Specific cation sequences

SPECIFIC CATION SEQUENCES IN THE REVERSAL OF CHARGE OF COLLOIDS OF ACIDIC NATURE WITH INORGANIC CATIONS... 

Specific cation sequences in the reversal of charge of colloids of acidic... 

Essentially identical results were obtained by a second group with fcj = 1.4+0.3 l.mole . sec at 25 °C (/i = 0.02 M). Specific cation effects were also found with rate sequences K > Na" N(C2H40H)4. > Li" " and positive deviations of the reaction orders above unity were also noted. 

The stabilization of the radical cation by forming a polaron is a trade-off between its delocalization and the energy required to distort the DNA structure. The former lowers the kinetic energy of the intrinsically quantum mechanical migrating radical cation, and the latter will be determined by factors that are independent of specific base sequence, such as the force constants of bonds in the sugar diphosphate backbone. 

Sears and Schulman (51) measured surface pressures and potentials vs. molecular area (20 to 110 sq. A. per molecule) for the alkali metal stearates over 0.5N solutions of LiOH, NaOH, and KOH. Like Adam and Miller, they detected a specific cation effect on the 7r-A and AV-A isotherms of the ionized monolayer at high pH the ir-A curves were expanded in the order of the crystalline sizes of the alkali metal cations K > Na > Li. The sequence is the reverse observed for the long-chain... 

Similarities between reversal of charge spectra for colloids with solubility sequences of salts in bulk solution have been indicated (7, 37)— for example, for salts possessing different cations but the same anion, the solubility sequence of the phosphates is K+ > Na+ > Li+, while it is the reverse for the sulfates (7, 30). In view of this similarity, it is natural to introduce this fact as another possible link to explain the reversal of the specific cation effect in tt-A isotherms, though the precise relationship to monolayers is not clear at this time. 

Salts are known to influence several properties of aqueous solutions in a systematic way (122,123). The effect of different aiuons and cations seems to be ordered in a sequence this theory was already proposed by Hofmeister in 1888 (124) from a series of experiments on the salts ability to precipitate hen-egg white protein. Numerous other properties of aqueous salt solutions are also found to be systematically salt dependent, such as the surface tension or the surface potential (122). However, the exact reason for the observed specific cation and anion sequences is still not fully understood (125). Model calculations (126), as well as nuclear magnetic relaxation experiments (127), propose a delicate balance between ion adsorption and exclusion at the solute interface. This balance is tuned by the solvent (water) stmcture modification according to the ion hydration (128, 129) and hence is possibly subject to molecular details. 

There is strong evidence in favour of the point of view 1. in the variants colloid anion + micro cation or colloid cation -f micro anion in the specific ion sequences for reversal of charge or for coacervation or flocculation. We remind the reader for example of the sequences Cs < Rb < K < Na < Li which occur with sulphate colloids and carboxyl colloids (p. 289). Here polarisation phenomena are still in the background and here the largest ion, that is to say, the least hydrated ion, is most suitable for reversal of charge or coacervation. This points strongly therefore to a direct contact between cation and ionised group of the colloid. 

In the suppression of the tricomplex flocculation, gelatin + carrageen + Ca, the same specific ion sequence of the monovalent cations and amons was also found. For the interpretation we must go through the same arguments again bearing in mind that the two complex relations are now ... 

Ascorbic acid is oxidized by Ni(III) complexes of N4 macrocycles (cyclam, etc.) by a sequence of two one-electron steps.Both H2A and HA react, and the rate constants for a series of [NiL2] complexes are correlated by the Marcus cross relation. These reactions go by way of the free radical (H2A 7HA ), as does the oxidation by V(V) which induces the polymerization of acrylonitrile. The oxidations by [IrCy and [IrBre], which are also known to occur by parallel one-electron reactions of H2A and HA , have been examined in (H, Li, Na)C104 media at constant and variable ionic strength. Specific cation effects are important at higher electrolyte concentrations. The results reaffirm LiC104 as a substitute for HCIO4 in studies seeking to vary [H ] with minimal medium effects. ... 

Note Some of Grahame s values for and included in this table. For a common cation, the sequence of anions in order of increasing adsorption is similar to that of the Hofmeister series in coagulation studies, and it is evident that specific adsorption properties are involved. 

The entropy of formation of the interface was calculated from the temperature coefficient of the interfacial tension.304 The entropy of formation has been found to increase with the nature of the electrolyte in the same sequence as the single cation entropy in DMSO.108, 09,329 The entropy of formation showed a maximum at negative charges. The difference in AS between the maximum and the value at ff=ocan be taken as a measure of the specific ordering of the solvent at the electrode/solution interface. Data 108,109304314 have shown that A(AS) decreases in the sequence NMF > DMSO > DMF > H90 > PC > MeOH. 

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