Cells are heterogeneous on every length scale. The cytoplasm contains thousands of proteins, lipids, and small biomolecules. Excluded volume effects, donor-acceptor imbalance, and electrostatic interactions disrupt the extended H-bond networks that support fast (sub-picosecond) H-bond dynamics in liquid water. The effects of crowding and heterogeneity in complex, multi-component systems remain difficult to characterize experimentally, and for this reason, there is a need to understand how disrupted H-bond networks affect the structure, stability, and dynamics of biomolecules.<br/><br/>Ultrafast multidimensional spectroscopy is ideally suited to probe H-bond dynamics in water with sub-picosecond time resolution. In this talk, I will discuss our recent studies of H-bond dynamics in crowded environments, including a range of commonly-used artificial crowders including polysaccharides and PEG, as well as cell lysates. The spectroscopic measurements are interpreted through molecular dynamics (MD) simulations and vibrational frequency maps. Simulations reveal distance-dependent effects of the crowders on the tetrahedral H-bond networks. Interestingly, artificial crowders can increase H-bond order at distances &gt;1nm. In other words, water becomes more “ice-like” even compared to bulk water. This structural analysis is consistent with the dynamics observed in experiments and predicted by MD simulations. These studies have implications for understanding the non-specific effects of crowders on water, which in turn may influence the dynamics of biomolecules.

Hydrogen-bond dynamics in crowded environments: Insights from ultrafast spectroscopy

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ACS Fall 2022

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