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Protic Ionic Liquids (PILs) build hydrogen bonds between cations and anions leading to the formation of neutral ion pairs. This is well reflected in their motional behaviour. The dynamics of cations and anions can be simultaneously investigated by means of NMR relaxometry, provided that both species contain different NMR active nuclei. Therefore, appropriate PILs were investigated by Fast Field Cycling NMR relaxometry and by high-field NMR. The validity of a relaxation model considering solely isotropic rotations was examined and cases of anisotropic or internal rotations were scrutinized.eng
In this work, translational and rotational diffusion in neat ionic liquids and dilute ionic liquid solutions were investigated using nuclear magnetic resonance (NMR) spectroscopy. Two distinct studies of translational diffusion were performed. The first focuses on solutions prepared in 1-alkyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imde ionic liquids ([Prn1][Tf2N], n=3,4, and10) with quasi-spherical solutes, such as methane, ammonium, and tetramethylsilane. The second study entails measurement of self-diffusion coefficients in homologous series of neat ionic liquids: 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [CnC1im][Tf2N] and [(n-2)mCn-1C1im][Tf2N] n = 3, 4, 5, 6, 7. The majority of the measurements of translational diffusion were carried out using a Bruker AV-III-850 NMR spectrometer with a Diff-30 probe with triple axis gradients using a longitudinal-eddy-current delay stimulated echo NMR pulse sequence. The Stokes-Einstein (SE) model is a starting point for understanding the solute diffusion coefficients measured. While the SE model can often predict diffusion coefficients that are close to experimental values, there are several factors that can lead to deviations. The primary simplification of this model is to treat the solvent as a structureless continuum, thereby implicitly assuming that the solute is much larger than the size of the solvent molecules. Since ionic liquids are typically larger than conventional solvents, deviations from SE predictions are commonly observed for smaller solutes translating in ionic liquids. In addition to size, intermolecular interactions between the solute and solvent hinder the diffusion, leading to deviations. In the first translational diffusion study, charged and uncharged quasi-spherical solutes with various sizes were chosen to better understand deviations from SE predictions. By selecting these types of probes, shape effects are minimized and any deviation would be attributed to the fiction coefficient of the solute. The data collected here were important in verifying the accuracy of molecular dynamics simulations of these same systems. These simulations were able to provide new insight into the mechanisms of diffusion of small neutral and charged solutes in ionic liquids.Translational diffusion experiments were also performed on two series of neat ionic liquids which differed in either having a linear or branched alkyl chain on the cation. These liquids were provided by the Quitevis group from Texas Tech University. From their findings, it was observed that ionic liquids with the same composition but different alkyl chain connectivity exhibited large deviations in viscosity at certain chain lengths, while other physical properties, such as density, remained consistent. The self-diffusion coefficients of the cations and anions of two homologous series of neat ionic liquids were investigated to determine if analogous behavior was observed when compared to the viscosity. Rotational diffusion studies analyzed dilute solutions of p-xylene-d10 (pXy0), 1,4-dimethylpyridinium-d7 hexafluorophosphate (DMPy+), and p-tolunitrile-d7 (CMBz[mu]) in 1-butyl-3-methylimidazolium tetrafluoroborate ([Im41][BF4]). For rotational diffusion experiments, data were collected using the DPX-300 spectrometer with a broadband multinuclear probe in addition to the AV-III-850. The pulse sequence used in these experiments was the inversion recovery for deuterium.Determining rotational correlation times,[tau]_c, from deuterium longitudinal relaxation, T1, is often oversimplified to the point of inaccuracy as a result of assuming exponential relaxation of rotational correlations. Factors such as symmetry and structure lead to molecules possessing several unique rotations and thus rotational correlation functions will have much more complex functional forms. In a previous study, correlation times for the rotational dynamics of benzene in ionic liquids were studied by fitting NMR data with the aid of MD simulations, eliminating the need for simplification. In the present study, the same type of analysis was used to determine rotational correlation times for probes having similar size and shape, but very different solvent interactions. The goal was to investigate the effect intermolecular interactions have on rotational diffusion.
Field-cycling NMR relaxometry is evolving into a methodology of widespread interest with recent technological developments resulting in powerful and versatile commercial instruments. Polymers, liquid crystals, biomaterials, porous media, tissue, cement and many other materials of practical importance can be studied using this technique. This book summarises the expertise of leading scientists in the area and the editor is well placed, after four decades of working in this field, to ensure a broad ranging and high quality title. Starting with an overview of the basic principles of the technique and the scope of its use, the content then develops to look at theory, instrumentation, practical limitations and applications in different systems. Newcomers to the field will find this book invaluable for successful use of the technique. Researchers already in academic and industrial settings, interested in molecular dynamics and magnetic resonance, will discover an important addition to the literature.
Diffusion and Eletrophoretic NMR experiments resolve chemical compounds based on their molecular motion. This publication introduces the basics of these methods and explains how they can be used to measure the size of molecules and aggregates, to determine degree of polymerization and to solve other chemical problems. Supplied with many case studies, the book is a must-have for students and researchers who work with practical NMR measurements.
This volume deals with substances in the liquid state that range from high melting salts, such as calcium fluoride, through slags, such as silicates, down to lower melting salts, such as lithium nitrate, molten hydrated salts, such as magnesium chloride hexahydrate, to room temperature ionic liquids, such as 1,3-dimethylimmidazolium tetraphenylborate. It provides the reader with annotated, critically examined, and compiled data for such materials. The data includes a variety of thermochemical, structural, and transport properties. The book includes correlations of measured properties; these correlations should enable the reader to estimate, on a sound basis, properties for ionic liquids that have not yet been measured.
Many chemists and biochemists require to know the ionization constants of organic acids and bases. This is evident from the Science Citation Index which lists The Determination of Ionization Constants by A. Albert and E. P. Serjeant (1971) as one of the most widely quoted books in the chemical literature. Although, ultimately, there is no satisfactory alternative to experimental measurement, it is not always convenient or practicable to make the necessary measure ments and calculations. Moreover, the massive pK. compilations currently available provide values for only a small fraction of known or possible acids or bases. For example, the compilations listed in Section 1. 3 give pK. data for some 6 000--8 000 acids, whereas if the conservative estimate is made that there are one hundred different substituent groups available to substitute in the benzene ring of benzoic acid, approximately five million tri-substituted benzoic acids are theoretically possible. Thus we have long felt that it is useful to consider methods by which a pK. value might be predicted as an interim value to within several tenths of a pH unit using arguments based on linear free energy relationships, by analogy, by extrapolation, by interpolation from existing data, or in some other way. This degree of precision may be adequate for many purposes such as the recording of spectra of pure species (as anion, neutral molecule or cation), for selection of conditions favourable to solvent extraction, and for the interpretation of pH-profiles for organic reactions.
In Protein Dynamics: Methods and Protocols, expert researchers in the field detail both experimental and computational methods to interrogate molecular level fluctuations. Chapters detail best-practice recipes covering both experimental and computational techniques, reflecting modern protein research. Written in the highly successful Methods in Molecular BiologyTM series format, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible laboratory protocols, and key tips on troubleshooting and avoiding known pitfalls. Authoritative and practical, Protein Dynamics: Methods and Protocols describes the most common and powerful methods used to characterize protein dynamics.
Both an introductory course to broadband dielectric spectroscopy and a monograph describing recent dielectric contributions to current topics, this book is the first to cover the topic and has been hotly awaited by the scientific community.
Specific ion effects are important in numerous fields of science and technology. This book summarizes the main ideas that came up over the years. It presents the efforts of theoreticians and supports it by the experimental results stemming from various techniques.
This series provides the chemical physics field with a forum for critical, authoritative evaluations of advances in every area of the discipline.