Mass Spectrometry. MS 1 and MS n measurements of oxidation products were conducted using a Velos Pro or an Eclipse mass spectrometer (Thermo Fisher Scientific, Bremen, Germany). The instruments were equipped with either a heated electrospray ionization (HESI-II) probe (Thermo Fisher Scientific) or a nanoESI source. HESI settings included a voltage of ± 3.5 kV, an inlet temperature of 300 °C, a sheath gas flow of 10, and an aux gas flow of 8. nanoESI settings included a voltage of 1 kV. In all experiments, the isolation window was ±0.5 m/z, the collision setting (HCD/CID) was 30 NCE, and the MS n resolution was 15,000 at m/z 400. Detailed information about RPLC experiments and MS settings are included in the Supporting Information.