Abstract
The synthesis and chromogenic properties of 1 as a sodium and lithium ion selective indicator system are described. The pK/sub a/ values of 1 in the absence and presence of various metal ions were measured in 80% dioxane-20% water (v/v). Observed values were as follows: Li/sup +/, 5.9; Na/sup +/, 6.9; K/sup +/, 12.7; Ca/sup 2 +/, 12.8; Mg/sup 2 +/, 13.2; 1,5-diazabicyclo(4.3.0)non-5-ene (DBN), 13.0. The noncomplexing model system 21 gave a pK/sub a/ of 10.8 in the same medium. Spherand 1 is yellow (lambda/sub max/ 396 nm; epsilon/sub max/ 17,500 L/(mol x cm)), whereas spheraplexes 1/sup -/ x Li/sup +/ (lambda/sub max/ 586 nm, epsilon/sub max/ 35,500 L/(mol X cm)), and 1/sup -/ x Na/sup +/ (lambda/sub max/ 596 nm, epsilon/sub max/ 35,500 L/(mol x cm)) as well as uncomplexed 1/sup -/ (lambda/sub max/ 610 nm, epsilon/sub max/ 53,000 L/(mol x cm)) are deep blue or violet in 80% dioxane-20% water (v/v) and other solvents. Thus 1 is a chromogenic ion-selective indicating system capable of detecting Li/sup +/ and Na/sup +/ at concentrations as low as 10/sup -8/ M in the presence of other common ions. The binding free energies of spherands 4-6 binding lithium picrate and sodium picratemore » at 25/sup 0/C in CDCl/sub 3/ saturated with D/sub 2/O were measured and found to range between 8.4 and 12.5 kcal mol/sup -1/, somewhat higher than those for 7, but much lower than those for 2.« less
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