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Gradual Crossover from Subdiffusion to Normal Diffusion: A Many-Body Effect in Protein Surface Water.
Pan Tan1,2, Yihao Liang1,2, Qin Xu3
1School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China.
Physical Review Letters
|June 30, 2018
Summary
Water molecules exhibit subdiffusion on biomacromolecules due to random jumps between trapping sites. This behavior transitions to normal diffusion over time because of volume-exclusion effects.
Area of Science:
- Biophysics
- Physical Chemistry
- Materials Science
Background:
- Hydration water dynamics are crucial for biomacromolecule function.
- Previous research indicated subdiffusion of water on biomacromolecule surfaces, but the underlying mechanism was unclear.
Purpose of the Study:
- To elucidate the microscopic mechanism behind water molecule subdiffusion on protein surfaces.
- To investigate the transition from subdiffusion to normal diffusion.
Main Methods:
- Neutron scattering experiments on hydrated protein powders.
- Molecular dynamics simulations.
- Analytic modeling.
Main Results:
- Identified random jumps of water molecules between trapping sites on protein surfaces.
- Demonstrated that waiting times for these jumps follow a broad distribution, causing subdiffusion.
- Observed an increase in the subdiffusive exponent with observation time, approaching normal diffusion.
Conclusions:
- The random hopping mechanism with broad waiting time distributions explains water molecule subdiffusion on proteins.
- A many-body volume-exclusion effect drives the transition from subdiffusion to normal diffusion over longer observation times.
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