Proton Transfer In Histidine-Tryptophan Heterodimers Embedded In Helium Droplets

We used cold helium droplets as nano-scale reactors to form and ionize, by electron bombardment and charge transfer, aromatic amino acid heterodimers of histidine with tryptophan, methyl-tryptophan, and indole. The molecular interaction occurring through an N-H center dot center dot center dot N hydrogen bond leads to a proton transfer from the indole group of tryptophan to the imidazole group of histidine in a radical cationic environment. (C) 2015 AIP Publishing LLC.