Proton bond observed in a better light

A clearer picture of the intermolecular proton bond that forms when a proton (hydrogen ion) is shared between two Lewis-base solvent molecules is now possible thanks to a gas-phase ion spectroscopy study carried out by J. Robert Roscioli, Laura R. McCunn, and Mark A. Johnson of Yale University (Science 2007, 316, 249). Lewis bases, such as water, alcohols, and ammonia, can use a lone pair of electrons to trap protons to form cations. When two molecules compete for the same proton, a complex forms with the proton bound in the middle. This binding motif is important in biological and physical proton-transport processes, the researchers note. Previous infrared spectroscopy studies of these complexes in the solid and liquid phases have yielded broad absorption peaks bearing only modest information. But in the gas phase, the infrared spectra of complexes studied by the Yale team using argon nanomatrix methods showed sharp bands that clarify how the proton affinities and molecular vibrations of the flanking bases influence the confined proton.