| The first portion of this dissertation describes our efforts to obtain structural information on complex ions from studies of their solvation behavior in the gas phase. In the case of protonated alkylamines, we found that all of them showed a preference for combining with 20 water molecules regardless of the size and structure of their alkyl chains. These so called "magic number" ions are structurally related to the first one of their kind to be identified, H+(HO2)21. We found that the now widely accepted structure of H+(H2O) 21, comprising a protonated water molecule residing in a pentagonal dodecahedron cage formed by 20 neutral water molecules, becomes problematic for the case of protonated alkylamines and quaternary ammonium ions because some of them are much too large to fit in such a cage. Based on this unique hydration behavior of protonated amines we have resolved a long debated issue about the location of the proton on aromatic amine molecules.; The studies of gas phase hydration of electrospray (ES) ions from some small peptides indicated that the hydration degrees of these ions can be related to the hydrophilicities of their corresponding neutral molecules in solution phase, i.e., ES ions of more hydrophilic molecules were hydrated to a greater extent than their counterparts. Having shown this tendency we then showed that the gas phase ion hydration can be used to obtain information on the structure of a non-covalent complex if the formation of this complex involves a change in hydrophilicity relative to its constituent components. Furthermore, our studies indicated that gas phase ion hydration can be a unique tool to reveal the number of charges on ions and "hidden" identities of ions based on the mass analyses with a low resolution mass spectrometer.; The second portion of this dissertation is devoted to the study of the adduction of anions to acid-denatured proteins in solution. Our experimental results seem to provide the most direct evidence yet obtained in support of the suggestion that the anion-induced refolding of acid-denatured proteins is due to the ion pairing between the anions and positively charged basic amino acid residues. |
