Potassium ion, complexing with

Dobler. M. Dunitz, J.D. Krajewski, J. Structure of the potassium ion complex with enniatin B, a macrocyclic antibiotic with potassium ion transport properties. J. Mol. Biol. 1969, 42. 603-606. 

Fig. 7 Correlation of stability of crown ether-potassium ion complex with physical properties of various solvents. View this art jn color at www.dekker.com.)...

With respect to the carrier mechanism, the phenomenology of the carrier transport of ions is discussed in terms of the criteria and kinetic scheme for the carrier mechanism the molecular structure of the Valinomycin-potassium ion complex is considered in terms of the polar core wherein the ion resides and comparison is made to the Enniatin B complexation of ions it is seen again that anion vs cation selectivity is the result of chemical structure and conformation lipid proximity and polar component of the polar core are discussed relative to monovalent vs multivalent cation selectivity and the dramatic monovalent cation selectivity of Valinomycin is demonstrated to be the result of the conformational energetics of forming polar cores of sizes suitable for different sized monovalent cations. 

Fehling s solution is a basic solution of copper (II) ions complexed with sodium or potassium tartrate. When Fehling s solution reacts with aldehydes Cu+2 ions, which are a dark-blue color in the complex, are reduced to brick-red copper (I) oxide (Cu20). At the same time, the aldehyde is oxidized to the carboxylate ion... 

In black lipid membranes containing phospholipid In combination with hopanold, the mobility of a potassium Ion complex can he measured [48]. The mobility of this complex Is decreased by Increasing the molecular fraction of the hopanold. These experiments demonstrate viscosity enhancing property of hopanolds. 

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. 

H NMR investigations with alkali metal cations revealed that the host displayed a remarkable selectivity and fast kinetics of complexation for potassium cation over all other group 1 metal cations. Compound 40 only binds halide and acetate anions very weakly in 2 1 CDCl3 CD3CN, but its sodium and potassium ion complexes form much more stable complexes with these anions, with anion-binding enhancements of over 30-fold in the case of bromide anion. 

To illustrate which components are necessary to prepare an ISE membrane, let us again go back to a simple extraction experiment as it was similarly described in Section 3.1.1. Consider an aqueous potassium chloride solution equilibrated with an immiscible organic phase containing an electrically neutral ionophore for K+, that is, a receptor compound that binds the potassium ion selectively. How does the phase boundary potential between these two phases depend on the KCl concentration in the aqueous phase Upon equilibration of the two phases, some KCl will be present in the organic phase (Figure 5). For low amounts of KCl in the system, the potassium ions in the organic phase will be present in the form of ionophore complexes, and there will be an excess of free ionophore, L. In comparison to the concentration of the ionophore complex, the organic phase concentration [K+] of free potassium ions that are not bound by the ionophore is very low and can be calculated from the formation constant, of the potassium ion complex, [LK+] ... 

Favretto and coworkers demonstrated a spectrophotometric method based upon the extraction of picrate ion from water into an organic solvent in association with potassium ion complexes of polyoxyethylene chains (89-92). This procedure, due to the greater molar absorptivity of the picrate ion, is about eight times more sensitive than the cobaltithiocyan-ate method (at 620 nm when the cobaltithiocyanate method is used at 320 nm, the sensitivity of the two methods is similar). The barium-surfactant-picrate complex is reported to be extracted more readily, and have a higher apparent absorptivity, than the potassium complex (93). The procedure is more sensitive to AE and APE than to ethoxylated esters or to EO/PO copolymers (94). The method has been successfully applied to environmental... 

The metal-ion complexmg properties of crown ethers are clearly evident m their effects on the solubility and reactivity of ionic compounds m nonpolar media Potassium fluoride (KF) is ionic and practically insoluble m benzene alone but dissolves m it when 18 crown 6 is present This happens because of the electron distribution of 18 crown 6 as shown m Figure 16 2a The electrostatic potential surface consists of essentially two regions an electron rich interior associated with the oxygens and a hydrocarbon like exterior associated with the CH2 groups When KF is added to a solution of 18 crown 6 m benzene potassium ion (K ) interacts with the oxygens of the crown ether to form a Lewis acid Lewis base complex As can be seen m the space filling model of this... 

Frensch and Vdgtle have recently appended three crown ether units to the cyclo-triveratrylene unit . Note that Hyatt had previously prepared the open-chained relatives of this structure (see Sect. 7.3 and Eq. 7.6). Whereas Hyatt prepared the cyclo-triveratrylene skeleton and then appended polyethyleneoxy arms to it, Frensch and Vogtle conducted the condensation reaction (formaldehyde/HCl) on the preformed benzocrown. Thus benzo-15-crown-5 was converted into the corresponding tris-crown (IS) (mp 203.5—205.5°) in 4% yield. The yield was somewhat higher for the condensation of benzo-18-crown-6, but in both cases, yield ranges were observed. These species formed 1 3 (ligand/salt) complexes with sodium and potassium ions. 

Figure 4.11 Molecular structures of typical crown-ether complexes with alkali metal cations (a) sodium-water-benzo-I5-crown-5 showing pentagonal-pyramidal coordination of Na by 6 oxygen atoms (b) 18-crown-6-potassium-ethyl acetoacetate enolate showing unsymmelrical coordination of K by 8 oxygen atoms and (c) the RbNCS ion pair coordinated by dibenzo-I8-crown-6 to give seven-fold coordination about Rb.

Poloxamers are used primarily in aqueous solution and may be quantified in the aqueous phase by the use of compleximetric methods. However, a major limitation is that these techniques are essentially only capable of quantifying alkylene oxide groups and are by no means selective for poloxamers. The basis of these methods is the formation of a complex between a metal ion and the oxygen atoms that form the ether linkages. Reaction of this complex with an anion leads to the formation of a salt that, after precipitation or extraction, may be used for quantitation. A method reported to be rapid, simple, and consistently reproducible [18] involves a two-phase titration, which eliminates interferences from anionic surfactants. The poloxamer is complexed with potassium ions in an alkaline aqueous solution and extracted into dichloromethane as an ion pair with the titrant, tet-rakis (4-fluorophenyl) borate. The end point is defined by a color change resulting from the complexation of the indicator, Victoria Blue B, with excess titrant. The Wickbold [19] method, widely used to determine nonionic surfactants, has been applied to poloxamer type surfactants 120]. Essentially the method involves the formation in the presence of barium ions of a complex be-... 

The proposed model for the so-called sodium-potassium pump should be regarded as a first tentative attempt to stimulate the well-informed specialists in that field to investigate the details, i.e., the exact form of the sodium and potassium current-voltage curves at the inner and outer membrane surfaces to demonstrate the excitability (e.g. N, S or Z shaped) connected with changes in the conductance and ion fluxes with this model. To date, the latter is explained by the theory of Hodgkin and Huxley U1) which does not take into account the possibility of solid-state conduction and the fact that a fraction of Na+ in nerves is complexed as indicated by NMR-studies 124). As shown by Iljuschenko and Mirkin 106), the stationary-state approach also considers electron transfer reactions at semiconductors like those of ionselective membranes. It is hoped that this article may facilitate the translation of concepts from the domain of electrodes in corrosion research to membrane research. 

It was assumed that tantalum, when added to the melt in the form of potassium heptafluorotantalate, K2TaF7, interacts with KF or KC1 to form a compound with an increased tantalum coordination number of up to eight. The compound is present in the melt in its dissociated form, yielding potassium ions and octa-coordinated complexes of tantalum, namely TaFg3 or TaF7Cl3. ... 

This reaction takes place quite rapidly on boiling, and hence hydrochloric add cannot be used in oxidations which necessitate boiling with excess of cerium(lV) sulphate in add solution sulphuric add must be used in such oxidations. However, direct titration with cerium(IV) sulphate in a dilute hydrochloric add medium, e.g. for iron(II) may be accurately performed at room temperature, and in this respect cerium(IV) sulphate is superior to potassium permanganate [cf. (2) above]. The presence of hydrofluoric add is harmful, since fluoride ion forms a stable complex with Ce(lV) and decolorises the yellow solution. 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

---