An experimental single-molecule force spectroscopy approach is developed to measure pairwise interactions between non-polar solutes in water. In this approach the non-polar molecules are tethered to the solid substrate and to the sharp probe of the atomic force microscope. The use of long (~30 nm) water-soluble tethers facilitates formation of single “hydrophobic bonds” between tethered molecules. In experiments the increasing load forces the molecular bond to rupture. The rupture forces are measured as a function of the probe velocity. These data are used to extract kinetic parameters characterizing the potential of mean force between non-polar solutes in water. Experimental measurements of pairwise interactions between the symmetric pairs of fullerenes, alkanes of different sizes (from dodecane to octadecane) and hydrophobic 12-mer fragment of alpha-synuclein are demonstrated. The systematic errors typical to force-spectroscopy measurements are considered in the data analysis. Measurements with fullerene molecules indicate that the transition state is separated from the equilibrium state by a distance of ~0.4 nm that is larger than a size of water molecule. Measurements with alkanes and peptides hint at possible conformational transitions in individual molecules upon dissociation from the dimeric state.
Water Mediated Interactions
8:20 AM-12:20 PM, Tuesday, August 19, 2008 Loews -- Commonwealth A, Oral