Lifetime of [ReI]* excited state of 10 μM [Re]–X–βC19 for (a) X = F and (b) X = F3Y peptide in the presence of α2 mutants at 20 μM, in a solution of 1 mM CDP, 3 mM ATP, 15 mM MgSO4, and 5% glycerol, in 50 mM borate (pH 8.3). For biexponential decays, the percentage contribution of short and long components to the decay is listed.