Interaction of ionic liquids ions with natural cyclodextrins.

The interaction of natural α-, ß-, and γ-cyclodextrins (CDs) with 14 hydrophobic ionic moieties of ionic liquids (ILs) was systematically examined in dilute aqueous solutions using isothermal titration microcalorimetry (ITC) and NMR spectroscopy. The studied cationic and anionic moieties involved some recently developed heavily fluorinated structures, as well as some others of common use. To isolate the effect of a given ion, the measurements were performed on salts containing the hydrophobic IL ion in question and a complexation-inactive counterion. Additional ITC experiments on ILs whose both cation and anion can interact appreciably with the CD cavity demonstrated that to resolve the effect of individual ions from such data is generally a tricky task and confirmed the superiority of the isolation strategy adopted for the purpose throughout this work. The binding constant, enthalpy and entropy determined at 298.15 K for the 1:1 (ion:CD) inclusion complex formation range in broad limits, being 0 < K < 2 × 10(5), 0 < -Δ(r)H°/(kJ·mol(-1)) < 44, and -28 < TΔ(r)S°/(kJ·mol(-1)) < 14, respectively. The stabilities of complexes of perfluorohexyl bearing ions with ß-CD belong to the highest ever observed with natural CDs in water. The established binding affinity scales were discussed in both thermodynamic and molecular terms. The concepts of hydrophobic interaction and guest-host size matching supported by simple molecular modeling proved useful to rationalize the observed widely different binding affinities and suggest possible binding modes. Enthalpy and entropy contributions to the stability of the ion-CD complexes were found to compensate each other considerably obeying more or less the linear compensation relationship marked by existing literature data on binding other guests to natural CDs. As outliers to this pattern, the most stable complexes of -C(6)F(13) bearing ions with ß-CD were found to receive an enhanced inherent entropy stabilization due to extraordinarily high extent of desolvation occurring in the course of binding.

The influence of hydrogen bonding on the physical properties of ionic liquids.

Potential applications of ionic liquids depend on the properties of this class of liquid material. To a large extent the structure and properties of these Coulomb systems are determined by the intermolecular interactions among anions and cations. In particular the subtle balance between Coulomb forces, hydrogen bonds and dispersion forces is of great importance for the understanding of ionic liquids. The purpose of the present paper is to answer three questions: Do hydrogen bonds exist in these Coulomb fluids? To what extent do hydrogen bonds contribute to the overall interaction between anions and cations? And finally, are hydrogen bonds important for the physical properties of ionic liquids? All these questions are addressed by using a suitable combination of experimental and theoretical methods including newly synthesized imidazolium-based ionic liquids, far infrared spectroscopy, terahertz spectroscopy, DFT calculations, differential scanning calorimetry (DSC), viscometry and quartz-crystal-microbalance measurements. The key statement is that although ionic liquids consist solely of anions and cations and Coulomb forces are the dominating interaction, local and directional interaction such as hydrogen bonding has significant influence on the structure and properties of ionic liquids. This is demonstrated for the case of melting points, viscosities and enthalpies of vaporization. As a consequence, a variety of important properties can be tuned towards a larger working temperature range, finally expanding the range of potential applications.

Comparative evaluation of two newly developed devices for capillary viscometry.

Viscometry is an often applied method in clinical chemistry. A variety of studies demonstrate an association of parameters related to blood viscosity with human pathology of varying origin. Whole blood and plasma viscosity are considered to be clinically useful indicators in the diagnostic workup and therapy monitoring of certain diseases. In this study, we compare the "Waegeviskosimeter" (WV) described in previous publications with a newly developed device, the "Reverse Flow Viscometer" (RFV). Both viscometers are capillary flow viscometers. Both overcome the disadvantage of common viscometers of the Ubbelohde and Cannon-Fenske type which require large amounts of plasma and which can be only applied to Newtonian fluids. The accuracy of the measurements of both viscometers, requiring less than 1.0 ml sample volume, is superior to most conventional methods. The major distinction in the functionality of the WV and the RFV is that the WV measures the kinematic viscosity whereas the RFV directly estimates dynamic viscosity without the requirement of additional density measurement. We found good reproducibility of viscosity with coefficient of variation CV < or =1.1% for both viscometers. Quality assurance measures have been carried out. Because no quality assurance scheme according to the guidelines proposed by the German Medical Association exists for plasma or whole blood viscosity, we tested reference material Lyphochek Unassayed Chemistry Control Level 1 and Level 2 (Bio-Rad Laboratories). We determined the viscosities 1.40 mPa s and 1.08 mPa s (37 degrees C) and the between-run precision from daily quality control runs with CV of 1.4% and 1.2% for the WV, and 1.7% and 1.4% for the RFV. For direct comparison reasons, we determined the viscosity in seventy human plasma and serum samples by both methods. Using the regression analysis described by Passing-Bablok, the RFV and the WV methods are highly correlated and show only little variations (r = 0.990, tau = 0.896). The regression equation is y(WV) = 1.035x(RFV) - 0.056 with a mean deviation of 0.4+/-3.6%. We conclude that both new devices for viscosity assessment fulfill all quality requirements as prescribed for clinical chemical laboratories. One advantage RFV is to measure the dynamic viscosity directly.