Models and mechanisms of Hofmeister effects in electrolyte solutions, and colloid and protein systems revisited

Abstract

Specific effects of electrolytes have posed a challenge since the 1880's. The pioneering work was that of Franz Hofmeister who studied specific salt induced protein precipitation. These effects are the rule rather the exception and are ubiquitous in chemistry and biology. Conventional electrostatic theories (Debye-Hückel, DLVO, etc.) cannot explain such effects. Over the past decades it has been recognised that additional quantum mechanical dispersion forces with associated hydration effects acting on ions are missing from theory. In parallel Collins has proposed a phenomenological set of rules (the law of matching water affinities, LMWA) which explain and bring to order the order of ion-ion and ion-surface site interactions at a qualitative level. The two approaches appear to conflict. Although the need for inclusion of quantum dispersion forces in one form or another is not questioned, the modelling has often been misleading and inappropriate. It does not properly describe the chemical nature (kosmotropic/chaotropic or hard/soft) of the interacting species. The success of the LMWA rules lies in the fact that they do. Here we point to the way that the two apparently opposing approaches might be reconciled. Notwithstanding, there are more challenges, which deal with the effect of dissolved gas and its connection to 'hydrophobic' interactions, the problem of water at different temperatures and 'water structure' in the presence of solutes. They take us to another dimension that requires the rebuilding of theoretical foundations.

Salt Dependence of the Tribological Properties of a Surface-Grafted Weak Polycation in Aqueous Solution

“…The most important factors on the enthalpy of the hydration for salt with water are the ion radius size and the ion charge, where an ion with a smaller radius (such as chloride) has greater hydration enthalpy than an ion with a larger radius (such as iodide) [61]. The amount of hydrogen bonding was found to reduce with smaller halide anions, as suggested by previous spectroscopic experiments [62].…”

Towards Versatile and Sustainable Hydrogen Production through Electrocatalytic Water Splitting: Electrolyte Engineering

“…As such, a further rationalization of the solubility of the gases is clearly more complicated, and it falls outside of our scope here. For details of such “specific ion effects”, the readers are referred to other articles 59, 61, 71…”

Biophysical and Structural Studies of Escherichia coli Mechanosensitive Channel of Large Conductance in Lipid Bilayers

“…Yang, 2009), but the effect of individual ions is more complicated. SO4 2-has a higher ionic strength than Cl -with respect to proteins (Baldwin, 1996;Salis & Ninham, 2014), but it has a weaker strength than Cl -with respect to liposomes (Clarke & Lupfert, 1999;Petrache et al, 2006). In this trial, SO4 2-was shown to induce larger membrane formation (Fig.…”

“…An additional consideration for 2D crystallography is that ions can facilitate the fusion of lipid bilayers either by attracting liposomes which would otherwise electrostatically repel each other (Akashi et al, 1998;Bentz & Duzgunes, 1985;Ruso et al, 2003), or through Hofmeister ion effects where ions of inorganic salts indirectly influence the solubility of organic molecules (primarily proteins but also applicable to phospholipids) via weak interactions with bulk water molecules (Baldwin, 1996;Salis & Ninham, 2014;Z. Yang, 2009).…”

“…The position of ions in the Hofmeister series affects the solubility/aggregation of both proteins (Baldwin, 1996;Salis & Ninham, 2014) and phospholipids (Clarke & Lupfert, 1999;Petrache et al, 2006;Z. Yang, 2009), but the effect of individual ions is more complicated.…”