Peptide Bond Formation in the Protonated Serine Dimer Following Vacuum UV Photon-Induced 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.

Hydrolytic (in)stability of phosphate isosteres.

For decades enzymatic hydrolysis of nucleotides, a cornerstone of life, was studied extensively along with the chemical hydrolytic reaction. The metabolic instability of nucleotides, in contrast with their enormous chemical stability, triggered development of metabolically stable phosphate isosteres. However, their chemical stability has not been reported. Here, we fill this gap by exploring the hydrolytic stability of the thiophosphate (PS) and dithiophosphate (PS2) monoester isostere families. Kinetic experiments with uridine-PS and -PS2 (UMPS and UMPS2) allow to chart their borders of stability. Furthermore, characterization of several chemical and structural features of UMPS and UMPS2 provide insights, which explain the dramatically different stability of PS or PS2 moieties at different positions of the nucleotide phosphate chain. Our conclusions may guide the broad scientific community that applies phosphate isosteres and allow the selection of optimal isosteres.

Gas Phase Bond Formation in Dipeptide Clusters.

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.