Glucose solvation by the ionic liquid 1,3-dimethylimidazolium chloride: A simulation study

Simulations of beta-glucose in the ionic liquid 1,3-dimethylimidazoliurn chloride have been performed in order to examine the solvation environment of the carbohydrate. Both single molecule and 1:5 glucose:ionic liquid (16.7 wt %) solutions are Studied, and the hydrogen bonding between sugar and solvent is examined. The primary solvation shell around the perimeter of the glucose ring consists predominantly of chloride anions which hydrogen bond to the hydroxyl groups. A small presence of the cation is also found, with the association Occurring through the weakly acidic hydrogen at the 2-position of the imidazolium ring interacting with the oxygen atoms of the sugar secondary hydroxyls. An average chloride coordination number of 4 is found around the glucose for both the single molecule and high concentration Simulations, despite the reduced chloride:glucose ratio in the latter case. In relation to the cation, the glucose molecules occupy positions above and below the plane of the imidazolium ring. Importantly, even at high glucose concentrations, no significant change in the anion-cation interactions and overall liquid structure of the ionic liquid is found, indicating that the glucose is readily accommodated by the solvent at this concentration. Dominant contributions to the sugar-ionic liquid interaction energy come from favorable hydrogen bonding (electrostatic) interactions between hydroxyls and chlorides, although a small favorable van der Waals energy contribution is also seen between the sugar and cations suggesting that the cation could be tailored in order to further improve the dissolution of glucose/cellulose in ionic liquid systems.

Reduced-size polarized basis sets for calculations of molecular electric properties. III. Second-row atoms

Reduced-size polarized (ZmPolX) basis sets are developed for the second-row atoms X = Si, P, S, and Cl. The generation of these basis sets follows from a simple physical model of the polarization effect of the external electric field which leads to highly compact polarization functions to be added to the chosen initial basis set. The performance of the ZmPolX sets has been investigated in calculations of molecular dipole moments and polarizabilities. Only a small deterioration of the quality of the calculated molecular electric properties has been found. Simultaneously the size of the present reduced-size ZmPolX basis sets is about one-third smaller than that of the usual polarized (PolX) sets. This reduction considerably widens the range of applications of the ZmPolX sets in calculations of molecular dipole moments, dipole polarizabilities, and related properties.

Probing warm dense lithium by inelastic X-ray scattering

One of the grand challenges of contemporary physics is understanding strongly interacting quantum systems comprising such diverse examples as ultracold atoms in traps, electrons in high-temperature superconductors and nuclear matter. Warm dense matter, defined by temperatures of a few electron volts and densities comparable with solids, is a complex state of such interacting matter. Moreover, the study of warm dense matter states has practical applications for controlled thermonuclear fusion, where it is encountered during the implosion phase, and it also represents laboratory analogues of astrophysical environments found in the core of planets and the crusts of old stars, Here we demonstrate how warm dense matter states can be diagnosed and structural properties can be obtained by inelastic X-ray scattering measurements on a compressed lithium sample. Combining experiments and ab initio simulations enables us to determine its microscopic state and to evaluate more approximate theoretical models for the ionic structure.

Imaging the cool stars in the interacting binaries AE Aqr, BV Cen and V426 Oph

It is well known that magnetic activity in late-type stars increases with increasing rotation rate. Using inversion techniques akin to medical imaging, the rotationally broadened profiles from such stars can be used to reconstruct `Doppler images' of the distribution of cool, dark starspots on their stellar surfaces. Interacting binaries, however, contain some of the most rapidly rotating late-type stars known and thus provide important tests of stellar dynamo models. Furthermore, magnetic activity is thought to play a key role in their evolution, behaviour and accretion dynamics. Despite this, we know comparatively little about the magnetic activity and its influence on such binaries. In this review we summarise the concepts behind indirect imaging of these systems, and present movies of the starspot distributions on the cool stars in some interacting binaries. We conclude with a look at the future opportunities that such studies may provide.

Fragmentation and plasmid strand breaks in pure and gold-doped DNA irradiated by beams of fast hydrogen atoms

The results of an investigation into the damage caused to dry plasmid DNA after irradiation by fast (keV) hydrogen atoms are presented. Agarose gel electrophoresis was used to assess single and double strand break yields as a function of dose in dry DNA samples deposited on a mica substrate. Damage levels were observed to increase with beam energy. Strand break yields demonstrated a considerable dependence on sample structure and the method of sample preparation. Additionally, the effect of high-Z nanoparticles on damage levels was investigated by irradiating DNA samples containing controlled amounts of gold nanoparticles. In contrast to previous (photonic) studies, no enhancement of strand break yields was observed with the particles showing a slight radioprotective effect. A model of DNA damage as a function of dose has been constructed in terms of the probability for the creation of single and double strand breaks, per unit ion flux. This model provides quantitative conclusions about the effects of both gold nanoparticles and the different buffers used in performing the assays and, in addition, infers the proportion of multiply damaged fragments.

Theory of laser-driven double-ionization of atoms at Ti : sapphire laser wavelengths

Progress in the theoretical understanding of non-sequential double-ionization of atoms is reviewed from its beginnings with Kuchiev's work in the late 1980s and Corkum's work in the early 1990s to the present day. The crucial role of laboratory experiment as a persistent stimulus to theoretical endeavour is underlined but the predictive roles of simple, yet fundamental, theory and also of a full quantum mechanical description are not forgotten. A theoretical forward look is provided.