Ab initio calculations have been performed to obtain analytical potential functions for describing the interactions between a platinum surface and both lithium and iodide ions. The accuracy of the results is tested by model calculations with large basis sets and the inclusion of correlation energy. The potentials obtained are to be used in computer simulations of electrochemical phenomena near solid-liquid interfaces.

Unlike chlorination fluorination of ammine complexes of platinum(IV) in aqueous solution does not lead to haloamido complexes. Instead, the triammine complexes [Pt(NH3)3Cl3]Cl and [Pt(NH3)3(NCl2)2Cl]Cl yield no definite main product, and the tetrammine and pentammine complexes trans-[Pt(NH3)4C12]C12, [Pt(NH3)4(NCl2)Cl]Cl2, [Pt(NH3)5Cl]Cl3, and [Pt(NH3)5(OH)]Cl3 form the sparingly soluble complex trans -[Pt (NH3 )4C12] (H2F3 )2 • 2 H-20 as the main product.

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Ion Transport, G ram icidin A, M olecular Dynamics, Functionality, W ater Structure M olecular Dynamics (M D) simulations were performed on a gramicidin A dimer model representing a transm em brane channel. Different from previous simulations the peptide was in contact with bulk water at both ends of the dimer to guarantee a realistic description o f the hydration of the biomolecule. The flexible BJH model for water was employed in the sim ula tions and the gramicidin-water, gramicidin-ion and ion-water potentials used are based on molecular orbital calculations. The water structure near the gramicidin was investigated first by a simulation w ithout ions, while for the energy profiles of the ion transport through the channel a potassium or a sodium ion was added. These investigations provide a detailed and conclusive picture on a molecular level of the role of water in the ion transport through a gramicidin A channel and can explain the experimental results on the selectivity between alkali ions, their double or even triple occupancy, the exclusion or permeability of anions depending upon cation concentration and the consequences of differences in the ionic charge. The investi gation dem onstrate that the water molecules around the gramicidin behave as an integral part of the peptide and the functionality is the result o f the whole complex biomolecule-water.

Statistical geometry is employed for a quantitative description of deviations from regular octahedrality of water around monovalent ions and from regular tetrahedrality of solvent water around water molecules. For these deviations a new criterion is presented by taking into account octahedral and tetrahedral spatial symmetry groups. A geometrical definition of structure making and structure breaking is proposed and illustrated on the basis of molecular dynamics simulations of 2.2 molal aqueous KCl and LiI solutions with the flexible BJH model of water.