Assessment of the macrocyclic effect for the complexation of crown-ethers with alkali cations using the Substructural Molecular Fragments method.

The Substructural Molecular Fragments method (Solov'ev, V. P.; Varnek, A. A.; Wipff, G. J. Chem. Inf. Comput. Sci. 2000, 40, 847-858) was applied to assess stability constants (logK) of the complexes of crown-ethers, polyethers, and glymes with Na+, K+, and Cs+ in methanol. One hundred forty-seven computational models including different fragment sets coupled with linear or nonlinear fitting equations were applied for the data sets containing 69 (Na+), 123 (K+), and 31 (Cs+) compounds. To account for the "macrocyclic effect" for crown-ethers, an additional "cyclicity"descriptor was used. "Predicted" stability constants both for macrocyclic compounds and for their open-chain analogues are in good agreement with the experimental data reported earlier and with those studied experimentally in this work. The macrocyclic effect as a function of cation and ligand is quantitatively estimated for all studied crown-ethers.