Complexation crown ether complex, potentiometric

In a potentiometric study in propylene carbonate, using Pb11 or Tl1 as auxiliary ions, stability constants have been determined for a variety of crown ethers. Some results464 are shown in Table 8. They show that the wrap-around ligand dibenzo-30-crown-10 is relatively quite effective, while the 2 1 complexes, presumably of the sandwich type, are favoured for larger lanthanides and smaller crowns. 

The main components of the membrane of the enantioselective, potentiometric electrode are chiral selector and matrix. Selection of the chiral selector may be done accordingly with the stability of the complex formed between the enantiomer and chiral selector on certain medium conditions, e.g., when a certain matrix is used or at a certain pH. Accordingly, a combined multivariate regression and neural networks are proposed for the selection of the best chiral selector for the determination of an enantiomer [17]. The most utilized chiral selectors for EPME construction include crown ethers [18-21], cyclodextrins [22-35], maltodextrins 136-421, antibiotics [43-50] and fullerenes [51,52], The response characteristics of these sensors as well as their enantioselectivity are correlated with the type of matrix used for sensors construction. 

Polycarboxylate crown ethers such as (205) are suitable ligands for potentiometric studies of mixed-metal complexes of Al3+ and alkali or alkaline-earth cations.303 A similar (+)-18-crown-6-tetracarboxylic acid, chemically immobilized on a chiral stationary phase (CSP), can selectively recognize both enantiomers of some analytes.304 Calixarene polycarboxylates such as (206) and (207) are useful ligands toward alkali-305,306 and also transition-metal ions,307 308 with applications in... 

Abstract. Crown ethers derived from tartaric acid present a number of interesting features as receptor frameworks and offer a possibility of enhanced metal cation binding due to favorable electrostatic interactions. The synthesis of polycarboxylate crown ethers from tartaric acid is achieved by simple Williamson ether synthesis using thallous ethoxide or sodium hydride as base. Stability constants for the complexation of alkali metal and alkaline earth cations were determined by potentiometric titration. Complexation is dominated by electrostatic interactions but cooperative coordination of the cation by both the crown ether and a carboxylate group is essential to complex stability. Complexes are stable to pH 3 and the ligands can be used as simultaneous proton and metal ion buffers. The low extractibility of the complexes was applied in a membrane transport system which is a formal model of primary active transport. 

The cation complexation behavior of the carboxylate crown ethers illustrated in Figure 1 was investigated by potentiometric titration. The principles have been discussed previously [10, 12] the primary constants determined are cumulative... 

Stability constants (log at 25°C and = 0.1 for complexes between LnlCFjSOjlj and various crown ethers in anhydrous propylene carbonate, as determined by a competitive potentiometric method. 

---