(648b) Unraveling the Morphology of Melanin Nanoparticles Using Atomistic Molecular Dynamics Simulations

Melanin is a natural pigment known for imparting color to human and animal skin, and bird feathers. Dihydroxynapthalene (DHN)-based melanin, commonly found in fungi, is also known to aid fungi’s survival in harsh climates with extreme temperatures. Thus, synthetic materials containing mimics of melanin find potential applications in paints (color), space crafts (thermal protection), radiation protective agents (shielding radiation). Experimental studies have focused on synthesizing nanoparticles made from assembly of oligomeric forms of dihydroxynapthalene (DHN). Spectroscopic characterization has suggested that oxidative oligomerization of 1,8 DHN leads to nanoparticles containing mixture of oligomers ranging from dimers up to 5-mers, with dimers being the most abundant. To provide molecular insight into the assembly of these oligomers, we use explicit-solvent atomistic molecular dynamics (MD) simulations. We first elucidate the molecular interactions underlying the assembly of dimers (2,2’; 2,4’ and 4,4’) and trimers (2,2,2 and 2,2,4) of 1,8 DHN. We also quantify the structural features of the resulting assembly like the molecular surface volumes, void fractions and the solvent accessible areas as a function of the dimer and trimer types. Lastly, to understand how these assembled nanoparticles would interact with other materials, we quantify the surface composition (i.e., hydrophobic vs. hydrophilic character) of the assembled particles as a function of dimer and trimer chemistries.