Coordination-induced switchable nanoparticle formation from naphthyl-bridged bis(ß-cyclodextrin).

Naphthyl-bridge bis(ß-cyclodextrin) (1) was synthesized via "click chemistry", and its self-assembly behavior was investigated by NMR, UV-vis, circular dichroism spectra, transmission electron microscopy, and atomic force microscopy. The results obtained indicate that the coordination of Hg(2+) with triazole rings in 1 induces the naphthyl moiety to move from being a self-included complex to the formation of nanoparticles through intermolecular self-aggregation. Furthermore, the formation and disassembly of nanoparticle was reversibly controlled by adding or removing Hg(2+).

Complexation-induced transition of nanorod to network aggregates: alternate porphyrin and cyclodextrin arrays.

Tetrakis(permethyl-beta-cyclodextrin)-modified zinc(II) porphyrin (1) and tetra(beta-cyclodextrin)-modified zinc(II) porphyrin (2) were synthesized via "click chemistry". Intermolecular inclusion complexation of these structurally similar 1 and 2 with tetrasodium tetraphenylporphyrintetrasulfonate (3) led to formation of two distinctly different nanoarchitectures with alternate porphyrin and cyclodextrin arrays, which were proven to be network and nanorod aggregates, respectively, by using transmission electron microscopy, atomic force microscopy, and scanning electron microscopy. From the results of comparative studies in different solutions, we elucidated the mechanisms that result in nanorod to network aggregates transition, concluding that the complexation strength of porphyrin with cyclodextrin is a crucial factor to activate the potential binding sites of a molecular building block.

Fluorescence sensing and selective binding of L- and D-tryptophan-modified permethylated beta-cyclodextrins for aliphatic oligopeptides.

Two tryptophan-modified permethylated beta-cyclodextrins, 6I-L-Trp-6I-deoxy-2I,3I-di-O-methyl-hexakis(2II-VII,3II-VII,6II-VII-tri-O-methyl-beta-cyclodextrin (3) and 6I-D-Trp- 6I-deoxy-2I,3I-di-O-methyl-hexakis(2II-VII,3II-VII,6II-VII-tri-O-methyl)-beta-cyclodextrin (4), were synthesized, and their binding behaviors were investigated with the aliphatic oligopeptides, Leu-Gly, Gly-Leu, Gly-Pro, Glu-Glu, and Gly-Gly. Fluorescence spectrophotometric studies indicated that 3 and 4 can act as efficient fluorescence sensors for aliphatic oligopeptides. Due to their intermolecular co-inclusion binding mode with substrates, 3 and 4 not only afforded high binding constants of up to 10(3)-10(4) M(-1) for guest oligopeptides but also good molecular selectivities of up to ca. 7 for Gly-Gly/Leu-Gly and Glu-Glu/Gly-Gly pairs.

Controllable DNA condensation through cucurbit[6]uril in 2D pseudopolyrotaxanes.

2D pseudopolyrotaxanes containing beta-cyclodextrins and cucurbit[6]urils can induce DNA condensation, and the number of cucurbit[6]urils threaded onto the side chains of beta-cyclodextrins plays important roles in this process.

Reversible 2D pseudopolyrotaxanes based on cyclodextrins and cucurbit[6]uril.

In this paper, a pseudorotaxane (2) was synthesized by reaction of cucurbit [6]uril with 6-[(6-aminohexyl)amino]-6-deoxy-beta-cyclodextrin chloride. Subsequently, pseudorotaxanes 2 were further assembled to form a 2D pseudopolyrotaxane (3) through an alpha,omega-PPG2000 diamino polymer threading the cavities of cyclodextrins in 2, and the resulting pseudopolyrotaxane was comprehensively characterized by FT-IR, NMR, TG-DTA, elemental analysis, and transmission electron microscopy. Significantly, the 2D pseudopolyrotaxane can turn into a main-chain pseudopolyrotaxane in the presence of base, and then the addition of alpha-cyclodextrins may result in a reversible switch between two different 2D pseudopolyrotaxanes.

Supramolecular aggregates constructed from gold nanoparticles and l-try-CD polypseudorotaxanes as captors for fullerenes.

A series of cyclodextrin-based polypseudorotaxanes (PPRs) were constructed by threading native beta-cyclodextrin or l-tryptophan-modified beta-cyclodextrin onto the amino-terminated PPG chains of different lengths. Subsequently, these PPRs were further assembled to form netlike supramolecular aggregates through the linkage of gold nanoparticles, and the resulting water-soluble Au-PPR aggregates were comprehensively characterized by FT-IR, UV, NMR, fluorescence spectroscopy, powder X-ray diffraction patterning, TG-DTA, and transmission electron microscopy. The results showed that the size and sedimentation rate of the Au-PPR aggregates were mainly dependent on the lengths of the PPG chains. Significantly, the Au-PPR aggregate 8, involving many l-tryptophan residues, showed not only a satisfactory water solubility but also a good capturing ability for fullerenes in aqueous solution. The 8-fullerene conjugate thus formed exhibited a good DNA cleavage ability under light irradiation.

Diastereomeric molecular recognition and binding behavior of bile acids by L/D-tryptophan-modified beta-cyclodextrins.

[reaction: see text] Binding behavior of L- and D-tryptophan-modified beta-cyclodextrins (L/D-Trp-beta-CD) (1 and 2) with four bile acids, i.e., cholate (CA), deoxycholate (DCA), glycocholate (GCA), and taurocholate (TCA), has been investigated by fluorescence, circular dichroism, and 2D-NMR spectroscopies and fluorescence lifetime measurement, as well as isothermal titration microcalorimetry. From the induced circular dichroism (ICD) and 2D NMR spectra, it is deduced that the D-Trp moiety of 2 attached to beta-CD is more deeply self-included in the cavity than that of the antipodal L-Trp moiety of 1, indicating appreciably enantioselective binding of the chiral sidearm by beta-CD. Interestingly, the original difference in conformation between 1 and 2 led to quite a large difference in affinity toward DCA, giving 3.3 times higher binding ability for 2 than for 1. Thermodynamically, the inclusion complexation of 1 and 2 with bile acids was entirely driven by favorable enthalpy change (DeltaH degrees) with accompanying negative entropy change (DeltaS degrees). The stronger binding of bile acids by L/D-Trp-beta-CD is attributable to higher enthalpic gains. The combined use of the calorimetric and NMR ROESY spectral examinations revealed the correlation between the thermodynamic parameters and the role of sidearm conformation in modified beta-cyclodextrins.