A dielectric relaxation study of aqueous solutions of the amphiphilic model peptide N-acetyl-leucine amide (NALA) at 298 K over a wide range of hydration levels is presented. The experiments range from states where water builds up several hydration layers to states where single water molecules or small water clusters are shared by several NALA molecules. The dielectric spectra reveal two modes on the 10 and 100 ps timescales. These are largely broadened with regard to the Lorentzian shape caused by simple Debye-type relaxation, and are well described by the Kohlrausch–Williams–Watts stretched exponential function. The fast mode is assigned to water reorientation comprising bulk water as well as hydration water. Even when all water molecules are in contact with the solute, this fast component is dominant, and its mean relaxation time is retarded by less than a factor of two relative to neat water. The amplitude of the slow process is far higher than expected for the dipolar reorientation of the solute. The observations are consistent with results from molecular dynamics simulations for a similar model peptide reported in the literature. They suggest that the slow relaxation mode is mainly founded in peptide–water dipolar couplings, with some additional contribution from slowly reorienting hydration water molecules. The results are discussed with regard to the hydration dynamics of proteins and the interpretation of dielectric spectra of protein solutions.

The state of water confined in Aerosol-OT–hydrocarbon–water reverse micelles with cyclohexane, n-pentane, n-octane, and n-dodecane as apolar solvents is investigated by small-angle X-ray scattering and near-infrared vibrational spectroscopy of the first overtone of the OH stretching mode of water. The experiments focus on water/AOT molecular ratios W₀=2–20, where water is strongly affected by the confinement and surface–water interactions. The pair-distance distribution functions derived from the small-angle scattering patterns allows a detailed characterization of the topology of these systems, and they indicate deviations from monodisperse, spherical water pools for some of these hydrocarbon systems. In contrast to a common assumption, the pool size does not scale linearly with W₀ in going from dry reverse micelles (W₀0) to essentially bulk-like water (W₀>20). The first overtone of the OH-stretching vibration exhibits highly structured spectra, which reveal significant changes in the hydrogen bonding environment upon confinement. The spectra are rationalized by a core/shell model developed by Fayer and co-workers. This model subdivides water into core water in the interior of the micelle and shell water close to the interface. Core water is modelled by the properties of bulk water, while the properties of shell water are taken to be those of water at W₀=2. The model allows the representation of the spectra at any hydration level as a linear combination of the spectra of core and shell water. Different approaches are critically reviewed and discussed as well.

Ionische Flüssigkeiten sind organische Salze, die Schmelzpunkte in der Nähe der Raumtemperatur (oder gemäß Konvention unter 100 °C) aufweisen. Ihre einzigartigen Material- und Lösungsmitteleigenschaften sowie das Ziel einer nachhaltigen, “grünen” Chemie haben in den letzten Jahren zu einer erstaunlichen Zunahme des Interesses an diesen Salzen geführt. Eine riesige Anzahl von Kationen- und Anionenfamilien und unterschiedliche Substitutionen ermöglichen die gezielte Einstellung von Eigenschaften für spezifische Anwendungen. Da es unmöglich ist, auch nur einen geringen Bruchteil der möglichen Kation-Anion-Kombinationen experimentell zu untersuchen, ist ein Verständnis ihrer Eigenschaften auf molekularer Ebene unabdingbar. Allerdings wird dies durch die Komplexität ihrer zwischenmolekularen Wechselwirkungen erschwert, weshalb in der Literatur zahlreiche Kontroversen, Spekulationen und Mythen über angebliche Eigenschaften ionischer Flüssigkeiten zu finden sind. In diesem Aufsatz wird das gegenwärtige Wissen über die molekularen Grundlagen des Verhaltens ionischer Flüssigkeiten diskutiert.

Ionic liquids (ILs) are organic salts with melting points near room temperature (or by convention below 100 °C). Recently, their unique materials and solvent properties and the growing interest in a sustainable, “green” chemistry has led to an amazing increase in interest in such salts. A huge number of potential cation and anion families and their many substitution patterns allows the desired properties for specific applications to be selected. Because it is impossible to experimentally investigate even a small fraction of the potential cation–anion combinations, a molecular-based understanding of their properties is crucial. However, the unusual complexity of their intermolecular interactions renders molecular-based interpretations difficult, and gives rise to many controversies, speculations, and even myths about the properties that ILs allegedly possess. Herein the current knowledge about the molecular foundations of IL behavior is discussed.