Interpretation of the Hofmeister Series

3 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]. 

TABLE 8.13 Cation Parameters that Might he Relevant to their ordering in the Hofmeister Series 

BostrOm et al. [121-123] emphasized the importance of dispersion forces regarding the specific ion effects on both protein-related and non-protein-related Hofmeister effects. Silica membranes show Hofmeister series effects in pH measurements with a glass electrode in moderately concentrated salt solutions, 0.8 M. The order of decreasing pH is NaCl NaBr NaNOj NaClO ascribed to competition between the polarizability of the anions and electrostatic interactions at the surface of the glass electrode. 

It is furthermore concluded that whereas the anion Hofmeister series is generally well established, with only few reversals that can be explained ad-hoc, this is not the case regarding the cation Hofmeister series. There are in general no head cations established in a series such as (5.8), erroneously termed chaotropic, nor general tail cations , erroneously termed cosmotropic, but for each surface the hydrophilic and hydrophobic character or balance between these properties is responsible for the order of cations interacting directly with sites at the surface, in addition to the ion properties mentioned above, see Table 5.4 for the latter. 

---