Photosynthesis of a combinatorial peptide library in the gas phase

A strategy for generating large numbers of peptides from a relatively small number of precursors based on photosynthetic combination in the gas phase is presented. In this approach, electrospray ionization is used to create a combination of proton-bound dimers from a specified set of peptides present in solution. The dimers are then accumulated and isolated in an ion trap mass spectrometer. Photoexcitation (at 157 nm) leads to water elimination and the formation of larger peptide sequences that are characterized by subsequent isolation and collision-induced dissociation. The method is illustrated by using a set of four enkephalin-related and acetylated peptides to generate 12 larger peptide sequences. The ability to synthesize, isolate, and characterize many amino acid sequences from only a few precursors provides a fast and efficient means of characterizing properties of such species (e.g., dissociation patterns and reactivities).