Soumen Ghosh

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).

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.

Highly sensitive and selective “naked eye” sensing of Cu(II) by a novel amido–imine based receptor: a spectrophotometric and DFT study with practical application

We report the synthesis of a novel compound (E)-bis-N′-((1H-pyrrol-2-yl)methylene)-pyridine-2,6-carbohydrazide and its sensing ability to detect copper(II) ion in aqueous medium by a sharp color change from yellow to brown, the sensing limit being 4.0 × 10−9 M. Theoretical modeling of the compound and its copper complex was performed. Practical utility was explored by successful paper strip response.

Hydrazine bridged coumarin-pyrimidine conjugate as a highly selective and sensitive Zn2 + sensor: Spectroscopic unraveling of sensing mechanism with practical application

We report the synthesis and Zn2+ sensing of a novel coumarin-hydrazine conjugate 3-{1-[(4, 6-Dimethyl-pyrimidin-2-yl)-hydrazono]-ethyl}-chromen-2-one (3). Compound 3 can act as a neat fluorescent Zn2+ sensor by an increment in fluorescence intensity along with an appreciable red shift. Fluorescence enhancement is caused by complexation through cis-trans isomerization process in the presence of Zn2+ ion. The practical utility of 3 was demonstrated by successful test kit experiment to detect Zn2+ in water under UV-light.

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.

Binding of a potential chloride channel blocker with an anionic surfactant and subsequent release in solution: effect of a hydrotropic solute in the post-micellar region

The present work demonstrates a thorough description of the differential interactions of a potential chloride channel blocker, 9-methyl anthroate (9-MA), with a charged surfactant, sodium dodecyl sulfate (SDS), in the pre- and post-micellar regime along with the consequences of the addition of a hydrotropic salt in the post-micellar region. The modulated photophysical properties of the emissive probe within the biomimetic environment have been spectroscopically monitored to gain an insight into the binding interaction. The moderate strength of the binding phenomenon as revealed by Benesi–Hildebrand analysis, as well as the hindrance exerted by the binding process towards the aggregation of the surfactants, paves the way to rationalize the observation of the exclusion of the drug to the bulk after micelle formation to be an outcome of a free energy advantage in the thermodynamically favorable micellization process. A substantial increase in the bulk viscosity of the medium in the presence of the hydrotrope in the post-micellar region coupled with a non-covalent binding between the alkane chains of the salt and the hydrophobic drug has also been unveiled from steady state and time-resolved fluorimetric perspectives.

Fluorometric detection of nitroaromatics by fluorescent lead complexes: A spectroscopic assessment of detection mechanism

Three Schiff base ligands such as 2‑[(2‑Hydroxy‑3‑methoxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL1), 2‑[(2‑Hydroxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL2), 2‑[(3,5‑Dichloro‑2‑hydroxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL3) have been synthesized by condensation of aldehydes (such as 3,5‑Dichloro‑2‑hydroxy benzaldehyde, 2‑Hydroxy‑benzaldehyde, and 2‑Hydroxy‑3‑methoxy‑benzaldehyde) with Tris‑(hydroxymethyl)amino methane and characterized by IR, UV-vis and 1H NMR spectroscopy. Then all these three ligands have been used to prepare Pb(II) complexes by reaction with lead(II) acetate tri-hydrate in methanol. In view of analytical and spectral (IR, UV-vis and Mass) studies, it has been concluded that, except HL2, other two ligands form 1:1 metal complexes (1 and 3) with lead. Between two complexes, complex 3 is highly fluorescent and this property has been used to identify the pollutant nitroaromatics. Finally, the quenching mechanism has been established by means of spectroscopic investigation.