title: Rigid versus flexible: how important is ligand "preorganization" for metal ion recognition by lower rim-functionalized calix[4]arenes?
abstract: For an assessment of the outcomes from use of an appropriately "preorganized" calixarene-based ionophore versus its conformationally mobile prototype, solvent extraction propensities of flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] for alkali, alkaline earth metal cations, Pb2+, Ag+ and Hg2+ are compared with those for seven new rigid analogs fixed in the cone, partial cone and 1,3-alternate conformations. For each of the metal ions, the preferred calix[4]arene conformation was determined from the NMR spectra for the metal salt of the flexible ligand. Except for Ag+, flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] were found to provide greater metal ion extraction efficiency and better selectivity than the corresponding "preorganized" ionophores.
authors.affiliation: Department of Chemistry, Howard University, 525 College Street, NW, Washington, DC 20059, USA. gtalanova@howard.edu
authors.forename: Galina G
authors.initials: GG
authors.lastname: Talanova
authors.forename: Vladimir S
authors.initials: VS
authors.lastname: Talanov
authors.forename: Hong-Sik
authors.initials: HS
authors.lastname: Hwang
authors.forename: Chunkyung
authors.initials: C
authors.lastname: Park
authors.forename: Kazimierz
authors.initials: K
authors.lastname: Surowiec
authors.forename: Richard A
authors.initials: RA
authors.lastname: Bartsch