Temperature-driven reorganization of hydrogen bond in astaxanthin studied by moving-window two-dimensional correlation Raman spectroscopy and DFT simulation.

The competition between the intramolecular hydrogen bonds (intra-HBs) in astaxanthin (AST) and the intermolecular hydrogen bonds (inter-HBs) between AST and ethanol (EtOH) controls the structural stability of AST in the solution during the cooling process. This study employs an integrated approach combining Moving window Two-Dimensional (MW2D) correlation Raman spectroscopy and density functional theory (DFT) simulations to investigate the interaction between ethanol (EtOH) and astaxanthin (AST) across a temperature range of 303 K-83 K. The MW2D analysis indicates that, below 253 K, EtOH reorganizes into cooperative multimers prior to any conformational change in AST. DFT simulations demonstrate that EtOH multimers weaken the intramolecular hydrogen bonds (intra-HBs) in AST through OH⋯OC interactions. These findings clarify the apparent contradiction between the extended conjugation length of AST and weakened inter-HBs.