In this award, funded by the Chemical Measurement & Imaging (CMI) Program in the Division of Chemistry, Professor Evan Williams at the University of California, Berkeley, and his group are developing methods to investigate the interactions of ions with water in small droplets. State-of-the-art techniques developed in the Williams lab enable new measurements of the strength of ion-water interactions, how ions affect the structure of surrounding water molecules, how ions interact with other ions, and how water stabilizes ion charge. These measurements provide new insights into important problems in chemistry where ions play a central role, such as ion-protein structural effects that are important in biochemistry, ion solvation that plays a central role in aerosol chemistry important in the atmosphere, electrochemistry that plays an important role in batteries and fuel cells, and desalination that will likely play an increasingly important role for providing a reliable source of fresh water. They provide benchmarks that can help theoreticians improve computational methods aimed at a deeper understanding of various processes at the molecular level. Students working in the laboratory learn about instrumentation, computational methods, and measurement science - training which prepares them for success in a wide variety of technical careers.
Isolated nanodrops provide an ideal, well-controlled environment in which to study ion-water interactions. These nanodrops are size-selected, and thermochemical information is obtained using a method developed in the lab called nanocalorimetry. The accuracy of this nanocalorimetry method is being improved using UV laser light at various wavelengths for calibration. The improved method is used to probe ion-electron recombination reactions, thereby obtaining electrochemical half-cell potentials previously immeasurable using conventional methods, and to establish an absolute electrochemical scale. The concept of an absolute electrochemical scale has been hotly debated, but no definitive method for establishing such a scale currently exists. The research also seeks to extend the wavelength range of infrared photodissociation spectroscopy in order to provide complementary information about how water molecules directly interact with ions and ion-pairs inside the nanodrops. These methods are being used to improve understanding of the role of ion-water interactions for ions in the "Hofmeister" series, which orders ions based on their propensity to either stabilize or destabilize the native structures of proteins.