Core cations, charge

Given in Table 3.3 are the species formed by hydrolysis of cations in water at 25 C and between pH 2 to 12. The nature of these species is broadly related to ionic potentials of the core cations in Table 3.1, and more qualitatively a function of core cation charge as apparent from the listing in Table 3.3. Complex formation in natural waters will involve the replacement of one or more coordinating hydroxyls or water molecules in these species by other ligands. 

Chromaffin granules, platelet dense core vesicles, and synaptic vesicles accumulate ATP. ATP uptake has been demonstrated using chromaffin granules and synaptic vesicles and the process appears to depend on A(.lh+. It has generally been assumed that ATP is costored only with monoamines and acetylcholine, as an anion to balance to cationic charge of those transmitters. However, the extent of ATP storage and release by different neuronal populations remains unknown, and the proteins responsible for ATP uptake by secretory vesicles have not been identified. 

As Ip increases above values as low as 8.5, and we enter the upper-left portion of Fig. 3.4, the bonding between core cation and associated oxygen or hydroxyl is even stronger and largely covalent. The result is the formation of oxyanionic species such as silicate, selenate, borate, carbonate, arsenate, and sulfate, which, because of their relatively low charge densities as oxyanions, form rather weak bonds with cations and are soluble. 

In another study, a library of potential flnoiescent probes for nucleotides was built from simple condensation reactions of a benzimidazolium core with 96 aromatic aldehydes. Some rationale was introduced into this library—the fixed cationic charge of the benzimidazolium as a receptor for phosphate moieties the two halves would be joined directly to allow binding events to influence the whole molecule through conjugation (and to minimize molecular weight, a lesson... 

Similar studies were carried out using photoionization of benzidine derivatives (Narayanaetal., 1982), phenothiazine(Alkaitisetal., 1975), or pyrene (Gratzel and Thomas, 1974) dissolved in the hydrophobic core of charged micelles. A laser pulse ejects an electron which is rapidly hydrated and then decays into hydroxy radicals, or reacts with the excited cation. The charge of the micelle has a dramatic effect on the rate of the latter reaction but the presence of the former reaction forbade a precise kinetic analysis of the overall reaction. 

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