Conductivity in Hydrated Proteins: No Signs of the Fragile-to-Strong Crossover

Abstract

Dielectric spectroscopy studies of hydrated protein demonstrate smooth temperature variations of conductivity. This observation suggests no cusplike fragile-to-strong crossover (FSC) in the protein's hydration water. The FSC at T approximately 220 K was postulated recently on the basis of neutron scattering studies [Chen, Proc. Natl. Acad. Sci. U.S.A. 103, 9012 (2006)] and was proposed to be the main cause for the dynamic transition in hydrated proteins. Following Swenson et al. , we ascribe the neutron results to a secondary relaxation. We emphasize that no cusplike solvent behavior is required for the protein's dynamic transition.

Investigating hydration dependence of dynamics of confined water: Monolayer, hydration water and Maxwell–Wagner processes

“…This was recently suggested for water in different confinements 13 and also experimentally verified for hydrated lysozyme. 37 This study shows that dielectric relaxation does not participate in a FST up to 240 K. A change in fragility should be visible in dielectric relaxation measurements which have been proven to probe reorientational motions better than most other techniques for polar liquids. An inspection of the H diffusivity in ice 38 shows that ice exhibits a very high diffusion rate of water molecules.…”

Cause of the fragile-to-strong transition observed in water confined in C-S-H gel

“…9 Some of these, or similar confining systems, have also been studied by using other different experimental techniques, such as broadband dielectric spectroscopy (BDS), [10][11][12][13][14][15] nuclear magnetic resonance (NMR), 16 or a combination of different techniques. [17][18][19][20][21][22] In such studies, most likely due to the broadband frequency range analyzed such crossover for water was either not observed, or attributed to other causes different to that of the fragile-to-strong transition scenario. Thus, no correlation was found by studies of the same sample by QENS and other techniques.…”

Hydration-dependent dynamic crossover phenomenon in protein hydration water

“…Magazù et al [16] and Schirò et al [19] draw opposite conclusions on the role that the dynamic crossover plays in the onset of the PDT with resolution-dependent neutron scattering experiments. Swenson et al [14], Pawlus et al [15], and Fenimore et al [18] propose that the appearance of the dynamic crossover in the hydration water is due to the existences of two different relaxation processes, the structural relaxation and a secondary relaxation, rather than a qualitative * Corresponding author: sowhsin@mit.edu change from an Arrhenius behavior to a super-Arrhenius behavior of the structural relaxation time.…”

“…This phenomenon is of particular interest, partially because (i) the crossover temperature T X of the hydration water is close to the transition temperature of the so-called protein dynamic transition (PDT) [13] T D and thus it is conjectured that the PDT is induced by the dynamic crossover of the hydration water [12] and (ii) this crossover is interpreted as an anomalous feature of the structural relaxation of the hydration water and is ascribed to the existence of the high-density liquid and low-density liquid phases in the supercooled water [12]. To date, this phenomenon and its physical implications are still largely debated [14][15][16][17][18][19]. Doster et al [17] state that the crossover observed in Ref.…”