Carboxylic polyethers

Calcium-selective electrodes have long been in use for the estimation of calcium concentrations - early applications included their use in complexometric titrations, especially of calcium in the presence of magnesium (42). Subsequently they have found use in a variety of systems, particularly for determining stability constants. Examples include determinations for ligands such as chloride, nitrate, acetate, and malonate (mal) (43), several diazacrown ethers (44,45), and methyl aldofuranosides (46). Other applications have included the estimation of Ca2+ levels in blood plasma (47) and in human hair (where the results compared satisfactorily with those from neutron activation analysis) (48). Ion-selective electrodes based on carboxylic polyether ionophores are mentioned in Section IV.B below. Though calcium-selective electrodes are convenient they are not particularly sensitive, and have slow response times. 

Macrocyclic compounds with ion-chelating properties occur naturally and often function as ionophores, translocating ions across biological membranes many of these compounds are small cyclic polypeptides. Some natural carboxylic polyethers are selective for Li+ and are, therefore, ionophores for Li+. Monensin, shown in Figure Id, is a natural ionophore for Na+ but it will also complex with Li+ and it has been shown to mediate the transport of Li+ across phospholipid bilayers [21]. It has been proposed that synthetic Li+-specific ionophores have a potential role as adjuvants in lithium therapy, the aim being to reduce the amount of... 

The sensor reported by Shirai(69) used a natural carboxylic polyether antibiotic (Aem = 481 nm) for the detection of magnesium and calcium. Detection limits of I0 5 and KT4 M, respectively, were reported but, interference from other metals was difficult to overcome. Ishibashi(69) used a bulkier hexadecyl-acridine orange dye (Xem = 525 nm) plasticized in a PVC membrane for the fluorescent detection of ammonium ions. Signal interference due to superfluous ions and poor detection limits of KT5 M restricted the use of the probe. 

K. Suziki, K. Tohda, Y. Tanda, H. Ohzora, S. Nishihama, H. Inoue, and T. Shirai, Fiber-optic magnesium and calcium ion sensor based on a neutral carboxylic polyether antibiotic, Anal. Chem. 61, 382-384 (1989). 

Polyester-silicone Polyesters, thermoplastic Polyesters, unsaturated Polyester urethanes Polyester-wool blends Polyether antibiotics Polyether carboxylates Polyether elastomers... 

Quantification of five different drugs in pigs kidney Separation of carboxylic polyether antibiotics (monensin, salinomycin, and narasin) with an amino bonded phase and 15% methanol in carbon dioxide using light-scattering detector Analysis of hydroxylated metabolites of dialkyldithio-carbamates... 

Structually much more complex molecules have also been submitted to re-gioselective enzymatic hydroxylation. Two such examples have been described involving milbemycin, a sixteen-membered macrolide which exhibits broad-spectrum insecticidal and acaricidal activity, and monensin, a carboxylic polyether antibiotic193- 94l Milbemycin (Fig. 16.1-19) was thus regioselectively hydroxylated at the 13(3 position (followed eventually by a C-29 hydroxylation) to afford the 13P,29-... 

Monensln Is another member of this family of carboxylic polyether lonophores. The kinetics of sodium binding (k ) and... 

Introduction. Calcimycin (or A.23187) belongs to the growing family of bacterial carboxylic polyether ionophores (1). 11 was isolated from a strain of treptomyc s Chart eus s NRRL 3882 (2). ... 

Critical micelle concentration (Section 19 5) Concentration above which substances such as salts of fatty acids aggre gate to form micelles in aqueous solution Crown ether (Section 16 4) A cyclic polyether that via lon-dipole attractive forces forms stable complexes with metal 10ns Such complexes along with their accompany mg anion are soluble in nonpolar solvents C terminus (Section 27 7) The amino acid at the end of a pep tide or protein chain that has its carboxyl group intact—that IS in which the carboxyl group is not part of a peptide bond Cumulated diene (Section 10 5) Diene of the type C=C=C in which a single carbon atom participates in double bonds with two others... 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

A classification based first on ion specificity, then on stmctural features has been suggested for the polyethers (7). Another method uses the presence of unsaturation or of aromatic groups in the molecular skeleton (8). In this review the compounds are classified based on the number of carbons in the backbone according to the numbering system proposed in reference 9. The carbon backbone or skeleton refers to the longest chain of contiguous carbons between the carboxyl group and the terminal carbon. 

Cholanic acid also possesses the ability of transporting cations across a lipophilic membrane but the selectivity is not observed because it contains no recognition sites for specific cations. In the basic region, monensin forms a lipophilic complex with Na+, which is the counter ion of the carboxylate, by taking a pseudo-cyclic structure based on the effective coordination of the polyether moiety. The lipophilic complex taken up in the liquid membrane is transferred to the active region by diffusion. In the acidic region, the sodium cation is released by the neutralization reaction. The cycle is completed by the reverse transport of the free carboxylic ionophore. 

In mimicking this type of function, noncyclic artificial carboxylic ionophores having two terminal groups of hydroxyl and carboxylic acid moieties were synthesized and the selective transport of alkali metal cations were examined by Yamazaki et al. 9 10). Noncyclic polyethers take on a pseudo-cyclic structure when coordinating cations and so it is possible to achieve the desired selectivity for specific cations by adjusting the length of the polyether chain 2). However, they were not able to observe any relationship between the selectivity and the structure of the host molecules in an active transport system using ionophores 1-3 10). (Table 1)... 

The result is explained by considering the stacking structure between the quinoline moiety and the benzene ring linked to the carboxylic acid, which gives the cavity size adequate for Li+. (Fig. 3) Several selective host molecules for Li+ such as [13]crown-4 18), [14]crown-4 19), [16]crown-4 20>, or noncyclic polyether amide derivatives 21) also possess trimethylene moiety, and this is an interesting finding from the point of view of molecular design of new host molecules for Li+. 

Aliphatic carboxylic acids Alkyl ethyl ethers Cyclic polyethers Phosphorous compounds Rearrangement peak in dioxanes... 

Ether carboxylates are known for a long time. In 1934 a patent was applied for [1] in which some sodium salts of polyether carboxylated acids of the general formula... 

Comparison of C12-C14 polyether carboxylates with 3, 4, and 5 mol EO with sodium lauryl ether sulfate (2 mol EO) indicated approximately the same detergency and a little better wetting using the ether carboxylates, with the remark that 4 EO gave the optimum [10]. 

Van Paassen [57] describes the CMC of some polyether carboxylates with different fatty chains and EO degrees (Fig. 2). In an extensive study, Binana-Limbele et al. [59] investigated the micellar properties of the alkylpolyether carboxylates of the general formula CnH + OCF CH OCI COONa with n = 8, x = 5, and n = 12 and x = 5,1, and 9, by means of electrical conductivity (CMC, apparent micellar ionization degree) and time-resolved fluorescence probing (micelle aggregation number A7) as a function of temperature and surfactant concentration (Table 1). 

---