Department of Chemistry

Indian Institute of Technology Palakkad&nbsp;(IIT Palakkad or IIT PKD) is a public autonomous&nbsp;engineering&nbsp;and&nbsp;research&nbsp;institute located in&nbsp;Palakkad,&nbsp;Kerala. It was&nbsp;one of the five new&nbsp;IITs&nbsp;proposed in the&nbsp;2014 Union budget of India. The campus was inaugurated on 3 August 2015. The institute has 94 faculty, 978 students, and 63 non-teaching staffs.

IT Palakkad currently offers four-year Bachelor of Technology (B.Tech) and two years MS programmes in 8 different engineering disciplines including&nbsp;Computer Science, Electrical, Mechanical, Civil among others.

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IIT Palakkad

Rising global concerns posed by chemical and biological threat agents highlight the critical need to develop reliable strategies for the real-time detection of such threats. While wearable sensing technology is well suited to fulfill this task, the use of on-body devices for rapid and selective field identification of chemical agents is relatively a new area. This work describes a flexible printed textile-based solid-contact potentiometric sensor for the selective detection of fluoride anions liberated by the biocatalytic hydrolysis of fluorine-containing G-type nerve agents (such as sarin or soman). The newly developed solid-contact textile fluoride sensor relies on a fluoride-selective bis(fluorodioctylstannyl)methane ionophore to provide attractive analytical performance with near-Nernstian sensitivity and effective discrimination against common anions, along with excellent reversibility and repeatability for dynamically changing fluoride concentrations. By using stress-enduring printed inks and serpentine structures along with stretchable textile substrates, the resulting textile-based fluoride sensor exhibits robust mechanical resiliency under severe mechanical strains. Such realization of an effective textile-based fluoride-selective electrode allowed biosensing of the nerve-agent simulant diisopropyl fluorophosphate (DFP), in connection to immobilized organophosphorus acid anhydrolylase (OPAA) or organophosphorus hydrolase (OPH) enzymes. A user-friendly portable electronic module transmits data from the new textile-based potentiometric biosensor wirelessly to a nearby smartphone for alerting the wearer instantaneously about potential chemical threats. While expanding the scope of wearable solid-contact anion sensors, such a textile-based potentiometric fluoride electrode transducer offers particular promise for effective discrimination of G-type neurotoxins from organophosphate (OP) pesticides, toward specific field detection of these agents in diverse defense settings. © 2021

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Biosensors and Bioelectronics

Textile-based wearable solid-contact flexible fluoride sensor: Toward biodetection of G-type nerve agents

Copper oxide (CuO) is used as a reusable solid reagent for hydrogenation of nitroarenes to aminoarenes. The use of CuO resulted in 100 % conversion of 2.9 mmol of nitrobenzene to aniline in 45 s at room temperature using hydrazine hydrate as the reducing agent. During the reaction, CuO is converted to inactive metallic Cu which can be regenerated to active CuO by thermal oxidation. DFT simulations indicated facile formation of oxygen vacancies (EO,vac = −3.8 kJ/mol) on the surface of CuO (111) in reducing environment which is consistent with the XPS analysis. Oxygen vacancies facilitate stronger nitrobenzene binding (−148.5 kJ/mol) and reduced activation barrier (Ea = 36.4 kJ/mol) for N[sbnd]O dissociation. Motivated from this mechanistic insight -NO2 groups in various nitroarenes were selectively hydrogenated to [sbnd]NH2 groups using CuO. © 2021 Elsevier B.V.

Applied Catalysis B: Environmental

CuO as a reactive and reusable reagent for the hydrogenation of nitroarenes

The 3d transition metal-catalyzed enantioselective C-H functionalization provides a sustainable strategy for the construction of chiral molecules. A better understanding of the catalytic nature of the reactions and the factors controlling the enantioselectivity is important for rational design of more efficient systems. Herein, the mechanisms of Ni-catalyzed enantioselective C-H cyclization of imidazoles are investigated by density functional theory (DFT) calculations. Both the π-allyl nickel(ii)-promoted σ-complex-assisted metathesis (σ-CAM) and the nickel(0)-catalyzed oxidative addition (OA) mechanisms are disfavored. In addition to the typically proposed ligand-to-ligand hydrogen transfer (LLHT) mechanism, the reaction can also proceed via an unconventional σ-CAM mechanism that involves hydrogen transfer from the JoSPOphos ligand to the alkene through P-H oxidative addition/migratory insertion, C(sp2)-H activation via σ-CAM, and C-C reductive elimination. Importantly, computational results based on this new mechanism can indeed reproduce the experimentally observed enantioselectivities. Further, the catalytic activity of the π-allyl nickel(ii) complex can be rationalized by the regeneration of the active nickel(0) catalyst via a stepwise hydrogen transfer, which was confirmed by experimental studies. The calculations reveal several significant roles of the secondary phosphine oxide (SPO) unit in JoSPOphos during the reaction. The improved mechanistic understanding will enable design of novel enantioselective C-H transformations. This journal is © 2021 The Royal Society of Chemistry.

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Chemical Science

Understanding the unique reactivity patterns of nickel/JoSPOphos manifold in the nickel-catalyzed enantioselective C-H cyclization of imidazoles

Two β-diketiminato-magnesium anthracene complexes, [{(ArNacnac)Mg}2(μ-C14H10)] (ArNacnac = [HC(MeCNAr)2]−, Ar = mesityl (Mes) or 2,6-diethylphenyl (Dep)) react with 1 atm. CO at room temperature to give tetra-magnesium enediolate complexes [{(ArNacnac)Mg}4(O2C16H10)2]viacoupling of two molecules of CO with the anthracenediyl fragment. Similarly, reaction of magnesium anthracene, [Mg(THF)3(C14H10)], with CO afforded a low isolated yield of a tetra-magnesium complex bearing both dianthraceneylenediolate and dibenzocyclohepteneolateyl ligands. The presented reactions represent very rare examples of magnesium alkyl carbonylations that occur under mild conditions and in the absence of catalysts. © The Royal Society of Chemistry 2021.

Chemical Communications

Reductive coupling of CO with magnesium anthracene complexes: formation of magnesium enediolates

A modular synthetic platform for selective sensing and removal of Hg2+ was developed. This modular system possesses a unique feature to gradually increase the sensitivity even in competitive environments via increasing the number of Hg2+-coordinating units. This was made possible by synthesising a sequence-defined oligomer (SDO) with dithiocarbamate (DTC) as the Hg2+-coordinating unit in its backbone. Because it is a SDO, the Hg2+-coordinating unit was systematically increased to achieve a detection limit of 3 × 10-13 M, which is, to the best of our knowledge, the lowest reported. Any fluorophore can be synthetically attached via post-synthetic modification of the SDO to improve the efficiency of the sensor. Additionally, any functional group can be incorporated via custom synthesis of monomer to modulate the chemical property of the sensor. The same platform was shown as a removal system for Hg2+ with >95% removal efficiency via complexation and precipitation methods. © 2021 The Royal Society of Chemistry.

Polymer Chemistry

Sequence-defined oligomer as a modular platform for selective sub-picomolar detection and removal of Hg2+

The sudden outburst of Coronavirus disease (COVID-19) caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) poses a massive threat to global public health. Currently, no therapeutic drug or vaccine exists to treat COVID-19. Due to the time taking process of new drug development, drug repurposing might be the only viable solution to tackle COVID-19. RNA‐dependent RNA polymerase (RdRp) catalyzes SARS-CoV-2 RNA replication and hence, is an obvious target for antiviral drug design. Interestingly, several plant-derived polyphenols effectively inhibit the RdRp of other RNA viruses. More importantly, polyphenols have been used as dietary supplementations for a long time and played beneficial roles in immune homeostasis. We were curious to study the binding of polyphenols with SARS-CoV-2 RdRp and assess their potential to treat COVID-19. Herein, we made a library of polyphenols that have shown substantial therapeutic effects against various diseases. They were successfully docked in the catalytic pocket of RdRp. The investigation reveals that EGCG, theaflavin (TF1), theaflavin-3’-O-gallate (TF2a), theaflavin-3’-gallate (TF2b), theaflavin 3,3'-digallate (TF3), hesperidin, quercetagetin, and myricetin strongly bind to the active site of RdRp. Further, a 150-ns molecular dynamic simulation revealed that EGCG, TF2a, TF2b, TF3 result in highly stable bound conformations with RdRp. The binding free energy components calculated by the MM-PBSA also confirm the stability of the complexes. We also performed a detailed analysis of ADME prediction, toxicity prediction, and target analysis for their druggability. Overall, our results suggest that EGCG, TF2a, TF2b, TF3 can inhibit RdRp and represent an effective therapy for COVID-19. Communicated by Ramaswamy H. Sarma. © 2020 Informa UK Limited, trading as Taylor & Francis Group.

Journal of Biomolecular Structure and Dynamics

Plant-derived natural polyphenols as potential antiviral drugs against SARS-CoV-2 via RNA‐dependent RNA polymerase (RdRp) inhibition: an in-silico analysis

This work reports the catalytic activity of the trimetallic mixed-metal oxyhydroxide WFeCoO(OH) for the direct oxidation of cyclohexane to adipic acid (AA) without the use of concentrated HNO3. WFeCoO(OH) displayed a 40% conversion of cyclohexane and a 67% selectivity to AA under relatively milder conditions of temperature (90 °C) and pressure (1 atm). Experimental evidence confirmed the presence of acidic, basic, and redox sites on WFeCoO(OH). The detailed investigation revealed that doping W in the Co-FeO(OH) matrix increased the amount of surface lattice oxygen (OS-L) and caused a significant surge in acidity (5.1 mmol/g). The calculated deprotonation energy of WFeCoO(OH) was 1434 kJ/mol, and the trend in acidity was WCoO(OH) &lt; WFeCoO(OH) &lt; FeCoO(OH) ∼ CoO(OH). Energy calculations showed that WFeCoO(OH) had a high propensity to generate oxygen vacancies by the loss of either a water molecule or an oxygen atom (−132.2 or −140.9 kJ/mol, respectively). Basicity was generated due to the presence of conjugate pairs of the surface hydroxyl groups. The combined action of the trifunctional acidic, basic, and redox-active metal centers along with the oxygen vacancies was responsible for the enhanced catalytic performance. © 2021 American Chemical Society

ACS Catalysis

Direct Oxidation of Cyclohexane to Adipic Acid by a WFeCoO(OH) Catalyst: Role of Brønsted Acidity and Oxygen Vacancies

The folding–unfolding of a 16 residue polypeptide, a β–hairpin in B1 domain of protein G is investigated here to account for the factors assisting the extra stability of the polypeptide in the presence of an explicit solvent and even when a denaturant like urea is present in the medium. It is observed here that the backbone H–bond network well defines the folded state and is even capable of forming the folded state, but it is not the only criteria for making a stable β–hairpin fold. Factors such as the side chain H–bonds and the alignment of the certain hydrophobic group side chains play a prominent role in preserving the β–hairpin structure and thus providing an extra stability to the hairpin architecture. It is also affirmed that the mentioned hydrophobic groups side chain interactions are very crucial in holding the β–hairpin together and without which the hairpin collapses completely. We also confirm that the denaturant urea acts on the GB1–hairpin backbone H–bonds and in the presence of strong hydrophobic interactions with a consistent side chain H–bonding network, the denaturation being comparatively a slower process with respect to the protein devoid of the side chain interactions. Communicated by Ramaswamy H. Sarma. © 2021 Informa UK Limited, trading as Taylor & Francis Group.

An account on the factors determining the extra stability of the β–hairpin from B1 domain of protein G

A new hyper-crosslinked 4-amino-1,8-naphthalimide Tröger’s base containing pyridinium covalent organic polymer, TBNap-COP, was synthesised and employed as a ‘turn-off’ fluorescent chemosensor for nitroaromatic explosives. TBNap-COP was synthesised in quantitative yield using a one-step nucleophilic substitution reaction between a dipyridyl scaffold (TBNap, bis-[N-(2-(pyridine-4-yl)ethyl)]-9,18-methano-1,8-naphthalimide-[b,f][1,5]diazocine) and 1,3,5-tris(bromomethyl)benzene by heating in DMF for 3&nbsp;days. The formation and phase-purity of TBNap-COP were fully characterised by using various spectroscopic and microscopy analyses. The suspension of TBNap-COP in water showed strong fluorescence emission characteristics owing to the ‘push-pull’ based ICT transition and it was used as a fluorescent sensor for discriminative detection of nitroaromatic explosives. TBNap-COP displayed selective fluorescence quenching responses for phenolic-nitroaromatics, with particularly high sensitivity for picric acid which is a powerful secondary chemical explosive and a harmful environmental pollutant widely used in the dye industries.

Supramolecular Chemistry

Hyper-crosslinked 4-amino-1,8-naphthalimide Tröger’s base containing pyridinium covalent organic polymer (COP) for discriminative fluorescent sensing of chemical explosives

Distinct selectivity control in Cp*CoIII-catalyzed domino C-H activation/pyridine directing group migration/alkyne annulation has been accomplished through the nucleophilicity of an organometallic cobalt intermediate with a d6 electron configuration. Detailed mechanistic studies provided compelling evidence for a facile C-H activation along with a favorable migration of the directing group for the Cp*CoIII catalysis, rather than the β-oxygen elimination observed for a (CO)3MnI manifold. Copyright © 2020 American Chemical Society.