Neurotransmitters in the gas phase: Infrared spectroscopy and structure of protonated ethanolamine

A potentially general approach to the infrared spectroscopic detection and structural assignment of protonated molecules in general, and neurotransmitters in particular, generated in high concentration in the gas phase has been implemented, and applied to ethanolamine. Proton transfer in the cationic [phenol-ethanolamine](+) complex, generated by resonant two photon ionisation, creates a [phenoxy-protonated ethanolamine] complex. Its infrared photodissociation spectrum is almost identical to vibrational spectrum of free protonated ethanolamine; the perturbation introduced by the phenoxy ligand is highly localised and it has very little effect on the structure of its protonated partner. In this respect, the strategy should be able to provide a direct view of the vibrational spectroscopy and structure of a wide range of protonated molecules, including many of biological importance. It is a close relative of the 'messenger' technique, involving the infrared photodissociation of molecular clusters, that has been exploited by Lee and co-workers (J. C. Jiang, C. Chaudhuri, Y. T. Lee and H.-C. Chang, J Phys. Chem. A, 2002, 106, 10 937), Solca and Dopfer (N. Solca and O. Dopfer, Angew. Chem., Int. Ed. Engl., 2002, 41, 3628) and Mikami and co-workers (A. Fujii, E. Fujimaki, T. Ebata and N. Mikami, J Chem. Phys., 2000, 112, 6275) in infrared photodissociation studies of protonated clusters of methanol and benzene and of alkyl benzene cations.