Steady state and time-resolved fluorescence spectroscopy of quinine sulfate dication in ionic and neutral micelles: Effect of micellar charge on photophysics

Steady State and Time-Resolved Fluorescence Spectroscopy of Cinchonine Dication in Sodium Dodecylsulphate Micellar System

This paper reports the influence of surface charge of the micelles on to the photophysical properties of a cinchonine dication (C2+) fluorophore in anionic, sodium dodecylsulphate (SDS), surfactant at premicellar, micellar and post-micellar concentrations in aqueous phase at room temperature. The magnitude of edge excitation red shift (EERS) in the fluorescence maximum of C2+ in bulk water solution is 1897 cm- 1 whereas, in the case of SDS it is observed to be 1984 cm- 1. The fluorescence decay curve of C2+ fits with multi exponential functions in the micellar system. The increase in lifetime of C2+ in SDS has been attributed to the increase in radiative rate due to the incorporation of C2+ at the micelle -water interface. The value of dynamic quenching constant determined is 16.9 M- 1. The location of the probe molecule in micellar systems has been justified by a variety of spectral parameters such as dielectric constant, ET (30), viscosity, EERS, average fluorescence decay time, radiative and non-radiative rate constants. All experimental results suggest that the C2+ molecule binds strongly with the SDS micelles and resides at micellar-water interface. The binding constant (Kb) calculated (3.85 × 105 M- 1) for C2+ in SDS revealed that the electrostatic forces mediate charge probe-micelle association.

The Study of the Effect of Dimethylsulfoxide (or Diethylsulfoxide) on Quinine Sulfate-DNA Binding by UV-Vis and Steady-State Fluorescence Spectroscopies

The effect of dimethylsulfoxide (DMSO) and diethylsulfoxide (DESO) on binding between quinine sulfate (QS) and DNA was studied by virtue of UV-Vis absorption, steady-state fluorescence spectroscopies, and fluorescence polarization measurements. The binding constant was determined at three different temperatures and the values of standard Gibbs energy change, enthalpy and entropy of binding were determined. The mechanism of binding and the effect of sulfoxides on this process was revealed. The values of binding constant, fluorescence polarization and iodide quenching studies confirmed that the main binding mode in QS-DNA system is groove binding. Addition of sulfoxides does not change the binding mechanism. Moreover, with addition of sulfoxides binding constant increases due to the removal of water molecules from DNA grooves making them more available for QS molecules. To explain the effect of DMSO and DESO on QS-DNA binding the photophysical properties of QS in aqueous solutions of DMSO and DESO were also studied. On the basis of quantum yield of QS in water, DMSO and DESO the types of intermolecular interactions were discussed. The obtained results show that quantum yield of QS in sulfoxides is lower compared with that in water and aqueous solution of 0.1 M H2SO4. QS forms ground state complexes with both DMSO and DESO that are stronger fluorophores compared with free QS molecules.

Photophysical Properties of Some Fluorescent Dyes in SDS Micellar Solutions

Photophysical properties of fluorescent dyes such as Safranin T, Acridine Orange, Pyronin B and Pyronin Y in SDS micelles were examined by using spectroscopic techniques. Firstly, spherical micelles in deionized water were prepared with Sodium Dodecyl Sulfate (SDS) surfactants and they were transformed into their layered structures (lamellar micelles) by the aid of NaCl (sodium chloride). SEM studies confirmed the transformation of SDS micelles from the spherical structures to the lamellar structures. Secondly, absorption and fluorescence characteristics of the dyes in deionized water and the SDS micelles aqueous solutions were characterized in the presence of various NaCl concentrations at above the critical micelle concentration (CMC). Moreover, the photophysical properties of the dyes in various media were discussed by fluorescence quantum yield and fluorescence lifetime data. The micellar structures called a mimetic membrane system changed the photophysical properties of the dyes compared to those in deionized water.

Excited-State Dynamics of Quinine Sulfate and Its Di-Cation Doped in Polyvinyl Alcohol Thin Films Near Silver Nanostructure Islands

The present study demonstrates the near-field effect of silver nanostructure island films (SNIFs) on the photophysics and exited-state dynamics of quinine sulphate (QS) and its di-cation (QSD), doped in polyvinyl alcohol (PVA) films. The results indicate a nearly 3.8-fold enhancement in absorption and 4000-fold enhancement in fluorescence in SNIF-coated QS-doped PVA films, whereas only twofold enhancement in absorption and sevenfold enhancement in fluorescence intensity are found in SNIF-coated QSD-doped PVA films. However, an increase in photostability and a decrease in decay time have been observed in both the SNIF-coated films as compared to their uncoated forms. Further, a decrease in the magnitude of the edge excitation red shift in emission spectra along with a red shift in the L_a band and a rise in the intensity of the L_b band of excitation is observed in SNIF-coated QSD films because of strong coupling of the L_b band with the surface plasmons of silver nanoparticles. Moreover, X-ray photoelectron spectroscopic measurement of silver nanoparticle-coated QS-PVA films shows no change in 3d_3/2 and 3d_5/2 transitions of silver, whereas the decrease in energy in these silver transitions in the QSD-PVA system is observed as compared to silver nanoparticle-coated PVA films. These results indicate the formation of a field-governed radiating plasmon and plasmon-coupled unified fluorophore system, respectively. This affects the photophysics of both of the molecules by plasmonic coupling of the Frank-Condon state, solvent relaxation state, and charge-transfer state by different orders of magnitude.

Testing Fluorescence Lifetime Standards using Two-Photon Excitation and Time-Domain Instrumentation: Fluorescein, Quinine Sulfate and Green Fluorescent Protein

It is essential for everyone working with experimental science to be certain that their instruments produce reliable results, and for fluorescence lifetime experiments, information about fluorescence lifetime standards is crucial. A large part of the literature on lifetime standards dates back to the 1970s and 1980s, and the use of newer and faster measuring devices may deem these results unreliable. We have tested the three commonly used fluorophores fluorescein, quinine sulfate and green fluorescent protein for their suitability to serve as lifetime standards, especially to be used with two-photon excitation measurements in the time-domain. We measured absorption and emission spectra for the fluorophores to determine optimal wavelengths to use for excitation and detector settings. Fluorescence lifetimes were measured for different concentrations, ranging from 10^− 3 − 10^− 5 M, as well as for various solvents. Fluorescein was soluble in both ethanol, methanol and sulfuric acid, while quinine sulfate was only soluble in sulfuric acid. Green fluorescent protein was prepared in a commercial Tris-HCl, EDTA solution, and all three fluorophores produced stable lifetime results with low uncertainties. No siginificant variation with concentration was measured for any of the fluorophores, and all showed single-exponential decays. All lifetime measurements were carried out using two-photon excitation and lifetime data was obtained in the time-domain using time-correlated single-photon counting.

Interaction of 6-methoxyquinoline with anionic sodium dodecylsulfate micelles: Photophysics and rotational relaxation dynamics at different pH

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 (Kb) 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, ET(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.

Interaction of quinine sulfate with anionic micelles of sodium dodecylsulfate: A time-resolved fluorescence spectroscopy at different pH

Photophysical behavior and rotational relaxation dynamics of quinine sulfate (QS) in anionic surfactant, sodium dodecylsulfate (SDS) at different pH have been studied using steady state and time resolved fluorescence spectroscopy. It has been observed that the cationic form of quinine sulfate (at pH 2) forms a fluorescent ion pair complex with the surfactant molecules at lower concentrations of surfactant. However, for higher concentrations of SDS, the probe molecules bind strongly with the micelles and reside at the water-micelle interface. At pH 7, QS is singly protonated in bulk aqueous solution. At lower concentrations of SDS aggregation between probe and surfactant molecules has been observed. However, for higher concentrations of SDS, an additional fluorescence peak corresponding to dicationic form of QS appears and this has been attributed to double protonation of the QS molecule in micellar solution. At pH 7, in the presence of SDS micelles, the photophysical properties of QS showed substantial changes compared to that in the bulk water solution. At pH 12, an increase in fluorescence intensity and lifetime has been observed and this has been attributed to the increase in radiative rate due to the incorporation of QS at the micelle-water interface. The local pH at micellar surface has been found different from the pH of bulk solution.

Effect of nanosize micelles of ionic and neutral surfactants on the photophysics of protonated 6-methoxyquinoline: time-resolved fluorescence study

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, ET (30), EERS, average fluorescence decay time, radiative and non radiative rate constants, and rotational relaxation time.

Silver(I)-directed growth of metal-organic complex nanocrystals with bidentate ligands of hydroquinine anthraquinone-1,4-diyl diethers as linkers at the water-chloroform interface

Immiscible liquid-liquid interfaces provide unique double phase regions for the design and construction of nanoscale materials. Here, we reported Ag(I)-directed growth of metal-organic complex nanocrystals by using AgNO3 as a connector in the aqueous solution and bidentate ligand of 1,4-bis(9-O-dihydroquininyl)anthraquinone [(DHQ)2AQN] and its enantiomer of (DHQD)2AQN in the chloroform solutions as linkers. The Ag-(DHQ)2AQN and Ag-(DHQD)2AQN complex nanocrystals were formed at the liquid-liquid interfaces and characterized by using UV-vis absorption and fluorescence spectroscopy and X-ray photoelectron spectroscopy, as well as by using scanning electron microscopy. Screw-like nanocrystals were formed at the initial 30 min after the interfacial coordination reaction started, then they grew into nanorods after several days, and finally became cubic microcrystals after 2 weeks. The pure ligand showed two emission bands centered at about 363 and 522 nm in the methanol solution, the second one of which was quenched and shifted to about 470 nm in the Ag-complex nanocrystals. Two couples of reversible redox waves were recorded for the Ag-complex nanocrystals; one centered at about -0.25 V (vs. Ag/AgCl) was designated to one electron transfer process of Ag - (DHQ)2AQN and Ag - (DHQ)2AQN(+), and the other one centered at about 0.2 V was designated to one electron transfer process of Ag - (DHQ)2AQN and Ag(+) - (DHQ)2AQN.