parenchymal cells and duodenal enterocytes. It was shown that the spontaneous formation of final reaction product was enzymatic and dependent on the presence of oxygen in the medium. Sulphide decreased the reaction, which may indicate that cytochrome c oxidase was partially involved. Benzoquinone and histidine, which are scavengers of superoxide anions and singlet oxygen respectively, reduced the amount of final reaction product considerably. Furthermore, the formation of final reaction product was sensitive to specific inhibitors of NADH:coenzyme Q reductase and aldehyde oxidase, indicating that these enzymes were at least partly responsible for the generation of superoxide anions and singlet oxygen and for the formation of the DAB-cobalt complex.

In situ detection of constitutive superoxide anion production in granules of mast cells.

3,3'-Diaminobenzidine, in the presence of manganese and cobalt ions, was applied for the detection of superoxide anions in unfixed cryostat sections of rat oesophagus, trachea, skin and intact mesenterium. In all connective tissues, a blue final reaction product was found in a granular form in mast cells. The amount of final reaction product formed after incubation with diaminobenzidine and cobalt ions was increased by the addition of manganese ions. Electron microscopical analysis revealed that the electron-dense final reaction product was exclusively present in the granules of mast cells and on elastin fibres. It was found that the constitutive spontaneous formation of final reaction product in mast cells was enzymatic and dependent on the presence of oxygen in the medium. Of all the enzyme inhibitors and free radical scavengers tested, only azide strongly reduced the amount of final reaction product. It was concluded that the reaction was partly caused by peroxidase activity, but that superoxide anions are also constitutively and spontaneously produced in mast cell granules. The exact enzymatic source could not be established. Whether this property of mast cell granules plays an antimicrobial role in connective tissues can only be speculated.

Demonstration of 5′-nucleotidase activity in unfixed cryostat sections of rat liver using a combined light- and electron-microscope procedure

In the present study a technique was developed to demonstrate 5'-nucleotidase activity in unfixed cryostat sections of rat liver at the light- and electron-microscope level using a semipermeable membrane. In order to retain the ultrastructure of the unfixed material as much as possible, incubations were also performed at 4 degrees C rather than at 37 degrees C. The optimized incubation medium contained 300 mM Tris-maleate buffer, pH 7.2, 5 mM adenosine monophosphate as substrate, 30 mM cerium chloride as capturing agent for liberated phosphate, 10 mM magnesium chloride as activator and 1.5% agar. At the light-microscope level, similar localizations of 5'-nucleotidase activity were obtained when incubations were performed at 37 degrees C and 4 degrees C. Enzyme activity was present mainly at bile canalicular membranes and at sinusoidal membranes of hepatocytes; total activity was higher in pericentral than in periportal areas. Cytophotometric analyses revealed that specific formation of final reaction product (FRP) (test minus control reaction) at 37 degrees C followed a hyperbolic curve with time. A linear relationship was found between specific amounts of FRP and section thickness up to 8 micrograms. 5'-Nucleotidase activity was about three-fold higher after incubation for 30 min at 37 degrees C than at 4 degrees C. At the electron-microscope level, it was demonstrated that the ultrastructure of rat liver was rather well-preserved after incubating unfixed cryostat sections attached to a semipermeable membrane and electron-dense FRP was found at bile canalicular and sinusoidal plasma membrane of hepatocytes. The most distinct changes in ultrastructure after incubation at 37 degrees C, in comparison with that at 4 degrees C, were the appearance of multi-lamellar structures at bile canaliculi at 37 degrees C. We conclude that the present method is valid for the demonstration of 5'-nucleotidase activity in unfixed cryostat sections of rat liver at both the light- and electron-microscope levels and that hypothermic incubations improve ultrastructural morphology substantially.

Electroreduction of SOCl2: I . System on Pt Electrode

The mechanism of reduction on Pt electrodes is examined by linear sweep voltammetry and IR reflectance spectroscopy with the interpretation aided by molecular orbital calculations. The present model emphasizes structural aspects of bulk electrolyte as well as the electrode/electrolyte interphase region. Initially this region is enriched by preferential adsorption of ions occurring through the S atom of the complexed molecule. Further enhancement is noted at low cathodic overpotentials. At higher overpotentials, and unidentified species, and , are observed. The model requires stability of both and when in an adsorbed state. The acceptance of the first electron is an irreversible process while the acceptance of the second electron is quasi‐reversible. The formation of final reaction products, viz., Cl−, S, and occurs within the reaction layer.

Localization and cytophotometric analysis of cathepsin B activity in unfixed and undecalcified cryostat sections of whole rat knee joints.

Cathepsin B activity is demonstrated histochemically with a post-coupling method using Z-Arg-Arg-4-methoxy-2-naphthylamide as substrate and Fast Blue BB as coupling reagent in unfixed and undecalcified cryostat sections of whole rat knee joints. Sections were attached to transparent tape to keep the integrity of the tissue intact, such attachment being essential for precise precipitation of the final reaction product at sites of enzyme activity. Also essential was inclusion of polyvinyl alcohol in the enzyme incubation medium. High cathepsin B activity was found in osteoclasts, chondrocytes, fibroblasts, synovial cells, and bone marrow cells in knee joints after induction of arthritis. The final reaction product was precipitated as fine cytoplasmic granules probably corresponding to lysosomes. The reaction was specific because addition to the incubation medium of selective inhibitors of cathepsin B-like activity completely blocked the activity. The amount of final reaction product in synovium and in bone marrow cells was analyzed cytophotometrically. Specific formation of final reaction product was linear with incubation time up to 60 min at 37 degrees C and with section thickness up to 12 microns. Variation of the substrate concentration in the incubation medium revealed a KM value of 1.86 +/- 0.36 mM in synovial cells and 2.48 +/- 0.51 mM in bone marrow cells and Vmax values (expressed as mean integrated absorbance) of 1.18 +/- 0.10 in synovial cells and 1.02 +/- 0.11 in bone marrow cells. Both KM and Vmax values were significantly different in synovial cells and bone marrow cells (p less than 0.01) which could be owing to the presence of different isoenzymes in these tissues. We conclude that the described post-coupling method is sufficient to yield precise localization and that the method is valid for quantitative purposes.