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Start of funding 01.07.2005

Water at biological interfaces

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Most biological function occurs at interfaces, bei it membrane surfaces or the surfaces of proteins or other macromolecules. For the modelling of biological function, the presence of water at these surfaces is either ignored or taken into account in some approximate and coarse-grained fashion. Our goal is, by using the coordinated efforts of ab-initio quantum-mechanics, analytical theory, and dynamic simulation methods, to elucidate the effects of surface-specific water structure and ion specificity. We shall be able to predict surface potentials and surface tensions of electrolyte solutions as a function of the ion type. The calculation of counterion density profiles is theoretically quite straightforward, but experimentally more demanding. Still, we expect progress to be made using anomalous scattering techniques.

Final report:
The main theme of the research project "Water at Biological Interfaces" were biologically relevant problems that have to do with water structure and ion-specific effects at surfaces. In 2005 we hosted Dr. Yong-Woon Kim from the group of Prof. P. Pincus at the University of California, Santa Barbara, for two weeks and we discussed in detail the time frame and scope of our planned collaborative research. In 2006 three of my collaborators could in turn visit UCSB and perform research over there.

Using Molecular-dynamics simulation we looked at the water structure at self-assembled monolayers (SAMs) and at hydrophobic single-crystal diamond surfaces. We determined the distributions of the halogenid ions Fluoride, Chloride, Bromide and Iodide. The ion polarizability turns out to be important and has to be included. In agreement with experiments, the large ions Iodide and Bromide adsorb at hydrophobic surfaces, whereas the small ions Fluoride and Chloride are repelled. In the future we will use the effective ion-surface interactions (which follow from the distribution function) as an input for coarse-grained analytical theories to gain a deeper understanding of charged and neutral surfaces immersed in water.