Enzymatic poly(gallic acid): A stable multiradical polyanion

In this work we re-examined the molecular structure of enzymatic poly(gallic acid) (PGAL), for which we identified a multiradical and polyanionic nature, in contrast to a previous assignment where it was mistakenly assumed as a neutral and diamagnetic molecule. Here, we present a profound investigation of its ground-state structure by the use of both experimental and theoretical methods, featuring ESR measurements and quantum chemical computations. It was found that its multiradical nature is remarkably stable thanks to an extended hydrogen bonding network occurring within its structure, with interaction energies in the 3-11 kcal/mol regime, according to DFT computations at the M06-2X/6-311++G** level of theory. This multiradical polymer displays several appealing features, including air, thermal and photostabilities, water solubility and, most remarkably, the fact that it is obtained in a multi-gram scale from the naturally abundant gallic acid in mild and green conditions. (C) 2019 Elsevier B.V. All rights reserved.