Ultraviolet and infrared spectra of mono-, di- and tri-hydrated clusters of protonated noradrenaline – Solvation and conformational variations

Abstract

Ultraviolet (UV) and infrared (IR) spectra of hydrated clusters of protonated noradrenaline (NAdH+) are measured by the electrospray – cold ion trap laser spectroscopy. NAdH+-(H2O)1,2 show complicated UV transitions, while NAdH+-(H2O)3 gives simple and blue-shifted spectrum. Conformer-selected IR spectra and the IR-UV hole burning spectra reveal that 4, 3 and 2 conformers coexist in hydrated complexes of n = 1 ∼ 3, respectively. Gauche conformations for all observed conformers are assigned from the comparison to the theoretical IR spectra obtained by the DFT calculations. The blue shift in NAdH+-(H2O)3 is rationalized by the πσ*interaction between the third water to OH in catechol.