Computational investigation of the electronic and energetic landscape of the scytonemin-glucose complex

Abstract

Scytonemin plays a vital role in cellular protection, as a primary UV-dissipating agent found within the cyanobacterial polysaccharide frameworks. It has attracted significant interest in its potential application in sunscreens, cosmetics, and materials science. This paper explores the unexplored intermolecular interactions of scytonemin within the extracellular polysaccharide (EPS) sheath and lipopolysaccharide (LPS) framework. Specifically, the interactions of scytonemin with β-D-glucose, a common component of the EPS/LPS. Our computational workflow integrated an initial automated docking phase (GFN2-xTB and ALPB) for broad conformational sampling. This is followed by geometry optimization, single point energy calculations, and time dependent DFT (TDDFT) simulations. By employing ωB97X-3c with the SMD solvation model (water as the solvent), we quantify the ground and first excited state influence of glucose binding with the scytonemin monomer. Calculated interaction energies for the scytonemin-glucose complexes ranged from −0.267 to −0.426 $eV$. Analysis of the first excited state energies revealed notable stabilization upon photoexcitation. Orbital analysis and TDDFT simulations revealed that the frontier molecular orbitals remain nearly completely localized on the scytonemin monomer, resulting in the UV absorption maxima of the scytonemin monomer (≈ 307 to 309 nm) showing small red shifting upon binding with β-D-glucose. These findings suggest that scytonemin maintains its electronic structure and photoprotective characteristics even when integrated into the diverse carbohydrate environments of the EPS/LPS matrix.