Electron attachment step in electron capture dissociation (ECD) and electron transfer dissociation (ETD)

Area of Science:

• Computational Chemistry
• Mass Spectrometry
• Chemical Dynamics

Background:

• Electron capture dissociation (ECD) and electron transfer dissociation (ETD) are crucial techniques for peptide and protein analysis.
• Understanding the mechanisms of electron attachment and transfer is key to optimizing these methods.
• Model systems are used to investigate fundamental processes in dissociation.

Purpose of the Study:

• To estimate cross sections for electron attachment in ECD and electron transfer in ETD for a model system with an S-S bond and a positive charge.
• To compare the efficiency of electron transfer/capture at the positive site versus the S-S bond site.
• To infer implications for peptide and protein dissociation.

Main Methods:

• Classical dynamics trajectory simulations.
• Ab initio electronic structure calculations.
• Landau-Zener-Stueckelberg curve-crossing approximation.

Main Results:

• Electron transfer dissociation (ETD) rates were estimated using a curve-crossing approximation.
• The cross section for ETD at the positive site is predicted to be an order of magnitude larger than at the S-S bond site.
• In ECD, electron capture at the positive site is predicted to be up to three orders of magnitude larger than at the S-S bond site.

Conclusions:

• Electron attachment to positive sites is predicted to dominate S-S bond cleavage.
• Cleavage efficiency is distance-dependent, potentially making Coulomb-assisted S-S sigma* attachment competitive.
• These findings have implications for understanding SS and N-C(alpha) bond cleavage in peptides and proteins via ECD and ETD.