Showing papers on "Water cluster published in 2003"

A Computer Simulation Study of the Mesoscopic Structure of the Polyelectrolyte Membrane Nafion

Abstract: We studied the mesoscopic structure of the perfluorinated sulfonic acid membrane Nafion containing water using a dissipative particle dynamics (DPD) simulation. A Nafion polymer is modeled by connecting coarse-grained particles, which correspond to the hydrophobic backbone of polytetrafluoroethylene and perfluorinated side chains terminated by hydrophilic end particles of sulfonic acid groups. Water is also modeled by the same size particle as adopted in the Nafion model, corresponding to a group of four H2O molecules. The Flory–Huggins χ-parameters between DPD particles are estimated from the mixing energy calculation using an atomistic simulation. In the DPD simulation, water particles and hydrophilic particles of Nafion side chains spontaneously form aggregates and are embedded in the hydrophobic phase of the Nafion backbone. This structure is a bicontinuous phase of Nafion and water regions and has a continuous path in the cavity of water in any direction. Although this sponge-like structure is essentially identical to the cluster-network model proposed from the experimental studies, the shape of the water clusters is not spherical but irregular, and the water regions are indistinguishable structures of water clusters and their channels. The cluster size and its dependence on the water content are in good agreement with experimental reports; therefore, the simulated mesoscopic structure is confirmed to be a highly possible one.

Investigations of Protonated and Deprotonated Water Clusters Using a Low-Temperature 22-Pole Ion Trap

Abstract: A new tandem mass spectrometer, containing a temperature-variable 22-pole ion trap, has been constructed. It is applied, as a first application, to kinetic and spectroscopic investigation of charged water clusters produced from a supersonic expansion. Using low-pressure He or H2 as buffer gas for collisional thermalization, refrigeration of the ion trap allows a good control of the cluster temperature over the range 77−350 K. It provides an accurate means of determining the dissociation energies of both protonated and deprotonated water cluster ions [H+(H2O)n and OH-(H2O)m] by measuring the dissociation rates at various temperatures along with their internal energies calculated from vibrational frequencies provided by density functional theory calculations. In this report, results of the thermochemical measurements for H+(H2O)4-10 and OH-(H2O)3-7 at well-defined cluster temperatures are presented. The feasibility of using this ion trap to acquire temperature-dependent infrared spectra of charged water clu...

A discrete solvent reaction field model within density functional theory

Abstract: In this work we present theory and implementation for a discrete reaction field model within Density Functional Theory (DFT) for studying solvent effects on molecules. The model combines a quantum mechanical (QM) description of the solute and a classical description of the solvent molecules (MM). The solvent molecules are modeled by point charges representing the permanent electronic charge distribution, and distributed polarizabilities for describing the solvent polarization arising from many-body interactions. The QM/MM interactions are introduced into the Kohn–Sham equations, thereby allowing for the solute to be polarized by the solvent and vice versa. Here we present some initial results for water in aqueous solution. It is found that the inclusion of solvent polarization is essential for an accurate description of dipole and quadrupole moments in the liquid phase. We find a very good agreement between the liquid phase dipole and quadrupole moments obtained using the Local Density Approximation and results obtained with a similar model at the Coupled Cluster Singles and Doubles level of theory using the same water cluster structure. The influence of basis set and exchange correlation functional on the liquid phase properties was investigated and indicates that for an accurate description of the liquid phase properties using DFT a good description of the gas phase dipole moment and molecular polarizability are also needed.

The Nature and Absolute Hydration Free Energy of the Solvated Electron in Water

Abstract: We report the first first-principles solvation-included electronic structure study to energetically compare a variety of candidate structures of the hydrated electron and to determine its absolute hydration free energy ΔGhyd298(e-). The calculated results show that both the thermal motion and bulk solvent effects can qualitatively change the relative thermodynamic stability of different structures of the hydrated electron on the basis of a cluster of a given size, and that the most stable structure in solution is not necessarily the most stable one in the gas phase. For a given number of explicitly included solvent water molecules, the most stable structure in solution reveals a unique feature of the chemical nature of the solvated electron in water, i.e., the electron forms two strong electron−hydrogen bonds of the e-···HO type with the hydrogen-bonded water cluster and two of the hydrogen bonds in the neutral water cluster are broken. On the basis of the most stable structures, the calculated electronic...

A cyclic (H2O)4 cluster characterized in the solid state disappears on heating and regenerates from water vapor: A supramolecular reversible gas–solid reaction

Abstract: An unusual trinuclear iron(III) cluster described herein, [Fe3(μ3-O)(μ2-CH3COO)6(C5H5NO)2(H2O)] ClO4·4H2O (1) (C5H5NO = 2-pyridone), features a cyclic hydrogen bonded supramolecular water tetramer at one of the iron centres, as characterized by X-ray crystallography and thermogravimetry. The water cluster is formed by one iron-coordinated water and three lattice/solvent water molecules. The molecular environment of the water tetramer in the crystal structure consists of a Fe3+ ion (which is covalently bonded to one water of the (H2O)4 cluster), a perchlorate anion and the fourth lattice water. The facile removal of the lattice water molecules was anticipated from the knowledge of the type of interaction of these water molecules with their surroundings. Indeed, this hydrogen bonded water tetramer disappears with the formation of dehydrated solid [Fe3(μ3-O)(μ2-CH3COO)6(C5H5NO)2(H2O)] ClO4 (2), when the compound 1 is heated at ∼135 °C. Interestingly, when the dehydrated solid 2 is exposed to water vapor, it regenerates to 1 in a gas–solid reaction. The exposure of 2 to D2O vapor yields partially deuterated complex [Fe3(μ3-O)(μ2-CH3COO)6(C5H5NO)2(H2O)] ClO4·4D2O (3). As expected, the material 3 changes to 2 on heating at ∼135 °C, which again, on exposure to water vapor, returns to 1. The reversible loss/formation of (H2O)4 cluster in a gas–solid reaction has been established by elemental analyses, IR and X-ray powder diffraction studies including the single crystal X-ray structural analysis of 1.

Zero temperature quantum properties of small protonated water clusters (H2O)nH+ (n=1–5)

Abstract: The study of the energetics and structure of small protonated water clusters (H2O)nH+ (n = 1–5) has been carried out employing the OSS3 potential energy surface developed by Ojamae, Singer, and Shavitt [J. Chem. Phys. 109, 5547 (1998)]. By comparing it with accurate ab initio MP2 calculations for (H2O)nH+, this all-atom potential is also shown to reproduce quantitatively the geometry and the relative energetics of small neutral and protonated water clusters containing up to five molecules. To correct the total and binding energy for vibrational motion, the zero point energy of the clusters has been calculated by means of the harmonic approximation and by simulating the exact ground state using the diffusion Monte Carlo method. From these 0 K results, it appears that the anharmonicity accounts for a decrease (increase) of 1.5–5.5 mhartree (1.0–3.5 kcal/mol) in the total (binding) energy of the protonated clusters. Moreover, we found all the cyclic isomers of (H2O)4H+ and (H2O)5H+ to be unstable during the diffusion Monte Carlo simulations, and to convert into treelike or linear isomers. Employing the same interaction potential, we also simulated the ground state of (H2O)n (n = 1–5) to compute the proton binding energy to a water cluster. This quantity is decreased by roughly 12 mhartree (7.5 kcal/mol) by including the zero point energy correction to the total energy. The relevance of these findings with respect to the experimental detection and probing of the protonated water clusters is discussed.

Solvent rearrangement for an excited electron of I−(H2O)6: Analog to structural rearrangement of e−(H2O)6

Abstract: The study of electron solvation dynamics is vital for understanding the phenomena related to the electron transfer process in solvents. On the basis of a recent femtosecond dynamics study of charge-transfer-to-solvent states in photoexcited iodide–water clusters [Lehr et al., Science 284, 635 (1999)], we have investigated the solvent rearrangement process for the excited electron in the iodide–water hexamer using ab initio calculations. Upon excitation of iodide–water hexamer, an electron transfers from the iodide anion to the water cluster. This results in release of the iodine atom and thereby formation of anionic water hexamer which undergoes rearrangement process toward the most stable conformation. The transformation pathway from the low-lying energy structures of the iodide–water hexamer to those of the electron–water hexamer is thus elucidated from the potential energy surface including the global and local minima and transition states of the electron–water hexamer.

Elucidating the Role of Many-Body Forces in Liquid Water. I. Simulations of Water Clusters on the VRT (ASP-W) Potential Surfaces

Abstract: We test the new VRT(ASP-W)II and VRT(ASP-W)III potentials by employing Diffusion Quantum Monte Carlo simulations to calculate the vibrational ground-state properties of water clusters. These potentials are fits of the highly detailed ASP-W ab initio potential to (D{sub 2}O){sub 2} microwave and far-IR data, and along with the SAPT5s potentials, are the most accurate water dimer potential surfaces in the literature. The results from VRT(ASP-W)II and III are compare to those from the original ASP-W potential, the SAPT5s family of potentials, and several bulk water potentials. Only VRT(ASP-W)II and the spectroscopically ''tuned'' SAPT5st (with N-body induction included) accurately reproduce the vibrational ground-state structures of water clusters up to the hexamer. Finally, the importance of many-body induction and three-body dispension are examined, and it is shown that the latter can have significant effects on water cluster properties despite its small magnitude.

Ab Initio Study of an H24O12 Zwitterion

Abstract: An H24O12 zwitterionic water cluster based on the 4454 cage geometry is described and studied at the B3LYP/6-311++G** level. The cluster's PES has two zwitterionic local minima, which are connected by low barrier pathways involving transfers of two protons, denoted H82 and H5U, along hydrogen bonds. The two zwitterionic minima sit in a broad megabasin that also contains two shallow saddles and a hilltop. All features lie within 0.5 kcal/mol of each other. The zwitterion converts to neutralized (H2O)12 clusters via proton transfers along any of eight embedded water wires. Optimized geometries for transition states and products for these neutralization reactions are computed. These neutralization pathways are endothermic at 77 K, suggesting that the zwitterion could be detected in a low temperature experimental system. Activation energies for neutralization range from 2.9 to 3.8 kcal/mol at 77 Κ and from 2.3 to 3.1 kcal/mol at 25 °C. Computed IR spectra for the zwitterion and its neutralized geometries are ...

Properties of Water Clusters on a Graphite Sheet

Abstract: A many-body polarizable potential model has been used to investigate the interaction of the H2O monomer and the (H2O) n=2-6 clusters with a graphite sheet. The water clusters on the graphite sheet are predicted to have geometries similar to those of the isolated gas-phase clusters. In the case of the water hexamer, the most stable isomer on the polarizable graphite surface is predicted to be the “open-book” species, followed by the ring, “prism” and “cage” isomers in terms of decreasing stability. In contrast, in the gas-phase, the most stable isomers of the water hexamer have prism and cage structures, followed by the book and ring isomers. The changes in the relative stability of water clusters when bound to the graphite surface arise primarily from dispersion interactions between the water molecules and the surface.

A computational study of interactions between acetic acid and water molecules.

Abstract: Density functional theory calculations were performed for the title reactions to elucidate the difference between the strong cyclic hydrogen bond of (Me-COOH)(2) and the electrolytic dissociation, MeCOOH Me-COO(-) + H(+), as a weak acid. The association of water clusters with acetic acid dimers strengthens the cyclic hydrogen bond. A nucleophilic attack of the carboxylic carbon by a water cluster leads to a first zwitterionic intermediate, MeCOO(-) + H(3)O(+) + (HO)(3)C-Me. The intermediate is unstable and is isomerized to a neutral interacting system, MeCOOH...(HO)(3)C-Me + H(2)O. The ethanetriol, (HO)(3)-CMe is transformed to an acetic acid monomer. The monomer may be dissociated to give a second zwitterionic intermediate with reasonable proton-relay patterns and energy changes. In proton relay reaction channels, H in MeCOOH is not an acidic proton but is always a hydroxy proton.

Nucleation of Ice in Large Water Clusters: Experiment and Simulation

Abstract: Experimental studies of water in greatly confined spaces carried out at the University of Michigan are reviewed. In particular, measurements of rates of homogeneous nucleation of ice in large clusters of water probed by electron diffraction are discussed. Nucleation rates were astronomically higher than any previously observed in the laboratory. Measurements of rates permit inferences to be drawn about interfacial free energies of the ice-water boundary. Diffraction patterns also show that the phase of ice formed when supercooling is deep is the metastable cubic ice. This is because the interfacial free energy for the cubic ice boundary is lower than that for the stable hexagonal phase. Moreover, it is shown that very finely divided water can be cooled substantially below the temperature at which bulk water has been proposed to freeze catastrophically. Possible reasons for small drops avoiding such a critical point are proposed. Molecular dynamics simulations of large, crystalline and deeply supercooled liquid clusters were carried out with a variety of potential functions. They indicated that, despite the disorder found in the surface layers of the crystalline clusters, this disorder was not responsible for the nonideal profiles of the Bragg reflections seen in experiments. Simulations show promise in the field of nucleation. Fully realistic simulations of the freezing of water would be much more enlightening than the traditional nucleation experiments because of the detailed accounts of the underlying cooperative molecular motions they would afford. Such simulations have proven to be elusive, partly because of the enormous demands on computer times involved. Even with advances in computer technology showing signs of overcoming that obstacle, it is not clear that a suitable interaction potential function is available for the purpose. Steps that may be necessary to resolve the problem are discussed briefly.

Vapor Pressure Isotope Effects of Water Studied by Molecular Orbital Calculations

Abstract: H/D and 16O/18O fractionation factors between liquid water and water vapor in the temperature range of 0 to 100°C were calculated using the reduced partition function ratios of small water clusters, (H2O) n with n=1 to 10, obtained at the HF/6-31G(d) and B3LYP/6-311G(d) levels of theory. The calculated fractionation factor values were heavily dependent on the choice of the MO theory and the basis set. Both the calculation levels showed that the formation of hydrogen bonds in liquid water caused the heavier isotopes of hydrogen and oxygen to be preferentially fractionated into the liquid water phase. While the HF/6-31G(d) level calculations yielded better results of the absolute values of the H/D and 16O/18O fractionation factors, the B3LYP/6-311G(d) level calculations reproduced the slopes of their temperature dependence better than the HF/6-31G(d) level calculations. As a whole, the quantitative agreements between the experiment and the present calculations were not satisfactory. It was indicated that a ...

Hyperthermal surface-collisions of water cluster cations

Abstract: Size-selected, protonated water cluster cations (H2O)nH+, 4 ≤ n ≤ 32, are scattered at normal incidence from the surface of a diamond-coated silicon wafer at collision energies 0 ≤ Ecoll ≤ 500 eV. The size distribution of collision-induced fragment-ions and the ion yield of scattered particles are analyzed, using a secondary time-of-flight mass spectrometer, as a function of the cluster size, n, and the collision energy, Ecoll. Even at low impact energies only very small fragment-ions can be detected, with a maximum fragment size of ∼35% of the colliding parent cluster ions. For clusters consisting of more than 10 molecules, the protonated water dimer (H2O)2H+ becomes the predominant fragment-ion. The total charge survival yield obeys a nonlinear increase with cluster size; for the largest clusters investigated, more than 35% of the impacting ions survive the surface collision in the cationic charge state.

Ab initio treatment of magnesium water cluster anions [Mg,nH2O]−, n≤11

Abstract: Geometrical as well as electronic structures of magnesium water cluster anions with the formal stoichiometry [Mg,nH2O]−, n≤11, are investigated through application of various correlated ab initio methods. Different structural archetypes emerge and the excess electron localization mode within them are elucidated. Their stability against electron detachment are predicted through calculation of vertical and adiabatic detachment energies of the most stable cluster geometries. Minimum cluster sizes of vertically and adiabatically stable [Mg,nH2O]− clusters are discussed. The impact of the excess electron on cluster structures is explored and the extent of the cluster structure reorganization upon electron detachment in [Mg,nH2O]− is quantified.

Remote Effects Modulating the Spin Equilibrium of the Resting State of Cytochrome P450cam –An Investigation Using Active Site Analogues

Abstract: The crystal structure of the resting state of cytochrome P450cam (CYP101), a heme thiolate protein, shows a cluster of six water molecules in the substrate binding pocket, one of which is coordinating to iron(III) as sixth ligand. The resting state is low-spin and changes to high-spin when substrate camphor binds and H2O is removed. In contrast to the protein, previously synthesised enzyme models such as H2O[BOND]FeIII(porph)(ArS−) were shown to be purely high-spin. Iron(S−)porphyrins with different distal sites mimicking proposed remote effects have been prepared and studied by cw-EPR. The results indicate that the low-spin of the resting state of P450cam is due to the fact that the water molecule coordinating to iron has an OH−-like character because of hydrogen bonding and polarisation of the water cluster, respectively.

Unraveling Water Structure Inside and Between Nanocapsules

Abstract: Among Achim Muller's prolific crystal structure database, we have selected two crystalline phases in order to perform a whole and complete characterization of water structure at the nanometer scale. The first chosen example involves the Na3(NH4)12[Mo57Fe6(NO)6O174(OH)3(H2O)24] 76H2O compound synthesized and characterized in 1994. Some very interesting yet unnoticed water clusters may be evidenced in the voids generated by the stacking of the polyanionic units. Among them, we have been able to characterized a pure water crown (H2O)18, a loose association of three strongly solvated ammonium ions [H3N–H⋅⋅⋅OH2]+ mediated by two water dimers and one water molecule, a perfectly planar alternating six-member ring [(NH4)3(H2O)3]3+, a puckered chair-shaped hexagonal ring [(NH4)2(H2O)4]3+ and two triangular pyramidal water tetramers (H2O)4. It was also shown that the crown and the chair ring was involved through further hydrogen bonding into the formation of a quite novel supramolecular layer modeling the structure of water in contact with a polyelectrolyte. The second example involves the (gua)32[Mo132O372(H2O)72(SO4)10(H2PO2)20(gua)20]⋅nH2O compound synthesized and characterized in 2002. Here, we provide for the first time a complete structural analysis of all the various hydrogen bond patterns encountered in this system. Among them we may cite, an intramolecular web covering the internal cavity, an intramolecular finite system involving the guanidinium cations and the nine-member ring pores of the Mo132 shell and a central pure water cluster of one hundred water molecules. In this last case, the evolution of the hydrogen bond strengths on a per H-bond basis or within supramolecular aggregates ([H2O]20, [H2O]40, and [H2O]100) is quantitatively studied from standpoints involving both geometry (H–O⋅⋅⋅O bond angles distribution) and energy (partition functions). A survey of other crystalline phases involving water clusters is also presented. It is hoped that the study of these new clusters in a very next future will allow us to solve the well-known water puzzling behaviors.

Conduction of water clusters in modified aged oil

Abstract: Dissolved water in insulating liquids has been regarded as a kind of impurity that degrades electrical properties. Recently, the state and the behavior of water molecules in liquid have been measured by infrared methods, making it possible to analyze where water molecules are bound to dielectric molecules and how many molecules gather around polar radicals on the alkyl chain. In the case of transformer oil, which consists almost entirely of saturated hydrocarbons, the content of oxidation products is gradually increased by aging during use. These oxidation products include polar radicals such as carbonyl and ketone radicals. When water dissolves in such oil, water molecules interact with these polar radicals to form water clusters, which can make the conductivity increase. In the research reported here, partially oxidized hydrocarbon was mixed with saturated hydrocarbon and the effect of water clusters around ketone radicals on the conductivity was investigated. When the content of oxidation products was less than 10%, the conductivity did not increase with an increase in the amount of water. But when the ratio exceeded 10%, specific kinds of water clusters increased the conductivity. It appears that these clusters consist of water molecules gathered around one ketone radical. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(2): 21–27, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10178

The effect of acetic acid on the conduction of water in oil

Abstract: The effect of organic acid, which is one of the deteriorated compounds of aged oil in transformer, on the state of dissolved water and on the conduction of water, was discussed. Dissolved water molecules do not always diffuse uniformly in oil. Some water clusters are formed and interact with liquid molecules by hydrogen bond. The interacting water cluster contributes conduction phenomena in oil. In practical use, the aged oil contains some ketonic, ester, carbonic compounds. And water molecules, which bond these polar bases, can increase conductivity. The acetic acid, which is one of the organic acids in aged oil, can interact with water molecules. In this paper, the acetic acid was dropped in the liquid that was modified aged oil. The state and the amount of water cluster were observed by FT-IR method. As a result, the dropping of a little amount of acetic acid, a part of water cluster was removed from liquid and conductivity was decreased.

Vibrational spectroscopy and reactions of water clusters

Abstract: The condensed phase of water is probably the most investigated substance in Physical Chemistry. On the one hand, there are numerous anomalous properties of the liquid like the heat capacity and the density as well as the many configurations of ice that make water with its tendency to form a network of hydrogen bonds so interesting [1]. On the other hand, water plays a key role as ubiquitous solvent on earth and as promotor of reactions in atmospheric and extraterrestrial chemistry. In spite of all the efforts and the progress made in the last 20 years, a unified description of all the phenomena starting from the basic molecular interaction is still missing. We do not have a consistent description of liquid water nor do we understand completely the spectral and surface properties of the different conformations of ice. One of the reasons is certainly the lack of good, flexible interaction potentials that correctly account for all the many-body effects which play a crucial role in the hydrogen-bonded network of the water interaction [2]. In many of the simulations many-body effects are included by effective two-body interactions and are thus mostly valid in that range of applications to which their parameters are fitted. The other problem is the lack of detailed experimental results that would allow us to derive explicit conclusions about the underlying molecular models. In liquids, for instance, the information is often restricted by averaging processes and only a global picture results.

Hydrogen Bonding Patterns in Water Clusters: Trimer, Tetramer and Pentamer #

Abstract: In elucidating the thermodynamic properties, it is important to know all the possible structures in an aggregated system. Water molecules are assembled in a water cluster and form a hydrogen bond network. The most important feature of the hydrogen bond is that it possesses the direction. To represent the feature of the hydrogen bond, we use digraphs. All the possible topology–distinct hydrogen bonded structures for water trimer, tetramer and pentamer, (H2O)n (n = 3–5), are enumerated by means of digraphs and all the corresponding digraphs are shown. Using those structures as the theoretical framework, the local minima on the potential energy surfaces of those water clusters are obtained using the ab initio MO method at the HF/6–31G* level of theory. The electron density maps are also calculated. It is shown that the hydrogen bonding pattern as well as the number of the hydrogen bonds influences the stability of a water cluster.

Thermodynamics of small electron-bound water clusters

Abstract: Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, KoreaReceived April 24, 2003The relative stabilities of weak binding clusters are sensitive to temperature due to the entropy effect. Thus,here we report significant changes in relative stabilities between two low-energy electron-water trimerstructures and those between three low-energy electron-water pentamer structures, as the temperatureincreases. The trimer and pentamer show structural changes around 200 K.Key Words : Solvated electron, Electron-bound water cluster, Electron-water clusters, Thermodynamics,Vertical-electron detachment energyIntroductionAs water is the most important solvent, the electron-waterclusters have been an interesting subject in physics,chemistry and biochemistry.

Nature of Many-Body Forces in Water Clusters and Bulk

Abstract: All the properties of water clusters and of bulk water can in principle be predicted by solving the Schrodinger equation for the motion of nuclei on the potential energy surface of a given system. This level of theory does neglect several physical effects such as nonadiabatic couplings of electronic and nuclear motions or relativistic effects, but these effects would contribute much below the current uncertainties of both measurements and theory for systems of this size. Several properties of bulk water can be described reasonably well by solving classical rather than quantum equations of motion, a significant further simplification. However, accuracy of all predictions depends critically on the accuracy of the potential energy surface. This surface can be decomposed into intramonomer contributions, i.e., the potentials within single water molecules, the pair potentials, and the so-called nonadditive potentials. Since derivatives of potential energy surfaces define forces, one may alternatively use the term “force fields” equivalently with “potentials”. This chapter will be devoted to many-body potentials of water molecules with emphasis on elucidating the physical origins of interactions.

Ab initio molecular dynamics study of Zundel's and Eigen's, H5O+2 and H9O+4, proton complexes in the triplet state

Abstract: Ab initio molecular dynamics (MD) study of Zundel's (H 5 O + 2) and Eigen's (H 9 O + 4) cation complexes in the triplet state is carried out. This study deals with isolated complexes (gas phase) and the complexes in the cluster composed of 32, 64, and 128 water molecules mimicking the behavior of a realistic solution. For the isolated complexes, MD runs reveal three distinct periods, which are assigned to the intermediate and final products. In the water cluster, these periods are smoothed out. The H 5 O + 2 and H 9 O + 4 in the triplet state undergo structural rearrangements, which finally result in hydrogen elimination. For Zundel's complex, the hydrogen is pushed away from the center of the bulk water, whereas for Eigen's complex the hydrogen is removed from a near-surface water molecule. The rate of hydrogen elimination decreases with the increasing number of water molecules surrounding the cation.