Article
Extended Data Fig. 6 | Optimization study of Fe(ii)-mediated protein
modification reaction with pySOOF. a, In the photochemical modification
reaction with pySOOF, Fe(ii) likely acts as a reductive quencher for the
photoredox cycle and as a single-electron reductant of the on-protein radical
intermediate forming the enolate intermediate. However, side products, such
as H3-imine-DfeGly9, H3-hemiaminal-DfeGly9 or H3-diDfeGly9, can be
generated because of inefficient quenching of the on-protein radical
intermediate. b, In an initial experiment with 200 equiv. pySOOF, 280 equiv.
FeSO 4 , 5 equiv. Ru(bpy) 3 Cl 2 and 66 μM histone H3-Dha9 with a protein
concentration of 0.5 mg ml−1, 70% conversion to a mixture of H3-DfeGly9 and
H3-diDfeGly (57:43) was observed. The formation of the mono-addition
product was favoured at higher protein concentration (1 mg ml−1) and the
conversion was increased to 92% (Supplementary Table 13). c, For the Fe(ii)-
mediated reaction, various metallo- and organophotocatalysts with different
*Ered values (−0.56 to −1.37 V) and radical precursors were tested, and Ru(bpy) 3
and pySOOF were identified as the best combination (Supplementary Table 17).
d, The 100% stacked bar charts (n = 1, single data values represented by the y-
axis span of the corresponding bars) summarize the results of the optimization
studies of the FeSO 4 -mediated photochemical reaction with different reaction
times, concentrations of pySOOF and FeSO 4 , and catalytic amounts of Fe(ii)
and photocatalyst, respectively (Supplementary Tables 10–15, 18, 20). Short
reaction times and high efficiency with low concentrations of pySOOF were
found. However, in cases with high levels of reactivity with <100 equiv. FeSO 4 ,
only oxidation-derived products were created, indicating the dual role of Fe(ii)
for the single-electron reduction of the on-protein radical intermediate.
e, With the optimized conditions in hand, good to excellent conversion
efficiencies to histone H3-DfeGly9 were obtained at various protein
concentrations (0.1–5 mg ml−1). SET, single-electron transfer.