Complexation alkali metal ions

Macrocyclic Polyethers Complex Alkali Metal Ions, Chem. and Eng. News, March 2, 1970, p. 26. 

Cation binding by permethylated cycloinulohexose (Figure 13) and cyclo-inuloheptose has been studied by Sawada et al. [24]. This 18-crown-6 analogue complexed alkali metal ions with association constants roughly two orders of magnitude lower than those observed with 18-crown-6 itself. Analysis of the crystal structure of the complex with Ba showed that the metal ion was complexed in the pocket with the upper-rim 3-methoxy and the crown ether oxygens. 

The crown ether-complexed alkali metal ions are large and hydrophobic, and their salts tend to be soluble in organic solvents. For example, whereas KMn04 is water-soluble but insoluble in benzene, [K(18-crown-6)][Mn04] is soluble in benzene mixing benzene with aqueous KMn04 leads to the purple colour being transferred from the aqueous to the benzene layer. This phenomenon is very useful in... 

Unlike simple inorganic ligands, polyethers and, in particular, cyclic polyethers complex alkali metal ions quite strongly. The crown ethers are cyclic ethers which include... 

Gramicidin S is a cyclic decapeptide isolated from Bacillius brevis whose antibiotic activity is derived from its ability to complex alkali metal ions and transport them across membranes. It acts as a channel for ion leakage which is not difficult to imagine when it is noted that it has a doughnut... 

Simplest examples are prepared by the cyclic oligomerization of ethylene oxide. They act as complexing agents which solubilize alkali metal ions in non-polar solvents, complex alkaline earth cations, transition metal cations and ammonium cations, e.g. 12—crown —4 is specific for the lithium cation. Used in phase-transfer chemistry. ... 

Poly (macrocyclic) compounds. The analytical application of compounds such as crown polyethers and cryptands is based on their ability to function as ligands and form stable stoichiometric complexes with certain cations. Special importance is due to their preference for alkali metal ions which do not form complexes with many other ligands. A number of these compounds are commercially available and their properties and analytical applications have been described by Cheng et a/.11... 

Structures of organic complexes with alkali metal ions. M. R. Truter, Struct. Bonding (Berlin), 1973,16, 71-111 (107). 

There is an interesting similarity in the character of the solution absorption spectra of the isoelectronic ions Np3+ and Pu1 even though the absorption bands in Pu1 + are all shifted toward higher energies due to increases in both the electrostatic (Fk) and spin-orbit ( ) parameters, Table VI. We have also examined the spectra of complex alkali-metal Pu(IV)... 

Tributsch H (1982) Photoelectrochemical Energy Conversion Involving Transition Metal d-States and Intercalation of Layer Compounds. 49 127-175 Truter MR (1973) Structures of Organic Complexes with Alkali Metal Ions. 16 71-111 Tytko KH, Mehmke J, Kurad D (1999) Bond Length-Bond Valence Relationships, With Particular Reference to Polyoxometalate Chemistry. 93 1-64 Tytko KH (1999) A Bond Model for Polyoxometalate Ions Composed of M06 Octahedra (MOk Polyhedra with k > 4). 93 65-124... 

Truter, M. R. Structures of Organic Complexes with Alkali Metal Ions. Vol. 16, pp. 71-111. 

Especially sensitive and selective potassium and some other ion-selective electrodes employ special complexing agents in their membranes, termed ionophores (discussed in detail on page 445). These substances, which often have cyclic structures, bind alkali metal ions and some other cations in complexes with widely varying stability constants. The membrane of an ion-selective electrode contains the salt of the determined cation with a hydrophobic anion (usually tetraphenylborate) and excess ionophore, so that the cation is mostly bound in the complex in the membrane. It can readily be demonstrated that the membrane potential obeys Eq. (6.3.3). In the presence of interferents, the selectivity coefficient is given approximately by the ratio of the stability constants of the complexes of the two ions with the ionophore. For the determination of potassium ions in the presence of interfering sodium ions, where the ionophore is the cyclic depsipeptide, valinomycin, the selectivity coefficient is Na+ 10"4, so that this electrode can be used to determine potassium ions in the presence of a 104-fold excess of sodium ions. 

A number of substances have been discovered in the last thirty years with a macrocyclic structure (i.e. with ten or more ring members), polar ring interior and non-polar exterior. These substances form complexes with univalent (sometimes divalent) cations, especially with alkali metal ions, with a stability that is very dependent on the individual ionic sort. They mediate transport of ions through the lipid membranes of cells and cell organelles, whence the origin of the term ion-carrier (ionophore). They ion-specifically uncouple oxidative phosphorylation in mitochondria, which led to their discovery in the 1950s. This property is also connected with their antibiotic action. Furthermore, they produce a membrane potential on both thin lipid and thick membranes. 

These heterobimetallic M1-M2-binol complexes constitute a new class of widely applicable chiral catalysts as shown in Scheme 3.16. The new catalysts consist of a central metal ion (e.g., La3+, Al3+, Sm3+, Ga3+), three alkali metal ions (e.g., Li+, Na+, K+), and three chiral diphenol... 

Nakamura H., Takagi M., Ueno K., Complexation and extraction of alkali metal ions by 4 -picrylaminobenzo-18-crown-6 derivatives, Anal. Chem. 1980 52 1668. 

For (203), models indicated that the isomer containing cis-syn-cis hydrogen atoms on the cyclohexane ring should be able to form clam-type complexes, provided the cyclohexane ring is in the flexible or twist conformation. The models suggested that the cavity defined by the ten oxygen donors would be ideal for K+. However, for the potassium and barium thiocyanate complexes, configurations of type (204) do not occur in the solid state. Instead, two molecules of the bis-crown coordinate simultaneously to two alkali metal ions - both these 2 2 complexes have structures of type (205). 

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