Multi-charged cationic species

The tetraammlne species, [Pt(NH3)4] ", dlpositlve cation, exhibits the highest brain uptake which suggests the possible utility of multi-charged cationic species/metal ions as brain Imaging agents. 

The effect of multi-charged cationic species on the retention observed for different metals is illustrated in Table 6.3. Here, the ion-exchange capacity of a column (Cig) is varied by using different mobile phase concentrations of n-octanesulfonate. Equations (17) and (18) show the relationship between the ion-exchange capacity of a column and the retention of a metal species. The concentrations of complexing agents used throughout these experiments were constant 58.2 mM a-HIBA and 8.8 mM tartaric acid, pH 4.1. 

Carbocations having more than four cationic centers are rare species, and very few have been isolated as isolable salts. A tetrahedrally-arrayed tetracation, which was stable only at low temperature was generated by G. A. Olah et al. in 1995 (22). Recently, R. Rathore et al. prepared isolable tetra- and hexatrityl cations utilizing tetraphenylmethane and hexaphenylbenzene as platforms (25). Tetracation 254 is one of the new multi-charged methylium compounds with considerable high stability. 

Cationic surfactants and polymers adsorb readily on silica due to electrostatic interaction since pH of most practical systems is above 2 and silica is negatively charged under these conditions. Anionic surfactants or polymers do not adsorb on silica at neutral pH due to the presence of similar charge on the solid and the adsorbate. However, anionic surfactants can adsorb on silica in the presence of multi-valent metal cations in the pH range in which metal ions hydrolyze to their first hydroxyl complex. This has been attributed to the chemisorption of the first hydroxyl species of metal ions on silica and modification of the quartz surface [3]. 

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