| Autor: |
Shenault DM; Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States., Fabijanczuk KC; Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States., Murtada R; Department of Chemistry and Biochemistry, Montclair State University, Montclair, New Jersey 07043, United States., Finn S; Department of Chemistry and Biochemistry, Montclair State University, Montclair, New Jersey 07043, United States., Gonzalez LE; Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States., Gao J; Department of Chemistry and Biochemistry, Montclair State University, Montclair, New Jersey 07043, United States., McLuckey SA; Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States. |
| Abstrakt: |
Methyl branching on the carbon chains of fatty acids and fatty esters is among the structural variations encountered with fatty acids and fatty esters. Branching in fatty acid/ester chains is particularly prominent in bacterial species and, for example, in vernix caseosa and sebum. The distinction of branched chains from isomeric straight-chain species and the localization of branching can be challenging to determine by mass spectrometry (MS). Condensed-phase derivatization strategies, often used in conjunction with separations, are most commonly used to address the identification and characterization of branched fatty acids. In this work, a gas-phase ion/ion strategy is presented that obviates condensed-phase derivatization and introduces a radical site into fatty acid ions to facilitate radical-directed dissociation (RDD). The gas-phase approach is also directly amenable to fatty acid anions generated via collision-induced dissociation from lipid classes that contain fatty esters. Specifically, divalent magnesium complexes bound to two terpyridine ligands that each incorporate a ((2,2,6,6-tetramethyl-1-piperidine-1-yl)oxy) (TEMPO) moiety are used to charge-invert fatty acid anions. Following the facile loss of one of the ligands and the TEMPO group of the remaining ligand, a radical site is introduced into the complex. Subsequent collision-induced dissociation (CID) of the complex exhibits preferred cleavages that localize the site(s) of branching. The approach is illustrated with iso- , anteiso- , and isoprenoid branched-chain fatty acids and an intact glycerophospholipid and is applied to a mixture of branched- and straight-chain fatty acids derived from Bacillus subtilis . |
