Debabrata Seth

Interaction of ionic liquid with water with variation of water content in 1-butyl-3-methyl -imidazolium hexafluorophosphate ( [bmim ] [PF6 ] )/TX-100/water ternary microemulsions monitored by solvent and rotational relaxation of coumarin 153 and coumarin 490

The interaction of water with room temperature ionic liquid (RTIL) [bmim][PF6] has been studied in [bmim][PF6]/TX-100/water ternary microemulsions by solvent and rotational relaxation of coumarin 153 (C-153) and coumarin 490 (C-490). The rotational relaxation and average solvation time of C-153 and C-490 gradually decrease with increase in water content of the microemulsions. The gradual increase in the size of the microemulsion with increase in w0 (w0=[water]/[surfactant]) is evident from dynamic light scattering measurements. Consequently the mobility of the water molecules also increases. In comparison to pure water the retardation of solvation time in the RTIL containing ternary microemulsions is very less. The authors have also reported the solvation time of C-490 in neat [bmim][PF6]. The solvation time of C-490 in neat [bmim][PF6] is bimodal with time constants of 400 ps and 1.10 ns.

Dynamics of Solvent and Rotational Relaxation of Coumarin 153 in a Room Temperature Ionic Liquid, 1-Butyl-3-methylimidazolium Octyl Sulfate, Forming Micellar Structure

The solvent and rotational relaxation of Coumarin 153 (C-153) was investigated by picosecond time-resolved fluorescence spectroscopy in a room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium octyl sulfate ([C4mim][C8SO4]). This is a typical RTIL, which form micellar structure above certain concentration of the RTIL (0.031 M). Dynamic light scattering (DLS) measurements show that the average hydrodynamic diameter ( Dh) of a [C4mim][C8SO4]-water micelle is 2.8 (+/-0.2) nm. Both the solvent and rotational relaxation of C-153 are retarded in this micelle compared to the solvation time of a similar type of dye in neat water. However, the solvent relaxation in this ionic liquid surfactant is different from that of a conventional ionic surfactant. The slow component of the solvation dynamics in C8H17SO4Na or TX-100 micelle is on the nanoseconds time scale, whereas in [C4mim][C8SO4] micelle the same component is on the subnanoseconds time scale. The different molecular motions with different time scale is the main reason behind this difference in the solvation time in micelles composed of RTIL with other conventional micelles.

Solvent and Rotational Relaxation of Coumarin 153 in a Protic Ionic Liquid Dimethylethanolammonium Formate

The solvent relaxation and orientational dynamics of coumarin 153 (C-153) was investigated in N,N-dimethylethanolammonium formate (DAF) with a variation of temperature. DAF is a protic room-temperature ionic liquid, comprised of nonaromatic cations. Both solvent relaxation and orientational dynamics of C-153 in DAF are linearly well-correlated with the bulk viscosity at different temperatures. We optimized the geometry of DAF using quantum chemical calculations using density functional theory methods. The optimized structure of DAF shows a nonbonded interaction between cation and anion, which suggests that a hydrogen bond is formed between hydrogen atoms attached to the nitrogen atom of the cation with the oxygen atom of the anion in DAF.

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.

Photophysical Properties of 7-(diethylamino)Coumarin-3-carboxylic Acid in the Nanocage of Cyclodextrins and in Different Solvents and Solvent Mixtures

The photophysical properties of 7‐(diethylamino) coumarin‐3‐carboxylic acid (7‐DCCA) were studied in cyclodextrins (α, β, γ,‐CDs), different neat solvents and solvent mixtures by using steady state absorption, emission and time‐resolved fluorescence spectroscopy. We have observed that with gradual increase in concentration of β‐CD the fluorescence quantum yield and lifetime decreased in a regular pattern whereas with gradual increase in concentration of γ‐CD the fluorescence quantum yield and lifetime gradually increased. With addition of urea, the fluorescence quantum yield and lifetime of 7‐DCCA in CDs increased. Binding constant calculation shows that 7‐DDCA forms 1:1 complex with β‐CD and with γ‐CD it forms 1:1 and 1:2 (guest:host) inclusion complex. We proposed that the dye molecule formed capping complex with β‐CD by means of hydrogen bonding and after addition of urea the hydrogen bonding network broke down and part of dye molecule entered inside the cavity of β‐CD. The photophysics of 7‐DCCA was studied in dioxane‐water mixture and ethylene glycol‐acetonitrile mixture to know the effect of polarity and viscosity of the media. The photophysics of 7‐DCCA was also studied in different neat solvents. It was found that the photophysics of 7‐DCCA depended on the structural feature of the solvents and solvent mixtures.

Photoinduced electron transfer reaction in polymer-surfactant aggregates: Photoinduced electron transfer between N,N-dimethylaniline and 7-amino coumarin dyes.

Photoinduced electron transfer between coumarin dyes and N,N-dimethylaniline has been investigated by using steady state and picosecond time resolved fluorescence spectroscopy in sodium dodecyl sulphate (SDS) micelles and PVP-polyvinyl pyrrolidone (SDS) polymer-surfactant aggregates. A slower rate of electron transfer is observed in PVP-SDS aggregates than in polymer-free SDS micelles. A Marcus type inversion is observed in the correlation of free energy change in comparison with the electron transfer rate. The careful investigation reveals that C-151 deviates from the normal Marcus inverted region compared to its analogs C-152 and C-481 due to slower rotational relaxation and smaller translational diffusion coefficient.

Photoinduced electron transfer from N,N-dimethylaniline to 7-amino Coumarins in protein-surfactant complex: Slowing down of electron transfer dynamics compared to micelles

Photoinduced electron transfer from N,N-dimethylaniline to different Coumarin dyes has been investigated in dodecyl trimethyl ammonium bromide (DTAB) micelles and in Bovine serum albumin (BSA)-DTAB protein-surfactant complex using steady-state and picosecond time-resolved fluorescence spectroscopy. We observed a slower fluorescence quenching rate in the DTAB micelles and in the protein-surfactant complex as compared to that in pure acetonitrile solution. Moreover, the observed fluorescence quenching in BSA-DTAB complex was found to be slower than that in DTAB micelles. In the correlation of free-energy change with the fluorescence quenching constant we observed a deviation in the fluorescence quenching electron transfer rate for Coumarin 151 (C-151) from the normal Marcus curve. This observation is ascribed to the stronger interaction of C-151 with the surfactant molecules present in the micelles. This is evident from the slower translation diffusion (D(L)) of Coumarin 151 compared to other probe molecules.

Supramolecular Interaction between a Hydrophilic Coumarin Dye and Macrocyclic Hosts: Spectroscopic and Calorimetric Study

The photophysics of a hydrophilic molecule, 7-(diethylamino)-coumarin-3-carboxylic acid (7-DCCA), was studied in the presence of two macrocycles, (2-hydroxypropyl)-γ-cyclodextrin and cucurbit[7]uril. We have used steady-state absorption, fluorescence, and time-resolved fluorescence emission spectroscopy; Fourier transform infrared (FTIR) spectroscopy; (1)H NMR spectroscopy; and isothermal titration calorimetry (ITC) to confirm the supramolecular host-guest complex formation. The spectral properties of 7-DCCA were modulated in the presence of both macrocycles. It was assigned that 7-DCCA forms a 1:2 complex with (2-hydroxypropyl)-γ-cyclodextrin and cucurbit[7]uril. The large modulation of the emission properties of 7-DCCA in the presence of the macrocycles indicates the formation of supramolecular complexes. A significant shift in the bond vibration frequencies in the FTIR studies showed encapsulation of the dyes in the hydrophobic cavity of the macrocycles. This is further substantiated by the (1)H NMR studies, in which the upfield and downfield shifts of the protons were observed in both the aliphatic and aromatic region in the presence of macrocycles. The time-resolved anisotropy measurements further reinforce the conception of host-guest supramolecular complex formation because, in both cases, the rotational relaxation time increases significantly compared to that in water. A deeper understanding between the differences in interaction of an anionic molecule with cucurbit[7]uril and (2-hydroxypropyl)-γ-cyclodextrin will be achieved through this work. From the ITC measurement, we have formulated the forces due to complex formation.

To probe the structure of methanol and Aerosol OT (AOT) in AOT reverse micelles by FTIR measurements

We have reported the study of methanol/AOT/n-heptane reverse micellar aggregates using Fourier Transform Infrared (FTIR) spectroscopy. We have divided our whole work into two parts. In the first part we have studied the structural properties of Aerosol OT (AOT) reverse micelles by monitoring the changes in the symmetrical sulfonate stretching region (1000-1100 cm(-1)), asymmetrical sulfonate stretching region (1130-1330 cm(-1)) and carbonyl frequency region (1695-1770 cm(-1)), and in the other part we have measured the changes in the maximum position of OH stretching frequency region (3140-3650 cm(-1)) with increasing methanol content of the reverse micellar solution. Finally we have defined and established the presence of different types of methanol inside the reverse micelle by splitting the OH frequency region using multiple Gaussian curve fitting. Though methanol is partially soluble in n-heptane, this work certainly proves the existence of stable methanol/AOT/n-heptane reverse micelles.

Interaction of the nonsteroidal anti-inflammatory drug indomethacin with micelles and its release.

In this study, we have reported the binding interaction and photophysics of a nonsteroidal anti-inflammatory drug (NSAID) indomethacin (IMC) in the presence of different micelles. We have used several spectroscopic techniques such as UV-vis absorption, steady state fluorescence and time-resolved fluorescence emission spectroscopy. The spectral properties of IMC were modulated in the presence of micelles compared to that in neat water. The weak emitting drug molecule (IMC) becomes highly fluorescent after binding with the micelles. The fluorescence quantum yield and fluorescence lifetime increase in the presence of micelles compared to those in neat water. The isothermal titration calorimetry (ITC) method was used to study the binding interaction of IMC with different micelles. The thermodynamic parameters and the nature of binding between IMC and different micelles have been estimated. Moreover, addition of KCl salt in the respective micelles releases IMC molecule from the micelles to the aqueous medium. This study will help elicidate the binding behavior of IMC in the presence of different micelles for possible use as potential drug delivery systems.