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The evaporation residue cross section, the anisotropy of the fission fragments angular distribution, the fission probability, the mass-energy distribution of the fission fragments, and the average prescission neutron multiplicity have been calculated for the compound nucleus 210Rn by using four-dimensional Langevin equations with dissipation generated through the chaos-weighted wall and window friction formula. Three collective shape coordinates plus the projection of the total spin of the compound nucleus to the symmetry axis K were considered in the four-dimensional dynamical model. In the dynamical calculations dissipation coefficient of K,γk was considered as a free parameter, and its magnitude was inferred by fitting measured data on the evaporation residue cross section and the anisotropy of the fission fragments angular distribution for the compound nucleus 210Rn. It was shown that the results of the calculations are in good agreement with the experimental data by using values of the dissipation coefficient of K, equal to γk=(0.185-0.200)(MeV zs)-1/2. It also was shown that the influence of the dissipation coefficient of K on the results of the calculations of the fission probability, the mass-energy distribution of the fission fragments, and the average prescission neutron multiplicity for the compound nucleus 210Rn is small. [ABSTRACT FROM AUTHOR]

The functionalized 2-pyridone-3-carboxylic acids were synthesized starting from 3-formylchromone. Meanwhile, a decarboxylation reaction of 2-pyridone-3-carboxylic acid was performed by potassium carbonate in toluene. All compounds were evaluated against two Gram-negative bacteria ( Escherichia coli (E. coli) , Acinetobacter baumannii (A. baumannii )) and two Gram-positive ( Staphylococcus aureus (S. aureus) ) and fungus ( Candida albicans ( C. albicans) ) using serial broth dilution method. The antimicrobial screening revealed that S. aureus is the highest sensitive microorganism towards the synthesized compounds. Among all analogs, derivatives, 4p and 5c showed excellent activities in comparison with the other compounds against S. aureus . Molecular docking showed that the most active anti S. aureus are compounds 4p and 5c exhibiting primary interaction as with fluoroquinolones by cross-linking over DNA gyrase active site via metal ion bridge and H-bonding interaction with Ser84 and Glu88 from GyrA subunit along with Arg458 and Asp437 located at GyrB subunit. In addition, based on the molecular dynamic simulation as like the standard fluoroquinolones, the mentioned compounds were stabilized for significant amount of simulation time over DNA gyrase which potentiate the importance of the mentioned residues in the DNA gate region of DNA gyrase.

In the title compound, [CuCl2(C7H7NO2)2], the square-planar-coordinated Cu(II) ion lies on a centre of symmetry and is bonded to two monodentate methyl-isonicotinate ligands through their N atoms and by two chloride ligands. The mol-ecules pack in a herringbone pattern. Perpendicular to [100] there are weak inter-molecular C-H⋯Cl and C-H⋯O contacts. Along [100] there are infinite chains of edge-sharing octa-hedra linked through the chlorido ligands.

Electrospray ionization (ESI) generates intact gas-phase ions from analytes in solution for mass spectrometric investigations. ESI can proceed via different mechanisms. Low molecular weight analytes follow the ion evaporation model (IEM), whereas the charged residue model (CRM) applies to large globular species. A chain ejection model (CEM) has been proposed for disordered polymers.

The mechanism whereby macromolecular analytes are transferred into the gas phase during the final stages of electrospray ionization (ESI) remains a matter of debate. In this work, we employ molecular dynamics simulations to examine the temporal behavior of nanometer-sized aqueous ESI droplets containing a polymer chain and excess ammonium ions. The polymer is modeled using a coarse-grained framework where a bead-string backbone is decorated with side chains that can be nonpolar, cationic, or anionic. Polymers that adopt compact conformations and that carry a large number of charged side chains remain close to the droplet center, where the charges are extensively hydrated. The ESI process for these compact/hydrophilic macromolecules must involve solvent evaporation to dryness. This behavior is consistent with the charged residue model (CRM). A completely different scenario is encountered for disordered (extended) chains that carry a large number of nonpolar side chains. In this case, the macromolecule tends to be rapidly expelled from the droplet surface in a stepwise sequential fashion. This process produces metastable structures where one end of the extended polymer chain remains connected with the droplet via charge solvation. Disruption of these last interactions will then produce a free gas phase macromolecular ion. The data of this work imply that the ESI process for unfolded/hydrophobic polymers proceeds via an ion evaporation (IEM)-like mechanism that is facilitated by hydrophobic solute/solvent interactions. Our model predicts that the ESI efficiency of the latter scenario is considerably higher than for the CRM. This prediction is verified experimentally through ESI mass spectrometry measurements on myoglobin.

The ejection of solvated small ions from nanometer-sized droplets plays a central role during electrospray ionization (ESI). Molecular dynamics (MD) simulations can provide insights into the nanodroplet behavior. Earlier MD studies have largely focused on aqueous systems, whereas most practical ESI applications involve the use of organic cosolvents. We conduct simulations on mixed water/methanol droplets that carry excess NH(4)(+) ions. Methanol is found to compromise the H-bonding network, resulting in greatly increased rates of ion ejection and solvent evaporation. Considerable differences in the water and methanol escape rates cause time-dependent changes in droplet composition. Segregation occurs at low methanol concentration, such that layered droplets with a methanol-enriched periphery are formed. This phenomenon will enhance the partitioning of analyte molecules, with possible implications for their ESI efficiencies. Solvated ions are ejected from the tip of surface protrusions. Solvent bridging prior to ion secession is more extensive for methanol/water droplets than for purely aqueous systems. The ejection of solvated NH(4)(+) is visualized as diffusion-mediated escape from a metastable basin. The process involves thermally activated crossing of a ~30 kJ mol(-1) free energy barrier, in close agreement with the predictions of the classical ion evaporation model.

Aqueous nanodroplets that contain excess charge carriers play a central role during the electrospray ionization (ESI) process. An interesting question concerns the charge carrier location in these systems. In analogy to the behavior of metallic conductors, it is often assumed that excess ions are confined to a thin layer on the droplet surface. However, it is unclear whether simple electrostatic arguments adequately reflect the nanodroplet behavior. In particular, most ions tend to be heavily solvated, such that placing them at the liquid/vapor interface would be enthalpically unfavorable. In this work, molecular dynamics simulations are used to study the properties of Na(+)-containing water nanodroplets close to the Rayleigh limit. In apparent violation of the surface charge paradigm, it is found that the ions reside inside the droplet. Electrostatic mapping reveals that all of the excess charge is nonetheless located on the surface. This conundrum is resolved by considering the effects of orientational water polarization. Buried Na(+) ions cause large-scale dipole ordering that extends all the way to the droplet periphery. Here, the positive ends of water dipoles preferentially point into the vapor phase. These half-dipoles in the outermost droplet layers assume the role of surface charge, while solvation effectively neutralizes Na(+) ions in the interior. Overall, our data reaffirm the validity of the surface charge paradigm for ESI nanodroplets, albeit with the caveat that this paradigm does NOT require charge carriers (ions) to be located at the water/vapor interface.

Water nanodroplets charged with excess protons play a central role during electrospray ionization (ESI). In the current study molecular dynamics (MD) simulations were used for gaining insights into the nanodroplet behavior based on classical mechanics. The SPC/E water model was modified to permit the inclusion of protons as highly mobile point charges at minimum computational cost. A spherical trapping potential was assigned to every SPC/E oxygen, thereby allowing the formation of protonated water molecules. Within a tightly packed nanodroplet the individual potential wells merge to form a three-dimensional energy landscape that facilitates rapid proton hopping between water molecules. This approach requires short-range modifications to the standard Coulomb potential for modeling electrostatic proton-water interactions. Simulations on nanodroplets consisting of 1248 water molecules and 10 protons (radius, ca. 21 A) result in a proton diffusion coefficient that is in agreement with the value measured in bulk solution. Radial proton distributions extracted from 1 ns MD runs exhibit a large peak around 14 A, in addition to substantial population density closer to the droplet center. Similar radial distributions were found for nanodroplets charged with Na+ ions. This behavior is dramatically different from that expected on the basis of continuum electrostatic theory, which predicts that excess charge should be confined to a thin layer on the droplet surface. One important contributor to this effect seems to be the ordering of water molecules at the liquid/vacuum interface. This ordering results in an electrical double layer, generating a potential gradient that tends to pull positive charge carriers (such as protons, but also others such as Na+ ions) toward the droplet interior. This deviation from the widely assumed surface charge paradigm could have implications for the mechanism by which protonated analyte ions are formed during ESI.