Role Of Hydration Water Research Articles

Effects of hydration water on bioresponsiveness of polymer interfaces revealed by analysis of linear and cyclic polymer-grafted substrates.

Given that the hydration water of polymer matrices may differ from that of outermost polymer surfaces, processes at biomaterial-biofluid interfaces and role of hydration water therein cannot be adequately examined using most conventional characterization methods. To bridge this gap, a gold substrate was herein modified with linear and cyclic poly(2-methoxyethyl acrylate) to prepare gl-PMEA and gc-PMEA surfaces, respectively, as models for the outermost surfaces of blood-contacting medical devices. Both surfaces suppressed the adhesion of human platelets but differed in the adhesion behaviors of normal and tumor cells despite having the same areal density of fixed-end units. The surfaces were analyzed using quartz crystal microbalance (QCM), frequency modulation atomic force microscopy (FM-AFM), and X-ray emission spectroscopy (XES) measurements under wet conditions to clarify the relationship between bioresponsivity and hydration water. QCM measurements provided evidence that both grafted-PMEA were hydrated. FM-AFM observations revealed that the swelling layer was thicker for gc-PMEA. To rationalize the differences in the surface hydration states, we performed XES measurements under conditions enabling control over the number of hydration water molecules. In the low-water-content region, hydrogen bonds or interactions between water molecules developed in the vicinity of gl-PMEA but not gc-PMEA. Thus, the initial hydration behavior of the gc-PMEA surface, which promoted intermediate water formation, was different from that of the gl-PMEA surface. The results suggested that the adjustment and optimization of the hydration state of outermost biomaterial surfaces enable the control of bioresponsivity, including the selective isolation of tumor cells.

The role of hydration water in inorganic M+n -magadiites (M+n = K+, Ca+2, Mg+2): Advances in structural and electronic analysis by DFT calculations.

This work reports a detailed study of the K-, Mg-, and Ca-magadiites simulated from the structure of Na-magadiite. Several molecular geometries were tested in each model, and the results showed a hydration sphere similar to the initial sodium material. In the interlayer region, Na- and K-magadiites showed longer coordinated bond lengths, leading to higher basal spacing values (15.43 Å and 15.71 Å, respectively). Solids containing divalent cations presented the strongest H-bonds between the water molecules and the layers, also reinforced by the charge density distribution. Different stretching (3000 − 3800 cm−1) and bending (1500 − 1750 cm−1) of water molecules were identified in the vibrational analysis, and the simulated-experimental comparison of spectra suggested that dehydrated samples adsorb water molecules initially in axial positions and, later, in equatorial positions. Thermodynamics analysis at 298.15 K confirmed the difficulty of obtaining complete sodium to potassium exchanged forms (ΔG = 126.03 kJ.mol−1), while Ca-magadiite can be formed spontaneously (ΔG = −190.86 kJ.mol−1).

Cholesterol enhances surface water diffusion of phospholipid bilayers.

Elucidating the physical effect of cholesterol (Chol) on biological membranes is necessary towards rationalizing their structural and functional role in cell membranes. One of the debated questions is the role of hydration water in Chol-embedding lipid membranes, for which only little direct experimental data are available. Here, we study the hydration dynamics in a series of Chol-rich and depleted bilayer systems using an approach termed (1)H Overhauser dynamic nuclear polarization (ODNP) NMR relaxometry that enables the sensitive and selective determination of water diffusion within 5-10 Å of a nitroxide-based spin label, positioned off the surface of the polar headgroups or within the nonpolar core of lipid membranes. The Chol-rich membrane systems were prepared from mixtures of Chol, dipalmitoyl phosphatidylcholine and/or dioctadecyl phosphatidylcholine lipid that are known to form liquid-ordered, raft-like, domains. Our data reveal that the translational diffusion of local water on the surface and within the hydrocarbon volume of the bilayer is significantly altered, but in opposite directions: accelerated on the membrane surface and dramatically slowed in the bilayer interior with increasing Chol content. Electron paramagnetic resonance (EPR) lineshape analysis shows looser packing of lipid headgroups and concurrently tighter packing in the bilayer core with increasing Chol content, with the effects peaking at lipid compositions reported to form lipid rafts. The complementary capability of ODNP and EPR to site-specifically probe the hydration dynamics and lipid ordering in lipid membrane systems extends the current understanding of how Chol may regulate biological processes. One possible role of Chol is the facilitation of interactions between biological constituents and the lipid membrane through the weakening or disruption of strong hydrogen-bond networks of the surface hydration layers that otherwise exert stronger repulsive forces, as reflected in faster surface water diffusivity. Another is the concurrent tightening of lipid packing that reduces passive, possibly unwanted, diffusion of ions and water across the bilayer.

The role of water dynamics in mediating protein‐DNA interactions (549.4)

The role of hydration water on protein and DNA surfaces is fundamental to their interaction and processes, yet experimentally challenging to study. We recently applied a novel Overhauser dynamic nuclear polarization‐enhanced NMR method to the study of biological hydration water which provides unprecedented insights into ps to sub‐ns water dynamics within 5‐10 Angstrom of molecular surfaces: waters loosely associated with DNA have surprisingly high degrees of mobility, nearly unperturbed, while waters surrounding protein surfaces are significantly fortified, compared to the dynamics of bulk water. Here we investigated how water mobility contributes to the site location mechanisms of several DNA binding proteins. Dimethyl sulfoxide increases this water mobility on molecular surfaces (DNA or protein) and is predicted to increase the site location efficiency of proteins that rely extensively on a sliding mechanism; we confirmed this to be the case with EcoRI endonuclease when adding 1% DMSO. In contrast, glycerol is predicted to have a retarding (or sometimes neutral) effect on surface water mobility and thus sliding translocation kinetics, which we again confirm to be the case with EcoRI endonuclease when adding 1% glycerol. In contrast, the translocation efficiency of DNA adenine methyltransferase (Dam) that does not rely extensively on sliding is not altered with either osmolyte addition. The observed effects on processivity have been corrected for minor changes in catalytic efficiency in the presence of osmolytes. Our results reveal that water’s fast moving properties around DNA are important for protein‐DNA interactions and in particular, the translocation along the double helix, whose efficiency can be slowed or enhanced when the water barrier on the DNA or protein surfaces is strengthened or weakened by the addition of glycerol or DMSO.

One role of hydration water in proteins: key to the "softening" of short time intraprotein collective vibrations of a specific length scale.

High resolution inelastic X-ray scattering (IXS) experiments show that the "phonon energy softening" and "phonon population enhancement" observed in a hydrated native protein when increasing the temperature from 200 K to physiological temperature are not directly related to the protein structure. Such phenomena were also observed in a denatured sample without a defined tertiary structure and with a limited residual secondary structure. However, in a dry sample, such "softening" is strongly suppressed. These facts suggest that the above-mentioned protein "softening" phenomenon is water-induced. In addition, increasing the hydration level can also induce "phonon energy softening" at room temperature, but not at 200 K. This change may be due to a qualitative difference in the dynamics of hydration water at 200 K and at room temperature.

Role of hydration water in dynamics of biological macromolecules

We present an overview of neutron scattering studies of the dynamics in hydrated and dry protein and RNA. We demonstrate that the difference observed in the dynamics of dry lysozyme and dry RNA is related to the methyl group contributions to the protein dynamics. Hydration of biological macromolecules leads to significant activation of conformational transitions. They appear in neutron scattering spectra as an additional slow relaxation process that exhibits a strongly stretched spectral shape and slightly non-Arrhenius temperature dependence of the characteristic relaxation time. Our analysis suggests that the appearance of this relaxation process in the experimentally accessible frequency window is the main cause for the sharp rise of the atomic mean-squared displacements (the so-called dynamic transition) that takes place in hydrated biomolecules at T ≈ 200–220 K.

Protein dynamics studied by neutron scattering.

This review of protein dynamics studied by neutron scattering focuses on data collected in the last 10 years. After an introduction to thermal neutron scattering and instrumental aspects, theoretical models that have been used to interpret the data are presented and discussed. Experiments are described according to sample type, protein powders, solutions and membranes. Neutron-scattering results are compared to those obtained from other techniques. The biological relevance of the experimental results is discussed. The major conclusion of the last decade concerns the strong dependence of internal dynamics on the macromolecular environment.

Role of Hydration Water in Protein Unfolding

In this paper, following our work on the two-state outer neighbor mixed bonding model of water, it is proposed that polar groups promote the formation of the low density ice Ih-type bonding in their neighborhood, whereas nonpolar groups tend to promote the higher density ice II-type structure. In a protein, because of the large numbers of exposed polar and nonpolar groups, large changes in the neighboring water structure can occur. These changes, of course, depend on whether the protein is in its native or its unfolded state and will be shown here to have a direct impact on the thermodynamics of protein unfolding at both high and low temperatures. For example, it is known that the polar hydration entropies become rapidly more negative with increasing temperature. This very unusual behavior can be directly related to the promotion in the outer bulk liquid of the more stable Ih-type bonding at the expense of II-type bonding by polar groups of the protein. In contrast, nonpolar groups have an opposite effect on the thermodynamics. It is the delicate balance created by these outer hydration contributions, mixed with ordinary thermodynamic contributions from the inner hydration shell and those from hydrogen-bond and van der Waals forces within the protein molecule itself that is responsible for both heat and cold denaturation of proteins.

The Temperature Dependence of Internal Molecular Motions in Hydrated and Dry α-Amylase: The Role of Hydration Water in the Dynamical Transition of Proteins

Internal molecular motions of proteins are strongly affected by environmental conditions, like temperature and hydration. As known from numerous studies, the dynamical behavior of hydrated proteins on the picosecond time scale is characterized by vibrational motions in the low-temperature regime and by an onset of stochastic large-amplitude fluctuations at a transition temperature of 180–230 K. The present study reports on the temperature dependence of internal molecular motions as measured with incoherent neutron scattering from the globular water-soluble protein α-amylase and from a protein-lipid complex of rhodopsin in disk membranes. Samples of α-amylase have been measured in a hydrated and dehydrated state. In contrast to the hydrated sample, which exhibits a pronounced dynamical transition near 200 K, the dehydrated α-amylase does not show an appreciable proportion of stochastic large-amplitude fluctuations and no dynamical transition in the measured temperature range of 140–300 K. The obtained results, which are compared to the dynamical behavior of protein-lipid complexes, are discussed with respect to the influence of hydration on the dynamical transition and in the framework of the glass transition.

Role of hydration water in the reduction process of PbO 2 in lead/acid cells

The influence of ‘hydrogen loss’ on the electrochemical properties of both ;-PbO 2 and ;-PbO 2 was studied using galvanostatic discharge and cyclic voltammetry. The thermal decomposition of electroformed PbO 2 shows two types of hydration water: the first type, which disappears at low temperature, is adsorbed on the surfaces of the PbO 2 particles, and the second one is localized within the PbO 2 crystal structure. The reduction process of PbO 2 in lead/acid cells is mainly determined by diffusion processes within the oxide. The hydrogen diffusion coefficient t H in lead dioxide has been determined at 25 °C; the values obtained are between 0.42 and 1.67 × 10 7 cm 2 s 1. The remo. The removing of ‘structurally bonded’ water, by heating the samples at 230 °C, affects considerably the electrochemical properties of PbO 2 and leads to a decrease in t H..

Tribochemical Synthesis and Study of Mixed Potassium-Ferrous Ferrocyanide and its RuII and OsII Analogs

Mixed potassium -ferrous ferrocyanide and its RuII and OsII analogs have been synthesized tribochemically by grinding Fe (SO4)·7H2O with the equivalent amount of K4[Fe(CN )6]·3H2O and the RuII and OsII compounds. Their XRD powder patterns and Mössbauer and IR spectra were recorded and interpreted. The role of hydration water on the feasibility of the tribochemical synthesis is discussed.

The role of hydration water in isothermal step annealing of neutron irradiated sodium nitroprusside

A kinetic study of isothermal step annealing of neutron-irradiated sodium nitroprusside has been performed. The influence of water and γ-irradiation on the behaviour of the compound is analyzed and compared with previous results obtained with the analogous compound Na2/Fe/CN/5NO/.2H2O. It is possible to characterize two different fundamental processes that, in spite of occurring at two different temperatures, present the same activation energy than the hydrated system.