A novel supramolecular assembly has been fabricated by the inclusion complexation between organo-selenium bridged bis(β-cyclodextrin)s 2 and calix[4]arene derivative 3 in water-acetonitrile (1:1) mixture solution and characterized by fluorescence, 2D NMR, TEM, SEM, and STM images, showing the nanometer structural wire-shaped aggregates.

Nanometer-sized supramolecular assemblies created by the simple inclusion complexation of host cyclodextrins (CDs) and guest molecules have attracted more and more attention in recent years because of their potential to serve as molecular devices and molecular machines, as well as functional materials. [1-4] Indeed, CDs can be threaded on a polymer chain to form a polyrotaxane and extended to molecular tubes through the cross-linking of adjacent CD units in a polyrotaxane.[5] Furthermore, b- and g-cyclodextrins can also be constructed into nanometer-sized molecular tubes linked by diphenylhexatrienes,[6] and conjugated polyrotaxanes can be used as building blocks to form insulated molecular wires on which a- or b-CDs are threaded.[7] We recently showed that the resulting complex formed from an organoseleniumbridged b-CD dimer and a platinum ion could be fabricated into bis(molecular tube)s through formation of a pesudorotaxane with poly(propylene glycol), and the bridged bis(bcyclodextrin) s and calix[4]arene derivatives could also form nanometer-sized linear aggregations by simple host-guest inclusion complexation.[8-10] Molecular semiconductors can also be exploited for organic electronics and single molecules can be manipulated and incorporated into nano-engineered devices at a supramolecular level by threading a chargetransport macromolecule.[11-15] However, higher order polymeric rotaxanes fabricated by metal-ion binding to the inclusion complexes formed between CDs and aromatic molecules have not been investigated so far. Dipyridine-metal complexes have very interesting photochemical and other properties, and therefore many studies have been devoted to this topic.[16] Herein we report our investigations on two uncommon supramolecular aggregations: assembly 1, formed from the reaction of b-CD with 4,4'-dipyridine (DPD), and polymeric rotaxane 2, which was synthesized by coordination of 1 with NiII ions. The binding behavior of 1 and 2 was examined, both in solution and in the solid state, by 1H NMR spectroscopy, X-ray crystallography, induced circular dichroism, powder X-ray diffraction studies, thermogravimetric (TG) and differential thermal analysis (DTA), scanning tunneling microscopy (STM), and transmission electron microscopy (TEM). The binding behavior of the supramolecular assembly formed by the molecular recognition of the host and guest in solution and in the solid state is of particular interest, since the inclusion complex and the polymeric rotaxane display different photophysical behavior. The present investigations have revealed that the resulting complex of CDs with guest molecules is the first step in the formation of a polymeric rotaxane, which provides access to coordination polymeric supramolecules with CDs, and will serve to further our understanding of this developing, but less investigated, area of electroactive organic materials that contain CDs and a coordination linkage.

A series of novel 6,6'-bis(bcyclodextrin) s linked by 2,2'-bipyridine-4,4'-dicarboxy tethers; that is, 2,2'-bipyridine-4,4'-dicarboxy-bridged bis(6-O-bcyclodextrin) (2) and N,N'-bis(2-aminoethyl)-2,2'-bipyridine-4,4'-dicarboxamide-bridged (3), N,N'-bis(5-amino-3-azapentyl)-2,2'-bipyridine-4,4'-dicarboxamide-bridged (4) and N,N'-bis(8-amino-3,6-diazaoctyl)-2,2'-bipyridine-4,4'-dicarboxamide-bridged bis(6-amino-6-deoxy-b-cyclodextrin) (5), has been synthesized as cooperative multipoint-recognition receptor models. The inclusion complexation behavior of 2-5 with organic dyes; that is, ammonium 8-anilino-1-naphthalenesulfonate, Brilliant Green, Methyl Orange, Acridine Red, and Rhodamine B, has been investigated in aqueous phosphate buffer solutions (pH7.20) at 25℃ by means of ultraviolet, fluorescence, and circular dichroism spectrometry as well as by fluorescence lifetime measurements. The spectral titrations gave the complex stability constants (KS) and Gibbs' free energy changes (△℃) for the inclusion complexation of 2-5 with the organic dyes and other thermodynamic parameters (△H°and △S°) for the inclusion complexation of 2-4 with the fluorescent dyes Acridine Red and Rhodamine B. Bis(b-cyclodextrin)s 2-5 displayed higher binding abilities toward most of the examined dye molecules than native b-cyclodextrin 1; this is discussed from the viewpoints of the size/shape-fit concept, the induced-fit interaction, and cooperative, multipoint recognition by the bridging chain and the dual hydrophobic cavities. Thermodynamically, the inclusion complexation of 2-4 with Acridine Red is totally enthalpy driven with a negative or minor positive entropic contribution, but the inclusion complexation with Rhodamine B is mainly entropy-driven with a mostly positive, but occasionally negative, enthalpic contribution; in some cases this determines the complex stability.

The complex stability constants (KS) and thermodynamic parameters (△G°, △H°, and T△S°) for 1:1 inclusion complexation of β-cyclodextrin (β-CD) derivatives, 6-O-phenyl-β-CD (2) 6-O-(4-formylphenyl)-β-CD (3), 6-O-(4-nitrophenyl)-β-CD (4), 6-O-(4-bromophenyl)-β-CD (5), 6-O-(4-chlorophenyl)]-β-CD (6), and 6-O-(4-hydroxybenzoyl)-β-CD (7) with representative guest molecules, cyclic alcohols (cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol), (±)-borneol, and (±)-camphor, have been determined by means of titration microcalorimetry in an aqueous phosphate buffer solution (pH=7.20) at 298.15K. The results obtained indicate that the introduction to β-CD of an aromatic ring bearing different substituent groups significantly enhances the molecular binding ability and moderately alters the chiral discrimination ability for the guests examined here, displaying the highest enantioselectivity of up to 4.01 for the inclusion complexation of 6 with (±)-camphor. The enhanced molecular/chiral discrimination ability caused by derivatization is attributed solely to increased positive entropy changes due to the expanding hydrophobic interaction and desolvation effects. The binding modes of host-guest interactions derived from ROESY spectroscopy data show that the resulting complex of 4 and (+)-borneol possesses better induced-fit interaction as compared to (-)-borneol, which is responsible for the enhanced molecular/chiral recognition ability.

Two channel-type supramolecular aggregations 1 and 2 were prepared by the inclusion complex of β-cyclodextrin with 2,2'-dipyridine and 4,4'-dipyridine, respectively, and their binding ability and assembly behavior were investigated comprehensively by X-ray crystallography, 1H NMR, circular dichroism spectra, and microcalorimetric titration in solution and the solid state. The obtained results revealed that the hydrogen bonds and π-πstacking interactions are crucial factors for the formation of the molecular aggregations containing β-cyclodextrin and dipyridines. The disparity of nitrogen atom position in dipyridines leads not only to the distinct crystal system and space group, i.e., monoclinic system (C2) for 1 and triclinic system (P-1) for 2, but also different binding modes and thermodynamical parameters upon complexation of 2,2'-dipyridine and 4,4'-dipyridine with β-cyclodextrin in aqueous solution.