From the analysis of different frequency regions, the effects of morphology change due to PEG depletion interactions can be investigated for three types of backbone structures: α-helix, β -sheet, and loop structures. Because of the presence of multiple bands in the amide I stretch region, the dynamics extracted from the 2D IR lineshape are used for a qualitative comparison among different actin morphologies rather than a quantitative analysis of water dynamics in the local environment. For α-helix and loop structures, there is a fast decay of 1-2 ps (Tables and), corresponding to the fluctuations in hydrogen-bonded water molecules around the actin amide I mode. These timescales compare favorably with measured water dynamics . The primary structure, α-helix, displays a fast decay in 2 ps with a close-to-zero offset for the filament and weakly bundled network, indicating rapid hydrogen-bond exchange dynamics. In the strong-bundle sample, hydrogen bond fluctuation occurs in 1 ps, after which the environment is more restricted and undergoes other slower dynamical processes, as indicated by the presence of an offset. The dynamics analysis for α-helix demonstrates a more static environment in a strongly bundled network, likely due to the attractions among filaments and less solvent exposure along the backbone.