Water Dynamics in Cytoplasm-Like Crowded Environment Correlates with the Conformational Transition of the Macromolecular Crowder

Abstract

Polyethylene glycol (PEG) is a unique polymer material with enormous applicability in many industrial and scientific fields. Here, its use as macromolecular crowder to mimic the cellular environment in vitro is the focus of the present study. We show that femtosecond mid-IR pump-probe spectroscopy using three different IR probes, HDO, HN, and azido-derivatized crowder, provides complete and stereoscopic information on water structure and dynamics in the cytoplasm-like macromolecular crowding environment. Our experimental results suggest two distinct subpopulations of water molecules: those that interact with other water molecules and those that are part of a hydration shell of crowder on its surface. Interestingly, water dynamics even in highly crowded environment remains bulk-like in spite of significant perturbation to the tetrahedral H-bonding network of water molecules. That is possible because of the formation of water aggregates (pools) even in water-deficient PEGDME-water solutions. In such a crowded environment, the conformationally accessible phase space of the macromolecular crowder is reduced, similar to biopolymers in highly crowded cytoplasm. Nonetheless, the hydration water on the surface of crowders slows down considerably with increased crowding. Most importantly, we do not observe any coalescing of surface hydration water (of the crowder) with bulk-like water to generate collective hydration dynamics at any crowder concentration, contrary to recent reports. We anticipate that the present triple-IR-probe approach is of exceptional use in studying how conformational states of crowders correlate with structural and dynamical changes of water, which is critical in understanding their key roles in biological and industrial applications.

On the origin of the extremely different solubilities of polyethers in water

“…This indicates that two types of water OD groups are present: those unaffected by the dioxane, and those whose reorientation dynamics is slowed down because of solvation interactions. The residual anisotropy increases with the amount of added dioxane, which confirms that these slowly reorienting OD bonds solvate the dioxane 29,39–41 . The decaying component of the anisotropy is similar to that of bulk water, which indicates that beyond the solvation shell the OH orientational dynamics is not influenced by the presence of the solute, in agreement with previous findings 33 .…”

Molecular Crowding Effect in Aqueous Electrolytes to Suppress Hydrogen Reduction Reaction and Enhance Electrochemical Nitrogen Reduction

“…The poly(ethylene glycol) (PEG) (Figure 1b) caught our attention due to its significant molecular crowding effect in aqueous solutions. [ 41,42,45–47 ] It is expected that the electronegative O atoms in PEG can readily attract H 3 O + to form the hydrogen bond and reduce its activity; [ 34,46 ] in contrast, N 2 molecules with the nonpolar NN covalent bonds can migrate freely in an aqueous solution since no hydrogen‐bonding interactions are available between N 2 molecules and the PEG framework.…”

Programming in situ accelerated DNA walkers in diffusion-limited microenvironments

“…The diffusivity of nanosized objects in the cytoplasmic microenvironments of mammalian cells varies over orders of magnitude and dictates the kinetics of biochemical processes 1–4. However, it challenges the effective assembly and operation of nucleic acid modules as functional motors in living cells.…”