We are investigating charge-remote fragmentation of oxo fatty acids to develop a structural method to determine the location of the carbonyl (oxo) group in fatty acids. The need for this capability became apparent to us recently in a collaboration with F. Schmitz (U. of Oklahoma) on the structural investigation of unusual lipids from marine organisms. Indeed, charge-remote fragmentation does permit the carbonyl to be located. Furthermore, the fragmentation in the vicinity of the oxo group is unusual, and seems to contradict the concept of """"""""charge remote"""""""". Mechanistic studies demonstrate that the same fragmentations occur for systems in which the oxo acid is separated from the charge site by a rigid steroid moiety. Related studies show for the first time that charge-remote simple cleavages and rearrangements compete; remarkably the simple cleavages dominate when the fatty acid ions are produced by the lower energy ESI method. Strategies involving charge-remote fragmentations have been applied to triacylglycerols for which has emerged a completely instrumental (tandem mass spectrometric) method for proving their structure. When fatty acids in general are activated as carboxylates or as metal-cationized species, they produce a host of interesting low-mass fragment ions. The structures are being probed by ab initio calculations, which has become a routine tool of this resource.
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