Wasser: von Clustern in die Flüssigkeit

Abstract

Wasser ist für jede Form des Lebens von fundamentaler Bedeutung und spielt in vielen biologischen und chemischen Prozessen eine wichtige Rolle. Obwohl Wasser zu den am häufigsten vorkommenden Substanzen zählt, ist es bei Weitem keine einfache Flüssigkeit. Wasser weist stark polare Wasserstoffbrücken auf, die für eine Reihe anomaler physikalischer und chemischer Eigenschaften verantwortlich sind. Seit mehr als einem Jahrhundert inspirieren die Bedeutung und die Besonderheiten des Wassers Wissenschaftler zur Entwicklung von Modellen, die das beobachtete Verhalten von Wasser reproduzieren können. Die Kenntnisse über Struktur und Bindung in kleinen Wasserclustern sind ein Schlüssel für das Verständnis von Wasser in der flüssigen Phase und im Eis sowie seiner Lösungsmitteleigenschaften. Moderne quantenmechanische und hochauflösende spektroskopische Methoden konnten in jüngster Zeit große Erfolge bei der Charakterisierung solcher Cluster erringen. Mit Clustermodellen versucht man, den Übergang von solchen Strukturen in die Flüssigkeit nachzuvollziehen. Die wichtige Frage lautet nun: Wie müssen solche Cluster beschaffen sein, damit sie Wasser im flüssigen Zustand beschreiben können?

Control over the Structure of Ice and Water by Block Copolymer Additives

“…[29] The crude product was cleaned by exhaustive ultrafiltration (membrane MWCO 1 kDa, Millipore) until the signals of the 1,5-cyclooctanol side product were no longer visible in the 13 C NMR. The product was characterized by 1 H NMR and GPC. The phosphorylation of the hydroxyl side groups and product cleaning by two-day dialysis was performed as described by Penczek et al [30] and Rudloff et al [11] The degree of phosphorylation was determined by quantitative 31 P NMR spectroscopy.…”

“…The properties of water, including the lower density of solid ice compared to water, are due to a locally highly ordered superstructure, that is, water is a ™supramolecular∫ solvent. [1] Recent force measurements between objects on the nanoscale reveal that colloidal interaction in water is indeed by far more complicated than assumed, [2] and that the classical view of water increacingly becomes a hindrance for refining the molecular understanding of some basic effects.…”

“…The properties of water, including the lower density of solid ice compared to water, are due to a locally highly ordered superstructure, that is, water is a ™supramolecular∫ solvent. [1] Recent force measurements between objects on the nanoscale reveal that colloidal interaction in water is indeed by far more complicated than assumed, [2] and that the classical view of water increacingly becomes a hindrance for refining the molecular understanding of some basic effects.Antifreeze proteins are a remarkable example of the specific interaction of polymers with water or ice. [3] They are found in the blood and tissues of Antarctic marine fish or cold-resistant plants and insects and are essential to avoid organisms freezing to death by the uncontrolled formation of ice crystals.…”

“…A large number of theoretical models for the structure of water has been developed in order to explain its anomalous properties, as recently reviewed. [1] Most models describe the structure of water based on an infinite hydrogen bonded network with short-range ordering. Other models have been described based on the presence of water clusters within cavities in the hydrogen bonded network.…”

Nonempirical Quantification of Molecular Interactions in Supramolecular Assemblies

“…By comparison, computations of this charge transfer term of water clusters by rigorous ab initio methods (RHF/6-31 G* level) lead to values between 0.009 and 0.017. [42] This good agreement is obviously linked to the fact that our atomic parameterization (c 0 , r) is completely free of any empirical parameters, allowing us a direct comparison with ab initio results.…”