Special Solvation Behaviour of Salts in Ionic Liquid

In a previous study1 from the Welton Group, the reactivity resulting from mixing two different and reactive salts together was observed to be highly dependent on the type of solvent, with molecular and ionic liquids exhibiting fundamentally different reaction pathways. Ionic liquids were shown to be extremely dissociating solvents and the salts behaved as discrete reactive species. Conversely, in molecular solvents neutral ion pairs or clusters were formed. In this thesis, further evidence of the charge screening behaviour of ionic liquids will be presented. The investigation was carried out by using Kosower's charge-transfer complex, 1-ethyl-4-(methoxycarbonyl)pyridinium iodide,2 which is only spectroscopically active when its ions are in direct contact, hence allowing charge transfer to occur. The behaviour of this salt is therefore a good indicator of the number of pyridinium iodide contact ion pairs in solution and can be used as a probe for the amount of ion-pairing in both ionic and molecular liquids. In the second part of the investigation, the SN2 reaction of two reactive salts (1-butyl-1-methylpyrrolidinium bromide and dimethyl-4-nitrophenylsulfonium bis(trifluoromethanesulfonyl)imide) in ionic liquid/molecular liquid mixtures was studied. The aim was to examine whether complete charge screening behaviour could be achieved in ionic liquid/molecular liquid mixtures of different compositions. This research also provided some insights of general behaviour of salts in ionic liquid/molecular solvent mixtures

Neutron and X-ray diffraction studies on complex liquids

The above examples illustrate the extent to which present day neutron and X-ray diffraction methods are being used to determine interatomic structure in a wide range of liquid and amorphous systems. The determination of pair radial distribution functions not only offers a means to characterise different structures in liquids, but also provides theorists with information to construct realistic model potentials that can be used to calculate macroscopic behaviour and structural properties in regimes not currently accessible to experiment.\ud The well-established NDIS difference methods remain superior to all other methods for the determination of interatomic pairwise structure. The relatively new AXD (or DAS) difference methods have the potential to answer long-standing questions about the structure around species with mass number greater than about 30. However, the relatively low X-ray scattering power from light elements such as hydrogen, carbon, nitrogen etc. means that it will never be possible to resolve completely structures of biologically important liquids by X-ray methods alone. EXAFS spectroscopy has the distinct advantage over both diffraction techniques as it can be used to study local structure around particular species at high dilution. Therefore studies which combine reference data from AXD or NDIS, with extensive EXAFS data, are likely to be useful in studies of structure in regimes which prove difficult for AXD and NDIS. \ud It is clear that no one method will be sufficient to resolve structure at the required level of detail around all species in a complex liquid. Instead one must rely on a full complement of diffraction and other techniques including computer simulation to determine the complete atomic structure of a complex liquid or amorphous system.\ud On the technical front, the construction and commissioning of new neutron diffractometers with higher count rates, such as D20 and D4C at ILL, and GEM at ISIS with an optimised sample environment for work at non-ambient conditions, will enable new and more extensive research to be undertaken. Additionally, the new custom-built X-ray diffractometer for liquids proposed for the DIAMOND synchrotron being established at RAL will provide a much-needed boost for wide-ranging AXD and EXAFS investigations of complex liquids. \ud Besides the many studies of immediate interest suggested at the end of some sections, there are several investigations that will become feasible in the longer term as the technology develops. These include 1. the use of isotopes such as 12C and 13C and 33S and 32S which will enable detailed and extensive structural studies to be carried out on a wide range of biologically significant materials, and 2. the exploitation of higher neutron and X-ray count rates to facilitate real time experiments to investigate changes of structure as a chemical or biochemical reaction occurs. \ud The one strong theme which emerges from all the work described in this paper is that diffraction, especially that based on difference techniques, remains the best means to determine structure at atomic resolution in complex liquids

Neutron diffraction studies on liquids

The above examples serve to illustrate the extent to which neutron diffraction isotopic substitution methods have been used to determine interatomic structure in a wide range of liquid and amorphous systems. The direct determination of pair radial functions not only offers a means of characterising the different structures in liquids, but also provides theorists with information to construct more realistic model potentials which can be used to explore properties in regimes not currently accessible to experiment.\ud \ud It is anticipated that the NDIS methods will continue to be developed and applied to a wider range of systems. The construction and commissioning of new diffractometers with higher count rates, such as D20 and D4C at ILL, and GEM at ISIS with an optimised sample environment for work at non-ambient conditions will enable new and more extensive research to be undertaken. Besides the many problems of immediate interest suggested at the end of some sections, there are several investigations which will become feasible in the longer term as the technology develops. These include: (i) the use of isotopes such as 12C and 13C which will enable detailed and extensive structural studies to be carried out on a wide range of biologically significant materials, and (ii) the exploitation of higher count rates to investigate changes of structure as a chemical reaction occurs

Hydration Shell Water Structure and Aggregation of Small Amphiphilic Solutes

My research aims to address long-standing questions in physical chemistry about water-mediated hydrophobic and ionic interactions of biological relevance. For example, my research has provided some of the first experimental evidence of water driving hydrophobic groups apart rather than pushing them together in solution, thus damping rather than enhancing the contact free energy of oily molecules in water. I have also obtained some of the first experimental evidence concerning the structure of water structure around nonpolar groups in solution, thus demonstrating that hydrophobic hydration-shells have a clathrate hydrate-like structure. In addition, I am currently studying ionic interactions in water, which are important due to the ubiquity of solvated ions in living systems, along with three additional projects investigating solute polarity, charge, and substituent placement effects on solute aggregation and water structure. Finally, I have contributed to one project that probes aggregation of hydrophobic solutes in binary alcohol/water mixtures and to another, highly collaborative project that addresses the continued debate regarding the structure of hydrated protons in liquid water. Here, the combined application of Raman spectroscopy and multivariate curve resolution (Raman-MCR) to aqueous solutions has been used to reveal solute-correlated (SC) spectra, which contain vibrational spectral features arising from the hydration shell around a dissolved solute, as well as the solute itself. Such spectra are used to obtain information about changes in water structure, as a function of solute identity, size, shape, polarity, and charge. Moreover, Raman-MCR is used to probe water-mediated interactions between solute molecules, by detecting interaction-induced changes in the SC spectra of variable solution concentrations

Ionic Liquid Effects on Nucleophilic Substitutions

In this thesis we demonstrate a fundamental difference between nucleophilic substitution reaction mechanisms in ionic liquids versus conventional solvents. Reported herein are the effects of ionic liquid solvents on substitution reactions between a cationic electrophile and the chloride anion of various organic and inorganic salts. We have combined novel quantitative studies of the nucleophilic source [Cat]Cl with our studies of [C4C1im]Cl and compared their reactivities, k2. For the first time, Eyring activation parameters have been calculated for substitution reactions between charged species in ionic liquid solvents and reveal a hitherto unprecedented role of the cation in the transition state. The activation parameters (ΔH≠ and ΔS≠) suggest the reactivity of the chloride anion can be manipulated by varying the size and chemical nature of the cation, and also shed light on cation hydrogen bond donating effects. The superior ability of ionic liquid solvents to fully screen the charges of reactant ions is shown to break down as ions become larger, less charge dense and display a tendency to self-aggregate.Open Acces

Electromotive Force and Measurement in Several Systems

This book is devoted to different sides of Electromotive Force theory and its applications in Engineering science and Industry. The covered topics include the Quantum Theory of Thermoelectric Power (Seebeck Coefficient), Electromotive forces in solar energy and photocatalysis (photo electromotive forces), Electromotive Force in Electrochemical Modification of Mudstone, The EMF method with solid-state electrolyte in the thermodynamic investigation of ternary copper and silver chalcogenides, Electromotive Force Measurements and Thermodynamic Modelling of Electrolyte in Mixed Solvents, Application of Electromotive Force Measurement in Nuclear Systems Using Lead Alloys, Electromotive Force Measurements in High-Temperature Systems and finally, Resonance Analysis of Induced EMF on Coils