Pritam Ghosh

Recognition of fluoride anions at low ppm level inside living cells and from fluorosis affected tooth and saliva samples

A simple Schiff base chemosensor 2-((2-(2,4-dinitro phenyl)hydrazono)methyl)-4-nitrophenol (L) has been developed as a colorimetric and fluorimetric ‘turn on’ sensor for fluoride (F−). F− recognition at ppm levels from mouth rinses and a toothpaste water solution has been successful. Significantly, L can detect F− from fluorosis affected tooth and saliva samples by similar colorimetric changes. A test kit for F− detection from a DMSO–water (1 : 1) mixture is also engineered. Intracellular F− from pollen grains of Techoma stans and Candida albicans (a diploid fungus), grown in 10−6 (M) F− contaminated water has been successfully detected under a fluorescence microscope.

A simple and dual responsive efficient new Schiff base chemoreceptor for selective sensing of F− and Hg2+: application to bioimaging in living cells and mimicking of molecular logic gates

A novel colorimetric hydrazine-functionalized Schiff base chemoreceptor, NPMP, was synthesized following a simple one-step Schiff base condensation pathway. NPMP showed selective colorimetric change from faint yellow to yellowish orange in the presence of biologically ubiquitous fluoride (F−). It also showed a ‘turn off’ fluorescent response in the presence of F− that could effectively distinguish it from all anions tested except acetate. Acetate (OAc−) caused a weak response, while other anions like chloride, bromide, iodide, phosphate, hydrogen sulfate and nitrate did not have any observable effect on the NPMP receptor (E)-4-nitro-2-((2-(perfluorophenyl)hydrazono)methyl)phenol. Recognition of F− in the presence of NPMP can be explained in light of multiple H-bonding interactions, as well as acid–base interactions between host receptor and guest F−. Interestingly, NPMP also showed enormous potential as a staining agent in determining the presence of low levels of intracellular fluoride. Moreover, it was found that in NPMP⋯F− solutions, incorporation of Hg2+ showed observable optical changes, revealing that this compound is a smart material. Optical responses of NPMP can mimic a molecular logic gate (INHIBIT gate). This can be interpreted as a combination of an AND gate with a NOT function. It also represented a potential ‘Write–Read–Erase–Read’ memory function reflecting multi-writing ability.

Exploratory studies towards various anion recognition chemistry by two different sized cleft shaped organic ligands

Indole and urea based two organic receptors have been synthesized by an easy synthetic process. These two receptors have strong sensitivity and selectivity for several bio-relevant anions. Receptor 1 and 2 were synthesized from indole-2-carboxylic acid and p-anisidine respectively, which are low cost starting materials. Receptor 1 can selectively sense anions like F(-), OAc(-) and H2PO4(-), while receptor 2 can only sense F(-) and H2PO4(-). Both receptors are silent toward anions like Cl(-), Br(-), I(-) and NO3(-). It is the difference in their shape and size which are responsible for different anion sensing. The nature of these host-guest type interactions was analyzed by convenient spectrophotometric techniques like UV-Vis, fluorescence, (1)H NMR, FT-IR studies and also confirmed by electrochemical techniques like cyclic voltammetry studies of the two ligand receptors with convenient anions. Between receptor 1 and 2, receptor 2 was crystallographically characterized also.

How explosive TNP interacts with a small tritopic receptor: a combined crystallographic and thermodynamic approach

Herein, the interaction of explosive and pollutant nitroaromatics (epNACs) like 2,4,6-trinitrophenol (TNP) with a small molecular probe has been explored by X-ray crystallography and thermodynamics of the crystallization. The supramolecular host with an unusual crystal packing has been used for the detection of TNP. Fluorescence quenching through the RET–PET–ICT–ACQ mechanism results in a strong pi–pi interaction between the receptor and TNP. Both simulated and experimental FTIR spectroscopies have been performed to investigate the sensing event from solid phase perspective. The enhancement in enthalpy (ΔH) of the host–guest adduct suggests an endothermic reaction suitable for sensing a heat-sensitive explosive like the TNP molecule. On the other hand, entropy (ΔS) enhancement in the crystal formation suggests trapping or releasing of the solvent molecule. In reality, it is noticed from the SCXRD study that acetonitrile undergoes co-crystallization in the host–guest adduct. Ultimate energy (Efinal = Eadduct − Eprecursor) of adduct is lowered up to −919.89 Hartree, which favors the crystallization. The recognition event is highly selective for TNP, Cu2+, and F− among the other analytes, where TNP shows fluorescence turn-off and Cu2+ and F− show turn-on response at different spectroscopic energy levels. Indeed, the receptor proves to be a novel tritopic receptor for selective detection of cation, anion, and neutral analytes with a distinguishable signal. In real time stepping, chromatographic strips have been designed for on-spot chromogenic and fluorogenic detection of the TNP-like explosive molecule for homeland safety.

A novel ditopic chemosensor for cadmium and fluoride and its possible application as a pH sensor

A urea-based BPC [1,5-bis(perfluorophenyl)carbonohydrazide] molecule with four acidic NH protons has been synthesized by a facile synthetic process. The molecule was found to be a ditopic chemosensor for Cd2+ and F− ions. BPC was synthesized from low-cost starting materials, dinitrophenyl hydrazine and triphosgene. The host–guest interactions between the ions (Cd2+ and F−) were not only confirmed by convenient spectroscopic techniques such as UV-Vis, PL, 1H-NMR, FT-IR, and cyclic voltammetry but also through modern DFT, the results of which were in good agreement with the experimental results. In vitro studies in human cancer cells (HeLa cells) were successfully performed with BPC and Cd2+ using fluorescence microscopy. The reversible UV-Vis response for BPC with F−, OH− and H+ mimics multiple logic functions and can be used for several complex electronic circuits based on logic operations. The pH sensor (BPC) can be further interfaced with suitable circuitry interfaced with appropriate programming for ease of access and enhancement of its practical applications.

Solid Waste Management in India: A Brief Review

In the twenty-first century, major emphasis should be levied on environmental safety and concern regarding human health. In this relevance, solid waste management need major attention. Awareness in society is profusely obligatory for minimization of solid waste generation. Careful study reveals that municipal solid waste (MSW) provides a major contribution to the total amount of solid waste. But e-wastes are the most frequently growing waste which is also an efficient source of various toxic elements. Globally, upsurge in the demand of nuclear energy enhances the generation of radioactive solid waste (RSW) that may be responsible for harmful effect of radiation. On the other hand, hospital solid wastes (HSWs) have great impact on environment and public health as it is the carrier of infectious diseases and other toxic elements. Biodegradable organics are the major content of agriculture solid waste (ASW) along with some pesticides and heavy metals. The total amount of solid waste (SW) is enhancing day by day, and as a consequence proper solid waste management (SWM) methods are necessary which could minimize the total amount of SW as well as its hazardous effect on environment. This review is focused on generation of different SWs and corresponding techniques of SWM starting from conventional tools to modern technique like refuse-derived fuel (RDF), pyrolysis, incineration together with their advantages and limitations.

A quinoline-based compound for explosive 2,4,6-trinitrophenol sensing: experimental and DFT-D3 studies

A quinoline-based Schiff base compound, 2,5-dimethylbis(quinolin-2-ylmethylene)benzene-1,4-diamine (DQB), has been found to be a chemosensor for 2,4,6-trinitrophenol (TNP). DQB has been synthesized by condensation between two equivalents of quinoline-4-carboxaldehyde and one equivalent of 2,5-dimethyl-1,4-diaminobenzene in methanol under ambient reaction conditions and characterized by using standard spectroscopic methods. It shows an emission band at 440 nm with high intensity (λex = 390 nm). The emission intensity is quenched severely in the presence of TNP while other nitroaromatic compounds fail to reduce the intensity, signifying high selectivity towards TNP. The fluorescence quenching mechanism can be explained by theoretical calculations as an RET-ICT based pathway.