Non-classical hydrophobic effects

A mainstay of the classical partition model is the experimental observation that the major thermodynamic driving force for sorption is the hydrophobic effect. The hydrophobic effect results from gain in free energy when non- or weakly-polar molecular surface is transferred out of the polar medium of water 2-4), The hydrophobic effect is manifested by a linear free energy relationship (LFER) between the NOM-normalized partition coefficient (A om) and the w-octanol-water partition coefficient K ) [i.e.. In nom a n + b where a and b are regression constants], or the inverse of the compound s liquid (or theoretical subcooled liquid) saturated water solubility CJ) [i.e.. In AT om = -c In + d. ... 

Although there is overwhelming experimental evidence that the hydrophobic interaction is entropy-driven , this classical view is still a matter of debate [79a, 167, 227, 229-231, 343-347]. For example, it has been claimed that the major eontribution to the hydrophobic interaction between the methylene groups of n-alkanes is an enthalpic and not an entropic effect [230]. In other words, the poor solubility of non-... 

ILs can act as both hydrogen bond acceptors (anions) and donors (cations), and as expected, they interact with substances with both acceptor and donor sites. In particular, 1,3-dialkylimidazolium ILs can dissolve a plethora of classical polar and non-polar compounds. All 1,3-dialkylimidazolium ILs reported to date are hygroscopic, and their miscibility with water is largely controlled by the nature of the anion. While salts containing nitrate, chloride, and perchlorate anions are usually miscible with water in all compositions, those associated with hexafluorophosphate and bis(trifluoromethane) sulfonylamidate anions are almost completely immiscible with water.It is also known that an increase in the A-alkyl chain length increases the hydrophobicity for a series of l-alkyl-3-methylimidazolium hexafluorophosphate ILs." The miscibility of water in ILs can be increased by the addition of short-chain alcohols or lowered by the addition of salts (salting-out effect). ... 

As described earlier, the lifetimes and quantum yields of emissive Ln complexes vary dramatically due to the extremely sensitive nature of the 4/-centred excited states to 0-H, N-H and C-H vibrational manifolds, which can provide efficient, non-radiative deactivation pathways the efficiency of energy transfer between the antenna and lanthanide ion also determines overall quantum yields. A classical approach to maximising the emissivity of Ln complexes is to therefore inhibit the approach of water solvent to the inner coordination sphere (and where q denotes the number of coordinated solvent molecules) high denticity, metal ion encapsulating ligands with hydrophobic peripheries can achieve this very effectively, reducing q to zero [4]. 

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