Time-resolved structural investigations of crystallization of water in lipid/protein/salt mesophases at cryogenic temperatures are significant for comprehension of ice nanocrystal nucleation kinetics in lipid membranous systems and can lead to a better understanding of how to experimentally retard the ice formation that obstructs the protein crystal structure determination. Here, we present a time-resolved synchrotron microfocus X-ray diffraction (TR-XRD) study based on ∼40,000 frames that revealed the dynamics of water-to-ice crystallization in a lipid/protein/salt mesophase subjected to cryostream cooling at 100 K. The monoolein/hemoglobin/salt/water system was chosen as a model composition related to protein-loaded lipid cubic phases (LCP) broadly used for the crystallization of proteins. Under confinement in the nanoscale geometry, metastable short-living cubic ice (Ic) rapidly crystallized well before the formation of hexagonal ice (Ih). The detected early nanocrystalline states of water-to-ice transformation in multicomponent systems are relevant to a broad spectrum of technologies and understanding of natural phenomena, including crystallization, physics of water nanoconfinement, and rational design of anti-freezing and cryopreservation systems.
Keywords: Crystallization kinetics; Cubic ice; In situ microfocus beam X-ray diffraction; Lipid cubic phase; Monoolein/hemoglobin/water assembly; Nanoconfinement; Structural dynamics.
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