Hofmeister series of ions

Figure 6.9. The Hofmeister Series of ions a ranking of organic and inorganic ions in terms of their effects on protein solubility and several features of water structure (see Collins and Washabaugh, 1985 Leberman and Soper, 1995 von Hippel and Schleich, 1969). Note that several of the stabilizing ions are incorporated into the structures of protein-stabilizing osmolytcs (see text).

Interpretation of the Hofmeister Series Many different explanations of the Hofmeister series of ions have been proposed over the years. Specific ion interactions with specific sites of the biomolecules must be taken into account and a subtle balance of several competing evenly matched interactions, such as differences in hydration strength, dispersion forces, polarization, ion size effects, and the impact on interfacial water structure, is involved according to Koelsch et al. [116] and Tobias and Hemminger [117]. 

Figure 8.6 Hofmeister series of kosmotropic and chaotropic ions.

Sulfate is one of the Hofmeister series of anions, a ranking of the ability of various ions to precipitate proteins (Kunz et al. 2004). In simple terms, precipitation of proteins by kosmotropic anions occurs due to salting out - a competition between the anion and the protein for water of solvation resulting in a loss of water from the protein surface. This process is classically applied in ammonium sulfate precipitation as the first step in many protein purification schemes, although the levels employed are several fold higher than those in wine. In the particular case of white wine, this loss of water of solvation, even by a relatively low amount of sulfate anion, by a protein in a solution containing a variety of cations and other anions and... 

Thus, it is urged on the researchers on solution chemistry and biophysics to call what they studied specific ion effects if the study does not pertain to aqueous electrolytes (ions) near surfaces at appreciable concentrations (where the Hofmeister series or effect is appropriate) nor should they invoke kosmotropic and chaotropic properties if their study does not pertain to dilute aqueous electrolytes (ions) in homogeneous solutions. The fact, that the order in a series of ions correlates with the Hofmeister series or with the series of ions according to their kosmotropic and chaotropic properties does not justify per se having such epithets in the title of the paper rather than specific ion effects with which the paper really deals. This field was... 

Leontidis E, Aroti A (2009) Liquid expanded monolayers of lipids as model systems to understand the anionic Hofmeister series 2. Ion partitioning is mostly a matter of size. J Phys Chem B 113 1460-1467... 

With the help of selectivity coefficients, such as in Eqs. (4.51) and (4.52) a general order of affinity can be given. For most clays the Hofmeister series (the same series as was given in Eq. (2.17) for the affinity of ions to oxide surfaces)... 

A number of studies have reported the abilities of different eluting salts to produce both different resolution and different selectivities.17 23 As expected, polyvalent ions are stronger eluters than monovalent ions. Some studies have suggested a correlation between eluting ability and ranking in the Hofmeister series. Others fail to observe this correlation, but nevertheless note differences in elution behavior. Overall, it is impossible to predict which eluting ions, if any, may produce a... 

An empirically derived relationships that describes the systematic effects of different neutral salts on the solubility of proteins. Collins and Washabaugh indicate that the order of ionic species eluding from a Sephadex G-10 column corresponds to the known order of effectiveness ions in the Hofmeister series on protein solubility ... 

Substances destroying the water structure, fhe so-called chao-tropic substances such as urea, guanidinium hydrochlorid, or some organic solvents such as mefhanol, efhanol, or acetonitrile, suppress hydrophobic interactions. Ions also alter the water structure. The power of destruction of water structure is given by the Hofmeister series ... 

Differences in both the charge density and the hydration of ions determine the Hofmeister series (lyotropic series).91... 

Negative values ofN —N0, the electrolyte effect on the association numbers of water, are called the structure-breaker effect. One can speak of negative hydration31. The estimation of the hydration numbers by spectroscopic or solubility methods gives only an approximation of the sum effect. The spectra of the H-bond bands show in second approximation distinct differences between the ion effects on the H-bonds7 ). — The partial molar volume Vx of water in electrolyte solutions is negative in all solutions but the series of -values corresponds to the Hofmeister ion series too. The negative V1 volume indicates an electrostriction effect around the ions. 

In considering the differential or selective binding of one anion or another, the intrinsic properties of anions mean that we are not on a level playing field it is considerably easier to bind some anions than others. In general, in the absence of specific chemical recognition between anion and host, anion binding selectivity, particularly in solvent extraction experiments or in the detection of anions by membrane-based ion selective electrodes, follows the order of anion hydrophobicity. This order is termed the Hofmeister series, or lyotropic series and was first outlined in 1888 from experiments based on the... 

Several of the polymer membrane anion-selective electrodes described in the literature use quaternary ammonium salts as ion carriers (ionophores) (7). These electrodes respond according to the Hofmeister series (CIO4 > SCN > I > NO3 > Br - N3 > NC>2 > Cl > HCO3 acetate) (2, 5), which is the order of relative lipophilicity of the anions. Therefore, in strict terms, electrodes that respond according to this series could be considered "nonselective". 

The potentiometric behavior of electrodes based on these films was studied (Figure 8). These ISEs presented sub-Nemstian slopes for thiocyanate (from -40 to -53 mV/decade, depending on the buffer used), and had detection limits of 5xl0 7 M. The response time of the electrodes was typically less than 25 s. The selectivity pattern observed was thiocyanate > perchlorate > iodide > nitrite - salicylate bromide > chloride > bicarbonate > phosphate. This anion-selectivity behavior does not follow the Hofmeister series, with thiocyanate and nitrite being the ions that deviate the most from it. This indicates that there is a selective interaction of the immobilized porphyrin with the two anions. 

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