Liquid water specific interactions

In comparison with traditional biphasic catalysis using water, fluorous phases, or polar organic solvents, transition metal catalysis in ionic liquids represents a new and advanced way to combine the specific advantages of homogeneous and heterogeneous catalysis. In many applications, the use of a defined transition metal complex immobilized on a ionic liquid support has already shown its unique potential. Many more successful examples - mainly in fine chemical synthesis - can be expected in the future as our loiowledge of ionic liquids and their interactions with transition metal complexes increases. 

Here we present and discuss an example calculation to make some of the concepts discussed above more definite. We treat a model for methane (CH4) solute at infinite dilution in liquid under conventional conditions. This model would be of interest to conceptual issues of hydrophobic effects, and general hydration effects in molecular biosciences [1,9], but the specific calculation here serves only as an illustration of these methods. An important element of this method is that nothing depends restric-tively on the representation of the mechanical potential energy function. In contrast, the problem of methane dissolved in liquid water would typically be treated from the perspective of the van der Waals model of liquids, adopting a reference system characterized by the pairwise-additive repulsive forces between the methane and water molecules, and then correcting for methane-water molecule attractive interactions. In the present circumstance this should be satisfactory in fact. Nevertheless, the question frequently arises whether the attractive interactions substantially affect the statistical problems [60-62], and the present methods avoid such a limitation. 

This very specific ability of perfluorinated compounds to dissolve gases has found an application in oxygen carrier liquids (short-time blood substitutes). A perfluorocarbon dissolves three times more oxygen than the corresponding hydrocarbon, and ten times more than water. This property can be explained by the presence of large cavities in the liquid and by the weak intermolecular interactions of the medium, and not by specific interactions. 

BiCl3 is, however, little conducting in the liquid phase, and it resembles nonionic rather than ionic fluids. This may warn that specific interactions may destroy the peculiar effects of ionic criticality. Likewise, water (Tc = 647 K) shows Ising behavior [61]. At the critical point, autoprotolysis of water is enhanced by three orders of magnitude relative to ambient conditions [62]. 

Besides, the review could conditionally be divided in accord with another criterion, (a) In Sections III-V and VII we discuss so-called unspecific interactions, which take place in a local-order structure of various polar liquids, (b) In Sections VI-IX we also consider specific interactions [16]. These are directly determined by the hydrogen bonds in water, are reflected in the band centered at 200 cm-1, which is termed here the R-band, and is characterized by some spectral features in the submillimeter wavelength range (from 10 to 100 cm-1). Note that sometimes in the literature the R-band is termed the translational band, since the peak frequency of this band does not depend on the moment of inertia I of a water molecule. 

Thus, specific interactions directly determine the spectroscopic features due to hydrogen bonding of the water molecules, while unspecific interactions arise in all or many polar liquids and are not directly related to the H-bonds. Now it became clear that the basis of four different processes (terms) used in Ref. [17] and mentioned above could rationally be explained on a molecular basis. One may say that specific interactions are more or less cooperative in their nature. They reveal some features of a solid state, while unspecific interactions could be understood in terms of a liquid state of matter, if we consider chaotic gas-like motions of a single polar molecule, namely, rotational motions of a dipole in a dense surroundings of other molecules. The modem aspect of the spectroscopic studies leads us to a conclusion that both gas-like and solid-state-like effects are the characteristic features of water. In this section we will first distinguish between the following two mechanisms of dielectric relaxation ... 

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