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Debi D. Pant - One of the best experts on this subject based on the ideXlab platform.
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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, 2016Co-Authors: Tej Varma Y, Debi D. PantAbstract: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.
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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, 2016Co-Authors: Y. Tej Varma, Debi D. PantAbstract: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.
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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, 2014Co-Authors: Y. Tej Varma, Sunita Joshi, Debi D. PantAbstract: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.
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Estimation of ground and excited state dipole moments of 6-Methoxyquinoline from solvatochromic effect on absorption and fluorescence spectra
2013Co-Authors: Y. Tej Varma, Sunita Joshi, Debi D. PantAbstract:The electronic absorption and fluorescence spectra of 6-Methoxyquinoline (6MQ) have been recorded at room temperature in solvents of different polarities. The spectral data have been used to evaluate the ground and first excited singlet state dipole moments using the solvatochromic shift method. Higher dipole moment is obtained for the excited state as compared to ground state. The results indicate a more polar excited state, which may be due to charge transfer character of 6MQ.
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Solvatochromatic shift of absorption and fluorescence spectra of 6-Methoxyquinoline: Estimation of ground and excited state dipole moments
Journal of Molecular Liquids, 2013Co-Authors: Tej Varma Y, Sunita Joshi, Debi D. PantAbstract:Abstract Electronic absorption and fluorescence spectra of protonated 6-Methoxyquinoline (6MQ+) and neutral 6-Methoxyquinoline (6MQ) have been recorded at room temperature in wide range of solvents of different polarities. The absorption maximum remains almost unchanged with the increase in solvent polarity, whereas a red shift in fluorescence emission maximum was observed. The ground-state dipole moment and the first excited singlet state dipole moment of 6MQ+ and 6MQ were obtained from Bakhshiev's and Bilot–Kawski's equations by means of solvatochromic shift method. High values of dipole moment are observed for excited state as compared to the corresponding ground state dipole moment values of 6MQ+ and 6MQ and this is attributed to the more polar excited states of 6MQ+ and 6MQ.
Robert W. Townsend - One of the best experts on this subject based on the ideXlab platform.
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Hydrolysis kinetics of photo-excited 6-Methoxyquinoline in aqueous ethanol
Analytica Chimica Acta, 2002Co-Authors: Stephen G. Schulman, Robert W. Townsend, Susumu Kimura, Shangxian ChenAbstract: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.
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Hydrolysis kinetics of photoexcited 6-Methoxyquinoline in aqueous acetonitrile solutions
Journal of Fluorescence, 1995Co-Authors: Stephen G. Schulman, Robert W. TownsendAbstract: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.
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Photohydrolysis of 6-Methoxyquinoline in aqueous acetonitrile : pOH in alkaline acetonitrile-water solutions
Analytica Chimica Acta, 1994Co-Authors: Robert W. Townsend, Stephen G. Schulman, Willy R. G. BaeyensAbstract: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 - One of the best experts on this subject based on the ideXlab platform.
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Hydrolysis kinetics of photo-excited 6-Methoxyquinoline in aqueous ethanol
Analytica Chimica Acta, 2002Co-Authors: Stephen G. Schulman, Robert W. Townsend, Susumu Kimura, Shangxian ChenAbstract: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.
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Hydrolysis kinetics of photoexcited 6-Methoxyquinoline in aqueous acetonitrile solutions
Journal of Fluorescence, 1995Co-Authors: Stephen G. Schulman, Robert W. TownsendAbstract: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.
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Photohydrolysis of 6-Methoxyquinoline in aqueous acetonitrile : pOH in alkaline acetonitrile-water solutions
Analytica Chimica Acta, 1994Co-Authors: Robert W. Townsend, Stephen G. Schulman, Willy R. G. BaeyensAbstract: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.
H.b. Tripathi - One of the best experts on this subject based on the ideXlab platform.
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Fluorescence quenching of 6-Methoxyquinoline: an indicator for sensing chloride ion in aqueous media
Journal of Luminescence, 2002Co-Authors: M.s Mehata, H.b. TripathiAbstract:Abstract The quenching of fluorescence intensity and decay time of protonated form of 6-Methoxyquinoline (6MQ + ) with chloride ion (Cl − ) in aqueous solution at ambient temperatures have been investigated. The quenching follows linear Stern–Volmer relation. The values of Stern–Volmer quenching constant/quenching efficiency ( K sv ) and quenching rate constant ( K q ) for the Cl − ion are close to 75 M −1 and 3.21×10 9 M −1 S −1 , respectively. The quenching is found to be collisional or dynamical in nature. The study reveals that the system can be used as a sensor for the detection of chloride ion.
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Edge excitation red shift and charge transfer study of 6-Methoxyquinoline in polymer matrices
Journal of Luminescence, 2001Co-Authors: M.s Mehata, Hem Chandra Joshi, H.b. TripathiAbstract:Excitation wavelength dependence of the emission of 6-Methoxyquinoline (6MQ) in three polymer matrices, viz. polyvinyl alcohol (PVA), cellulose acetate (CA) and polymethyl methacrylate (PMMA) has been investigated at room temperature. 6MQ in polymer matrices exhibits dual emission and the fluorescence decays show a non-exponential behaviour throughout the emission profile. The results are interpreted in terms of two groups (normal and charge transfer species) of ground state conformers that assume different geometries in the polymer matrices. The inhomogeneous distribution of species, each possessing different absorption and relaxation properties is manifested by red edge excitation effects and distribution of decay time across the emission profile.
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Time resolved fluorescence spectroscopy of quinine sulphate, quinidine and 6-Methoxyquinoline: pH dependence
Journal of Luminescence, 1992Co-Authors: Debi D. Pant, H.b. Tripathi, D.d. PantAbstract:Abstract The excited state dynamics of quinine sulphate (QS), quinidine (Qd) and 6-Methoxyquinoline (6MQ) has been studied as a function of pH in steady state and nanosecond time resolved fluorescence experiments. The solvent relaxation process is a dominant process for all the molecules studied, irrespective of pH. Moreover, 6MQ undergoes a proton transfer reaction in the excited state at pH 7 whereas QS and Qd do not exhibit excited state protonation.
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Photophysics of quinidine dication in relation to quinine dication and 6-Methoxyquinoline monocation
Journal of Luminescence, 1991Co-Authors: Debi D. Pant, H.b. Tripathi, D.d. PantAbstract:Nanosecond time resolved emission spectroscopy was used to investigate the excited state solute-solvent interaction in quinidine dication. The emission spectrum is susceptible to the wavelength of excitation and the viscosity of the medium. The fluorescence lifetime is dependent on the emission wavelength. Spectral relaxation is observed on a nanosecond time scale. The room temperature data have been explained using Bakshiev's formulation of solvent relaxation. However, transient and steady state fluorescence studies from 80 to 290 K reveal that at 160 K, a rapid relaxation process other than the solvent relaxation occurs. A comparison of the photophysical data of protonated quinidine, quinine and 6-Methoxyquinoline shows close similarities among these three molecules. The major two relaxation processes in these molecules are solvent relaxation and charge transfer.
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Excited state solvation dynamics of 6-Methoxyquinoline
Journal of Photochemistry and Photobiology A-chemistry, 1991Co-Authors: H.b. Tripathi, Debi D. PantAbstract:Abstract Steady state and transient studies of 6-Methoxyquinoline (6MQ) were undertaken. 6MQ undergoes a large change of dipole moment on excitation. The low energy absorption band L b does not change in position with solvent polarity whereas the emission maxima shift towards lower frequencies with broadening of the spectra. The edge excitation red shift, which is associated with the time-dependent red shift of emission, is observed in all polar solvents. The fluorescence decay is monoexponential and is dependent on emission wavelength. The data are explained with the help of the Bakhshiev model of solvent relaxation. The solvent relaxation time τ r and the fluorescence lifetime τ f increase with the polarity of the solvent. In aqueous solution, 6MQ undergoes a protolytic reaction in the excited state. The rate constant for the proton transfer is 1.2×10 8 s −1 .
Hitoshi Hoshino - One of the best experts on this subject based on the ideXlab platform.
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Dissociation kinetic analysis of Ce(III) complex with Quin2 by microchip capillary electrophoretic reactor.
Analytical Sciences, 2013Co-Authors: Kei-ichirou Ohtsuka, Hitoshi Hoshino, Toru TakahashiAbstract:: Dissociation kinetic analysis of a complex of Ce(3+) with a polyaminocarboxylic ligand, 8-amino-2-[(2-amino-5-methylphenoxyl)methyl]-6-Methoxyquinoline-N,N,N',N',-tetraacetic acid (Quin2), was studied by microchip capillary electrophoretic reactor. Dissociation rate constants, k(d), of Ce(3+)-Quin2 complex in alkaline conditions at pH 8.3 - 9.8 were determined. The linear relationship of k(d) with the concentration of hydroxide ion indicates the existence of a hydroxide ion-assisted path in the dissociation reaction of Ce(3+)-Quin2 complex in alkaline conditions. The solvolytic dissociation rate constant, and the hydroxide ion-assisted dissociation rate constant of Ce(3+)-Quin2 complex were determined to be 1.55 × 10(-3) and 3.24 × 10(2) s(-1) in the analysis of the dependence of k(d) with the concentration of hydroxide ion, respectively.
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A microchip capillary electrophoretic reactor: a new methodology for direct measurement of dissociation kinetics of metal complexes
Analyst, 2005Co-Authors: Toru Takahashi, Kei-ichirou Ohtsuka, Hitoshi HoshinoAbstract:A microchip capillary electrophoretic reactor has been proposed and successfully demonstrated in the direct evaluation of the solvolytic dissociation rate constant of the complex of Ce3+ with a polyaminocarboxylic ligand, 8-amino-2-[(2-amino-5-methylphenoxyl)methyl]-6-Methoxyquinoline-N,N,N′,N′-tetraacetic acid.
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Entropy-controlled solvolytic dissociation kinetics of lanthanide(III) complexes with polyaminocarboxylates in aqueous solutions.
Inorganic Chemistry, 2001Co-Authors: Shingo Saito, Hitoshi Hoshino, Takao YotsuyanagiAbstract:The factors involved in the formation of an inert complex in terms of solvolysis reaction have been studied for lanthanide(III)−acyclic polyaminocarboxylate complexes, as the basis for kinetically controlled selectivity used in analytical methodologies such as HPLC and HPCE. The rate constants for solvolysis and acid-assisted dissociation processes of the lanthanide complexes were determined in a batch system through metal- and ligand-exchange reactions. The reagents used were 8-amino-2-[(2-amino-5-methylphenoxy)methyl]-6-Methoxyquinoline-N,N,N‘,N‘-tetraacetic acid (Quin2) and O,O‘-bis(2-aminophenyl)ethylene glycol-N,N,N‘,N‘-tetraacetic acid (BAPTA) as octadentate ligands and trans-1,2-diaminocyclohexane-N,N,N‘,N‘-tetraacetic acid (CyDTA) as a hexadentate ligand. It has been found that the rate constants for solvolysis vary from 5.7 × 10-3 s-1 (La3+) to 1.7 × 10-6 s-1 (Lu3+) depending on the ionic radii of Ln(III) ions for the Quin2 complexes, while no such monotonic dependence was observed for the BAPTA ...
