Hydration Of Complexes Research Articles

Hydration and dynamics of L-glutamate ion in aqueous solution.

Aqueous solutions of sodium l-glutamate (NaGlu) in the concentration range 0 < c/M ≤ 1.90 at 25 °C were investigated by dielectric relaxation spectroscopy (DRS) and statistical mechanics (1D-RISM and 3D-RISM calculations) to study the hydration and dynamics of the l-glutamate (Glu-) anion. Although at c → 0 water molecules beyond the first hydration shell are dynamically affected, Glu- hydration is rather fragile and for c ⪆ 0.3 M apparently restricted to H2O molecules hydrogen bonding to the carboxylate groups. These hydrating dipoles are roughly parallel to the anion moment, leading to a significantly enhanced effective dipole moment of Glu-. However, l-glutamate dynamics is determined by the rotational diffusion of individual anions under hydrodynamic slip boundary conditions. Thus, the lifetime of the hydrate complexes, as well as of possibly formed [Na+Glu-]0 ionpairs and l-glutamate aggregates, cannot exceed the characteristic timescale for Glu- rotation.

Fenton reaction mechanism generating no OH radicals in Nafion membrane decomposition

Mechanism of Fenton reaction, which is a most widely-used degradation test for organic materials using hydrogen peroxide (H_2O_2) and iron (Fe) cations, is revealed for the decomposition of hydrated Nafion membrane. This reaction mechanism has been assumed to generate OH radicals. For a doubly-hydrated Nafion membrane model, Fenton reaction with divalent and monovalent Fe (Fe^{2+} and Fe^+) cation hydration complexes is explored for experimentally-supported hydration numbers using long-range correction for density functional theory. As a result, it is found that H_2O_2 coordinating to the Fe^{2+} hydration complexes first approaches Nafion side chains in high humidity, then leads to the C–S bond dissociation of the side chain to produce carbonic acid group and sulfonic acid ion. On the other hand, once electron transfer proceeds between iron ions, the O–O bond of the coordinating H_2O_2 is extended, then the C–S bond is dissociated to produce trihydroxymethyl group and sulfur trioxide, which are rapidly transformed to carboxyl group and sulfonic acid ion in aquo. This mechanism is confirmed by the vibrational spectrum analysis of the decomposed product. Collective Nafion decomposition mechanisms also suggest that the decomposition reaction uses the recycle of generated Fe cation hydration complexes under acidic condition near membrane surface.

MRI evaluation of the hydration status of non-pathological lumbar intervertebral discs in a pediatric population

IntroductionThe intervertebral disc (IVD) is made up of the annulus fibrosus (AF) and the nucleus pulposus (NP) – an inert hydrated complex. The ability of the IVD to deform is correlated to that of the NP and depends on its hydration. As the IVD ages, its hydration decreases along with its ability to deform. In adolescent idiopathic scoliosis, one of the etiological hypotheses pertains to the IVD, thus making its condition relevant for the diagnosis and monitoring of this pathology. HypothesisIVD hydration depends on sex, age and spine level in an asymptomatic pediatric population. The corollary is data on a control group of healthy subjects. Material and methodsA cohort of 98 subjects with normal spine MRI was enrolled; their mean age was 13.3 years. The disc volume and hydration of each IVD was evaluated on T2-weighted MRI sequences, using previously validated image processing software. This evaluation focused on the lumbar spine, from the thoracolumbar junction to the lumbosacral junction. It was assumed that IVD hydration was related to the ratio of NP and AF volumes. A mixed multivariate linear analysis was used to explore the impact of age, sex and spinal level on disc hydration. ResultsDisc hydration was higher overall in boys than in girls, but this difference was not significant. Hydration increased with age by +0.005 for each additional year (p=0.0213). Disc hydration appears to be higher at the thoracolumbar junction than the lumbar spine, although this difference was not significant. ConclusionThrough this MRI study, we established a database of non-pathological lumbar disc hydration as a function of age, sex and spinal segment along with 95% confidence intervals. Level of evidenceIV.

Adsorption of rare earth elements in regolith-hosted clay deposits

Global resources of heavy Rare Earth Elements (REE) are dominantly sourced from Chinese regolith-hosted ion-adsorption deposits in which the REE are inferred to be weakly adsorbed onto clay minerals. Similar deposits elsewhere might provide alternative supply for these high-tech metals, but the adsorption mechanisms remain unclear and the adsorbed state of REE to clays has never been demonstrated in situ. This study compares the mineralogy and speciation of REE in economic weathering profiles from China to prospective regoliths developed on peralkaline rocks from Madagascar. We use synchrotron X-ray absorption spectroscopy to study the distribution and local bonding environment of Y and Nd, as proxies for heavy and light REE, in the deposits. Our results show that REE are truly adsorbed as easily leachable 8- to 9-coordinated outer-sphere hydrated complexes, dominantly onto kaolinite. Hence, at the atomic level, the Malagasy clays are genuine mineralogical analogues to those currently exploited in China.

Liquid-liquid equilibrium of aqueous two-phase systems formed by non-ionic surfactant (Triton X-165 or Triton X-305) and ionic liquid based on the choline cation (choline bitartrate or choline dihydrogen citrate)

Liquid-liquid equilibrium data for aqueous two-phase systems (ATPSs) formed by Triton X-165 or Triton X-305 + ionic liquid based on the choline cation (choline bitartrate or choline dihydrogen citrate) + water were obtained at different temperatures (298.2, 313.2, and 328.2 K). The effects of temperature, electrolyte anion, and surfactant on the equilibrium data were evaluated. For all the ATPSs investigated, the upper phase was found to be surfactant-rich and the lower phase was electrolyte-rich. An increase of the biphasic region was observed with increasing temperature, showing that the phase separation process was endothermic and entropically driven. The potential of phase segregation between the different anions studied was in the order bitartrate > dihydrogen citrate, which was attributed to the different capacities of the anions to form hydration complexes and induce a surfactant salting-out effect. The TX-305 surfactant was more efficient in inducing phase segregation, compared to the TX-165 surfactant, indicating that the molar mass/hydrophobicity balance of the surfactant determined the immiscibility region of the ATPS.

Graphite oxide as a polymer-like hydrophilic system with peculiar coordinating properties

Structure-energetic and dynamic characteristics of graphite oxide model segments, as a basic element of which the C54 fragment of a carbon sheet was taken, and their hydration complexes involving a restricted number of water molecules are analyzed. The structure optimization and calculation of normal vibrations were performed at the density functional approximation with the B3LYP hybrid exchange-correlation functional with the basis that involves atomic functions of the 6–31G sets on the skeleton carbon atoms and terminal CH groups of the skeleton and of the 6–31G(d,p) sets on the atoms of all functional groups and water molecules. The ability of the hydroxyl groups of graphite oxide to initiate the reorganization of a three-dimensional H-bonded structure of water into the two-dimensional surface structure and to form very strong hydrogen bonds with water molecules providing their partial ionization was revealed.

On the similarity in some thermodynamic properties of N-dimethylureas and their bis-derivatives as solutes in water

Densities of aqueous 1,1-dimethylurea (1,1-DMU) solutions, with a molality ranged up to 0.2 mol·kg−1, were measured using an Anton Paar DMA 5000 M vibrating-tube densimeter. All the experiments were performed with a density uncertainty did not exceeding 0.03 kg·m−3·in the temperature range between (278.15 and 318.15) K at pressure to be 99.6 ± 0.8 kPa. The standard (partial at infinite dilution) molar volumes and expansibilities of 1,1-DMU in water were derived from the density data. The influence of nature of N-dimethyl-substitution in urea and achiral glycoluril (bisurea) molecules on structure-packing effects at forming the hydration complex was discussed. A nontrivial fact of the similarity in changing both volume (δV2o) and enthalpy (δΔsolH2o) effects of a solute dissolution in water during the isomeric replacements of 1,1-DMU → 1,3-dimethylurea and 2,8-dimethylglycoluril → 2,4-dimethyglycoluril was established. It was found that δV2o ~7 × 10−6 m3·mol−1 and δΔsolH2o ~11 kJ·mol−1 at T = 298.15 K in both transfer cases considered. The comparability in differently overlapping thermodynamic effects during the dissolution process at the specified replacements can be the main cause for the phenomenon discovered.

Kinetic Ionic Permeation and Interfacial Doping of Supported Graphene.

Due to its outstanding electrical properties and chemical stability, graphene finds widespread use in various electrochemical applications. Although the presence of electrolytes strongly affects its electrical conductivity, the underlying mechanism has remained elusive. Here, we employ terahertz spectroscopy as a contact-free means to investigate the impact of ubiquitous cations (Li+, Na+, K+, and Ca2+) in aqueous solution on the electronic properties of SiO2-supported graphene. We find that, without applying any external potential, cations can shift the Fermi energy of initially hole-doped graphene by ∼200 meV up to the Dirac point, thus counteracting the initial substrate-induced hole doping. Remarkably, the cation concentration and cation hydration complex size determine the kinetics and magnitude of this shift in the Fermi level. Combined with theoretical calculations, we show that the ion-induced Fermi level shift of graphene involves cationic permeation through graphene. The interfacial cations located between graphene and SiO2 electrostatically counteract the substrate-induced hole doping effect in graphene. These insights are crucial for graphene device processing and further developing graphene as an ion-sensing material.

Equimolecular cocrystal of cis- and trans-coordinated N,N′-dimethylglycolurils: Some standard thermodynamic properties in the aqueous solution between 278.15 K and 318.15 K

In this paper, we have discussed the results of densimetric and calorimetric studies of dissolution process in water for the (1:1) cocrystal consisting of two heterocyclic isomers being cis- and trans-coordinated dimethylglycolurils (2,8-DMGU and 2,6-DMGU, respectively) in the temperature range from (278.15 to 318.15) K at the ambient pressure. The standard (apparent or partial at infinite dilution) molar volumes and isobaric expansibilities of cocrystal as a solute in water were derived from the experimental data on solution density. Using thermochemical measurements, the standard molar enthalpies and isobaric heat capacities of the dissolution of cocrystal in water were also determined at the temperatures of interest. Based on the previously obtained similar results for aqueous 2,6-DMGU and 2,8-DMGU, a comparative analysis of packing and interaction changes in the hydration complex induced by the cocrystallization process has been carried out. It was found that the formation of cocrystal leads to a peculiar “synergism” in both volume and heat capacity effect of N,N′-dimethylglycoluril hydration at all temperatures studied.

Synthesis, Characterization, Hydrolytic Cleavage, and Biological Activity Studies of 2-[(1e)-N-{2-[(2-{(Z)-[1-(2-Hydroxyphenyl)Ethylidene] Amino}Ethyl)Amino]Ethyl}Ethanimidoyl]Phenol

A Schiff base ligand 2-[(1E)-N-{2-[(2-{(Z)-[1-(2-hydroxyphenyl) ethylidene] amino}ethyl)amino]ethyl} ethanimidoyl]phenol L was hydrolyzed by copper cation which lead to formation of 8,8-dichloro-2H,3H,5H,6H-1,3-diaza-2-cupracyclopenta[1,3-a]1,3-diaza-2-cupracyclopentane hydrate (Complex), characterized by UV, IR, Powder XRD and by elemental analysis. In vitro antioxidant and anticoagulant, activities of L were evaluated. Antioxidant potential of L was assessed by DPPH scavenging, β-carotene bleaching test, hydroxyl radical scavenging method, ABTS radical scavenging test, and by reducing power test. In vitro anticoagulant effect of L at the 84 µg/mL; showed the maximum prolongation of plasma recalcification time which is comparable with that of the anticoagulant drug; heparin. In conclusion, results of the present investigation indicate that the ligand L can be a potential anticoagulant agent.&#x0D; Keywords: Schiff base; Antioxidant; Free radicals; Anticoagulant.

Gibbsite (100) and Kaolinite (100) Sorption of Cadmium(II): A Density Functional Theory and XANES Study of Structures and Energies

Due to the potential toxicity of cadmium (Cd2+) and its presence in various waste products found in the environment, it is necessary to develop methods to attenuate and remediate Cd2+ waste. Sorption of Cd2+ to mineral surfaces is a potential route to accomplish this goal. This work focused on improving our molecular-scale understanding of the chemistry of Cd2+ interactions with gibbsite and kaolinite mineral surfaces. Plane-wave density functional theory (DFT) energy minimization calculations and molecular dynamics simulations were used to study the adsorption energies and the nature of the bonds between Cd2+ and the mineral surfaces for possible inner- and outer-sphere surface complexes. Models resulting from the DFT calculations were used to calculate theoretical XANES spectra that were compared with experimental Cd LIII XANES of aqueous Cd2+ as a proxy for outer-sphere Cd2+ hydrated complexes associated with the mineral surfaces. These studies suggest that Cd2+ would favorably bond to the (100) surfaces of both kaolinite and gibbsite through a bidentate mononuclear interaction. However, the results indicate that mixtures of surface complexes on these minerals are likely.

Modeling of pH of concentrated aqueous solutions of sodium metaborate

A phenomenological model is developed to take into account the effect of hydration complexes on the properties of electrolytes. The results of validation of the model are demonstrated for experimental pH values of aqueous solutions of sodium metaborate within a molal concentration range of 10−3–4.0 mol kg−1 at the temperatures 20, 25, and 50 °C.

Potential Instability of Gas Hydrates along the Chilean Margin Due to Ocean Warming

In the last few years, interest in the offshore Chilean margin has increased rapidly due to the presence of gas hydrates. We have modelled the gas hydrate stability zone off Chilean shores (from 33° S to 46° S) using a steady state approach to evaluate the effects of climate change on gas hydrate stability. Present day conditions were modelled using published literature and compared with available measurements. Then, we simulated the effects of climate change on gas hydrate stability in 50 and 100 years on the basis of Intergovernmental Panel on Climate Change and National Aeronautics and Space Administration forecasts. An increase in temperature might cause the dissociation of gas hydrate that could strongly affect gas hydrate stability. Moreover, we found that the high seismicity of this area could have a strong effect on gas hydrate stability. Clearly, the Chilean margin should be considered as a natural laboratory for understanding the relationship between gas hydrate systems and complex natural phenomena, such as climate change, slope stability and earthquakes.

Density Functional Theory Investigations on the Mechanism of Formation of Pa(V) Ion in Hydrous Solutions.

Due to the enormous threat of protactinium to the environment and human health, its disposal and chemistry have long been important topics in nuclear science. [PaO(H2O)6]3+ is proposed as the predominant species in hydrous and acidic solutions, but little is known about its formation mechanism. In this study, density functional theory (DFT) calculations demonstrate a water coordination-proton transfer-water dissociation mechanism for the formation of PaO3+ in hydrous solutions. First, Pa(V) ion preferentially forms hydrated complexes with a coordination number of 10. Through hydrogen bonding, water molecules in the second coordination sphere easily capture two protons on the same coordinated H2O ligand to form [PaO(H2O)9]3+. Water dissociation then occurs to generate the final [PaO(H2O)6]3+, which is the thermodynamic product of Pa(V) in hydrous solutions.

Hydration Energies of Iron Hydroxide Cation: A Guided Ion Beam and Theoretical Investigation.

We present experimental collision-induced dissociation (CID) cross sections as a function of kinetic energy for FeOH+(H2O) n, where n = 1-4, with xenon (Xe) obtained using a guided ion beam tandem mass spectrometer. Complexes with n = 2-4 are observed to undergo water loss, followed by sequential water loss at higher collision energies. In addition, we find that loss of the neutral hydroxide group is competitive with the primary water loss for n = 1. Bond dissociation energies (BDEs) at 0 K are derived through modeling of the experimental cross sections after accounting for multiple collisions, kinetic shifts, and reactant internal and kinetic energy distributions. Quantum chemical calculations include geometry optimizations performed at the B3LYP/6-311+G(d,p) level of theory and then used for single point calculations at B3LYP, B3P86, MP2, and CCSD(T) levels with a 6-311+G(2d,2p) basis set. Additional geometry optimizations at the cam-B3LYP/def2-TZVP were also performed as well as empirical dispersion corrections at all levels. The various structures for the FeOH+(H2O) n complexes and their relative energies are discussed in detail. We also derive experimental BDEs for the OH loss from FeOH+(H2O) n, with n = 2-4, using the experimental BDE of n = 1 in combination with literature data for water loss from Fe+(H2O) n species. Measurements of BDEs for hydroxide and water loss from FeOH+(H2O) n ( n = 1-4) are the first such experimental measurements. Theoretically calculated BDEs are in reasonable agreement for water loss from both FeOH+(H2O) n and Fe+(H2O) n complexes and for D0(Fe+-OH) but are too low for the loss of OH from the larger hydrated complexes.

Conformational equilibria in o-anisic acid and its monohydrated complex: the prevalence of the trans-COOH form.

The conformation of ortho-anisic acid and its monohydrated clusters generated in a supersonic jet has been studied by rotational spectroscopy to analyze the structural implications of ortho substitution. The dominant monomer species shows a trans-COOH arrangement stabilized by an intramolecular O-HO hydrogen bond from the acid to the methoxy group. The spectra of two non-planar skeleton monomer forms with a cis-COOH arrangement have also been detected. A tunneling doublet has been observed for the most stable cis-COOH conformer. The periodic potential energy function for the COOH internal rotation connecting these cis forms has been estimated from the experimental data. For the first time a water complex with an acid in a trans-COOH configuration has been observed. This is more abundant than the other weak form observed for the complex, characterized by a cis-COOH arrangement. The observation of the rotational spectra of salicylic acid, methyl salicylate and methyl 2-methoxybenzoate, formed upon heating of ortho-anisic acid, gives additional interest in the chemistry of ortho substituted benzoic acids.

The State of Copper Ions in Aqueous and Aqueous Ammonia Solutions of Copper Acetate

Stabilization of Cu2+ ions in aqueous and aqueous ammonia solutions of copper acetate was studied for a wide range of ammonia concentrations. The structure of copper acetate hydrate complexes was shown to markedly change upon dissolution in water. In aqueous solutions, copper is stabilized as strongly bound Cu2+ associates (dimers) in a distorted octahedral environment composed of water molecules and acetate groups oxygen atoms in equatorial positions with strong exchange interaction via acetate groups. In solutions of copper acetate in aqueous ammonia, the concentration of ammonia has a crucial effect on the ordering of Cu2+ ions in associates. At high ammonia concentration, disordered copper tetra-ammoniate associates with the $${d_{{x^2} - {y^2}}}$$ ground state are formed, whereas at low ammonia concentration, bulky Cu2+ ion associate structures are generated, with the $${d_{{x^2} - {y^2}}}$$ ground state, hydroxyl groups in the equatorial plane, and water molecules in the axial positions.

Humidity effect on ion behaviors of moisture-driven CO2 sorbents.

Ion hydration is a fundamental process in many natural phenomena. This paper presents a quantitative analysis, based on atomistic modeling, of the behavior of ions and the impact of hydration in a novel CO2 sorbent. We explore moisture-driven CO2 sorbents focusing on diffusion of ions and the structure of ion hydration complexes forming inside water-laden resin structures. We show that the stability of the carbonate ion is reduced as the water content of the resin is lowered. As the hydration cloud of the carbonate ion shrinks, it becomes energetically favorable to split a remaining water molecule and form a bicarbonate ion plus a hydroxide ion. These two ions bind less water than a single, doubly charged carbonate ion. As a result, under relatively dry conditions, more OH- ions are available to capture CO2 than in the presence of high humidity. Local concentrations of dissolved inorganic carbon and water determine chemical equilibria. Reaction kinetics is then driven to a large extent by diffusion rates that allow water and anions to move through the resin structure. Understanding the basic mechanics of chemical equilibria and transport may help us to rationally design next-generation efficient moisture-driven CO2 sorbents.

Collision induced dissociation of positive ions of dimethylnitramine, a model system for nitramine energetic molecules

Positive ions of dimethylnitramine (DMNA), a model system for nitramine energetic molecules, have been produced in the gas phase by electrospray ionization. Protonated dimethylnitramine ion [DMNA+H]+ and its hydrated complex [2DMNA+H2O+2H]2+ have been investigated by both low energy collision induced dissociation (CID) and ab initio MP2 level of theory. Ion structure has been calculated. Fragments have been experimentally determined and dissociation mechanisms have been elucidated. Interestingly, the favored fragmentation pathways depend on the local environment of the ion: the hydrated complex primarily loses NO via nitro nitrite isomerization, while only OH elimination is observed in the case of protonated DMNA.

Highly Enantioselective [3+2] Annulation of Indoles with Quinones to Access Structurally Diverse Benzofuroindolines

AbstractA facile and efficient method to produce optically pure benzofuroindolines, especially those without 3‐substituents that are susceptible to rearomatization, through [3+2] annulation of indoles with quinones is described. The suitable combination of a BOX ligand CuII hydrate complex and freshly activated molecular sieves functions to give controllably dynamic release of water, which enables the success of this reaction. This reaction can be performed on a gram scale with only 0.5 mol % catalyst loading.