Polydopamine and eumelanin models in various oxidation states

Area of Science:

• Materials Science
• Computational Chemistry
• Biomaterials

Background:

• Polydopamine (PDA) and eumelanin are complex biopolymers with diverse applications.
• Their precise molecular structures and stability under various oxidation states remain incompletely understood.

Purpose of the Study:

• To conduct a comprehensive ab initio structural investigation of polydopamine (PDA) and eumelanin.
• To systematically generate and evaluate probable molecular structures, from dimers to tetramers, of oxidized 5,6-dihydroxyindole (DHI) oligomers.

Main Methods:

• Utilized a computational approach combining brute-force algorithmic generation of chemical isomers.
• Employed density functional theory (DFT) to evaluate the stability of over 43,000 probable molecular structures.
• Systematically analyzed oxidized 5,6-dihydroxyindole (DHI) oligomers, ranging from dimers to tetramers.

Main Results:

• Identified a set of the most stable molecular structures for PDA and eumelanin, reflecting their chemical diversity.
• Observed a tendency for more planar molecular structures to exhibit greater stability.
• Discovered that cyclic molecular structures can significantly reduce the energy of DHI tetramers, enhancing their stability.

Conclusions:

• The study proposes novel, energetically favorable cyclic molecular models for eumelanin-like materials.
• These cyclic models are more stable than previously suggested porphyrin-like structures.
• The findings provide crucial insights into the structural diversity and stability of PDA and eumelanin.