Properties of Water Molecules in Hydrated Ionic Liquids and Their Potential as Solvents for Biomolecules

Mordenite ((Ca,Na2,K2)Al2Si10O24·7H2O) is a natural and synthetic nanoporous zeolite containing several channels of different sizes in its structure. Because of this, its structure provides an important opportunity to study the relationship between confined and ultraconfined water as these channels have sizes between those typical of these water environments. In this study, the properties of water molecules in these environments were analyzed using inelastic and quasielastic neutron spectroscopy of a natural mordenite. The quasielastic spectra showed the presence of nonfreezing, mobile water molecules through the entire temperature range of the measurements, but very little anisotropy of the dynamics measured along and perpendicular to the channels. Faster and slower quasi-elastic neutron scattering (QENS) components may be consistent with the presence of two separate classes of water molecules in mordenite. Inelastic neutron spectroscopy also found no evidence of directional anisotropy. The strong intensity characteristic of neutron recoil on protons from highly mobile water molecules at low temperature (5 K), along with a significant shift of water librational band to lower energies and the O-H stretching modes to high energies, indicate that the hydrogen bonds acting on these water molecules in mordenite resemble those in liquid water rather than ice.

The water molecule, H2O is a very simple and most stable molecule. It displays a discrete but nevertheless exceptional property that has far-reaching consequences, one of them being that without it life would not exist. At ambient conditions, water remains in liquid form, becomes ice below freezing temperatures and turns into vapor form at high temperatures. In this paper, we use molecular dynamics (MD) simulation method to study the hydrodynamic properties of water molecule. The interactions that exist in the water molecule is described using the 3 site transferable inter-molecular potential model. The properties of water molecule that occur at nano level are studied and compared with those at the bulk.

The dynamics of water surrounding a solute is of fundamental importance in chemistry and biology. The properties of water molecules near the surface of a bio-molecule have been the subject of numerous, sometimes controversial experimental and theoretical studies, with some suggesting the existence of rather rigid water structures around carbohydrates and proteins [Pal, S. K., Peon, J., Bagchi, B. and Zewail A. H. (2002) J. Phys. Chem. B 106, 12376-12395]. Hydrogen bond rearrangement in water occurs on the picosecond time scale, so relevant experiments must access these times. Here, we show that terahertz spectroscopy can directly investigate hydration layers. By a precise measurement of absorption coefficients between 2.3 THz and 2.9 THz we could determine the size and the characteristics of the hydration shell. The hydration layer around a carbohydrate (lactose) is determined to extend to 5.13 +/- 0.24 A from the surface corresponding to approximately 123 water molecules beyond the first solvation shell. Accompanying molecular modeling calculations support this result and provide a microscopic visualization. Terahertz spectroscopy is shown to probe the collective modes in the water network. The observed increase of the terahertz absorption of the water in the hydration layer is explained in terms of coherent oscillations of the hydration water and solute. Simulations also reveal a slowing down of the hydrogen bond rearrangement dynamics for water molecules near lactose, which occur on the picosecond time scale. The present study demonstrates that terahertz spectroscopy is a sensitive tool to detect solute-induced changes in the water network.

Structural Properties of Water at Interfaces

Molecular dynamics study on water desalination performance and related mechanism of hydrophobic α-Al2O3 ceramic membrane

We study the structures of Hras-GTP and Hras-GDP complexes in water in order to investigate the mechanism of hydrolysis of GTP in the Hras-GTP complex. Understanding of the mechanism of hydrolysis of GTP in the Hras-GTP complex plays a key role in overcoming the human cancer. We performed molecular dynamics (MD) simulations of Hras-GTP complex and Hras-GDP complex in water using AMBER03 parameters and our calculated parameters around Mg2+. Using the trajectories of the MD simulations, we calculated the radial distribution functions of water molecules around the phosphorus atoms in guanine nucleotide in each complex. We also calculated the radius of the first hydration sphere, the averaged number of water molecules in the first hydration sphere, and the distribution of duration time of water molecules in the first hydration sphere. We also calculated the distribution of water molecules with respect to the angle around the PG in GTP and PB in GDP. It is suggested that the hydrolysis is triggered by water molecules attacking γ–phosphate from the direction rotated 35° to the O1B from the axis defined by PG and O3B.

The Malomuzh–Orlov theory is used to analyze the experimental shear viscosity data obtained for aqueous solutions of human serum albumin (HSA) at pH = 7.0 in wide temperature and concentration intervals, which allowed the effective radii of HSA macromolecules to be calculated. It is shown that three intervals of the effective molecular radius of HSA with different behaviors can be distinguished in a temperature interval of 278–318 K: 1) below the crossover concentration, the effective molecular radius of HSA remains constant; 2) in the interval from the crossover concentration to about 10 wt%, the effective molecular radius of HSA in the aqueous solution nonlinearly decreases; and 3) at concentrations of 10.2–23.8 wt%, the effective radius of HSA macromolecules linearly decreases, as the concentration grows. The assumption is made that the properties of water molecules in the solution bulk play a crucial role in the dynamics of HSA macromolecules at the vital concentrations of HSA in the solutions. The role of water near the surface of HSA macromolecules and the corresponding changes of its physical properties have been discussed.

Effect of ectoine on hydration spheres of peptides–spectroscopic studies

Applications of graphene sheets in the fields of biosensors and biomedical devices are limited by the aqueous solubility of graphene. Consequently, understanding the role of water molecules in the aggregation or dispersion of graphene in aqueous solution with a biomolecule is of vital importance to its application. Herein, protein is spontaneously released by the layer-to-layer aggregation of two single-layer graphene sheets due to van der Waals force between the sheets. The properties of water molecules, including density and dynamics, are discussed in detail. The dynamic behavior of aggregation of graphene sheets is triggered by the dynamics of water molecules. To stabilize dispersed graphene sheets in aqueous solution, the density of water molecules between the graphene sheets should be larger than 0.83 g cm(-3), and graphene modified by hydroxyl groups could be a good choice. The stability of a model protein on the graphene sheet is studied to investigate the biological compatibility of graphene sheets. To be a material with good biocompatibility, graphene should be functionalized by hydrophilic groups. The results presented herein could be helpful in the research and application of graphene sheets in the fields of biomaterials, biosensors, and biomedical devices.

Properties of Water Molecules in the Active Site Gorge of Acetylcholinesterase from Computer Simulation

The properties of water molecules in nano-confined geometries have significant roles in different fields such as adsorption, electrochemistry, biology, earth science, materials science, and nanoflu...

Properties of water molecules at the interface between contrast agents (CAs) for magnetic resonance imaging and macromolecules could have a valuable impact on the effectiveness of metal chelates. Recent studies, indeed, demonstrated that polymer architectures could influence CAs' relaxivity by modifying the correlation times of the metal chelate. However, an understanding of the physico-chemical properties of polymer/CA systems is necessary to improve the efficiency of clinically used CAs, still exhibiting low relaxivity. In this context, we investigate the impact of hyaluronic acid (HA) hydrogels on the relaxometric properties of Gd-DTPA, a clinically used CA, to understand better the determining role of the water, which is crucial for both the relaxation enhancement and the polymer conformation. To this aim, water self-diffusion coefficients, thermodynamic interactions and relaxometric properties of HA/Gd-DTPA solutions are studied through time-domain NMR relaxometry and isothermal titration calorimetry. We observed that the presence of Gd-DTPA could alter the polymer conformation and the behaviour of water molecules at the HA/Gd-DTPA interface, thus modulating the relaxivity of the system. In conclusion, the tunability of hydrogel structures could be exploited to improve magnetic properties of metal chelates, inspiring the development of new CAs as well as metallopolymer complexes with applications as sensors and memory devices.

Confinement effects can lead to drastic changes in the structural and dynamical properties of water molecules. In this work, we have performed classical molecular dynamics simulations of endohedral fullerenes of type (H2O)n@Cm (n = 1, 12, 21, 62, 108 and m = 60, 180, 240, 500 and 720) to explore the effects of spherical confinement on water properties. It is shown that these confined water molecules can form distinct solvation pattern depending upon the available space inside the fullerene cavity. For the systems with smaller diameter, cage-like structure is predominant whereas bulk-like structure is observed for larger fullerenes. The orientational relaxation of these confined water molecules showed slower relaxation as the cavity diameter increases except for the (H2O)21@C240. In this case, stable cage-like structure hinders the overall dynamics of the trapped water molecules. Finally, we have calculated the hydrogen bond lifetimes from the hydrogen bond time correlation functions and compared with that of bulk water.

The conformation in aqueous solution and the adsorption ability to water molecules of polycarboxylate ether (PCE) superplasticizer have important effects on its the properties. In this work, molecular dynamics (MD) simulations were employed to investigate the conformation of PCE molecules and the interaction between PCE and water molecules at microscopic level. Five kinds of PCE molecular models (PCE-2, PCE-6, PCE-10, PCE-14 and PCE-18) with different lengths of main chain were constructed, and the simulation results show that the longer length of main chain makes PCE molecules more stretched. The steric hindrance of PCE enhances from PCE-2 to PCE-14, and then declines from PCE-14 to PCE-18, which result from the greater molecules aggregation. The radial distribution functions (RDFs) indicate that the water absorption capacity of PCE molecule enhanced with the increasing of main chain length, and main chain plays an important role of water molecule capture. Both steric hindrance and water absorption capacity of PCE molecules can effectively affect the diffusion properties of water molecules, and prevent water molecules from contacting with cement particles, which retards the hydration process of cement.

Ionic liquids (ILs) such as choline dihydrogen phosphate exhibit an extraordinary solubilizing ability for proteins such as cytochrome C when mixed with 20 wt % water. Most widely used imidazolium-based ionic liquids coupled with dihydrogen phosphate do not exhibit the same solubilizing properties, suggesting that a multifunctional cation such as choline might play a key role in enhancing these properties of ionic liquid mixtures with water. In this theoretical work, we compare intermolecular interactions between the water molecule and ionic liquid ions in two ion-paired clusters of choline- and 1-butyl-3-methyl-imidazolium-based ionic liquids coupled with acetate, dihydrogen phosphate, and mesylate. Gibbs free energy (GFE) of solvation of water in these ionic liquids was calculated. Incorporation of a water molecule into ionic liquid clusters was accompanied by negative GFEs of solvation in both types of cations. These results were in good agreement with previously reported experimental GFEs of solvation of water in ILs. Compared to imidazolium-based clusters, strong interionic interactions of choline ionic liquids resulted in more negative GFEs due to their smaller deformation upon the addition of a water molecule, with dihydrogen phosphate and mesylate predicting the lowest GFEs of -30.1 and -43.5 kJ/mol-1, respectively. Lower GFEs of solvation of water in choline-based clusters were also accompanied with smaller entropic penalties, suggesting that water easily incorporates itself into the existing ionic network. Analysis of the intramolecular bonds within the water molecule showed that the choline hydroxyl group donates electron density to the neighboring water molecule, leading to additional polarization. The predicted infrared spectra of clusters of ionic liquids with water showed a pronounced red shift due to strongly polarized O-H bonds, in excellent agreement with the experimentally measured infrared spectra of ionic liquid mixtures with water. Increased polarization of water in choline-based ionic liquids undoubtedly creates more effective solvents for stabilizing biological molecules such as proteins.