Anion exchange molecular interaction

Finally, we discuss the effects of chalcogen (S to Se) substitution. Although in (EDS-TTF)2FeBr4 remarkably close Se---Br contacts exist between donor and anion layers, little magnetic exchange interaction exists between the magnetic anions. The molecular orbital calculation reveals that the contribution of Se 4p orbital to the HOMO of the EDS-TTF molecule is considerably smaller than the contribution of... 

In addition to true ion exchange, other interactions can take place between the sample solutes and the resin. Adsorption is one of the commonest of these interactions. For example, the benzoate anion appears to be adsorbed somewhat by the poly-styrene-divinylbenzene polymeric matrix of organic ion exchangers. This may be due to an attraction of the k electrons of the aromatic polymer for the benzoate. Benzoic acid, which exists mostly in the molecular form, is absorbed to a much greater degree than benzoate salts. 

The explanation offered by the authors is that the MIP was cross-reactive for naphthalene sulfonates. However, at pH 2.3, only the naphthalene sulfonates were anionic (pfCa 0.5-0.6). It is quite plausible that in this example, molecular recognition was predominantly an anion-exchange mechanism, and that this overshadowed the influence of any molecularly imprinted cavities. In this way, the MeOH wash step could be seen to have disrupted non-covalent, non-ionic interactions, leaving behind the anionic naphthalene sulfonates, which were retained much more strongly via ionic interactions with the protonated pyridyl moieties. Unfortunately, this is always a poten-... 

---