Single particle and collective hydration dynamics for hydrophobic and hydrophilic peptides

Abstract

We have conducted extensive molecular dynamics simulations to study the single particle and collective dynamics of water in solutions of N-acetyl-glycine-methylamide, a model hydrophilic protein backbone, and N-acetyl-leucine-methylamide, a model (amphiphilic) hydrophobic peptide, as a function of peptide concentration. Various analytical models commonly used in the analysis of incoherent quasielastic neutron scattering (QENS), are tested against the translational and rotational intermediate scattering function, the mean square displacement of the water molecule center of mass, and fits to the second-order rotational correlation function of water evaluated directly from the simulation data. We find that while the agreement between the model-free analysis and analytical QENS models is quantitatively poor, the qualitative feature of dynamical heterogeneity due to caging is captured well by all approaches. The center of mass collective and single particle intermediate scattering functions of water calculated for these peptide solutions show that the crossover from collective to single particle-dominated motions occurs at a higher value of Q for high concentration solutions relative to low concentration because of the greater restriction in movement of water molecules due to confinement. Finally, we have shown that at the same level of confinement of the two peptides, the aqueous amphiphilic amino acid solution shows the strongest deviation between single particle and collective dynamics relative to the hydrophilic amino acid, indicating that chemical heterogeneity induces even greater spatial heterogeneity in the water dynamics.

Quasielastic neutron scattering in soft matter

“…The study of the hydrogen bonding network dynamics shows an evolution with temperature from librations to hindered rotations (due to the strong association with hydrophilic sites) as well as surface translational diffusion with increased hydration [107]. Anomalous diffusion and strong spatial heterogeneous dynamics are observed for water around hydrophobic sites [108][109][110]. The hydrogen bonding network softens with temperature and water rotational dynamics trigger translational motions which propagate through the protein to allow larger scale motions [111].…”

Hydration Dynamics of Water near an Amphiphilic Model Peptide at Low Hydration Levels: A Dielectric Relaxation Study

“…At C = 2 m, the data in Table 2 and Figure 3 imply a fraction of about 10 %. The neutron scattering studies of aqueous NALMA by Head-Gordon and coworkers [24][25][26][27][28] indicate some strongly retarded water molecules as well. The role of slowly retarded water molecules for hydration dynamics of biomolecular solutes is controversially debated.…”

Quantitative cw Overhauser effect dynamic nuclear polarization for the analysis of local water dynamics

“…Rather, its exact value will also depend on the nature of the interaction probed by a particular measurement [49]. Thus, we can expect that, even though they should exhibit similar trends and relative values, the translational correlation times obtained by dynamics Stokes shift spectroscopy [50], dipolar relaxation driven ODNP [8], as well as various scattering measurements [51–53] might yield different absolute numbers, even though the relative trends should remain. By analogy, the rotational correlation time differs for different measurements, depending on whether the measurement probes the relaxation of an interaction that depends on rank one spherical harmonics ( e.g.…”