chiniofon and 6-hydroxyquinoline

6-Hydroxyquinoline (6HQ) is an ideal photoacid system for exploring excited-state proton transfer (ESPT) reactions. We have previously (Mahata et al. (2002)) shown that the ESPT reaction between 6HQ and trimethylamine (TMA) leads to an "unusual" emission in the 440-450 nm range, containing two decay components (∼5 ns and ∼12 ns). The observed results suggest the presence of a contact ion-pair and a solvent separated ion-pair. In this work, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) have been employed to study the nature of the contact ion-pair formed between 6HQ and TMA and to determine why the decay component ∼12 ns is absent in a non-polar solvent. Calculations of the hydrogen-bonded complexes formed between 6HQ and TMA and its ESPT reaction product, namely 6HQ-TMA and 6HQ-TMA-PT, respectively, have been carried out, both in the electronic ground and excited states. Moreover, by using the CPCM model, different dielectric constants have been introduced into the calculations. On increasing the dielectric constant, the hydrogen bond in 6HQ-TMA-PT becomes weaker and the hydrogen bond length becomes larger; this effectively facilitates the proton transfer reaction and formation of separated ion-pair. Thus, the separation and diffusion of the contact ion-pair can be controlled by changing the polarity of the surroundings.

Topics: Hydroxyquinolines; Methylamines; Models, Chemical; Protons

Spectroscopic studies on excited-state proton transfer (ESPT) of hydroxyquinoline (6HQ) have been performed in a previous paper. And a hydrogen-bonded network formed between 6HQ and acetic acid (AcOH) in nonpolar solvents has been characterized. In this work, a time-dependent density functional theory (TDDFT) method at the def-TZVP/B3LYP level was employed to investigate the excited-state proton transfer via hydrogen-bonded AcOH wire for 6HQ. A hydrogen-bonded wire containing three AcOH molecules at least for connecting the phenolic and quinolinic -N- group in 6HQ has been confirmed. The excited-state proton transfer via a hydrogen-bonded wire could result in a keto tautomer of 6HQ and lead to a large Stokes shift in the emission spectra. According to the results of calculated potential energy (PE) curves along different coordinates, a stepwise excited-state proton transfer has been proposed with two steps: first, an anionic hydrogen-bonded wire is generated by the protonation of -N- group in 6HQ upon excitation to the S(1) state, which increases the proton-capture ability of the AcOH wire; then, the proton of the phenolic group transfers via the anionic hydrogen-bonded wire, by an overall "concerted" process. Additionally, the formation of the anionic hydrogen-bonded wire as a preliminary step has been confirmed by the hydrogen-bonded parameters analysis of the ESPT process of 6HQ in several protic solvents. Therefore, the formation of anionic hydrogen-bonded wire due to the protonation of the -N- group is essential to strengthen the hydrogen bonding acceptance ability and capture the phenolic proton in the 6HQ chromophore.

Topics: Acetic Acid; Electrons; Hydrogen Bonding; Hydroxyquinolines; Models, Molecular; Molecular Conformation; Protons; Quantum Theory

Photophysical properties of the organocatalyst cupreidine (CPD) and its chromophoric building block 6-hydroxyquinoline (6HQ) in protic and nonprotic polar solvents (methanol and acetonitrile) were investigated by means of UV-vis absorption, and steady state and time resolved fluorescence spectroscopy. The effects of the catalytically relevant interactions with electrophilic and hydrogen bonding agents (p-toluene sulfonic acid and water) on their spectral characteristics were studied. In neutral CPD in acetonitrile, quenching of fluorescence occurs due to electron transfer from the quinuclidine nitrogen to the excited quinoline chromophore. Protonation suppresses this process, while complexation with water leads to enhanced excited state proton transfer from the 6'-OH group to the quinuclidine nitrogen, and emission occurs from the anionic form of the chromophore. The weakly emitting zwitterionic form of the hydroxyquinoline chromophore is readily formed in methanol, but not in acetonitrile.

Topics: Cinchona; Cinchona Alkaloids; Hydroxyquinolines; Protons; Quinine; Solvents; Spectrometry, Fluorescence; Spectrophotometry

The excited-state proton transfer and geminate recombination of 6-hydroxyquinoline (6HQ) encaged in catalytic Na(+)-exchanged faujasite zeolites X (NaX) and Y (NaY) have been explored by measuring steady-state and picosecond time-resolved spectra. The pathways and rate constants of proton transfer of excited 6HQ are determined by the microscopic environment of zeolitic hosts surrounding the guest molecules. The excited-state proton transfer of a 6HQ molecule encapsulated in a zeolitic nanocavity is initiated by deprotonation of the enolic group to form an anionic intermediate and completed by subsequent protonation of the imino group to form a zwitterionic tautomer. Geminate recombination occurs to compete with proton transfer at each tautomerization step of excited-state 6HQ because of the confined environment of dehydrated zeolitic supercages. Consequently, excited-state equilibria among three prototropic species of 6HQ are established in microporous catalytic faujasite zeolites. Kinetic differences in NaX and NaY are attributed to dissimilarities in acidity/basicity.

Topics: Catalysis; Hydrogen-Ion Concentration; Hydroxyquinolines; Kinetics; Magnetic Resonance Spectroscopy; Molecular Structure; Protons; Time Factors; Zeolites

The title compound, C(9)H(7)NO, has two symmetry-independent molecules in the asymmetric unit, which have different conformations of the hydroxy group with respect to the quinoline ring. One of the molecules adopts a cis conformation, while the other shows a trans conformation. Each type of independent molecule links into a separate infinite O-H...N hydrogen-bonded chain with the graph-set notation C(7). These chains are perpendicular in the unit cell, one extended in the a-axis direction and the other in the b-axis direction. There is also a weak C-H...O hydrogen bond with graph-set notation D(2), which runs in the c-axis direction and joins the two separate O-H...N chains. The significance of this study lies in the comparison drawn between the experimental and calculated data of the crystal structure of the title compound and the data of several other derivatives possessing the hydroxy group or the quinoline ring. The correlation between the IR spectrum of this compound and the hydrogen-bond energy is also discussed.

Topics: Crystallization; Crystallography, X-Ray; Hydrogen Bonding; Hydroxyquinolines; Models, Molecular; Quinolines

A hydrogen-bonded network formed between 6-hydroxyquinoline (6-HQ) and acetic acid (AcOH) has been characterized using a time-resolved fluorescence technique. In the bridged hydrogen-bonded complex of cis-6-HQ and AcOH, an excited-state reaction proceeds via proton transfer along the hydrogen bond, resulting in a keto-tautomer (within approximately 200 ps) that exhibits large Stokes-shifted fluorescence. The unbridged complex also undergoes excited-state proton transfer, but the Stokes shift is rather smaller.

Topics: Acetic Acid; Electrons; Hydrogen Bonding; Hydroxyquinolines; Molecular Structure; Photochemistry; Protons

Fluorescence characteristics of 6-hydroxyquinoline (6-HQ) have been studied at room temperature in Nafion(R) film by steady state and nano-second time-resolved fluorescence spectroscopy. The fluorescence spectrum exhibits single emission band corresponding to the protonated form of 6-HQ in this matrix. However, the decay fits with two or three exponential functions depending on the emission wavelength monitored. At blue edge of the emission, the decay fits to three-exponential function, whereas at longer wavelengths, the decay fits to bi-exponential function. Two tentative mechanisms have been proposed to explain the experimental data, viz. a closely lying charge transfer state (CT) or an excited state proton transfer (ESPT) process. The photophysical parameters appear to be sensitive to the change in microstructure due to swelling of the membrane by the solvents.

Topics: Fluorocarbon Polymers; Hydroxyquinolines; Methanol; Photochemistry; Protons; Spectrometry, Fluorescence; Spectrophotometry; Water

Selective acylation of the phenolic hydroxyl group of 10-hydroxycamptothecin has been accomplished using phenyl dichlorophosphate. Additional modification of the 10-OH as an ether permits a 20-acyl derivative to be synthesized. This result along with data from a 6-hydroxyquinoline model strongly suggests that powerful intermolecular hydrogen bonding exists in the parent molecule.

Topics: Acylation; Animals; Antineoplastic Agents; Camptothecin; Carboxylic Acids; Hydrogen Bonding; Hydroxyquinolines; Indicators and Reagents; Leukemia P388; Magnetic Resonance Spectroscopy; Neoplasms; Polyethylene Glycols; Rats; Tumor Cells, Cultured

Two strains, using 6-hydroxyquinoline as sole source of energy, carbon and nitrogen, have been isolated. These bacteria, designated 31/1 Fa1 and 31/2 A1, are also able to degrade quinoline. According to their physiological properties strain 31/1 Fa1 has been identified as Pseudomonas diminuta and strain 31/2 A1 as Bacillus circulans. 6-Hydroxy-2-oxo-1,2-dihydroquinoline was found as intermediate in the degradation of 6-hydroxyquinoline and quinoline. 2-Oxo-1,2-dihydroquinoline was the first metabolite in the degradation of quinoline.

Topics: Bacillus; Biotransformation; Hydroxyquinolines; Methylnitronitrosoguanidine; Molecular Structure; Mutagenesis; Pseudomonas; Quinolines

Topics: Hydroxyquinolines; Inactivation, Metabolic; Quinolines; Urine