Study of methylation of nitrogen‐containing compounds in the gas phase

Abstract

The methyl migration between the protonated N,N-dimethylisopropylamine and other neutral aliphatic amines in the gas phase has been investigated by a hybrid external chemical ionization source ion trap mass spectrometer. Similar reactions have been found in the aqueous solution by Callahan and Wolfenden (J. Am. Chem. Soc. 2003; 125: 310). At the same time, density functional theory (DFT) calculations show that in contrast with the neutral N,N-dimethylisopropylamine, protonated N,N-dimethylisopropylamine is a better methyl donor. These results indicate that protonation promotes the methyl migration between aliphatic amines both in the gas phase and in the aqueous solution. In addition, methyl transfer also exists between the protonated N,N-dimethylisopropylamine and some other nitrogen-containing compounds.

Proposal for a chemically consistent way to annotate ions arising from the analysis of reference compounds under ESI conditions: A prerequisite to proper mass spectral database constitution in metabolomics

“…They are favored at low desolvation voltage. The main bimolecular “in‐source” reactions encountered are addition‐elimination type reactions such as carboxylic acid esterification or ester hydrolysis, alkyl group exchanges allowing for instance amine alkylation, [2 + 2] and [2 + 4] cycloadditions, S N , S N Ar, or S E Ar reactions (as discussed above in the case of covalent adduct formation) as well as oxidation and reduction. For the latter cases, even though, H 2 and O 2 are not formal neutral gain or loss, they may be considered as such to simplify the resulting ion annotation because the mechanistic processes underlying the redox reactions are scarcely documented …”

The Protonation Site of para-Dimethylaminobenzoic Acid Using Atmospheric Pressure Ionization Methods

“…For protonated p-DMABA, the fragmentations of Oand N-protonated species are expected to produce different product ions (Scheme 2). Loss of methyl radical from the Nprotonated N-methyl compounds is commonly observed in mass spectrometry [37,38]. Fragmentation of N-protonated p-DMABA gives rise to a radical cation at m/z 151.…”

Ortho‐hydroxyl effect and proton transfer via ion–neutral complex: the fragmentation study of protonated imine resveratrol analogues in mass spectrometry

“…Electrospray ionization (ESI) mass spectrometry combined with collision‐induced dissociation (CID) has been widely used in organic chemistry, biochemistry and pharmaceutical research . The fragmentation pattern studies of gaseous ions have always been necessary because of complexity and variability of rearrangement reactions occurring in the CID process …”

“…[1][2][3][4] The fragmentation pattern studies of gaseous ions have always been necessary because of complexity and variability of rearrangement reactions occurring in the CID process. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Ion-neutral complexes (INCs) are important intermediates and widely observed in unimolecular fragmentation reactions in mass spectrometry. [17,[21][22][23][24][25][26][27][28][29][30][31][32][33][34] An INC consists the ionic fragment and neutral species that are binding together by electrostatic interactions and maintain their individual mobility.…”

“…In this temporary system, various chemical reactions can take place before its final decomposition. Proton transfer, [5,6,20] benzyl cation transfer, [7,8,11,20,[35][36][37][38][39][40][41][42][43][44][45][46] transacylation, [9] electron transfer, [10] hydride transfer [11,19,20,33] and other group transfers [13][14][15][16][17][18]34] could occur within the INC via unimolecular reaction in the gas phase. Benzyl cations are highly reactive intermediates in various chemical and biochemical reactions and usually short-lived in solution.…”