Aniruddha Ganguly

Solvent modulated photophysics of 9-methyl anthroate: exploring the effect of polarity and hydrogen bonding on the emissive state.

Photophysical properties of an anthracene derivative 9-methyl anthroate (9-MA) have been investigated using absorption and emission spectroscopy, in combination with quantum chemical calculations. Solvatochromic effects on the Stokes shifted emission band clearly demonstrate the highly polar character of the excited state, which is also supported by the enhancement of dipole moment of the molecule upon photoexcitation. The emission band has been found to be dependent on polarity and hydrogen-bonding ability of the solvents. Multiple linear regression analysis method has been utilized to rationalize the effect of hydrogen bonding interaction on the emissive state, which was further confirmed by the analysis of the non-radiative decay constants and urea induced H-bonding disruption study. The experimental results correlate well with theoretical predictions obtained via density functional theory (DFT).

Deciphering the interaction of a model transport protein with a prototypical imidazolium room temperature ionic liquid: effect on the conformation and activity of the protein.

The present contribution reports the interaction of a prototypical surface-active room temperature ionic liquid (RTIL) viz., 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) with a globular transport protein bovine serum albumin (BSA). The BSA-RTIL binding isotherm constructed from conductometric measurements is found to be well reproduced from fluorescence spectroscopy and thus revealing the various interaction zones as a function of the RTIL concentration. The present work delivers particular emphasis to delineate the denaturing action of RTIL on the native protein and in complementarity the effect of RTIL binding on functionality of BSA is explored in terms of esterase-like activity of BSA. The intrinsic time-resolved fluorescence decay and rotational-relaxation dynamics of the protein suggests swelling of the protein rather than aggregation during RTIL-induced denaturation. The result of molecular modeling based on blind docking simulation is found to abet the inferences drawn from experimental results reasonably well. The molecular modeling technique reveals the favorable binding location of the RTIL to be in the hydrophobic domain IIIA (drug site 2) of BSA. The thermodynamic parameters evaluated for the RTIL-BSA binding phenomenon also identifies the pivotal role of hydrophobic force in the interaction.

Selective fluorescence sensing of Cu(II) and Zn(II) using a simple Schiff base ligand: naked eye detection and elucidation of photoinduced electron transfer (PET) mechanism.

A simple Schiff base compound 2-((cyclohexylmethylimino)-methyl)-naphthalen-1-ol (2CMIMN1O) has been synthesized and characterized by (1)H NMR, (13)C NMR and FT-IR spectroscopic techniques. A significantly low emission yield of the compound has been rationalized in anticipation with photo-induced electron transfer (PET) from the imine receptor moiety to the naphthalene fluorophore unit. Consequently, an evaluation of the transition metal ion-induced modification of the fluorophore-receptor communication reveals the promising prospect of the title compound to function as a chemosensor for Cu(2+) and Zn(2+) ions selectively, through remarkable fluorescence enhancement as well as visual changes. While perturbation of the PET process has been argued to be the plausible mechanism behind the fluorescence enhancement, the selectivity for these two metal ions has been interpreted on the grounds of an appreciably strong binding interaction. Particularly notable aspects regarding the chemosensory activity of the compound is its ability to detect the aforesaid transition metal ions down to the level of micromolar concentration (detection limit being 2.74 and 2.27ppm respectively), along with a simple and efficient synthetic procedure.

Amido-Schiff base derivatives as colorimetric fluoride sensor: Effect of nitro substitution on the sensitivity and color change

A series of Schiff bases synthesized by the condensation of benzohydrazide and -NO2 substituted benzaldehyde have been used as selective fluoride ion sensor. Test paper coated with these synthetic Schiff bases (test kits) can detect fluoride ion selectively with a drastic color change and detection can be achieved by just using the naked-eye without the help of any optical instrument. Interestingly, the position of -NO2 group in the amido Schiff bases has an effect on the sensitivity as well as on the change of color of species.

Quantum chemical exploration of the intramolecular hydrogen bond interaction in 2-thiazol-2-yl-phenol and 2-benzothiazol-2-yl-phenol in the context of excited-state intramolecular proton transfer: a focus on the covalency in hydrogen bond.

The present work demonstrates a computational exploration of the intramolecular H-bond (IMHB) interaction in two model heterocyclic compounds - 2-thiazol-2-yl-phenol (2T2YP) and 2-benzothiazol-2-yl-phenol (2B2YP) by meticulous application of various quantum chemical tools. Major emphasis is rendered on the analysis of IMHB interaction by calculation of electron density ρ(r) and Laplacian ∇(2)ρ(r) at the bond critical point using the Atoms-In-Molecule methodology. Topological features based on ρ(r) suggest that at equilibrium geometry the IMHB interaction develops certain characteristics typical of a covalent interaction. The interplay between aromaticity and Resonance-Assisted H-Bond (RAHB) has also been discussed using both geometrical and magnetic criteria. The occurrence of IMHB interaction in 2T2YP and 2B2YP has also been criticized under the provision of the Natural Bond Orbital (NBO) analysis. The ESIPT phenomenon in the molecular systems is also critically addressed on the lexicon of potential energy surface (PES) analysis.

Modulation in prototropism of the photosensitizer Harmane by host:guest interactions between β-cyclodextrin and surfactants

The present contribution demonstrates the photophysics of a prospective cancer cell photosensitizer Harmane (HM) belonging to the family of β-carboline in mixed microheterogeneous environments of β-cyclodextrin (β-CD) and surfactants having varying surface charges using steady-state and time-resolved fluorescence spectroscopic techniques. The remarkable modulations in prototropic activities of the micelle-bound drug in the presence of β-CD evinces for disruption of the micellar structural integrity by β-CD. The results are meticulously discussed in relevance to the effect of a potential drug delivery vehicle (CD) on the membrane-mimetic micellar system. Further, application of an extrinsic fluorescence probe for monitoring such interactions is fraught by the possibilities of no less than three equilibria that can operate simultaneously viz., (i) surfactant-cyclodextrin, (ii) surfactant-fluorophore and (iii) cyclodextrin-fluorophore. This aspect highlights the enormous importance of the issue of suitability of the fluorescence probe to study such complicated systems and interaction phenomena. Also the varying interaction scenario of β-CD with the nature of the surfactant highlights the importance of precise knowledge of the strength and locus of drug binding in delineating such complex interactions. The results of the present investigation advocate for the potential applicability of the drug (HM) itself as a fluorescence reporter in study of such complex microheterogeneous interactions.

Inclusion of an Anthracene-based Fluorophore within Molecular Containers: A Comparative Study of the Cucurbituril and Cyclodextrin Host Families

In this paper, the binding interaction of a promising chloride channel blocker, 9-methyl anthroate (9-MA), with two different classes of molecular containers, β-cyclodextrins (β-CD and methyl-β-CD) and cucurbit[7]uril, having comparable cavity dimensions, has been thoroughly demonstrated via inspection of the modulation of the excited-state properties of the emissive molecule. Spectral data suggest that CB7 encapsulates the probe more efficiently in a 1:2 fashion, whereas the efficacies of β-CDs are relatively less and the corresponding stoichiometry is 1:1. Interestingly, despite being thermodynamically much more favorable than the probe-β-CD complexation equilibria, the fraction of probe-CB7 complex formed is appreciably smaller with respect to that of probe-β-CD complexes. This apparent inconsistency has been addressed via the proposition that since the formation of a 1:2 complex is entropically disadvantageous, it is anticipated that the activation barrier of the corresponding reaction is reasonably high, and thus only a small fraction of the reactants are able to surpass the energy barrier to form the products. This proposition has been thoroughly corroborated by fluorescence lifetime measurements at different temperatures.

Selective chromo-fluorogenic molecular sensor for dual channel recognition of Cu2+ and F−: effect of functional group on selectivity

The sensor HNHCB (3-hydroxy-naphthalene-2-carboxylic acid (4-cyano-benzylidene)-hydrazide) comprises a –CONH– group, –OH group, –CHN– linkage and an electron withdrawing –CN group that can act as both an anion (fluoride) and a cation (copper) sensor by two distinct output modes. It can detect fluoride by naked eye color change and copper by fluorescence enhancement. Interestingly, the nature of the substituent in HNHCB has an effect on the selectivity. The detection limit can be as low as 160 nM for Cu2+ and 1.3 μM for F−. DFT calculations have been performed to demonstrate the structure of HNHCB and its copper complex. Biological applications of HNHCB have been evaluated in HEK 293 and it was found to exhibit membrane permeability for the detection of Cu2+. The sensor HNHCB is also sensitive towards fluoride in commercially available toothpaste.

Interaction of a synthesized pyrene based fluorescent probe with CT-DNA: spectroscopic, thermodynamic and molecular modeling studies

The present study demonstrates the synthesis of a new pyrene based water soluble fluorescent probe and its interaction with Calf-thymus DNA. The interaction has been studied using various biophysical methods like absorption and fluorescence spectroscopy, optical melting, isothermal titration colorimetry and circular dichroic studies. Experimental results indicate the binding mode between the probe and DNA to be principally intercalative having a binding energy in the range of −7 to −8 kcal mol−1 and the binding process is favored by both negative enthalpy change and positive entropy change. A salt dependent study revealed that the binding is favored by both small ionic interaction and large nonionic interactions. All the data obtained from biophysical studies have been validated by a molecular modeling study.

Probing the location of methanol in methanol/AOT/n-heptane system: true microemulsion or bi-continuous medium?

Whether methanol can be effectively encapsulated within a reverse micellar core to form a true microemulsion is still a matter of debate. Thus, in this contribution, we have reported the modified photophysics of a potential chloride channel blocker 9-methyl anthroate (9-MA) in methanol/AOT/n-heptane reverse micelles and methanol/n-heptane binary mixture in order to assess the location of methanol by means of steady-state and time-resolved fluorescence spectroscopic techniques. By comparing the striking similarity between the photophysics of the probe in the methanol/AOT/n-heptane system and in the methanol/n-heptane binary mixture, we conclude that methanol does not form a true microemulsion but rather remains dissolved in the bulk nonpolar phase forming a bi-continuous medium owing to an appreciable mutual solubility between n-heptane and methanol.