A non-commutative Priestley duality

We prove that the category of left-handed strongly distributive skew lattices with zero and proper homomorphisms is dually equivalent to a category of sheaves over local Priestley spaces. Our result thus provides a non-commutative version of classical Priestley duality for distributive lattices and generalizes the recent development of Stone duality for skew Boolean algebras.     

On the transition from cellular to wavelike patterns during solutal Marangoni convection

We study characteristic convection patterns emerging during the mass transfer of acetic acid from a glycerol-water layer to a superposed acetone layer by means of experiments and numerical simulations. The patterns form as a result of the stationary Marangoni instability. The initial phase of the pattern evolution is studied using high-resolution simulations. They show hierarchically ordered cellular structures which closely resemble experimental observations. In the later stages presently accessible to the experiments, the cells are locally replaced by relaxation oscillation waves. The emergence of these structures is favored when the experiment is performed in narrow cuvettes.     

Binary liquid mixtures. The relation between surface tension and surface composition as studied by MIES (metastable induced electron spectroscopy)

For a binary liquid mixture, we define the surface fraction of a component as the fraction of the surface which is covered by this species. The perfectly surface-sensitive electron spectroscopy MIES (metastable induced electron spectroscopy) allows to derive this quantity in a very direct manner from experiment with no model assumption needed. We find for several binary mixtures that the surface tension depends linearly on the surface fraction with striking accuracy. Even more surprising is the fact that for a system which deviates from this simple linear behavior the surface tension turns out to be a piecewise linear function of the surface fraction. Tentatively, we introduce as possible explanation the concept of phase separation within the surface layer. Further, we show that the surface molar fraction, i.e., the molar fraction within the top surface layer, deviates significantly from a linear or a piecewise linear relation to the surface tension.     

Thiol-specific and nonspecific interactions between DNA and gold nanoparticles

The contribution of nonspecific interactions to the overall interactions of thiol-ssDNA and dsDNA macromolecules with gold nanoparticles was investigated. A systematic investigation utilizing dynamic light scattering and cryogenic transmission electron microscopy has been performed to directly measure and visualize the changes in particle size and appearance during functionalization of gold nanoparticles with thiol-ssDNA and nonthiolated dsDNA. The results show that both thiol-ssDNA and dsDNA do stabilize gold nanoparticle dispersions, but possible nonspecific interactions between the hydrophobic DNA bases and the gold surface promote interparticle interactions and cause aggregation within rather a short period of time. We also discuss the adsorption mechanisms of dsDNA and thiol-ssDNA to gold particles.     

Relating chromatographic retention and electrophoretic mobility to the ion distribution within electrosprayed droplets

Ions that are observed in a mass spectrum obtained with electrospray mass spectrometry can be assumed to originate preferentially from ions that have a high distribution to the surface of the charged droplets. In this study, a relation between chromatographic retention and electrophoretic mobility to the ion distribution (derived from measured signal intensities in mass spectra and electrospray current) within electrosprayed droplets for a series of tetraalkylammonium ions, ranging from tetramethyl to tetrapentyl, is presented. Chromatographic retention in a reversed-phase system was taken as a measure of the analyte’s surface activity, which was found to have a large influence on the ion distribution within electrosprayed droplets. In addition, different transport mechanisms such as electrophoretic migration and diffusion can influence the surface partitioning coefficient. The viscosity of the solvent system is affected by the methanol content and will influence both diffusion and ion mobility. However, as diffusion and ion mobility are proportional to each other, we have, in this study, chosen to focus on the ion mobility parameter. It was found that the influence of ion mobility relative to surface activity on the droplet surface partitioning of analyte ions decreases with increasing methanol content. This effect is most probably coupled to the decrease in droplet size caused by the decreased surface tension at increasing methanol content. The same observation was made upon increasing the ionic strength of the solvent system, which is also known to give rise to a decreased initial droplet size. The observed effect of ionic strength on the droplet surface partitioning of analyte ions could also be explained by the fact that at higher ionic strength, a larger number of ions are initially closer to the droplet surface and, thus, the contribution of ionic transport from the bulk liquid to the liquid/air surface interface (jet and droplet surface), attributable to migration or diffusion will decrease.     

Excited-state properties and emission spectra of nonplanar heterocyclic helicenes

We discuss the electron-vibration coupling in mono-aza-[5]helicenes on the basis of a Franck-Condon analysis and density functional theory (DFT) calculations of the fluorescence and phosphorescence spectra measured in ethanol. The geometries of the initial states were obtained from time-dependent DFT (S(1)) and unrestricted DFT (T(1)) excited-state optimizations. In general, the position of the nitrogen atom has only a minor impact on the vibronic fine-structure in both absorption and emission. The shapes of the emission spectra from the lowest singlet and triplet states are found to be determined by contributions from multiple normal modes. The results of the calculations demonstrate how the interplay among these normal modes results in qualitatively and quantitatively different spectra for fluorescence and phosphorescence.     

Interplay between barrier width and height in electron tunneling: photoinduced electron transfer in porphyrin-based donor-bridge-acceptor systems

The rate of electron tunneling in molecular donor-bridge-acceptor (D-B-A) systems is determined both by the tunneling barrier width and height, that is, both by the distance between the donor and acceptor as well as by the energy gap between the donor and bridge moieties. These factors are therefore important to control when designing functional electron transfer systems, such as constructs for photovoltaics, artificial photosynthesis, and molecular scale electronics. In this paper we have investigated a set of D-B-A systems in which the distance and the energy difference between the donor and bridge states (DeltaEDB) are systematically varied. Zinc(II) and gold(III) porphyrins were chosen as electron donor and acceptor because of their suitable driving force for photoinduced electron transfer (-0.9 eV in butyronitrile) and well-characterized photophysics. We have previously shown, in accordance with the superexchange mechanism for electron transfer, that the electron transfer rate is proportional to the inverse of DeltaEDB in a series of zinc/gold porphyrin D-B-A systems with bridges of constant edge to edge distance (19.6 A) and varying DeltaEDB (3900-17 600 cm(-1)). Here, we use the same donor and acceptor but the bridge is shortened or extended giving a set of oligo-p-phenyleneethynylene bridges (OPE) with four different edge to edge distances ranging from 12.7 to 33.4 A. These two sets of D-B-A systems-ZnP-RB-AuP+ and ZnP-nB-AuP+-have one bridge in common, and hence, for the first time both the distance and DeltaEDB dependence of electron transfer can be studied simultaneously in a systematic way.     

Ab initio cluster calculations on the electronic structure of oxygen vacancies at the polar ZnO(0001) surface and on the adsorption of H2, CO, and CO2 at these sites

Oxygen vacancies at the polar O terminated (0001) surface of ZnO are of particular interest, because they are discussed as active sites in the methanol synthesis. In general, the polar ZnO surfaces are stabilized by OH groups, therefore O vacancies can be generated by removing either O atoms or OH or H2O groups from the surface. These defects differ in the number of electrons in the vacancy and the number of OH groups in the neighborhood. In the present study, the electronic structure and the adsorption properties of four different types of oxygen vacancies have been investigated by means of embedded cluster calculations. We performed ab initio calculations on F+ like surface excitations for the different defect types and found that the transition energies are above the optical band-gap, while F+ centers in bulk ZnO show a characteristic optical excitation at 3.19 eV. Furthermore, we studied the adsorption of CO2 and CO at the different defect sites by DFT calculations. We found that CO2 dissociates at electron rich vacancies into CO and an O atom which remains in the vacancy. At the OH vacancy which contains an unpaired electron CO2 adsorbed in the form of CO2-, while it adsorbed as a linear neutral molecule at the H2O defect. CO adsorbed preferentially at the H2O defect and the OH defect, both with a binding energy of 0.3 eV.