Charge-remote fragmentation characteristics of functionalized alkanes in high-energy collision-induced dissociation

Abstract

In this study we report on high‐energy, collision‐induced dissociation processes leading to charge‐remote fragmentations, using three alkyl cations, namely n‐hexadecylpyridinium, n‐hexadecyltriphenylphosphonium and n‐hexadecyltriethylammonium, each with and without 2H2‐labelling at the C(9) position of the hexadecyl chain. The characteristic patterns corresponding to the formal elimination of alkane elements were observed, and the 2H2‐labelling at C(9) clearly affected only one charge‐remote fragment ion of the homologous series. However, in addition to the expected fragment ion containing only one deuterium atom, a significant ion retaining two deuterium atoms was observed. MS/MS/MS experiments demonstrated clearly that the latter ion showed partial deuteration around the charge site, the level of deuteration depending on the structure of the original precursor cation. These results can be interpreted in terms of two novel, distinct mechanisms, one of which involves an excited state in an aromatic ring. Mixed‐site fragmentation (MSF) ions were also observed from the phosphonium and ammonium ion precursors. We believe that the observation of the MSF process occurring at an sp2‐hybridized center in the phosphonium series has not been reported previously. It thus becomes apparent that high‐energy collisions leading to charge‐remote reactions in fact lead to a broad range of pathways. © 2000 John Wiley & Sons, Ltd.

Characterization of poly(ethylene glycol) esters using low energy collision-induced dissociation in electrospray ionization mass spectrometry

“…Carbocations are notorious for their ability to isomerize before fragmentation and lead to a complicated spectrum difficult to interpret. The well-established approach to solve this problem is via high-energy chargeremote fragmentation [65][66][67][68][69][70][71][72][73][74][75][76]. Nevertheless, the resulting spectrum from our approach still contains information from alkyl chain as well as acid proximity.…”

Applications and mechanisms of charge-remote fragmentation

“…The 1,4-H 2 elimination mechanism, however, also involves C±H bond breaking in its transition state, and should show a kinetic isotope effect. Denekamp et al (2000) showed in another study the unusual isotope effect for cleavage along an alkyl chain. For three alkyl cations (i.e., n-hexadecylpyridinium, nhexadecyltriphenylphosphonium, and n-hexadecyltriethyl-SCHEME 8.…”

“…We think the more likely reaction of a distonic product is a radical-triggered loss of ethene. Denekamp et al (2000) also presented evidence that interactions occur between the charge site and the reaction center via coiled conformations. We would not deny the possibility of coiling; the issue is whether that interaction has an important in¯uence on the reactions along the alkyl chain.…”

An isomer-specific high-energy collision-induced dissociation MS/MS database for forensic applications: a proof-of-concept on chemical warfare agent markers

“…Several mechanisms have been proposed for the CRF of functionalized saturated alkanes . One example of these mechanisms that deserved consideration was the mechanism proposed by Claeys et al .…”