(452c) Single Molecule Studies of Ion Specific Effects On the Hydrophobic Interaction At the Solid-Liquid Interface

Understanding the effects of salts on the dynamics of single molecules is important for many biologically and industrially relevant systems. Ions are present in many industrial processes and in all in vivoenvironments and have long been known to impact molecular properties such as water solubility and surfactant self-assembly. A particularly interesting category of salts is the Hofmeister series.  In this series, salts such as sodium fluoride increase the strength of the hydrophobic effect, whereas salts on the other end of the spectrum, such as sodium thiocyanate, decrease the strength of hydrophobic interactions.

While there are a large number of studies detailing the macroscopic effects of ions in solution, there is a dearth of experimental data describing the effect of these salts on the molecular level. Data presented here represent molecular level insights into the impact of salts on the behavior of molecules at the solid-liquid interface. These data were obtained using single molecule fluorescence techniques to determine the effect various ions have on the adsorption rate, surface diffusion, and surface residence time of fluorescently labeled fatty acids.  Sodium fluoride greatly increased the adsorption rate of the fatty acid compared to sodium thiocyanate, but probe dynamics after adsorption remained relatively unchanged.  This indicates that an ionic species in solution will have a significant impact on the behavior of that molecule while in the bulk, but has limited effect on individual molecules once they are adsorbed to the solid-liquid interface.