Understanding the mechanism responsible for the low-temperature crossover observed in supercooled protein solutions at T≈220 K can help to improve current vitrification and cryopreservation technologies. This crossover has been associated with changes in the dynamics of the system, such as in the mean-square displacement, whereas structural experimental evidence is sparse. The purpose of the current study is to investigate the protein hydration water structure by using a combination of wide-angle X-ray scattering and molecular dynamic (MD) simulations. Experimentally, crystallization is suppressed by controlling the protein hydration level, which allows to access temperatures down to T=175 K and resolve the scattering intensity originating purely from hydration water. Water’s first diffraction peak shift upon cooling and exhibits a crossover at T≈220 K. The MD simulations reproduce the experimental results well and indicate that the observed transition correlates with a structural crossover in the second coordination shell, reflecting changes in the local density of hydration water upon crossing the Widom line at T=224 K.

Low-temperature structural crossover in protein hydration water

ACS Spring Meeting 2021

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