Electron-capture dissociation

Electron-capture dissociation (ECD) is a method of fragmenting gas-phase ions for tandem mass-spectrometric analysis (structural elucidation). ECD involves the direct introduction of low-energy electrons to trapped gas-phase ions. It was developed by Roman Zubarev and Neil Kelleher while in Fred McLafferty's lab at Cornell University.

Electron-capture dissociation typically involves a multiply protonated molecule M interacting with a free electron to form an odd-electron ion:

Liberation of the electric potential energy results in fragmentation of the product ion.

ECD produces significantly different types of fragment ions (although primarily c- and z-type, b-ions have been identified in ECD) than other MS/MS fragmentation methods such as electron-detachment dissociation (EDD) (primarily a and x types),collision-induced dissociation (CID) (primarily b and y type) and infrared multiphoton dissociation. CID and IRMPD introduce internal vibrational energy in some way or another, causing loss of post-translational modifications during fragmentation. In ECD (and in EDD as well), fragments retain post-translational modifications such as phosphorylation and O-glycosylation. In ECD, unique fragments (and complementary to CID) are observed, and the ability to fragment whole macromolecules effectively has been promising. The low fragmentation efficiencies and other experimental difficulties, which are being studied, have prevented widespread use. Although ECD is primarily used in Fourier transform ion cyclotron resonance mass spectrometry, investigators have indicated that it has been successfully used in an ion-trap mass spectrometer.

ECD is a recently introduced MS/MS fragmentation technique and is still being investigated. The mechanism of ECD is still under debate but appears not to necessarily break the weakest bond and is therefore thought to be a fast process (nonergodic) where energy is not free to relax intramolecularly. Suggestions have been made that radical reactions initiated by the electron may be responsible for the action of ECD.

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