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Fragmentation pathways arising from protonation at different sites in aminoalkyl‐substituted 3‐hydroxy‐1,2,5‐oxadiazoles (3‐hydroxyfurazans)
Author(s) -
Grossert J. Stuart,
Boschi Donatella,
Lolli Marco L.,
White Robert L.
Publication year - 2018
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.8166
Subject(s) - protonation , chemistry , fragmentation (computing) , ion , tautomer , collision induced dissociation , quadrupole ion trap , dissociation (chemistry) , mass spectrometry , mass spectrum , computational chemistry , molecule , stereochemistry , photochemistry , ion trap , medicinal chemistry , tandem mass spectrometry , organic chemistry , chromatography , computer science , operating system
Rationale The gas‐phase fragmentation chemistry of multifunctional cations is highly influenced by the site of protonation. Possible relationships between protonation site and fragmentation processes were studied using 4‐aminoalkyl‐3‐hydroxyfurazans. For these heterocyclic amines, the starting points for competing fragmentation pathways varied with protonation at multiple sites in two tautomers. Methods Mass spectra were acquired using electrospray ionization (positive mode) coupled to triple quadrupole and ion trap mass spectrometers; precursor–product ion relationships were studied by collision‐induced dissociation. Quantum mechanical computations were performed at the MP2/6–311++G(2d,p)//ωB97X‐D/6–311+G(d) level of theory. Results Prominent successive losses of NO and CO and competing losses of CH 2 =NH or NH 3 were observed as fragmentation processes. The lowest barrier computed for the initial step in a fragmentation pathway was associated with the [M + H] + ion protonated at N5 in the heterocyclic ring, whereas an alternative ring cleavage leading to complementary product ions was initiated by protonation of the ring at N2. Side‐chain protonation led to loss of NH 3 without cleavage of the 3‐hydroxyfurazan ring. Conclusions The product ions obtained by the competing fragmentation processes varied with the site of protonation. Interestingly, the most abundant product ions observed at low collision energies were formed by cleavage of protonated molecules possessing more internal energy than other isomers.