Primary Solvation Sphere Research Articles

Dominant Role of Entropy in Stabilizing Sugar Isomerization Transition States within Hydrophobic Zeolite Pores

Lewis acid sites in zeolites catalyze aqueous-phase sugar isomerization at higher turnover rates when confined within hydrophobic rather than within hydrophilic micropores; however, relative contributions of competitive water adsorption at active sites and preferential stabilization of isomerization transition states have remained unclear. Here, we employ a suite of experimental and theoretical techniques to elucidate the effects of coadsorbed water on glucose isomerization reaction coordinate free energy landscapes. Transmission IR spectra provide evidence that water forms extended hydrogen-bonding networks within hydrophilic but not hydrophobic micropores of Beta zeolites. Aqueous-phase glucose isomerization turnover rates measured on Ti-Beta zeolites transition from first-order to zero-order dependence on glucose thermodynamic activity, as Lewis acidic Ti sites transition from water-covered to glucose-covered, consistent with intermediates identified from modulation excitation spectroscopy during in situ attenuated total reflectance IR experiments. First-order and zero-order isomerization rate constants are systematically higher (by 3-12×, 368-383 K) when Ti sites are confined within hydrophobic micropores. Apparent activation enthalpies and entropies reveal that glucose and water competitive adsorption at Ti sites depend weakly on confining environment polarity, while Gibbs free energies of hydride-shift isomerization transition states are lower when confined within hydrophobic micropores. DFT calculations suggest that interactions between intraporous water and isomerization transition states increase effective transition state sizes through second-shell solvation spheres, reducing primary solvation sphere flexibility. These findings clarify the effects of hydrophobic pockets on the stability of coadsorbed water and isomerization transition states and suggest design strategies that modify micropore polarity to influence turnover rates in liquid water.

Evaluating the Free Energies of Solvation and Electronic Structures of Lithium-Ion Battery Electrolytes.

Adaptive biasing force molecular dynamics simulations and density functional theory calculations were performed to understand the interaction of Li(+) with pure carbonates and ethylene carbonate (EC)-based binary mixtures. The most favorable Li carbonate cluster configurations obtained from molecular dynamics simulations were subjected to detailed structural and thermochemistry calculations on the basis of the M06-2X/6-311++G(d,p) level of theory. We report the ranking of these electrolytes on the basis of the free energies of Li-ion solvation in carbonates and EC-based mixtures. A strong local tetrahedral order involving four carbonates around the Li(+) was seen in the first solvation shell. Thermochemistry calculations revealed that the enthalpy of solvation and the Gibbs free energy of solvation of the Li(+) ion with carbonates are negative and suggested the ion-carbonate complexation process to be exothermic and spontaneous. Natural bond orbital analysis indicated that Li(+) interacts with the lone pairs of electrons on the carbonyl oxygen atom in the primary solvation sphere. These interactions lead to an increase in the carbonyl (C=O) bond lengths, as evidenced by a redshift in the vibrational frequencies [ν(C=O)] and a decrease in the electron density values at the C=O bond critical points in the primary solvation sphere. Quantum theory of atoms in molecules, localized molecular orbital energy decomposition analysis (LMO-EDA), and noncovalent interaction plots revealed the electrostatic nature of the Li(+) ion interactions with the carbonyl oxygen atoms in these complexes. On the basis of LMO-EDA, the strongest attractive interaction in these complexes was found to be the electrostatic interaction followed by polarization, dispersion, and exchange interactions. Overall, our calculations predicted EC and a binary mixture of EC/dimethyl carbonate to be appropriate electrolytes for Li-ion batteries, which complies with experiments and other theoretical results.

Thermodynamic and Spectroscopic Studies of Lanthanides(III) Complexation with Polyamines in Dimethyl Sulfoxide

The thermodynamic parameters of complexation of Ln(III) cations with tris(2-aminoethyl)amine (tren) and tetraethylenepentamine (tetren) were determined in dimethyl sulfoxide (DMSO) by potentiometry and calorimetry. The excitation and emission spectra and luminescence decay constants of Eu3+ and Tb3+ complexed by tren and tetren, as well as those of the same lanthanides(III) complexed with diethylenetriamine (dien) and triethylenetetramine (trien), were also obtained in the same solvent. The combination of thermodynamic and spectroscopic data showed that, in the 1:1 complexes, all nitrogens of the ligands are bound to the lanthanides except in the case of tren, in which the pendant N is bound. For the larger ligands (trien, tren, tetren) in the higher complexes (ML2), there was less complete binding by available donors, presumably due to steric crowding. FT-IR studies were carried out in an acetonitrile/DMSO mixture, suitably chosen to follow the changes in the primary solvation sphere of lanthanide(III) due to complexation of amine groups. Results show that the mean number of molecules of DMSO removed from the inner coordination sphere of lanthanides(III) is lower than ligand denticity and that the coordination number of the metal ions increases with amine complexation from approximately 8 to approximately 10. Independently of the number and structure of the amines, linear trends, similar for all lanthanides, were obtained by plotting the values of DeltaGj degrees, DeltaHj degrees, and TDeltaSj degrees for the complexation of ethylenediamine (en), dien, trien, tren, and tetren as a function of the number of amine metal-coordinated nitrogen atoms. The main factors on which the thermodynamic functions of lanthanide(III) complexation reactions in DMSO depend are discussed.

Solvation of Lithium Ion in Organic Electrolyte Solutions and Its Isotopie Reduced Partition Function Ratios Studied by ab initio Molecular Orbital Method

To explore local structures around lithium ions and to estimate lithium isotopic reduced partition function ratios (RPFRs) ofsolvated lithium ions in ethylene carbonate (EC), methylethyl carbonate (MEC) and EC/MEC mixed solvent systems, ab initio molecular orbital calculations at the HF/6-31G(d) level of theory were carried out. Both EC and MEC were coordinated to lithium ions using their carboxyl oxygens and the Li-O bond distance increase with increasing solvation number up to 4 in the primary solvation sphere both in EC and MEC systems. Binding energy calculations suggested that EC was preferentially coordinated to the lithium ion in the EC/MEC mixed solvent system. RPFRs of solvated lithium ions were convex functions of the solvation number between 1 and 4 and took the maxima at 3 both in EC and MEC systems. The RPFR value in EC/MEC mixed solvent system was estimated to be 1.07818 at 25°C.

Solvation of Lithium Ion in Organic Electrolyte Solutions and Its Isotopic Reduced Partition Function Ratios Studied by ab initio Molecular Orbital Method.

To explore local structures around lithium ions and to estimate lithium isotopic reduced partition function ratios (RPFRs) ofsolvated lithium ions in ethylene carbonate (EC), methylethyl carbonate (MEC) and EC/MEC mixed solvent systems, ab initio molecular orbital calculations at the HF/6-31G(d) level of theory were carried out. Both EC and MEC were coordinated to lithium ions using their carboxyl oxygens and the Li-O bond distance increase with increasing solvation number up to 4 in the primary solvation sphere both in EC and MEC systems. Binding energy calculations suggested that EC was preferentially coordinated to the lithium ion in the EC/MEC mixed solvent system. RPFRs of solvated lithium ions were convex functions of the solvation number between 1 and 4 and took the maxima at 3 both in EC and MEC systems. The RPFR value in EC/MEC mixed solvent system was estimated to be 1.07818 at 25°C.

Ab initio Molecular Orbital Calculations of Reduced Partition Function Ratios of Hydrated Lithium Ions in Ion Exchange Systems

Abstract Molecular orbital (MO) calculations at the HF/6-31G(d) level were carried out for the aquolithium ions, Li+(H2O)n (n = 3, 4, 5, 6, 8, 10 and 12) and the aquolithium ions interacting with the methyl sul­fonate ion (MeS-), Li+MeS-(H2O)n (n = 0, 3,4, 5, 6, 7, 8 and 10) which were, respectively, intended to be substitutes for lithium species in the solution and resin phases of ion exchange systems for lithium isotope separation. For each of the species considered, at least one optimized structure with no negative frequency was obtained, and the 7Li-to-6Li isotopic reduced partition function ratio (RPFR) was esti­mated for the optimized structure. The solvation number in the primary solvation sphere was four, both in the solution and resin phases; three waters and MeS" formed the primary solvation sphere in the res­ in phase. Additional water molecules moved off to the secondary solvation sphere. It was found that consideration on the primary solvation sphere alone was insufficient for estimations of reduced parti­tion function ratios of aquolithium ions. Although the agreement between the experimentally obtained lithium isotope fractionation and the calculated results is not satisfactory, it is pointed out that the HF/6-31 G(d) level of the theory is usable for elucidation of lithium isotope effects in aqueous ion exchange systems.

Coordination of perchlorate ion in the secondary solvation sphere of Am3+ in the tracer concentrations in mixed system of dimethyl sulfoxide/water with 1.00M (H,Na)(Cl,ClO4)

The stability constants, β1, of monochloride complex of Am(III) have been determined in a mixed system of dimethyl sulfoxide (DMSO) and water at 1.00 mol·dm−3 ionic strength using solvent extraction. The values of β1 in mixed DMSO+H2O solutions decrease rapidly with an increase in the mole fraction of DMSO (Xs) in mixed solvents and become negative ones, which is not in a definition of stability constant, inXs>0.04. The variation of β1 inXs≦0.02 was accounted for by the size-variation of the primary solvation sphere around Am(III), which was present as a solventshared ion-pair, and by a little effect due to an invasion (coordination) of ClO4− into the secondary solvation sphere of Am3+. On the other hand, it was concluded that the β1 obtained by solvent extraction inXs>0.02 was an apparent value, because of a large effect due to an invasion (coordination) of ClO4− into the secondary solvation sphere of Am(III).

The variation of the stability constant of AmCl2+ in a mixed system of methanol and water

The stability constants, β1, of each monochloride complex of Am(III) have been determined in a mixed system of methanol and water at 1.0 mol·dm−3 ionic strength using a solvent extraction technique. The values of β1 of Am(III) decrease up to about 0.1 mole fraction of methanol (Xs) in the bulk solutions and then increase with increasingXs when 0.1<Xs≤0.4. The distance of Am3+−Cl− in the mixed system was estimated using a Born-type equation. From the estimated distance of Am3+−Cl− (dAm−Cl), it is concluded that AmCl2+ in the aqueous solution is present as a solvent-shared ion-pair. Further, based on the variation of dAm−Cl with increasingXs, the variations of β1 in the system are accounted for by the size-variation of the primary solvation sphere around Am(III) and by an effect due to the presence of a slight covalency in the solvation of Am(III).

On the variation of the stability constants of EuCl2+ in the mixed system of dimethyl sulfoxide and water

The stability constantsOpen image in new window, of monochloride complex of Eu(III) in the tracer concentrations have been determined in the mixed system of dimethyl sulfoxide (DMSO) and water with 1.0 mol·dm−3 ionic strength using a solvent extraction technique. The values ofOpen image in new window decrease up to about 0.2 mole fraction of DMSO (Xs) in the mixed solvent system and then increase. Calculation of Eu3+−Cl− distance using a Born-type equation of the Gibbs' free energy derived from theOpen image in new window revealed that the estimated distance between Eu3+ and Cl− (dEu−Cl) increases linearly withXs in 0≤Xs<0.043 and 0.043<Xs<0.172, but their slopes are different. The line in the first region means a linear enlargement of the thickness of the primary solvation sphere of Eu3+ with increasingXs. The larger slope againstXs in 0.043<Xs<0.172 is attributable to lowering ofOpen image in new window, based on the increase in the solvation number of the primary solvation sphere of Eu3+. The considerably large value ofdEu−Cl atXs=0.202 might result from lowering ofOpen image in new window by a coordination of ClO4− into the secondary solvation sphere of Eu3+ and the extremely drop ofdEu−Cl atXs=0.276 might reflect on a conversion of the ion-pair type, i.e., the coexistence of two kinds of a solvent-shared ion-pair and a contact one by the appearance of the contact one.

On the variation of the distances of Nd3+−Cl− and Tm3+−Cl− in mixed system of dimethyl sulfoxide and water

The stability constants, β1, of each monochloride complex of Ln(III) (Ln=Nd or Tm) have been determined in the mixed system of dimethyl sulfoxide (DMSO) and water with 1.0 mol·dm−3 ionic strength using a solvent extraction technique. The values of β1 of Ln(III) decrease to about 0.2 mole fraction of DMSO (Xs) in the mixed solvent system and then increase withXs (>about 0.2). However, the variation mode of β1 of Nd(III) withXs somewhat differs from that of Tm(III). Calculation of Ln3+−Cl− distance using a Born-type equation of the Gibbs' free energy derived from the β1 evealed the followings: (1) For Tm3+ with coordination number 8, the estimated distance between Tm3+ and Cl− (dTm-Cl) increases linearly withXs in 0.00≤Xs≤0.17. This means an enlargement of the primary solvation sphere size of Tm3+ withXs. On the other hand, thedTm-Cl shows a decrease withXs in 0.17<Xs<0.28. (2) The estimateddNd-Cl increases linearly withXs in 0.00≤Xs<0.06 and 0.06<Xs≤0.17, but their slopes are different. The larger slope againstXs in 0.06<Xs≤0.17 is attributable to a lowering of the β1 by a coordination of ClO4− into the secondary solvation sphere of Nd3+ and/or by an increase in the solvation number of the primary solvation sphere of Nd3+.

Spectrochemistry of solutions. part 29.[1] intrusion ion pairing: Identification of a new form of ion pair in transition metal salt solutions in pyridine through their visible spectra

A new ion associate structure, an “intrusion” ion pair, is reported in which small anions like Cl − and Br − intrude into the hexacoordinate primary solvation sphere of [Ni(py) 6] 2+ in pyridine. This cation-anion interaction is identified by significant spectral shifts to lower frequency of the 3 A 2g( F)- 3 T 2g( F), 3 A 2g( F)- 3 T 1g( F ) and 3A 2 g (F)- 3T 2 g (P) transitions in the d- d spectra compared with the frequencies observed with [Ni(py) 6] 2+ solutions containing the larger anions NO 3 −, BF 4 − and SO 4 2-. A similar spectral shift identifies the presence of an “intrusion” ion pair in Cl − solutions of [Cr(py) 6] 3+ in pyridine versus NO 3 − and NCS-solutions; in the case of the Br − solution of [Cr(py) 6] 3+ the absence of any shift in the positions of the bands due to the 4A- 4T 2(F) and 4A- 4T 1(F) transitions of Cr III indicates that the Br − anion does not enter the primary solvation sphere of [Cr(py) 6]3 3+ to form an “intrusion” ion pair.

On the size variation of the primary solvation sphere of Nd3+ and Tm3+ in mixed system of methanol and water

The stability constants, α1, of each monochloride complex of Nd(III) and Tm(III) have been determined in the mixed system of methanol and water with 1.0 mol·dm−1 ionic strength using a solvent extraction technique. The values of α1 of Nd(III) and Tm(III) increase as the mole fraction of methanol in the mixed solvent system (Xs) increases. However, the variation mode of α1 againstXs in the region of 0.00≤Xs≤0.40 differs from each other, a concave curve for the Nd(III) and a convex curve for the Tm(III). The LnCl2+ formed is present as a solvent-shared ion-pair. Since Cl− is a structure breaking ion, it was assumed that the primary solvation sphere of Ln3+ directly contacted with Cl−. Calculation of Ln3+−Cl− distance using Bom-type equation revealed the followings: (1) for Tm3+ with coordination number 8, the estimated distance between Tm3+ and Cl− increases linearly withXs in 0.00≤Xs≤0.40. The results mean an increase of the primary solvation sphere size of Tm3+ withXs. (2) For Nd3+, the distance between Nd3+ and Cl− decreases linearly withXs in 0.00≤Xs<0.13, where both coordination numbers of 9 and 8 coexist, while it increases withXs in 0.13<Xs≤0.40. The results mean a decrease of the primary solvation-sphere size of Nd3+ withXs in 0.00≤Xs<0.13 and an increase of that withXs in 0.13<Xs≤0.40.

Solvation of SCN- and SeCN- Anions in Hydrogen-Bonding Solvents

The primary solvation sphere surrounding the thiocyanate or the selenocyanide anion in protic solvents, such as methanol, N-methylformamide and formamide, forms intimate hydrogen bonds with these anions. These interactions perturb the electron density and vibrational modes of these anions and can therefore be studied by NMR and infrared spectroscopies. In neat solutions, these solvents form hydrogen bonds to the nitrogen end along the molecular axis and nonaxially to the π cloud of the C−N bond, although a substantial proportion of the anions is not hydrogen bonded. In nitromethane solutions, the thiocyanate and selenocyanide anions form weak complexes with methanol and the amide solvents (K < 1 M-1), which is an order of magnitude smaller than that of OCN- with the same solvents, determined in our previous investigation of the cyanate anion. The remarkable differences in the solvation of these singly charged anions can be understood by theoretical calculations of their electrostatic potentials.

Electrode kinetics of the system V(III)/V(II) in aqueous dimethylsulphoxide

The rate constants for the reduction of V(III) and oxidation of V(II) were measured on a mercury electrode in water and water-dimethylsulphoxide mixtures. Their dependance on the concentration of DMSO differs from that in mixtures of water with an organic solvent of lower basicity. This can be attributed to the existence of different solvates of vanadium in solutions and to different values of the rate constant for these solvates on the electrode surface at different coverages with the organic component. The influence of DMSO both in the primary solvation sphere and in the electrode double layer on the electrode reaction rate is discussed.

ChemInform Abstract: ELECTRO‐DONICITY OF THE SOLVENTS AND KINETICS OF SIMPLE ELECTRODE REACTIONS. THE EUROPIUM(III)/EUROPIUM(II) COUPLE IN COMMON SOLVENTS

AbstractDie Kinetik des Eu(III)/Eu(ll)‐Redoxsystems an Hg‐EIektroden wurde in Wasser, Acetonitril (AN), DM F, DMSO und HMPA untersucht.

Electro-donicity of the solvents and kinetics of simple electrode reactions: The Eu(III)/Eu(II) couple in common solvents

The kinetics of the Eu(III)/Eu(II) system at mercury electrodes has been investigated in water, acetonitrile (AN), N,N-dimethylformamide (DMF) dimethylsulphoxide (DMSO) and hexamethylphosphoramide (HMPA). Formal potentials E f o move towards more negative values in the order AN<H 2O<DMF<DMSO <HMPA, indicating increasing solvation ability of the solvents in agreement with their donor numbers (DN). Logarithms of standard rate constants corrected for the double-layer effect do not show any straightforward relation with the basicity of the solvents used. However, λ i, the reorganization energy of the inner sphere, correlates with DN similarly to E f o. It has been suggested that λ i determines mostly the reaction kinetics in the case of basic solvents, while λ 0, the reorganization energy of the solvent around the ion, with its primary solvation sphere, is essential for solvents of low basicity.

Radiative and Nonradiative Transitions of Eu3+in Binary Solvent Systems

Abstract The fluorescence efficiency of the rare-earth ions in solution increases upon deuteration of the solvent(1–3) and is dependent upon the presence in the solvent molecule of such groups as etc. Lower fluorescence quantum yields observed for Eu3+ and Tb3+ in protic solvents were accounted for, at least qualitatively, by electronic excitation energy transfer from the excited rare-earth ion to some of the vibrational modes in the solvent molecule. The fluorescence quantum yield of Dy3+ in solution is also lower in the presence of groups.(7) Furthermore, significant fluorescence enhancement and long fluorescence lifetimes were observed for both Sm3+ and Eu3+ in such aprotic solvents as POCl3:SnCl4, POCl3:ZrCl4 and POCl3:TiCl4, where both the fluorescence intensities and lifetimes were enhanced by a factor of 1000 and 300, respectively, relative to those in aqueous solutions.(8,9) The fluorescence efficiency of Sm3+ and Eu3+ was also found to depend upon the composition of the primary solvation sphere o...

Nuclear Magnetic Resonance Studies of Solvation of Halides: 19F Studies of Solvent and Counterion Effects on Chemical Shift

We report new measurements adding to the literature on solvent and counter ion dependence of 10F− chemical shift. These are compared to earlier results for 35Cl−, 79Br−, and 127I−. The observations support the following points: (1) there are few systematic differences between behavior of anion shifts in dilute and moderately concentrated aqueous solution, (2) anion shifts commonly show larger sensitivity to solvent than counter ion over convenient ranges of variation so that "solvent shift" may be easily measured. Using the concept of collision effects on shifts developed by Richards and his collaborators, it is possible to separate, in many cases, the large effects arising from contact, or primary solvation sphere, collisions from the smaller effects of outer sphere interactions.We find no preferential solvation of F− by H2O in mixtures with CH3OH; at most, small preference over C2H5OH and formamide, and a small opposite preference in favor of diols. However, water appears strongly preferred in the primary solvation shell over acetone, acetonitrile, dioxane, and (in contrast to other halides), dimethylsulfoxide. Solvation by amines involving both outer and inner sphere site occupation is considered.The inter-anion effects on fluoride ion chemical shifts tend to undermine the concept of additivity of ionic effects on shifts.

Radiative and radiationless processes of Eu 3+ in dimethyl sulfoxide

Solutions of Eu 3+ in dimethyl sulfoxide (DMSO) exhibit a considerable enhancement in the intensities of bands associated with ▵ J = 2 both in the absorption and in the emission spectra. This effect is so strong that addition of considerable amounts of either D 2O or H 2O has no effect at all. Contrary to that, addition of very small quantities of DMSO in solutions of Eu 3+ in D 2O is accompanied by drastic changes in the appropriate transition probabilities. In solutions of Eu 3+ in DMSO containing relatively small [H 2O] or [D 2O], the primary solvation sphere appears to consist mainly of DMSO. Secondary and primary fluorescence quenching rate constants have been determined such as: k sec D 2 O ⩾ 5.1 M -1 s -1; k sec DMSO ⩾ 20 M -1 s -1 and k fl + k ≈ h ⩽ 4.5 × 10 2 s -1.

Fluorescence Enhancement of Eu3+in POCl3:SnCl4and of Sm3+in POCl3:ZrCl4

Abstract The fluorescence efficiency of the rare-earth ions in organic solvents depends strongly upon the solvent molecules in the primary solvation sphere and to a lesser extent upon the molecules located in the secondary solvation sphere of the ion(1-4). The fluorescence efficiency of the rare-earth ions in many organic solvents is relatively low probably due to an efficient electronic excitation energy transfer from the lowest excited state of the rare-earth ion to the organic solvent, via some high overtones of certain vibrational modes associated with the solvent under consideration. Contrary to this behavior, solutions of the rare-earth ions in solvents associated with very low-energy vibrational modes, “aprotic” solvents, like POCl3:SnCl4, POCl3:ZrCl4, POCl3:SbCl5 etc., exhibit a remarkable enhancement in both the fluorescence efficiencies and lifetimes of the rare-earth ions(5). Neither the organic nor the “aprotic” solvents used absorb light in the excitation region i.e., 370 mμ to 410 mμ. Since ...