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RDD-HCD Provides Variable Fragmentation Routes Dictated by Radical Stability.
Jacob W Silzel1, Ryan R Julian1
1Department of Chemistry, University of California, Riverside, California 92521, United States.
Journal of the American Society for Mass Spectrometry
|February 14, 2023
Summary
Radical-directed dissociation (RDD) using higher-energy collisional dissociation (HCD) offers tunable fragmentation. RDD-HCD spectra vary with energy, favoring radical pathways at low energies and mobile proton pathways at high energies.
Area of Science:
- Mass Spectrometry
- Analytical Chemistry
- Chemical Physics
Background:
- Radical-directed dissociation (RDD) is a fragmentation technique utilizing photodissociation of carbon-iodine bonds to generate radicals.
- Previous RDD experiments employed ion-trap collision-induced dissociation (CID) for collisional activation.
- Higher-energy collisional dissociation (HCD) presents a distinct activation method with different ion excitation and fragmentation patterns compared to CID.
Purpose of the Study:
- To investigate the application of higher-energy collisional dissociation (HCD) for activation in radical-directed dissociation (RDD) experiments.
- To compare RDD-HCD fragmentation patterns with those obtained from RDD-CID.
- To explore the influence of HCD energy on RDD fragmentation pathways.
Main Methods:
- Selective 213/266 nm photodissociation of carbon-iodine bonds to generate radicals.
- Reisolation of generated radicals.
- Collisional activation of reisolated radicals using higher-energy collisional dissociation (HCD) at varying energy levels.
- Comparison of fragmentation spectra obtained from RDD-HCD and RDD-CID.
Main Results:
- RDD-HCD spectra exhibit significant variation with HCD energy.
- Lower HCD energies favor radical-directed pathways (a/z-ions, side chain losses), characteristic of RDD.
- Higher HCD energies promote fragmentation directed by mobile protons (b/y-ions), indicating a shift from RDD pathways.
- The abundance of radical products decreases as HCD energy increases, supporting RDD's preference for lower energy barriers.
Conclusions:
- Higher-energy collisional dissociation (HCD) provides tunable fragmentation control in radical-directed dissociation (RDD) experiments.
- RDD-HCD allows for selective activation of different fragmentation pathways based on applied energy.
- The observed differences between RDD-HCD and RDD-CID spectra confirm distinct dissociation mechanisms and multiple dissociation events in HCD.
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