Hydrogen Atoms Of Water Molecules Research Articles

First Principles Calculations Study of Lithium-Montmorillonite for Humidity Sensor Application

In this study, we performed calculations on the water molecule adsorbed on lithium montmorillonite using first principles-calculation by means of electronic-structure calculation, with emphasis on approaches based on Density Functional Theory (DFT). The mechanism of water molecule adsorption on the surface of lithium-montmorillonite was investigated from the electronic structure point of view to seek the possibility of using montmorillonite as humidity sensor. The effects of the Van der Waals force to the electronic properties of water molecule on the surface of montmorillonite was also considered and obtained that the structure is more stable energetically. The interaction of water molecule with surface of montmorillonite yields the rotation of the hydrogen atoms of water molecule due to the occurrence of repulsive interaction between two positive ions of hydrogen of water molecule and lithium. From the calculations, lithium-montmorillonite can be considered as a good material for humidity sensor application since there is an electrical change observed even though it is a relatively small that is 0.657 eV.

Structures and acidity constants of arsenite and thioarsenite species in hydrothermal solutions

We report a first principles molecular dynamics (FPMD) study of structures and acidity constants of arsenite and thioarsenite species in liquid water from ambient temperature to 573K. The analyses show that at all temperatures, the OH ligands of arsenite species form H-bonds with solvating water molecules as both donors and acceptors, whereas there are only very weak H-bonds between the SH ligands of thioarsenite species and water. For both arsenites and thioarsenites, the dangling O/S sites form strong H-bonds with hydrogen atoms of water molecules, but the As atoms have almost no interaction with water molecules. The FPMD based vertical energy gap method was applied to calculate the acidity constants. With the evaluated acidity, the species distributions with respect to pH have been derived. The pKa1s of H3AsO3 and H3AsS3 demonstrate a decreasing trend with temperature. For arsenites, H3AsO3 and H2AsO3− can coexist, whereas HAsO32− almost does not exist, due to the notably high pKa2s of H3AsO3. For thioarsenites, H2AsS3− and HAsS32− are always the dominant species in the near neutral pH range from ambient temperature to 573K.

Hepta- and tetra-nuclear copper(II) clusters self-assembled by cyano- and azacyano-carbanions

Two polynuclear copper(II) complexes with hydroxido-bridging ligands and polycyanide units, [Cu{Cu(tn)}6(μ2-OH)2(μ3-OH)4Cl2](tcm)4Cl2·2H2O (1) and [{Cu(bpy)}4(OH)4(dca)2](dca)2·bpy·2H2O (2) (tn=NH2(CH2)3NH2; tcm−=[C(CN)3]−, bpy=2,2′-bipyridyl, dca−=[N(CN)2]−) have been prepared by one-pot reactions. The structure of 1 consists of a centrosymmetric heptanuclear ion [Cu{Cu(tn)}6(μ2-OH)2(μ3-OH)4Cl2]6+. The tcm− and the halide anions which appear as counter-ions in the formula unit, play an important role in the stabilization of the complex since the hydrogen bonding between nitrogen atoms of the tcm− anion and halide anions, and hydrogen atoms of the terminal water molecule and of the bridging hydroxido ligands generate an overall three-dimensional structure. The crystal structure of 2 is essentially built on discrete centrosymmetric tetranuclear [{Cu(bpy)}4(μ2-OH)2(μ3-OH)2(dca)2]2+ units including two μ2- and two μ3-OH ligands. As observed for 1, the dca− anions form a network of hydrogen bonding between their nitrogen atoms and hydrogen atoms of water molecules generating a two-dimensional structure. The magnetic susceptibility data indicate antiferromagnetic interactions in 1 and ferromagnetic ones in 2.

Three-dimensional Inversion of Magnetic Resonance Sounding (MRS) for Groundwater Detection

For this paper, we consider the resulting 3-D inversion using inversion modeling, which is motivated by developing theory and the recent application of the Magnetic Resonance Sounding (MRS) technique in detecting and mapping of subsurface groundwater. MRS is a non-invasive method which directly detects the groundwater’s existence from surface measurements. A pulse current, at a proper frequency, is transmitted into a loop. After hydrogen atoms of water molecules in the subsurface are energized by pulses of alternative currents, the magnetic resonance field is produced by the H protons is measured within the same loop. Generally, MRS has two observable factors: initial amplitude and decay time. The aim of threedimensional inversion is to extract the information, i.e., the value and distribution of two physical parameters of the subsurface conditions: water content and subsurface properties (pore and grain size). Additionally, we present a general formulation for inverting the initial amplitude and decay time of the MRS data to recover a 3-D distribution of groundwater. The forward problem was solved using an integral equation method in the spatial domain. An improved Levenberg-Marquardt strategy was employed to solve the inverse problem. Two synthetic examples are illustrated to determine the basic functionality of the inversion algorithm. The real data results show applicability and relevance in larger-scale field examples.

First-Principles Study of Water Reaction and H2 Formation on UO2 (111) and (110) Single Crystal Surfaces

Molecular and dissociative adsorption behavior of H2O along with the accompanying H2 formation mechanism on the UO2 (111) and (110) surfaces have been investigated by using DFT+U calculations. According to our calculations, the higher stability of the (111) surface leads to higher oxygen vacancy formation energy compared to the (110) surface. On the stoichiometric (111) and (110) surfaces, the first hydrogen atom of water molecule can dissociate readily with very small or no energy barrier. On the contrary, dissociation of the second one becomes the rate-determining step, and water-catalysis leads to the decrease of energy barrier from 0.92 to 0.70 eV and from 2.36 to 1.21 eV on the stoichiometric (111) and (110) surfaces, respectively. H2 formation resulting from water dissociation may undergo two pathways in the presence of surface oxygen vacancy on the reduced UO2 (111) surface. One is characterized by direct combination of two hydrogen atoms of one water molecule, and the other is characterized by dis...

Structural Arrangement of Water Molecules around Highly Charged Nanoparticles: Molecular Dynamics Simulation

Molecular dynamics simulations were performed to understand the structural arrangement of water molecules around highly charged nanoparticles under aqueous conditions. The effect of two highly charged nanoparticles on the solvation charge asymmetry has been examined. We calculated the radial distribution functions of the components of water molecules around nanoparticles which have four charge types at two different salt concentrations. Even though the distributions of water molecules surrounding a sodium ion and a chloride ion are hardly affected by the charges of nanoparticles and the salt concentrations, those around highly charged nanoparticles are strongly influenced by the charges of nanoparticles, but hardly by the charges of nanoparticles and salt concentrations. We find that the distributions of hydrogen atoms in water molecules around one highly charged nanoparticle are dependent on the magnitude of the nanoparticle charge.

Dynamics of water molecules adsorbed by silica and resin SGK-7

This paper has presented neutron spectroscopy data on the dynamics of light water molecules adsorbed in the cation exchanger (ion-exchange resin) SGK-7 and on the surface of aerosils (highly dispersed pyrogenic silica) with different levels of hydration. The measurements have been performed on a DIN-2PI spectrometer (Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research, Dubna, Russia). The characteristics of the diffusive and vibrational motions of adsorbed water molecules have been determined from the experimental neutron scattering spectra. The data obtained in the quasi-elastic neutron scattering region have been analyzed using a model accounting for the effects of restricted translational and rotational diffusion. The results have demonstrated a significant decrease in the diffusion mobility of adsorbed water molecules as compared to conventional (bulk) water. In particular, the self-diffusion coefficient decreases several times, and the diffusion rate is the lower, the smaller is the thickness of the hydration layer. The dependences of the intensity and half-width of the quasi-elastic scattering peak on the magnitude of the neutron momentum transfer q in the scattering process exhibit a nonmonotonic character. This indicates manifestation of the effects of restricted translational diffusion, rotational diffusion, and jump diffusion. The partial distributions of vibrational frequencies of hydrogen atoms of water molecules adsorbed by the cation exchanger and aerosils have been obtained from the inelastic neutron scattering data.

Ordering of cations in the voids of the anionic framework of the crystal structure of catapleiite

The pseudohexagonal crystal structure of the mineral catapleiite Na1.5Ca0.2[ZrSi3(O,OH)9] · 2(H2O,F) from the Zhil’naya Valley in the central part of the Khibiny alkaline massif (Kola Peninsula, Russia) is studied by X-ray diffraction (XCalibur-S diffractometer, R = 0.0346): a = 20.100(4), b = 25.673(5), and c = 14.822(3) A; space group Fdd2, Z = 32, and ρcalcd = 2.76 g/cm3. Fluorine atoms substituting part of H2O molecules in open channels of the crystal structure have been found for the first time in the catapleiite composition by microprobe analysis. The pattern of distribution of Na and Ca atoms over the voids of the mixed anionic framework consisting of Zr-octahedra and three-membered rings of Si-tetrahedra accounts for the pronounced pseudoperiodicity along the a and c axes of the pseudohexagonal unit cell and for the lowering of crystal symmetry to the orthorhombic one. It is shown that part of the hydrogen atoms of water molecules is statistically disordered; their distribution correlates with the pattern of the population of large eight-vertex polyhedra by Na and Ca atoms.

Coexistence of solvated electron and benzene-centered valence anion in the negatively charged benzene-water clusters

We present a combined M06 functional calculation and ab initio molecular dynamics simulation study of an excess electron (EE) in a microhydrated aromatic complex (modeled by benzene (Bz)-water binary clusters, Bz(H(2)O)(n)). Calculated results illustrate that Bz ring and water clusters are indeed linked through the π···HO interactions in the neutral Bz(H(2)O)(n) (n = 1-8) clusters, and the size of the water cluster does not influence the nature of its interaction with the π system for the oligo-hydrated complexes. The states and the dynamics of an EE trapped in such Bz-water clusters were also determined. All of possible localized states for the EE can be roughly classified into two types: (i) single, ring-localized states (the Bz-centered valence anions) in which an EE occupies the LUMO of the complexes originating from the LUMO (π*) of the Bz ring, and the π···HO interactions are enhanced for increase of electron density of the Bz ring. In this mode, the carbon skeleton of the Bz part is significantly deformed due to increase of electron density and nonsymmetric distribution of electron density induced by the interacting H-O bonds; (ii) solvated states, in which an EE is trapped directly as a surface state by the dangling hydrogen atoms of water molecules or as a solvated state in a mixed cavity formed by Bz and water cluster. In the latter case, Bz may also participate in capturing an EE using its C-H bonds in the side edge of the aromatic ring as a part of the cavity. In general, a small water cluster is favorable to the Bz-centered valence anion state, while a large one prefers a solvated electron state. Fluctuations and rearrangement of water molecules can sufficiently modify the relative energies of the EE states to permit facile conversion from the Bz-centered to the water cluster-centered state. This indicates that aromatic Bz can be identified as a stepping stone in electron transfer and the weak π···HO interaction plays an important role as the driving force in conversion of the two states.

Crystal structures and properties of divalent transition metal decahydro-closo-decaborate hydrates [M(H2O)6][B10H10] · 2H2O (M = Mn, Fe, Co, Ni, Zn)

Transition metal(II) decahydro-closo-decaborate hydrates [M(H2O)6][B10H10] · 2H2O (M = Fe, Co, Ni) were synthesized by reacting an aqueous solution of (H3O)2[B10H10] with the corresponding metal powders. The manganese(II) compound [Mn(H2O)6][B10H10] · 2H2O could be obtained by the reaction of an aqueous solution of Ba[B10H10] with Mn(SO4) · H2O after the precipitation of Ba(SO4). For the zinc salt [Zn(H2O)6][B10H10] · 2H2O an aqueous solution of (H3O)2[B10H10] was reacted with the basic zinc(II) carbonate [Zn(CO3)]2 · [Zn(OH)2]3. All five compounds crystallize isotypically in the monoclinic space group C2/c with four formula units per unit cell. Their crystal structure contains crystallographically unique transition metal(II) cations, which are octahedrally coordinated by oxygen atoms of six water molecules. Another six water molecules are bound to each hexaaqua-transitionmetal( II) cation through hydrogen bonds, again erecting a distorted octahedron. The second octahedra are linked to each others via common edges to build up a layer containing [M(H2O)6]2+ cations and second-sphere crystal water molecules. Between these layers the bicapped square-antiprismatically shaped decahydro-closo-decaborate anions [B10H10]2- are situated and held there through non-classical hydrogen bonds between the positively polarized hydrogen atoms of water molecules and the negatively polarized hydrogen atoms of boron-cluster anions. The closo-decaborate clusters themselves show only slight distortions away from their ideal D4d symmetry as vibrational spectroscopy studies prove. Stepwise thermal decomposition takes place not only under water removement, but finally also under hydrogen evolution.

The influence of water on dielectric property in cocrystal compound of [orotic acid][melamine]·H2O

An organic cocrystal compound consisting of melamine, orotic acid and water molecules was synthesized under hydrothermal conditions. Investigation of its temperature- and frequency-dependent dielectric behaviors reveals that the fluctuation of hydrogen atoms of water molecules between the layers plays a key role in its dielectric anomaly.

Hindering of rotational motion of guest molecules in the Type I clathrate hydrate

Guest–host interactions in the Type I mixed clathrate hydrate with ethylene oxide and carbon monoxide guest molecules at temperature below 110 K are studied. By means of both molecular dynamics simulations and FTIR spectroscopy we investigate the hindering of rotational motion of guests molecules, the origin of this hindering, and the spectroscopically measurable consequences. Steric effects are responsible for restriction of rotational displacements of carbon monoxide. For ethylene oxide the rotational hindering is caused predominantly by van der Waals interactions between oxygen atom of guest and hydrogen atoms of water molecules. Creation of host–guest hydrogen bonds was not observed.

Molecular imaging contrast media for visualization of liver function

Diagnosis of liver disease has improved because of progress in imaging technology. Among the imaging methods, magnetic resonance imaging (MRI) has the advantage of a lack of radiation exposure, but the basis of the method (imaging of hydrogen atoms in water molecules) makes it hard to detect changes in tissue or the location of the diseased tissue in the liver. The aims of this study are to develop new contrast media for visualization of functional changes in the liver and to check the effectiveness of the media. We developed a new molecular imaging contrast media that targets the asialoglycoprotein receptor (ASGP-R), a membrane protein that is specific to hepatocytes. We first checked the contrast media diameter and the cytotoxicity. Next, we examined the interaction of the media with ASGP-R through observation of fluorescein isothiocyanate (FITC)-labeled molecular imaging contrast media bound to normal hepatocellular ASGP-R using confocal laser scanning microscopy. Finally, we used MRI to observe hepatocyte interactions with the molecular imaging contrast media. The contrast media forms a nanoparticle of about 30 nm diameter in aqueous solution and the cytotoxicity is low. In vitro, the media has high specificity for ASGP-R in normal rat hepatocyte RLN-8 cells and this interaction was blocked by lactose (which has a similar molecular structure to that of galactose) and by an anti-ASGP-R antibody. The contrast media markedly enhanced T1-weighted images in MRI of normal rat hepatocytes compared to the signal strength for rat liver cancer cells. We have shown that our new contrast media for molecular imaging of hepatocytes by MRI is effective in vitro.

Crystal structure of Li(H2O)3[GaEdta

The ethylenediaminetetraacetate complex Li(H2O)3[Ga(Edta)] was synthesized and its crystal structure composed of octahedral (Ga(Edta)− anions connected to the Li(H2O)3+ ion through the oxygen atom was studied. Five of the six hydrogen atoms of water molecules are involved in weak hydrogen bonds with the oxygen atoms of four Ga(Edta)− complexes, the complex anion is hydrogen-bonded to five water molecules. In addition, shortened contacts C(221)–H(22A)…O(112) between the Ga(Edta)− anions were found. As a result, the molecular packing in the crystal is determined by the three-dimensional lace of hydrogen bonds. The results are compared with published data for the lithium salts of Bi(III), Sb(III), Fe(III), Ni(II), and Hg(II) ethylenediaminetetraacetates.

All-atom Molecular Dynamic Simulations and NMR Spectra Study on Intermolecular Interactions of N,N-dimethylacetamide-Water System

N,N-dimethylacetamide (DMA) has been investigated extensively in studying models of peptide bonds. An all-atom MD simulation and the NMR spectra were performed to investigate the interactions in the DMA-water system. The radial distribution functions (RDFs) and the hydrogen-bonding network were used in MD simulations. There are strong hydrogen bonds and weak CHO contacts in the mixtures, as shown by the analysis of the RDFs. The insight structures in the DMA-water mixtures can be classified into different regions by the analysis of the hydrogen-bonding network. Chemical shifts of the hydrogen atom of water molecule with concentration and temperatures are adopted to study the interactions in the mixtures. The results of NMR spectra show good agreement with the statistical results of hydrogen bonds in MD simulations.

Determination of Water Content in Olive Oil by 31P NMR Spectroscopy

A method for moisture determination in olive oil using 31P NMR spectroscopy is developed. This method is based on the replacement of the hydrogen atoms of water molecules with the tagging agents 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane and diphenylphosphinic chloride. Both reagents were successful in determining moisture in olive oil. However, only the second reagent provided a clean and instantaneous reaction under mild condition with no side reactions as observed with the first reagent. A study comparison was made to assess the agreement between the present analytical NMR method and the well-established methods of Karl Fischer titration.

Structure and hydrogen bonding in polyhydrated complexes of guanine

Molecular structure of complexes of guanine with 12, 13, 16, and 17 water molecules were calculated using B3LYP/6-311G(d,p) level of theory. Interaction with water results in some deformation of geometrical parameters of guanine, which can be described as contribution of zwitter-ionic resonant form into the structure of DNA base. Saturation of water binding sites within guanine creates possibilities for the formation of the N···H–O hydrogen bond where the nitrogen atom of amino group acts as proton acceptor. The NBO analysis of guanine–water interactions reveals that hydrogen bonds involving the N(3) and N(7) atoms of guanine represent a case of mixed N···H–O/π···H–O hydrogen bonds where contribution of π-system into total energy of interaction varies from 3% to 41%. This contribution significantly depends on orientation of the hydrogen atom of water molecule with respect to plane of purine bicycle and influence of neighboring water molecules.

An Explanation for the Very Large Breathing Effect of a Metal–Organic Framework during CO2 Adsorption

The very large breathing effect of a metal-organic framework during CO 2 adsorption is discussed. An experiment was conducted for the case of CO2 adsorption at room temperature for porous chromium (III) terephthalate MIL-53. The structural topology of MIL-53 consists of a 4 4 net with tilted chains of CrIIIO4(OH) 2 octahedra sharing trans hydroxyl groups solid. These chains are linked through the carboxylate groups of the terephthalate ions forming a 3D framework. An in situ solid-state NMR study of the hydration of MIL-53HT showed that the shrinkage that occurred upon insertion of water molecules resulted from the onset of two types of strong hydrogen bonds. The first type involves the hydrogen atoms of water molecules and the oxygen atoms of the bridging carboxylate groups. The second type, which seems to be more energetically favorable, links OH groups to inserted water molecules.

Three-dimensional square water in the presence of an external electric field

In this work we study a tridimensional statistical model for the hydrogen-bond (HB) network formed in liquid water in the presence of an external electric field. This model is analogous to the so-called square water, whose ground state gives a good estimate for the residual entropy of the ice. In our case, each water molecule occupies one site of a cubic lattice, and no hole is allowed. The hydrogen atoms of water molecules are disposed at the lines connecting nearest-neighbor sites, in a way that each water can be found in 15 different states. We say that there is a hydrogen bond between two neighboring molecules when only one hydrogen is in the line connecting both molecules. Through Monte Carlo simulations with Metropolis and entropic sampling algorithms, and by exact calculations for small lattices, we determined the dependence of the number of molecules aligned to the field and the number of hydrogen bonds per molecule as a function of temperature and the intensity of the external field. The results for both approaches showed that, different of the two-dimensional case, there is no maximum in the number of HBs as a function of the electric field. However, we observed nonmonotonic behaviors as a function of the temperature of the quantities of interest. We also found the dependence of the entropy on the external electric field at very low temperatures. In this case, the entropy vanishes for the value of the external field for which the contributions to the total energy coming from the HBs and the field become the same.

Inhibition of Ice Nucleus Growth in Water by Alanine Dipeptide

A molecular dynamics simulation has been carried out for the mixture of an ice nucleus, supercooled water and a molecule of alanine dipeptide (AD). The dipeptide molecule has been allocated near the nucleus surface which corresponds to the prism plane of ice crystal. The molecule is found to approach the ice surface so that the two hydrophilic sites on one side of the molecule (Oc2 and Hn1) are closest to the surface. The hydrogen bond between Hn1 site and the oxygen atom on the prism plane of the ice nucleus is expected. The perturbations of two hydrophilic sites (Oc1 and Hn2), which are surrounded by hydrophobic sites and are pointing away from the surface, attenuate the approach of water molecules to these sites. Thus, these water molecules diffuse. The hydrogen bond between the oxygen atoms on the prism plane and the hydrogen atoms of water molecules is attenuated by the diffusion.