Flavylium Network of Chemical Reactions in Confined Media: Modulation of 3′,4′,7‐Trihydroxyflavilium Reactions by Host–Guest Interactions with Cucurbit[7]uril

In moderately acidic aqueous solutions, flavylium compounds undergo a pH‐, and in some cases, light‐dependent array of reversible chemical reactions. This network can be described as a single acid–base reaction involving a flavylium cation (acidic form) and a mixture of basic forms (quinoidal base, hemiketal and cis and trans chalcones). The apparent pK′_a of the system and the relative mole fractions of the basic forms can be modulated by the interaction with cucurbit[7]uril. The system is studied by using ¹H NMR spectroscopy, UV/Vis spectroscopy, flash photolysis, and steady‐state irradiation. Of all the network species, the flavylium cation possesses the highest affinity for cucurbit[7]uril. The rate of interconversion between flavylium cation and the basic species (where trans‐chalcone is dominant) is approximately nine times lower inside the cucurbit[7]uril.     

Gold nanoparticles in organic capsules: a supramolecular assembly of gold nanoparticles and cucurbituril

Gold nanoparticles (相似文献   

Application of the Generalized Molar‐Ratio Method to the Determination of the Stoichiometry and Apparent Binding Constant of Nanoparticle‐Organic Capping Systems

A generalization of the molar‐ratio method is applied to the determination of the stoichiometry and apparent binding constant of metal nanoparticle‐organic capping complexes (M_mL_x) using voltammetric data for the oxygen reduction reaction (ORR) in air‐saturated aqueous phosphate buffer solutions. The method is applied to the formation of binary nanohybrids consisting of gold nanoparticles (AuNPs) capped with a rigid spacer, cucurbit[7]uril (CB), termed AuNP@CB, as well as to the formation of their ternary complexes (M_mL_xB_z) with methylene blue (MB), termed AuNP@CB@MB. The obtained stoichiometries correspond to binding of four Au surface atoms for each CB unit.     

Self‐Assembly of Anionic Porphyrins and Alkaline or Alkaline Earth Metal Ions Mediated by Cucurbit[7,8]uril

Nanoscaled coordination polymers based on biologically prevalent ions have potential applications in drug delivery and biomedical imaging. Herein, coordination polymer nanoparticles of anionic porphyrins, including meso‐tetra(4‐carboxyphenyl)‐porphyrin (H₂TCPP^4?) and meso‐tetra(4‐sulfonatophenyl)‐porphyrin (H₂TPPS^4?), and alkaline or alkaline earth metal cations, such as K⁺ and Ca²⁺, were constructed in aqueous solution in the presence of cucurbit[7]uril (CB7) or cucurbit[8]uril (CB8). UV/Vis absorption and fluorescence spectroscopy, dynamic light scattering (DLS), scanning electron spectroscopy (SEM), and atomic force microscopy (AFM) were applied to explore the assembly and particle formation of porphyrin anions and metal cations mediated by CBn. The particle size depends on the kinds of CBn and metal cations and their concentrations. The uptake of H₂TPPS^4? particles by tumor cells (A549 cells) was found to be more efficient than H₂TPPS^4? at 37 °C, showing the application potential of such assembled particles in biology and medicine.     

Complex Formation of Crown Ethers with the Cucurbit[6]uril–Spermidine and Cucurbit[6]uril–Spermine Complex in Aqueous Solution

Alkyl amines are able to form complexes with either crown ethers or cyclodextrins or cucurbit[6]uril. The same is known for polyamines such as spermidine and spermine. However, the simultaneous formation of such polyamines with crown ethers and cucurbit[6]uril has not been studied. The ability of polyamines such as spermidine and spermine to form mixed complexes with different ligands, e.g. crown ethers and cucurbit[6]uril has been studied in aqueous solution using pH-metric and calorimetric titrations. The thermodynamic data of reaction between crown ethers with spermidine, spermine and their cucurbit[6]uril complexes have been determined. The presence of cucurbit[6]uril on the polyamines has no important influence upon the reaction of these amines with crown ethers. The reactions between polyamines, cucurbit[6]uril and crown ethers are simple examples for the self organization of molecules due to specific interactions. Received in final form: 26 January 2005     

Platinum Nanoparticles Stabilized by Cucurbit[6]uril with Enhanced Catalytic Activity and Excellent Poisoning Tolerance for Methanol Electrooxidation

Three sub‐10 nm platinum nanoparticles (PtNPs) with distinctive morphologies were developed by using cucurbit[6]uril (CB[6]) as stabilizing agent and support. Both the size and shape of the PtNPs were simultaneously controlled by tuning the reducing agents. The prepared NPs have been comprehensively characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy, transmission electron microscopy, and cyclic voltammetry. On account of the presence of CB[6] and its unique structural features, the as‐prepared PtNPs are homogeneous in morphologies and exhibit higher activities toward methanol electrooxidation than commercial Pt/C. CB[6] has the ability to bind small molecules that can promote CO oxidation, therefore, all the three PtNPs showed enhanced poisoning tolerance. Such unique abilities of CB[6] can even promote the poisoning tolerance of commercial Pt/C through simple physical mixing.     

One-pot synthesis–assembly–separation of cucurbit[6]uril via SO3H-functionalized ionic liquids

A novel microwave-assisted route to synthesize cucurbit[n]uril in SO₃H-functionalized ionic liquids was reported, which enabled the automatic separation of cucurbit[6]uril through anion assembly. For the first time, the route has realized synthesis–assembly–separation of cucurbit[6]uril in one pot. The reaction yield and separation efficiency can be tuned by choice of anionic groups in ionic liquids.     

Constraining the Teratogenicity of Pesticide Pollution by a Synthetic Nanoreceptor

The teratogenicity of the pesticide nereistoxin (NTX) and its derivative thiocyclam (THI) towards aquatic life was dramatically constrained by a synthetic nanoreceptor, cucurbit[7]uril, through selective encapsulation of the pesticides (K_CB[7]‐NTX of 3.24(±0.31)×10⁶ m ^?1 and K_CB[7]‐THI of 7.46(±0.10)×10⁵ m ^?1), as evidenced by the rate of hatchability, morphology development, and tyrosinase activity of zebrafish larvae incubated with the pesticides (3–300 μm ) in the absence and in the presence of 300 μm cucurbit[7]uril, demonstrating the significant potential of the nanoreceptor in managing ecological pollution of these pesticides.     

Dual‐Mode Controlled Self‐Assembly of TiO2 Nanoparticles Through a Cucurbit[8]uril‐Enhanced Radical Cation Dimerization Interaction

The realization of controllable multicomponent self‐assembly through reversible supramolecular interactions is a challenging goal, and is an important strategy for the fabrication of switchable nanomaterials. Herein we show that the self‐assembly of TiO₂ nanoparticles (NP) functionalized with methyl viologen can be controlled both by light irradiation and chemical reduction through cucurbit[8]uril‐enhanced radical cation dimerization interactions. Moreover, the controlled assembly and disassembly of this system are accompanied by switchable photocatalytic activity of the TiO₂ NPs, which shows potential application as a novel smart and recyclable photocatalyst.     

Cucurbit[5]uril, Decamethylcucurbit[5]uril and Cucurbit[6]uril. Synthesis, Solubility and Amine Complex Formation

A simple way to prepare cucurbit[5]uril is described. The macrocycles of the cucurbituril type are nearly insoluble in water. The solubilities of cucurbit[5]uril, decamethylcucurbit[5]uril and cucurbit[6]uril in hydrochloric acid, formic acid and acetic acid of different concentrations have been investigated. Due to the formation of complexes between cucurbit[n]urils and protons the solubility increases in aqueous acids. The macrocyclic ligands are able to form complexes with several organic compounds. Thus, the complex formation of the cucurbituril macrocycles with different amines has beenstudied by means of calorimetric titrations. The reaction enthalpy gives noevidence of the formation of inclusion or exclusion complexes. ¹H-NMR measurements show that in the case of cucurbit[5]uril and cucurbit[6]uril the organic guest compound is included within the hydrophobic cavity. Decamethylcucurbit[5]uril forms only exclusion complexes with organicamines. This was confirmed by the crystal structure of the decamethylcucurbit[5]uril-1,6-diaminohexane complex.     

Highly Selective Separation of Minimum‐Boiling Azeotrope Toluene/Pyridine by Nonporous Adaptive Crystals of Cucurbit[6]uril

The production of high purity toluene and pyridine is of significance in both industrial production and synthetic chemistry. The present protocols available to separate toluene/pyridine mixtures are several energy‐intensive distillation methods, which are not environmentally friendly and cost‐effective. Herein, we provide an energy‐efficient and simple adsorptive separation protocol using nonporous adaptive crystals of cucurbit[6]uril ( Q[6] ). Q[6] crystals separate pyridine from toluene/pyridine mixtures with nearly 100 % purity. Furthermore, removal of the guest from guest‐loaded Q[6] leads to the guest‐free cucurbit[6]uril, which can be recycled without losing performance.     

Uptake of Hydrocarbons in Aqueous Solution by Encapsulation in Acyclic Cucurbit[n]uril‐Type Molecular Containers

The ability of two water‐soluble acyclic cucurbit[n]uril (CB[n]) type containers, whose hydrophobic cavity is defined by a glycoluril tetramer backbone and terminal aromatic (benzene, naphthalene) sidewalls, to act as solubilizing agents for hydrocarbons in water is described. ¹H NMR spectroscopy studies and phase‐solubility diagrams establish that the naphthalene‐walled container performs as well as, or better than, CB[7] and CB[8] in promoting the uptake of poorly soluble hydrocarbons into aqueous solution through formation of host–hydrocarbon complexes. The naphthalene‐walled acyclic CB[n] container is able to extract large hydrocarbons from crude oil into aqueous solution.     

Supramolecular Polymerization Promoted and Controlled through Self‐Sorting

A new method in which supramolecular polymerization is promoted and controlled through self‐sorting is reported. The bifunctional monomer containing p‐phenylene and naphthalene moieties was prepared. Supramolecular polymerization is promoted by selective recognition between the p‐phenylene group and cucurbit[7]uril (CB[7]), and 2:1 complexation of the naphthalene groups with cucurbit[8]uril (CB[8]). The process can be controlled by tuning the CB[7] content. This development will enrich the field of supramolecular polymers with important advances towards the realization of molecular‐weight and structural control.     

Defection-selective solubilization and chemically-responsive solubility switching of single-walled carbon nanotubes with cucurbit[7]uril

Single-walled carbon nanotubes (SWCNTs) were suspended in aqueous media with cucurbit[7]uril (CB7), while SWCNTs were insoluble with cucurbit[5]uril (CB5). Moreover, defection-selective solubilization of SWCNTs with CB7 was demonstrated.     

Electrochemical detection of amino acids based on cucurbit[7]uril-mediated three-dimensional gold nanoassemblies

In this paper, cucurbit[7]uril (CB[7])-mediated three-dimensional gold nanoassemblies were successfully prepared to increase the loaded amount of CB[7] and enhance the electrochemical detection of amino acids. Particle sizes of gold nanoparticles (AuNPs) significantly affect stability and detection sensitivity of nanoassemblies. The volume of gold nanoassemblies first increased and then decreased with the increase of CB[7] concentration. The 3D gold nanoassemblies composed of 16 nm AuNPs and 100 µmol/L CB[7] had excellent stability and maximum volume, exhibiting more sensitive detection for a variety of amino acids. And the detection limits of aromatic amino acids are lower in virtue of the higher binding constant between aromatic amino acids and CB[7]. This study will develop and deepen our understanding of molecular recognition in amino acids detection.     

A facile synthesis of dynamic supramolecular aggregates of cucurbit[n]uril (n=5-8) capped with gold nanoparticles in aqueous media

Supramolecular capping of cucurbit[n]uril (CB[n]), where n=5-8, by narrowly dispersed gold nanoparticles has been achieved through a facile synthetic route with metastable gold nanoparticles as a labile intermediate. The resultant assemblies were stable in solution, and were found to form dynamic aggregates consisting of a controllable ratio of singly and doubly capped CB[n]. The stability of the system was attributed to the presence of sodium cations bound on the vacant carbonyl portals of the singly capped CB[n] molecules. These dynamically capped CB[n] systems can find potential use in a range of applications varying from ultrasensitive multiplexed in situ sensing to photocatalysis.     

Selective Release of Doxorubicin from Cucurbit[8]uril Stabilized Gold Supra-Pyramid Host at pH of Small Intestine

Gold supra-pyramid structures were obtained by the addition of acidic solution of cucurbit[8]uril (CB[8]) to an aqueous solution of citrate stabilized gold nanoparticles (AuNP). The reaction resulted in the precipitation of supra-pyramid from the solution after just 1 min of shaking. Microscopic images confirmed formation of the supra-pyramid. The stepwise structural transformation towards the supra-pyramid was examined with variable concentrations of CB[8] to AuNP solution. Anionic counter parts of these acids (Br⁻, NO₃⁻, SO₄²⁻ and Cl⁻) controlled the size of the synthesized supra-pyramids. These supra-pyramid hosts showed uptake of three anticancer drugs: oral drugs etoposide, prednisolone and intravenous drug doxorubicin. Releases of drugs from these hosts were emulated at acidic stomach pH, basic small intestinal pH and in the presence of human serum albumin (HSA). The specific release of doxorubicin was confirmed at small intestinal pH 7.4. Poor release of drugs in presence of CB[8] specific guest 1-adamantanamine confirmed the role of the supra-pyramid as the exclusive host. The release of doxorubicin from the supra-pyramid at pH 7.4 was confirmed by fluorescence microscopic imaging with prostate cancer DU-145 cell line.     

Primary photoprocesses of 3,3’-diethylthiacarbocyanine in the presence of cucurbit[7]uril: Laser flash photolysis and quantum chemical calculations

The effect of cucurbit[7]uril on the phototransformation of 3,3′-diethylthiacarbocyanine iodide dye in aqueous solution has been investigated by nanosecond laser flash photolysis. The presence of cucurbit[7]uril results in the formation of its complex with the dye molecule producing a dimer. The dimer formation is evident from the ground and triplet-triplet absorption spectra. The dimers in the triplet state are capable of electron transfer. The structure of the complexes is suggested on the basis of quantum chemical calculations.     

Preorientation of olefins toward a single photodimer: cucurbituril-mediated photodimerization of protonated azastilbenes in water

With the view to establishing the generality of cucurbit[8]uril as a template, the photodimerization of hydrochloride salts of eight azastilbenes has been investigated in an aqueous medium. Whereas in solution upon excitation all of these olefins yield products of geometric isomerization, cyclization, and hydration, in the presence of cucurbit[8]uril the predominant product is that of dimerization. Such a change in product distribution is attributed to the localization of the olefins by the host cucurbit[8]uril. Most importantly, instead of a mixture of dimers, predominantly a single dimer was obtained in each case. The nature of the dimer that was formed could be rationalized on the basis of the principles of "best fit" and "minimization of electrostatic repulsion". The superior ability of cucurbit[8]uril compared to micelles to act as a templating agent is attributed to its ability to provide a reaction cavity that is tight and time-independent.     

Inclusion complex of riboflavin with cucurbit[7]uril: study in solution and solid state

The aqueous solution of riboflavin and cucurbit[7]uril complex has been studied based on fluorescence and ¹H NMR spectroscopic results. Upon addition of cucurbit[7]uril, the fluorescence intensity of riboflavin was quenched and a slight red shift was observed for the maximum emission peak. These results indicated that the cucurbit[7]uril–riboflavin complex was formed at a 1:1 mole ratio. The temperature-dependent inclusion constants were calculated, from which ΔH and ΔS values were calculated. Meanwhile, rationale of the interaction mechanism was also discussed based on ¹H NMR results. The solid inclusion complex was prepared from co-evaporation method and characterised by differential thermal analysis and fluorescence lifetime analysis methods. The experimental results indicated that riboflavin and cucurbit[7]uril formed stable host–guest inclusion complex in both solution and solid states.