Determination of Ion−Solvent Equilibria in the Gas Phase. Hydration of Diprotonated Diamines and Bis(trimethylammonium) Alkanes

Abstract

Many ions of interest in condensed phase chemistry cannot be produced in the gas phase by conventional methods. This is particularly the case for multiply charged inorganic and bio-organic ions. However, these species can be produced by electrospray, which is a method with which electrolyte ions present in a solution can be transferred to the gas phase. An ion-source reaction chamber was developed with which the equilibrium constants of ion−molecule equilibria and their temperature dependence can be determined, where the ions involved are produced by electrospray. The hydration equilibria Mz+(H2O)n-1 + H2O = Mz+(H2O)n were determined for Mz+ = Na+, K+, n-C3H7NH3+, n-C6H13NH3+. The ΔG°n-1,n, ΔH°n-1,n, and ΔS°n-1,n were found to be in good agreement with previous determinations where these ions were produced by conventional techniques. Equilibria determinations were also obtained for the diprotonated α,ω-alkyldiammonium ions: H3N(CH2)pNH32+ where p = 5, 6, 7, 8, 9, 10, 12. The ΔH° values obtained for these...