Protein bonds between amino acids are one of the most important biological linkages that create life. The detection of amino acids in the interstellar environments and in meteorites may lead to the suggestion that amino acids came from outer space and that peptides bonds may have been created in the gas phase. Here we show experimentally the creation of covalent bonds, most likely peptide bonds, between serine dipeptides in the gas phase. More specifically, we show that spraying a solution of Ser-Ser dipeptides results, in addition to dipeptide clusters, in a peak with the same mass as the serine tetrapeptide, which also has the same fragmentation pattern. Moreover, we show that this mass is formed upon collision induced dissociation of clusters containing four serine dipeptides. Thence, if the dipeptide can be generated abiotically the polymerization process may occur spontaneously.

Possible routes for intra‐cluster bond formation (ICBF) in protonated serine dimers have been studied. We found no evidence of ICBF following low energy collision‐induced dissociation (in correspondence with previous works), however, we do observe clear evidence for ICBF following photon absorption in the 4.6–14 eV range. Moreover, the comparison of photon‐induced dissociation measurements of the protonated serine dimer to those of a protonated serine dipeptide provides evidence that ICBF, in this case, involves peptide bond formation (PBF). The experimental results are supported by ab initio molecular dynamics and exploration of several excited state potential energy surfaces, unraveling a pathway for PBF following photon absorption. The combination of experiments and theory provides insight into the PBF mechanisms in clusters of amino acids, and reveals the importance of electronic excited states reached upon UV/VUV light excitation.

Possible routes for intra‐cluster bond formation (ICBF) in protonated serine dimers have been studied. We found no evidence of ICBF following low energy collision‐induced dissociation (in correspondence with previous works), however, we do observe clear evidence for ICBF following photon absorption in the 4.6–14 eV range. Moreover, the comparison of photon‐induced dissociation measurements of the protonated serine dimer to those of a protonated serine dipeptide provides evidence that ICBF, in this case, involves peptide bond formation (PBF). The experimental results are supported by ab initio molecular dynamics and exploration of several excited state potential energy surfaces, unraveling a pathway for PBF following photon absorption. The combination of experiments and theory provides insight into the PBF mechanisms in clusters of amino acids, and reveals the importance of electronic excited states reached upon UV/VUV light excitation.

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