Pamela M. Dean

Understanding the effect of the C2 proton in promoting low viscosities and high conductivities in imidazolium-based ionic liquids: part I. weakly coordinating anions

1,3-Disubstituted imidazolium ionic liquids have been the subject of numerous theoretical and experimental studies due to their low viscosity-often the very lowest for any given cation/anion family. One of the mysteries in the imidazolium family of salts is the sharp increase in viscosity that is observed on methylating at the C2 position in the ring. In the nonmethylated case, the C2 proton is observed to be distinctly acidic and, where this is undesirable, substitution of the C2 position removes the problem, but produces an unexpected increase in viscosity. Methylation at other positions on the ring does not produce such a significant effect. In this study, two possible structural or energetic sources of the increased viscosity were investigated: (1) ion association, as probed by the Walden rule, and (2) differences in the potential energy surface profiles that favor ionic transport in the non C2-methylated imidazolium ionic liquids. The second hypothesis was investigated using high-level ab initio theory. The higher viscosity of C2-methylated imidazolium ionic liquids is shown to be a result of high potential energy barriers (significantly above the available thermal energy) between the energetically preferred conformations on the potential energy surface, thus restricting movement of ions in the liquid state to only small oscillations and inhibiting the overall ion transport.

Structural analysis of low melting organic salts: perspectives on ionic liquids

Ionic liquid-forming salts often display low melting points (a lack of crystallisation at ambient temperature and pressure) as a result of decreased lattice energies in the crystalline state. Intermolecular interactions between the anion and cation, and the conformational states of each component of the salt, are of significant interest as many of the distinctive properties ascribed to ionic liquids are determined to a large extent by these interactions. Crystallographic analysis provides a direct insight into the spatial relationship between the cations and anions and provides a basis for an enhanced understanding of the physico-chemical relationship of the ionic liquids. This perspective article examines the crystallographic studies of relevance to ionic liquid-forming organic salts as a basis for the rational design and synthesis of novel ionic liquids.

Crystal packing in the 2-R,4-oxo-[1,3-a/b]-naphthodioxanes - Hirshfeld surface analysis and melting point correlation

The crystal structures of an array of 2-R,4-oxo-[1,3-b]-naphthodioxanes (R = H, Me, Et, i-Pr, n-Bu, CCl3, i-propylideneglyceral) have been determined at 100 K, together with a more limited series of the isomeric 2-R,4-oxo-[1,3-a]-naphthodioxanes (R = Et, i-Pr, n-Bu, i-propylideneglyceral), permitting a study of the effects of substituent and ring fusion variation on the crystal packing of neutral molecules that are otherwise essentially planar. We have conducted an analysis of Hirshfeld surfaces (a definition of an outer contact surface of a molecule within a crystal) for all eleven compounds and follow the changes of different properties on these surfaces upon systematic variation of the substituent R. Not only qualitative information by means of fingerprint plots, but also quantitative information by means of melting point correlations are presented. The results show the extent to which C–H⋯O hydrogen bonds and C–H⋯π/π⋯π interactions contribute positively to the lattice energies on the one hand, and H⋯H contacts negatively on the other. The percentage of H⋯H contacts as closest contacts on the Hirshfeld surfaces is a universally applicable measure of the crystal lattice energy and can be used as a reference for the importance of other types of contacts.

Interactions in bisamide ionic liquids—insights from a Hirshfeld surface analysis of their crystalline states

The intermolecular interactions of a series of crystallised bis(trifluoromethanesulfonyl)amide (NTf2) and bis(methanesulfonyl)amide (NMes2) ionic liquids are qualitatively investigated and compared using Hirshfeld surface and thermal analysis techniques. The NMes2 salts are known to exhibit higher glass transitions and higher viscosities than those of the NTf2 salts. The origins of these differences were analysed in terms of the importance of factors such as the C–H⋯O hydrogen bond, fluorination, presence of an aromatic moiety and length of alkyl chain, using the Hirshfeld surfaces and their associated fingerprint plots. Additionally, the existence of C–F⋯π and C–H⋯π interactions were elucidated and the significance of anion–anion interactions was recognised. Overall, these results demonstrate the applicability of the Hirshfeld surface approach in investigating the molecular origins of the physical properties.

Structural Characterization of Novel Ionic Salts Incorporating Trihalide Anions

The crystal structures of several low-melting salts containing trihalide ions, namely 1-ethyl-3-methylimidazolium tribromide ([C2mim][Br3]), 1-ethyl-1-methylpyrrolidinium tribromide ([C2mpyr][Br3]), and 1-propyl-1-methylpyrrolidinium triiodide ([C3mpyr][I3]), are reported for the first time. Thermal analysis reveals that the tribromide salts are lower-melting than their monohalide analogues. Analysis of the crystal structures allows examination of the influence of the anions on the physical properties of the salts.

Sodium pyridine-3-carboxylate.

The title compound, also known as sodium nicotinate, Na(+).C(6)H(4)NO(2)(-), consists of two unique Na atoms coordinated to two unique pyridine-3-carboxylate ligands through the N atoms and carboxylate groups. One Na atom and one pyridine-3-carboxylate ligand lie on a twofold axis. Extensive Na coordination results in a three-dimensional array comprising infinite NaO(2)CR chains linked by intrachain Na-N bonds.

1-Methyl-1-propyl­pyrrolidinium chloride

The aymmetric unit of the title compound, C8H18N+·Cl−, consists of one crystallographically independent 1-methyl-1-propylpyrrolidinium cation and one chloride anion, both of which lie in general positions. Minor hydrogen-bonded C—H⋯Cl interactions occur. However, no classical hydrogen bonding is observed.

Efficient Synthesis of Ellagic Acid Salts Using Distillable Ionic Liquids

A direct, one pot synthesis of an ellagic acid salt was achieved at room temperature by dimerization of ethyl gallate using N,N-dimethylammonium N′,N′-dimethylcarbamate, a distillable ionic liquid, as solvent.

Immunological effects among workers who handle engineered nanoparticles

Objective To determine whether exposure of workers handling engineered nanoparticles (ENPs) may result in increased inflammation and changes in lung function. Methods A prospective panel study compared changes in several markers of inflammation for ENP handling and non-ENP handling control workers. Nanoparticle exposure was measured during ENP handling and for controls. Lung function, fraction of exhaled nitric oxide (FeNO), C-reactive protein (CRP), blood cell counts and several serum cytokines were measured at baseline, at the end of the shift and at the end of the working week. Results Nanoparticle exposure was not higher when ENPs were being handled; nanoparticle counts were higher in offices and in ambient air than in laboratories. There were no differences at baseline in lung function, FeNO, haemoglobin, platelet, white cell counts or CRP levels between those who handled nanoparticles and those who did not, with or without asthmatic participants. There were statistically significant increases in sCD40 and sTNFR2 over the working day for those who handled ENPs. The changes were larger and statistically significant over the working week and sCD62P also showed a statistically significant difference. The changes were slightly smaller and less likely to be statistically significant for atopic than for non-atopic participants. Conclusions Even at low ENP exposure, increases in three cytokines were significant over the week for those who handled nanoparticles, compared with those who did not. However, exposure to low and transient levels of nanoparticles was insufficient, to trigger measurable changes in spirometry, FeNO, CRP or blood cell counts.

Methyl 9H-xanthene-9-carboxyl­ate

The title compound, C15H12O3, was obtained unintentionally as the by-product of an attempted recrystallization from methanol of propantheline bromide, an antimuscarinic drug. The xanthone unit is folded, with a dihedral angle of 24.81 (9)° between the benzene rings. The ester substituent adopts a trans staggered conformation, with a C—C—O—C torsion angle of 178.4 (1)°. The molecules pack in distinct layers, facilitated by C—H⋯π and weak π–π ring interactions. A weak C—H⋯O interaction also occurs; however, no classical hydrogen bonding is observed.