Potassium cation properties

Only Cram (36) has published a rationale for the very high (99%) enantiomeric excess achieved in the reaction of methyl vinyl ketone and the hydrindanone in the presence of the chiral crown ether. This mechanism envisions a bimolecular complex comprising the potassium cation and chiral host as one entity and the enolate anion of the hydrindanone as the counterion. Methyl vinyl ketone lies outside this complex. The quinine-catalyzed reaction appears to have a termo-lecular character, since the hydroxyl of the alkaloid probably hydrogen bonds with the methyl vinyl ketone—enhancing its acceptor properties—while the quin-uclidine nitrogen functions as the base forming the hydrindanone—alkaloid ion pair. 

Guo et al. prepared a phenylfulgide (18) possessing a benzo-15-crown-5 moiety, and examined its photochromic properties in the presence and absence of metal cations.1161 The absorption both of the colored and of the colorless forms shifted hyp-sochromically by 28 nm in the presence of sodium cation, while shifting only 12 nm in the presence of potassium cation. Hypsochromic shifts greater than 40 nm were observed for alkaline earth metal cations. Addition of sodium cation also inhibited the thermal 1,5-sigmatropic rearrangement of the colored form to the nonphoto-chromic species 19. 

Recall that the chemical properties of an atom depend on the number and configuration of its electrons. Therefore, an atom and its ion have different chemical properties. For example, a potassium cation has a different number of electrons from a neutral potassium atom, but the same number of electrons as an argon atom. A chlorine anion also has the same number of electrons as an argon atom. However, it is important to realize that an ion is still quite different from a noble gas. An ion has an electrical charge, so therefore it forms compounds, and also conducts electricity when dissolved in water. Noble gases are very unreactive and have none of these properties. 

In 1967, Pedersen described the preparation and properties of crown ethers,3 which are macrocyclic polyethers capable of sequestering metal cations. These catalysts can enhance the solubility and reactivity of salts in nonpolar solvents. For example, 18-crown-6, i.e., yxo-anhydro-hexaethylene glycol, forms a host-guest complex with potassium cation (K+) (Equation (1)). This association enables ionic potassium fluoride (KF) to dissociate in nonpolar benzene. And since the nucleophilic F counterions are not complexed,4 the yield of the Finkelstein reaction,5 i.e., halide-halide exchange, is increased 6... 

The cobaltocenium fragment is involved in anion recognition and complexation, whereas the crown ether moiety can interact with alkali metal ions. The result is that the anion recognition properties can be switched on and off through the absence or presence of potassium cation simultaneously bound by the crown. 

Whereas sodium participates in metabolism mainly by its cationic properties, potassium is more directly involved in metabolism. Potassium stimulates the activity of a specific enzyme— pyruvic kinase—and is required for the phosphorylation of fructose-1-phosphate to fructose-1,6-diphosphate. Similarly, potassium stimulates acetyl kinase activity. Many alterations in the bioenergetic pathways of the cell are accompanied by changes in the intracellular concentration of potassium. After insulin administration, some of the potassium of the extracellular fluid is transferred inside the cells. During oxidative phosphorylation, potassium accumulates inside the mitochondria, and dinitrophenol uncouples the ion penetration and the oxidation. 

It should be also pointed out that compounds able to complex sodium or potassium cations, giving them lipophilic properties (crown ethers, cryptands etc.), are also acting as catalysts in these reactions. 

By changing the nature of the base and the solvent a certain control of the stereochemical outcome has been achieved in few alkylation [15] and acylation [24] reactions of calix[4]arenes. Recently, in collaboration with the group of Prof. D.N. Reinhoudt, several stereoisomeric calix[4]arene crown ethers have been synthesized and their ionophoric properties toward alkali metal cations determined by the Gam s extraction method [25]. In all cases it was found that these ligands are very selective for potassium cation and that the compounds in the partial cone structure are more efficient and more selective than those in the fixed cone conformation. The highest difference in... 

However, whereas the free receptor complexed and recognized electrochemically the halide anions, the introduction of sodium cations 380 had little effect on strengthening the halide anion complexing properties of the receptor. The potassium complex 379 did not complex anions, because of the conformation of the rigid receptor which did not allow the access of the anion to the mid-CO-NH moiety. A novel potential molecular switch has thus been developed, whereby the binding of halide anions can be switched on and off via the absence or presence of potassium cations (Equation (63)). 

Orthophosphate salts are generally prepared by the partial or total neutralization of orthophosphoric acid. Phase equiUbrium diagrams are particularly usehil in identifying conditions for the preparation of particular phosphate salts. The solution properties of orthophosphate salts of monovalent cations are distincdy different from those of the polyvalent cations, the latter exhibiting incongment solubiUty in most cases. The commercial phosphates include alkah metal, alkaline-earth, heavy metal, mixed metal, and ammonium salts of phosphoric acid. Sodium phosphates are the most important, followed by calcium, ammonium, and potassium salts. 

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