Nitin Chattopadhyay

Dopamine is a clinically significant neurotransmitter whose abnormal concentration is associated with neurological disorders, while lemon yellow is a widely used synthetic food dye that poses potential health risks when consumed beyond permissible limits. Thus, the selection of these two analytes establishes the versatility of the carbon quantum dots (CQDs) across biologically and environmentally relevant systems. In this work, fluorescent CQDs are synthesized from locally available sour spinach via a hydrothermal route and employed for the simultaneous detection of dopamine and lemon yellow. The as‐prepared CQDs are thoroughly characterized using fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy, transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS) analyses. These CQDs exhibit strong blue photoluminescence centered around 450 nm and show efficient fluorescence “turn‐off” responses toward both the aforesaid analytes. CQDs can detect the analytes in the micromolar range. The quenching arises primarily from static interactions between the oxidized dopamine or the chromophoric groups of lemon yellow and the CQDs in the ground state. The practical applicability of the sensor is demonstrated through the successful detection of dopamine in human serum samples and lemon yellow in commercially available soft drinks.

Optical and spectroscopic detection of Fe( iii ) and TNP using an AIE promoting Schiff base chemosensor, HL.

Photophysics of 1,2-dicarbonyl compounds-benzil being a classic example-exhibiting multiple emissions has been the subject of extensive investigation over the past decades, targeting principally to their interesting, so called, cis-trans photoisomerization. Despite a host of explorations, several issues remained obscured, such as assignment of the high energy fluorescence observed in benzil and α-naphthil, as well as the possible coexistence of multiple conformers in the photoexcited states. The present account, mostly based on a series of our own experiments combining indigenous as well as state-of-the-art steady-state and time-resolved spectroscopic techniques, supported by quantum chemical calculations, offers an in-depth exploration of the complex photophysics of a series of 1,2-dicarbonyl compounds namely, benzil, α-naphthil, 2,2′-pyridil, α-furil, and 9,9′-anthril. The pioneering and ground-breaking features of the report include assignment of the high energy fluorescence of benzil and α-naphthil to originate from the respective S2 states, a challenge to Kasha’s rule; and coexistence of multiple conformers in the lowest excited singlet as well as triplet states. Interestingly, these characteristics are not found to be general behavior of the 1,2-dicarbonyl family but are very much specific to the individual molecular systems, as validated from the potential energy profiles simulated from the DFT and TDDFT based quantum chemical calculations. While unravelling the complex photophysics involving photoisomerization processes of the molecular systems in the series and capturing the intricate excited-state dynamics therein with enhanced clarity, we have cunningly adopted our pioneering experimental technique of freezing the solutions at 77 K independently in the presence and absence of the exciting radiation. Overall, this vivid and progressive account presents a pivotal step forward in understanding the photophysics of 1,2-dicarbonyl compounds.

One mono-nuclear Ni(II) complex [NiL(CH₃COO)] (1) and one di-nuclear Cu(II) complex, [Cu₂L₂(CH₃COO)2] (2), with pendant and bridging acetate moieties, respectively, have been synthesized using a novel N,N,O donor Schiff base ligand HL, 1-(((piperidine-2-ylmethyl)imino)methyl)naphthalene-2-al, prepared by the simple condensation of 2-hydroxy-1-naphthaldehyde and 2-amino methyl piperidine. With the aid of numerous spectroscopic studies, the three compounds described above have been properly characterized. The single crystal data analyses of both the complexes reveal that in complex 1, one deprotonated ligand, one pendant acetate ion, and one Ni(II) ion form a mononuclear distorted square planar geometry and in complex 2, each Cu(II) center connects with one deprotonated ligand and a double μ1.1-acetato-bridge forming a distorted trigonal bipyramidal geometry, while two acetate bridges connect two Cu(II) centers forming a dinuclear complex. After rigorous characterization, both the complexes are investigated to check their binding efficacy with biomacromolecules like DNA and HSA, and the results, obtained from a variety of biophysical studies like absorption, fluorescence, and circular dichroism-based titrations, clearly disclose that both the complexes have an affinity for binding with DNA and HSA. Fluorescence displacement analysis and a DNA melting study demonstrate different modes of binding for the two complexes with the DNA host, namely intercalative mode associated with groove binding for complex 1 and only groove binding for complex 2. Circular dichroism spectral analysis of HSA during interaction with the complexes confirms some structural changes in HSA upon binding. Determination of the thermodynamic parameters implies the binding interactions of HSA with the two complexes to be spontaneous. After a convincing study of the complex–biomacromolecule binding interactions, an MTT assay study on both cancer and normal cells reveals that of the two complexes, complex 2 is the better one, showing superior anticancer properties together with low toxicity to a normal cell. Finally, an apoptotic cell-killing pathway of the studied complexes has been confirmed by a nuclear staining study.

Perpetual exigency for environment friendly clean energy and powerful soft electronics has elevated the research on hydrogels in past two decades. Hydrogels are the amplifiers of material properties using manipulation in structure–property relationship via simple, economic yet effective routes. Herein, a set of composite and hybrid hydrogels are developed by hierarchical assembling of clay nanosheets and surfactant micelles those divulge the first example of memcapacitor gels and offer exceptional proton conductivity (1.66–4.34 × 10^–2 S cm⁻¹) as a gel material. Further, Congo red, Eosin Y, and Orange G are used to hybridize one of the composites to achieve three hybrid hydrogels. Such hybridization is found to regulate the memristive function selectively from the coupled effect of memcapacitance from the composite. The composite hydrogel highlights its volatile memory with encouraging robustness under environmental conditions, established through various current–voltage (I–V) experiments. The electrochemical behaviors including the high proton conductivity are realized from impedance measurements. Material characterizations, experimental results, and in silico optimized structures rationalize composite/hybrid network formation, capacitive/memristive responses, and enhanced proton conduction in the fabricated composite superstructures. Proposed structural models demonstrate two orthogonally oriented structural encryptions to be accountable for the expressed bifunctionality in the hierarchically designed superstructures.

The effect of ionic strength on the aggregation of planar dyes like nile red (NR) and coumarin-30 (C30) in aqueous medium has been explored. The dyes are known to undergo dimerization, resulting in fading of their respective colors in the visible range. The present study demonstrates that the fading process is accelerated appreciably upon increasing ionic strength of the solution through addition of soluble salts. Experiments consist of variation of cations (Na⁺, Mg²⁺ and Al³⁺) with different valencies in a series of salts keeping the anion same and a similar set with a variation of anions (NO₃ ⁻, SO₄ ²⁻ and PO₄ ³⁻), keeping the cation same. The question of involvement of ‘primary kinetic salt effect’ or ‘salting-out effect’ for accelerating the aggregation process has also been resolved. Using Na⁺, K⁺ and NH₄ ⁺ ions with the same counterpart NO₃ ⁻, our experimental results do not show any differential effect, in terms of making the aggregation process faster, and hence rule out any effect of Hofmeister series on the self-aggregation process. The detailed study explicitly establishes that it is the ‘primary kinetic salt effect’ and not the ‘salting-out effect’ that is involved in the present case.

Steady-state and time-resolved spectroscopic studies demonstrate that two members of the coumarin class of dyes, coumarin 7 (C7) and coumarin 30 (C30), undergo self-aggregation in water. The development of hypsochromically shifted new absorption bands in addition to the existing monomer bands with an increase in concentration of the dyes in an aqueous medium suggests that the aggregates are of H-type. An absorption-based kinetic study reveals that the rate of aggregation of C30 is an order of magnitude faster than that of C7. Second-order rate kinetics, as obtained from the half-life (t_1/2) data, implies that the aggregates are dimeric in nature. Observations of isosbestic points in area-normalized absorption spectra (ANAS) and isoemissive points in area-normalized fluorescence excitation spectra (ANFES) and time-resolved area-normalized emission spectra (TRANES) establish that ground-state monomer ⇌ dimer equilibria for both of the systems are preserved in the photoexcited state. The present study further establishes that β-cyclodextrin is the most efficient of the three common cyclodextrins in shifting the equilibria toward the monomer by encapsulating the monomers within its cavity, making β-CD a convenient modulator to control the self-aggregation process. Dynamic light scattering (DLS), quantum chemical calculations, and molecular docking studies provide further support to our propositions.