Ralf Brodbeck

Molecular Dynamics Simulations of Dendrimer-Encapsulated α-Keggin Ions in Trichloromethane Solution

We report on molecular dynamics simulations of dendrimer-encapsulated alpha-Keggin ions in trichloromethane solution. The simulations were done within the NVE ensemble at temperatures around T = 300 K. The eight examined systems are model compounds for dendrizymes, a hybrid material where a polyoxometalate ion (the core) is surrounded by amphiphilic cationic dendrimers (the shell) such that the complete system may exhibit enzyme-like regioselectivity and substrate selectivity, e.g., in olefin oxidation. The influence of dendrimer type, dendrimer generation, and number of dendritic cations bound by electrostatic interaction to the polyoxometalate core on the structure and dynamics of the shell has been studied. It is shown that the resulting distribution of trichloromethane molecules within the shell may serve as an indicator for the shells permeability for small molecules. The dendritic shell causes a size exclusion effect that influences the access of small molecules to the central polyoxometalate ion, i.e., to that part where the enzyme-like reaction of a dendrizyme is supposed to take place.

Controlling the self assembly of arene functionalised 2-aminopyrimidines by arene-perfluoroarene interaction and by silver(I) complex formation

The arene functionalised 2-aminopyrimidines 4–6 have been synthesized. These compounds bear an aminopyrimidine unit for self assembly based on hydrogen bonding and an arene moiety which is suitable for solid state π–π-interactions. The crystal structures show networks built up by coexisting non covalent interactions. Also the hexafluorobenzene co-crystals of this series of compounds were investigated by X-ray structure determination. Herein, the arene–perfluoroarene interaction is crucial for crystal structure organisation, but still in coexistence with hydrogen bonding motives. The silver tetrafluoroborate complexes of the aminopyrimidines [Ag(L)2]+ BF4− (L = 4–6) were synthesized and the solid state structures determined. Here, the hydrogen bonding motive is replaced by the silver coordination and the arene–arene interaction was investigated joining the silver assembling motive.

Formation of Heterodimeric Resorcin[4]arene Capsules on Surfaces: An X-Ray Photoelectron Spectroscopy Investigation

A perfect fit: Hydrogen bond formation of heterodimeric molecular capsules assembled from complementary functionalized resorcinarene cavitands is of considerable interest from the viewpoint of multicomponent molecular assemblies. The formation of hydrogen-bonded heterodimeric capsules AB (see picture) based on a monolayer of tetrapyridyl resorcinarenes B is verified by means of X-ray photoelectron spectroscopy analyzing N 1s signatures.

A Theoretical Study of Polyoxometalates and Dendrizyme Model Compounds

We firstly report on a density functional study of molecular structures and other properties of several molybdenum and tungsten polyoxometalates. These are, respectively, of the Lindqvist, α-Keggin, α-Wells–Dawson, and Preyssler type. A force field for classical molecular dynamics (MD) simulations is derived from quantum chemical data for two α-Keggin tungstates. The second part of this report is devoted to results from MD simulations performed for eight dendrimer-encapsulated polyoxometalates in trichloromethane solution. These neutrally charged ion clusters are model compounds for ‘dendrizymes’, a novel class of biomimetic supramolecular catalysts with enzyme-like activity profile. The influence of dendrimer type and number on the solvent molecule distribution within the dendrimer shell is studied. Our approach may prove helpful in searching potentially promising dendrizyme compounds without requiring to perform separate MD simulations for every dendrizyme/substrate combination.