DEVELOPMENT OF NANOPHOTOCHEMICALS FOR AGRI-BIOMASS DERIVED LIGNIN VALORIZATION AND PHOTODYNAMIC APPLICATIONS

Abstract

Abstract Lignin, the second most abundant biopolymer on Earth after cellulose, plays a crucial role in providing rigidity and microbial resistance in higher plants. It holds significant potential as a sustainable alternative to depleting fossil fuels for energy generation and the production of platform chemicals. However, due to its recalcitrant nature, heterogeneous composition, inherent resistance, and challenges in fractionation, lignin remains largely underutilized. Currently, a major portion of industrial lignin (~ 70 million tons per year) is burned for electricity generation or released into water bodies, leading to environmental contamination and adverse effects on living systems, including humankind. Consequently, there is a pressing need for a greener and more sustainable approach to address this issue. Concurrently, the emergence of microbial infections poses a serious threat to human health, ranking as the second leading cause of death worldwide. While current therapeutic regimens rely heavily on chemotherapy, the indiscriminate use of antimicrobial agents has contributed to the development of drug-resistant microorganisms. To tackle both the challenges associated with lignin transformation and microbial disinfection, the utilization of light-based processes such as photocatalysis and photodynamic applications holds promise. These approaches rely on the use of a photosensitizer/light harvester, a crucial component for harnessing light energy effectively. In our study, we aimed to synthesize various pyrrole-based compounds, which serve as starting materials for naturally occurring photosensitizers like BODIPYs and porphyrins. However, the hydrophobic nature of these compounds limits their applicability to non-aqueous environments. Nevertheless, they can be employed directly in organic media or encapsulated within polymer-based nanoparticles to enhance their hydrophilicity and enable their use in photocatalytic applications. To overcome limitations such as recyclability and photobleaching associated with polypyrroles, we addressed these issues by utilizing visible light activatable metal organic frameworks. On another note, Rose Bengal, a naturally occurring drug molecule and photosensitizer, possesses hydrophilic properties that primarily restrict its use to diagnostic applications rather than phototherapeutic purposes. To overcome this limitation, we explored the potential of in-situ growth of nano-metal organic frameworks within starch/polyacrylamide hydrogels. This approach shows promise for loading and controlling the release kinetics of drugs in antimicrobial photodynamic applications, thereby expanding the possibilities for therapeutic utilization of Rose Bengal.