Effect of monovalent ions

Lessard, J. G. Fragata, M., Micropolarities of lipid bilayers and micelles. 3. Effect of monovalent ions on the dielectric constant of the water-membrane interface of unilamellar phosphatidylcholine vesicles, J. Phys. Chem. 90, 811-817 (1986). 

Effect of Monovalent Ions on Cucumber Softening Rates... 

The conformational stability of biomolecules is greatly dependent on the solvent species. It is also affected by coexisting solutes such as salts (e.g., NaCl). The salt effects [47, 48, 49] on the solubility and the conformational stability of proteins in aqueous solutions are experimentally known to follow the order called the Hofmeister series. The series for anions is [S04 > CHsCOO" > Cl > Br > NOa" > CIOJ > 1 > CNS ], and that for cations is [(CH3)4N+ > NH > Rb+,K+,Na+, Cs+ > Li+ > Mg + > Ca + > Ba +j. In each of these series, the species to the left decrease the solubility of proteins and stabilize their native structures. The species to the right, on the contrary, increase the solubility and cause destabilization of the native structures. Though the Hofmeister series is not valid for acidic and basic proteins [50, 51], it is generally applicable to neutral proteins. The series, except for divalent cations, is also applicable to the other neutral substances such as benzene [52]. That is, the effects of monovalent ions on the solubility of various neutral substances follow the Hofmeister series. The microscopic mechanisms of these experimentally known properties, however, have not been elucidated yet. 

So far, for PEMs mainly the effects of monovalent ions are reported, which follow more or less the Hofmeister series. It is stUl unclear if this simple image as illustrated in Fig. 1 can be generalized to other ion types. Another open question is If the polarizability [25] or rather the ion hydrophobicity [17] presents the decisive parameter. 

Loosley-Millman M, Rand BR, Parsegian VA. (1982) Effects of monovalent ion binding and screening on measured electrostatic forces between charged phospholipid bilayers. BiophysJ40 221-232. 

Divalent and trivalent ions can precipitate PAA, and this phenomenon is related to the loss of a hydration region. Such precipitation is to be distinguished from salting-out effects which occur with high concentrations of monovalent ions. 

The charge screening effect of Ca2+ in increasing XCPS adsorption is more clearly seen in Figure 13 for the case of SiC where the NaCl content is lower (lg/1). Due to the low initial ionic strength, no adsorption is detected for both XCPS samples at low calcium concentration. The maximum adsorption level in this case is the same as that obtained in the presence of monovalent ions only (26). 

While for nonionic systems, the effect of inorganic salt on CMC is small, it is large for ionic surfactants and this difference is expected since the micelle - small ion interaction must be completely different in the two cases. The decrease in CMC for ionic systems corresponds usually to a linear relation between the logarithm of the CMC and the total counterion concentration, if a salt of the counterion is added. For divalent ions, the slope of the plot of log CMC versus counterion concentration is half of that of monovalent ions. 

The experiments demonstrate the development of a streaming potential in consolidated bentonite clay when flushed by a NaCl-solution of either low or high concentration. The streaming potential measured in our experiments is at least 5 to 10 times larger than values reported for bentonite in the literature. Apparently this is caused by a very low electric conductivity of the bentonite samples studied. This low conductivity might be ascribed to overlapping diffuse double layers on the clay particles, caused by the high compaction and the presence of monovalent ions in the equilibrium solution. The bentonite, thus compacted, will be a very effective medium for active application of electroosmosis. Compared with electrically shorted conditions, chemical osmosis will be reduced when the clay is not short-circuited. 

Recently, Schultes Spasic, Mohanty and Bartel studied in exquisite detail the effects of monovalent and divalent cations on the conformation order of random RNA sequences [115, 116]. These authors investigated the following questions Can arbitrary RNA sequences fold into a unique structure Is this is an evolutionary property of RNA sequences [115, 116] Schultes et al. utilized biochemical tools, such as lead ion induced cleavage, ultracentrifugation, and gel electrophoretic mobility, to probe the structure of evolved and random RNA sequences [115, 116]. 

The effect of divalent ions such as SO4 " has been studied either by electric permittivity techniques, or by viscosimetry. It was experimentally observed that the dielectric increment is larger than in the presence of monovalent ions. In the presence of the bivalent counterions there are two opposite effects. From one hand, the bivalent ions tend to increase the dielectric increment through a charge effect, while from the other hand the observed reduction of the viscosity proves that in the presence of SO4 - the polyions contract76). 

To eliminate this effect of ammonium ions, [Pd(en)2]2+ can be used. The results again show that a basal spacing is 1.200 nm, characteristic of monovalent ions. Therefore, we can conclude that a significant portion of palladium ions are sorbed on the edge sites. 

Some other recent studies have been concerned with the effects of monovalent cations. Hiraoka and Sugai (1984) showed that one Na(I) ion binds to a specific site in a-lactalbumin, presumably the Ca(II) binding site. The bound Na(I) stabilizes the native form of the protein. Hiraoka and Sugai (1985) reported that both Na(I) and K(I) stabilize the nativelike state of a-lactalbumin. However, the conformational change induced by these ions, from the partially unfolded apo form to the native form, is slow compared to that brought about by Ca(II). 

Two possibly related phenomena have been found to be dependent on the flux of monovalent ions. The hypothetical common link is represented by a newly discovered family of intracellular proteases whose activity may be influenced by concentrations. Interleukin converting enzyme (ICE) is the best studied member of this family. Efflux of from monocytes leads to activation of ICE, so that the cells rapidly process and export IL-16 (Walev etal., 1995). An ICE-related protease is involved in regulating programmed cell death, which may be the reason why formation of K -permissive pores by alpha-toxin in human T-lymphoctes causes apoptosis (Jonas et a/., 1994). Both apoptosis and ICE-activation are inhibited when alpha-toxin treated cells are suspended in K" -rich medium. It is of interest that simultaneous flooding of cells with Ca , such as occurs when larger pores are formed in lymphocytes (e.g. at high alpha-toxin concentrations or with . coli hemolysin) counteracts the apoptosis-promoting effect of K -efflux (Jonas et a/., 1994). 

House, W.A., The role of surface complexation in the dissolution kinetics of silica Effects of monovalent and divalent ions at 25 °C, J. Colloid Interf. Sci., 163, 379, 1994. 

The Donnan equilibrium theory implies that dilution of a clay/water system containing monovalent and divalent cations displaces the equilibrium in such a manner that the absorption of divalent ions increases, whereas the absorption of monovalent ions decreases. The ionic charge is not the only determining factor in the absorption effect. Factors such as temperature, pH, and specific ions also play important roles. Hydration energy, which appears to be one of the most important factors for the absorption and fixation of cations, displaces the ionic equilibria in a manner opposing the Donnan equilibrium theory. According to Sawhney (1972), "cations with low hydration energy such as Ca, Mg and Sr, produce expanded interlayers and are not fixed". 

Up to now only monovalent ions have been investigated. For multivalent ions the prediction of the PB theory is that for the distribution function P(r) only the product of the Manning parameter and the counterion valence v matters. Therefore a system of monovalent ions at ln = 3a is claimed to have the same distribution function as a system of trivalent ions at B = lo It will now be shown that this statement is an artifact of the PB approximation. Figure 9 shows examples of systems that are complementary in the described sense. Not only is the condensation enhanced as compared to PB theory, but the enhancement is stronger for the case involving multivalent ions. Two different reasons may be suggested to explain this effect ... 

The ability of metal ions to modify the texture of fruit and vegetable tissue has been studied since 1939, when Kertesz (l) found that calcium ions improved the firmness of tomatoes. A very simplified generalization of the effects of metal ions on fruit and vegetable texture is that monovalent cations, usually Na+ and K, cause tissue softening. Examples of this softening effect include results with peas (2.31, dried peas (4), carrots (5), potatoes (6) and green beans (7). On the other hand calcium, a divalent cation,... 

Besides potential-determining ions, other electrolytes can have a strong influence on surface charge. The effect of adding trivalent or divalent ions versus monovalent ions is accounted for by the ionic strenth term in EDL theory. Within a given valence state the lyotropic series indicates, in decreasing order, the effectiveness of different ions in terms of coagulating power ... 

---