Roadmap for fragmentation of protonated methylarginines in the gas phase

Sabu, Sahadevan; Han, Ching-Chih

doi:10.1016/j.ijms.2015.01.005

Cited by 1 publication

(1 citation statement)

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“…The structures of the resulting product ions from LysH + ( 4a ) and OrnH + ( 3a ) are consistent with those of protonated pipecolic acid (PipH + , 4b ) 7,19,21,28,34 and proline (ProH + , 3b ), 13,21 respectively, indicating cyclization upon nucleophilic displacement of the protonated side‐chain amino group by the α‐amino group 7,11 . The displacement reaction is also indicated by the analogous loss of N 2 H 3 when the hydrogens on nitrogen and oxygen in lysine were exchanged for deuterium, 21 the loss of NH 3 from protonated diamino alkanes, 11 and the major loss of guanidine from the terminal position in the side chain of protonated arginine (ArgH + ) 17,19,31,34,37 . In the latter instance, the accompanying formation of protonated guanidine, the complementary product ion, reinforces the importance of the loss of the side‐chain functional group.…”

Section: Introductionsupporting

confidence: 53%

Fragmentation reactions of protonated α,ω‐diamino carboxylic acids: The importance of functional group interactions

Grossert

White

2021

J Mass Spectrom

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Protonated members of a homologous series of biologically significant α,ω‐diamino carboxylic acids were subjected to collision induced dissociation (CID). The resulting fragmentation patterns were studied using isotopic labeling, quantum mechanical computations, and pseudo MS3 experiments conducted primarily on an ion trap mass spectrometer. Each protonated α,ω‐diamino acid showed a primary neutral loss of either ammonia or water; a clear explanation was developed for the observed variation of the two losses within the series. Protonated 2,3‐diaminopropanoic acid, 2,4‐diaminobutanoic acid, and 2,7‐diaminoheptanoic acid gave secondary losses of water, carbon monoxide, and a loss of water plus carbon monoxide, respectively. In the parallel pathways characterized for the fragmentations of protonated ornithine and lysine, the α‐nitrogen of the diamino acid was maintained in the cyclic iminium product formed by successive losses of NH3 and (H2O + CO), whereas the side‐chain nitrogen was retained by consecutive losses of H2O and (CO, NH3). The 1‐piperideine ion from protonated lysine was fragmented further, losing ethylene from carbons 4 and 5. Protonated 2,6‐diaminopimelic acid fragmented by analogous reactions. Detailed mechanistic schemes for the fragmentation of both protonated 2,3‐diaminopropanoic and ornithine were generated from MP2/DFT computations. This work highlights the participation of the side‐chain amino group, which distinguishes the gas‐phase chemistry of protonated α,ω‐diamino acids from the well‐documented fragmentation reactions of protonated α‐amino acids bearing a hydrogen atom or an alkyl side chain. In general, the results further illustrate the importance of intramolecular separations affecting the specific interactions between functional groups leading to the fragmentation of multifunctional ions.

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