Where 𝑅 1 is the longitudinal relaxation rate, 𝑘 H 2 𝑎 is the rate of hydrogen association to the complex, 𝑘 𝐻2 𝑑 is the dissociation rate of H2 from the complex, 𝑀 𝑧 𝐶 (𝑡) is the magnetization of complex bound H2 and 𝑀 𝑧 𝑒𝑞 is the equilibrium magnetization of free H2without saturation. For simplicity, we assume that hydrogen bound to the complex is immediately saturated upon application of the saturation pulse, meaning 𝑀 𝑧 𝐶 (𝑡) = 0 at all times. Under these conditions, the equation S1 is readily solved and yields a simple exponential dependence: