Neurotransmitters in the gas phase: hydrated noradrenaline

The conformational and molecular structures of singly hydrated noradrenaline complexes have been explored through a combination of electronic structure computation (at the B3LYP/ 6- 31+ G*, MP2/ 6- 31+ G* and MP2/ aug-cc-pVDZ levels of theory) and mass-selected ultraviolet and infrared ion-dip spectroscopy following laser ablation of the neurotransmitter into a freely expanding moist argon jet. Under these conditions, almost all the hydrated complexes are located in the global minimum energy configuration, associated with an extended, AG1a, ethanolamine side-chain conformation; the water molecule, which is located slightly above the plane of the catechol ring, is bound primarily as a proton acceptor to the m-OH substituent, and only weakly, as a proton donor, to the hydroxyl group on the side chain.