Interaction Energy Of Water Molecules Research Articles

Adsorption mechanism of water molecule on goethite (010) surface

Goethite widely exists among ocean sediments; it plays an important role in fixing heavy metals and adsorbing organic contaminants. So the understanding of the adsorbing process of water molecule on its surface will be very helpful to further reveal such environmental friendly processes. The configuration, electronic properties and interaction energy of water molecules adsorbed on pnma goethite (010) surface were investigated in detail by using density functional theory on 6-31G (d,p) basis set and projector- augment wave (PAW) method. The mechanism of the interaction between goethite surface and H2O was proposed. Despite the differences in total energy, there are four possible types of water molecule adsorption configurations on goethite (010) surface (Aa, Ab, Ba, Bb), forming coordination bond with surface Fe atom. Results of theoretical modeling indicate that the dissociation process of adsorbed water is an endothermic reaction with high activation energy. The dissociation of adsorbed water molecule is a proton transportation process between water’s O atoms and surface. PDOS results indicate that the bonding between H2O and (010) surface is due to the overlapping of water’s 2p orbitals and Fe’s 3d orbitals. These results clarify the mechanism on how adsorbed water is dissociated on the surface of goethite and potentially provide useful information of the surface chemistry of goethite.

Moisture adsorption isotherms of the borojó fruit (Borojoa patinoi. Cuatrecasas) and gum arabic powders

Sorption mechanisms of borojó pulp (BPP), three borojó phases (liquid phase (LP), medium phase (MP) and solid phase (SP)), gum arabic (GA), and a mixture of these (BP) produced by freeze-drying were interpreted through adsorption isotherms. The adsorption models adequately describe the experimental data over the entire measured range of aw; R2 was close to 1 for the studied conditions. For the thermodynamic properties, the differential and integral enthalpy of BP showed a synergic effect of the combined components. This shows that using a combination of polymers increases the interaction energy of water molecules with the surface of the material. The monolayers from the BET and GAB models showed similar moisture content values that corresponded to the minimum integral entropy. Finally, the behavior of the enthalpy–entropy compensation of water adsorption for the SP, MP and GA powders at low moisture contents demonstrated that the content is controlled by an entropic mechanism, for BP, BPP and LP powders, the water adsorption may be considered as mainly enthalpy-driven.

Water Absorbed by Polyaniline Emeraldine Tends to Organize, Forming Nanodrops

Interactions, in terms of both binding energies and microscopic organization, of water molecules absorbed by hydrophilic polyaniline emeraldine base have been investigated using quantum mechanical calculations, molecular dynamics simulation, FTIR spectroscopy, and (1)H NMR. From an enthalpic point of view, water molecules interact more favorably with imine nitrogen atoms than with amine ones, even though the latter are entropically favored with respect to the former because of their two binding sites. Quantum mechanical results show that interaction energies of water molecules reversibly absorbed but organized individually around a binding site range from 3.0 to 6.3 kcal/mol, which is in good agreement with activation energies of 3-5 kcal/mol previously determined by thermodynamic measurements. The irreversible absorption of water to produce C-OH groups in rings of diimine units has been examined considering a three steps process in which water molecules act as both acidic and nucleophilic reagent. Although calculations predict that the whole process is disfavored by 5-8 kcal/mol only, FTIR and (1)H NMR detected the existence of reversibly absorbed water but not of C-OH groups. Both the binding energies and the structural information provided by molecular dynamics simulations have been used to interpret the existence of two types of physisorbed water molecules: (i) those that interact individually with polymer chains and (ii) those immersed in nanodrops that are contained within the polymeric matrix. The binding energies calculated for these two types of water molecules are fully consistent with the thermodynamic activation energies previously reported.

Nature of Hydrogen Bond in Water

The work is devoted to the investigation of the physical nature of H-bonds. The H-bond potential ΦH (r, Ω ) is studied as an irreducible part of the interaction energy of water molecules. It is defined as a difference between the generalized Stillinger–David potential and the sum of dispersive and multipole interactionpotentials. The relative contribution of ΦH (r, Ω ) to the intermolecular potential does not exceed (10–15)%.

Molecular dynamics study of hydration of the protein interior

Molecular dynamics (MD) simulations were performed to study the patterns of hydration of cavities in the interior of staphylococcal nuclease (SN) and of the variants V66E and V66K. In these variants the polar groups of Glu and Lys are internal, and they affect the polarity and size of a small internal cavity. Internal water molecules were identified in the simulations based on their coordination state. They were characterized in terms of their residence times, average locations, dipole moment fluctuations, hydrogen bonding interactions, and interaction energies. The best agreement in the locations of MD and crystallographically determined water molecules was found for molecules that have residence times of several ns, and which display small mean square displacements in the MD simulations. In the simulations the hydrophobic cavity near Val-66 in the wild type contains a relatively disordered water molecule that has never been seen crystallographically. Consideration of the protein dynamics was found to be important when studying hydration in the protein interior: inside the protein the interaction energies of water molecules fluctuate less than in bulk water, giving rise to a favorable contribution to the chemical potential. The analysis of the MD trajectories revealed that the fluctuations in the protein structure (especially the loop elements) can strongly influence protein hydration by changing the patterns or strengths of hydrogen bonding interactions between water molecules and the protein, or by providing potential energy barriers for water penetration.

Electrostatic potential and interaction energies of molecular entities occluded in the AlPO 4-15 molecular sieve: determination from X-ray charge density analysis

Electrostatic interaction energies of water molecules, hydroxyl and ammonium ions occluded in AlPO 4-15 molecular sieve are estimated from the modeling of the experimental X-ray charge density by numerical integration using a partitioning of the density based on multipolar pseudo-atoms.

The electrostatic interaction energy of water molecules in polymorphs of ice

The Coulombic interaction energy of water molecules in hexagonal and cubic ice and in ice III, IV, V and VI has been calculated. The calculations take into account nearest neighbours up to the third shell and the probability of each orientation of these neighbours in a dendritic manner. The energy is found to increase when mutual polarization of molecules is taken into account. It is highest for molecules in cubic ice and lowest in ice VI. For a polymorph of ice the energy depends significantly upon interactions of a molecule with its second and third neighbours, with the result that breaking of some H-bonds in the ices leads to the weakening of others. The interactions with the second and third neighbours increases the energy of an isolated pair by 20 % to 35 %. Implications of these results for the use of pair-additive potentials in computer simulations of water and ice and for our understanding of the mechanical deformation of ice are pointed out.

Computer Simulations of Complex Chemical Systems: Solvation of DNA and Solvent Effects in Conformational Transitions

As is known, atomic and small molecular systems can be realistically simulated with quantum-mechanical models. In complex chemical systems, however, the natural parameters for a description are not only the electronic density and energy but also entropy, temperature, and time. We have considered as an example for a complex chemical system the structure of water surrounding DNA with counterions. No direct experimental determination of the solvent structure around a single DNA macromolecule is available from experimental data, despite continuous efforts during the last twenty years to obtain both single crystals of DNA and scattering data from solutions. A very detailed representation is now available concerning the structure and interaction energy of water molecules in the first solvation shell or in the “grooves” of the DNA. The data obtained by our computer simulation are in good agreement with indirect data from DNA fibers at different relative humidities and with other indirect evidence. In addition, our simulated results allow us to present a preliminary model for the solvent effects in transition processes between different DNA conformations. The model presented is also in agreement with available experimental data. Finally, our results report the first determination of the position of counterions in DNA at different relative humidities and at room temperature. This application demonstrates the flexibility of the computational approach. The method we have used is very general; namely, it is not limited to a biological system but is valid for any organic or inorganic problem requiring systematic simulation on a class of compounds interacting either as a few molecules or as a large ensemble of molecules.

The dipolar correlation factor, the electrostatic field, the dipole moment, and the Coulombic interaction energy of water molecules in clathrate hydrates

The dipolar correlation factor g, the electrostatic field E, the dipole moment μ, and the Coulombic interaction energy U of water molecules in clathrate hydrates of structure I and structure II have been calculated from the molecular data for their crystal structures in space groups Pm3n and Fd3m, respectively. For dendritic probabilities of orientation of water molecules in fully proton-disordered structures, the values of g are 2.876 and 2.899, of E are 0.2861 and 0.262 Mesu cm−2, of μ are 2.4133 and 2.4135 D, and of U are −7.99 and −7.93 kJ/mole H bond. The dipole moment of H2O is increased by nearly 30% over its vapor phase value. The dielectric permittivity of the two clathrate hydrates calculated from the above values of g and μ are significantly higher than those measured. The values of g, μ, E, and U are somewhat lower than in ice Ih and Ic. The results are discussed in terms of the lack of complete disorder of proton positions in the two structures of clathrate hydrates.