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Differential cationization of fatty acids with monovalent cations studied by electrospray ionization tandem mass spectrometry and a computational approach
Author(s) -
Sudarshana Reddy B.,
Pavankumar P.,
Sridhar L.,
Saha Soumen,
Sastry G. Narahari,
Prabhakar S.
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.8143
Subject(s) - chemistry , adduct , electrospray ionization , ion , molecule , mass spectrometry , dissociation (chemistry) , tandem mass spectrometry , mass spectrum , analytical chemistry (journal) , inorganic chemistry , organic chemistry , chromatography
Rationale The intercellular and intracellular transport of charged species (Na + /K + ) entail interaction of the ions with neutral organic molecules and formation of adduct ions. The rate of transport of the ions across the cell membrane(s) may depend on the stability of the adduct ions, which in turn rely on structural aspects of the organic molecules that interact with the ions. Methods Positive electrospray ionization (ESI) mass spectra were recorded for the solutions containing fatty acids (FAs) and monovalent cations (X = Li + , Na + , K + , Rb + and Cs + ). Product ion spectra of the [FA + X] + ions were recorded at different collision energies. Theoretical studies were exploited under both the gas and solvent phase to investigate the structural effects of the FAs during cationization. The stability of [FA + X] + adduct ions was further estimated by means of AIM topological analyses and interaction energy (IE) values. Results Positive ion ESI‐MS analyses of the solution of FAs and X + ions showed preferential binding of the K + ions to FAs. The K + ion binding increased with the increase in the number of double bonds in the FAs, while it decreased with the increase in the number of carbon atoms in FAs. Dissociation curves of [FA + X] + ions indicated the relative stability order of the [FA + X] + ions and it was in line with the observed trends in ESI‐MS. The solvent phase computational studies divulged the mode of binding and the binding efficiencies of different FAs with monovalent cations. Conclusions Among the studied monovalent cations, the cationization of FAs follows the order K + > > Na + > Li + > Rb + > Cs + . Docosahexaenoic acid showed high efficiency in binding with the K + ion. The K + ion binding efficiency of FAs depends on the number of double bonds in unsaturated FAs and the carbon chain length in saturated FAs. The cationization trends of FAs obtained from the ESI‐MS and ESI‐MS/MS analyses were in good agreement with solvent‐phase computational studies.