ION-DIPOLE INTERACTIONS OF MACROCYCLIC ETHERS USING C-13 DIPOLE-DIPOLE RELAXATION-TIME MEASUREMENTS .11. THE COMPLEXATION OF 1,4,7,10,13,16-HEXAOXA-2,6-DIOXOCYCLOOCTADECANE WITH CA2+ IN CD3OH

The association constants, K-a, of Ca2+ complexes with the nonequivale nt binding site macrocycle, 1, 4, 7, 10, 13, 16-hexaoxa-2, 6-dioxocycl ooctadecane, were determined in CD3OH solution using C-13 dipole-dipol e relaxation time, T-1(DD), studies. The measurements of T-1(DD) of th e macrocyclic backbone for different stoichiometries (n : m) of comple x formation were conducted under extreme narrowing experimental NMR co nditions. The general equilibria given with 1/K-a[L(0)](n+m-l) = (1 - nP')(n) (1 - mP')(m)/P' was used for identical cation and macrocyclic ether-ester concentrations in CD3OH and the association constants foun d were comparatively small depending on the cyclic ether-ester segment s. The log K-a values varied from 1.09 to 0.231 for 1 : 1 and from 2.4 3 to 3.61 for 1 : 2 and from 2.29 to 4.24 for 2 : 1 ligand to cation c omplex stoichiometries.