Knowledge Bank

A balance of competing electrostatic and hydrogen bonding interactions directs the structure of hydrated gas-phase cluster ions. In K$+$(Tryptamine) cluster ions, a favorable electrostatic interaction between the potassium cation and the tryptamine NH$2$ lone pair stabilizes the high-energy Gph(in) and Gpy(in) conformers of neutral tryptamine. Previous studies of Tryptamine(H$2$O) clusters indicate that the hydrating water molecules stabilize the neutral minimum energy Gpy(out) tryptamine conformer. In this scheme, the first water molecule interacts directly with the NH$2$ lone pair and is located to the side of the tryptamine monomer. By incorporating a potassium cation, however, the minimum energy tryptamine$\cdots$water configuration is disrupted in order to maximize the electrostatic interactions with the cation, shifting so that the tryptamine$\cdots$water interaction includes a $\pi$-hydrogen bond between the water and the phenyl ring of tryptamine. The infrared photodissociation spectra of K$+$(Tryptamine)(H$2$O) and K$+$(Tryptamine)(H$2$O)Ar will be presented along with parallel \textit{ab initio} and thermodynamics calculations to assist with the identification of the isomers present in each experiment.