UC Berkeley

In this dissertation, phenomena related to ion hydration are investigated in gas-phase clusters of ions and water molecules. Hydrated ions are generated using electrospray ionization and trapped using a Fourier transform ion cyclotron resonance mass spectrometer. A variety of ion activation techniques are used to probe the structures and reactivities of these ions, including infrared photodissociation (IRPD), ultraviolet photodissociation, blackbody infrared dissociation, and electron capture dissociation. IRPD spectra of alkali metal ions, ion pairs, and the protein denaturant guanidinium reveal how the delicate balance of noncovalent interactions between ions and water molecules establishes inner shell hydration motifs that can affect the hydrogen bond network of surrounding water molecules. In the case of guanidinium, molecular hydration structures determined by IRPD spectroscopy and ab initio calculations reveal that the ion is amphiphilic, and this is related to its bulk property as a protein denaturant in solution. The effects of ions on the hydrogen bond network of water are investigated by studying extensively hydrated ions in nanometer-sized droplets, or “nanodrops”. IRPD spectra of nanodrops containing a single La3+ ion and up to 550 water molecules indicate that the trivalent ion can frustrate the onset of crystallinity in these cold water clusters by altering the hydrogen bond network of water located remotely from the ion. Spectroscopy of nanodrop surfaces provides further evidence that multiply charged ions can affect the structural and electrostatic properties of nanodrops. These experimental data are supported by molecular dynamics simulations analyzed with custom-built software, and provide compelling evidence that ions can affect the structure of water well outside the first solvation shell – a point of contentious debate in the current literature. Using an extrapolation method, properties derived from cluster measurements such as surface “free” O–H stretching frequencies are related to their corresponding values at neutral interfaces, providing a link between cluster and bulk measurements. In addition to the aforementioned structural studies, thermodynamic information about the reductions of hydrated transition metal ions is obtained using the ion nanocalorimetry technique. A major improvement to this technique is introduced where ion-electron recombination energies are derived from laser calibration experiments. A value for the absolute reduction potential of the standard hydrogen electrode is deduced from the absolute reduction potential measured for the Cu2+/Cu+ redox pair, which should be more accurate than previously reported values. Ion nanocalorimetry is also used to measure, for the first time, the one-electron reduction potentials of several transition metal ions that are difficult to probe in solution due to the phenomenon of potential inversion.