How Solvation Structures Define the Cryoprotection Efficiency of Ethylene Glycol

Understanding the molecular mechanisms of cryopreservation is crucial for optimizing antifreeze formulations. In this study, we investigate the hydrogen bond (HB) configurations of aqueous ethylene glycol (EG) solutions using a combined approach of Fourier transform infrared (FTIR) spectroscopy and molecular dynamics (MD) simulations. Our results reveal that EG progressively integrates into the HB network, modifying the structural organization of water across different concentrations. At low EG content, water maintains its percolating HB-network, while at intermediate concentrations (X_EG ≈ 0.3-0.6), a mixed HB configuration emerges, balancing EG-water and water-water interactions. This structural transition correlates with the lowest freezing point and the most efficient cryoprotective behavior. Beyond X_EG > 0.6, EG self-association dominates, reducing water's HB connectivity and inducing hydrophobic clustering effects. The analysis of HB populations and tetrahedral order parameters (TOP) confirms that EG disrupts the extended tetrahedral HB framework of water, thereby delaying ice nucleation. These findings establish a direct correlation between local solvation structures and cryoprotective efficiency, highlighting the importance of mixed HB environments in tuning antifreeze functionality.