Sayeed Ashique Ahmed

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.

Host-guest interaction of 3-hydroxyflavone and 7-hydroxyflavone with cucurbit [7]uril: A spectroscopic and calorimetric approach

The modulation of photophysical behaviour of small organic molecules in the presence of macrocycles is one of the most interesting areas of research. In this work we reported the interaction of two biologically active molecules 3-hydroxyflavone and 7-hydroxyflavone with macrocyclic host cucurbit [7]uril in aqueous medium. To investigate the change of photophysical properties of these two flavones, we have used steady state absorption, fluorescence, time resolved fluorescence emission spectroscopy and isothermal titration calorimetric technique. It is observed that on complexation with cucurbit [7]uril, the excited state proton transfer processes in both flavones have been facilitated. Isothermal titration calorimetric method was used in order to investigate the involvement of thermodynamic parameters in complexation between flavone with cucurbit [7]uril. The changes in thermodynamic properties due to the complexation of the flavones molecules with cucurbit [7]urils help to understand about the governing parameters involved in this complexation. The inclusion of flavone molecules inside the cavity of cucurbit [7]uril molecules was studied theoretically to decipher the molecular orientation of flavones in the presence of cucurbit [7]uril. The structure of HOMO and LUMO of the complexes between cucurbit [7]uril with flavones was reported. This study will be helpful to get the knowledge about the modulation of photophysical properties of the flavones molecules on addition of macrocyclic host cucurbit [7]uril. This study will be helpful for the use of cucurbit [7]uril as a potential drug delivery system.

Supramolecular interaction of a cancer cell photosensitizer in the nanocavity of cucurbit[7]uril: A spectroscopic and calorimetric study.

The interaction of small biologically active molecules in the nanocavity of supramolecular host is very interesting and thriving research area. In the presence of supramolecular host the absorption and emission properties of small biologically active molecules were modulated several folds compared to bulk solution. In this study we have investigated the supramolecular interaction of a cancer cell photosensitizer molecule harmane in the presence of cucurbit[7]uril (CB7) as host in aqueous buffer solution (pH∼7.2). We have used steady state absorption, emission and time resolved fluorescence spectroscopy techniques. The thermodynamics of the binding between harmane in the nanochannel of CB7 were studied by using isothermal titration calorimetry (ITC) method. The emission properties of harmane are modulated several fold in the presence of CB7. ITC study indicates that the complexation between harmane and CB7 are enthalpically favourable.

Surfactants induced release of a red emitting dye from the nanocavity of a molecular container: A spectroscopic and calorimetric study.

Supramolecular interaction of a red emitting dye Nile blue A (NBA) with Cucurbit[7]uril (CB7) in aqueous solution was studied and the release of the dye from the hydrophobic cavity of CB7 was reported. To investigate the supramolecular host-guest complex formation and release of dye, we have used the steady state absorption, fluorescence and time resolved fluorescence emission spectroscopy, (1)H NMR spectroscopy and isothermal titration calorimetry (ITC). The spectral properties of NBA were changed in the presence of CB7. The change in spectral features of NBA in presence of CB7 indicates the formation of supramolecular host-guest complexes. By using the SED equation the diameter of the complex was estimated. The complex formation further affirmed by the (1)H NMR study. Upfield and downfield shifts of the protons of NBA was observed in both the aliphatic and aromatic region. From the ITC measurement, we have drawn up the forces involved for the complexation of NBA with CB7. We have studied the release of NBA from the hydrophobic cavity of CB7 by using ionic, neutral surfactants and ionic liquid with the help of spectroscopic and calorimetric techniques. It is observed that on addition of SDS and ionic liquid (<cmc) ion-pair formation takes place between NBA and surfactant monomer whereas, it was not observed for neutral and cationic surfactant. Above cmc of the surfactants, complex is formed between NBA and micelle.

Supramolecular Interactions of Nonsteroidal Anti‐inflammatory Drug in Nanochannels of Molecular Containers: A Spectroscopic, Thermogravimetric and Microscopic Investigation

Supramolecular host-guest complexation between the nonsteroidal anti-inflammatory drug indomethacin (IMC) and molecular containers were investigated. The weakly fluorescent drug molecule becomes highly fluorescent on complexation with different molecular containers, and time-resolved fluorescence emission spectroscopy reveals that the lifetime components of IMC significantly increase in the presence of molecular containers, compared with the lifetimes in neat water. The respective solid host-guest complexes were synthesised and characterised by Fourier transform infrared and (1) H nuclear magnetic resonance spectroscopic analysis. Microscopy techniques were used to analyse modifications of the surface morphology, owing to the formation of supramolecular complexes. The effect of the molecular container on the optical properties of IMC has also been investigated to determine the effect of nanochannels of different size and structure.

Interaction of Biologically Active Flavins inside Bile Salt Aggregates: Molecular Level Investigation.

In this work we have studied the photophysics of biologically active flavin molecule lumichrome (LCM) in different bile-salt aggregates. With alteration of the functional groups of the bile salts, the photophysics of confined fluorophore is largely affected and shows difference in their spectral behavior. This study also reveals the selective prototropic species of LCM present in bile salt aggregates. In the presence of the bile salt aggregates, LCM molecule shows excitation and emission wavelength-dependent emission properties, indicating switch over of the structural change of different prototropic form of the LCM molecule. The observation of higher rotational relaxation time in NaDC aggregates compared to NaTC aggregates clearly reflects that NaDC aggregates are more rigid due to its greater hydrophobicity and large in size, which is capable to bind the guest molecule more into their nanoconfined medium. Moreover, due to less acidic nature, NaDC aggregates have more ability to accept hydrogen bond from the LCM molecule and show the selective formation of isoalloxazine N10 anion (A1 monoanionic form) of LCM.

Photophysics of crystal violet lactone in reverse micelles and its dual behaviour

In this article, the photophysics of Crystal Violet Lactone (CVL) in aqueous and non-aqueous reverse micelles (RMs) have been explored using UV-vis absorption, steady-state emission and picosecond time-resolved fluorescence emission spectroscopic techniques. CVL exhibits dual emission bands (CTA and CTB states of CVL) in a polar aprotic solvent, whereas when this molecule is entrapped in the RMs, it exhibits a single emission band (CTA). In the case of all the RMs, the CTA → CTB transformation is retarded due to the influence of polarity, viscosity and proticity. Moreover, in the case of viscous solvents (ethylene glycol and glycerol), a single emission band is found. The hydrogen-bond-donating solvent molecule also quenches the CTB emission band of CVL. This is the first report on the photophysics of the CVL molecule in biomimicking organised assemblies, in which the opposite spectral features were observed in the RMs at different excitation wavelengths. The average rotational relaxation time increases in the respective RMs compared to their respective solvent, with the exception of neat glycerol, wherein the rotation of CVL is practically hindered. In the case of EG and glycerol RMs, the rotational relaxation is even more retarded due to the gradual swelling of the RM cores. Herein, the hydrodynamic friction, coupled with the dielectric friction, causes such rotational motion to be quite slow.

Photophysics and Rotational Dynamics of a Hydrophilic Molecule in a Room Temperature Ionic Liquid

We have studied the photophysics and rotational diffusion of hydrophilic solute 7‐(N, N′‐diethylamino)coumarin‐3‐carboxylic acid (7‐DCCA) in a room temperature ionic liquid methyltrioctylammonium bis(trifluoromethylsulfonyl) imide ([N1888][NTf2]). Comparison of activation energies of viscous flow and nonradiative decay shows that the photophysical properties of 7‐DCCA are not guided by the bulk viscosity of the medium but are dependent on the specific solute solvent interaction and structural heterogeneity of the medium. The rotational relaxation behaviour of 7‐DCCA in [N1888][NTf2] shows significant deviation from the Stokes Einstein Debye hydrodynamic model of rotational diffusion. This is indicative of the influence of specific solute solvent interaction on the rotational relaxation behaviour of 7‐DCCA. Comparison of activation energy of rotational relaxation with activation energy of viscous flow clearly reinforces our assumption that the structural heterogeneity of the medium and specific solute solvent interaction plays a dominant role on the rotational diffusion instead of bulk viscosity.