where δ 13 C and δ 13 C 0 are the C isotope signatures of the residual substrate after the reaction and its original value, respectively. [S] and [S] 0 are the final and initial substrate concentrations, respectively, and are documented in Section S2.6. Parameter n C is the number of carbon atoms in the substrate to account for the isotopic dilution of the isotope effect assuming an asynchronous hydroxylation mechanism. Non-linear regression fits including the standard deviation of triplicate measurements were carried out in Igor Pro (WaveMetric Inc).