Why are arginine and arginine-containing di- and tripeptides significant in H/D exchange reactions?

One study investigates the gas-phase H/D exchange reactions of protonated arginine (R) and arginine-containing di- and tripeptides, including gly-arg (GR), arg-gly (RG), gly-gly-arg (GGR), gly-arg-gly (GRG), and arg-gly-gly (RGG), with deuterated ammonia (ND3). Three H/D exchanges are observed for arginine and arginine-containing tri-peptide [M+H] + ions, while di-peptide [M+H] + ions undergo a single H/D exchange. The protonation typically occurs on the guanidine group due to its high proton affinity.

Arginine and its di- and tripeptides are key subjects for understanding H/D exchange mechanisms in the gas phase. Arginine and arginine-containing tripeptides exhibit three H/D exchanges, whereas dipeptides show a single exchange. The high proton affinity of the guanidine group in arginine dictates its protonation site, which is crucial for these reactions.