Sensing potassium

Ertekin K, Tepe M, Yenigii B, Akkaya EU, Henden E (2002) Fiber optic sodium and potassium sensing by using a newly synthesized squaraine dye in PVC matrix. Talanta 58 719-727... 

Ueyama, H., Takagi, M., Takenaka, S. (2002). A novel potassium sensing in aqueous media with a synthetic oligonucleotide derivative fluorescence resonance energy transfer associated with guanine quartet-potassium ion complex formation. J Am Chem Soc 124, 14286-14287. 

Valinomycin-based membranes (Table 2.4) have been the predominant choice for potassium sensing in soil and other environmental samples. Considerable research effort has focused on improving the adhesion of the PVC membrane to extend the consistent sensitivity period, and thus, the lifetime of the electrode. Valinomycin ionophores have exhibited strong K selectivity and sensitivity sufficient to quantify variations in the typical range in soil K where additional fertilizer is recommended. ... 

If the equilibrium were established rapidly, reduction of the free ketone as it formed would result in a substantial loss of product. Lithium enolates are more covalent in character than are those of sodium and potassium and consequently are the least basic of the group. This lower thermodynamic basicity appears to be paralleled by a lower kinetic basicity several workers have shown that lithium enolates are weaker bases in the kinetic sense than are those of sodium and potassium." As noted earlier, conjugated enones... 

Of the many tests which have been submitted, the determination of active oxygen or peroxide content seems to give rather good correlation of data. During the oxidation of fat, certain oxygen-containing compounds are formed which are active in the sense that they are capable of liberating iodine from potassium iodide (19). The liberated iodine may be determined quantitatively and it thus becomes a measure of rancidity. 

The diastereoselectivity and the stereochemical outcome of the addition of 2,3,4,6-tetrahydro-3, 4-dimethyl-2-phenyl-1,4-oxazepine-5,7-dione, derived from ephedrine and methyl hydrogen malonate, to 1 -nitrocyclohexene was found to be dependent on the nature of the base and the solvent. The highest diastereoselectivity was obtained when potassium /tr/-butoxide in the presence of dicyclohcxyl-18-crown-6 was employed. In the absence of crown ether the diastereoselection was poor and the sense of the stereochemical outcome was reversed26. 

Sensory receptors expressed in particular in taste receptor cells of the taste buds that sense the five basic tastes salt, sour, sweet, bitter and umami (glutamate taste). Sodium type ion channels sense salty taste whereas sour taste is transduced by potassium type ion channels. The underlying cause of sweet, bitter, and umami tastes is the selective activation of different groups of G protein coupled receptors that discriminate between sweet, bitter, and umami tasting molecules. 

As we can see from the last entry in this table, we have deduced only a rule. In InBi there are Bi-Bi contacts and it has metallic properties. Further examples that do not fulfill the rule are LiPb (Pb atoms surrounded only by Li) and K8Ge46. In the latter, all Ge atoms have four covalent bonds they form a wide-meshed framework that encloses the K+ ions (Fig. 16.26, p. 188) the electrons donated by the potassium atoms are not taken over by the germanium, and instead they form a band. In a way, this is a kind of a solid solution, with germanium as solvent for K+ and solvated electrons. K8Ge46 has metallic properties. In the sense of the 8-A rule the metallic electrons can be captured in K8Ga8Ge38, which has the same structure, all the electrons of the potassium are required for the framework, and it is a semiconductor. In spite of the exceptions, the concept has turned out to be very fruitful, especially in the context of understanding the Zintl phases. 

Ionophore-based solvent polymeric membranes were used as sensing layers for the development of LAPS selective for lithium [70], potassium and calcium ions [71]. Anion-selective LAPS for the determination of nitrate and sulfate ions were described [72],... 

K.C. Ho and C.L. Lin, A novel potassium ion sensing based on Prussian blue thin films. Sens. Actuators B-chem. 76, 512-518 (2001). 

The fourth type of mediator-based cation optical sensing is using potential sensitive dye and a cation selective ionophore doped in polymer membrane. Strong fluorophores, e.g. Rhodamine-B C-18 ester exhibits differences in fluorescence intensity because of the concentration redistribution in membranes. PVC membranes doped with a potassium ionophore, can selectively extract potassium into the membrane, and therefore produce a potential at the membrane/solu-tion interface. This potential will cause the fluorescent dye to redistribute within the membrane and therefore changes its fluorescence intensity. Here, the ionophore and the fluorescence have no interaction, therefore it can be applied to develop other cation sensors with a selective neutral ionophore. 

Similar to the history of many other elements, iodine s discovery was serendipitous in the sense that no one was looking for it specifically. In 1811 Bernard Courtois (1777—1838), a French chemist, attempted to remove sodium and potassium compounds from the ash of burned seaweed in order to make gunpowder. After removing these chemicals from the ash, he added sulfuric acid (H SO j) to the remaining ash. However, he mistakenly added too much acid, which produced a violet-colored vapor cloud that erupted from the mixture. This violet vapor condensed on all the metallic objects in the room, leaving a layer of sohd black iodine crystals. Sir Humphry Davy (1778—1829) confirmed this discovery of a new element and named it iodine after the Greek word iodes, which means violet, but it was Courtois who was given credit for the discovery of iodine. 

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