Fragmentation, gas phase

Keywords retro-Diels-Alder fragmentation occurring in gas-phase, fragmentation in mass spectrometry... 

A further indication of formation of monomeric metaphosphoric esters or monomeric metaphosphoric acid itself by gas phase fragmentation comes from the behavior of 3-oxo-2-butyl phosphates in the mass spectrometer 1U). 

E. Gas-phase Fragmentation of Ligated Magnesium Ions to Yield... 

Wu and Brodbelt have studied the gas-phase fragmentation reactions of HOMg(L) complexes of crown ethers and glymes . A common loss involves units of C2H4O, which can either directly occur from the precursor ion, or can be triggered by an initial interligand reaction between HO and L. This latter reaction is illustrated in Scheme 11 for the complex of 12-Crown-4. Thus loss of H2O from the initial adduct 56 yields the ring-opened complex 57, which contains a coordinated alkoxide moiety, which can then lose an epoxide to form the related complex 58. 

Figure 5. Effect of gas phase fragmentation upon peak shapes observed using different mass analyzers for SIMS.

Kauffmann and coworkers have described the reaction of alkylsilver compounds with cyclohexenone (Scheme 1.6).29 It was found that the alkylsilver derivatives reacted preferentially, and in some cases exclusively, in the (3 position. A significant amount of 3-methylcyclohex-2-enol was observed for the reaction of Me2AgMgBr, which has been attributed to the elimination and subsequent reaction of silver(I) hydride. Silver(I) hydride has been observed in the gas-phase fragmentation of other organosilver compounds.30... 

The top-down approach, which sequences intact proteins by gas-phase fragmentation in the mass spectrometer, can also be used to characterize mutant proteins [103]. The position of the mutated amino acid can be unambiguously determined in each case by the characterization of product ions resulting from fragmentation on either side of the mutation site. 

Palumbo AM, Tepe JJ, Reid GE. Mechanistic insights into the multistage gas-phase fragmentation behavior of phosphoserine- and phosphothreonine-containing peptides. J. Proteome Res. 2008 7 771-779. 

Gas-phase fragmentation of the oligonucleotide anions by CID in MS-MS was pioneered by McLuckey et al. [28] using an ion-trap instrament. It is readily compatible with LC-ESI-MS. They also proposed the nomenclature, commonly applied to designate DNA fragments in MS-MS (Figure 22.4). 

MS/MS Experiments Coupled mth Eabeling. These experiments are the mainstays for the determination of gas-phase fragmentation mechanisms. Often there are similar functional groups in molecules and thus it is important to differentiate between them using either isotopic or structural labeling. 

Table 1 Tools Available to Examine Gas Phase Fragmentation Mechanisms MS/MS experiments coupled with labeling Isotopic labeling...

The gas-phase fragmentation of cationic tribenzotriquinacene derivatives is also remarkable. For example, the electron-impact (El) mass spectrum of tribromotribenzotriquinacene 145 is void of the peak corresponding to radical cation 213 due to extremely facile loss of a bromine atom to give the benzhy-drylic cation 214. However, loss of the residual bromines is very pronounced, and both the radical cation 215 and the dication 216 give rise to dominating peaks in the El mass spectrum [100]. 

An, X. Stone, J.A. Eiceman, G.A., Gas phase fragmentation of protonated esters in air at ambient pressure through ion heating by electric field in differential mobility spectrometry and by thermal bath in ion mobility spectrometry, Int. J. Mass Spectrom. 2011, 303(2-3), 181-190. 

FIGURE 11.7 Dispersion plot for propyl acetate in a DMS analyzer at a temperature of 100°C, from 59 Td (500 V) to 176 Td (1,500 V). The CV range is -5 (-43 V) to 1.8 Td (15 V). The signal intensity is both shaded and contour coded, and the trajectory of RIP, M2H, MH, fragment (protonated acetic acid) are labeled as RIP, M2H, MH, and F, respectively. (From An et al.. Gas phase fragmentation of protonated esters in air at ambient pressure through ion heating by electric field in differential mobility spectrometry and by thermal bath in ion mobility spectrometry, Int. J. Mass Spectrom. 2011. With permission.)... 

SCHEME 4.2 Fixed-charge derivatization and selective gas-phase fragmentation of methionine fixed-charge sulfonium ion derivatized peptides. (Reproduced from Amunugama, M. Roberts, K.D. Reid, G.E., J. Am. Soc. Mass Spectrom. 2006,17,1631-1642. With permission from the American Society for Mass Spectrometry, published by Elsevier Inc.)... 

---