Effects of Various Types of Molecular Dynamics on 1D and 2D 2H NMR Studied by Random Walk Simulations

The Journal of Chemical Physics

2012

We use (2)H NMR spectroscopy to investigate the rotational motion of glycerol molecules in matrices provided by the connective tissue proteins elastin and collagen. Analyzing spin-lattice relaxation, line-shape properties, and stimulated-echo decays, we determine the rates and geometries of the motion as a function of temperature and composition. It is found that embedding glycerol in an elastin matrix leads to a mild slowdown of glycerol reorientation at low temperatures and glycerol concentrations, while the effect vanishes at ambient temperatures or high solvent content. Furthermore, it is observed that the nonexponential character of the rotational correlation functions is much more prominent in the elastin matrix than in the bulk liquid. Results from spin-lattice relaxation and line shape measurements indicate that, in the mixed systems, the strong nonexponentiality is in large part due to the existence of distributions of correlation times, which are broader on the long-time flank and, hence, more symmetric than in the neat system. Stimulated-echo analysis of slow glycerol dynamics reveals that, when elastin is added, the mechanism for the reorientation crosses over from small-angle jump dynamics to large-angle jump dynamics and the geometry of the motion changes from isotropic to anisotropic. The results are discussed against the background of present and previous findings for glycerol and water dynamics in various protein matrices and compared with observations for other dynamically highly asymmetric mixtures so as to ascertain in which way the viscous freezing of a fast component in the matrix of a slow component differs from the glassy slowdown in neat supercooled liquids.

Section: B Solid-echo Experimentsmentioning

confidence: 80%

2H NMR studies of glycerol dynamics in protein matrices

Herbers

Sauer

The Journal of Chemical Physics

2012

“…By contrast, the signal is not reduced for much faster and slower dynamics when ω Q is time-averaged and time-invariant, respectively. Detailed random-walk simulations for different motional models show that the solid-echo amplitude is a minimum for a correlation time of about 3 µs [18,32]. Hence, the coincidence of the minima of a w shows that the hydration waters of myoglobin, elastin and collagen exhibit a correlation time τ aw = 3 µs at 205 K. In Fig.…”

Section: Fig 2: A) Arrhenius Plot Of the Mean Slr Times T1wmentioning

confidence: 81%

2H and 13C NMR studies on the temperature-dependent water and protein dynamics in hydrated elastin, myoglobin and collagen

Lusceac

Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics

Herbers

2010

118

2 H NMR spin-lattice relaxation and line-shape analyses are performed to study the temperaturedependent dynamics of water in the hydration shells of myoglobin, elastin, and collagen. The results show that the dynamical behaviors of the hydration waters are similar for these proteins when using comparable hydration levels of h = 0.25 − 0.43. Since water dynamics is characterized by strongly nonexponential correlation functions, we use a Cole-Cole spectral density for spin-lattice relaxation analysis, leading to correlation times, which are in nice agreement with results for the main dielectric relaxation process observed for various proteins in the literature. The temperature dependence can roughly be described by an Arrhenius law, with the possibility of a weak crossover in the vicinity of 220 K. Near ambient temperatures, the results substantially depend on the exact shape of the spectral density so that deviations from an Arrhenius behavior cannot be excluded in the hightemperature regime. However, for the studied proteins, the data give no evidence for the existence of a sharp fragile-to-strong transition reported for lysozyme at about 220 K. Line-shape analysis reveals that the mechanism for the rotational motion of hydration waters changes in the vicinity of 220 K. For myoglobin, we observe an isotropic motion at high temperatures and an anisotropic largeamplitude motion at low temperatures. Both mechanisms coexist in the vicinity of 220 K.13 C CP MAS spectra show that hydration results in enhanced elastin dynamics at ambient temperatures, where the enhancement varies among different amino acids. Upon cooling, the enhanced mobility decreases. Comparison of 2 H and 13 C NMR data reveals that the observed protein dynamics is slower than the water dynamics.

“…[30][31][32][33][34][35][36][37][38][39] For polymer melts, it was reported that the isotropic reorientation of the polymer segments during the ␣ process results from successive rotational jumps about small angles. [30][31][32][33][34][35][36][37][38][39] For polymer melts, it was reported that the isotropic reorientation of the polymer segments during the ␣ process results from successive rotational jumps about small angles.…”

Section: H Nmr Spectra For Various Solid-echo Delaysmentioning

confidence: 99%

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. I. Insights from NMR line-shape analysis

The Journal of Chemical Physics

Torbrügge

2006

We investigate ion and polymer dynamics in polymer electrolytes PPO-LiClO4 performing 2H and 7Li NMR line-shape analysis. Comparison of temperature dependent 7Li and 2H NMR spectra gives evidence for a coupling of ion and polymer dynamics. 2H NMR spectra for various salt concentrations reveal a strong slowdown of the polymer segmental motion when the salt content is increased. The 2H NMR line shape further indicates that the segmental motion is governed by dynamical heterogeneities. While the width of the distribution of correlation times G(log tau) is moderate for low and high salt content, an extremely broad distribution exists for an intermediate salt concentration of 15:1 PPO-LiClO4. For the latter composition, a weighted superposition of two spectral components, reflecting the fast and the slow polymer segments of the distribution, describes the 2H NMR line shape over a broad temperature range. Analysis of the temperature dependent relative intensity of both spectral components indicates the existence of a continuous rather than a discontinuous distribution G(log tau). Such continuous distribution is consistent with gradual fluctuations of the local salt concentration and, hence, of the local environments of the polymer segments, whereas it is at variance with the existence of large salt-depleted and salt-rich domains featuring fast and slow polymer dynamics, respectively. Finally, for all studied PPO-LiClO4 mixtures, the 2H NMR line shape strongly depends on the echo delay in the applied echo-pulse sequence, indicating that the structural relaxation of the polymer segments involves successive rotational jumps about small angles gamma < 20 degrees .