Figure 9.

Use of photoRNRs to unmask rates of chemical steps. A Schematic of photoβ2 with rhenium photooxidant [Re] attached covalently to C₃₅₅ and Y₁₂₂OH-β2 (that is, Y₁₂₂• is reduced) complexed with CDP, ATP, and α2 (49). In the case shown, Y₃₅₆ in β is replaced with the unnatural amino acid 2,3,5-F₃Y₃₅₆. (Figure 4). B Light initiates the reaction and the presence of the flash quencher, Ru(NH₃)₆Cl₃, prevents charge recombination (left) and generates [Re^II]-F₃Y-O⁻ (right), that rapidly drives 2,3,5-F₃Y₃₅₆ oxidation to the 3,5-F₃Y₃₅₆• that initiates chemistry within α2. Different mechanisms of oxidation shown are electron transfer (ET), PCET, proton coupled electron transfer, and HAT, hydrogen atom transfer.