Water-structure maker

More complicated and less known than the structure of pure water is the structure of aqueous solutions. In all cases, the structure of water is changed, more or less, by dissolved substances. A quantitative measure for the influence of solutes on the structure of water was given in 1933 by Bernal and Fowler 23), introducing the terminus structure temperature, Tsl . This is the temperature at which any property of pure water has the same value as the solution at 20 °C. If a solute increases Tst, the number of hydrogen bonded water molecules is decreased and therefore it is called a water structure breaker . Vice versa, a Tsl decreasing solute is called a water structure maker . Concomitantly the mobility of water molecules becomes higher or lower, respectively. 

Protein stabilization by trehalose in aqueous solution is also an example of the biological functions of trehalose [84-86]. According to reports by Timasheff and coworkers, preferential hydration should occur when the interaction of a cosolvent with water is stronger than its interaction with a protein [85]. In other words, a water structure maker like trehalose is a good cosolvent causing... 

Ions that are water structure formers, lower the cloud point of POE nonionics, OH > F > Cl > Br, by decreasing the availability of nonassociated water molecules to hydrate the ether oxygens of the POE chain. Ions that are water structure breakers (large, polarizable anions soft bases SCN I-) increase the cloud point by making more water molecules available to interact with the POE chain (Schott, 1984). Thus, chloride ions, which are water structure makers, lower the cloud point iodide ions, which are structure breakers, raise it bromide ions have no pronounced effect. 

These algebraic signs have led to the classification of ions into water-structure-makers (Bt,i>0) and water-structure-breakers (Bt I<0) (Gurney 1953), and such effects are fully discussed in Sect. 3.1. 

Probably the first scientific study on specific salt effects was performed by Jean Luis PoiseuUle in 1847 [1]. He discovered that some salts increase the viscosity of water, whereas others decrease it. In the first half of the twentieth century, the investigations on specific ion effects on viscosity were further refined by Jones and Dole in 1929 [2] and Cox and Wolfenden in 1934 [3], Based on these studies, Frank and Evans [4] proposed the expressions water structure-maker and water-structure breaker, a concept that recently turned out to be slightly misleading, at least for simple 1-1 electrolytes in water. 

However, it should be mentioned that specific ion effects were found even several decades before Hofineister. In 1847, Poiseuille was probably the first who noted that some salts increase the viscosity of water, whereas others decrease it. Jones and Dole in 1929, Cox and Wolfenden in 1934, and several other groups further refined the specific ion effect on water viscosity. From these viscosity smdies and in particular the Jones-Dole viscosity B coefficients, the expressions for water-structure maker and water-structure breaker were finally derived. They were first introduced in 1945 by Frank and Evans, who showed the relationship between viscosity and entropy of dilution. There is a third concept introduced by A. Voet [see also Eckfeldt ] the ordering ofions according to their lyotropic numbers. It nicely correlates with ion effects on the swelling... 

Fig. 16. Division of the group lA cations and the VIIA halide anions into [strongly hydrated] kosmotropes (water structure makers) and [weakly hydrated] chaotropes (water structure breakers). The ions are drawn approximately to scale. A virtual water molecule is represented by a zwitterion of radius 1.78 A for the anionic portion and 1.06 A for the cationic portion. In aqueous solution, Li+ has 0.6 tightly attached water molecules, Na+ has 0.25 tightly attached water molecules, F has 5.0 tightly attached water molecules, and the remaining ions have no tightly attached water molecules. (After ColKns. °)...

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