Pritam Mukhopadhyay

Single-Electron Transfer Driven Cyanide Sensing: A New Multimodal Approach

A new SET-driven reaction-based strategy is reported for sensing of cyanide with indicators having low LUMO levels. The cyanide-specific reaction produces an air-stable radical anion marker and by virtue of its spin, charge, and the SOMO-LUMO-based electronic transition generates multimodal signal outputs. High selectivity and sensitivity (0.2-16 microM) were observed when compared to other reducing anions. This new indicator system exhibits regenerability and dip-stick sensing, and fabrication of an electronic sensing device for cyanide is demonstrated.

Assemblies of perylene diimide derivatives with melamine into luminescent hydrogels

We report unique and spontaneous formation of hydrogels of perylene derivatives with melamine. The luminescent gel network is formed by H-type aggregation of the perylene core, supramolecularly cross-linked by melamine units. As a result of controlled aggregation in the extended nanofibers, strong exciton fluorescence emission is observed.

Extraordinary Stability of Naphthalenediimide Radical Ion and Its Ultra-Electron-Deficient Precursor: Strategic Role of the Phosphonium Group

Stabilization of radical ions and highly electron-deficient systems under ambient conditions is of great significance. A new design concept is presented that applies the multifaceted features of the phosphonium group to achieve isolation of (a) the first naphthalenediimide (NDI) radical ion [(1a•+)BPh4(–)] as single crystals and (b) an ultra-electron-deficient NDI [(1a(2+))2BF4(–)] having the lowest LUMO level recorded for an NDI, overwhelming the formative tetracyanoquinodimethane (TCNQ) molecule. Both 1a•+ and 1a(2+) exhibit unprecedented stability to normal workup procedures, chromatography, and anion metathesis in open air. To our knowledge, this is the first instance where radical ions stable toward chromatography have been obtained, which is a noteworthy development in the field of synthetic radical chemistry. The crucial components of thermodynamic and kinetic stabilization, namely, the nonbonded P···O interaction, hypervalency, and propeller-like shape of the phosphonium groups in 1a(2+) and 1a•+, were substantiated by crystallography and theoretical studies. Natural bond orbital (NBO) calculations validated the P···O contact to be an nO → σP–C* orbital interaction. Spontaneous electron transfer reactions of 1a(2+) even in nonpolar solvents, anion−π interactions of 1a(2+) with the naphthalene core, and panchromism of 1a•+ are the other emergent properties. The high-yielding (∼90%) in situ synthesis of 1a•+ and the extraordinary stability fostered by the phosphonium group have the potential to turn hitherto unstable organic systems into a new genre of stable off-the-shelf systems.

Laterally non-symmetric aza-cryptands: synthesis, catalysis and derivatization to new receptors

Abstract Cryptands where the two bridgehead atoms like N or C or benzene units are connected by three bridges such that the donor atoms about the bridgeheads are different can be called laterally non-symmetric cryptands. These cryptands constitute a class which can be useful in several contemporary areas of research. The present article describes the synthesis of the cryptands and the use of metal cryptates in homogeneous catalysis, in the photochemical splitting of water to generate H 2 , in the cleavage of nucleic acids as chemical nucleases. These cryptands can be derivatized to have new receptors which might be useful as well.

Single electron transfer-driven multi-dimensional signal read-out function of TCNQ as an "off-the-shelf" detector for cyanide.

Herein we report the first applications of TCNQ as a rapid and highly sensitive off-the-shelf cyanide detector. As a proof-of-concept, we have applied a kinetically selective single-electron transfer (SET) from cyanide to deep-lying LUMO orbitals of TCNQ to generate a persistently stable radical anion (TCNQ(•-)), under ambient condition. In contrast to the known cyanide sensors that operate with limited signal outputs, TCNQ(•-) offers a unique multiple signaling platform. The signal readability is facilitated through multichannel absorption in the UV-vis-NIR region and scattering-based spectroscopic methods like Raman spectroscopy and hyper Rayleigh scattering techniques. Particularly notable is the application of the intense 840 nm NIR absorption band to detect cyanide. This can be useful for avoiding background interference in the UV-vis region predominant in biological samples. We also demonstrate the fabrication of a practical electronic device with TCNQ as a detector. The device generates multiorder enhancement in current with cyanide because of the formation of the conductive TCNQ(•-).

Creation of 1D [60]fullerene superstructures and its polymerization by γ-ray irradiation

Conventional sublimable solid solvents such as naphthalene, ferrocene and camphor finely dissolve [60]fullerene (C60) in the solution state. After cooling to room temperature and removal of the solid solvents from the composites, C60 forms fibrous superstructures that are characterized by scanning electron microscopy. X-Ray powder diffraction study and ATR/IR analysis show that the C60 superstructures preserve the fcc lattice as in pristine C60. NMR together with elemental analysis reveals the presence of significantly less solvent in the superstructures. We have attempted to immobilize or polymerize the superstructures by a γ-ray irradiation technique that eventually leads to the formation of a rod-like fullerene polymer. HR-TEM and photoluminescence studies support the formation of the superstructures and the subsequent γ-ray induced polymerization of C60, which will provide new avenues for the realistic application of these with unprecedented materials properties.

Synthesis of Octabromoperylene Dianhydride and Diimides: Evidence of Halogen Bonding and Semiconducting Properties

A facile synthesis of octabromoperylene-3,4,9,10-tetracarboxylic dianhydride (Br8-PDA) (1), its diimides (Br8-PDIs) (2a-e), and bis-, tris-, and tetra-amino substituted diimides (5a-c) with six, five, and four remaining substitutable Br atoms, respectively, is reported. Octabromination results in facile chemical/electrochemical reduction, radical anion formation, and red-shifted optical properties. For the first time, diverse halogen-bonding interactions were identified in the PDA/PDI, which along with the attractive electronic features enhance the electron-transport characteristics compared to the di-/tetra-brominated PDIs (3/4).

Deconvolution of a multi-component interaction network using systems chemistry

We describe the stepwise construction of an 8-component self-sorted system (1 - 8) by the sequential addition of components. This process occurs via a large number of states (28 = 256) and even a larger number of pathways (8! = 40320). A pathway (5, 6, 7, 8, 4, 3, 2, then 1) that is self-sorted at every step along the way has been demonstrated experimentally. Another pathway (1, 8, 3, 5, 4, 7, 2, then 6) resembles a game of musical chairs and exhibits interesting shuttling of guest molecules among hosts. The majority of pathways - unlike the special ones described above - proceed through several non self-sorted states. We characterized the remainder of the 40320 pathways by simulation using Gepasi and describe the influence of concentration and binding constants on the fidelity of the self-sorting pathways.

Potent Antimalarial Activity of Acriflavine In Vitro and In Vivo

Malaria continues to be a major health problem globally. There is an urgent need to find new antimalarials. Acriflavine (ACF) is known as an antibacterial agent and more recently as an anticancer agent. Here, we report that ACF inhibits the growth of asexual stages of both chloroquine (CQ) sensitive and resistant strains of human malarial parasite, Plasmodium falciparum in vitro at nanomolar concentration. ACF clears the malaria infection in vivo from the bloodstreams of mice infected with Plasmodium berghei. Interestingly, ACF is accumulated only in the parasitized red blood cells (RBCs) and parasite specific transporters may have role in this specific drug accumulation. We further show that ACF impairs DNA replication foci formation in the parasites and affects the enzymatic activities of apicoplast specific Gyrase protein. We thus establish ACF as a potential antimalarial amidst the widespread incidences of drug resistant Plasmodium strains.

A new class of three dimensional D–π–A trigonal cryptand derivatives for second-order nonlinear optics

Synthesis, crystal structures, linear and nonlinear optical properties of tris D–π–A cryptand derivatives with C3 symmetry are reported. Three fold symmetry inherent in the cryptand molecules has been utilized for designing these molecules. Molecular nonlinearities have been measured by hyper-Rayleigh scattering (HRS) experiments. Among the compounds studied, L1 adopts non-centrosymmetric crystal structure. Compounds L1, L2, L3 and L4 show a measurable SHG powder signal. These molecules are more isotropic and have significantly higher melting points than the classical p-nitroaniline based dipolar NLO compounds, making them useful for further device applications. Besides, different acceptor groups can be attached to the cryptand molecules to modulate their NLO properties.