Melanin with putative p-coumaric acid-related structural features from tamarind (Tamarindus indica L.) and black pepper seeds (Piper nigrum L.)

This study investigates melanin isolated from tamarind and black pepper seeds to elucidate its molecular composition and structural features. Spectroscopic analysis by nuclear magnetic resonance and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry indicated that the melanin was predominantly composed of aromatic units, with mass spectral features consistent with those of p -coumaric acid ( p -CA) derived structures. Density functional theory calculations of the p -CA monomers and dimers revealed multiple reactive sites that may contribute to the formation of structurally diverse oligomeric assemblies. Furthermore, electron paramagnetic resonance (EPR) spectroscopy indicated that the experimental g-factors are compatible with cationic species, particularly for oligomeric models containing C 5 -O′ C4 linkages. These findings provide crucial insights into the molecular structure and potential reactivity of melanin from tamarind and black pepper seeds, supporting its relevance in future functional and application-oriented studies.