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Comparative Study
. 2007 Jun 1;92(11):4054-63.
doi: 10.1529/biophysj.106.092114. Epub 2007 Mar 9.

C-phycocyanin hydration water dynamics in the presence of trehalose: an incoherent elastic neutron scattering study at different energy resolutions

Frank Gabel  1 , Marie-Claire Bellissent-Funel
Affiliations
Comparative Study

C-phycocyanin hydration water dynamics in the presence of trehalose: an incoherent elastic neutron scattering study at different energy resolutions

Frank Gabel et al. Biophys J. .

Abstract

We present a study of C-phycocyanin hydration water dynamics in the presence of trehalose by incoherent elastic neutron scattering. By combining data from two backscattering spectrometers with a 10-fold difference in energy resolution we extract a scattering law S(Q,omega) from the Q-dependence of the elastic intensities without sampling the quasielastic range. The hydration water is described by two dynamically different populations--one diffusing inside a sphere and the other diffusing quasifreely--with a population ratio that depends on temperature. The scattering law derived describes the experimental data from both instruments excellently over a large temperature range (235-320 K). The effective diffusion coefficient extracted is reduced by a factor of 10-15 with respect to bulk water at corresponding temperatures. Our approach demonstrates the benefits and the efficiency of using different energy resolutions in incoherent elastic neutron scattering over a large angular range for the study of biological macromolecules and hydration water.

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Figures

FIGURE 1
FIGURE 1
Accessible energy and Q-ranges of the backscattering instruments IN13 and IN16 used in this study.
FIGURE 2
FIGURE 2
Guinier plots (lnS0 vs. Q2) at 120, 250, and 320 K (from top to bottom) for C-phycocyanin hydration water in the presence of trehalose on IN13 (open circles) and IN16 (solid circles). The lines show the linear fits used to extract MSDs in the Q-range 1 < Q2 [Å−2] < 3.3, covered by both instruments.
FIGURE 3
FIGURE 3
Apparent mean square displacements measured on IN13 (open circles) and IN16 (solid circles) with error bars. The IN13 error bars are bigger than the IN16 error bars, mainly due to the smaller number of detectors available on IN13 in the Q-range 1 < Q2 [Å−2] < 3.3 (Fig. 2).
FIGURE 4
FIGURE 4
Logarithm of the normalized elastic intensities on IN13 (open circles) and IN16 (solid circles) with error bars at the temperatures (a) 240, (b) 280, and (c) 320 K, as a function of Q2. The fits with the model function (Eq. 9b) are depicted by continuous lines. Two IN13 data points (at 2.58 and 2.76 Å−1) were not taken into account since their intensities were not stable during the experiment.
FIGURE 5
FIGURE 5
(a) Effective diffusion coefficient D (in 10−10 m2/s), (b) population p, (c) sphere radius a (in Å), and (d) relaxation parameter τ = 1/Γ (in ps) as a function of temperature. (e) Arrhenius plot of lnτ vs. 1/T. IN16 fit parameters are depicted with solid circles, IN13 fit parameters with open circles. The errors of the fit parameters were as follows: ΔD/D < 5%, Δp/p < 5%, Δa/a < 7%, and Δτ/τ < 200%.
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