Simple Hydroxybenzene Molecules as Thermally Stable Catalysts

Catalysis plays a central role in the creation of life and is vital for living systems. How catalysts have evolved over the years remains a mystery. The answer to this question is central for understanding enzyme evolution and developing new catalytic entities. Enzymes are folded sequences of coded amino acids. These building blocks may have been present under prebiotic conditions. However, how simple amino acids evolved to create complicated and functional macromolecules such as enzymes is still unknown. Previous reports have shown that coded amino acids, their assemblies, and complexes with metals can have catalytic activity. We have recently demonstrated that even a noncoded amino acid, l-3,4-dihydroxyphenylalanine (DOPA), can catalyze two hydrolysis reactions mediated by its hydroxybenzene moiety. DOPA is found in marine mussels' foot proteins. These proteins function in an environment characterized by high salt concentrations and UV radiation similar to suggested prebiotic conditions. Here, we show that other hydroxybenzene molecules, such as pyrogallol, can also catalyze hydrolysis reactions. The catalytic activity of the hydrolysis reactions of p-nitrophenylacetate and thioacetylcholine depended on the number of hydroxyl groups and their relative position on the benzene rings. The catalytic activity of pyrogallol and tannic acid is stable even at high temperatures, close to the boiling point of water, suggesting they can function as stable artificial catalysts.