Charge transfer mass spectrometry

Laali and Lattimer (1989 see also Laali, 1990) observed arenediazonium ion/crown ether complexes in the gas phase by field desorption (FD) and by fast atom bombardment (FAB) mass spectrometry. The FAB-MS spectrum of benzenediazonium ion/18-crown-6 shows a 1 1 complex. In the FD spectrum, apart from the 1 1 complex, a one-cation/two-crown complex is also detected. Dicyclo-hexano-24-crown-6 appears to complex readily in the gas phase, whereas in solution this crown ether is rather poor for complexation (see earlier in this section) the presence of one or three methyl groups in the 2- or 2,4,6-positions respectively has little effect on the gas-phase complexation. With 4-nitrobenzenediazonium ion, 18-crown-6 even forms a 1 3 complex. The authors assume charge-transfer complexes such as 11.13 for all these species. There is also evidence for hydride ion transfer from the crown host within the 1 1 complex, and for either the arenediazonium ion or the aryl cation formed from it under the reaction conditions in the gas phase in tandem mass spectrometry (Laali, 1990). 

More recently, Kim et al. synthesized dendritic [n] pseudorotaxane based on the stable charge-transfer complex formation inside cucurbit[8]uril (CB[8j) (Fig. 17) [59]. Reaction of triply branched molecule 47 containing an electron deficient bipyridinium unit on each branch, and three equiv of CB[8] forms branched [4] pseudorotaxane 48 which has been characterized by NMR and ESI mass spectrometry. Addition of three equivalents of electron-rich dihydrox-ynaphthalene 49 produces branched [4]rotaxane 50, which is stabilized by charge-transfer interactions between the bipyridinium unit and dihydroxy-naphthalene inside CB[8]. No dethreading of CB[8] is observed in solution. Reaction of [4] pseudorotaxane 48 with three equiv of triply branched molecule 51 having an electron donor unit on one arm and CB[6] threaded on a diaminobutane unit on each of two remaining arms produced dendritic [ 10] pseudorotaxane 52 which may be considered to be a second generation dendritic pseudorotaxane. 

Electron Transfer in Gaseous Positively Charged Peptides — Relation to Mass Spectrometry... 

Electron-transfer processes play many very important roles in chemistry and biology. Because the present work is focused on electron-transfer events occurring within positively charged gas-phase peptides as they occur in ETD and ECD mass spectrometry experiments, it is not appropriate or feasible to review the myriad of other places electron-transfer reactions occur in chemistry. Chapter 10 of the graduate level textbook by Schatz and Ratner [12] gives a nice introduction to the main kinds of electron-transfer events that chemists usually study as well as to the theoretical underpinnings. They also give, at the end of Chapter 10, several literature references to selected seminal papers on these subjects. 

HPLC runs involve relatively large volumes of a solvent however, by the nse of dedicated interfaces, this is no more a problem, and bands eluted from HPLC can be transferred to a GC or to a mass spectrometry (MS). The interface is the hearth of the HPLC-MS hyphenation, and it mnst be able to eliminate solvent and to perform the ionization of the analytes in order to separate them on the basis of the ratio mass/charge. 

Finally, two studies have reported on the reactions of carbocations with Mg atoms using mass spectrometry The types of products formed depend on the nature of the carbocation. The labeled methanium ion, CH4D+, reacts via proton transfer (equation 11), deuteron transfer (equation 12) and charge transfer (equation 13). The ethyl cation reacts via charge transfer (equation 14) while the tert-butyl cation reacts via proton transfer (equation 15). In all cases there was no evidence for formation of an organomagnesium species. 

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