Tapas Majumdar

A Strategic Design of an Opto-Chemical Security Device with Resettable and Reconfigurable Password Based Upon Dual Channel Two-in-One Chemosensor Molecule

A simple strategy is proposed to design and develop an intelligent device based on dual channel ion responsive spectral properties of a commercially available molecule, harmine (HM). The system can process different sets of opto-chemical inputs generating different patterns as fluorescence outputs at specific wavelengths which can provide an additional level of protection exploiting both password and pattern recognitions. The proposed system could have the potential to come up with highly secured combinatorial locks at the molecular level that could pose valuable real time and on-site applications for user authentication.

Kinetic exploration supplemented by spectroscopic and molecular docking analysis in search of the optimal conditions for effective degradation of malachite green

The degradation of malachite green (MG) by an alkaline hydrolytic process has been explored spectrophotometrically. The kinetics of the reaction have been meticulously studied under the influence of cationic alkyltrimethylammonium bromide (DTAB, TTAB and CTAB) surfactants, α-, β- and γ-cyclodextrins (CDs) and surfactant–β-CD mixed systems applying pseudo-first order conditions at 298 K. The surfactants and cyclodextrins individually catalyze the hydrolytic rate, whereas surfactant–β-CD mixed systems exhibit both an inhibiting and catalytic influence depending on the surfactant concentrations. The kinetic results have been explained precisely based on the pseudo-phase ion exchange (PIE) model of micelles and CD-catalyzed model of CD systems. The surfactants exhibit micellar surface catalysis, while CDs accelerate the rate by forming MG–CD inclusion complexes, thereby facilitating nucleophilic attack of its ionized secondary hydroxyl group on the carbocation center of MG. The encapsulation of MG within the supramolecular host cavity of the CDs has been investigated diligently using a steady-state absorption spectroscopic technique. The result shows 1 : 1 host–guest complexation with different relative orientations of the guest (MG) inside the hosts. Studies employing density functional theory (DFT) as well as molecular docking analysis provide valuable insight on the insertion mechanism. The results reveal that quantitative analysis can be utilized to predict the optimum conditions for the fastest degradation of MG in ambient environments.

Shipment of a Photodynamic Therapy Agent into Model Membrane and its Controlled Release: A Photophysical Approach

Harmine, an efficient cancer cell photosensitizer (PS), emits intense violet color when it is incorporated in well established self assembly based drug carrier formed by cationic surfactants of identical positive charge of head group but varying chain length, namely, dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB). Micelle entrapped drug emits in the UV region when it interacts with non-toxic β-cyclodextrin (β-CD). Inspired by these unique fluorescence/structural switching properties of the anticancer drug, in the present work we have monitored the interplay of the drug between micelles and non-toxic β-CDs. We have observed that the model membranes formed by micelles differing in their hydrophobic chain length interact with the drug differently. Variation in the surfactant chain length plays an important role for structural switching i.e. in choosing a particular structural form of the drug that will be finally presented to their targets. The present study shows that in case of necessity, the bound drug molecule can be removed from its binding site in a controlled manner by the use of non-toxic β-CD and it is exploited to serve a significant purpose for the removal of excess/unused adsorbed drugs from the model cell membranes. We believe this kind of β-CD driven translocation of drugs monitored by fluorescence switching may find possible applications in controlled release of the drug inside cells.

Photophysical, NMR and density functional study on the ion interaction of norharmane: proton transfer vs. hydrogen bonding

Interactions of norharmane (S), with different ions have been studied using spectroscopy, NMR and density functional studies. A significant gradual change both in absorption and emission spectra was observed upon addition of fluoride anions. The spectral change in the absorption and emission bands of norharmane (S) is found to be specific to fluoride ion; it is unaffected by the presence of other ions. Hydrogen bond mediated proton transfer from norharmane to fluoride is mainly attributed to the fluoride selective signaling behavior. Calculations of the transition energies of the norharmane (S), anionic species of norharmane (S−) and hydrogen bonded complexes (S⋯F−) show that the added fluoride anion could capture the proton in the free N–H moiety instead of the hydrogen-bonding one. Experimental results reveal that the long-wavelength absorption band in the presence of fluoride ion is due to the formation of anion.

Binding interaction of a newly developed bisindole drug molecule with α-cyclodextrin: face to face shielding of indole hoops

Binding interactions of a newly developed drug molecule namely 3,3′-bis(indolyl)-4-chlorophenylmethane (BICPM) with α-cyclodextrin have been studied using steady state and picosecond time resolved fluorometric techniques. A significant increase both in steady state anisotropy (r) and in the average rotational correlation time in the CD environments compared with that in a pure aqueous phase indicates that the rotational dynamics of BICPM are substantially slowed down upon binding with the α-cyclodextrin. Critical spectral analysis reveals the formation of two types of inclusion complex between the fluorophore and α-cyclodextrin (α-CD) depending on the relative population of the two. The stoichiometries and association constants of these complexes have been determined by monitoring the fluorescence data. Hydrodynamic radii of the formed 1 : 2 probe-α-cyclodextrin supramolecular complex have also been determined. From the determined hydrodynamic radii and from molecular docking analysis it is argued that probably two CD cavity shields the indole moiety in a face-to-face manner.