Solvation Dynamics of Concentrated Aqueous Polymer Mixtures: A Two Dimensional Infrared Spectroscopy Study

[摘要] Water-solute interactions still remain a challenge to study experimentally, though they are critical to protein and biomacromolecule stability, structure, and function. Hydration dynamics at interfaces are generally slower than bulk water. While many investigations into the dynamics of water using advanced spectroscopy methods have occurred, considerably less specific attention has been paid to biologically relevant highly crowded solutions. Macromolecular crowding is the result of both steric and chemical interactions of the crowding agent with the targeted molecule of study. Considering steric effects of crowding agents is not enough, and studies of chemical interactions are increasingly being done. Crowding agents typically are polymers, proteins, reverse micelles, or hydrogels, and in this study, we focus on polymers. We seek to understand how polymer crowders affect hydration dynamics. Using ultrafast two-dimensional infrared (2D-IR) spectroscopy of a new water-soluble transition metal complex acting as a vibrational probe, we look at a range of polymers at various lengths, concentrations, and temperatures. We find that PEG, which exhibits unusual structural and thermodynamic trends, has a very stable hydration shell at room temperature. The stable hydration shell promotes bulk like hydration dynamics even at high concentrations and viscosities. From temperature variance experiments, we calculate activation energies and find that the results are similar to activation energies of water. Our studies provide fundamental information about the hydration dynamics of concentrated polymer solutions and we find evidence for distinct dynamics sensed by the probe depending on the crowding agent.

[发布机构] University of Michigan

[效力级别] macromolecular crowding

[关键词] ultrafast spectroscopy;macromolecular crowding;Chemistry;Science;Chemistry