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6-Methoxyquinoline

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Debi D. Pant – 1st expert on this subject based on the ideXlab platform

  • Photophysics and Rotational Relaxation Dynamics of 6-Methoxyquinoline Fluorophore in Cationic Alkyltrimethylammonium Bromide Micelles
    World Academy of Science Engineering and Technology International Journal of Chemical and Molecular Engineering, 2016
    Co-Authors: Tej Varma Y, Debi D. Pant

    Abstract:

    Authors : Tej Varma Y, Debi D. Pant Abstract : Photophysics and rotational dynamics of the fluorescent probe, 6-Methoxyquinoline (6MQ) with cationic surfactant, alkyltrimethylammonium bromide (nTAB) micelle solutions have been investigated (n = 12, 14 and 16). Absorption and emission peaks of the dye have been observed to shift at concentrations around critical micellar concentration (cmc) of nTAB compared to that of bulk solutions suggesting probe is in a lower polar environment. The probe senses changes in polarity (ET (30)) brought about by variation of surfactant chain length concentration and is invariably solubilized in the aqueous interface or palisade layer. The order of change in polarity observed was DTAB > CTAB > TTAB. The binding constant study shows that the probe binds strongest with TTAB (is of the order TTAB > CTAB > DTAB) due to deeper penetration into the micelle. The anisotropy decay for the probe in all the nTAB micelles studied have been rationalized based on a two-step model consisting of fast-restricted rotation of the probe and slow lateral diffusion of the probe in the micelle that is coupled to the overall rotation of the micelle. Fluorescence lifetime measurements of probe in the cationic micelles demonstrate the close proximity of the 6MQ to the Br counterions. The fluorescence lifetimes of TTAB and DTAB are much shorter than in CTAB. These results indicate that 6MQ resides to a substantial degree in the head group region of the micelles. All the changes observed in the steady state fluorescence, microenvironment, fluorescence lifetimes, fluorescence anisotropy, and other calculations are in agreement with each other suggesting binding of the cationic surfactant with the neutral dye molecule.

  • Interaction of 6-Methoxyquinoline with anionic sodium dodecylsulfate micelles: Photophysics and rotational relaxation dynamics at different pH
    Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2016
    Co-Authors: Y. Tej Varma, Debi D. Pant

    Abstract:

    Abstract Interactions of different species of 6-Methoxyquinoline (6MQ) with anionic micelles have been studied at different pre-micellar, micellar and post-micellar concentrations using steady state, time resolved fluorescence and fluorescence anisotropy techniques. The sensitivity of fluorescence of 6MQ to change in its local environment was used to probe sodium dodecylsulfate (SDS) micelles. At post-micellar concentrations of SDS, the observed blue shift in the fluorescence spectrum and increase in quantum yield are attributed to the incorporation of solute molecule to micelles. 6MQ has been found to bind to the surface of the anionic micelles instead of penetrating inside the core of micelles. The binding constant (K b ) calculated for 6MQ revealed that the electrostatic forces mediate charged probe–micelle association, whereas, hydrophobic interaction allowed neutral 6MQ to associate with SDS micelles. The charged 6MQ gets inserted deeper into the micelle surface than its neutral form. The fluorescence anisotropy decay of 6MQ in SDS micelles studied at different pH allowed determination of restriction of motion of the fluorophore. The location of the probe molecule in micellar systems is justified by a variety of spectral parameters such as refractive index, dielectric constant, E T (30), average fluorescence decay time, radiative and non-radiative rate constants, and rotational relaxation time. The micro-environment around the fluorophore reveals that the photophysics of 6MQ is very sensitive to the microenvironment of SDS and probe molecules reside at the water–micelle interface.

  • Effect of nanosize micelles of ionic and neutral surfactants on the photophysics of protonated 6-Methoxyquinoline: Time-resolved fluorescence study
    Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014
    Co-Authors: Y. Tej Varma, Sunita Joshi, Debi D. Pant

    Abstract:

    Abstract The excited state dynamic studies have been carried out to investigate the effects of micellar surface charge on the photophysics of protonated 6-Methoxyquinoline (6MQ + ) in anionic, sodium dodecylsulphate (SDS), cationic, cetyltrimethylammonium bromide (CTAB) and neutral, triton X-100 (TX100) surfactant at premicellar, micellar and postmicellar concentrations in aqueous phase at room temperature. At premicellar concentrations of SDS, there is a slight decrease in emission intensity and at micellar and postmicellar concentrations, increase in emission intensity and blue shift of spectrum has been observed. The blue shift in fluorescence spectrum and slight increase in quantum yield are attributed to incorporation of solute molecule to the micelles. Edge excitation red shift (EERS) in fluorescence maximum of 6MQ + has been observed in all the surfactant solutions studied. The EERS has been ascribed in terms of solvent relaxation process. In SDS surfactant system, due to heterogeneous restricted motion of solvent molecules, the solvent viscosity increases which results in an increase in net magnitude of EERS. The fluorescence decay components of 6MQ + fit with multi exponential functions in all the micellar systems studied. The location of the probe molecule in micellar systems is justified by a variety of spectral parameters such as refractive index, dielectric constant, E T (30), EERS, average fluorescence decay time, radiative and non radiative rate constants, and rotational relaxation time.

Robert W. Townsend – 2nd expert on this subject based on the ideXlab platform

  • Hydrolysis kinetics of photo-excited 6-Methoxyquinoline in aqueous ethanol
    Analytica Chimica Acta, 2002
    Co-Authors: Stephen G. Schulman, Robert W. Townsend, Susumu Kimura, Shangxian Chen

    Abstract:

    Abstract The kinetics of hydrolysis in the lowest excited single state of 6-Methoxyquinoline in aqueous solutions can be evaluated from the pH-dependence of its fluorescence spectrum. In ethanol/water solutions, the rate constant for hydrolysis decreases exponentially with increasing mole fraction of ethanol and hydrolysis is completely inhibited at a mole fraction of ethanol greater than about 0.2. The slope of a plot of the logarithm of the hydrolysis rate constant against the mole fraction of ethanol was found to correlate well with the ratio of the diffusion volume of excited 6-Methoxyquinoline to the molecular volume of ethanol. This also appears to explain why the linear plot of the logarithm of the hydrolysis rate constant against the logarithm of the water activity has a slope of 31, suggesting that 30 molecules of water, beside the one that is split in hydrolysis, participate in the reaction.

  • Hydrolysis kinetics of photoexcited 6-Methoxyquinoline in aqueous acetonitrile solutions
    Journal of Fluorescence, 1995
    Co-Authors: Stephen G. Schulman, Robert W. Townsend

    Abstract:

    6-Methoxyquinoline undergoes pseudo-first-order hydrolysis and its conjugate acid, second-order proton abstraction by hydroxide ion, in the lowest excited singlet state. The proton transfer kinetics in water containing acetonitrile up to a mole fraction of about 0.1 have been evaluated as a function of acetonitrile concentration. At mole fractions above 0.13 of acetonitrile, proton transfer does not occur. At mole fractions below 0.1 steady-state and pulsed-source fluorimetries show the rate constant for hydrolysis to decrease exponentially with the mole fraction of acetonitrile. This is believed to be due to penetration of the aqueous solvent cage of the 6-Methoxyquinoline by acetonitrile rather than to specific solvation by the organic cosolvent. The rate of neutralization of the conjugate acid by hydroxide ion is found to vary only slightly and depends on the bulk dielectric properties of the solvent.

  • Photohydrolysis of 6-Methoxyquinoline in aqueous acetonitrile : pOH in alkaline acetonitrile-water solutions
    Analytica Chimica Acta, 1994
    Co-Authors: Robert W. Townsend, Stephen G. Schulman, Willy R. G. Baeyens

    Abstract:

    Abstract 6-Methoxyquinoline demonstrates proton transfer in the lowest excited singlet state in acetonitrile-water mixtures as well as in pure water. The photohydrolysis reaction of the directly excited neutral molecule is strongly solvent dependent and independent of solution alkalinity. Proton abstraction from the conjugate acid, however, depends predominantly on the alkalinity of the solution and only on the continuum properties of the solvent. The separability of the hydrolysis and proton abstraction reactions, using steady-state methodology, allows the proton abstraction to be treated independent of the hydrolysis. The linear relationship between the ratio of the relative fluorescence efficiencies of base and conjugate acid and hydroxide ion concentration is obtained only if proper Bronsted activity factors are included in the relationship. These factors can be calculated from classical electrostatics and are simple powers of the activity coefficients necessary to convert the formal hydroxide ion concentration to formal hydroxide ion activity. Using this approach it is possible to calculate pOH from hydroxide ion concentration in acetonitrile-water solutions containing a mole fraction of acetonitrile up to 0.13.

Stephen G. Schulman – 3rd expert on this subject based on the ideXlab platform

  • Hydrolysis kinetics of photo-excited 6-Methoxyquinoline in aqueous ethanol
    Analytica Chimica Acta, 2002
    Co-Authors: Stephen G. Schulman, Robert W. Townsend, Susumu Kimura, Shangxian Chen

    Abstract:

    Abstract The kinetics of hydrolysis in the lowest excited single state of 6-Methoxyquinoline in aqueous solutions can be evaluated from the pH-dependence of its fluorescence spectrum. In ethanol/water solutions, the rate constant for hydrolysis decreases exponentially with increasing mole fraction of ethanol and hydrolysis is completely inhibited at a mole fraction of ethanol greater than about 0.2. The slope of a plot of the logarithm of the hydrolysis rate constant against the mole fraction of ethanol was found to correlate well with the ratio of the diffusion volume of excited 6-Methoxyquinoline to the molecular volume of ethanol. This also appears to explain why the linear plot of the logarithm of the hydrolysis rate constant against the logarithm of the water activity has a slope of 31, suggesting that 30 molecules of water, beside the one that is split in hydrolysis, participate in the reaction.

  • Hydrolysis kinetics of photoexcited 6-Methoxyquinoline in aqueous acetonitrile solutions
    Journal of Fluorescence, 1995
    Co-Authors: Stephen G. Schulman, Robert W. Townsend

    Abstract:

    6-Methoxyquinoline undergoes pseudo-first-order hydrolysis and its conjugate acid, second-order proton abstraction by hydroxide ion, in the lowest excited singlet state. The proton transfer kinetics in water containing acetonitrile up to a mole fraction of about 0.1 have been evaluated as a function of acetonitrile concentration. At mole fractions above 0.13 of acetonitrile, proton transfer does not occur. At mole fractions below 0.1 steady-state and pulsed-source fluorimetries show the rate constant for hydrolysis to decrease exponentially with the mole fraction of acetonitrile. This is believed to be due to penetration of the aqueous solvent cage of the 6-Methoxyquinoline by acetonitrile rather than to specific solvation by the organic cosolvent. The rate of neutralization of the conjugate acid by hydroxide ion is found to vary only slightly and depends on the bulk dielectric properties of the solvent.

  • Photohydrolysis of 6-Methoxyquinoline in aqueous acetonitrile : pOH in alkaline acetonitrile-water solutions
    Analytica Chimica Acta, 1994
    Co-Authors: Robert W. Townsend, Stephen G. Schulman, Willy R. G. Baeyens

    Abstract:

    Abstract 6-Methoxyquinoline demonstrates proton transfer in the lowest excited singlet state in acetonitrile-water mixtures as well as in pure water. The photohydrolysis reaction of the directly excited neutral molecule is strongly solvent dependent and independent of solution alkalinity. Proton abstraction from the conjugate acid, however, depends predominantly on the alkalinity of the solution and only on the continuum properties of the solvent. The separability of the hydrolysis and proton abstraction reactions, using steady-state methodology, allows the proton abstraction to be treated independent of the hydrolysis. The linear relationship between the ratio of the relative fluorescence efficiencies of base and conjugate acid and hydroxide ion concentration is obtained only if proper Bronsted activity factors are included in the relationship. These factors can be calculated from classical electrostatics and are simple powers of the activity coefficients necessary to convert the formal hydroxide ion concentration to formal hydroxide ion activity. Using this approach it is possible to calculate pOH from hydroxide ion concentration in acetonitrile-water solutions containing a mole fraction of acetonitrile up to 0.13.