Different Numbers Of Water Molecules Research Articles

Hydration structure and dynamics of phosphoric acid and its anions-Ultrafast 2D-IR spectroscopy and abinitio molecular dynamics simulations.

The hydration shells of phosphate ions and phosphate groups of nucleotides and phospholipid membranes display markedly different structures and hydrogen-bond strengths. Understanding phosphate hydration requires insight into the spatial arrangements of water molecules around phosphates and in thermally activated structure fluctuations on ultrafast time scales. Femtosecond two-dimensional infrared spectroscopy of phosphate vibrations, particularly asymmetric stretching vibrations between 1000 and 1200cm-1, and abinitio molecular dynamics (AIMD) simulations are combined to map and characterize dynamic local hydration structures and phosphate-water interactions. Phosphoric acid H3PO4 and its anions H2PO4-, HPO42-, and PO43- are studied in aqueous environments of different pH value. The hydration shells of phosphates providing OH donor groups in hydrogen bonds with the first water layer undergo ultrafast structural fluctuations, which induce a pronounced spectral diffusion of vibrational excitations on a sub-300fs time scale. With a decreasing number of phosphate OH groups, the hydration shell becomes more ordered and rigid. The 2D-IR line shapes observed with hydrated PO43- ions display a pronounced inhomogeneous broadening, reflecting a distribution of hydration geometries without fast equilibration. The AIMD simulations allow for an in-depth characterization of the hydration geometries with different numbers of water molecules in the first hydration layer and different correlation functions of the fluctuating electric field that the water environment exerts on the vibrational phosphate oscillators.

A DFT Study on the Tautomerization of β‐Alanine

AbstractTautomerization paths of β‐alanine with explicit inclusion of water molecules, (H2O)n, were investigated by DFT calculations, wB97X‐D/6‐311+G(d,p) SCRF=PCM. Structures of zwitterions of the alanine of trans (t−) and gauche (g−) conformations with seven water molecules (n=7) were examined. On the basis of those geometries, elementary processes of the tautomerization were investigated. For the t‐conformer of β‐alanine, reaction models of n=8, 10, 14, 18 and 24 were scrutinized. While reaction processes are slightly modified with different number of water molecules, n=18 and 24 models afforded three elementary reactions, t‐alanine with cis‐COOH→t‐ion pair→t‐alanine with trans‐COOH→t‐zwitterion. The (H2O)4 hydrogen‐bonded chain participates in the reactions. For the g‐conformer, models of n=7, 10, 14 and 18 were investigated, and the tautomerization was found to take place concertedly via (H2O)2.

Golub N.P., Golub E.O., Kozma A.A., Hlebena H.F., Mikhalchuk H.M., Kuznietsova A.O. SYNTHESIS AND RESEARCH OF A COMPLEX MANGANESE-NICKELPHOSPHATE CATALYTIC SYSTEM

Individual Mn2P2O7 and Ni3(PO4)2 phosphate catalysts were synthesized. A new synthesis technique was developed and a new complex catalytic system хMn2P2O7×yNi3(PO4)2 was obtained based on them (К-1 – К-7), which has the predicted physicochemical properties. The composition of these phosphates in the structure of the catalyst was varied in the range of 0,5 – 99,5 wt.%. It was established that the conditions of synthesis of catalysts significantly influence the process of forming the composition, structure, and corresponding physicochemical parameters of the synthesized catalysts. On the thermogram of the differential thermal analysis of an individual manganese-phosphate catalyst, three endo-effects at 148°С, 220°С and 353°С and one exo-effect at 460°С are observed. The thermogram of individual Ni3(PO4)2 shows two endo-effects at 210°С and 372°С and one exo-effect at 803°С. The synthesized double manganese-containing systems are characterized by a significant difference in DTA curves for samples K-1 - K-7. All obtained air-dry samples are crystal hydras with different numbers of water molecules. The structure of the obtained series of complex manganese-nickel phosphate catalysts contains various forms of water. The process of dehydration contributes to its separation from the structure of the samples and leads to the occurrence of characteristic endothermic effects. On all synthesized complex samples, the transition of manganese (II) orthophosphate to its pyrophosphate is observed when the final heat treatment temperature is reached. Firing samples of synthesized catalysts above 700oC leads to their complete dehydration with the formation of anhydrous salts. DTA results for all synthesized manganese-nickel phosphate samples are in good agreement with their X-ray diffraction, IR spectroscopy, and surface acidity results. They confirmed the correct choice of the modifying ion to improve the structure and physicochemical parameters of the manganese (II) phosphate catalyst. It can be predicted that the synthesized new complex oxide catalysts will show improved catalytic properties (activity and selectivity) in the processes of partial oxidation of n-alkanes into valuable products. The synthesized double manganese-containing systems are characterized by a significant difference in DTA curves for samples K-1 - K-7. All obtained air-dry samples are crystal hydras with different numbers of water molecules. The structure of the obtained series of complex manganese-nickel phosphate catalysts contains various forms of water. The process of dehydration contributes to its separation from the structure of the samples and leads to the occurrence of characteristic endothermic effects. On all synthesized complex samples, the transition of manganese (II) orthophosphate to its pyrophosphate is observed when the final heat treatment temperature is reached. Firing samples of synthesized catalysts above 700oC leads to their complete dehydration with the formation of anhydrous salts. DTA results for all synthesized manganese-nickel phosphate samples are in good agreement with their X-ray diffraction, IR spectroscopy, and surface acidity results. They confirmed the correct choice of the modifying ion to improve the structure and physicochemical parameters of the manganese (II) phosphate catalyst. It can be predicted that the synthesized new complex oxide catalysts will show improved catalytic properties (activity and selectivity) in the processes of partial oxidation of n-alkanes into valuable products.
 Keywords: catalysis; catalyst; catalytic systems; complex oxides; heterogeneous catalysis; phosphates; oxidation; n-alkanes; hydrocarbons; ethane; ethylene; differential thermal analysis.

Study on intermolecular hydrogen bond of uric acid water-clusters

Cluster structures that may be associated between uric acid molecules and different numbers of water molecules were studied in detail using density functional theory (DFT) at the B3LYP-D3(BJ)/6–31 + G (d, p) level. When the number of water molecules increases from one to three, the cluster configuration changes from planar single-ring structure to double-ring structure. At the same time, the weak interactions were analyzed by atomic analysis (AIM) and reduced density gradient (RDG) methods. Finally, the theoretical Raman spectra show that the N–H Raman peak in the uric acid molecule is redshifted and the hydrogen bond interaction is enhanced.

Hydration of amino acids: An investigation using density functional theory

Herein, we have investigated the effect of hydration of seven amino acids (AAs) such as alanine, aspartic acid,cysteine, glutamine, lysine, methionine, and phenylalanine with different number of water molecules using density functional theory. Among the hydrophobic AAs, cysteine has the highest interaction with water whereas in hydrophilic AAs, aspartic acid has the highest interaction with water. With the increase in number of water molecules, it is noted that alanine forms the most stable complex with water and methionine+water complex has least stability.In addition, we have calculated the chemical descriptors like chemical potential, electronegativity, hardness, softness, electrophilicity index of AAs to validate their interaction with water molecules. Interestingly, the gas phase interaction energy results match with the trend of electrophilicity index valuesof AAs.

Dynamic Simulation Based on a Simplified Model of 1/3 Coking Coal Molecule and Its Formation Characteristics of Hydration Films.

To comprehensively elaborate the formation characteristics of hydration films on 1/3 coking coal molecule, this paper reports the construction of a realistic simplified model for calculations of electrostatic potentials on the coal molecular surface to foresee the major immersion locations. On this basis, interactions at the interface of coal molecules with different numbers of water molecules and their effects on each functional group of coal molecules were investigated. Using the scanning electron microscopy experiment, changes in the coal matrix before and after water leaching were compared and analyzed by fractal dimension calculations. Hydration characteristics of coal were described from a combined macroscopic and microscopic perspective. The results showed that both positive and negative electrostatic potential of coal molecules occurred near the O-containing functional groups. The hydroxyl group’s electrostatic potential (−OH) rose, resulting in higher electrostatic potential in coal–water molecules and providing many immersion sites. Deficiency in water molecules led to the complete immersion of water molecules. The interface of coal molecules could not be covered entirely, which led to the low number of active sites and Z values. The interface of coal–water molecules did not affect the average bond lengths of water molecules but decreased the bond angle by 3–4°. The influence ofwater molecules on the −OH groups of coal molecules was the most prominent when water molecules were incorporated into the coal molecules. Water damage for the coal matrix is more pronounced than in the raw coal itself. In view of above research, the formation characteristics of the hydration film from a microscopic point of view explained that the initial hydration of coal molecules was owing to H-bonds. From a macroscopic perspective, it was mainly due to structure changes for the coal matrix. This provides valuable references for field experiments in hydraulic fracturing and perforation.

Single-crystal-to-single-crystal transformations among three Mn-MOFs containing different water molecules induced by reaction time: crystal structures and proton conductivities.

Three Mn-MOFs {[Mn3(μ4-L)2(H2O)7]·4H2O}n (1), {[Mn3(μ5-L)2(H2O)6]·4H2O}n (2) and {[Mn3(μ7-L)2(H2O)2]}n (3) (H3L = 5-(6-carboxypyridin-3-yl)isophthalic acid) were obtained under different reaction times and temperatures. Interestingly, induced by reaction time, compound 1 can lose one water molecule and SC-SC transform into compound 2. Similarly, compound 2 can also SC-SC transform into 3. Studies on two SC-SC transformation processes were carried out and the transformation mechanisms were deduced, which were verified by TG analyses. Different numbers of water molecules in the three compounds resulted in different coordination environments of the metal cation, coordination modes of the L3- ligand, continuities of hydrogen bonds, dimensions of framework and porosities. The AC impendence spectra studies revealed that compounds 1-3 can enhance the proton conductivities of the Nafion composite membrane to about 47.77%, 36.88% and 21.28%, respectively. It is speculated that the highest proton conductivity of compound 1 may be due to its continuous hydrogen bond chain and highest water uptake, which were mainly decided by the number of water molecules.

Interfacial Diffusion of Hydrated Ion on Graphene Surface: A Molecular Simulation Study.

Hydration plays an important role in the diffusion and sieving of ions within nanochannels. However, it is hard to quantitatively analyze the contribution of hydration to the diffusion rates due to the complex hydrogen-bond and charge interactions between atoms. Here, we quantitatively investigated the interfacial diffusion rates of a single hydrated ion with different number of water molecules on graphene surface through molecular dynamics simulation. The simulation results show the ballistic diffusion mode by analyzing the mean-square displacement, and the diffusion rates change nonmonotonically with the hydration number. The potential energy profiles with the changing position of the hydrated ion on graphene surface were further analyzed, which shows the dominant factor for interfacial diffusion changing from ion-graphene interaction to water-graphene interaction as the number of water molecules increases. Besides, it was found that the surface hydrophilicity weakened the influence of hydration number on the diffusion rates of hydrated ion. Finally, the diffusion properties of different hydrated ions on graphene surface were investigated, and the hydrated Li+, Na+, and K+ containing three, four, and five water molecules, respectively, show the fastest diffusion rate. This work demonstrates the interfacial diffusion behavior and mechanism of hydrated ions at the molecular level, which can provide valuable guidance in nanosensors, seawater desalination, and other hydrated ion-related fields.

Water-vapochromic behavior of a mononuclear Pd(II) complex of piroxicam: A DFT and TD-DFT study

The vapochromic behavior of a mononuclear Pd(II) complex with piroxicam ligands (trans-[Pd(Pir)2] (Pir− is piroxicam anion)) in the presence of water vapor has been theoretically investigated using the time-dependent density functional theory (TD-DFT). The structure of Pd(II) complex interacting with different number of water molecules (n = 1–5) was optimized, separately. The electronic absorption spectra of the optimized structures were calculated using the TD-DFT method and the changes in the absorption spectrum of complex with the increase in the number of water molecules were followed. Comparison of the absorption spectrum of bare Pd(II) complex with those of its hydrated forms with different numbers of water molecules showed a considerable change in the region of 360–400 nm including the change in the intensity and peak position. The main electronic configurations of the intense absorption lines in the related absorption spectra were determined so that the molecular orbitals involved in these absorption lines were determined. The natural bonding orbital (NBO) analysis was performed to assign the NBOs contributing to these molecular orbitals and to see how the NBO composition of the involved molecular orbitals in the electron excitation change with the number of water molecules. It was observed that the change in the intensity and position of the inter- and intraligand π→π∗ transitions are responsible for the color change. Also, based on the NBO results, the contribution of the electronic transitions involving the Pd(II) ion in the color change of the complex was absent.

Temperature dependent DFT studies to understand the physiochemical interaction of lithium chloride cluster ions in presence of syringic acid

This work presents the results of the DFT for hydration of lithium ions in present of syringic acid and chloride ion. Herein, lithium ion is bonded to different number of water molecules (0–4) in presence of syringic acid in aqueous system. The stability of the different systems were studied at room temperature (298 K) using the thermodynamic parameters like change in Gibbs energy (ΔG), change in enthalpy (ΔH), change in energy (ΔE), energy of the system (E). Feasibility for the formation of hydrated lithium ion in presence of above moieties is studied using the DFT. Further, the impact of temperature was studied on the stability of each system i.e. at 308 and 318 K. To understand the many bodies interaction, polarization in each system is studied. Authors find that tetrahedral hydrated lithium ion with syringic acid (SA) and chloride ion has the maximum stability based on the enthalpy and Gibbs energy. Even, on changing the temperature i.e. at 308 and 318 K, tetrahedral hydrated lithium ion with SA and chloride ion is most stable. The outcome of the present work highlights the relation between the structures that used explain the intermolecular interaction between the hydration of the lithium ion and syringic acid along with chloride ion as well stability of the hydration of lithium ion. The obtained results may be valuable in determination of lithium ion on interaction with small molecules in aqueous solution. Further, TD-DFT of the stable system was studied.

Experimental and DFT studies on surface properties of sulfonate-based surface active ionic liquids

Two anionic surface active ionic liquids (SAILs), 3-methyl-1-ethoxycarbonylimidazolium decanesulfonate ([Etmim][C10H21SO3]) and 3-methyl-1-ethoxycarbonylimidazolium dodecanesulfonate ([Etmim][C12H25SO3]) were synthesized and studied. The surface properties, aggregation properties and thermodynamic parameters of [Etmim][C10H21SO3] and [Etmim][C12H25SO3] aqueous solutions were determined using surface tension and electrical conductivity. Micelle formation of [Etmim][C10H21SO3] and [Etmim][C12H25SO3] was spontaneous and entropy-driven.Density functional theory (DFT) calculation was used to optimize the configuration of the anions (C10H21SO3, and C12H25SO3), imidazolium cation ([Etmim]+), and SAILs ([Etmim][C10H21SO3] or [Etmim][C12H25SO3]) with different number of water molecules (1–3) using Gaussian 16 at B3LYP/6-31G(d,p) level.Typical hydrogen bonds, bond length changes, bond angle changes, and charge changes of typical atoms in hydrated complexes were analyzed. For imidazolium cation hydrates, H2O formed two types of hydrogen bonds with cation ([Etmim]+). For sulfonate anion hydrates, H2O formed two types of hydrogen bonds with anions ([C10H21SO3]- or [C12H25SO3]-). Hydrogen atoms in H2O formed hydrogen bonds with oxygen atoms of polar sulfonate anions in three ways: 1:1, 2:1, and 2:1. The typical electron withdrawing atoms (N and O) in imidazolium cation was beneficial for the micelles formation. The electrostatic repulsion and electrostatic attractive interaction between polar groups of SAILs affected the CMC values of [Etmim][C10H21SO3] or [Etmim][C12H25SO3] aqueous solutions. Binding energy (D0), difference of binding energy (ΔD0) of sulfonate ion hydrates and SAIL hydrates confirmed the tendency of [Etmim][C12H25SO3] micelle formation was higher than that of [Etmim][C10H21SO3].

Pair interaction energy decomposition analysis (PIEDA) and experimental approaches for investigating water interactions with hydrophilic and hydrophobic membranes

The origins of low and high interactions of polar groups with water molecules are still unknown and need to be further examined for effective future membrane synthesis and modification. The primary aim of this research study is to provide a comprehensive overview of the interactions at the molecular level occurring between water molecules and the fragments of hydrophobic and hydrophilic membranes based on pair interaction energy decomposition analysis (PIEDA) as part of the fragment molecular orbital (FMO) method’s framework. This direction is critical, since a research study of the reasons for water and membrane interactions can help design groundbreaking membranes with superior hydrophilicity characteristics. To accomplish this, the computational studies, the Polyvinylidene fluoride (PVDF [H(–CH2–CF2–)4CH3]) and Polyacrylonitrile (PAN [(H(–CH2–CH(CN)–)4CH3]) membranes were considered as models for hydrophobic and hydrophilic membranes, respectively. Density-functional theory (DFT), based on B3LYP functional and split-valance 6-311+G (d,p) basis sets, was used in order to optimize the geometry of PAN, PVDF, and their complexes with different numbers of water molecules. Furthermore, fragment molecular orbit (FMO) and the Pair Interaction Energy Decomposition Analysis (PIEDA) were carefully interrogated. These types of analyses included the inter fragment interaction energy (IFIE), like the electrostatic (ES), exchange repulsion (EX), charge-transfer and mixing term (CT + mix) energies. Furthermore, the hydrophilicity and hydrophobicity of the origins of membrane function groups were experimentally evaluated through Fourier-transform infrared spectroscopy (FTIR- ATR), 13C cross polarization magic angle spinning (13C CP MAS) Solid State Nuclear magnetic resonance SSNMR, and Fourier transform Raman (FT-Raman) spectroscopies. Confocal microscopic approach was used to interrogate water transport and the interactions between fluorescence particles and membrane layers. Furthermore, the Infrared (IR) spectroscopy was performed to investigate interaction between water molecules and PVDF and PAN. The theoretical results had a good agreement with experimental result.

Thermodynamics of the aggregation of the bile anions of obeticholic and chenodeoxycholic acids in aqueous solution

A complete characterization of the aggregation process of the sodium salts of chenodeoxycholic (NaCDC) and obeticholic (NaObC) acids has been carried out by using different experimental techniques. Since it is well known that the presence of hydrophobic groups strongly reduce the critical aggregation concentrations and modifies the type of aggregation structures which can be formed, it could be expected that the introduction of an ethyl group into the structure of the chenodeoxycholic acid, to form the obeticholic derivative, could give rise to important modifications in its aggregation behavior. However, it has been observed that the aggregation numbers (determined in the range of temperatures 10–40 °C from ITC measurements) are identical to each other, a fact which was supported by the determination of the hydrodynamic radius from dynamic light scattering. This similarity was also observed for the fraction of bound counterions determined from the well-known Corrin–Harkins plot, being equal to 0.33 for both compounds. Finally, the polarity of the interior of the aggregate as measured by the ratio of the fluorescence intensities of the first and third vibronic peaks, I1/I3, of monomeric pyrene solubilized within the aggregates is also identical within the experimental error. The main differences correspond to: (1) the temperatures at which the enthalpy of demicellization is zero (31.4 (NaObC) and 26.8 °C (NaCDC)); and (2) the cmc value for NaObC is roughly half the one for NaCDC as observed from surface tension, fluorescence and ITC measurements. This implies that the free energy for the demicellization process is around 2 kJ mol−1 larger for NaObC than for NaCDC. (3) Finally, the difference in the change in the heat capacity of the aggregation (being 60 J mol−1 K−1 higher for ObCA) is due to the different number of water molecules which are lost during the monomer transfer from the bulk solution to the micellar aggregate.

New Effects in the Poly-N-Vinylcaprolactam/Titanium(IV) Oxides Nanocomposite System and Their Nature

Nanocomposites based on poly-N-vinylcaprolactam (PVC), characterized by different drying temperatures of aqueous PVC solution at 25°С (PVC25) and 40°С (PVC40), with titanium(IV) oxide nanoparticles (TONs) (η-phase (TP: TiO2 – x · mH2O) with a superstructure to the anatase structure and ordered solid solution with partial replacement of oxygen atoms in the η-phase with peroxo group O 2 2– (PP: TiO x (O2)2 – x · nH2O)) have been obtained for the first time and characterized by X-ray diffraction and IR spectroscopy. It is found that a common feature of TP/PVC and PP/PVC obtained by dry mixing and grinding is the decrease in the number of water molecules for TP and PP in the interlayer space of the structure and their attachment to the PVC amide groups; the differences are related to the specificity of PVC behavior in these systems: mechanodestruction of PVC in PP/PVC40 and different numbers of water molecules in PVC25 and PVC40.

Molecular dynamics simulation of the interaction between methyl benzotriazole and Cu2O crystal

In circulating water system, methyl benzotriazole (TTA) is one of the common corrosion inhibitors for copper. But the inhibition mechanisms have not been clearly understood so far. In different number of water molecules, the interaction between TTA and Cu2O (copper surface) was investigated with molecular dynamics (MD) method. The results showed that the MD simulation result with water was more consistent with the experiment results. In different number of water molecules, the sequence of the interaction energies between TTA and Cu2O (001) was ∆E1 (150H2O) > ∆E1(200H2O) > ∆E1(100H2O) > ∆E1(50H2O) > ∆E1(0H2O). The number of water molecules had an important influence on the interaction between corrosion inhibitors and Cu2O crystal. From non‐bond energy and pair correlation functions, the interaction energies of the model system were mainly contributed by the non‐bond interaction. Strong adsorption could be raised by the Coulomb interaction between the negatively charged functional groups in TTA and the positive copper ions in the Cu2O (001) face, and further interaction between aggressive media and copper could be restricted. So, copper corrosion could be avoided. Chemical bonds and non‐bond interactions were formed between TTA and Cu2O (001) in different number of water molecules. Water molecules could not be ignored during the MD simulation, too. The results obtained here may provide theoretical supports for developing new corrosion inhibitors.

Time dependence of phase separation enthalpy recovery behavior in aqueous poly(N-isopropylacrylamide) solution

Thermosensitive LCST phase separation behaviors of poly(N-isopropylacrylamide) (PNIPAM) aqueous solutions have been investigated by a power compensation differential scanning calorimetry which can be subjected to relatively high cooling and heating scanning rates. Significant difference in the thermal properties is observed in four different concentration regions. The typical demixing enthalpy recovery behavior is observed in region III and IV, but cannot be observed in region II. In concentration region I, only one concentration-dependent glass transition behavior can be observed. The distinct thermal features in different concentration regions were interpreted by the complexity of chemical structure, and there are more than one polar groups in the repeating unit of PNIPAM, hydrogen bonded with different numbers of water molecules in different concentration regions. The endothermic phase separation process involved both a chemical process of the breakage of hydrogen bonding between polymer and water molecules and a physical process of the coil-to-globule transition of swelling polymer chains.

The Effect of Moisture on the Hydrolysis of Basic Salts.

A great deal of information exists concerning the hydration of ions in bulk water. Much less noticeable, but equally ubiquitous is the hydration of ions holding on to several water molecules in nanoscopic pores or in natural air at low relative humidity. Such hydration of ions with a high ratio of ions to water molecules (up to 1:1) are essential in determining the energetics of many physical and chemical systems. Herein, we present a quantitative analysis of the energetics of ion hydration in nanopores based on molecular modeling of a series of basic salts associated with different numbers of water molecules. The results show that the degree of hydrolysis of basic salts in the presence of a few water molecules is significantly different from that in bulk water. The reduced availability of water molecules promotes the hydrolysis of divalent and trivalent basic ions (S2- , CO32- , SO32- , HPO42- , SO42- , PO43- ), which produces lower valent ions (HS- , HCO3- , HSO3- , H2 PO4- , HSO4- , HPO42- ) and OH- ions. However, reducing the availability of water inhibits the hydrolysis of monovalent basic ions (CN- , HS- ). This finding sheds some light on a vast number of chemical processes in the atmosphere and on solid porous surfaces. The discovery has wide potential applications including designing efficient absorbents for acidic gases.

Effects of Aspect Ratio on Water Immersion into Deep Silica Nanoholes.

Understanding the influence of aspect ratio on water immersion into silica nanoholes is of significant importance to the etching process of semiconductor fabrication and other water immersion-related physical and biological processes. In this work, the processes of water immersion into silica nanoholes with different height/width aspect ratios (ϕ = 0.87, 1.92, 2.97, 4.01, 5.06) and different numbers of water molecules (N = 9986, 19972, 29958, 39944) were studied by molecular dynamics simulations. A comprehensive analysis has been conducted about the detailed process of water immersion and the influence of aspect ratios on water immersion rates. Five distinguishable stages were identified for the immersion process with all studied models. The results reveal that water can easily immerse into the silica nanoholes with larger ϕ and smaller N. The calculation also suggests that aspect ratios have a greater effect on water immersion rates for larger N numbers. The mechanism of the water immersion process is discussed in this work. We also propose a mathematical model to correlate the complete water immersion process for different aspect ratios.

Hydration of Bromine Ions in Water

A mass spectrographic method electrospraying electrolyte solutions in vacuum was used to determine the enthalpy of hydration of bromine ions by different numbers of water molecules. The mass spectra of negative ions from aqueous solutions of NaBr were measured over the temperature range of 15–50°C and showed that the most intense peaks correspond to the hydrated bromine ions with one and two water molecules. It was found that the Van't Hoff equation holds for bromine hydrates containing up to three water molecules, whereas addition of the fourth water molecule leads to a violation of the Van't Hoff equation. The enthalpy of bromine ion hydration by the first and the second water molecules was found to be –(28.5 ± 1.7) and –(21 ± 4.2) kJ/mol, respectively.

Theoretical investigation of proton-transfer in different membranes for PEMFC applications in low humidity conditions

A comparative theoretical study was performed to explore the effect of polymer backbone on the proton exchange in different sulfonated membranes such as poly(phenylene oxide), poly(benzimidazole), polyimide, poly(oxadiazole) and Nafion 117 at low hydration state. Geometry optimization of the membranes in the presence of different numbers of water molecules (1–3 water molecules) revealed that proton dissociation energies and hydrogen bond interactions (which are of critical importance in proton transfer) depend strongly on the polymer structure’s functional groups. When the polymer dose not stabilize hydronium ion or sulfonate anion, water molecules are arranged around sulfonate group and form a two-ring hydrogen bonded structure; in addition, this polymer showed high proton transfer energy (25.0, 27.2 and 19.4kcal/mol for sulfonated poly(phenylene oxide), sulfonated meta-poly(benzimidazole) and Nafion 117). Theoretical studies also demonstrated that the position of sulfonate group and functional groups in the polymer structure was effective in proton dissociation. In this regard, proton transfer energy for para-sulfonated poly(benzimidazole) was about 17.7kcal/mol less than sulfonated meta-poly(benzimidazole); this energy difference could be attributed to the imidazolium cation formation and its stabilizing effect on sulfonate anion. The molecular graphs for sulfonated poly(oxadiazole) indicated that, although this polymer had the highest proton transfer energy among the polymers, it formed a continuous and strong hydrogen bond chain that facilitated proton transfer by hopping mechanism.