Zwitter Ionization of Glycine at Outer Space Conditions due to Microhydration by Six Water Molecules
Gerhard Schwaab, Ricardo Pérez de Tudela, Devendra Mani, Nitish Pal, Tarun Kumar Roy, Fabio Gabas, Riccardo Conte, Laura Durán Caballero, Michele Ceotto, Dominik Marx, Martina Havenith
Abstract
We investigate glycine microsolvation with water molecules, mimicking astrophysical conditions, in our laboratory by embedding these clusters in helium nanodroplets at 0.37 K. We recorded mass selective infrared spectra in the frequency range $1500--1800\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ where two bands centered at 1630 and $1724\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ were observed. By comparison with the extensive accompanying calculations, the band at $1630\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ was assigned to the ${\mathrm{COO}}^{\ensuremath{-}}$ asymmetric stretching mode of the zwitter ion and the band at $1724\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ was assigned to redshifted $\mathrm{C}=\mathrm{O}$ stretch within neutral clusters. We show that zwitter ion formation of amino acids readily occurs with only few water molecules available even under extreme conditions.