Water Exchange Reactions Research Articles

Isothermal compressibility, internal pressure studies of aqueous rare earth nitrate solutions at 298.15 K: An attempt to estimate ionic radii and understand inner– and outer–sphere exchange water structural interactions

In this communication, we report our analysis and results concerning the determination of ionic radii in aqueous solution phase for Lanthanum (La+3), Neodymium (Nd+3), Erbium (Er+3) and Ytterbium (Yb+3) ions in presence of nitrate (NO3-) anion at 298.15 K. The literature data for density, adiabatic compressibility, and specific heat capacity of solutions at constant pressure have been used to compute isothermal compressibility, internal pressure of solutions in limiting concentration range. The apparent molar isothermal compressibility of electrolytes and hydration numbers have been obtained. The electrostriction for rare earth cations and intrinsic volumes have been calculated using thermodynamic equations. The ionic radii of cations have been obtained using the ionic partial molar volume data of NO3- ions and the results are compared with those obtained for rare earth chlorides. The two series affect is also observed for ionic radii and internal pressure. The results have been explained on the basis of water structural effects due to electrostatic field and water dipole interaction between the inner– and outer–sphere water exchange reaction.

Progressive enrichment in 18O and 2H in xylem water along sap flow paths in Fagus sylvatica trees

AbstractIsotopic signatures of xylem water in different tree compartments such as roots, boles and branches, differ due to physiological and physical processes occurring inside trees. Accordingly, we hypothesised that the extent of such differences among the isotopic signatures of tree compartments is coherent with the distance travelled by the water inside trees and to its residence time. To test this, we compared the O–H isotopic composition of xylem water collected using an in‐situ water extraction method from roots, boles and branches of Fagus sylvatica trees growing on three geomorphological units of the Weierbach experimental catchment, Luxembourg. There was progressive 18O and 2H enrichment in xylem waters along the root–branch flow path for all the studied trees. Three explanations could be considered for this progressive enrichment: internal fractionation by xylem–phloem water exchange, chemical reactions of metabolic pathways and variable ages of water retained in the xylem, reflecting historical variation in isotopic composition of uptake water. Support for the hypothesis of isotopic fractionation linked to xylem–phloem water exchange and chemical reactions is that enrichment was generally consistent with the distance travelled by the water and to its residence time inside the trees. However, the relative enrichment of 2H and 18O was not consistent along the flow path, with Δ2H/Δ18O ~7.5 from the soil into the roots and bole and ~4.7–6.5 for pathways that included smaller branches. This contrast suggests different processes controlling above‐ground isotopic enrichment. In particular, the slope of ~7.5 in the lower tree is also consistent with variation in tree water uptake varying along the local meteoric water line, with water in the roots being closer to the composition of rainfall close to the time of sampling and water in the bole being closer to the composition of rainfall from the previous summer. The timing of root and bole sampling in early spring, just before leaf‐out, means sap flow was very slow and makes it plausible that varying‐age water was present in the tree at that time. We also compared the O–H isotopic composition of those samples with the ones of the potential water sources to identify the origin of the water uptaken. The latter varied during the 3 years of sampling, with a preferential uptake from near‐surface waters. Our results suggest multiple biochemical, physiological and physical processes may play fundamental roles in the isotopic composition of xylem water within trees.

Investigation of water substitution at RuII complexes by conceptual density function theory approach.

In this paper, we investigated water exchange reactions and substitution of aqua RuII complexes of general formula [Ru(terpy)(N^N)(H2 O)]2+ (where N^N=ethylenediamine (en), 1,2-(aminomethyl)pyridine (ampy) and 2,2'-bipyridine (bipy)) by ammonia and thioformaldehyde. These reactions were studied in detail by applying conceptual density functional theory. This approach enabled us to gain further insight into the underlying reaction mechanism at the microscopic level (involving only direct participants of the reaction, without the influence of the solvent) and to put the concept of reaction mechanism on a quantitative basis. The course of the chemical reaction along the reaction coordinate ξ, is rationalized in terms of reaction energy, force, dipole moment, and reaction electronic flux (REF). The results yield and characterize the significant influence of an intermolecular hydrogen bond formed between the entering and the spectator ligand to the overall energy barrier of the reactions.

Mechanistic insight on the water exchange mechanism of [Zn(tren)H2O]2+ and related complexes from a DFT study

The mechanisms for water exchange on [Zn(L)H2O]2+⋅H2O (L = tren: tris(2-aminoethyl)amine, trep: tris(2-phosphinoethyl)phosphine, and tres: tris(2-arsinoethyl)arsine) were studied using density functional theory (B3LYP/6-311 + G**) and evaluated by MP2 and B3LYP(PCM) energy calculations. The activation barriers for the water exchange reaction on [Zn(L)H2O]2+⋅H2O (L = tren, trep and tres) are (B3LYP/6-311 + G**) 9.9, 10.13 and 11.23 kcal mol−1, respectively. Topological analyses of the investigated ground state complexes were performed. The energy and structural data support an associative interchange (Ia) water exchange pathway.

Strong Lewis and Brønsted Acidic Sites in the Borosulfate Mg3 [H2 O→B(SO4 )3 ]2.

Borosulfates provide fascinating structures and properties that go beyond a pure analogy to silicates. Mg3[H2O→B(SO4)3]2 is the first borosulfate featuring a boron atom solely coordinated by three tetrahedra. Thus, the free Lewis acidic site forms a Lewis acid–base adduct with a water molecule. This is unprecedented for borosulfate chemistry and even for borates. Quantum chemical calculations on water exchange reactions with BF3 and B(C6F5)3 revealed a higher Lewis acidity for the borosulfate anion. Moreover, proton exchange reactions showed a higher Brønsted acidity than comparable silicates or phosphates. Additionally, Mg3[H2O→B(SO4)3]2 was characterised by X‐ray diffraction, infrared spectroscopy, thermogravimetric analysis, and density functional theory (DFT) calculations.

Tuning the lability of a series of Ru(II) polypyridyl complexes: a comparison of experimental-kinetic and DFT-predicted reaction mechanisms

This report deals with a comparison of experimentally obtained kinetic and activation parameter data, and theoretical DFT computations, in terms of mechanistic information on the water exchange and water displacement reactions by thiourea for a series of complexes of the type [RuII(terpy)(N^N)(H2O)]2+, where terpy = 2,2′:6′,2″-terpyridine and N^N represents ethylenediamine (en), 2-(aminomethyl)pyridine (ampy), 2,2′-bipyridine (bipy), 1,10-phenantroline (phen), and N,N,N′,N′-tetramethylethylenediamine (tmen). The complexes were all isolated in the form of [Ru(terpy)(N^N)Cl]X (X = Cl– or ClO4 –) compounds and fully characterized in both the solid state and in solution. The DFT calculations revealed further mechanistic insight into the water exchange reactions as well as the water displacement reactions by thiourea. Both the experimental activation parameters and the DFT calculations suggest the operation of an associative interchange (Ia ) mechanism for both reaction types studied.

Effects of soil moisture, needle age and leaf morphology on carbon and oxygen uptake, incorporation and allocation: a dual labeling approach with 13CO2 and H218O in foliage of a coniferous forest.

The carbon and oxygen isotopic composition of water and assimilates in plants reveals valuable information on plant responses to climatic conditions. Yet, the carbon and oxygen uptake, incorporation and allocation processes determining isotopic compositions are not fully understood. We carried out a dual-isotope labeling experiment at high humidity with 18O-enriched water (H218O) and 13C-enriched CO2 (13CO2) with attached Scots pine (Pinus sylvestris L.) branches and detached twigs of hemiparasitic mistletoes (Viscum album ssp. austriacum) in a naturally dry coniferous forest, where also a long-term irrigation takes place. After 4h of label exposure, we sampled previous- and recent-year leaves, twig phloem and twig xylem over 192h for the analysis of isotope ratios in water and assimilates. For both species, the uptake into leaf water and the incorporation of the 18O-label into leaf assimilates was not influenced by soil moisture, while the 13C-label incorporation into assimilates was significantly higher under irrigation compared with control dry conditions. Species-specific differences in leaf morphology or needle age did not affect 18O-label uptake into leaf water, but the incorporation of both tracers into assimilates was two times lower in mistletoe than in pine. The 18O-label allocation in water from pine needles to twig tissues was two times higher for phloem than for xylem under both soil moisture conditions. In contrast, the allocation of both tracers in pine assimilates were similar and not affected by soil moisture, twig tissue or needle age. Soil moisture effects on 13C-label but not on 18O-label incorporation into assimilates can be explained by the stomatal responses at high humidity, non-stomatal pathways for water and isotope exchange reactions. Our results suggest that non-photosynthetic 18O-incorporation processes may have masked prevalent photosynthetic processes. Thus, isotopic variation in leaf water could also be imprinted on assimilates when photosynthetic assimilation rates are low.

Current Status of AMOEBA-IL: A Multipolar/Polarizable Force Field for Ionic Liquids.

Computational simulations of ionic liquid solutions have become a useful tool to investigate various physical, chemical and catalytic properties of systems involving these solvents. Classical molecular dynamics and hybrid quantum mechanical/molecular mechanical (QM/MM) calculations of IL systems have provided significant insights at the atomic level. Here, we present a review of the development and application of the multipolar and polarizable force field AMOEBA for ionic liquid systems, termed AMOEBA–IL. The parametrization approach for AMOEBA–IL relies on the reproduction of total quantum mechanical (QM) intermolecular interaction energies and QM energy decomposition analysis. This approach has been used to develop parameters for imidazolium– and pyrrolidinium–based ILs coupled with various inorganic anions. AMOEBA–IL has been used to investigate and predict the properties of a variety of systems including neat ILs and IL mixtures, water exchange reactions on lanthanide ions in IL mixtures, IL–based liquid–liquid extraction, and effects of ILs on an aniline protection reaction.

Hydrogeochemical characterization of the Complexe Terminal aquifer system in hyper-arid zones: the case of wadi Mya Basin, Algeria

The groundwater resources management of the wadi Mya basin, located in the North East of the Algerian Sahara and witnesses a hyper-arid climate, poses salinity problems. In order to identify the mechanisms involved in causing these problems, physicochemical analyses were performed on 114 water samples. The hydrogeological system of Complexe Terminal of the wadi Mya basin is very weakly recharged and contains two highly mineralized aquifer levels. These are the Mio-Pliocene sands aquifer and the underlying Senonian carbonates aquifer. They are separated to a great extent by an intermediate evaporitic Eocene layer. Both aquifers show analogous hydrochemical facies indicating, thus, intercommunication between them. The overall mineralization is dominated by chloride sulfate, sodium and magnesium facies and is explained by the dissolution of the evaporitic components of the intercalations in the aquifer matrix, but also by the old character (fossil) of water and cationic exchange reactions resulting from water-rock interactions over time. The salinity variation exhibit a trend that conform to the groundwater flow direction. Vertical transfer of water, sometimes saltier downward from the phreatic aquifer, sometimes softer upward from the deep Albian sandstone aquifer, was noticed. Areas of low mineralization were also identified in the western edge of the basin, where wadi’s floods, which drain the eastern side of the M’zab dorsal, are wide spread.

Density Functional Theory Studies on the Real and Apparent Water-Exchange Reaction Kinetics of Al3+ in Aqueous Solution

The dissociative (D) mechanistic water-exchange kinetics of aquated Al3+ in aqueous solution is systematically studied using the density functional theory-quantum chemical cluster model (DFT-CM) method. The modeled pathways include dehydration of the hexacoordinated Al(H2O)63+ and successive hydration of the pentacoordinated Al(H2O)53+. For the hydration of Al(H2O)53+, the attacking pathways corresponding to the second-shell solvent water molecules at different sites are investigated. The gas phase-supermolecule-polarizable continuum model (GP-SM-PCM) is used to simulate the explicit and bulk solvation effects. The reactant, transition state, and product geometries of the modeled reaction pathways are optimized at the B3LYP/6-311+G(d,p) level of theory. The real and apparent water-exchange reaction mechanisms of Al3+ are analyzed based on the Gibbs free energy changes for the dehydration and hydration pathways. The possible ligand competition with the solvent water molecules in the formation of aqueous Al...

Exponential Scaling of Water Exchange Rates with Ion Interaction Strength from the Perspective of Dynamic Facilitation Theory.

Water exchange reactions around ionic solutes are ubiquitous in aqueous solution-phase chemistry. However, the extreme sensitivity of exchange rates to perturbations in the chemistry of an ionic solute is not well understood. We examine water exchange around model ions within the language of dynamic facilitation theory, typically used to describe glassy and other systems with collective, facilitated dynamics. Through the development of a coarse-grained, kinetically constrained lattice model of water exchange, we show that the time scale for water exchange scales exponentially with the strength of the solute-solvent interactions.

Water exchange in lanthanide complexes for MRI applications. Lessons learned over the last 25 years.

The water exchange rates of water molecules coordinated to the metal ion in lanthanide complexes have been profusely investigated during the last 25 years, especially in the case of Gd3+ and Eu3+ complexes. This is mainly related to the important application of some Gd3+ complexes as contrast agents in magnetic resonance imaging (MRI), and the intensive investigation of Eu3+ complexes as contrast agent candidates providing contrast through the chemical exchange saturation transfer mechanism (CEST). Both applications require a fine tunning of the exchange rate of the coordinated water molecule to yield optimal response. Herein we review the progress made in this field to control water exchange in a rational way through ligand design, providing relationships between the observed trends, the structures of the complexes and the mechanisms responsible for the water exchange reaction.

Insight into the structures and reactivities of aqueous Al(III)-carboxylate complexes from cluster-based ab initio computational studies – Implications for the ligand-promoted mineral dissolution mechanism

The stable geometries of a series of mononuclear bidentate chelating Al(III)-carboxylate complexes in aqueous solution are optimized and their transition-states for water-exchange reactions are modeled with the density functional theory – quantum chemical cluster model (DFT-CM) method. The studied carboxylates include oxalate, malonate, succinate, phthalate, salicylate and benzoate. Thermodynamic stability constants Kaq and water-exchange reaction rate constants kex of the tested Al(III)-carboxylate complexes are estimated from calculated Gibbs free energy changes. The estimated kex values suggest that the coordination of dicarboxylate and salicylate ligands to Al3+ leads to the labilization of inner-shell coordinated waters and that the cis waters of chelate rings are more labile than trans waters. From estimated log Kaq and log kex values of aqueous mononuclear Al(III)-carboxylate complexes, linear correlations between log Kaq, log kex values and experimental apparent rate constants kL of carboxylate ligand-promoted δ-Al2O3 mineral dissolution are established. Based on the calculation results, cis labilizing effects of the carboxylate ligands, strong “log kL ∼ log Kaq” correlations, and weak “log kL ∼ log kex” correlations are discussed. This work offers further insight into intrinsic relationships between mineral surface and aqueous metal complexes and furthers understanding of mineral dissolution kinetics at the molecular level.

Quantum Chemical Study of the Water Exchange Mechanism of the Neptunyl(VI) and -(V) Aqua Ions.

The water exchange reaction of the neptunyl(VI) and -(V) aqua ions was investigated with quantum chemical methods. Associative ( a) and dissociative ( d) exchange mechanisms were studied. The geometries and vibrational frequencies were computed with density functional theory (DFT) and multiconfiguration self-consistent field (MCSCF) methods. The Gibbs activation energies (Δ G‡) for a and d pathways were calculated with DFT and wave function theory (WFT), extended general multiconfiguration quasi-degenerate second-order perturbation theory (XGMC-QDPT2) including spin-orbit (SO) coupling at the SO configuration interaction (CI) level. The DFT-WFT agreement for Δ G‡ was poor for the investigated functionals except for LC-BOP-LRD. Due to ligand-field effects, Δ G‡ for the associatively activated exchange reaction of NpO2(OH2)52+ with a fδ1 electron configuration is higher than for the actinyl(VI) aqua ions of U, Pu, and Am exhibiting f0, fδ2, and fδ2fϕ1 electron configurations.

Molecular dynamics investigation of water-exchange reactions on lanthanide ions in water/1-ethyl-3-methylimidazolium trifluoromethylsufate ([EMIm][OTf]).

We report a kinetic study of the water exchange on lanthanide ions in water/[1-ethyl-3-methylimidazolium][trifluoromethylsufate] (water/[EMIm][OTf]). The results from 17O-NMR measurements show that the water-exchange rates in water/[EMIm][OTf] increase with decreasing size of the lanthanide ions. This trend for water-exchange is similar to the previously reported trend in water/1-ethyl-3-methylimidazolium ethyl sulfate (water/[EMIm][EtSO4]) but opposite to that in water. To gain atomic-level insight into these water-exchange reactions, molecular dynamics simulations for lanthanide ions in water/[EMIm][OTf] have been performed using the atomic-multipole-optimized-energetics-for-biomolecular-application polarizable force field. Our molecular dynamics simulations reproduce the experimental water-exchange rates in terms of the trend and provide possible explanations for the observed experimental behavior. The smaller lanthanide ions in water/[EMIm][OTf] undergo faster water exchange because the smaller lanthanide ions coordinate to the first shell [OTf]- anions more tightly, resulting in a stronger screening effect for the second-shell water. The screening effect weakens the interaction of the lanthanide ions with the second-shell water molecules, facilitating the dissociation of water from the second-shell and subsequent association of water molecules from the outer solvation shells.

Density functional theory studies on the solvent effects in Al(H2O)63+ water-exchange reactions: the number and arrangement of outer-sphere water molecules.

Density functional theory (DFT) calculations combined with cluster models are performed at the B3LYP/6-311+G(d,p) level for investigating the solvent effects in Al(H2O)63+ water-exchange reactions. A "One-by-one" method is proposed to obtain the most representative number and arrangement of explicit H2Os in the second hydration sphere. First, all the possible ways to locate one explicit H2O in second sphere (Nm' = 1) based on the gas phase structure (Nm' = 0) are examined, and the optimal pathway (with the lowest energy barrier) for Nm' = 1 is determined. Next, more explicit H2Os are added one by one until the inner-sphere is fully hydrogen bonded. Finally, the optimal pathways with Nm' = 0-7 are obtained. The structural and energetic parameters as well as the lifetimes of the transition states are compared with the results obtained with the "Independent-minimum" method and the "Independent-average" method, and all three methods show that the pathway with Nm' = 6 may be representative. Our results give a new idea for finding the representative pathway for water-exchange reactions in other hydrated metal ion systems.

Investigation of mono-, bis- and tris-glycinatochromium(III): Comparisons of computational and experimental results

The synthesis and characterization of mono-, bis- and tris-glycinatochromium(III) complexes by elemental analysis, UV–Vis, electron paramagnetic resonance (EPR), ATR-FTIR and Raman spectroscopy has been performed in this work. IR stretching bands obtained from DFT calculations of the mono-, bis- and tris-glycinatochromium(III) complexes are in good agreement with experimental data. Different mechanistic pathways were explored for the water exchange reactions of [Cr(+NH3CH2COO−)(H2O)5]3+ and its conjugate base species including, associative interchange (Ia), and dissociative (D) mechanisms. The lowest activation enthalpies for the mono- and bis-complexes are obtained for the Ia pathways with explicit outer sphere solvation (88 and 76kJmol−1), which are in good agreement with the experimental values (87 and 75kJmol−1). In comparison, tris-glycinatochromium(III) undergoes aquation via the dissociative (D) mechanism. Investigation of these systems in the pH range ∼3.0 to ∼8.5 by UV–Vis monitoring, helps identify the speciation of these complexes in physiological environments.

Quantum Chemical Investigation of the Transition States and Intermediates for the Reaction of the Nitrosonium Ion with the Pentaammineazidocobalt(III) Ion.

The water exchange reaction on Co(NH3)5OH23+ was investigated with various density functionals and basis sets. A Gibbs activation energy (ΔG⧧) agreeing with experiment was obtained with the long-range-corrected functionals ωB97X-D3 and LC-BOP-LRD, SMD hydration, and modified Karlsruhe def2-TZVP basis sets. This computational technique was then applied to the reaction of NO+ with Co(NH3)5N32+. All of the possible pathways were investigated, NO+ attack at the terminal N of Co(NH3)5N32+ via the E and the Z isomers of the transition states, and NO+ attack at the bound N of azide, also via both isomers. The most favorable pathway proceeds via the attack at the bound N via the Z isomer. This leads to the intermediate with an oxatetrazole ligand bound to Co(III) at the N in the 3-position, Co(NH3)5(cycl-N4O)3+, which undergoes N2 elimination to yield the Co(NH3)5N2O3+ intermediate. The subsequent substitution of N2O by water follows the Id mechanism with retention of the configuration. No evidence for the existence of the square-pyramidal pentacoordinated intermediate Co(NH3)53+ was found. All of the investigated intermediates, Co(NH3)5N23+, Co(NH3)5[E-N(N2)(NO)]3+, Co(NH3)5(E-ON4)3+, Co(NH3)5ON23+, Co(NH3)5(cycl-N4O)3+, and Co(NH3)5N2O3+, exhibit short lifetimes of less than ∼60 μs and react via the Id mechanism.

Quantum Chemical Study of the Water Exchange Mechanism of the Americyl(VI) Aqua Ion.

The water exchange reaction of the americyl(VI) aqua ion was investigated with quantum chemical methods, density functional theory (DFT), and wave function theory (WFT). Associative and dissociative substitution mechanisms were studied, whereby DFT produced inaccurate results for the associative mechanism in contrast to WFT. The Gibbs activation energies (ΔG‡) for the dissociative (D) and the associative interchange (Ia) mechanisms, computed with WFT taking into account static and dynamic electron correlation, near-degeneracy, and spin-orbit coupling, are equal within the error limits of the calculations. ΔG‡ for the water exchange of americyl(VI) via the dissociative mechanism is considerably lower than those for uranyl(VI) and plutonyl(VI) (for which the Ia mechanism is preferred) due to ligand-field effects. On the basis of the present computations, it is not possible to distinguish the Ia from the D mechanism for americyl(VI). In contrast to two other theoretical studies, the dissociative mechanism cannot be ruled out.

Further Theoretical Studies of the Aquation of Chromium(III) Chloride Nutritional Supplement: Effect of pH and Solvation

We have explored speciation of halochromium(III) complexes under physiological conditions involving both conjugate-base formation and halide-water exchange using DFT. Conjugate base formation is spontaneous under neutral and alkaline conditions. Several different pathways were explored for the water exchange reaction of cis- or trans-Cr(III) complexes in the series trans-[Cr(H2O)3(OH)X2]0 (X=Cl− or Br−) and cis- or trans-[Cr(H2O)4(OH)X]+, (X= F−, Cl−, Br−, or I−) including, associative interchange (Ia), dissociative interchange (Id) and dissociative (D) mechanisms. We have also investigated nucelophilic attack by OH− on [Cr(H2O)5X]+ species, (X=Cl− or Br−). The lowest overall activation enthalpies (ΔH≠) obtained for the F and Cl systems of [Cr(H2O)4(OH)X]+, are from the Ia pathway, whereas for the Br and I systems the Id pathway was found, consistent with experiment. The importance of outer sphere solvation was investigated with the addition of up to five explicit water molecules in the second coordination sphere. The ΔH≠ values for the aquation of cis-[Cr(H2O)4(OH)X]+…3H2O, are lower than the corresponding values for [Cr(H2O)5X]2+. This indicates that there will be greater speciation of chromium(III) halides under physiological conditions. These values also imply that chromium(III) derivatives that may be active in the treatment of physiological disorders such as Type(II) diabetes will be formed at different rates depending on the identity of the starting halide.