Electron impact ionization studies with the amino acid valine in the gas phase and (hydrated) in helium droplets

Abstract

Here we report electron impact ionization studies with the amino acid valine in different environments, i.e., (i) isolated in the gas phase, (ii) embedded in superfluid helium droplets and (iii) co-embedded with water in superfluid helium droplets. Mass spectra are presented for all three environments for which changes in the fragmentation pattern of valine upon ionization are investigated. Comparison is made with previous electron impact ionization and photoionization studies with valine in the gas phase which confirms the fragile nature of this amino acid. Embedding valine in cold superfluid helium droplets leads to the formation of highly abundant protonated valine clusters. Co-embedding water with valine in helium droplets reduces fragmentation of valine.