Understanding the Polymerization Process of Eumelanin by Computer Simulations

We present and discuss a computational setup aimed at modeling the polymerization process of eumelanin by combining together molecular dynamics simulations and ab initio total-energy calculations. By simulating the oxidative polymerization process of eumelanin in methanol, we provide evidence that "in silico" synthesized samples are mostly composed of low-molecular-weight structures: an exponential distribution of the molecular weights is found, yielding an average weight less than 10. Adopting the scheme of chemical disorder, we also perform a statistical analysis on the variety of molecules formed, focusing on both their structural and electronic features. In particular, we identify the most frequent structural patterns within the molecules by analyzing the occurrence of the single chemical bonds. Moreover, we show how most of the molecules have a large number of nonterminated oxygen atoms, highlighting the pivotal role of O groups in the eumelanin molecular stability.