cucurbit(8)uril and cucurbit(6)uril

Cucurbit[n]uril (CB[n], n = 5-10), a new family of molecular hosts comprising n glycoluril units, have gained much attention in the new millennium for their exceptional molecular recognition ability. The CB homologues have brought dynamism to CB chemistry, as witnessed by the heightened interest in the field for the last several years. Compared to the chemistry of cyclodextrins and calixarenes, however, that of CB[n] has developed slowly until recently, which may be attributed mainly to their poor solubility in common solvents, and inability to functionalize these molecules. The direct functionalization method of CB[n] propelled CB chemistry to a new height as this new method not only solved the solubility problem but also opened up the gateway to the generation of tailor-made CB[n] derivatives. The functionalization of CB[n] led us to investigate numerous applications including artificial ion channels, vesicles, stationary phases in chromatography, ISEs, polymers, nanomaterials, and many others. This tutorial review describes the recent advances and challenges in the functionalization of CBs along with the applications of functionalized CBs.

Topics: Anti-Bacterial Agents; Binding Sites; Biomimetic Materials; Bridged-Ring Compounds; Chemistry Techniques, Analytical; Imidazoles; Solubility

The adsorption behavior and mechanism of Reactive Blue 19 (RB19) on cucurbit[6]uril (CB[6]) and cucurbit[8]uril (CB[8]) were investigated. The adsorption isotherm data obtained at different temperatures were fitted well to the Langmuir isotherm, and according to this model, CB[8] and CB[6] exhibited maximum monolayer adsorption capacities of 714.29 and 100.5 mg/g, respectively, at 298.15 K. The adsorption thermodynamic functions ΔG, ΔH, and ΔS were evaluated and revealed that RB19 adsorption onto CB[8] and CB[6] is a spontaneous and enthalpy-driven process. The adsorption process was determined to follow pseudo-second-order kinetics, indicating that chemisorption dominates the adsorption process. Fourier tranform IR spectroscopy, thermogravimetric analysis, and density functional theory (DFT) calculations revealed that the formation of an inclusion complex is the main driving force of adsorption. The phenyl and sulfone moieties of RB19 reside inside the cavity of CB[8], but because of the small cavity, only the sulfone of RB19 resides inside the cavity of CB[6]. Time-dependent DFT calculations revealed that all of the absorption bands of RB19 derive from π → π* transitions, while for the adsorption product of CB[8], the bands located at 590 and 287 nm derive from π → π* transitions and the bands located at 254 and 202 nm mainly derive from intermolecular charge transfer (ICT).

Topics: Adsorption; Anthraquinones; Bridged-Ring Compounds; Imidazoles; Particle Size; Quantum Theory; Surface Properties; Thermodynamics

Cucurbit[n]urils efficiently decreased the Fenton-mediated oxidation of encapsulated dyes, providing a mechanism for some control and selectivity over the degradation. The encapsulation of methylene blue into cucurbit[7]uril made it highly refractory against Fenton oxidation in the dark or under UVA light irradiation. However, the oxidation of the encapsulated dye was significantly enhanced under visible light irradiation. This behavior was selective for the cucurbit[7]uril complex and not for the cucurbit[8]uril complex, which achieved the same degree of protection irrespective of the irradiation conditions. This different reactivity of the complexes was further discussed in terms of their excited state properties. The main mechanism for protection was the seclusion of the dye into cucurbit[n]urils as shown by the fact that the non-encapsulated dye safranin was protected much less than methylene blue. Additionally, cucurbit[n]urils efficiently trapped hydroxyl radicals, which contributed significantly to the protection of the dyes from Fenton-mediated oxidation.

Topics: Bridged-Ring Compounds; Darkness; Hydroxyl Radical; Imidazoles; Methylene Blue; Oxidation-Reduction; Phenazines; Photochemical Processes; Ultraviolet Rays

The characteristics of host-guest complexation between cucurbit[n]uril (CB[n], n=5, 6, 7, 8) and sanguinarine (SA) were investigated by spectrofluorimetry. The result showed that CB[n] (n=5, 6, 7, 8) reacted with SA to form an inclusion complex. At the optimum reaction conditions, the rectilinear calibration graphs were obtained in the range from 0.1 to 2800 ng mL(-1) for the investigated drug, with correlation coefficients 0.9998, 0.9997, 0.9999 and 0.9997 and detection limits 0.052, 0.26, 0.03 and 0.058 ng mL(-1) using CB[5], CB[6], CB[7], and CB[8], respectively. The apparent association constants of the complexes were 1.23 x 10(4), 6.73 x 10(3), 4.53 x 10(4) and 1.21 x 10(4) L mol(-1), for the reagents in the same order. The result demonstrated that CB[7] exhibited a higher fluorescence signal than CB[5], CB[6], and CB[8]. The proposed method was successfully applied for the determination of the drug in human urine and serum samples.

Topics: Benzophenanthridines; Bridged-Ring Compounds; Humans; Imidazoles; Isoquinolines; Molecular Structure; Serum; Spectrometry, Fluorescence; Urine

We have examined the interaction of [(5,6-dimethyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)platinum(II)] (2+) (1, 56MESS), [(5-methyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)platinum(II)] (2+) (2, 5MESS), [(5,6-dimethyl-1,10-phenanthroline)(1R,2R-diaminocyclohexane)platinum(II)] (2+) (3, 56MERR), and [(5,6-dimethyl-1,10-phenanthroline)(ethylenediamine)platinum(II)] (2+) (4, 56MEEN) with reduced L-glutathione and L-methionine. Both thiols degrade all four complexes, mainly by displacing the ancillary ligand and forming a doubly bridged dinuclear complex. The degradation half-life of all the complexes with methionine is >7 days, indicating that these reactions are not biologically relevant. The rate of degradation by glutathione appears to be particularly important and shows an inverse correlation to cytotoxicity. The least active complex, 4 (t 1/2 glutathione: 20 h), degrades fastest, followed by 3 (31 h), 2 (40 h), and 1 (68 h). The major degradation product, [bis-mu-{reduced L-glutathione}bis{5,6-dimethyl-1,10-phenanthroline}bis{platinum(II)}] (2+) (5, 56MEGL), displays no cytotoxicity and is excluded as the source of the anticancer activity. Once bound by glutathione, these metal complexes do not then form coordinate bonds with guanosine. Partial encapsulation of the complexes within cucurbit[n]urils is able to stop the degradation process.

Topics: Animals; Antineoplastic Agents; Bridged-Ring Compounds; Cell Proliferation; Drug Screening Assays, Antitumor; Glutathione; Guanosine Monophosphate; Imidazoles; Intercalating Agents; Leukemia L1210; Ligands; Magnetic Resonance Spectroscopy; Methionine; Mice; Organoplatinum Compounds; Spectrometry, Mass, Electrospray Ionization; Stereoisomerism; Structure-Activity Relationship; Tumor Cells, Cultured

The partial encapsulation of platinum(II)-based DNA intercalators of the type [Pt(5-Cl-phen)(ancillary ligand)](2+), where 5-Cl-phen is 5-chloro-1,10-phenanthroline and the ancillary ligand is ethylenediamine, (1S,2S)-diaminocyclohexane (S,S-dach) or (1R,2R)-diaminocyclohexane, within cucurbit[n]uril (CB[n], where n is 6, 7 or 8) has been examined by (1)H and (195)Pt NMR and mass spectrometry. For CB[7], the molecule encapsulates over the ancillary ligand of all metal complexes, whether this is ethylenediamine or diaminocyclohexane. For CB[8], encapsulation occurs over the sides of the 5-Cl-phen ligand at low [Pt(5-Cl-phen)(S,S-dach)](2+) (5CLSS) to CB[8] ratios (i.e. 0.25:1) but over the ancillary ligand at higher ratios (i.e. 2:1). For CB[6] binding, 5CLSS exhibits both portal and cavity binding, with the ancillary ligand displaying chemical shifts consistent with fast exchange kinetics on the NMR timescale for portal binding and slow exchange kinetics for cavity binding. Binding constants could not be determined using UV-vis, circular dichroism or fluorescence spectrophotometry, but a binding constant for binding of 5CLSS to CB[6] of approximately 10(5) M(-1) was determined using (1)H NMR. Finally, the effect of CB[n] encapsulation on the cytotoxicity of the metal complexes was examined using L1210 murine leukaemia cells in vitro growth inhibition assays. The cytotoxicity is highly dependent on both the metal complex and the CB[n] size, and whilst CB[7] and CB[8] generally decreased cytotoxicity, it was found that CB[6] increased the cyotoxicity of 5CLSS up to 2.5-fold.

Topics: Animals; Bridged-Ring Compounds; Capsules; Cell Line, Tumor; DNA; Drug Screening Assays, Antitumor; Imidazoles; Intercalating Agents; Leukemia; Mice; Molecular Structure; Platinum; Spectrometry, Mass, Electrospray Ionization

The structures and fluorescence characteristics of cucurbit[n = 6-8]urils with quinoline, isoquinoline and 7-methyl quinoline have been investigated by fluorescence spectrophotometry. Compared to NMR techniques, thefluorometric analysis methodrevealed that there are not only obvious interactions of quinoline or its derivates and cucurbit[7]uril, but also interactions of quinoline or its derivates and cucurbit[6]uril or cucurbit[8]uril which can not be observed by using 1H NMR technique. The experimental results also revealed that quinoline, isoquinoline and 7-methyl quinoline were included by cucurbit[6-8]uril with different ratios. There could be three kinds of interactions of cucurbit[n]urils and the guests: (a) cavity interaction, including hydrophobic forces and Van der Waals contact forces between macrocycles and cages; (b) portals ion-dipole interaction, or electrostatic interaction of the positive charge of the guests and the carbonyl groups at the portals of cucurbit[n]uril; (c) size interaction which requires the size of the guest matching a cucurbit[n]uril.

Topics: Bridged-Ring Compounds; Fluorescence; Imidazoles; Isoquinolines; Magnetic Resonance Spectroscopy; Models, Chemical; Molecular Structure; Quinolines; Spectrometry, Fluorescence