Photochemically induced nucleation in supersaturated and undersaturated thaumatin solutions

We demonstrate photochemically induced nucleation in supersaturated and undersaturated solutions of thaumatin. The irradiation of supersaturated and undersaturated thaumatin solutions in 0.75 M potassium sodium tartrate (PST) at pH 5.6 in N-(2-acetamido)iminodiacetic acid (ADA) buffer with β = 2 or β = 0.5 increased the number of thaumatin crystals in the droplet. The photochemical reaction induced the formation of unstable small clusters, which led to the growth of nuclei. The mechanism of nucleation enhancement was investigated in steady state and transient absorption experiments. The photochemical intermediate, in which one tryptophan residue is changed to a neutral tryptophanyl radical, appears to be responsible for the nucleation of thaumatin, as well as for the photochemically induced nucleation of lysozyme.