# Indian Association for the Cultivation of Science

• Kolkata, west bengal, India
Recent publications
Let f be a normalized Hecke–Maass cusp form of weight zero for the group SL2(Z)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$SL_2({\mathbb {Z}})$$\end{document}. This article presents several quantitative results about the distribution of Hecke eigenvalues of f. Applications to the Ω±\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Omega _{\pm }$$\end{document}-results for the Hecke eigenvalues of f and its symmetric square sym2(f)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^2(f)$$\end{document} are also given.
Exosomes are extracellular vesicles released by all cell types; perform several important functions such as cell to cell communication, growth, differentiation, etc. Exosomes elicit several signalling mechanisms as they carry information in the form of DNA, RNA or protein docked on them. We show that exosomes released from Mtb infected macrophages not only induce differentiation of naïve monocytes but also generate functionally active macrophages via MAPK dependent signalling mechanism through MK‐2 and NF‐κβ activation which is completely different from the differentiation induced by exosomes from un‐infected macrophages. Further, we elucidate unequivocally the signalling mechanism behind the enhanced release of exosome generation from infected macrophages driven by AKT phosphorylation involving Rab7a and Rab11a. Genes of both ESCRT dependent and independent pathways are found to be involved in enhanced exosomes release and are modulated by AKT. However, interestingly, the genes of the ESCRT independent pathway are dependent on NF‐κβ activation while the genes of the dependent pathway are not, suggesting two parallel signalling cascades operating in tandem. This article is protected by copyright. All rights reserved.
Interfacial water associated with phospholipids plays an important role in different biological processes such as fibrillation of disorder protein, neurotransmitter interaction with lipids and hydrated proton translocation. However, understanding the structural change of interfacial water and phospholipids during these biological processes is difficult due to the lack of appropriate selective technique and soft nature of these interfaces. Vibrational sum frequency generation (VSFG) is a second order nonlinear spectroscopic technique which has the inherent surface selectivity as well as sensitivity and hence, has been utilized to understand the properties of interfaces. In this review, the utilization of VSFG technique has been discussed in understanding the structural change of interfacial water and lipids during several biological processes.
This paper reports the adsorptive behavior of the 4-mercaptopyridine (4MPy) molecule soaked in gold nanoparticles (AuNPs) that remain embedded in the bilayer Langmuir−Blodgett (LB) film matrix of stearic acid (SA) for various soaking times (STs). The as-fabricated substrate proved to be an efficient SERS sensing platform that can sense the analyte 4MPy molecules at trace concentrations of ∼1.0 × 10 −9 M. The XPS study not only reveals the adsorption of 4Mpy molecules with AuNPs via a sulfur atom but also suggests partial degradation of the analyte molecule upon adsorption. This observation is further substantiated from the SERS spectral profile, which shows unusual broadening of the enhanced Raman bands of the molecule at higher STs. The experimental observations are supported by Born−Oppenheimer on-the-fly molecular dynamics (BO-OF-MD), time-resolved wavelet transform theory (WT), and the DFT calculations based on adcluster models. Selective enhancements of Raman bands in the SERS spectra further suggest the involvement of charge transfer (CT) interaction to the overall enhancements of Raman bands of the analyte molecule. The molecule → CT contribution has been estimated from electron density difference calculations and the corresponding CT distance; the amount of CT is also envisaged.
Green synthesis of urea under ambient conditions by electrochemical co‐reduction of N2 and CO2 gases using effective electrocatalyst essentially pushes the conventional two steps (N2 + H2 = NH3 and NH3 + CO2 = CO(NH2)2) industrial process at high temperature and high pressure, to the brink. The single step electrochemical green urea synthesis process has hit a roadblock due to the lack of efficient and economically viable electrocatalyst with multiple active sites for dual reduction of N2 and CO2 gas molecules to urea. Herein, copper phthalocyanine nanotubes (CuPc NTs) having multiple active sites (such as metal center, Pyrrolic‐N3, Pyrrolic‐N2, and Pyridinic‐N1) as an efficient electrocatalyst which exhibits urea yield of 143.47 µg h–1 mg–1cat and faradaic efficiency of 12.99% at –0.6 V versus reversible hydrogen electrode by co‐reduction of N2 and CO2 are reported. Theoretical calculation suggests that Pyridinic‐N1 and Cu centers are responsible to form CN bonds for urea by co‐reduction of N2 to NN* and CO2 to *CO, respectively. This study provides the new mechanistic insight about the successful electro‐reduction of dual gases (N2 and CO2) in a single molecule as well as rational design of efficient noble metal‐free electrocatalyst for the synthesis of green urea.
Development of a robust catalyst for selective reduction of CO2 directly into hydrocarbon fuels is very challenging from both energy and environmental perspectives as it offers a renewable and green route for the production of fuels. Herein, we report a novel catalyst synthesized via excess solution impregnation of Ru and Fe3O4 nanoparticles (NPs) on ceria promoted mesoporous silica SBA-15 support. The selective catalytic reduction of CO2 to methane was carried out in the presence of H2 over novel Ru-Fe3O4/CeOx-SiO2 (Ce³⁺/Ce⁴⁺, x=1.64) catalyst in a fixed bed reactor. The CO2 conversion was found to be 82% at 0.25 wt% ruthenium loading, 2.5 wt% iron loading, 575 K temperature, 20 bar pressure, 3000 mLg⁻¹h⁻¹ gas hour space velocity and H2 to CO2 mole ratio of 5:1. The close contact between ruthenium and Fe3O4 nanoparticles facilitated the reduction of CO2 through hydrogen spill-over effect at lower temperature, whereas ceria NPs acted as a promoter for this reduction reaction. The catalysts were characterized thoroughly using physicochemical techniques such as CO chemisorption, BET, TPR, TPD, XRD, SEM, HR- TEM, ICP-AES and XPS analyses. High surface area and large mesopores of silica support facilitated the fine dispersion of the active catalytic sites and oxygen vacancy as supported from the DFT study on the catalytic activity. Optimal process conditions could render much higher CO2 conversion efficacy for selective methane synthesis in comparison with previous investigations.
Phosphate based organic polymer networks (OPNs) have been synthesized for the first time for dye sorption and heterogeneous catalysis. The OPNs were sythesized by the polycondensation of POCl3 with di- and tri-hydroxy organic linkers e.g., quinol, 4,4'-biphenol, phloroglucinol and 1,3,5-(4-hydroxyphenyl)benzene. These show remarkably selective adsorption of cationic dyes methylene blue and propidium iodide via the electrostatic interaction of the polymers with the dyes. These OPNs also allow the in situ synthesis and stabilization of gold nanoparticles within the polymer networks which demonstrate effective heterogeneous, catalytic reduction of the aromatic nitro to amino group.
A series of small organic molecules having bis‐amide backbone containing hydrogen‐bond functionalities were rationally designed, synthesized and characterized to examine their ability to act as potential low‐molecular‐weight gelators (LMWGs). All the bis‐amides were decorated with identical 3‐pyridyl amide of L ‐phenylalanine moieties along with variously substituted terminal benzoyl groups. Gelation studies revealed that only 4‐methylphenyl substituted bis‐amide ( PME ) was capable of gelling both aqueous (DMSO/water) and methyl salicylate (MS) (an important solvent for topical formulation for medical applications) solvents; whereas 4‐chlorophenyl and 4‐bromophenyl substituted bis‐amides ( PCL , PBR , respectively) acted as organogelator for various organic solvents. On the contrary, 4‐nitrophenyl as well as 3,5‐dinitrophenyl substituted bis‐amides ( PNI , DNI , respectively) were unable to gel any solvents studied herein. The corresponding aqueous gel namely PME‐HG and three methyl salicylate gels PME‐MS , PCL‐MS and PBR‐MS were characterized by dynamic and table top rheology followed by electron microscopy. Single crystal X‐ray diffraction (SXRD) data revealed crucial insights into the supramolecular assembly of all the gelator and nongelator bis‐amides. Both PME‐HG and PME‐MS were rheoreversible – an important property in material applications. Interestingly, PME‐MS displayed remarkable material properties such as shape‐sustaining, loadbearing and self‐healing. Selected MS and aqueous gels loaded with nano‐molar iodine were found to possess anti‐bacterial property as revealed by zone inhibition assay.
We investigate exchange bias (EB) effect in two members with x = 0.4 and 0.6 of multiferroic Cu1-xCoxCr2O4 series, which are close to the interface between two structures at room temperature and represent with structures having I41/amd and Fd 3¯ m space groups, respectively. Both the compounds exhibit EB effect having EB field (HE) of 244 and 870 Oe at 2 K for x = 0.4 and 0.6, respectively with a cooling field of 10 kOe, which decrease with increasing temperature and disappear near their ferrimagnetic ordering temperatures (TN) close to 100 K. We note that higher HE correlates the higher coercivity (HC), which is found highest for x = 0.6 in the entire series of compounds. Our low temperature synchrotron diffraction studies for x = 0.6 confirm magnetoelastic as well as electroelastic coupling observed close to TN and ferroelectric ordering temperature (TFE). A structural transition to a polar Ima2 structure from I41/amd is observed close to 154 K, which coincides with TFE. Below TFE, thermal variation of structural distortion defined by (a-b)/(a+b) demonstrates significant magnetoelastic coupling. More importantly, the distortion parameter is found significantly higher than the rest member of the series and provides a hint for the highest corecivity in the entire series and correlates the higher EB effect. Current study demonstrates a correlation between structural distortion and EB effect and provides a clue of improving EB effect through the crystal structural engineering.
Machine learning-assisted configuration interaction (MLCI) has been shown earlier as a promising method in determining the electronic structure of the model and molecular Hamiltonians. In the MLCI approach to molecular Hamiltonians, it has been noticed that prediction is strongly dependent on the connectedness of the training and validation spaces. In this work, we have tested three different models with different output parameters (abs-MLCI, transformed-MLCI, and log-MLCI) to verify the robustness of training these models. We define robustness as the extent of error in prediction even when the spaces (training and validation) are nected. We notice that the log-MLCI model is best suited to this approach and is, therefore, a powerful model for accurate one-shot variational energies. This is tested not confor chemical bond breaking in water, carbon monoxide, nitrogen, and dicarbon molecules.
Heme proteins are involved in several key life processes in higher animals as well as in microorganisms. These include metabolism, hormone synthesis, and defense against pathogens in higher organisms. In microorganisms they catalyze chemical processes involved in assimilation of sulfur and nitrogen. Additionally, heme proteins act as electron transfer catalysts for energy processes that are ubiquitous in the biosphere. Heme proteins and their functions have been investigated for more than a century. In this chapter, we focus on a set of very well‐known heme enzymes. In addition to a broad overview of the function and mechanism of action of these enzymes, the chapter highlights the key features of these active sites that allow the same heme cofactor to catalyze a wide variety of chemical reactions, including electron transfer.
Hydroxychloroquine (HCQ) is an important antimalarial drug which functions plausibly by targeting the DNA of parasites. Salts play a crucial role in the functionality of various biological processes. Hence, the effect of salts (NaCl and MgCl2) on the binding of HCQ with AT- and CG-DNAs as well as the binding-induced stability of both sequences of DNAs have been investigated using the spectroscopic and molecular dynamics (MD) simulation methods. It has been found that the effect of salts on the binding of HCQ is highly sensitive to the nature of ions as well as DNA sequences. The effect of ions is opposite for the binding of AT- and CG-DNAs as the presence of Mg2+ ions enhances the binding of HCQ with AT-DNA, whereas the binding of HCQ with CG-DNA gets decreased on the addition of both ions. Similarly, the presence of Mg2+ enhances the stabilization of HCQ-bound AT-DNA, whereas the effect is opposite for the CG-DNA in the presence of both the ions. The MD simulation study suggests that the hydration states of both ions are different and they interact differently in the minor and major grooves of both the sequences of DNA which may be one of the reasons for the different binding of HCQ with these two sequences of DNA in the presence of salts. The information about the effect of salts on the binding of HCQ with DNAs in a sequence-specific manner may be useful in understanding the mechanism of the action and toxicity effect of HCQ against malaria.
Singlet fission (SF) is the process of formation of multiple excitons (triplet) from a locally excited singlet state. The mechanism of SF in polyacenes has been shown to proceed via a charge transfer intermediate state. However, carotenoids are not understood in the context of SF. This is possibly due to the complicated multireference nature of the low-lying excited states of carotenoids and the presence of a dark 21Ag state below the optically bright 1Bu state. In this work, we show that the dark Ag state in polyenes and/or carotenoids, along with the charge transfer states, plays a pivotal role in the SF process. We notice that the relative importance of these states varies with a change in geometry and the overall presence of multiple pathways is crucial to the success of the SF process in carotenoid aggregates and disordered geometries.
Benign and inexpensive metal catalyzed carbon-carbon and carbon-heteroatom bond formation reactions are of much interest in organic synthesis as these reactions provide green and cost effective routes. This account summarizes our recent contributions on the construction of carbon-carbon and carbon-heteroatom bonds using benign metal catalysts. A number of carbon-heteroatom bond formations such as C–N, C–O, C–S, C–Se, C–Te and C–P has been discussed. Mechanistic insights of several reactions are also reported.
The bacterial flagellar type III secretion system (fT3SS) is a suite of membrane-embedded and cytoplasmic proteins responsible for building the flagellar motility machinery. Homologous nonflagellar (NF-T3SS) proteins form the injectisome machinery that bacteria use to deliver effector proteins into eukaryotic cells, and other family members were recently reported to be involved in the formation of membrane nanotubes. Here, we describe a novel, evolutionarily widespread, hat-shaped structure embedded in the inner membranes of bacteria, of yet-unidentified function, that is present in species containing fT3SS. Mutant analysis suggests a relationship between this novel structure and the fT3SS, but not the NF-T3SS. While the function of this novel structure remains unknown, we hypothesize that either some of the fT3SS proteins assemble within the hat-like structure, perhaps including the fT3SS core complex, or that fT3SS components regulate other proteins that form part of this novel structure. IMPORTANCE The type III secretion system (T3SS) is a fascinating suite of proteins involved in building diverse macromolecular systems, including the bacterial flagellar motility machine, the injectisome machinery that bacteria use to inject effector proteins into host cells, and probably membrane nanotubes which connect bacterial cells. Here, we accidentally discovered a novel inner membrane-associated complex related to the flagellar T3SS. Examining our lab database, which is comprised of more than 40,000 cryo-tomograms of dozens of species, we discovered that this novel structure is both ubiquitous and ancient, being present in highly divergent classes of bacteria. Discovering a novel, widespread structure related to what are among the best-studied molecular machines in bacteria will open new venues for research aiming at understanding the function and evolution of T3SS proteins.
Herein, we demonstrate a nonconventional photocatalytic generation of Cl• from a common chlorinated solvent, dichloroethane, under aerobic conditions and its successful utilization toward the cross-dehydrogenative coupling of alkanes and azaarenes via hydrogen atom transfer with Cl•. The process is free from chloride salt, toxic oxidant, and UV light. It is applicable to a broad spectrum of substrates. The proposed mechanism involving Cl• is supported by a series of mechanistic investigations.
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• Department of Spectroscopy
• Department of Materials Science
• Department of Inorganic Chemistry
• Department of Materials Science
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