Building on these results, we next inves=gated the IEDDA reac=vity of iTCO. In addi=on to predic=ng the rela=onship between reagent concentra=on and applica=on performance, the click kine=cs also provide context for more precise study of the release kine=cs, allowing experimental designs that take into account the expected click reac=on rate. Second-order rate constants (k2) for the reac=on of Tz 1 and 10-12 with iTCO-PEG4 (14) were determined by stopped-flow spectrophotometry in PBS (pH 7.4) at 37 °C (Fig. ). The observed k2 values of iTCO span a range from 71 M -1 s -1 for the less reac=ve bis-alkyl class to 10,200 M -1 s -1 for the highly reac=ve Pyr2 (1). Unsurprisingly, given the structural similarity, the measured rate constants for rTCO-PEG4 (13) with selected Tz 1 and 10 are well matched to the corresponding results for iTCO, confirming that installa=on of the TDG is essen=ally kine=cally neutral, exer=ng just a slight accelera=ng effect on aryl-Tz click rates.