Hydrogen Bond Network Of Water Research Articles

Dynamics of hydration water in gelatin and hyaluronic acid hydrogels.

We employed broadband dielectric spectroscopy (BDS), for the investigation of the water dynamics in partially hydrated hyaluronic acid (HA), and gelatin (Gel), enzymatically crosslinked hydrogels, in the water fraction ranges [Formula: see text]. Our results indicate that at low hydrations ([Formula: see text]), where the dielectric response of the hydrogels is identical during cooling and heating, water plasticizes strongly the polymeric matrix and is organized in clusters giving rise to [Formula: see text]-process, secondary water relaxation and to an additional slower relaxation process. This later process has been found to be related with the dc charge conductivity and can be described in terms of the conduction current relaxation mechanism. At slightly higher hydrations, however, always below the hydration level where ice is formed during cooling, we have recorded in HA hydrogel a strong water dielectric relaxation process, [Formula: see text], which has Arrhenius-like temperature dependence and large time scale resembling relaxation processes recorded in bulk low density amorphous solid water structures. This relaxation process shows a strong-to-fragile transition at [Formula: see text]C and our data suggest that the VTF-like process recorded at [Formula: see text]C is controlled by the same molecular process like long range charge transport. In addition, our data imply that the crossover temperature is related with the onset of structural rearrangements (increase in configurational entropy) of the macromolecules. In partially crystallized hydrogels ([Formula: see text]) HA exhibits at low temperatures the ice dielectric process consistent with the bulk hexagonal ice, whereas Gel hydrogel exhibits as main low temperature process a slow relaxation process that refers to open tetrahedral structures of water similar to low density amorphous ice structures and to bulk cubic ice. Regarding the water secondary relaxation processes, we have shown that the [Formula: see text]-process and the [Formula: see text] process are activated in water hydrogen bond networks with different structures.

Analysis of hydration water around human serum albumin using near-infrared spectroscopy

Hydration plays a fundamental role in maintaining the structure and function of proteins. To get a generalized picture of hydrogen bond network of water surrounding human serum albumin (HSA), near-infrared (NIR) spectroscopy was adopted to explore the hydration induced structural changes of water with HSA concentration from 0.015 to 0.746 mmol/L. As HSA concentration increases, there was a nonlinear change in molar extinction coefficients inconsistent with Beer-Lambert law indicating the changes of hydration water induced by HSA and subsequently confirmed by the hydration number. The decreasing of hydration number with HSA concentration was explained by an overlapping hydration layer model. Resolution of the difference spectra with McCabe-Fisher method and aquaphotomics clearly differentiated the hydrogen bonding of hydration water around HSA. A comparison of resolved hydration spectra highlights that free hydrogen bonded water is present in the hydration layer. As the concentration increased, a more ordered hydrogen bonded water network forms around HSA. These measurements provide unique insight into the relationship between the hydration water and HSA, which is important for understanding the dynamics of protein solution in many biochemical processes, and may serve as a basis for the purification in production.

A combined experimental and theoretical study of radon solubility in fat and water

Radon is a radioactive noble gas that can enter the human body, thus increasing the risk of lung cancer. But it is also used for treatment of various ailments, most notably rheumatoid arthritis. The accumulation of radon differs between tissues, with particularly high concentrations in fat tissue. To understand the underlying mechanisms, a combination of γ-spectroscopy and molecular dynamics simulations were performed, to study the accumulation of radon gas in contact with several liquids (water, fatty acids). The solubilities, specific for a defined radon activity concentration, are in good agreement and differ by two orders of magnitude between water and fat, caused by radon disrupting the hydrogen bond network of water. In contrast, the energy cost of introducing radon atoms into fat is low due to the dispersive interaction between radon and fat, which is a non-polar solvent. This correlation was also explicitly demonstrated in our simulations by changing the polarization of the solvent.

Enhancement of the local asymmetry in the hydrogen bond network of liquid water by an ultrafast electric field pulse

Condensed phase electron decomposition analysis based on density functional theory has recently revealed an asymmetry in the hydrogen-bond network in liquid water, in the sense that a significant population of water molecules are simultaneously donating and accepting one strong hydrogen-bond and another substantially weaker one. Here we investigate this asymmetry, as well as broader structural and energetic features of water’s hydrogen-bond network, following the application of an intense electric field square pulse that invokes the ultrafast reorientation of water molecules. We find that the necessary field-strength required to invoke an ultrafast alignment in a picosecond time window is on the order of 108 Vm−1. The resulting orientational anisotropy imposes an experimentally measurable signature on the structure and dynamics of the hydrogen-bond network, including its asymmetry, which is strongly enhanced. The dependence of the molecular reorientation dynamics on the field-strength can be understood by relating the magnitude of the water dipole–field interaction to the rotational kinetic energy, as well as the hydrogen-bond energy.

Kinetics of Aqueous Media Reactions via Ab Initio Enhanced Molecular Dynamics: The Case of Urea Decomposition.

Aqueous solutions provide a medium for many important reactions in chemical synthesis, industrial processes, environmental chemistry, and biological functions. It is an accepted fact that aqueous solvents can be direct participants in the reaction process and not act only as simple passive dielectrics. Assisting water molecules and proton wires are thus essential for the efficiency of many reactions. Here, we study the decomposition of urea into ammonia and isocyanic acid by means of enhanced ab initio molecular dynamics simulations. We highlight the role of the solvent molecules and their interactions with the reactants providing a proper description of the reaction mechanism and how the water hydrogen-bond network affects the reaction dynamics. Reaction free energy and rates have been calculated taking into account this important effect.

Proton-Induced Conformational and Hydration Dynamics in the Influenza A M2 Channel.

The influenza A M2 protein is an acid-activated proton channel responsible for acidification of the inside of the virus, a critical step in the viral life cycle. This channel has four central histidine residues that form an acid-activated gate, binding protons from the outside until an activated state allows proton transport to the inside. While previous work has focused on proton transport through the channel, the structural and dynamic changes that accompany proton flux and enable activation have yet to be resolved. In this study, extensive Multiscale Reactive Molecular Dynamics simulations with explicit Grotthuss-shuttling hydrated excess protons are used to explore detailed molecular-level interactions that accompany proton transport in the +0, + 1, and +2 histidine charge states. The results demonstrate how the hydrated excess proton strongly influences both the protein and water hydrogen-bonding network throughout the channel, providing further insight into the channel's acid-activation mechanism and rectification behavior. We find that the excess proton dynamically, as a function of location, shifts the protein structure away from its equilibrium distributions uniquely for different pH conditions consistent with acid-activation. The proton distribution in the xy-plane is also shown to be asymmetric about the channel's main axis, which has potentially important implications for the mechanism of proton conduction and future drug design efforts.

Intramolecular OH stretching analysis of hydrated lysozyme in presence of trehalose by IR spectroscopy

The present work reports the analysis of the intramolecular OH stretching band obtained by InfraRed spectroscopy measurements. In order to characterize the effect of trehalose on the hydration properties of lysozyme the so-called two-state model is adopted for the analysis of the intramolecular OH stretching band. This latter assumes that, provided that the trehalose OH stretching contribution is subtracted, water molecules can be partitioned into two different states of inter-molecular bonding: molecules with two OH groups both hydrogen-bonded within a tetrahedral network, and molecules with one or two dangling OH groups. What emerges from this study is that trehalose significantly influences the hydrogen bond network of water and its temperature behaviour. Such a result confirms that the trehalose induced strengthening of the hydrogen-bond network leads to a stabilization of the lysozyme structure. Moreover, the analysis of the spectra temperature dependence shows a trehalose-induced higher thermal restraint of the lysozyme-trehalose-water system in respect to the lysozyme-water mixture.

Hydrogen Bond Networks in Binary Mixtures of Water and Organic Solvents.

We here present an approach for the optical in situ characterization of hydrogen bond networks (HBNs) in binary mixtures of water and organic solvents (OSs), such as methanol, ethanol, and acetonitrile. HBNs are characterized based on (i) the analysis of experimental molar Raman spectra of the mixture, (ii) partial molar Raman spectra of the mixture constituents, and (iii) computed ideal molar Raman spectra of the mixture. Especially, the consideration of the partial molar Raman spectra provides insights into the development of hydrogen bonds of molecules of one species with their neighbors. The obtained Raman spectra are evaluated with respect to the centroid of the symmetric stretching vibration Raman signal of water and to the hydroxyl stretching vibration of alcohols. We show the influence of composition and temperature on the development of the HBN of the mixtures, the HBN of water, and the HBN of the OS molecules.

Solvent-mediated charge separation drives alternative hydrogenation path of furanics in liquid water

Compared to the vapour phase, liquid-phase heterogeneous catalysis provides additional degrees of freedom for reaction engineering, but the multifaceted solvent effects complicate analysis of the reaction mechanism. Here, using furfural as an example, we reveal the important role of water-mediated protonation in a typical hydrogenation reaction over a supported Pd catalyst. Depending on the solvent, we have observed different reaction orders with respect to the partial pressure of H2, as well as distinct selectivity towards hydrogenation of the conjugated C=O and C=C double bonds. Free energy calculations show that H2O participates directly in the kinetically relevant reaction step and provides an additional channel for hydrogenation of the aldehyde group, in which hydrogen bypasses the direct surface reaction via a hydrogen-bonded water network. This solution-mediated reaction pathway shows the potential role of the solvent for tuning the selectivity of metal-catalysed hydrogenation when charge separation on the metal surface is feasible. In heterogeneous catalysis, solvents—and their interaction with metal supports—have a complex effect on reactivity. This study shows that, in Pd-catalysed furfural hydrogenation, water influences the rate and selectivity by favouring a proton transfer rather than a purely surface-bound mechanism.

The role of hydrophobicity in the cold denaturation of proteins under high pressure: A study on apomyoglobin.

An exciting debate arises when microscopic mechanisms involved in the denaturation of proteins at high pressures are explained. In particular, the issue emerges when the hydrophobic effect is invoked, given that hydrophobicity cannot elucidate by itself the volume changes measured during protein unfolding. In this work, we study by the use of molecular dynamics simulations and essential dynamics analysis the relation between the solvation dynamics, volume, and water structure when apomyoglobin is subjected to a hydrostatic pressure regime. Accordingly, the mechanism of cold denaturation of proteins under high-pressure can be related to the disruption of the hydrogen-bond network of water favoring the coexistence of two states, low-density and high-density water, which directly implies in the formation of a molten globule once the threshold of 200 MPa has been overcome.

Intermediate Water on Calcium Phosphate Minerals: Its Origin and Role in Crystal Growth.

Water molecules are known to play crucial roles both in the formation and biological function of materials. Herein, we show the presence of "intermediate water" on an inorganic solidmaterial, hydroxyapatite. In vitro experiments revealed that Mg substitution of apatite significantly enriched the amount of intermediate water, possibly due to the proton transfer toa hydrogen-bonded network of water around HPO42- on divalent-cation-deficient apatite surfaces. The intermediate water formation related to a markedly suppressed protein adsorption on apatite. Analysis of bone apatites suggested that the intermediate water on minerals could play crucial roles in regulating crystal growth.

Thermostabilization of BSA in TMAO Water Mixtures by Infrared Spectroscopy

Background:Trimethylamine-N-Oxide (TMAO) is a small organic molecule derived from the metabolism of L-carnitine and choline after ingestion of animal food. TMAO has many functions such as electron acceptor, an osmolyte, stabilizer of macromolecules folding. It seems that TMAO plays an important role in nature but, in humans, it is a remnant of the evolution of the osmolyte system.Objective:The present paper is addressed on the study of thermal stability of hydrated Bovine Serum Albumins (BSA) in the presence of water and TMAO water solution by means of InfraRed spectroscopy. In particular, this work has investigated the protein amide I spectral regions, which is sensitive to protein secondary structure, and the intramolecular OH stretching region.Methods:The analysis has been performed by different approaches, namely by evaluating the Thermal Spectral Distance (SDT), the spectral shift (Δω), the spectral Fractal Dimension (FD) and the Wavelet Cross Correlation temperature variation (ΔTCXWT).Results:The obtained results revealed for BSA in TMAO, in respect to BSA, smaller values of SDT, Δω, FD and ΔTCXWT. Furthermore, the SDT, Δω and ΔTCXWT temperature trends to follow sigmoid trends that have been modeled by means of logistic functions; in all the above three cases BSA in TMAO shows a higher value of the inflection point temperature.Conclusion:These results can be interpreted by hypothesizing that TMAO influences the hydrogen bond network of water. In particular, the strengthening of the network intermolecular O-H interactions reduces the protein dynamic fluctuations and in turn leads to the stabilization of the protein tertiary structure.

Raman spectroscopic study of nonlinear modulation on Fermi resonance of acetonitrile by hydrogen-bonding network

Raman spectra of acetonitrile-water mixtures are measured in different acetonitrile concentration fractions. The nitrile stretch (v2) and the combination (v3 + v4) modes are coupled by Fermi resonance. We extract the Fermi resonance parameters and find that the frequency separation shows non-linear dependence as a function of acetonitrile concentration fractions. v2 ~ v3 + v4 Fermi doublets intensity ratio exhibits nonlinearity, which is accelerated with the decreasing of the Fermi coupling strength. The OH stretching region is also investigated in order to reveal the variation of the water structure. Our data show that there are strong relationships between the intensity of ~3225 cm−1 band and the v2~v3 + v4 Fermi resonance. Because the nitrile stretch and Fermi resonance are very environmental sensitive, the nonlinear modulation on Fermi resonance and the non-regular intensity ratio are attributed to the change of water hydrogen-bonding network. The results provide useful structural and spectral insights for the design of new experiments and the molecular structure modeling.

Impact of nuclear quantum effects on the structural inhomogeneity of liquid water

The 2D Raman-terahertz (THz) response of liquid water is studied in dependence of temperature and isotope substitution ([Formula: see text]O, [Formula: see text]O, and [Formula: see text]O). In either case, a very short-lived (i.e., between 75 and 95 fs) echo is observed that reports on the inhomogeneity of the low-frequency intermolecular modes and hence, on the heterogeneity of the hydrogen bond networks of water. The echo lifetime slows down by about 20% when cooling the liquid from room temperature to the freezing point. Furthermore, the echo lifetime of [Formula: see text]O is [Formula: see text] slower than that of [Formula: see text]O, and both can be mapped on each other by introducing an effective temperature shift of [Formula: see text] K. In contrast, the temperature-dependent echo lifetimes of [Formula: see text]O and [Formula: see text]O are the same within error. [Formula: see text]O and [Formula: see text]O have identical masses, yet [Formula: see text]O is much closer to [Formula: see text]O in terms of nuclear quantum effects. It is, therefore, concluded that the echo is a measure of the structural inhomogeneity of liquid water induced by nuclear quantum effects.

Probing surface water at submolecular level with scanning probe microscopy

Water-solid interfaces play important roles in a wide range of scientific areas and technique processes such as the dissolution, lubrication, erosion, electrochemistry and heterogeneous catalysis. Many remarkable physical and chemical properties of water are related to the hydrogen-bonding interaction. Thus it is a key issue to understand the hydrogen-bonding network and relevant dynamics of interfacial water at single molecule or even submolecular level. Scanning probe microscope has become a powerful tool to study the water-solid interfaces due to its capability of imaging with atomic resolution. In this feature article we will introduce the recent progress of our group on the development of submolecular-resolution imaging and spectroscopic techniques, and their applications to address the microscopic structure of the hydrogen-bonded network of water, the dynamics of proton transfer, nuclear quantum effect on the strength of hydrogen bond and water-ion interaction. Finally, future directions and challenges about the study of water-solid interface are remarked.

Cooperative Effects between Hydrophilic Pores and Solvents: Catalytic Consequences of Hydrogen Bonding on Alkene Epoxidation in Zeolites.

Hydrophobic voids within titanium silicates have long been considered necessary to achieve high rates and selectivities for alkene epoxidations with H2O2. The catalytic consequences of silanol groups and their stabilization of hydrogen-bonded networks of water (H2O), however, have not been demonstrated in ways that lead to a clear understanding of their importance. We compare turnover rates for 1-octene epoxidation and H2O2 decomposition over a series of Ti-substituted zeolite *BEA (Ti-BEA) that encompasses a wide range of densities of silanol nests ((SiOH)4). The most hydrophilic Ti-BEA gives epoxidation turnover rates that are 100 times larger than those in defect-free Ti-BEA, yet rates of H2O2 decomposition are similar for all (SiOH)4 densities. These differences cause the most hydrophilic Ti-BEA to also give the highest selectivities, which defies conventional wisdom. Spectroscopic, thermodynamic, and kinetic evidence indicate that these catalytic differences are not due to changes in the electronic affinity of the active site, the electronic structure of Ti-OOH intermediates, or the mechanism for epoxidation. Comparisons of apparent activation enthalpies and entropies show that differences in epoxidation rates and selectivities reflect favorable entropy gains produced when epoxidation transition states disrupt hydrogen-bonded H2O clusters anchored to (SiOH)4 near active sites. Transition states for H2O2 decomposition hydrogen bond with H2O in ways similar to Ti-OOH reactive species, such that decomposition becomes insensitive to the presence of (SiOH)4. Collectively, these findings clarify how molecular interactions between reactive species, hydrogen-bonded solvent networks, and polar surfaces can influence rates and selectivities for epoxidation (and other reactions) in zeolite catalysts.

Unveiling the Hydrogen Bonding Network of Intracellular Water by Fluorescence Lifetime Imaging Microscopy

Monitoring subtle changes in the local hydrogen bonding networks, which surround molecular crowding and guide cell functionality, is of paramount importance. Although the fluorescence based microsc...

Understanding the effect of nanoconfinement on the structure of water hydrogen bond networks.

Using an integrated approach of network theory and atomistic molecular dynamics simulations, we performed a detailed topological analysis on hydrogen bond networks of water confined between either two graphene sheets or two lipid bilayers to explore the structural perturbation of these networks under nanoscale confinement. The hydrogen bond network structure can be perturbed to a considerable extent when water is confined by such surfaces, yet no small-world behaviour is observed. The presence of ions also reduces the network complexity but its effect may be small depending on the type of confining surfaces. We developed an information flow model to evaluate the fluctuating nature of hydrogen bond networks and to characterise the dynamic, long-distance hydrogen-bonded chains in water. We found that the length and directionality of the hydrogen bond "trails" are highly susceptible to the type of confining surfaces and the degree of confinement. In particular, the endpoints of the hydrogen bond trails are not completely random in confined water, in which inherent distributions are determined by the density of water and the density of hydrogen bonds. This work forms the basis for the study of the pure effect of hydrogen bond network topology on various transport processes, such as proton transfer, that occur along a sequence of hydrogen bonds in a biochemical system. Our results suggest that a combined effect of the structure and lifetime of the hydrogen bond network of interfacial water may contribute to high lateral proton diffusivity at the surface of a lipid membrane.

Structural Relaxation Processes and Collective Dynamics of Water in Biomolecular Environments

In this simulation study, we investigate the influence of biomolecular confinement on dynamical processes in water. We compare water confined in a membrane protein nanopore at room temperature to pure liquid water at low temperatures with respect to structural relaxations, intermolecular vibrations, and the propagation of collective modes. We observe distinct potential energy landscapes experienced by water molecules in the two environments, which nevertheless result in comparable hydrogen bond lifetimes and sound propagation velocities. Hence, we show that a viscoelastic argument that links slow rearrangements of the water-hydrogen bond network to ice-like collective properties applies to both, the pure liquid and biologically confined water, irrespective of differences in the microscopic structure.

High temperature aqueous solvent effect on translational and hydrogen bond dynamics of the hydroxyl radical — MD simulation study

MD simulations using flexible models were performed to show how velocity autocorrelation functions, diffusion (DOH) and self-diffusion (Dw) coefficients, continuous and intermittent lifetimes of H-donor and H-acceptor bonds depend on: i) transformations in the hydrogen-bond network (HBN) of water below the critical point, and ii) decreasing density at the supercritical isotherm (∼670 K). Contrary to simulations neglecting short-range hydrogen-oxygen interactions, we show that complexation of OHaq with H2O is enhanced by breakage of the continuous HBN, resulting in the increase of OHaq hydrodynamic radius and the DOH values smaller than Dw by 30%. Difference between DOH and Dw increases to 65% at 670 K below the critical density. It is explained by enhanced aggregation of water molecules around OHaq, earlier recognized as the self-trapping mechanism. Except near-ambient conditions, the intermittent lifetime of H-bonds is longer than the translational time, indicating that OHaq is complexed with water and moves as a molecular aggregate.