Browsing by Author "Pischel, Uwe"
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- A photoinduced pH jump applied to drug release from cucurbit[7]urilPublication . Carvalho, Cátia Parente; Uzunova, Vanya D.; Silva, José P. da; Nau, Werner M.; Pischel, UweA proof-of-principle for the application of a photoinduced pH jump for delivery of the Hoechst 33258 drug by disassembly of its host-guest complex with cucurbit[7]uril is described.
- A supramolecular keypad lockPublication . Carvalho, Cátia Parente; Dominguez, Zoe; Silva, José P. da; Pischel, UweThe reversible photoswitching between an anthracene derivative and its [4+4] dimer, using the template effect of the CB8 macrocycle, was demonstrated. This example of supramolecular chemistry in water was harnessed to demonstrate the operation of a keypad lock device that is driven by means of light and chemicals as inputs.
- An aminonaphthalimide-putrescine conjugate as fluorescent probe for cucurbituril host-guest complexesPublication . Carvalho, Cátia Parente; Ferreira, Rita; Silva, José P. da; Pischel, UweA fluorophore-anchor dye based on the 4-amino-1,8-naphthalimide chromophore was designed and characterised with respect to its ability of forming supramolecular hostguest complexes with cucurbit[6]uril (CB6) and cucurbit[7]uril (CB7) hosts. It was found that CB6 encapsulates the anchor of the dye with a high binding constant [K = (1.11.4) X 107 M- 1], which was independent of acidic or neutral pH conditions. The 1:1 binding was accompanied by fluorescence quenching (ca. 20%) and a bathochromic shift (?? = +22 nm) of the charge-transfer absorption band of the dye. This is indicative of the occurrence of hydrogen bonding between a carbonyl-lined host portal and the aromatic NH group of the guest dye. In comparison, CB7 encapsulated the dye much less efficiently (K = 4.8 X 104 M- 1) and showed a significant fluorescence enhancement (Ff = 0.15 versus 0.52 for free and CB7-complexed dye at pH 4, respectively). The occurrence of hydrogen bonding with the aromatic NH was much less evident for CB7 as judged by the only minor bathochromic shift (?? = +4 nm) of the charge-transfer absorption band of the dye. The dyeCB6 assembly has the potential for the detection of biogenic amines under physiological pH conditions and at low analyte concentrations.
- Cucurbiturils as supramolecular inhibitors of DNA restriction by type II endonucleasesPublication . Parente Carvalho, Catia; Norouzy, Amir; Ribeiro, Vera; Nau, Werner M.; Pischel, UweCucurbiturils (CB6 and CB7) were shown to inhibit the enzymatically catalyzed restriction of plasmids and linear DNA. This effect can be inverted by supramolecular masking of the macrocycles through competitive complexation with polyamines. These experiments provide supramolecular control of biocatalytic processes.
- Five-Component Self-Assembly of Cucurbituril-Based Hetero-pseudorotaxanesPublication . Parente Carvalho, Catia; Dominguez, Zoe; Dominguez, Cristina; El-Sheshtawy, Hamdy S.; Da Silva, Jose Paulo; Arteaga, Jesus F.; Pischel, Uwe[5]Pseudorotaxanes can be obtained by self-sorting using heteroditopic guests and various cucurbituril homologues as hosts. The assembly and chemically induced disassembly of the pseudorotaxanes can be monitored by measuring the fluorescence of the anthracene guest in solution. Mass spectral evidence for the supramolecular assemblies is obtained in the gas phase. The disassembly in the gas phase can be achieved by collision-induced dissociation leading to the corresponding [2]- and [3]pseudorotaxanes.
- Switching properties of a spiropyran-cucurbit[7]uril supramolecular assembly: usefulness of the anchor approachPublication . Nilsson, Jesper R.; Carvalho, Cátia Parente; Li, Shiming; Silva, José P. da; Andreasson, Joakim; Pischel, UweA nitrospiropyran, which was modified with a cadaverine-derived anchor, was investigated with respect to its thermally induced isomerizations, hydrolytic stability of the merocyanine form, and photochromic ring closure. The hostguest complexation of the anchor by the cucurbit[7]uril macrocycle, evidenced by absorption titration, NMR spectroscopy, and electrospray ionization mass spectrometry, produced significant improvements of the switching properties of the photochrome: 1) appearance of the merocyanine form about 70 times faster, 2) practically unlimited hydrolytic stability of the merocyanine (two and a half days without any measureable decay), and 3) fast, clean, and fatigue-resistant photoinduced ring closure back to the spiro form. The importance of an adequate molecular design of the anchor was demonstrated by including control experiments with spiropyrans with a shorter linker or without such structural asset.
- Synthetic versus natural receptors: supramolecular control of chemical sensing in fishPublication . Silva, José P. da; Choudhury, Rajib; Porel, Mintu; Pischel, Uwe; Jockusch, Steffen; Hubbard, Peter; Ramamurthy, Vaidhyanathan; Canario, Adelino V. M.The encapsulation of odorants by the synthetic receptor cucurbit[7]uril (CB[7]) reduces the response of olfactory receptors in Mozambique tilapia (Oreochromis mossambicus) in vivo. For example, the olfactory receptor response to the odorant adamantan-1-amine, as measured by electro-olfactography, was suppressed by 92% in the presence of CB[7]. A reduction in olfactory response of 88% was observed for pentane-1,5-diamine (cadaverine), an odorant associated with carrion avoidance in some fish. The results reveal how the association constants and the concentrations of natural and synthetic receptors play a determinant role and show that synthetic receptors can be used to remove bioactive molecules from fish olfaction.