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Biological Water: Femtosecond Dynamics of Macromolecular Hydration

Pal, Samir Kumar and Peon, Jorge and Bagchi, Biman and Zewail, Ahmed H. (2002) Biological Water: Femtosecond Dynamics of Macromolecular Hydration. Journal of Physical Chemistry B, 106 (48). pp. 12376-12395. ISSN 1520-6106. doi:10.1021/jp0213506.

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The unique features of a macromolecule and water as a solvent make the issue of solvation unconventional, with questions about the static versus dynamic nature of hydration and the physics of orientational and translational diffusion at the boundary. For proteins, the hydration shell that covers the surface is critical to the stability of its structure and function. Dynamically speaking, the residence time of water at the surface is a signature of its mobility and binding. With femtosecond time resolution it is possible to unravel the shortest residence times which are key for the description of the hydration layer, static or dynamic. In this article we review these issues guided by experimental studies, from this laboratory, of polar hydration dynamics at the surfaces of two proteins (Subtilisin Carlsberg (SC) and Monellin). The natural probe tryptophan amino acid was used for the interrogation of the dynamics, and for direct comparison we also studied the behavior in bulk watera complete hydration in 1 ps. We develop a theoretical description of solvation and relate the theory to the experimental observations. In this theoretical approach, we consider the dynamical equilibrium in the hydration shell, defining the rate processes for breaking and making the transient hydrogen bonds, and the effective friction in the layer which is defined by the translational and orientational motions of water molecules. The relationship between the residence time of water molecules and the observed slow component in solvation dynamics is a direct one. For the two proteins studied, we observed a “bimodal decay” for the hydration correlation function, with two primary relaxation times:  ultrafast, typically 1 ps or less, and longer, typically 15−40 ps, and both are related to the residence time at the protein surface, depending on the binding energies. We end by making extensions to studies of the denatured state of the protein, random coils, and the biomimetic micelles, and conclude with our thoughts on the relevance of the dynamics of native structures to their functions.

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Additional Information:© 2002 American Chemical Society. Received: June 5, 2002; In Final Form: August 12, 2002. Publication Date (Web): November 7, 2002. This work was supported by the National Science Foundation.
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Issue or Number:48
Record Number:CaltechAUTHORS:20160817-150901402
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Official Citation:Biological Water:  Femtosecond Dynamics of Macromolecular Hydration Samir Kumar Pal, Jorge Peon, Biman Bagchi, and Ahmed H. Zewail The Journal of Physical Chemistry B 2002 106 (48), 12376-12395 DOI: 10.1021/jp0213506
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69725
Deposited By: Ruth Sustaita
Deposited On:18 Aug 2016 19:18
Last Modified:11 Nov 2021 04:18

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