- Tuning the emission of a water-soluble 3-hydroxyflavone derivative by host-guest complexation
-
3-Hydroxyflavone derivatives have great potential as fluorescent probes for bio-labeling in aqueous medium. They were extensively studied in various organic solvents for the "excited state intramolecular proton transfer" process, but seldom addressed in aqueous solution due to the poor water solubility. Herein, an amphiphilic molecule bearing 3-hydroxyflavone and oligo(ethylene oxide) (denoted as 3HF-EO) was designed and synthesized. Different from the fluorescence in organic solvents, 3HF-EO in aqueous solution showed a remarkable single fluorescence emission, which is ascribed to the fluorescence of its anionic species. We found that the fluorescence intensity could be efficiently tuned via host-guest complexation. α-CD has little effect on the emission, while β-CD and γ-CD lead to enhanced and reduced emissions of 3HF-EO, respectively. The 1H NMR and 2D NOESY NMR spectra indicate that α-CD barely had any interaction with 3HF-EO, while β-CD and γ-CD formed complexes with one and two 3HF-EO molecules, respectively. These results provide a sound explanation for the modulated fluorescence intensity.
- Li, Dahua,Xing, Yuzhi,Ding, Lan,Wu, Chengfeng,Hou, Guangliang,Song, Bo
-
p. 4231 - 4237
(2018/06/07)
-
- Self-assembly of tripodal squaraines: Cation-assisted expression of molecular chirality and change from spherical to helical morphology
-
(Figure Presented) Let's do the twist: Tripodal squaraines self-assemble from acetonitrile to form hollow spheres, the complexation of which with Ca 2+ or Mg2+ results in extended networks. An analogous chiral dye exhibits a bisignat
- Ajayaghosh, Ayyappanpillai,Chithra, Parayalil,Varghese, Reji
-
p. 230 - 233
(2008/02/07)
-
- Reversal of aryl bromide reactivity in Pd-catalysed aryl amination reactions promoted by a hemilabile aminophosphine ligand
-
Incorporation of a hemilabile amino group with a bulky, electron-rich phosphorus ligand led to a reversal in the order of aryl bromide reactivity in Pd-catalysed aryl amination reactions.
- Parisel, Sebastien L.,Adrio, Luis Angel,Pereira, Adriana Amoedo,Pérez, Marta Marino,Vila, José M.,Hii, King Kuok
-
p. 9822 - 9826
(2007/10/03)
-
- A controlled supramolecular approach toward cation-specific chemosensors: Alkaline earth metal ion-driven exciton signaling in squaraine tethered podands
-
Three different squaraine tethered bichromophoric podands 3a-c with one, two, and three oxygen atoms in the podand chain and an analogous monochromophore 4a were synthesized and characterized. Among these, the bichromophores 3a-c showed high selectivity toward alkaline earth metal cations, particularly to Mg2+ and Ca2+ ions, whereas they were optically silent toward alkali metal ions. From the absorption and emission changes as well as from the Job plots, it is established that Mg2+ ions form 1:1 folded complexes with 3a and 3b whereas Ca2+ ions prefer to form 1:2 sandwich dimers. However, 3c invariably forms weak 1:1 complexes with Mg2+, Ca2+, and Sr2+ ions. The signal output in all of these cases was achieved by the formation of a sharp blue-shifted absorption and strong quenching of the emission of 3a-c. The signal transduction is achieved by the exciton interaction of the face-to-face stacked squaraine chromophores of the cation complex, which is a novel approach of specific cation sensing. The observed cation-induced changes in the optical properties are analogous to those of the "H" aggregates of squaraine dyes. Interestingly, a monochromophore 4a despite its binding, as evident from 1H NMR studies, remained optically silent toward Mg2+ and Ca2+ ions. While the behavior of 4a toward Mg2+ ion is understood, its optical silence toward Ca2+ ion is rationalized to the preferential formation of a "Head-Tail-Tail-Head" arrangement in which exciton coupling is not possible. The present study is different from other known reports on chemosensors in the sense that cation-specific supramolecular host-guest complexation has been exploited for controlling chromophore interaction via cation-steered exciton coupling as the mode of signaling.
- Arunkumar, Easwaran,Chithra, Parayali,Ajayaghosh, Ayyappanpillai
-
p. 6590 - 6598
(2007/10/03)
-
- Mechanistic Studies on Dopamine β-Monooxygenase Catalysis: N-Dealkylation and Mechanism-Based Inhibition by Benzylic-Nitrogen-Containing Compounds. Evidence for a Single-Electron-Transfer Mechanism
-
Dopamine β-monooxygenase (DBM) readily catalyzes oxidative N-dealkylation of N-phenylethylenediamine (PEDA) and N-methyl-N-phenylethylenediamine (N-MePEDA) with the reaction characteriscics expected for a monooxygenase-catalyzed process.The products of this reaction have been quantitatively identified as aniline (or N-methylaniline for N-MePEDA) and 2-aminoacetaldehyde, the latter compound being successfully trapped by using NaBH4 reduction followed by N-succinimidyl p-nitriphenylacetate (SNPA) derivatization, and identified by HPLC and mass spectroscopy.In contrast, either analogues of PEDA, i.e. phenyl 2-aminoethyl ether (PAEE) and its p-hydroxy derivative (p-OHPAEE), as well as 2-phenoxycycloprpylamine are not substrates but are competitive inhibitors.Furthermore, 2-methyl-2-anilino-1-aminoethane (β-MePEDA) did not exhibit measurable substrate activity with DBM, in contrast to the excellent substrate activity of the sulfur analogue of β-MePEDA, 2-methyl-2-(phenylthio)-1-aminoethane (β-MePAES).DBM is inactivated during the N-dealkylation reaction in a time- and concentration-dependent manner, a phenomenon that has not, to our knowledge, been observed for any other oxygenase-catalyzed N-dealkylation reaction.Both PEDA and N-MePEDA, as well as β-MePEDA, inactivate DBM under turnover conditions.The inactivation exhibited pseudo-first-order saturable kinetics and expected protection by the DBM substrate, tyramine.No reappearance of enzyme activity was observed after extensive dialysis.Radioactive labeling experiments with ring-tritiated PEDA showed incorporation of nondialyzable radioactivity into DBM in the expected amount, consistent with covalent attachment of a reactive species derivd from PEDA to the DBM active site during enzyme inactivation.Although aniline, N-ethylaniline, N-(2-fluoroethyl)aniline, m- and p-anisidine, p-toluidine, and 5-hydroxyindole were found not to exhibit detectable DBM substrate activity, all of these inactivated the enzyme under turnover conditions.The isotope effect on partition ratio measured for dideuteriated PEDA was found to be a reflection of an isotope effect on Vmax and not on kinact.Our results provide a strong support for the conclusion that the initial nitrogen cation radical species is responsible for enzyme inactivation.Results with ring-deuteriated and ring-tritiated PEDA revealed that the amount of radioactivity incorporated into covalently inactivated DBM by ring-tritiated PEDA is in agreement with that expected for covalent attachment of the para carbon to the protein.An 18O labeling study was carried out to test for oxygen rebound into the aminoacetaldehyde product, and results demonstrated that the aldehyde oxygen of enzymatically produced 2-aminoacetaldehyde exchanges very rapidly with solvent water, in agreement with literature reports.On the basis ...
- Wimalasena, Kandatege,May, Sheldon W.
-
p. 4036 - 4046
(2007/10/02)
-