Asymmetric twisting and chirality probing properties of quadruple-stranded helicates: coordination versatility and chirality response of Na(+), Ca(2+), and La(3+) complexes with octadentate cyclen ligand.

A series of Na(+), Ca(2+), and La(3+) complexes with octadentate cyclen ligand were prepared and structurally characterized in the crystal and solution states. The employed cyclen ligand formed 6-, 7-, and 9-coordinated, crystalline complexes with Na(+), Ca(2+), and La(3+) cations, respectively, in which the parent cyclen ring and quinoline-functionalized side arms were cooperatively coordinated. These three metal cations provided the quadruple-stranded helicates in CH(3)CN-C(2)H(5)OH solutions. In each helicate, four quinoline-functionalized side arms were arranged in a propeller-like fashion to yield an enantiomer-pair of Delta- and Lambda- forms. Addition of a chiral anion to the cyclen-Ca(2+) complex solution induced circular dichroism (CD) signals around the quinoline chromophore, which indicated that 1:1 diastereomeric complexation between the Ca(2+) complex and the chiral anion imposed the stereoisomeric equilibrium. The intensity and sign of the observed CD signal were significantly dependent on both the absolute configuration and the enantiomeric purity of the added anion. The corresponding cyclen-Na(+) complex rarely induced a CD signal, while the La(3+) complex exhibited complicated anion-induced spectral changes. Thus, the octadentate cyclen ligand employed was demonstrated to form the quadruple-stranded helicate with the Ca(2+) cation in the solution state, which functioned as an effective CD probe for the determination of enantiomer excess (ee%) of the chiral anions.

"ON-OFF" switching of europium complex luminescence coupled with a ligand redox process.

A triarylamine-functionalized terpyridine ligand formed a highly coordinated complex with europium tris(ß-diketonate), which displayed reversible ''ON-OFF'' luminescence switching coupled with a ligand redox process of triarylamine/triarylaminium cations.

Cholesterol-armed cyclens for helical metal complexes offering chiral self-aggregation and sensing of amino acid anions in aqueous solutions.

Cholesterol-armed cyclens worked as octadentate receptors for Na+, Ca2+, and Y3+ complexes in which four chiral cholesterol-functionalized sidearms were bundled and asymmetrically twisted above cyclen-metal complex platforms. Since the resulting helical metal complexes included chiral, hydrophobic cholesterol residues and charged, hydrophilic metal sites as well as asymmetric coordination geometries, they exhibited unique amphiphilic properties and provided chiral self-aggregates in aqueous solutions. Light scattering, fluorescence, and TEM characterizations demonstrated that Na+ complex with cholesterol-armed cyclen gave a particularly stable self-aggregate in aqueous solution and offered supramolecular environments effective for sensing and detection of amino acid anions. Various dansylamino acid derivatives (dansyl = 5-(dimethylamino)-1-naphthalenesulfonyl) were nicely accommodated in the helicate aggregates to give highly enhanced fluorescence signals, which could be detected by the naked eye at 10(-7) mol/L level. Their inclusion behaviors were analyzed by a Langmuir-type equation, indicating that enantiomer-selective inclusion occurred. MM/MD calculations and circular dichroism (CD) studies further suggested that cholesterol-armed cyclen helicates have chiral and hydrophobic cavities upon self-aggregation, in which the dansylamino acid anions were specifically accommodated. Since these helicates exhibited nonselective binding abilities in solvent extraction experiments of dansylamino acid anions, uncommon chiral recognition and sensing functions were generated by supramolecular alignments of the chiral metal helicates in the aqueous solutions.