Exploring Tryptophan Self-Assembly and Its Inimical Impact on Model Membranes: Correlative Insights from Fluorescence Lifetime Imaging and Field Emission Scanning Electron Microscopy

Abstract l-Tryptophan (l-Trp) is one of the essential amino acids. Apart from taking part in protein synthesis in human body, it is also a precursor of essential neurotransmitters, including serotonin, neurohormones, including melatonin, and vitamins, including niacin, because of which it is often taken as a food supplement. However, prolonged uptake of l-Trp may lead to the formation and accumulation of l-Trp self-assembly in the human body, which may cause many health issues, such as neurodegenerative disorders. In this work, we have studied the crucial factors that control the self-assembly of l-Trp and investigated the adverse effects of this self-assembly on model membranes. A detailed investigation of the characteristics of the self-assembled structure and its modulation has been conducted using field emission scanning electron microscopy (FESEM), fluorescence lifetime imaging microscopy (FLIM), fluorescence spectroscopy, dynamic light scattering (DLS), and fluorescence microscopy. We have found that several factors, including chirality of the chiral center, complexation and substitution at the functional group, and presence of an enantiomer, can modulate self-assembly formation as well as the insertion into the model membrane. From the cell viability-based MTT assay, these self-assemblies are also found to be cytotoxic in nature.