The diversity of the water and acetonitrile structures in a binary system, caused by local structural inhomogeneities, has been investigated by molecular dynamic simulations. Our systems cover a broad range of acetonitrile mole fractions: dilute, moderate, and higher concentration mixtures. For reference, we perform simulations on pure water and pure acetonitrile systems. We examine concepts of analysis for an extraction of local structure information of anisotropic fluids. In general, the local water and acetonitrile structures can be roughly characterized by the radial distribution functions in terms of the classical site-site pair correlations. For a more thorough investigation of the local structure and the microheterogeneity of the systems, we use angular-dependent radial distribution functions. From the radial pair correlation functions, it is possible to extract coordination numbers and detailed local information of anisotropic water distributions around the acetonitrile molecules. To confirm the existence of the acetonitrile cluster and to gain qualitative insight into its stability, we examined the time-dependent radial and angular distribution functions. The results for the acetonitrile cluster arrangements are in line with experimental data of binary acetonitrile/water mixtures.

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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 shell's 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.

Using molecular simulations we have investigated the diversity of the mobility of water molecules in a three-component system of crosslinked PAA/water/acetonitrile affected by local structural inhomogeneities. We examine quantitative analysis concepts for the extraction of local structure and dynamics properties in anisotropic fluids from molecular dynamics simulations. By calculation of local translational and reorientational correlation functions on trajectories of individual molecules in equivalent local environments, it is possible to extract local reorientational and translational diffusion quantities. In our simulated liquid mixtures, we classify the environments of different centres like crosslinkers, side chains, pores and water regions in the complex structure. We get insight into the local molecular dynamics of water molecules from the calculation of local reorientational relaxation times and diffusion coefficients from the slope of the mean square displacements of the water molecules in the specific local environments. In addition, we calculate a distance dependent curve for the reorientational mobility of the water molecules on the PAA/water interface. Finally, we extract dynamical information by linking the ensemble-averaged diffusion data from the simulations to stimulated spin-echo experiments with pulsed magnetic field gradients to study time dependent local self-diffusion processes of the water solution in swollen crosslinked polyacrylamide gels.