Dipole Moment Of Water Molecule Research Articles

Dipole moment of water molecules in narrow pores

We use ab initio molecular dynamics simulation to calculate the dipole moment of water molecules in one-dimensional hydrogen bonded chains in narrow pores. The electronic charges are partitioned among the water molecules using maximally localized Wannier functions. For water molecules confined to the interior of a carbon nanotube we find an average dipole moment of about 2.7 D, almost 10% lower than the dipole moment of water molecules in the liquid phase calculated with the same method. The value of the water dipole moment in hydrogen bonded chains determines the effective interaction of excess protons and hydrogen bonding defects in the water chain. Using the dipole moment from our simulations we obtain an effective charge of 0.4 e and –0.4 e for the D-defect and the L-defect, respectively, and an effective charge of 0.6 e for an excess proton in the chain.

A Critical Analysis of Chromotherapy and Its Scientific Evolution

Chromotherapy is a method of treatment that uses the visible spectrum (colors) of electromagnetic radiation to cure diseases. It is a centuries-old concept used successfully over the years to cure various diseases. We have undertaken a critical analysis of chromotherapy and documented its scientific evolution to date. A few researchers have tried to discover the underlying scientific principles, but without quantitative study. Sufficient published material can be found about the subject that provides a complete system of treatment focused on the treatment methodologies and healing characteristics of colors. A number of studies have elaborated the relationship between the human body and colors. We also show the possibility of carrying out diverse research into chromotherapy that is pertinent to deciphering the quantum mechanical dipole moment of water molecules. The quantum mechanical dipole moment as a result of the absorption of different colors, we conjecture, produces charge quantization phenomena. This review illustrates that the development of science in the field of electromagnetic radiation/energy can be very helpful in discovering new dimensions of this old theory.

CHARMM fluctuating charge force field for proteins: I parameterization and application to bulk organic liquid simulations.

A first-generation fluctuating charge (FQ) force field to be ultimately applied for protein simulations is presented. The electrostatic model parameters, the atomic hardnesses, and electronegativities, are parameterized by fitting to DFT-based charge responses of small molecules perturbed by a dipolar probe mimicking a water dipole. The nonbonded parameters for atoms based on the CHARMM atom-typing scheme are determined via simultaneously optimizing vacuum water-solute geometries and energies (for a set of small organic molecules) and condensed phase properties (densities and vaporization enthalpies) for pure bulk liquids. Vacuum solute-water geometries, specifically hydrogen bond distances, are fit to 0.19 A r.m.s. error, while dimerization energies are fit to 0.98 kcal/mol r.m.s. error. Properties of the liquids studied include bulk liquid structure and polarization. The FQ model does indeed show a condensed phase effect in the shifting of molecular dipole moments to higher values relative to the gas phase. The FQ liquids also appear to be more strongly associated, in the case of hydrogen bonding liquids, due to the enhanced dipolar interactions as evidenced by shifts toward lower energies in pair energy distributions. We present results from a short simulation of NMA in bulk TIP4P-FQ water as a step towards simulating solvated peptide/protein systems. As expected, there is a nontrivial dipole moment enhancement of the NMA (although the quantitative accuracy is difficult to assess). Furthermore, the distribution of dipole moments of water molecules in the vicinity of the solutes is shifted towards larger values by 0.1-0.2 Debye in keeping with previously reported work.

NMR Study of the Water Dynamics in Aqueous Colloidal Magnetic Fluids at Different pH's and Grains Concentrations

In a previous NMR study [González, C.E.; et al. J. Chem. Phys. 1998, 109, 4670] we observed that the 1H and 2H spectra of both surfacted and ionic ferrofluids are broad and asymmetric. In ionic ferrofluids, this effect could be due to (i) electric interactions between the electrically charged magnetic grains and the electric dipole moments of water molecules and/or (ii) the interaction between water molecules and the distribution of magnetic field gradients in the intergrain volume. In this work we study a series of ionic ferrofluids prepared at different magnetic grains concentrations and with different surface charge densities. Our experiments clearly show that the sign and the density of the electric charge of the magnetic grains have no influence on the NMR spectra. On the other hand, spectral widths increase with the magnetic grains concentration, all the samples being far from the motional narrowing regime.

What can classical simulators learn from ab initio simulations?

We compare the electrostatic properties of individual water molecules in ab initio simulations and in some potential models used in classical simulations. We find that the standard rigid water models at room temperature and ambient pressure describe the average electrostatic properties of molecules quite well, although there are considerable fluctuations. Preliminary results show that the dipole moment of water molecules near either a sodium ion or a methane molecule are not significantly different from its average value in bulk water, which may justify the use of non-polarisable water models in simulations of biological molecules. In ice, however, the dipole induced by the surroundings is appreciably higher. Incorrect freezing points can be attributed to a bad description of the solid phase rather than to a bad description of the liquid phase.

Dielectric Relaxation Around a Charged Colloidal Cylinder in an Electrolyte

The polarizability and corresponding dielectric relaxation of the Debye–Hückel (DH) atmosphere surrounding a charged rod-like polyelectrolyte immersed in an ionic solution of a symmetrical electrolyte is determined following the method developed by J. A. Fornés [Phys. Rev. E57, 2110 (1998)]. Several formulas are given to estimate the DH atmosphere parameters, namely, the polarizability at zero frequency, α(0), the relaxation time, τ, the cloud capacitance, C, the average displacement of the ionic cloud, δ, the square root dipole moment quadratic fluctuation, 〈p2〉1/2, and the thermal fluctuating field, 〈E2〉1/2. The Poisson–Boltzmann equation is solved numerically to apply the theory to a highly charged polyelectrolyte such as DNA in solution, although formulas valid for the DH approximation are also given. A dispersion in the polarizability and correspondingly in the dielectric constant of these solutions in the microwave region is predicted. For instance, considering a DNA length of 1000 Å, with its reduced linear charge density ξ0=4.25 and ionization factor γ=0.5, immersed in a NaCl solution (40 mM), we predict a polarizability of the DH atmosphere at zero frequency α(0) of 1×10−33 Fm2 (≃6.1×106) times greater than the mean value of the polarizability of water) and the corresponding fluctuating dipole moment p of 2.1×10−27 Cm (≃600 times greater than the permanent dipole moment of water molecule). The relaxation time and the average displacement of the ionic cloud are τ=1.6 ns and δ=14. Å, respectively. This displacement is produced by the thermal fluctuating field, which, in this case, at room temperature is 〈E2〉1/2=2 ×106 V/m.

Structural, electronic, and bonding properties of liquid water from first principles

We study, from first principles, structural, electronic, and bonding properties of liquid water. Our system is twice as large as that used in previous ab initio simulations and our computed structural properties are in good agreement with the most recent neutron scattering experiments. Moreover, the use of a novel technique, based on the generation of maximally localized Wannier functions, allowed us to describe the molecular charge distribution and the polarization effects in liquid water with a degree of accuracy not previously possible. We find that, in the liquid phase, the water molecule dipole moment has a broad distribution around an average value of about 3.0 D. This value is 60% higher than that of the gas phase and significantly larger than most previous estimates. A considerable increase is also observed in the magnitude of the average eigenvalues of the quadrupole moment tensor. We also find that the anisotropy of the electronic charge distribution of the water molecule is reduced in the liquid. The relevance of these results for current modeling of liquid water is discussed.

Water Molecule Dipole in the Gas and in the Liquid Phase

We study with ab initio molecular dynamics the change that the electric dipole moment of water molecules undergoes in passing from the gas to the liquid phase. Our analysis is based on the recently introduced maximally localized Wannier functions and is devoid of the ambiguities that have affected previous attempts. We find that in the liquid the dipole moment has an average value of about 3 D, 60% higher than in the gas phase. This value is much larger than is currently assumed (2.6 D). Furthermore, a broad distribution around this average value is observed. The relevance of these results for current modeling of water is discussed.

An Alamethicin Channel in a Lipid Bilayer: Molecular Dynamics Simulations

We present the results of 2-ns molecular dynamics (MD) simulations of a hexameric bundle of Alm helices in a 1-palmitoyl-2-oleoylphosphatidylcholine bilayer. These simulations explore the dynamic properties of a model of a helix bundle channel in a complete phospholipid bilayer in an aqueous environment. We explore the stability and conformational dynamics of the bundle in a phospholipid bilayer. We also investigate the effect on bundle stability of the ionization state of the ring of Glu 18 side chains. If all of the Glu 18 side chains are ionised, the bundle is unstable; if none of the Glu 18 side chains are ionized, the bundle is stable. pK A calculations suggest that either zero or one ionized Glu 18 is present at neutral pH, correlating with the stable form of the helix bundle. The structural and dynamic properties of water in this model channel were examined. As in earlier in vacuo simulations (Breed et al., 1996. Biophys. J. 70:1643–1661), the dipole moments of water molecules within the pore were aligned antiparallel to the helix dipoles. This contributes to the stability of the helix bundle.

Alamethicin channels in a membrane: molecular dynamics simulations.

Alamethicin (Alm) is a 20 residue peptide which forms a kinked alpha-helix in membrane and membrane-mimetic environments. Ion channels formed by intramembraneous aggregates of Alm are thought to be formed by bundles of approximately parallel Alm helices surrounding a central bilayer pore. Different channel conductance levels correspond to different numbers of helices per bundle, ranging from N = 5 to N > 8. Calculation of the predicted pKA values of the ring of Glu18 sidechains at the C-terminal mouth of the pore suggests that at neutral pH most or all of these sidechains will remain protonated. Nanosecond molecular dynamics (MD) simulations of N = 5, 6, 7 and 8 bundles of Alm helices in a POPC bilayer have been run, corresponding to a total simulation time of 4 ns. These simulations explore the stability and conformational dynamics of these helix bundle channels when embedded in a full phospholipid bilayer in an aqueous environment. The structural and dynamic properties of water in these model channels are examined. As in earlier in vacuo simulations (J. Breed, R. Sankararamakrishnan, I. D. Kerr and M. S. P. Sansom, Biophys. J., 1996, 70, 1643) the dipole moments of water molecules within the pores are aligned antiparallel to the helix dipoles. This helps to contribute to the stability of the helix bundles.

Origin of Differences in Heats of Immersion of Silicas in Water

The origin of differences in immersional heats of various silicas in water has been investigated by measurements of water vapor adsorption isotherms, strength of electrostatic fields of surfaces, and concentration and infrared spectra of hydroxyl groups. The contribution of interaction energy between dipole moments of water molecules and the electrostatic fields of silica surfaces to immersional heat was 30–40% of the total heat of immersion. The differences in immersional heats of silicas in water significantly depend on the interaction of hydrogen bonds between water molecules and surface hydroxyl groups rather than on the interaction between dipole moments of water molecules and surface polarity. The hydrogen-bonded hydroxyl groups strongly interact with water molecules rather than the free hydroxyl groups and cause an increase in heat of immersion.

Molecular dynamics study of water clusters, liquid, and liquid–vapor interface of water with many-body potentials

The molecular dynamics computer simulation technique is used to develop a rigid, four-site polarizable model for water. The suggested model reasonably describes the important properties of water clusters, the thermodynamic and structural properties of the liquid and the liquid/vapor interface of water. The minimum energy configurations and the binding energies for these clusters are in reasonable agreement with accurate electronic structure calculations. The model predicts that the water trimer, tetramer, and pentamer have cyclic planar minimum energy structures. A prismlike structure is predicted to be lowest in energy for the water hexamer, and a cagelike structure is the second lowest in energy, with an energy of about 0.2 kcal/mol higher than the prismlike structure. The results are consistent with recent quantum Monte Carlo simulations as well as electronic structure calculations. The computed thermodynamic properties for the model, at room temperature, including the liquid density, the enthalpy of vaporization, as well as the diffusion coefficient, are in excellent agreement with experimental values. Structural properties of liquid water, such as the radial distribution functions, neutron, and x-ray scattering intensities, were calculated and critically evaluated against the experimental measurements. In all cases, we found the agreement between the observed data and the computed properties to be quite reasonable. The computed density profile of the water’s liquid/vapor interface shows that the interface is not sharp at a microscopic level and has a thickness of 3.2 Å at 298 K. These results are consistent with those reported in earlier work on the same systems. The calculated surface tension at room temperature is in reasonable agreement with the corresponding experimental data. As expected, the computed average dipole moments of water molecules near the interface are close to their gas phase values, while water molecules far from the interface have dipole moments corresponding to their bulk values.

Semi-empirical modelling of the properties of the electrode/electrolyte interface in the presence of specific anion adsorption

Calculation of the anion-solvent equilibrium on the electrode surface from our earlier model of the electrode/electrolyte interface requires the Gibbs energy and the mean dipole moment of the adsorbed solvent molecules. These data can be taken from other theories or from experimental results. The second manner is presented. A dipole component of the potential drop across the inner layer, the Gibbs energy and the mean dipole moment of water molecules adsorbed on the Hg electrode are determined from the capacity data of Hg in aqueous 0.1 N NaF solution at 289.15 K. These data were used to calculate the surface concentration of anions and the differential capacity of the interface. Influence of bulk electrolyte concentration, energy of specific anion interactions and anion diameter on the anion adsorption and differential capacity are also discussed.

Physical interpretation of the influence of humidity on an SO 2 sensor

SO 2 concentrations can be measured by organically modified ceramics that change their dielectric permitivities when they adsorb SO 2. The sensor considered here consists of a planar interdigital capacitor with this sensitive layer, whose capacity changes are proportional to the gas concentration in the ambient air. As a result of the sensor principle and the dipole moment of water molecules, the layer is also sensitive to humidity to a certain extent. All characteristic lines of the sensor, exposed to humidities ranging from 0 to 2 vol.% at temperature between 20 and 50 °C, are BET shaped. The characteristic lines can be fitted by BET isotherms with restricted accuracy. However, three further models, one of them comprising the Langmuir isotherm, lead to a very good modelling. To include the effect of temperature in the model, a physical model based on a dynamic equilibrium of two-step adsorption and desorption is established. The temperature dependence of the characteristic lines is fully described by this physical model and it provides a value of the activation energy.

Studies on the electrical double layer structure at the water/air interface

Effective dipole moments (calculated from experimental data of surface tension and electric surface potential) of some homologous normal alcohols and carboxylic acid were found to vary linearly with the number of carbon atoms in the hydrocarbon chain. Values of effective dipole moments were used for the determination of the effective dipole moments of water molecules\((\bar \mu _{{\text{H}}_{\text{2}} {\text{O}}} )\), and the dielectric permittivity of the water subphase (e1), as well as in the vicinity of the hydrophobic part of adsorbed molecule (e2). The latter was found to decrease with the increase of the hydrocarbon chain length. Knowing the effective dipole moment of surface water dipoles, the average orientation angle (α) of water molecules at the inteface was estimated. The calculated potential drop of water varies within the range −0.038 to −2.38 V for two extreme orientations of water dipoles at the surface.

A polarizable water model for calculation of hydration energies

A molecular model for electronic polarization of water is defined, consisting of interacting point dipole polarizabilities in an electric field generated by atomic point charges, which represent the gasphase dipole moment of water molecules. The induced dipole equations are solved self consistently. The model has been implemented in a Monte Carlo hydration simulation program, and its computational performance is discussed. Results of calculations of hydration and protonation energies of amines (including glycine) are presented and discussed, together with results for the water dimer and for liquid water. Solvent induction appears significant to describe quantitatively solvent screening of interactions between charges on the solute. In combination with solvent polarization a quantum chemical charge model is found superior to an empirical set of charges. Inadequacies of the Lennard-Jones type modelling of non-electrostatic interactions between water molecules are demonstrated.

The electrostatic field and the molecular dipole moment in the polymorphs of ice

The magnitude and the direction of the electrostatic field at the site of a water molecule in hexagonal and cubic ice and in ice III, IV, V, and VI have been calculated. The calculations take into account neighbors up to the third shell and the probability of each orientation of these neighbors in a dendritic manner. The electrostatic field has the direction of the dipole moment of the central molecule in all the polymorphs, but its magnitude decreases with increase in the density of the polymorphs. The field at a molecular site is lower the lower the symmetry of the molecular site. The increase in the dipole moment of water molecule resulting from this field has been calculated for all molecules in the unit cell, assuming that the increase is directly proportional to the field strength. The weighted average dipole moment in the ices is 30%–45% higher than the dipole moment of a water molecule in the vapor phase. The largest increase is for cubic ice and the smallest for ice VI. All calculated values of the dipole moments substantially differ from values anticipated from the model of point dipole at the center of an isotropically polarizable spherical cavity. The contribution to relative permittivity due to orientation polarization has been calculated using these values of the dipole moment and the known dipolar correlation factor. The relative permittivity agree reasonably well with the measured values for all polymorphs of ice.

Microscopically inhomogeneous nature of the stern layer

The microscopic environment between the surface of a metal electrode and the diffuse region in an electrolyte is examined. This layer, approximately one monolayer thick, consists of water molecules and adsorbed ions. The dipole moments of water molecules are not ordered under laboratory bias potential at room temperature, and this gives rise to a sizeable inhomogeneous electric field at the metal surface. Two manifestations of this effect have been reported: the large than expected level widths of surface states on single crystal surfaces of Ag as seen in electroreflectance measurements, and the lack of k II conservation in photoemission from single crystal metal surfaces into electrolytes. Across the layer the electric field is also nonuniform as a result of the molecular nature of ions and water dipoles. This has been seen in electroreflectance measurements on Ag surfaces as an anomalously strong dependence of the surface state contribution on the bias potential. Thus, optical measurements coupled with microscopic modeling have opened ways to probe the molecular nature of the Stern layer.

Microscopically inhomogeneous nature of the stern layer

The microscopic environment between the surface of a metal electrode and the diffuse region in an electrolyte is examined. This layer, approximately one monolayer thick, consists of water molecules and adsorbed ions. The dipole moments of water molecules are not ordered under laboratory bias potential at room temperature, and this gives rise to a sizeable inhomogeneous electric field at the metal surface. Two manifestations of this effect have been reported: the large than expected level widths of surface states on single crystal surfaces of Ag as seen in electroreflectance measurements, and the lack of k II conservation in photoemission from single crystal metal surfaces into electrolytes. Across the layer the electric field is also nonuniform as a result of the molecular nature of ions and water dipoles. This has been seen in electroreflectance measurements on Ag surfaces as an anomalously strong dependence of the surface state contribution on the bias potential. Thus, optical measurements coupled with microscopic modeling have opened ways to probe the molecular nature of the Stern layer.

Cooperative effects in water-biomolecule crystal systems.

Monte Carlo computer simulation techniques have been used to model non-pair-additive (cooperative) effects in the water organization around several biomolecules. Although most models for water assume pair-additive potentials, both quantum mechanical calculations and experimental data indicate that cooperative effects are not negligible in hydrogen-bounded systems such as water. The many-body polarizable electropole (PE) model for water is used to examine the extent and the consequences of this cooperative behavior in several biomolecule hydrate crystals. Increases in the dipole moments of water molecules are predicted in all systems studied so far and can be as much as 50% more than the monomer value of 1.855 debyes. The average value of the individual dipole moments for any one system differs from that of another system and, therefore, should be considered a property of the system and not of the water molecule itself. When this previously calculated average value of the dipole moment for water molecules in a given system is used as a fixed parameter in the simulation, we find differences between this fixed calculation and the original unfixed simulation. An alternative procedure, which allows for a spread in dipole moments and is not dependent on a predetermined average value, has been developed to make simulations of large water-protein systems, including cooperative effects, computationally feasible.