Supramolecular assembly activated single-molecule phosphorescence resonance energy transfer for near-infrared targeted cell imaging.

Pure organic phosphorescence resonance energy transfer is a research hotspot. Herein, a single-molecule phosphorescence resonance energy transfer system with a large Stokes shift of 367 nm and near-infrared emission is constructed by guest molecule alkyl-bridged methoxy-tetraphenylethylene-phenylpyridines derivative, cucurbit[n]uril (n = 7, 8) and ß-cyclodextrin modified hyaluronic acid. The high binding affinity of cucurbituril to guest molecules in various stoichiometric ratios not only regulates the topological morphology of supramolecular assembly but also induces different phosphorescence emissions. Varying from the spherical nanoparticles and nanorods for binary assemblies, three-dimensional nanoplate is obtained by the ternary co-assembly of guest with cucurbit[7]uril/cucurbit[8]uril, accompanying enhanced phosphorescence at 540 nm. Uncommonly, the secondary assembly of ß-cyclodextrin modified hyaluronic acid and ternary assembly activates a single intramolecular phosphorescence resonance energy transfer process derived from phenyl pyridines unit to methoxy-tetraphenylethylene function group, enabling a near-infrared delayed fluorescence at 700 nm, which ultimately applied to mitochondrial targeted imaging for cancer cells.

Inclusion-Activated Reversible E/Z Isomerization of a Cyanostilbene Derivative Based on Cucurbit[8]uril under 365 nm Ultraviolet Irradiation.

The photoisomerization behavior of cyanostilbene molecules is a hotspot in supramolecular configuration transformation research. Here, we reported a cyanostilbene derivative that converted from the Z,Z-isomer to the E,E-isomer under UV light irradiation at 365 nm. This process can be reversibly converted only in the presence of cucurbit[8]uril under the same light source, accompanied by the reversible conversion of fluorescence from green to yellow. No effective configuration transformation occurred with guest molecules only or upon the addition of cucurbit[7]uril. The photoisomerization was fully characterized by UV-vis and fluorescence spectroscopy, NMR, high-resolution mass spectrometry, and transmission electron microscopy. This work provides a new method for the supramolecular macrocyclic-activated configuration transformation.

Guest-induced supramolecular chirality transfer in [2]pseudorotaxanes: experimental and computational study.

To reveal the factors governing the chirality transfer from a chiral unimolecule to a supramolecular assembly, we constructed a series of [2]pseudorotaxanes through the intermolecular noncovalent interaction of a pair of chiral binaphthalene crown ethers with achiral secondary ammonium salts with different chromophores, and found that the binaphthalene groups can induce new circular dichroism (CD) signals only in the [2]pseudorotaxane structures between the host crown ethers and the guest molecule with the anthryl group. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations show that the generation of the new CD signal is mainly due to the intermolecular chiral induction between the anthryl group in the guest and the naphthalene groups in the host.

A highly efficient light-harvesting system with sequential energy transfer based on a multicharged supramolecular assembly.

A supramolecular assembly was constructed by the nonconvalent interaction of pillar[5]arene (WP5) with a pyridinium modified tetraphenylethene (Py-TPE) derivative, in which Py-TPE/WP5 acted as a donor, and sulforhodamine 101 and sulfonated aluminum phthalocyanine acted as acceptors to realize a highly efficient light-harvesting system with two-step sequential energy transfer.

Photo-controlled chirality transfer and FRET effects based on pseudo[3]rotaxane.

The use of light to regulate the chirality of supramolecular assemblies in a non-invasive manner remains a challenge. Herein, we report a novel photochromic pseudo[3]rotaxane based on a (R/S)-2,2'-binaphthyl secondary ammonium salt guest (2) and anthracene-bridged bis(dibenzo-24-crown-8) (1), which features a chirality transfer and fluorescence resonance energy transfer (FRET) from 2 to 1. Benefiting from the photo-oxidation of anthracene, the induced circular dichroism (ICD) signals of (R/S)-2@1 can be switched off/on by irradiation with 365 nm UV light and heating. This noncovalent supramolecular assembly strategy provides us with unique opportunities to design and construct further smart photo-responsive chiral molecular switches.

Photocontrolled morphological conversion and chiral transfer of a snowflake-like supramolecular assembly based on azobenzene-bridged bis(dibenzo-24-crown-8) and a cholesterol derivative.

A snowflake-like supramolecular clockwise-helical assembly was fabricated via the host-guest interaction of trans-azobenzene-bridged bis(dibenzo-24-crown-8) (trans-1) and a cholesterol derivative, while a snowflake-like supramolecular non-helical assembly can be obtained upon complexation of cis-1 after UV-irradiation, accompanying the disappearance of circular dichroism signals from the azobenzene zone of 1.

Light-controlled reversible self-assembly of nanorod suprastructures.

Nanorod suprastructures constructed by the coordination of zinc ions with the inclusion complex of 4,4'-dipyridine in ß-cyclodextrin can dissociate and rebuild repeatedly via alternate visible light irradiation in the presence of photoacid merocyanine in aqueous solution.

Tunable Luminescent Lanthanide Supramolecular Assembly Based on Photoreaction of Anthracene.

Lanthanide luminescence materials generally show great superiority in light-emitting materials, gaining increasingly exploration in the design of advanced functional materials. Herein, we prepared a supramolecular assembly via the coordination of a host molecule (1) and dilanthanide metal. Compound 1 possesses a 9,10-diphenylanthracene (ant) core with photosensitivity and terminal terpyridine (tpy), containing two-arm dibenzo-24-crown-8. The assembly could exhibit excellent lanthanide luminescence after undergoing a photoreaction from anthracene unit in 1. Significantly, the luminescence of the assembly could be reversibly switched on and off through a regulable photoreaction upon light irradiation or heating. The multiple functional behavior combined with the ease of assembly reveals that this photo/thermo-controlled lanthanide luminescence supramolecular polymer design method offers a convenient pathway for future engineering of multi-stimuli-responsive materials.

Insights into the Difference Between Rotaxane and Pseudorotaxane.

Rotaxane and pseudorotaxane are two types of mechanically interlocked molecular architectures, and there is a clear topological difference and boundary between them. In this work, a "suggested [2]rotaxane 1⊂α-CD" was constructed based on axle molecule 1 bearing two terminal ferrocene groups and a wheel component α-cyclodextrin (α-CD), but the result obtained indicated that the ferrocene group cannot prevent α-CD dethreading under UV irradiation. That is, 1⊂α-CD is just a pseudo[2]rotaxane. Furthermore, the two ferrocene groups in 1⊂α-CD were encapsulated by two cucurbit[7]uril (CB[7]) units to obtain a heteropseudo[4]rotaxane 1⊂α-CD⋅2CB[7]. This heteropseudo[4]rotaxane displayed high stability towards harsh temperatures and the isomerization of azobenzene in 1, so it can be regarded as a [2]rotaxane. In this [2]rotaxane, the stoppers are not the bulky groups covalently bonded to the axle, but the cyclic CB[7] units connected through noncovalent interactions.

Fluorescent supramolecular polypseudorotaxane architectures with Ru(II)/tri(bipyridine) centers as multifunctional DNA reagents.

A water-soluble supramolecular polypseudorotaxane was prepared via the host-guest interaction of cucurbit[8]uril and the Ru(bpy)3 complex with bis-naphthalene groups. By employing the intrinsic properties of the Ru(bpy)3 complex, the linear polypseudorotaxane can induce DNA condensation, be used as an inhibitor for DNA cleavage enzymes, and trace the translocation of DNA into 293T cells efficiently.

Mechanically selflocked chiral gemini-catenanes.

Mechanically interlocked and entangled molecular architectures represent one of the elaborate topological superstructures engineered at a molecular resolution. Here we report a methodology for fabricating mechanically selflocked molecules (MSMs) through highly efficient one-step amidation of a pseudorotaxane derived from dual functionalized pillar[5]arene (P[5]A) threaded by α,ω-diaminoalkane (DA-n; n=3-12). The monomeric and dimeric pseudo[1]catenanes thus obtained, which are inherently chiral due to the topology of P[5]A used, were isolated and fully characterized by NMR and circular dichroism spectroscopy, X-ray crystallography and DFT calculations. Of particular interest, the dimeric pseudo[1]catenane, named 'gemini-catenane', contained stereoisomeric meso-erythro and dl-threo isomers, in which two P[5]A moieties are threaded by two DA-n chains in topologically different patterns. This access to chiral pseudo[1]catenanes and gemini-catenanes will greatly promote the practical use of such sophisticated chiral architectures in supramolecular and materials science and technology.

Light-controlled reversible formation and dissociation of nanorods via interconversion of pseudorotaxanes.

Nanorod-like supramolecular aggregates are fabricated by the self-assembly of the amphiphilic [2]pseudorotaxane, which can be dissociated and rebuilt by the alternating UV/vis irradiation.

Supramolecular nanoassemblies of an amphiphilic porphyrin-cyclodextrin conjugate and their morphological transition from vesicle to network.

An amphiphilic compound, 5-(4'-dodecyloxyphenyl)-10,15,20-tri(permethyl-ß-CD)-modified Zn(II)-porphyrin (1; ß-CD = ß-cyclodextrin), was synthesized by means of the click reaction of an alkylated Zn-porphyrin derivative with 6-deoxy-6-azidopermethyl-ß-CD. The complexation between 1 and tetrasodium tetraphenylporphyrintetrasulfonate (5) with different molar ratios led to the formation of two distinctly different nanoarchitectures, which were proven to be vesicle and network aggregates, respectively, by using dynamic light scattering, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. On the basis of the results of the time-dependent TEM studies, fluorescence, and NMR spectroscopic measurements, we have determined that the mechanism of the morphology transition from vesicles to networks is controlled by the stepwise complexation of 1 with 5. Furthermore, these supramolecular nanoarchitectures show the controlled- release property of doxorubicin as potential candidates for drug delivery.

A supramolecular brush polymer via the self-assembly of bridged tris(ß-cyclodextrin) with a porphyrin derivative and its magnetic resonance imaging.

Accurate imaging of soft tissues is one of the ultimate goals in biomedical imaging. Different imaging modalities can improve their disadvantages, and promote the imaging ability. However, once an imaging agent has been prepared, it is usually hard to adjust it according to the actual needs. Herein, we developed a supramolecular brush polymer (SBP) as a versatile imaging agent platform. The SBP platform (SBPP) is constructed by the intermolecular inclusion complexation of bridged tris(ß-cyclodextrin) (1) with Mn(iii)-porphyrin-bearing poly(ethylene glycol) (PEG) side chains (Mn(iii)-TPP), and can further bind other functional groups by host-guest interactions of cyclodextrin and adamantine. The SBPP is characterized by UV/vis absorption spectroscopy, NMR, dynamic light scattering (DLS), atomic force microscopy (AFM) and transmission electron microscopy (TEM). We demonstrated that this SBPP not only has no cellular toxicity against NIH 3T3 cells in in vitro cell experiments, but it also shows an efficient enhanced T1 relaxivity in in vitro MR imaging experiments. When used as multifunctional imaging agents, different imaging probes and/or targeting agents can be introduced to this SBPP as needed through simple host-guest interactions. In in vitro imaging experiments, it shows accurate imaging of different kinds of cancer cells by choosing on-demand targeting agents. These results suggest a promising strategy for engineering multifunctional imaging agents with SBPs.

Dual-stimulus luminescent lanthanide molecular switch based on an unsymmetrical diarylperfluorocyclopentene.

A [2]pseudorotaxane formed from an unsymmetrical diarylperfluorocyclopentene (1) and a Eu(3+) complex of terpyridinyldibenzo-24-crown-8 (2) revealed excellent reversible lanthanide luminescence switching behavior dual-modulated by host-guest and optical stimuli.

Self-sorting of four organic molecules into a heterowheel polypseudorotaxane.

The social self-sorting supramolecular assembly is described by non-covalent interactions among four organic components. Toward this goal, a series of self-sorting systems have been investigated by mixing two or three different compounds; naphthyl-bridged bis(α-cyclodextrin), N,N'-dioctyl-4,4'-bipyridinium, 2,6-dihydroxynaphthalene, and cucurbit[8]uril. The influence of alkyl chains of viologen derivatives and the binding abilities of these systems have also been studied. Their integrative self-sorting led to the exclusive formation of the purple supramolecular heterowheel polypseudorotaxane. The heterowheel polypseudorotaxane is a thermodynamically stable self-sorted product, and consists of two different macrocycles with three sorts of different non-covalent interactions. Its structure was established by NMR spectroscopy and UV/Vis absorption spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light-scattering (DLS), diffusion-ordered spectroscopy (DOSY), and viscosity measurements.

A double-leg donor-acceptor molecular elevator: new insight into controlling the distance of two platforms.

A double-leg elevator with an electron-rich anthracene moiety at the platformlike component and an electron-deficient naphthalenediimide unit in the middle of a double-leg riglike component was prepared through "click chemistry", in which the reversible elevator movement between different levels could be controlled upon the addition of base and acid.

High affinity crown ether complexes in water: thermodynamic analysis, evidence of crystallography and binding of NAD+.

Improving traditional crown ether to the water-soluble and high binding ability host molecule is critical to our efforts to model or mimic biological supramolecular systems. In this paper, we converted two traditional crown ethers, 1,5-dinaphtho-32-crown-8 and 1,5-dinaphtho-38-crown-10, into the water-soluble tetrasulfonated 1,5-dinaphtho-32-crown-8 and tetrasulfonated 1,5-dinaphtho-38-crown-10, evaluated their complexation with three dicationic bipyridiniums in aqueous solution by microcalorimetric titration, UV-vis, and NMR experiments, and then determined the crystal structures of three tetrasulfonatocrown ether-bipyridinium complexes. The equilibrium association constants of tetrasulfonated 1,5-dinaphtho-32-crown-8 with these bipyridiniums reach up to 10(7) M(-1), while those of tetrasulfonated 1,5-dinaphtho-38-crown-10 are just in the range of 10(5) M(-1) order of magnitude. The thermodynamic data obtained show that the complexation of two tetrasulfonatocrown ethers with dicationic bipyridiniums is absolutely enthalpy-driven in water with an accompanying little entropic gain, and each monocationic pyridinium moiety in guest molecules can provide about -10 to -15 kJ·mol(-1) enthalpy contribution irrespective of the size of ether crowns. Moreover, we also investigated the recognition capability of the two water-soluble crown ethers with NAD(+) and NADH by microcalorimetric titration and NMR experiments, indicating that tetrasulfonated 1,5-dinaphtho-32-crown-8 shows exclusive selectivity to NAD(+). The water-solubility and high affinity of this system as well as the flexible and non-preorganized characteristic of these crown ethers make it suitable to serve as a model for mimicking biological systems.

Interconversion between [5]pseudorotaxane and [3]pseudorotaxane by pasting/detaching two axle molecules.

An acceptor-donor-acceptor-type linear molecule 1(2+) containing one electron-rich naphthoxy (NP) unit and two monocharged viologen (MCV) units was synthesized. Through the noncovalent interaction of cucurbit[8]uril (CB[8]) with one NP and one MCV in 1(2+), we first obtained a [2]pseudorotaxane ([1(2+)]⊂CB[8]), and the excess CB[8] included simultaneously the two bare MCV units of two [2]pseudorotaxanes to form a [5]pseudorotaxane ([1(2+)](2)⊂[CB[8]](3)). Its transformation to [3]pseudorotaxane was achieved through detaching the two axle molecules in the presence of acid, and then the addition of base may result in a reversible switch between two different pseudorotaxanes. This novel methodology elongating reversibly linear molecules by noncovalent interactions will benefit the development of stimuli-responsive functional molecular devices.