An empirical potential function for the interaction between univalent ions in water

A hydration-shell model has been developed for calculating the interaction energy between ions in water. The hydration shell around each ion contains a few tightly bound water molecules and a larger number of less tightly bound molecules. The energies of their interaction with the ion and the size of the hydration shell have been derived from published experimental data for ion-water clusters in the gas phase. An expression derived for the interaction energy of two univalent ions in water incorporates the following effects: a Lennard-Jones 6–12 interaction, a Coulomb interaction between the charges, the polarization of the hydration shells by a neighboring ion, and an energy term for the removal of water from the hydration shells when the hydration shells of two ions overlap. The effective dielectric constant at small ion-ion distances is the only adjustable parameter. Computed interaction energies for aqueous solutions of twelve alkali halides match experimental values, derived from conductimetric measurements, with an average error of ±14%.     

Untersuchung der Fette

Ohne Zusammenfassung     

Applications of theorems of Jean Leray to the Einstein-scalar field equations

The Einstein-scalar field theory can be used to model gravitational physics with scalar field sources. We discuss the initial value formulation of this field theory, and show that the ideas of Leray can be used to show that the Einstein-scalar field system of partial differential equations is well-posed as an evolutionary system. We also show that one can generate solutions of the Einstein-scalar field constraint equations using conformal methods. Dedicated to the memory of Jean Leray     

Stereocontrolled preparation of bicyclic alkaloid analogues: an approach towards the kinabalurine skeleton

An approach towards the construction of bicyclic analogues of monoterpene alkaloids belonging to the kinabalurine, incarvilline and skytanthine families of natural products is reported. These syntheses rely on a stereoselective intramolecular Pauson-Khand cyclisation of a chiral pool-derived enyne in order to prepare the bicyclic core. Stereoselective further elaboration generates diastereomeric analogues of the naturally occurring alkaloids.     

Global Wave Maps on Robertson–Walker Spacetimes

We prove the global existence and uniqueness of wave maps onexpanding universes of dimension three or four, that is Robertson–Walkerspacetimes whose inverse radius is integrable with respect to the cosmictime. A result is obtained for small initial data by using the first andsecond energy estimates.     

Ultrasonic excitation affects friction interactions between food materials and cutting tools

In the food industry, ultrasonic cutting is used to improve separation by a reduction of the cutting force. This reduction can be attributed to the modification of tool–workpiece interactions at the cutting edge and along the tool flanks because of the superposition of the cutting movement with ultrasonic vibration of the cutting tool. In this study, model experiments were used to analyze friction between the flanks of a cutting tool and the material to be cut. Friction force at a commercial cutting sonotrode was quantified using combined cutting–friction experiments, and sliding friction tests were carried out by adapting a standard draw-off assembly and using an ultrasonic welding sonotrode as sliding surface. The impact of material parameters, ultrasonic amplitude, and the texture of the contacting food surface on friction force was investigated. The results show that ultrasonic vibration significantly reduces the sliding friction force. While the amplitude showed no influence within the tested range, the texture of the contact surface of the food affects the intensity of ultrasonic transportation effects. These effects are a result of mechanical interactions and of changes in material properties of the contact layer, which are induced by the deformation of contact points, friction heating and absorption heating because of the dissipation of mechanical vibration energy.     

Stable DOPG/Glycyrrhizin Vesicles with a Wide Range of Mixing Ratios: Structure and Stability as Seen by Scattering Experiments and Cryo-TEM

Phosphatidylglycerols represent a large share of the lipids in the plasmamembrane of procaryotes. Therefore, this study investigates the role of charged lipids in the plasma membrane with respect to the interaction of the antiviral saponin glycyrrhizin with such membranes. Glycyrrhizin is a natural triterpenic-based surfactant found in licorice. Vesicles made of 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1’-glycerol) (DOPG)/glycyrrhizin are characterized by small-angle scattering with neutrons and X-rays (SANS and SAXS). Small-angle scattering data are first evaluated by the model-independent modified Kratky–Porod method and afterwards fitted by a model describing the shape of small unilamellar vesicles (SUV) with an internal head-tail contrast. Complete miscibility of DOPG and glycyrrhizin was revealed even at a ratio of lipid:saponin of 1:1. Additional information about the chain-chain correlation distance of the lipid/saponin mixtures in the SUV structures is obtained from wide-angle X-ray scattering (WAXS).     

The Solvent-Like Nature of Silica Particles in Organic Solvents

Summary.   Kamlet-Taft’s α (hydrogen bond donor acidity) and π^* (dipolarity/polarizability) values of various silica batches measured in various solvents are presented. The α and π^* parameters for the various solid acids are analyzed by means of Fe(phen)₂(CN)₂ (cis-dicyano-bis-(1,10)-phenanthroline-iron(II), 1), Michler’s ketone (4,4′-bis-(dimethylamino)-benzophenone, 2), and two hydrophilic derivatives of 2, (4-(dimethylamino)-4′-(di-2-hydroxyethyl)-amino-benzophenone (3a) and 4,4′-bis-(di-(2-hydroxyethyl)-amino)-benzophenone (3b) as well as coumarin 153 (4) as solvatochromic surface polarity indicators. Apparent β (hydrogen bond acceptor basicity) parameters for bare silica have been evaluated by means of an aminobenzodifuranone dye (5) as solvatochromic probe. The chemical interpretation of the α and π^* parameters and the nature of the solvent/surface interaction which they reflect are discussed. It can be shown that an increase of the HBA (hydrogen bond accepting) capacity of the solvent significantly decreases the HBD (hydrogen bond donating) capacity of the surface environment, whereas the dipolarity/polarizability value of the silica/solvent interface is a composite of many effects. The classification of the polarity of silica particles in organic solvents compared to pure liquids is outlined. Theoretical E _T(30) values of the solid/solvent interfaces are calculated by applying linear solvation energy (LSE) relationships using the independently measured α and π^* values of the solid acids according to Received February 2, 2001. Accepted (revised) March 3, 2001     

Salts of two pentahalo(N‐donor)­bismuthate(III) anions: [BiX5L]2− (X = Cl,Br; L = pyridine, 4‐picoline)

Two pentahalo(N‐donor)­bismuthate(III) salts, bis­[hydrogen bis(4‐picoline)(1+)] penta­bromo(4‐picoline‐N)bismuthate(III), (C₁₂H₁₅N₂)₂[BiBr₅(C₆H₇N)], (I), and bis­(pyridinium) penta­chloro­(pyridine‐N)­bismuthate(III), (C₅H₆N)₂[BiCl₅(C₅H₅N)], (II), are described which show modest deviations from octahedral geometry at bismuth. In (I), the cations comprise two 4‐picoline mol­ecules sharing a proton and in (II), pyridinium cations are present. The anion in (I) has twofold and that in (II) has mirror crystallographic symmetry. Both structures show a layered packing formed by the anions with the cations between the layers. Ring–ring interactions seem important in (I), whilst in (II), N/­C—H?Cl—Bi hydrogen bonding is abundant.