Protein Confinement Decouples Dynamical Heterogeneity from Structural Preordering in Supercooled Monolayer Water

Monolayer-confined supercooled water exhibits unique dynamic behavior with broad implications in science and engineering, from biomolecular interactions and energy storage to cryopreservation. However, under such extreme confinement, its dynamical heterogeneity, which links closely to early ice formation, remains poorly understood. We used isoconfigurational analysis and van Hoff correlation functions to study dynamical heterogeneity in protein-confined water monolayers at 240 K. Protein confinement was found to markedly attenuate the local-environment dependence of water dynamical heterogeneity. As a result, the usual coupling between slow dynamics and incipient ice-like order seen in bulk water is greatly diminished under confinement, especially in the ice-nucleation protein PsINP. Consistently, no precrystallization slowdown occurs for water at protein interfaces, whereas bulk water shows a pronounced slowdown long before ice nucleation, indicating a distinct freezing mechanism under confinement. These findings provide new insights into how protein environments modulate deeply supercooled water's behavior, with implications for controlling ice formation at the nanoscale.