ECD analysis at cone voltages of 20 and 160 V was also attempted for 17+ CRP, 21+ PhosB, and 15+ TRAP, however, no fragments were obtained for these complexes. We did observe extensive gas phase electron capture charge reduction (ECCR) with the average charge state being 12+ for CRP, with a precursor charge state range of 8+ through 17+. For PhosB, the average charge was 14+ with a range encompassing 7+ through the 21+ precursor. The average charge for TRAP decreased to 12+, with a range of 6+ to 15+. We did attempt to tune the Transfer collision energy and Transfer cell pressure to release ECD fragments, but those efforts did not result in ECD fragments being released from the protein complexes. We also attempted to tune the transfer RF amplitude to help capture possible ECD fragments, but to no avail. As we checked PDB 1GNH for CRP we found that the N-terminus is solvent accessible in the native structure while the C-terminus is buried in an interfacial interaction. For PDB 1GPB for PhosB both N-and C-termini are solvent accessible, while 1GTN for TRAP features N-and Ctermini that are involved in interfacial interactions, some of which are present as hydrogen bonds. Because charge reduction without observed fragmentation was observed for CRP, PhosB, and TRAP, they can be classified as 'group II' following the Loo lab's designation scheme, which suggests that inter-and intra-subunit interactions limit the number of fragments that can be obtained after ECD. For CRP, whose N-terminus was solvent accessible, it is possible that ionization into the gas phase resulted in the N-terminus becoming protected by new non-covalent interactions during desolvation, thereby limiting c-type fragmentation. Additionally, we suppose that CRP's higher mass, compared to SA, could have contributed to low kinetic energy that Transfer CID could not overcome to liberate fragments. Thus, a heavier collision gas, such as argon or xenon, could increase the collision energy enough to free the ECD fragments from the complex or AI-ETD could be attempted.