Concept, Structure, and Binding in Complexation

Comparison of dibenzo‐16‐crown‐5 compounds with pendent amide groups as sodium ionophores in ion‐selective electrodes and in solvent extraction

“…Compared with 1, for which the geminal group is hydrogen, the log KEa value obtained for 2 is larger by 0.77, while the log K,", value is smaller by 0.36. These data reveal that the preorganized ionophore structure in 2, which is caused by attachment of the geminal propyl group, enhances formation of the nesting complex [8] Na' and disfavors formation of the perching complex [8] for K' , in which the metal ion is too large to fit completely within the polyether cavity. Thus the enhanced Na'/K' selectivity of ISE's containing lariat ether amide 2 as the ionophore relative to 1 is ascribed to improved Na' binding and diminished K+ complexa tion.…”

“…The calculated log K,N,"/KE values for the former members of each pair lie in the range of 1.93-2.00, whereas those for the latter are in the range of 2.07-2.12 ( Table 2). The log K E values for all six of the lariat ethers amides 2-7 are in the range of 5.73-5.83 which indicates that variation of the geminal alkyl group from propyl to isopropyl and the N,N-dialkyl group from pentyl to octyl to decyl has little influence on formation of the nesting complex [8] for Na'. However, the log KZ values for lariat ether amides 2-4, which have a geminal propyl group, are in the range of 3.73-3.90; whereas those for 5-7, which have a geminal isopropyl group are in the range of 3.65-3.69.…”

“…However, the log KZ values for lariat ether amides 2-4, which have a geminal propyl group, are in the range of 3.73-3.90; whereas those for 5-7, which have a geminal isopropyl group are in the range of 3.65-3.69. Thus the increase in bulkiness of the geminal alkyl group appears to disfavor formation of the perching complex [8] for K'. This suggests that the somewhat higher log K g / K : ratios observed when the geminal alkyl group is isopropyl result from diminished extraction of K' .…”

“…Attachment of an alkyl group to the polyether ring carbon which bears the aniide-containing side arm produced a substantial increase in the Na' selectivity [4--6]. It was proposed that the presence of such a geminal alkyl group positions the potential coordinating side arm over the polyether ring cavity which preorganizes the binding site [8,9] and enhances selectivity [4-61. In these earlier studies, it was not possible to determine if the enhanced Na+ selectivity of the ion-selective electrodes (ISE's) induced by incorporation of a geminal alkyl group resulted from increased binding of Na+ or poorer complexation of the competing alkali metal cation or a combination of both factors.…”

Selective Recognition of Calcium Ion through Liquid Membrane

“…Macrocyclic compounds such as crown ethers, azacrowns, criptands, and calixarenes have been well known for selective recognition of specific metal ions or molecules (1)(2)(3)(4)(5). Acyclic polyether (podand), which is of the acyclic form, has also received a great deal of attention for many years (5).…”