Activation energy of hydrogen migration by relay in the O2/Pt19/SnO2/H2 + n H2O system

In the framework of investigation of active and stable electrocatalysts for fuel cells, the hydrogen migration by relay with the consecutive formation of H₂O molecules in the O₂/Pt₁₉/SnO₂/H₂·nH₂O → O/Pt₁₉/SnO₂·nH₂O + H₂O system was simulated. The simulations were performed by the density functional theory (DFT) method with the generalized gradient adjustment (GGA=PBE) under periodic boundary conditions in the projector augmented plane wave (PAW) basis set with a pseudo-potential using the VASP program package. At the cathode on the platinum cluster surface, the oxygen molecules without a barrier form peroxide complexes that dissociate with an energy decrease. The protons transferred via the proton-conducting channels from the anode to cathode form first OH groups bound to the platinum cluster and then H₂O molecules that are easily separated from the cluster (～0.2 eV). The proton transfer process proceeds by relay and involves several water molecules.     

Density Functional Theory Study on Hydrogen Bonding Interaction of Catechin-(H2O)n

Density functional theory B3LYP method with 6‐31G* basis set has been used to optimize the geometries of the catechin, water and catechin‐(H₂O)_n complexes. The vibrational frequencies have been studied at the same level to analyze these complexes. Six and eleven stable structures for the catechin‐H₂O and catechin‐(H₂O)₂ have been found, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) have been utilized to investigate the hydrogen bonds involved in all the systems. The interaction energies of all the complexes corrected by basis set superposition error, are from ?13.27 to ?83.56 kJ/mol. All calculations also indicate that there are strong hydrogen‐bonding interactions in catechin‐water complexes. The strong hydrogen‐bonding contributes to the interaction energies dominantly. The O–H stretching motions in all the complexes are red‐shifted relative to that of the monomer.     

CO2 capture through halogen bonding: A theoretical perspective

Halogen bonding interactions between several halogenated ion pairs and CO2 molecules have been investigated by means of density functional theory calculations. To account for the influence of solvent environment, the implicit polarized continuum model was also employed. The bromide and iodide cations of ionic liquids (ILs) under study can interact with CO2 molecules via X O interactions, which become much stronger in strength than those in the complexes of iodo-perfluorobenzenes, very effective halogen bond donors, with CO2 molecules. Such interactions, albeit somewhat weaker in strength, are also observed between halogenated ion pairs and CO2 molecules. Thus, the solubility of CO2 may be improved when using halogenated ILs, as a result of the formation of X O halogen bonds. Under solvent effects, the strength of the interactions tends to be weakened to some degree, with a concomitant elongation of intermolecular distances. The results presented here would be very useful in the design and synthesis of novel and potent ILs for CO2 physical absorption.     

DFT,AIM, and NBO study of the interaction of simple and sulfur-doped graphenes with molecular halogens,CH3OH,CH3SH,H2O,and H2S

Graphene is an important material in adsorption processes because of its high surface. In this work, the interactions between graphene (G), S-doped graphene (SG), and 2S-doped graphene (2SG) with eight small molecules including molecular halogens, CH₃OH, CH₃SH, H₂O, and H₂S were studied using density functional theory calculations. The adsorption energies showed that the SG was the best adsorbent, fluorine was the best adsorbate, and all molecular halogens were adsorbed on graphenes better than the other molecules. Most adsorption processes in the gas phase were exothermic with small positive ΔG _ads. Moreover, the solvent effect on the adsorption process was examined and all ΔH _ads and ΔG _ads values for adsorption processes tended to be more negative in all solvents. Therefore, most adsorption processes in the solvents were thermodynamically favorable. The second order perturbation energies obtained from NBO calculations confirmed that the interactions between molecular halogens and our molecules had more strength than those of other molecules. The Laplacian of ρ values obtained from the AIM calculations indicated that the type of interaction in all our complexes was one of closed shell interaction. The MO results and DOS plots also revealed that sulfur doping could increase the conductivity of graphene and this conductivity was enhanced more when they interacted with molecular halogens.     

Ab initio study of NH3 and H2O adsorption on pristine and Na-doped MgO nanotubes

We have investigated, on the basis of density functional theory calculations, the structural and electronic properties of chemical modification of pristine and Na-doped MgONTs with NH₃ and H₂O molecules. We found that the NH₃ and H₂O molecules can be barrierlessly adsorbed on the Mg atom of the tube sidewall along with a charge transfer from the adsorbate to MgONT. The adsorption is chemical in nature with adsorption energies about ?22.3 and ?21.5 kcal/mol for H₂O and NH₃, respectively. The calculated density of state (DOS) shows that the chemical modification of MgONTs with these molecules can be generally classified as certain type of “harmless modification.” In other words, the electronic properties of the MgONT are little changed by the adsorption processes. The substitution of an Mg atom in the tube surface with an Na atom results in a semi-insulator to p-type semiconductor transition based on DOS analysis. It was also found that the doping process reduces the adsorption energies and the electronic properties of Na-doped MgONT is slightly more sensitive toward NH₃ and H₂O molecules, compared with the pristine one.     

Adsorption behavior of Co and C2H2 on the graphite basal surface: A quantum chemistry study

The adsorption of CO and C₂H₂ molecules on the perfect basal surface of graphite is investigated by adopting cluster models in conjunction with quantum chemical calculations. The noncovalent interaction potential energy curves for three different orientations of CO and C₂H₂ molecules with respect to the inert basal plane of graphite are calculated via semi-empirical and Möller-Plesset ab initio methods. Then, we have considered the effects of interaction energies on the C≡O and C≡C bond lengths by performing the partial geometry optimization procedure on the CO-graphite and C₂H₂-graphite systems in various intermolecular distances. The computational analysis of all physical noncovalent potential energy curves reveals that the relative configurations in which CO and C₂H₂ molecules approach the graphite sheet from out of the plane have stronger interaction energy and so is more favorable from the energetic viewpoint. This means that the graphite layer prefers to increase its thickness via the chemical vapor deposition of CO and C₂H₂ on the graphite.     

Theoretical studies of O2−:(H2O)n clusters

The interaction of superoxide ion O₂^? with up to four water molecules [O₂^?: (H₂O)_n, n = 1, 2, 4] has been investigated using ab initio molecular orbital theory. The binding energy of O₂^?: H₂O is calculated to be ?20.6 kcal/mol in good agreement with gas phase experimental data. At the MP3/6-31G^* level the O₂^?:H₂O complex has a C_2v structure with a double (cyclic) hydrogen bond between O₂^? and H₂O. A C_s structure with a single hydrogen bond is only 0.7 kcal/mol less stable. Interaction of H₂O with the doubly occupied π^* orbital of O₂^? is preferred slightly over interaction with the singly occupied π^* orbital. Natural bond orbital analysis suggests that both electrostatic and charge transfer interactions are important in anionic complexes. The charge transfer occurs predominantly in the O₂^? → H₂O direction and is important in determining the relative stabilities of the different structures and states. Singly and doubly hydrogen-bonded structures for the O₂^?: (H₂O)₂ and O₂^?: (H₂O)₄ clusters were found to be similar in stability and the increase in binding of the cluster becomes smaller as each additional water molecule is added to the cluster.     

Raman and DFT study of static,dynamic interactions and isotope effect in pyridazine + H2O/D2O systems

Polarized Raman and density functional theory (DFT) approach have been applied to study the static and dynamic properties of pyridazine (PRD) in H₂O(W) and D₂O(D) environment. The possible hydrogen bonded (HB) complexes of PRD with H₂O in gas phase and in the water solvation (using IEF-PCM and Onsager models) have been calculated using a B3LYP functional and 6-31+G(d,p)/6-311++G(d,p) basis sets. The static interaction in the PRD + H₂O complex leads to a blue shift in all the Raman modes of PRD and red shift in the O–H modes of water. The IEF-PCM solvation model gives the Raman wavenumbers closest to the experimental values. Raman spectra of ～962 and 1061 cm^?1 mode of PRD in the mixture of PRD + H₂O and PRD + D₂O at different mole fractions of PRD (x) have been measured. A difference in the wavenumber shift of the two modes of PRD is observed experimentally when PRD is diluted with H₂O and D₂O. The wavenumber shift at maximum dilution (x = 0.1), however, takes the same value in both H₂O and D₂O. In view of the similar chemical properties of H₂O and D₂O, the difference in the trend of the wavenumber shift is not trivial. It has been explained on the basis of relative values of dipole moments of H₂O, D₂O, and conjugated molecules of PRD with H₂O/D₂O calculated theoretically and the role of larger diffusive property of H₂O compared to D₂O. The dynamical process in the mixture of PRD+ H₂O/D₂O is discussed by studying the variation of the linewidth with concentration. A theoretical model, which is based on the fact that the concentration in microscopic volume fluctuates, fits the experimental results nicely.     

Complex formation reactions between [Pd(piperazine)(H2O)2]2+ and biorelevant ligands: synthesis and equilibrium constants

[Pd(pip)Cl₂], [Pd(pip)(cbdca)] ? 2H₂O, and [Pd(pip)(malonate)] ? 2H₂O complexes were synthesized and characterized, where pip is piperazine and cbdca is cyclobutanedicarboxylate. The stoichiometry and stability of the complexes formed between [Pd(pip)(H₂O)₂]²⁺ and various biologically relevant ligands (amino acids, peptides, DNA constituents, and dicarboxylic acids) were investigated at 25°C and 0.1 M ionic strength. The stability constant of the complexes formed in solution was determined and the binding centers of the ligands were assigned. The concentration distribution diagrams of the complexes were evaluated.     

Densimetric Studies of Binary Solutions Involving H2O or D2O as a Solute in Dimethylsulfoxide at Temperatures from (293.15 to 328.15) K and Atmospheric Pressure

Densities of H₂O and D₂O solutions in dimethylsulfoxide, with solute mole fractions ranging up to 0.037, were measured with an uncertainty of 1.5×10^?5?g?cm^?3 at eight temperatures between 293.15 and 328.15?K (with a step of 5?K) under atmospheric pressure using a sealed vibrating-tube densimeter. Apparent molar volumes and isobaric expansibilities (down to infinite dilution) of water isotopologues, as well as excess molar volumes of both solutes and solutions as a whole, were calculated. The temperature-dependent behavior of H₂O??D₂O solute isotope effects on the studied molar volumetric characteristics was interpreted by taking into account the structural and related interaction peculiarities of the dissolving medium in question.     

BrO-H2O 及 HOBr-H2O复合物偶合方式的理论研究

在6-311++G(d,p)水平上采用四种方法讨论了两种BrO-H₂O和三种HOBr-H₂O复合物的构型性质。在两种BrO-H₂O复合物中，结合能为11.37–13.92 J/mol的复合物2 （电子态为²A′）最稳定，该复合物是通过BrO中的Br原子和水中的O原子结合的。三种HOBr-H₂O复合物中，复合物3和4的结合能约为16.30–21.32 J/mol，三种复合物的稳定顺序为：复合物3 ≈ 复合物4 > 复合物5。     

Surface interaction of H2O and H2S onto Ca12O12 nanocluster: Quantum‐chemical analyses

To find the selectivity of H₂S, we explicate the adsorption properties of water (H₂O) and hydrogen sulfide (H₂S) molecules on the external surfaces of free Ca₁₂O₁₂ nanocages using the density functional theory method. More specifically, binding energies, natural bond orbital charge transfer, dipole moment, molecular electrostatic potential, frontier molecular orbitals, density of states, and global indices of activities are calculated to deeply understand the impacts of the aforementioned molecules on the electronic and chemical properties of Ca₁₂O₁₂ nanocages. Our theoretical findings indicate that although H₂O seems to be adsorbed in molecular form, the H₂S molecule is fully dissociated during the adsorption process because of the weak bond between sulfur and hydrogen atoms of the molecule. Interestingly, the highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap of the nanocage is decreased by 1.87 eV upon H₂S adsorption, indicating that the electrical conductivity of the nanocage is strongly increased by the dissociation process. In addition, the values of softness and electrophilicity for the H₂S‐Ca₁₂O₁₂ complex are higher than those for the free nanocage. Our results suggest that Ca₁₂O₁₂ nanoclusters show promise in the adsorption/dissociation of H₂S molecules, which can be used further for designing its selective sensor.     

H2O and H2 interaction with ZnO surfaces: A MNDO,AM1, and PM3 theoretical study with large cluster models

We investigated the adsorption and heterolytic dissociation of H₂O and H₂ molecules on a (ZnO)₂₂ cluster corresponding to ZnO (0001), (000(OVERBAR)1), and (10(OVERBAR)10) surfaces using MNDO , AM 1 and PM 3 semiempirical procedures. The geometry of the adsorbed molecule has been optimized in order to analyze binding energies, charge transfer, and preferential sites of interaction. The adsorbed species interact most strongly when it is bonded to the twofold coordinated zinc atom of the cluster surface. The interaction of the H₂O molecule with the surface of ZnO has a charge transfer from H₂O to the surface ranging between 0.17 and 0.27 au. The neighboring atoms of the surface are the main receptors during the process of charge transfer. Our results indicate that there is a weak bonding of the hydrogen atom from OH with the oxygen surface atom that could produce the O(SINGLE BOND)H·O band. The interaction of the H₂ molecule with the surface is generally weak and only the PM 3 method yields a strong binding energy for this interaction. There is a charge transfer from the H₂ molecule to the surface. The chemisorption of H on oxygen atom of the surface transfer charge from the surface to the H. We also calculated the vibrational analyses for these interactions on ZnO surface and compared our results with available experimental data. © 1996 John Wiley & Sons, Inc.     

A pseudopotential study of the hydrogen bond in H2O·H2S,H2S·H2S and H2O·H2Se systems

Intermolecular potential energy curves for the hydrogen bonded systems H₂O·H₂S, H₂O·H₂Se and H₂S·H₂S were calculated with nonempirical pseudopotentials using optimized-in-molecules basis sets augmented by polarization functions. The H₂O·H₂O interaction energy curve has been also considered as a test case. The present results for H₂O·H₂S and H₂S·H₂S indicate much weaker intermolecular interactions than those found in previous ab initio calculations. The H₂O·H₂Se interaction was found to be quite similar to H₂O·H₂S.This work was partly supported by the Polish Academy of Sciences within the Project PAN-09, 7.1.1.1On leave from Quantum Chemistry Laboratory, Dept. of Chemistry, University of Warsaw, Pasteura 1, 02-093. Warsaw, Poland     

A model study of the intermolecular interactions of amino acids in aqueous solution: The glycine-water system

We have performed calculations of the glycine zwitterion surrounded by water molecules with the help of the mutually consistent field (MCF) method and perturbation theoretical expressions. Two different models for the hydration shell have been chosen, the glycine·6H₂O and glycine·12H₂O complexes, representing the most probable first and second solvation shell, respectively. To calculate the exchange and charge transfer energy contributions we have applied approximative expressions derived from perturbation theory for weakly overlapping subunits. For the sake of comparison we also calculated the interaction energy in the supermolecule approach for the smaller of the two solvation complexes. Furthermore, we have investigated the part of the potential energy surface which is determined by varying the lengths of the hydrogen bonds between glycine and water in the complex glycine·12H₂O using the electrostatic approach. The exchange energy contribution to the interaction energy for different points on the surface was approximated with the help of an analytical expression fitted to three directly calculated points. For the charge transfer energy a polynomial expansion of second order was established on the basis of five values, computed with the aid of the perturbation theoretical expression. To get a more detailed insight in the relatively strong hydrogen bonds between the water molecules and the ionic hydrophilic parts of glycineab initio model studies on NH ₄ ⁺ ·3H₂O and HCOO⁻·3H₂O systems are reported.     

AlCl3.6H2O as a catalyst for simple and efficient synthesis of gem-dihydroperoxides from ketones and aldehydes using aqueous H2O2

AlCl₃.6H₂O was explored as an efficient catalyst for the synthesis of ingem-dihydroperoxides (DHPs) from ketones and aldehydes. The reactions took place within a short period of time using (30%) aqueous H₂O₂ as a ??green?? oxidant in acetonitrile under neutral conditions at room temperature to afford the products in high yields.     

Determination of long-range intermolecular interaction energies using RPA/moment function methods. Application to H2O,H2O2 and H2O/H2O2 mixtures

The fully expanded expression for the Boltzmann-averaged pairwise intermolecular interaction energy of two molecules of arbitrary symmetry in the long-range (interaction < kT) limit has recently been determined explicitly as a series in r⁻ⁿ (r is the intermolecular separation) for n < 11. The resultant expression contains only multipolar products (point moment functions: PMFs) and energy terms which are characteristic of the ground state and excitation properties of the isolated molecules. These quantities are determined for H₂O and H₂O₂ using the single particle-hole RPA method, and the interaction energy contributions determined by direct state summation. Static electric dipole polarizabilities are determined as a by-product of the procedure, and are shown to agree closely with finite field results using a comparable basis. For the chiral H₂O₂/H₂O₂ system, the r⁻⁶ and r⁻⁹ discrimination energies are also calculated, suggesting that the r⁻⁹ contributions could well exceed the r⁻⁶ discriminatory terms for separations less than 20 au.     

H2O, H2S与双卤分子间相互作用的电子密度拓扑研究

运用量子化学微扰理论MP2和密度泛函B3LYP方法, 采用6-311＋＋G(d,p)基组, 对H₂O, H₂S与双卤分子XY (XY＝F₂, Cl₂, Br₂, ClF, BrF, BrCl)形成的卤键复合物进行构型全优化, 并计算得到了这些体系的分子间相互作用能. 利用电子密度拓扑分析方法对卤键复合物的拓扑性质进行了分析研究, 探讨了该类分子间卤键的作用本质. 结果表明, 形成卤键后, 作为电子受体的双卤分子X—Y键长增长, 振动频率减小. 复合物体系中的卤键介于共价键与离子键之间, 偏于静电作用成分为主.     

Theoretical study of the desorption of neutral and ionic alkali metal atoms from the excited Li+(H2O)n = 1-4 and Na+(H2O)n = 1-4 cluster models: Electronic excitation charge transfer

In this work, the potential energy curves of several low-lying excited states of M⁺(H₂O)_{n = 1-4} (M = Li and Na) clusters with one M─O bond, related to the stretching of their M─O bond, were calculated in the gas phase. The time-dependent density functional theory and direct-symmetry-adapted cluster-configuration interaction were used in this study separately. Theoretical calculations showed that the charge transfer occurred between M⁺ and (H₂O)_n in the excited clusters so that the neutral metal atom was obtained at the dissociation limit of the potential curves. The excited potential curves of clusters were also calculated in the presence of the electrostatic field of water (EFW), and it was found that the charge transfer was blocked in the presence of EFW. The effect of the size of the (H₂O)_n cluster on the shape of the excited potential curves was investigated to observe how the M─O bond was affected in the excited states depending on the (H₂O)_n size. It was found that the increase in the size of the (H₂O)_n cluster increased the number of bonding excited potential curves. The difference between the electron density of the excited and ground electronic states was calculated to see how the charge transfer was affected by the size of the (H₂O)_n cluster.