The effect of membrane fluidity on FRET parameters: an energy transfer study inside small unilamellar vesicle.

The fluorescence resonance energy transfer (FRET) in a lipid bilayer system containing two different donors and one common acceptor at below and above transition temperature has been studied and all the FRET parameters are analyzed using steady state and time-resolved fluorescence spectroscopy. Using dynamic light scattering measurement, we have followed the process of preparation of small unilamellar vesicles, and by following the FRET parameters of C-153-Rh6G and C-151-Rh6G pairs inside SUVs at 16 °C and 33 °C (T(m) = 23.9 °C) we have noticed that there is greater effect of temperature on the FRET parameters in case of the C-153-Rh6G pair than that of the C-151-Rh6G pair. Finally we have concluded that this difference is due to their different location inside the lipid bilayer in which fluidity of the long alkyl chain markedly affects the FRET parameters for C-153-Rh6G pair embedded inside a small unilamellar vesicle of size 20-50 nm.

Characterization of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][Tf2N])∕TX-100∕cyclohexane ternary microemulsion: investigation of photoinduced electron transfer in this RTIL containing microemulsion.

In this study we have characterized a ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethyl- sulfonyl)imide containing ternary nonaqueous microemulsion ([Emim][Tf(2)N]∕∕TX-100∕cyclo- hexane). The phase behavior and dynamic light scattering study show that the [Emim][Tf(2)N]∕TX-100∕cyclohexane three component system can form microemulsion with [Emim][Tf(2)N] as polar core at suitable condition. We have investigated photoinduced electron transfer (PET) using dimethyl aniline as electron donor and several Coumarin dyes as electron acceptor molecules at two different R values (R = [ionic liquid]∕[surfactant]) to observe how the dynamics of the PET rate is affected in this type of confined microenvironment compared to that of the PET dynamics in neat ionic liquid and other pure solvent media. The plot of observed k(q) values with the free energy change (ΔG(0)) for electron transfer reaction shows an apparent inversion in the observed rate as predicted by the Marcus theory.

Effect of polymer, poly(ethylene glycol)(PEG-400), on solvent and rotational relaxation of coumarin-480 in an ionic liquid containing microemulsions.

The effect of a polymer, polyethylene glycol with a molecular weight of 400 (PEG-400), on the dynamics of solvent and rotational relaxation have been investigated in [bmim][BF4]/TX100/cyclohexane microemulsions using steady state and time resolved fluorescence spectroscopy as a tool and coumarin 480 (C-480) as a fluorescence probe. The size of the microemulsions increases with addition of PEG-400, which was revealed by dynamic light scattering (DLS) measurement. This leads to faster collective motion of the cations and anions of [bmim][BF4], which contributes to faster solvent relaxation in microemulsions.

Direct observation of solvation dynamics in an aqueous reverse micellar system containing silver nanoparticles in the reverse micellar core.

In this work we have reported the synthesis of silver nanoparticles in aqueous AOT (dioctylsulfosuccinate, sodium salt) n-heptane reverse micelles and then carried out the study of solvation dynamics keeping the system unaltered, i.e., inside the reverse micelles containing silver nanoparticles. Solvation dynamics and anisotropy studies showed that they were highly affected and became slower in reverse micelles containing silver nanoparticle in comparison to the pure reverse micellar system.

Photophysical studies of a hemicyanine dye (LDS-698) in dioxane-water mixture, in different alcohols, and in a room temperature ionic liquid.

In this paper, we have investigated the photophysics of 1-ethyl-2-(4-(p-dimethylaminophenyl)-1,3-butadienyl)pyridinium perchlorate (LDS-698) molecule in dioxane-water mixture and in a room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]). Both photoisomerization and twisted intramolecular charge transfer (TICT) are possible in this molecule. We have shown that TICT is favorable in this molecule in the dioxane-water mixture and in neat [bmim][BF4]. The change in absorption energy of LDS-698 molecule with mole fraction of water is nonlinear in these systems. The Stern-Volmer plot also deviates from linearity in these systems. This nonlinearity is due to the specific solvation of water molecules in the mixture.

To probe the interaction of methanol and acetonitrile with the ionic liquid N,N,N-Trimethyl-N-propyl ammonium bis(trifluoromethanesulfonyl) imide at different temperatures by solvation dynamics study.

The dynamics of solvent and rotational relaxation of coumarin 153 (C-153) has been studied in neat N,N,N-trimethyl-N-propyl ammonium bis(trifluoromethanesulfonyl) imide ([N(3111)][Tf(2)N]) and its mixtures with polar solvents, namely, methanol and acetonitrile at three different temperatures from 294 to 303 K. Both the solvent and rotational relaxation dynamics of C-153 in neat [N(3111)][Tf(2)N] are linearly correlated with the bulk viscosity at different temperatures. The solvent relaxation time and rotational relaxation time of C-153 decrease with gradual addition of cosolvents in [N(3111)][Tf(2)N]. The gradual addition of cosolvent decreases the viscosity of the medium, and consequently, the solvation and rotational relaxation time also decrease. The decrease of solvation time is more pronounced on addition of acetonitrile compared to methanol.

Photoluminescence Imaging of Polyfluorene Surface Structures on Semiconducting Carbon Nanotubes: Implications for Thin Film Exciton Transport.

Single-walled carbon nanotubes (SWCNTs) have potential to act as light-harvesting elements in thin film photovoltaic devices, but performance is in part limited by the efficiency of exciton diffusion processes within the films. Factors contributing to exciton transport can include film morphology encompassing nanotube orientation, connectivity, and interaction geometry. Such factors are often defined by nanotube surface structures that are not yet well understood. Here, we present the results of a combined pump-probe and photoluminescence imaging study of polyfluorene (PFO)-wrapped (6,5) and (7,5) SWCNTs that provide additional insight into the role played by polymer structures in defining exciton transport. Pump-probe measurements suggest exciton transport occurs over larger length scales in films composed of PFO-wrapped (7,5) SWCNTs, compared to those prepared from PFO-bpy-wrapped (6,5) SWCNTs. To explore the role the difference in polymer structure may play as a possible origin of differing transport behaviors, we performed a photoluminescence imaging study of individual polymer-wrapped (6,5) and (7,5) SWCNTs. The PFO-bpy-wrapped (6,5) SWCNTs showed more uniform intensity distributions along their lengths, in contrast to the PFO-wrapped (7,5) SWCNTs, which showed irregular, discontinuous intensity distributions. These differences likely originate from differences in surface coverage and suggest the PFO wrapping on (7,5) nanotubes produces a more open surface structure than is available with the PFO-bpy wrapping of (6,5) nanotubes. The open structure likely leads to improved intertube coupling that enhances exciton transport within the (7,5) films, consistent with the results of our pump-probe measurements.

Förster resonance energy transfer among a structural isomer of adenine and various Coumarins inside a nanosized reverse micelle.

In this article we have studied Förster Resonance Energy Transfer (FRET) using 2-aminopurine (2-AP), a structural isomer of adenine as donor and various Coumarins as acceptors inside AROSOL-OT (AOT)-water reverse micelles (RM) using steady-state and time-resolved fluorescence spectroscopies. We have used three sets of FRET and all the pairs except 2-AP-Coumarin-480 exhibited quite efficient FRET. For the efficient pairs, overlap integral J(λ) and Förster distance (R0) are of high values but the rate constant of energy transfer (kET) are quite low. The rate is gradually amplified with increase in water content for the 2-AP-Coumarin-440 pair while the reverse is observed for 2-AP-Coumarin-460. In future our FRET pair can be used in more modified and sophisticated confined media such as biomembranes of varying size, physical properties and chemical compositions etc.

Photoinduced electron transfer in a room temperature ionic liquid 1-butyl-3-methylimidazolium octyl sulfate micelle: a temperature dependent study.

The effect of temperature on the dynamics of photoinduced electron transfer (PET) between different coumarin dyes and N,N-dimethyl aniline in a room temperature ionic liquid 1-butyl-3-methylimidazolium octyl sulfate ([C(4)mim][C(8)SO(4)]) micelle have been investigated using steady-state and time-resolved fluorescence quenching measurements at four different temperatures: 208, 298, 308, and 318 K. The quenching rates (k(q)(TR)) of the PET process in this micellar system are found to be lower than the PET rate in sodium dodecyl sulfate and Triton-X 100 micelle and almost comparable to the dodecyl trimethyl ammonium bromide and cetyl trimethyl ammonium bromide micelle due to larger donor­acceptor separation in the micellar phase. The temperature dependent PET rates are well correlated with the Arrhenius type of correlation for all the coumarin dyes. Marcus type of inversion in PET rates has been observed at relatively lower exergonicity, and the correlation plots gradually move upward with the increase of temperature.

Room temperature ionic liquid in confined media: a temperature dependence solvation study in [bmim][BF4]/BHDC/benzene reverse micelles.

In this work, we reported a detailed study of the solvation dynamics of coumarin-480 in [bmim][BF(4)]/BHDC/benzene reverse micelles (RMs) with varying [bmim][BF(4)]/BHDC molar ratio (R) 1.00, 1.25, 1.50, and also study the solvation dynamics at five different temperatures from 15 to 35 °C RMs at [bmim][BF(4)]/BHDC molar ratio 1.25 for the first time. The average solvation time constant becomes slightly faster with the increase in R values at a temperature 25 °C. The solvation dynamics of the RMs with R value 1.25 becomes faster with the increase in temperature. We have also investigated temperature-dependent solvation dynamics in neat [bmim][BF(4)]. The solvation dynamics in neat [bmim][BF(4)] has a substantial temperature effect but for the [bmim][BF(4)]/BHDC/benzene RMs the temperature effect on the solvation dynamics is not that significant. Time-resolved fluorescence anisotropy studies reveal a decrease in the rotational restriction on the probe with increasing temperature. Wobbling-in-cone analysis of the anisotropy data also supports this finding.

Effects of 1-butyl-3-methyl imidazolium tetrafluoroborate ionic liquid on Triton X-100 aqueous micelles: solvent and rotational relaxation studies.

The effect of added room-temperature ionic liquids on the nature of water molecules in the palisade layer of a Triton X-100 (TX-100) micelle has been investigated using solvation and rotational relaxation studies of coumarin 153 in the presence of different wt % of [bmim][BF(4)] and thus to understand the changes in micellar palisade layer, especially the entrapped water structures in the palisade layer. It has been observed that in the presence of added [bmim][BF(4)] the solvation dynamics becomes faster. It has previously been demonstrated (Behera et al. J. Chem. Phys.2007, 127, 184501) that in the present micellar systems, in the presence of [bmim][BF(4)] micellar size and aggregation number (N(agg)) decreases giving rise to more water molecules penetrating in to the micellar phase which results in increased microfluidity. In accordance with solvation dynamics results, fluorescence anisotropy studies also indicate an increased microfluidity for the palisade layer of the TX-100 micelle with the added [bmim][BF(4)]. Wobbling-in-cone analysis of the anisotropy data also supports this finding.

Nanocavity effect on photophysical properties of colchicine: a proof by circular dichroism study and picosecond time-resolved analysis in various reverse micellar assemblies.

In August 2009, colchicine won Food and Drug Administration (FDA) approval in the United States as a stand-alone drug for the treatment of acute flares of gout and familial Mediterranean fever. Recently, it is now the center of attraction in medicinal research. In this present paper, we have employed two other analogues of colchicine for exploring the photophysical properties inside nanocavity environment in details. Here we have a series of interesting results that have interesting similarity with the colchinoid-tubulin interaction. To monitor fluorescence properties of colchinoids, we have used absorption, emission, and time-resolved spectroscopy and to monitor structural properties we have measured circular dichroism. Steady-state anisotropy and dynamic light scattering results give an idea about the microenvironment sensed by the colchinoids molecules. A sharp increment for colchicine, very small increment for isocolchicine and no increment for colcemid in fluorescence and different circular dichroism (CD) spectra of all of these colchinoids upon embedment inside nanocavity of reverse micelle made a supposition that all these changes of fluorescence properties and CD results of colchinoids is not solely due to viscosity effect but also the constraint, that is, very narrow space to spread over, given by the nanocavity of reverse micelle. Moreover, we have noticed that the B ring of the colchinoids also have a pronounced effect on the interaction nature as well as on conformational change of these compounds after entrapment.

Photophysics and photodynamics of 1'-hydroxy-2'-acetonaphthone (HAN) in micelles and nonionic surfactants forming vesicles: a comparative study of different microenvironments of surfactant assemblies.

The effect of different microenvironments inside various biomimicking supramolecular assemblies of ionic (SDS/CTAB) and nonionic (TX100) micelles and nonionic surfactants (Tween-80/PEG-6000) forming vesicles (niosome) on the photophysical and rotational dynamical properties of 1'-hydroxy-2'-acetonaphthone (HAN) have been studied using steady-state and time-resolved fluorescence spectroscopy. Enhanced fluorescence intensity with a significant blue shift and longer emission lifetime of the caged tautomers of HAN indicate modulation of photophysics of HAN upon encapsulation in both micellar assemblies and the niosome system. The binding constant and free energy change for the complexation of HAN with micelles and niosome demonstrate a comparative study on the binding efficiency of the different assemblies depending on the nature of microenvironments toward HAN. The enhancement in the steady-state anisotropy in niosome solutions compared with that in pure aqueous solution indicates that HAN is located inside the motionally restricted bilayer region of niosome. The fluorescence quenching experiment further reveals the probable location of HAN in micelles and niosome. In TX100 micelles, the obtained lifetime values are 417 ps and 1.63 ns for the caged tautomers, whereas in the comparatively more rigid and confined environment provided by niosome those values are 444 ps and 2.5 ns. The rotational relaxation time constants for the caged tautomers in niosome are also found to be higher than those in micelles. The observed difference in binding ability of the different assemblies is due to the difference in the extent of water penetration and different extent of rigidity around the fluorophore.

Ionic liquid containing microemulsions: probe by conductance, dynamic light scattering, diffusion-ordered spectroscopy NMR measurements, and study of solvent relaxation dynamics.

Room-temperature ionic liquid (RTIL), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([P(13)][Tf(2)N]), was substituted for polar water and formed nonaqueous microemulsions with benzene by the aid of nonionic surfactant TX-100. The phase behavior of the ternary system was investigated, and microregions of [P(13)][Tf(2)N]-in-benzene (IL/O), bicontinuous, and benzene-in-[P(13)][Tf(2)N] (O/IL) were identified by traditional electrical conductivity measurements. Dynamic light scattering (DLS) revealed the formation of these IL microemulsions because with gradual increase of RTIL contents the droplet sizes of the microemulsions are also gradually increasing. Pulsed-field gradient spin-echo NMR have been studied to measure the diffusion coefficients of neat [P(13)][Tf(2)N] and [P(13)][Tf(2)N] in microemulsions which indicate ionic liquid containing microemulsions is formed. Moreover, the dynamics of solvent relaxation have been investigated in [P(13)][Tf(2)N]/TX100/benzene microemulsions using steady-state and time-resolved fluorescence spectroscopy using coumarin 153 (C-153) and coumarin 480 (C-480) fluorescence probe with variation of RTIL contents in microemulsions. For both of the probes with increasing amount of ionic liquids in microemulsions the relative contribution of the fast components increases and the slow components contribution decreases; therefore the average solvation time decreases.

Solvation and rotational dynamics of coumarin-153 in ethylammonium nitrate containing γ-cyclodextrin.

Carbohydrates are known to serve as an abundant, diverse, and reusable source of carbon, but their derivatization for industrial applications is still a challenging task because of their low solubility in solvents other than water; they are only sparingly soluble in common organic solvents as well as in weakly coordinating ionic liquids, such as 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)). In this manuscript, we have shown that the solubility of cyclodextrins (CDs) in ethylammonium nitrate (EAN), at 298 K is comparable to that in water. This combination of EAN and γ-CD can be useful in many ways: (i) combination of both γ-CD and EAN can provide selectivity and resolution for separations that otherwise are not possible (vide infra); (ii) the combination of these two can find interesting applications in protein-detergent systems (vide infra), and (iii) they can improve chiral resolutions in simultaneous enantioseparation by capillary electrophoresis method (vide infra). In this study, we have characterized this system using the following techniques: By the use of the competitive fluorescence method we have shown that there is no inclusion complex formation between EAN and γ-CD. Using the Benesi Hildebrand equation, we have shown the variation of binding constant of the C-153/γ-CD complex with temperature. The negative entropy and enthalpy changes indicated that the formation of the above C-153/γ-CD complex is entropically unfavorable and enthalpy-driven. We have also investigated the effect of temperature on the fluorescence anisotropy decays and the solvation dynamics of coumarin-153 (C-153) using picosecond time-resolved spectroscopy. Finally, we have shown that the aggregation behavior of γ-CD in EAN is entirely different from that in water, and the increase in average solvation time on going from neat EAN to EAN containing γ-CD is very small compared to the increase in solvation time on going from pure water to water containing γ-CD.

Ionic liquid-induced changes in properties of aqueous cetyltrimethylammonium bromide: a comparative study of two protic ionic liquids with different anions.

In this work we have shown a comparative study of changes in physicochemical properties of an aqueous solution of a common cationic surfactant cetyltrimethylammonium bromide (CTAB) upon addition of two protic ionic liquids N,N-dimethylethanolammonium [corrected] hexanoate (DAH) and N,N-dimethylethanolammonium [corrected] formate (DAF). The aim of this manuscript is to offer a comparative study and establish the role of the alkyl chain length of the anion of the added protic ionic liquids on the physicochemical properties of aqueous solution of CTAB. At lower concentration (i.e., ≤ 30 mM) both ionic liquids show the same trend in modifying the properties of aqueous CTAB solution, but DAH as an additive shows a more dramatic increase in aggregation number and size of the CTAB micelle compared to that of DAF as an additive. At higher concentrations of additives (DAF and DAH), the properties of aqueous CTAB solution change in an entirely different way. The size of the CTAB micelle was found to be 0.9 nm. With the addition of 215 mM DAH, the size of the CTAB micelle increases to 25.0 nm, whereas with the addition of 215 mM DAF it increases to only 5.6 nm. Zeta potential, electrical conductance, microviscosity, and dipolarity measurements were performed to gain insight into this abrupt size change in the case of DAH. It is proposed that the formate and hexanoate anions undergo Coulombic attractive interaction with cationic head groups of the CTAB micelle at all concentrations. In the case of DAH, the presence of a hexyl chain on the hexanoate ion allows it to align with the tail part of CTAB, whereas in the case of DAF the absence of an alkyl chain in the formate ion is apparently unable to align the formate anion with the tail part of CTAB. So this difference in the location of the anions of DAF and DAH is responsible for the different size changes and different behaviors of the two ionic liquids.

Probing the interaction of 1-ethyl-3-methylimidazolium ethyl sulfate ([Emim][EtSO4]) with alcohols and water by solvent and rotational relaxation.

The effect of the addition of cosolvents in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium ethyl sulfate ([Emim][EtSO(4)]) was probed by the solvent and rotational relaxation studies of coumarin 153 in neat ionic liquid [Emim][EtSO(4)] and [Emim][EtSO(4)]-cosolvent mixtures by using steady-state and time-resolved fluorescence spectroscopy. With gradual addition of cosolvents in the RTIL, both the average solvation time and rotational relaxation times gradually decrease. Addition of cosolvents in the IL decreases the viscosity of the medium. We have optimized the geometry of [Emim][EtSO(4)] and [Emim][EtSO(4)]-cosolvent mixtures by using quantum chemical calculations using density functional theory methods, which show the formation of hydrogen bond between cosolvents with [Emim][EtSO(4)]. With addition of the same amount of alcohols in neat [Emim][EtSO(4)], the rotational relaxation time decreases more compared to the addition of the same amount of water.

Synthesis of silver nanoparticle inside the nonaqueous ethylene glycol reverse micelle and a comparative study to show the effect of the nanoparticle on the reverse micellar aggregates through solvation dynamics and rotational relaxation measurements.

In this work, we have reported the application of less familiar ethylene glycol-AOT reverse micelle for the synthesis of silver nanoparticle using glucose as mild reducing agent and isooctane as the continuous media. We have also studied the pure ethylene glycol-AOT reverse micelle and the perturbed reverse micelle (containing silver nanoparticle in its womb) through solvation dynamics measurement using steady-state and time-resolved fluorescence spectroscopy. Finally, we compared both of the results to get the valuable information about the perturbed reverse micellar system containing silver nanoparticle. Through the work, we found that in the pure reverse micellar system, with increasing ethylene glycol loading, solvation time was decreasing and anisotropy value became slower. In the perturbed reverse micellar system (containing silver nanoparticle) having the same environmental state, that is, at the same ethylene glycol content, solvent and rotational relaxation became slower and faster, respectively.

Microemulsions with surfactant TX100, cyclohexane, and an ionic liquid investigated by conductance, DLS, FTIR measurements, and study of solvent and rotational relaxation within this microemulsion.

Room-temperature ionic liquids (RTILs), N,N,N-trimethyl-N-propyl ammonium bis(trifluoromethanesulfonyl) imide ([N(3111)][Tf(2)N]), were substituted for polar water and formed nonaqueous microemulsions with cyclohexane by the aid of nonionic surfactant TX-100. The phase behavior of the ternary system was investigated, and microregions of [N(3111)][Tf(2)N]-in-cyclohexane (IL/O), bicontinuous, and cyclohexane-in-[N(3111)][Tf(2)N] (O/IL) were identified by traditional electrical conductivity measurements. Dynamic light scattering (DLS) revealed the formation of the IL microemulsions. The FTIR study of O-H stretching band of TX100 also supports this finding. The dynamics of solvent and rotational relaxation have been investigated in [N(3111)][Tf(2)N]/TX100/cyclohexane microemulsions using steady-state and time-resolved fluorescence spectroscopy as a tool and coumarin 480 (C-480) as a fluorescence probe. The size of the microemulsions increases with gradual addition of [N(3111)][Tf(2)N], which revealed from DLS measurement. This leads to the faster collective motions of cation and anions of [N(3111)][Tf(2)N], which contributes to faster solvent relaxation in microemulsions.