Quantitative NMR Analysis of Ion Pair Formation in Highly Concentrated Lithium Salt Solutions

The Raman scattering cross section (RSCS) is an important parameter in the applications of Raman spectroscopy to make quantitative analysis. To date, the dependence of the RSCS on concentration has remained unclear. Nitrate aerosols can easily achieve a supersaturated state, which provides a way to obtain the RSCS especially under this state. In this study, Raman spectra of NaNO3 and Mg(NO3)2 solutions are obtained with molar water‐to‐solute ratios (WSRs) ranging from 84.2 to 2.30 and 93.8 to 7.32, respectively. With decreasing WSR, a shift to higher wavenumbers of the symmetric stretching band of nitrate ion, i.e. ν1(NO3−), is observed, indicating the formation of various ion pairs. Meanwhile, the area ratio between the strongly and weakly hydrogen‐bonded components of water OH stretching envelope, i.e. ν(H2O), reduces as the WSR decreases, implying the transformation of water molecules from strong hydrogen‐bonding structures to the weak ones. However, a good linear relationship is revealed between the integrated intensity ratio of the ν(H2O) band to ν1(NO3−) band and WSR. The results suggest that the RSCSs of NO3− and H2O are insensitive to the structures of both ion pairs and hydrogen‐bonding structures. This observation points to the possibility of conducting quantitative analysis through the area ratio of the ν(H2O) band to the ν1(NO3−) band with Raman spectra without considering the formation of ion pairs and the variation of the hydrogen‐bonding structure. Copyright © 2011 John Wiley & Sons, Ltd.

As the world is witnessing a notable climate change mainly due to carbon dioxide emissions from fossil fuel consumption, the effort to utilize alternative forms of energy is steadily increasing. Renewable energy sources, such as wind, solar, hydropower, biomass and geothermal, are increasingly being used to generate energy to replace fossil fuels in recent years. Howerver, they have not been able to replace fossil fuels in a significant way in part because of discontinuities in the generation of energy from these alternative sources. Energy from wind or the sun is not always available when the demand arises. To solve this problem, development of efficient storage systems such as rechargeable batteries are essential to store the energy generated at peak hours. Rechargeable lithium batteries are expected to play a significant role in this respect. The first chapter summarizes the fundamentals of batteries and gives a general overview of different types of lithium batteries. The main focus in the introduction is on the basic chemistry of non-aqueous lithium air (Li-O2) batteries and the use of Hard Soft Acid-Base (HSAB) theory to explain oxygen reduction and evolution reactions (ORR/OER) in non-aqueous electrolytes. The effect of solvents' Donor Number on the ORR catalysis is explained as well. In chapter 2 we studied the chemical structures of lithium and tetrabutylammonium (TBA) salt solutions in two high Donor Number organic solvents namely, N,N-dimethylacetamide (DMAc) and N,N-diethylacetamide (DEAc). In lithium salt (LiX) solutions (where X= PF6−, CF3SO3−, ClO4− and NO3−), solvation occurs when the Li+ bonds with the solvent's carbonyl group forming Li+[O=C(CH3)N(CH3)2]nX− ion pairs. Infrared and 13C-NMR spectra are consistent with the ion pair being solvent-separated when the anion is PF6−, ClO4− or NO3−, and a contact ion pair in the case of CF3SO3−. Chemical interactions between TBA+ and the solvents to form conducting solutions appeared to be dipolar in nature. Ionic conductivities of TBAX and LiX containing electrolytes were measured and correlated with their viscosities. In chapter 3 the microelectrode technique was used to measure the O2 solubility and diffusion coefficient in 0.1M TBAPF6/DMAc (3.09×10−6 mol cm−3 and 5.09×10−5 cm2 s−1, respectively) as well as 0.1M TBACF3SO3, TBACLO4 and TBANO3 solutions. The values were found to be typical of these properties measured in several TBA+ solutions. Microelectrode voltammetry revealed steady-state limiting current behavior for oxygen reduction reactions (ORR) in TBAX/DMAc electrolytes indicating a reversible ORR process. Conversely, microelectrode current-voltage data for ORR in LiX/DMAc electrolytes revealed irreversible behavior mainly ascribed to the blockage of the electrode surface by insoluble ORR products. The ORR in DMAc correlated with its high Donor Number and the overall process conformed to the Hard-Soft Acid-Base theory. Metal macrocycles are among the most important catalytic systems in electrocatalysis and biocatalysis owing to their rich redox chemistry. Precise understanding of the redox behavior of metal macrocycles under operando conditions is essential for fundamental studies and practical applications of this catalytic system. In chapter 4 we present electrochemical data for the representative iron phthalocyanine (FePc) in both aqueous and non-aqueous media coupled with in situ Raman and X-ray absorption analyses to challenge the traditional notion of the redox transition of FePc at the low potential end in aqueous media by showing that it arises from the redox transition of the ring. Our data unequivocally demonstrate that the electron is shuttled to the Pc ring via the Fe(II)/Fe(I) redox center. The Fe(II)/Fe(I) redox transition of FePc in aqueous media is indiscernible by normal spectroscopic methods owing to the lack of a suitable axial ligand to stabilize the Fe(I) state. Chapter 5 is dedicated to the study of the application of DMAc-based electrolytes and FePc-based catalysts in a Li-O2 battery cell. The analytical techniques SEM, NMR and FTIR were used to better understand the role of LiNO3 in stabilizing the lithium metal anode surface and protecting the metal from being consumed in the decomposition of DMAc. A three-electrode cell was used to study the ORR in DMAc solutions in the presence of FePc-based catalyst and little catalytic effect was observed. This behavior is typical of high Donor Number solvents (such as DMAc) which drives the ORR to proceed via an outer Helmholtz plane (OHP) reaction pathway. Li-O2 cells were constructed and tested with DMAc-based electrolytes. Both the catalyzed and uncatalyzed cell did not exhibit the ability to support long cycle life but the catalyzed cell showed slightly better performance than the uncatalyzed cells. Chapter 6 summarizes the conclusions of the research conducted in this investigation and offers suggestions for future work.

1H CRAMPS and MAS-only NMR experiments have been examined systematically from a quantitative point of view. Silicone rubber was characterized as a proton NMR intensity standard and found to be successful in quantitative analysis for typical solids. Important parameter variations involved in the CRAMPS experiment, especially for quantitative analysis, are discussed. The application of the silicone rubber intensity standard for quantitative 1H NMR analysis (spin-counting) to silica is described, demonstrating the utility and power of 1H NMR for quantitative analysis.

The Raman spectra of the mixtures containing the low-temperature ionic liquid ethylmethylimidazolinium bis(trifluoromethanesulfonyl)imide (EMIIm), the salt component lithium bis(trifluoromethylesulfonyl)-imide (LiIm), and the aprotic solvent ethylene carbonate (EC) are studied. It is found that the addition of the lithium salt to the ionic liquid results in the formation of ion pairs or more complex cation-anion aggregates. Dilution of these systems with ethylene carbonate leads to the solvation of lithium ions.

This contribution aims to elucidate the connection between ion-ion-solvent interactions in the bulk of aqueous electrolyte solutions and the properties of their liquid-air interface. In particular, we were interested in the conditions under which ion pairs form at the surface and whether this is linked to ion pairing in the bulk. For this reason different combinations of hard (Cl(-), Li(+)) and soft ions (I(-), Cs(+)) were investigated. Ion hydration and possible ion association in the bulk was probed with dielectric relaxation spectroscopy. This technique monitors the cooperative reorientation of the dipolar solvent molecules and detects all ion-pair species possibly present in the solution. At the interface, the formation of contact ion pairs was investigated by infrared-visible-sum frequency spectroscopy (SFG). This nonlinear optical technique possesses an inherent surface specificity and can be used for the characterization of interfacial water. The intensity of the SFG-active vibrational stretching modes depends on the number of oriented water molecules. The electric field at the surface of a charged aqueous interface aligns the water dipoles, which in turn increases the SFG response. Hence, the enhancement of the oscillator strengths of the water vibrational modes can be used to draw some conclusions on the strengths and geometrical extension of the electric field. The formation of ion pairs at the interface reduces the intensity of the band associated with hydrogen-bonded water. The underlying theory is presented. The combined data show that there are no contact ion pairs in the bulk of the fluid and--at best--only small amounts of solvent shared ion pairs. On the other hand, the combination of hard/hard or soft/soft ions leads to the formation of ion pairs at the liquid-air interface.

The liquid-phase deposition (LPD) reaction and the deposition mechanisms for the preparation of hazy TiO2, transparent TiO2, and NH4TiOF3 films were investigated by quantitative 19F NMR analysis. Contrary to the conventional understanding, the 19F NMR spectra indicated that BF3(OH)− formed within a short reaction time, and the concentration of BF3(OH)− was always much higher than that of BF4– during the LPD reaction. Quantitative analysis also indicated that several types of titanium complexes coordinated by fluoride ions dissolved in the LPD reaction solutions, but they were not detected by 19F NMR measurement because of rapid ligand substitution. A highly dense and transparent anatase TiO2 thin film was obtained at pH 3.5, and the growth of the particles comprising the films was accelerated by increasing the pH. Conversely, nucleation and crystal growth in the thin films were suppressed at lower pH. Furthermore, in the induction period of the LPD reaction, a shift of chemical equilibrium, which decrease...

In situ simultaneous formation of both covalent linkages and ion pair is challenging yet necessary to control the biological properties of a hydrogel. We report that the generation of covalent linkages (+N-C) facilitates the simultaneous formation of ion pairs between polyelectrolytes (PEs) in a hydrogel network. Co-injection of tertiary amine functional macromolecules and reactive poly(ethylene glycol) (PEG) containing negatively charged PE leads to the formation of hydrogel conetworks consisting of covalent junctions and ion pairs. Our design is based on the gradual appearance of +N-C junctions followed by formation of ion pairs. This strategy provides an easy access to hydrogel networks bearing a predetermined proportion of ion pair and covalent cross-linking junction. The proportion of ion pair could be varied by introducing a precalculated proportion of mono- and difunctional reactive PEG in the hydrogel system. The topology of the prepolymer and the hydrogel could be modulated (graft) during hydrogel formation. This approach is applicable to obtain covalent/ionic, covalent bond induced purely ionic, and purely covalent hydrogels of several macromolecular entities. The effect of ion pairing in the hydrogels is strongly reflected in the modulus, strain bearing, degradation, free volume, swelling, and drug release properties. The hydrogels exhibit microscopic recovery of modulus after application of high amplitude strain depending on the prepolymer concentration (chain entanglement) and nature of hydrogel network. The hydrogels are hemocompatible, and the covalent/ionic hydrogels show a slower release of methotrexate than that of the purely covalent hydrogel. This work provides an understanding for the in situ construction and manipulation of biological properties of hydrogels through the covalent bond induced formation of a strong ion pair.

Interfacial regions attached to hydrophobic and hydrophilic surfaces have very low relative permittivities (ε ∼ 3–5), and these low values induce the formation of ion pairs. A detailed description of ion pairing will be possible only after the development of adequate experimental probing methods. The scheme described in this work detects the ion pair (or multistage ion association) formation in water solutions in the interfacial region. Forces acting on the tip when immersed in the interfacial region attached to hydrophilic substrates, such as mica where ε < 7, are attractive (AFM tip dielectric constant = 7). These attractive force steps with extensions equal or smaller than the Bjerrum length at hydrophilic substrates are associated with ion pair formation in interfacial regions. Measurements show that the interfacial water molecular arrangement and ion pairs form an ordered structure (ε < 7) induced by mica interfacial charges. The interfacial region attached to hydrophobic substrates, however, form separated arrangements of ion pairs and water molecular structures as observed by the repulsive steps (ε > 7) intercalated in between attractive regions (ε < 7).

Our recent Raman studies of cation and anion solvation and ion pairing in solutions of lithium salts in dimethyl sulfoxide, propylene carbonate, and dimethyl carbonate are briefly overviewed. Special attention is paid to differences in our and existing data and concepts. As follows from our results, cation solvation numbers in solutions are low (~2) and disagree with previous measurements. This discrepancy is shown to arise from correct accounting for dimerization, hydrogen bonding, and conformation equilibria in the solvents disregarded in early studies. Another disputable question touches upon the absence of free ions in solutions of lithium salts in carbonate solvents and the statement that the charge transfer in carbonate solutions is caused by SSIPs. Direct proofs of the nature of charge carriers in the solvents studied have been obtained by means of analyses of vibrational dynamics. It has been found that collision times for free anions are short and evidence weak interactions between anions and solvent molecules. In SSIPs, collision times are an order of magnitude longer thus signifying strong interactions between anions and cations. In CIPs, collision times become shorter than in SSIPs reflecting the transformation of the structure of concentrated solutions to that of molten salts.

A 13C NMR method has been developed for obtaining simultaneously structural and quantitative information on mixtures of pyrrolizidine alkaloids from Senecio vulgaris L. (Compositae). The samples contained seneciphylline, senecionine, retrorsine and the corresponding E geometrical isomers, spartioidine, integerrimine and usaramine. The spin‐lattice relaxation times were measured and, after establishing the instrumental requirements for quantitative 13C FT NMR, all the alkaloids of the mixture could be determined. Quantitative 1H and 13C FT NMR analyses were carried out, and the advantages and limitations of these methods are discussed.

Quantitative 1H NMR analysis of a difficult drug substance and its exo-isomer as hydrochloride salts using alkaline deuterated methanol

Preparation of Submicron Size Gamma Lithium Aluminate Particles from the Mixture of Alumina Sol and Lithium Salt by Ultrasonic Spray Pyrolysis

In this paper we study the influence of the formation of intrachain ion pairs (salt bonds) and the distribution of counterions on the behavior of single polyampholyte chains in a dilute solution. It has been shown that neutral polyampholyte chains can undergo jump-like collapse transition from the swollen state to the globular state with the formation of ion pairs between oppositely charged ions of the chain. A polyampholyte chain with an excess charge shows the behavior of a conventional polyelectrolyte chain and counterions play an important role in the chain behavior. We distinguish three possible states of counterions: free counterions inside and outside the macromolecule, and a bound state of counterions forming ion pairs with the corresponding ions of the polymer chain. We found a non-monotonous behavior of the chain upon increasing the excess charge on the chain: the chain swells from a compact state to elongated conformation and shrinks again to the compact state when the excess charge of the chain is increased.

Fondaparinux sodium is a synthetic pentasaccharide representing the high affinity antithrombin III binding site in heparin. It is the active pharmaceutical ingredient of the anticoagulant drug Arixtra®. The single crystal X-ray structure of Fondaparinux sodium is reported, unequivocally confirming both structure and absolute configuration. The iduronic acid adopts a somewhat distorted chair conformation. Due to the presence of many sulfur atoms in the highly sulfated pentasaccharide, anomalous dispersion could be applied to determine the absolute configuration. A comparison with the conformation of Fondaparinux in solution, as well as complexed with proteins is presented. The content of the solution reference standard was determined by quantitative NMR using an internal standard both in 1999 and in 2016. A comparison of the results allows the conclusion that this method shows remarkable precision over time, instrumentation and analysts.

Glass transition, viscosity, and conductivity correlations in solutions of lithium salts in PEGylated imidazolium ionic liquids