Probing spatial locality in ionic liquids with the grand canonical adaptive resolution molecular dynamics technique.

We employ the Grand Canonical Adaptive Resolution Simulation (GC-AdResS) molecular dynamics technique to test the spatial locality of the 1-ethyl 3-methyl imidazolium chloride liquid. In GC-AdResS, atomistic details are kept only in an open sub-region of the system while the environment is treated at coarse-grained level; thus, if spatial quantities calculated in such a sub-region agree with the equivalent quantities calculated in a full atomistic simulation, then the atomistic degrees of freedom outside the sub-region play a negligible role. The size of the sub-region fixes the degree of spatial locality of a certain quantity. We show that even for sub-regions whose radius corresponds to the size of a few molecules, spatial properties are reasonably reproduced thus suggesting a higher degree of spatial locality, a hypothesis put forward also by other researchers and that seems to play an important role for the characterization of fundamental properties of a large class of ionic liquids.

Electrostatic properties of liquid 1,3-dimethylimidazolium chloride: role of local polarization and effect of the bulk.

The molecular polarization in a 1,3-dimethylimidazolium chloride ([DMIM][Cl]) ionic liquid is analyzed for a bulk liquid via the Car-Parrinello approach. The analysis reveals that the electric dipole moments of cations and anions are characterized by large fluctuations, however these are primarily due to the molecules in the immediate surroundings. These results on one hand shed light on some basic physical and chemical features of this liquid, and on the other represent a fundamental handle for the development of accurate classical force fields; this aspect is extensively discussed and some suggestions are made.

A theoretical investigation of the vibrational states of HCO2- and its isotopomers.

Making use of the coupled cluster variant CCSD(T) and the aug-cc-pVQZ basis set a six-dimensional (6D) potential energy surface has been calculated for HCO2-, a fundamental organic anion. Therefrom, a variety of vibrational term energies and wavefunctions has been obtained by means of the discrete variable representation in an approach termed DVR(6). Calculated wavenumbers of the fundamentals of HCO2- and DCO2- agree with recent experimental values from neon matrix isolation IR spectroscopy within 15 cm(-1). The out-of-plane bending vibrations v4 are predicted at 1030 and 894 cm(-1). Moderately strong Fermi resonance interaction is calculated between vibrational states v1 and 2v4 of DCO2-. Excellent agreement with experiment (differences less than 0.7 cm(-1) is observed for the 13C and 18O isotopic shifts. Accurate ground-state rotational constants are predicted for eight different isotopomers of the formate ion and the dissociation process HCO2- --> H- + CO2 is investigated in some detail, with the dissociation energy D0 predicted to be 216 kJ mol(-1).

Physical methods for characterization of microbial surfaces.

There are different concepts for explaining the adsorption of microorganisms to solid surfaces: the DLVO theory and the surface free energy. Basic aspects of both theories are discussed. Established methods for determining the surface properties of microbial cells are reviewed: Electrophoretic mobility, colloid titration, electrostatic interaction chromatography, bacterial adherence to hydrocarbons, partitioning in an aqueous two-phase system, hydrophobic interaction chromatography, contact angle measurement and X-ray photoelectron spectroscopy. They are discussed and classified according to their potential for the correlation of cell surface characteristics and adsorption behavior.