Department of Chemistry

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Weakly antiferromagnetic vanillin and acetate bridged dinuclear Ni(II) compound exhibiting catecholase-like activity and biological properties
(Royal Society of Chemistry, 2024) Vernekar, Beena K.; Harmalkar, Nikita N.; Gaonkar, Sanket K.; Sannigrahi, Jhuma; Dhuri, Sunder N.
A dinuclear nickel compound that features vanillin (van) and acetate (OAc) bridging ligands, [Ni sub(2)(Mu-van) sub(2)(Mu-OAc)(NCS) sub(3)(H sub(2)O)].5H sub(2)O 1, was synthesized and characterized using various techniques. Crystal structure analysis revealed a pair of Ni(II) ions bridged by an acetate anion through a Mu sub(2)-Eta sup(1):Eta sup(1) coordination mode. At the same time, vanillin bridges both nickel(II) centers through phenolic oxygen, separating the two Ni ions by a distance of 3.001(7) angstrom. The temperature-dependent magnetism indicates weak antiferromagnetic behaviour in compound 1, following the Curie-Weiss law with Curie constant C = 1.0145 cm sup(3) K mol sup(-1) and Weiss constant Theta = -4.1 K. Compound 1 was evaluated for its ability to mimic the catechol oxidase enzyme using 3,5-di-tert-butylcatechol as a model substrate with a K sub(cat) value of 157.1 x 102 h sup(-1). Furthermore, compound 1 was tested for its cytotoxicity against HepG2 cancer cells and DNA cleavage properties.
Experimental and Theoretical Investigation on the Extractive Mass Transfer of Eu3+ Ions Using Novel Amide Ligands in 1-Hexyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide
(American Chemical Society, 2023) Ghosh, Ayan; Pandey, Amit; Sengupta, Arijit; Kathirvelu, Velavan; Harmalkar, Sarvesh S.; Dhuri, Sunder N.; Singh, Keisham S.; Ghanty, Tapan K.
Novel amide ligands in the ionic liquid (1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) were utilized for the liquid–liquid biphasic mass transfer of Eu3+ ions from aqueous acidic waste solution. The cation exchange mechanism was found to be operative with the formation of [Eu(NO3)2L3]+ species (L = 4-chloro-N-(1-methyl-1H-pyrazol-3-yl)picolinamide). However, the presence of an inner-sphere water molecule was revealed by density functional theory (DFT) calculations. The viscosity-induced slower kinetics was evidenced during mass transfer, which was improved by increasing temperature. The process was exothermic in nature. The improvement in the kinetics of extractive mass transfer at higher temperatures is evinced by a reduction in the distribution ratio value. The spontaneity of the reaction was evidenced through the negative Gibbs free energy value, whereas the process enhances the entropy of the system, probably by releasing water molecules at least partially during complexation. The structures of bare ligands and complexes have been optimized by using DFT calculations. A high value of complexation energy, solvation energy, and associated enthalpy and free energy change reveal the efficacy in binding Eu with O and N donor atoms. In addition, natural population analysis, atoms-in-molecules analysis, and energy decomposition analysis have been employed to explore the nature of bonding existing in Eu–O and Eu–N bonds.
Thiourea modulated supercapacitive behavior of reduced graphene oxide
(Elsevier, 2024) Naik, Arti K.; Samant, Purnakala V.
In this report, we investigated the role of the concentration of nitrogen and sulfur containing thiourea in modulating the electrochemical properties of reduced Graphene Oxide (rGO) by controlling the percentage of heteroatoms on the rGO surface. The synthesis route involved the preparation of Graphene Oxide (GO) using an improved method of synthesis in an economical way by reducing the volume of concentrated acids used. Furthermore, GO is reduced by using different mass proportions of thiourea via a simple reflux method. Characterization of the rGO samples by Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDAX) and elemental analysis through CHNS analyzer exhibited successful doping and impact of nitrogen and sulfur atoms on the graphene framework. The comparative electrochemical performance from Cyclic Voltammograms (CV), Galvanostatic Charge Discharge (GCD) profiles and Electrochemical Impedance Spectroscopy (EIS) measurements on the various rGO samples revealed the superiority of 1:8rGO having 15.190 wt% of nitrogen and 26.849 wt% of sulfur and S/N ratio of 1.768, in delivering highest specific capacitance of 465.21 F·g−1 at 1 mV·s−1 scan rate with a remarkable cyclic stability exhibiting a capacitive retention of 119 % and offering lowest charge transfer resistance and diffusion resistance. The study also demonstrated detrimental effect of excess thiourea on electrochemical properties of rGO. This work suggests an effective and simple approach for optimizing the nitrogen and sulfur content in rGO to enhance its electronic properties using thiourea.
C–H hydrogen bond and halogen bond directed self-assembly of ethereal podands and C–X⋯F−/HF2− halogen bonding in solution
(Royal Society of Chemistry, 2023) Dutta, Dipjyoti; Gogoi, Anamika; Dutta, Rupjyoti; Harmalkar, Sarvesh S.; Lama, Prem; Dey, Sandeep Kumar
A series of halogenated podands (P1–P8) have been synthesized from 1,3,5-tris(bromomethyl)mesitylene and halogen-substituted phenols to study the structure-directing roles of C–H hydrogen bonds and halogen bonds in the formation of self-assembled supramolecular frameworks. The ethereal podands are suitable for the study of C–H hydrogen bonds in the crystalline state due to the presence of three different types of C–H donors, such as methyl, methylene, and aromatic –CH groups, and three different types of acceptors such as ethereal oxygen, halogens, and aromatic rings. Single crystal X-ray structures of three halophenyl-functionalized podands (P2, P3 and P4) and a cyanophenyl-functionalized podand (P9) were determined at room temperature (298 K), and detailed Hirshfeld surface analysis of the crystal structures was performed to quantify the close contact contributions (in %) from different types of non-covalent interactions involved in the self-assembly of podands. The crystal structures of the halophenyl-functionalized podands (P2, P3, and P4) showed self-assembly primarily via intermolecular C–H⋯O, C–H⋯π, and halogen bonding interactions. Hirshfeld surface analysis of the crystal structures revealed significantly higher contributions from H⋯C and H⋯X (X = halogen) close contacts in comparison to H⋯O and X⋯C close contacts in 2D-fingerprint plots. The self-assembly of the cyanophenyl-functionalized podand (P9) was largely governed by intermolecular C–H⋯O and C–H⋯N interactions. The podand crystals showed relatively high thermal stability in thermogravimetry analysis (250–290 °C), which can be attributed to the hydrogen and halogen bond assisted formation of 3D supramolecular frameworks. 19F-NMR spectra of tetraethylammonium fluoride in the presence of an equivalent amount of tris(2-halophenoxymethyl)mesitylene podand (P5 or P6) showed a downfield shift of the fluoride signal (Δδ 3.2 ppm) indicating C–X⋯F− halogen bonding in solution. Further, 19F-NMR spectra of hydrogen bifluoride (HF2−) in the presence of P5 or P6 showed a large upfield shift of ≈21–22 ppm suggesting C–X⋯F−⋯H–F halogen bonding in solution.
Interaction of metal ions with Schiff bases having N2O2 donor sites: Perspectives on synthesis, structural features, and applications
(Elsevier, 2023) Vernekar, Beena K.; Sawant, Pradnya S.
Metal Schiff base complexes are versatile platforms for the development of potential catalysts, potent biomaterials, or luminescent compounds. Transition metals possess a diverse array of properties that can be manipulated to yield promising candidates for the future in various industrial applications. Metal Schiff base complexes represent a class of compounds that have become a field of immense interest because of their intriguing chemical and physical properties and their wide range of applications in several scientific fields. The reaction of transition metal elements with a polydentate Schiff base ligand to form metal complexes offers a good platform for combining the chemical, electronic, magnetic, optical, and redox properties of metal complexes with those of the organic materials, generating new functional materials with useful mechanical, catalytic, thermal and chemical, optoelectronic, structural and magnetic properties. The transition metal complexes can often mimic biological sites; they are, therefore, of great interest as enzyme models. This review discusses the structural features of metal complexes of the first series of transition metals with Schiff bases as ligands having N2O2 coordination sites. Further perspectives concerning the synthesis, structural aspects, characterization, and applications are presented.
Crystal structure, biological and docking studies of solvothermally isolated novel Schiff base
(Elsevier, 2023) Vernekar, Beena K.; Kotkar, Gayatri D.; D'souza, Luann R.; Hathwar, Venkatesha R.; Dhuri, Sunder N.
Solvothermal condensation of 4-hydroxy-3-methoxy benzaldehyde and ethylenediamine resulted in single crystals of the novel Schiff base N,N'-Bis(4-hydroxyl-3-methoxybenzylidene)ethane-1,2-diamine (H2L) while the conventional method yielded microcrystalline H2L. Single crystals of H2L were characterized by various techniques, including single crystal X-ray diffraction. The structural analysis revealed crystallization of H2L in the monoclinic P21 space group with z = 4 and z′ = 2 indicating the presence of two independent H2L molecules in the asymmetric unit of the crystal structure connected by O6-H6…N2 weak contacts involving H and N atoms of the hydroxyl and amine groups respectively. The biological activities, namely DNA binding and cell viability studies of H2L, were performed. H2L exhibited potent activity against mushroom tyrosinase enzyme. In this work, in-silico docking studies have been conducted to evaluate the effective binding modes of H2L with 2y9x mushroom tyrosinase protein. The docking studies revealed minimum binding energy of -6.43 kcal mol−1 for H2L compared to the value of -3.64 kcal mol−1 for standard Kojic acid. The antibacterial performance of H2L was tested, and the results are presented.
Stereochemical influence of 4ʹ-methyl substitutions on truncated 4ʹ-thioadenosine derivatives: Impact on A3 adenosine receptor binding and antagonism
(Elsevier, 2024) Kim, Minjae; Naik, Siddhi D.; Jarhad, Dnyandev B.; Aswar, Vikas R.; Tripathi, Sushil K.; Aslam, Muhammad Arif; Huh, Joo Young; Jeong, Lak Shin
Herein, we investigated the stereochemical effects of 4ʹ-methyl substitution on A3 adenosine receptor (A3AR) ligands by synthesizing and evaluating a series of truncated 4ʹ-thioadenosine derivatives featuring 4ʹ-α-methyl, 4ʹ-β-methyl, and 4ʹ,4ʹ-dimethyl substitutions. We successfully synthesized these derivatives, using the stereoselective addition of an organometallic reagent, KSAc-mediated sulfur cyclization, and Vorbrüggen condensation. Binding assays demonstrated that the 4ʹ-β-methyl substitution conferred the highest affinity for A3AR, with compound 1 h exhibiting a Ki = 3.5 nM, followed by the 4ʹ,4ʹ-dimethyl and 4ʹ-α-methyl substitutions. Notably, despite the absence of the 5ʹ-OH group, compound 1 h unexpectedly displayed partial agonism. Computational docking studies indicated that compound 1 h, the β-methyl derivative, adopted a South conformation and maintained strong interactions within the receptor, including a critical interaction with Thr94, a residue known to be notable for agonistic effects. Conversely, compound 2 h, the α-methyl derivative, also adopted a South conformation but resulted in a flattened structure that hindered interactions with Thr94 and Asn250. The dimethyl derivative 3 h exhibited steric clashes with Thr94, contributing to a reduction in binding affinity. However, the docking results for 3 h indicated a North conformation, suggesting that the change in sugar conformation due to the additional 4ʹ-methyl group altered the angle between the α-methyl group and the sugar plane, enabling binding despite the increased steric bulk. These findings suggest that not only do the substituents and their stereochemistry influence receptor–ligand interactions, but the conformation and the resulting spatial orientation of the substituents also play a crucial role in modulating receptor–ligand interaction. This stereochemical insight offers a valuable framework for the design of new, selective, and potent A3AR ligands, potentially facilitating the development of novel therapeutics for A3AR-related diseases such as glaucoma, inflammation, and cancer.
Design, Synthesis, and Molecular Docking Analysis of Fluorinated MLN4924 Derivatives as Antiviral Agents
(John Wiley & Sons, 2023) Sung, Kisu; Hyeon, Seokhwan; Kim, Minjae; Sahu, Pramod K.; Naik, Siddhi D.; Aswar, Vikas R.; Tripathi, Sushil K.; Chang, Tong-Shin; Ahn, Jin-Hyun; Yu, Jinha; Jeong, Lak Shin
MLN4924 is known for its potential in cancer treatment and antiviral activity as a NEDD8-activating enzyme (NAE) inhibitor. We designed and synthesized fluorinated MLN4924 derivatives by electrophilic fluorination at the 6′-position and nucleophilic fluorination at the 2′-position of the sugar moiety, respectively. The compounds were then evaluated for their anti-HCMV activity, and compound 2 a exhibited the most potent HCMV inhibitory activity, showing similar results to MLN4924 but with no toxicity at a high concentration. Docking studies highlighted the importance of the sugar conformation in the binding interaction with the target protein. This research offers critical insights into the optimization of MLN4924 derivatives and provides a promising pathway towards the development of effective antiviral agents.
Exploring C2 and N6 Substituent Effects on Truncated 4′-Thioadenosine Derivatives as Dual A2A and A3 Adenosine Receptor Ligands
(John Wiley & Sons, 2024) Naik, Siddhi D.; Kim, Minjae; Choi, Jiyoung; Kim, Gibae; Woo Kim, Seung; Aswar, Vikas R.; Tripathi, Sushil K.; Gaikwad, Vidyasagar; Yu, Jinha; Shin Jeong, Lak
Based on high binding affinity of truncated 2-hexynyl-4′-thioadenosine (3 a) at both A2A adenosine receptor (AR) and A3 AR, we explored structure-activity relationship (SAR) of the C2-substitution by altering chain length of the 2-hexynyl moiety, thereby evaluating the hydrophobic pocket size. A series of truncated N6-substituted 4′-thioadenosine derivatives with C2-alkynyl substitution were successfully synthesized from D-mannose, using a palladium-catalyzed Sonogashira coupling reaction as the key step, whose structures were confirmed by the X-ray crystal structure of 4 h. As the size of the alkynyl group at the C2-position increased, the binding affinity improved; however, when the substituted group was larger than hexynyl, the binding affinity decreased. The introduction of a bulky hydrophobic group such as 3-halobenzyl group at the free N6-amino group decreased the binding affinity at hA2AAR. These results confirm our previous findings that a free amino group at N6-position and longer hydrophobic chain at C2-position are essential for hA2A AR binding affinity. The introduction of a bulky hydrophobic group at free N6-amino group maintained the binding affinity at hA3 AR. The binding mode of truncated 2-substituted-4′-thioadenosine derivatives to hA2A and hA3 AR were predicted by a molecular docking study.
Larvicidal activity of pristine α-MnO2 nanostructures: An environmentally benign approach for combating mosquito (Diptera: Culicidae) menace
(Elsevier, 2021) Naik, Shrikant R.; Javeer, D. S.; Gawde, C. S.; Palni, S. S.; Koli, S. C.; Jalmi, S.S.; Ghotge, Y. V.; Naik, N. U.; Fernandes, R.; Velho-Pereira, Sheryanne
Diseases transmitted by mosquitoes claim more than 700,000 lives annually. Mosquitoes are the vectors for the transmission of parasites, bacteria and viruses. The present work highlights the mosquito larvicidal activity of manganese oxide (MnO2) nanoparticles. MnO2 nanoparticles synthesized by the wet chemical redox method were characterized using Powder X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron microscope (TEM). XRD and TEM studies reveal that the synthesized MnO2 nanocrystals have a hollandite (α-MnO2) structure with a sea-urchin like morphology having a high surface area. Larvicidal activity of MnO2 nanoparticles was assessed against the larvae of Culex quinquefasciatus (Cx. quinquefasciatus), Aedes aegypti (Ae. aegypti), and Anopheles stephensi (An. stephensi), and reveals the toxic nature of the nanoparticles against larvae of all the three mosquito species tested. Maximum efficacy has been observed against Cx. quinquefasciatus larvae, with LC50 value of 5.39 ppm, followed by Ae. aegypti at 8.283 ppm and 168.324 ppm against An. stephensi. This study demonstrates toxic effects exerted by the chemically synthesized MnO2 nanoparticles in a species-specific manner. Overall, this study highlights the potential of MnO2 nanoparticles as an effective mosquito control agent.
Fe hotspots in the Ni–Ni3B nanocatalyst unravel remarkable cooperativity to boost hydrogen production from ammonia borane with enzyme-like catalysis
(Royal Society of Chemistry, 2022) Borah, Rajani Kumar; Fatrekar, Adarsh P.; Bakre, Pratibha; Tilve, Santosh G.; Vernekar, Amit A.
Cooperative catalysis is a well-known phenomenon exhibited by some enzymes wherein multiple entities function in tandem to catalyze reactions efficiently and/or with selectivity. However, designing advanced heterogeneous catalysts that can cooperatively regulate reactions is exciting, but it is a challenging task. Herein, the fractional incorporation of Fe like hotspots in the Ni–Ni3B nano-matrices (10% Fe–Ni–Ni3B) furnishing remarkable cooperativity that can finely regulate the hydrogen production from the chemical hydrogen storage material, ammonia borane (AB), under ambient conditions is unveiled. Experimental evidence and dehydrogenation kinetic studies reveal that Fe acts as an activator by inducing strong electronic communication in the catalyst matrix. These interactions boost the H2 generation rate to ∼8500 mL min−1 gcatalyst−1 and significantly reduce the activation energy (Ea) to 39.95 kJ mol−1 from 55.14 kJ mol−1 calculated for Ni–Ni3B alone. The Fe-incorporated catalyst shifts the half-order dehydrogenation kinetics of Ni–Ni3B to Michaelis Menten-like kinetics, typically observed for enzymes, showing a rate max (Rmax) ∼18 000 mL min−1 gcatalyst−1. Heterogeneous catalysts rarely exhibit such a cooperative property and enzyme-like catalysis for a non-enzymatic reaction. The catalyst shows 100% H2 generation efficiency and a high turnover frequency (TOF) of ∼293 molH2 molFe−1 min−1. Upon interaction of dopamine with the Fe active centers, the electronic communications attenuate, diminishing the dehydrogenation rate, and confirming that electronic communication is necessary for cooperative catalysis. This investigation highlights the engineering of materials to induce electronic interactions and cooperativity, which may spur interest in developing inexpensive catalysts for meeting the energy demand.
ESR Spectral Characterisation of Mn doped Zn (II) Trisethylenediamine Sulfidometalate Complexes
(Blue Eyes Intelligence Engineering and Sciences Publication, 2019) Vernekar, Beena K.
Aqueous reaction of Zn(II) and Mn(II) salts with ammonium tetrasulfidometalate (NH4)2[MS4] (M = Mo, W) in the presence of ammonia or ethane 1,2-diamine (en) or propane 1,2-diamine (1,2-pn) results in the formation of [M'(L)n][MS4] (M’ = Zn or Mn; L = NH3 or en or 1,2-pn). Using this strategy, Mn doped Zn complex of formula [Zn0.99Mn0.01(en)3][MS4], which exhibits characteristic hyperfine ESR spectra have been synthesized. The synthetic aspects, spectral and thermal characterization are described.
Comparison of degradation of methylene blue dye by zno, n doped zno and iron ore rejects
(European Chemical Bulletin, 2014) Borker, Vrinda; Mordekar, Rajashri Karmali; Rane, Koyar
Textile effluent containing unused dye when released in surroundings pollutes water bodies. It requires processing before disposal. Iron ore reject created during mining creates environmental pollution but contains minerals of technological importance. It has ~30-50 % iron in the form of γ-Fe2O3, α-Fe2O3 and Fe3O4 is wasted if thrown in fields, so can be used to degrade organic dyes. Mineralization of methylene blue, MB a model dye is carried out using photocatalyst either iron ore reject, synthesized ZnO or ZnO1-xNx and the results are compared. ZnO is synthesised from oxalate and nitrogen doped ZnO from hydrazinated oxalate precursors. FTIR study of zinc complexes indicates formation of precursors and XRD of decomposed complexes reveal formation of zinc oxide with wurtzite structure. The presence of nitrogen in ZnO1- xNx is confirmed by chemical estimation and XPS studies. SEM reveals the particle size of ZnO1-xNx ~69 nm and ZnO ~0.5-1μm. ZnO1-xNx absorbs in the visible region and ZnO in UV region. Band gap energy calculated using Diffuse reflectance Spectrum is 2.48 eV for the former, 3.19eV for the later and 2.38 eV for ore reject. Mineralizing property of ore reject, ZnO and ZnO1-xNx are compared by electrons spray ionisation mass spectrometry study (ESI-MS) of degradation products, COD measurement and CO2, NO3- and SO4-2 estimation. Reusability study, kinetic study of degradation of MB dye using photocatalysts and ESI-MS study of degraded products of MB reveal better efficacy of iron ore rejects amongst three. Thus efficiency of iron ore reject > ZnO1-xNx. > ZnO as photocatalyst.
Silver substituted cobalt zinc ferrites as magnetic antimicrobials
(Elsevier, 2023) Mordekar, Rajashri Karmali; Samant, Pranita; Mishra, Puja; Joseph, Jaison
Silver-substituted cobalt zinc ferrite series, CoxAg0.5-xZn0.5Fe2O4 (x = 0.4, 0.3, 0.2, 0.1), is synthesized using the citrate gel method, wherein ferrite formation is achieved at 600 °C. The low-temperature crystallization results in agglomerated and porous ferrites. In this sample preparation methodology, as the silver content in the series increases, metallic silver deposits at the grain boundaries, and vacancies are created at the octahedral sites. With a further increase in silver content, the magnitude of magnetic properties decreases. Antimicrobial activity increases and further decreases with an increase in silver content. The composition Co0.4Ag0.1Zn0.5Fe2O4 exhibits both magnetic and antimicrobial behaviour. These materials can potentially be beneficial in the manufacture of removable antimicrobial agents for water purification and drug delivery systems.
Insitu FTIR studies for the enhanced activity of Pt(HY) and Pt-Ru(HY) zeolite catalysts for electrooxidation of methanol in fuel cells
(Chemical Physics Letters, 2020) Samant, Purnakala V.; Fernandes, Julio B.
Insitu FTIR (Fourier transform infrared spectroscopy) technique has been employed to study the oxidation of methanol on Platinum and Platinum - Ruthenium catalysts supported on HY zeolites [Pt-Ru (HY)/C]. The reaction has been studied by recording the spectra at different temperature ranges from room temperature till 170 °C. The catalytic activity has been studies in presence and absence of oxygen supply. The mechanism for oxidation of methanol has also been interpreted from the data obtained. The decomposition of methanol on Platinum (HY)/C catalyst occurs via carbonate/formate pathway in presence of oxygen and carbonate/carboxylate in absence of oxygen. The optimum efficiency of the Pt (HY) catalyst occurs at 120 °C. But on the surface of Pt- Ru (HY)/C catalyst, methanol oxidation occurs at room temperatures, thus emphasizing higher catalytic efficiency. The enhanced activity of the Platinum–Ruthenium/HY has been explained on the basis of intermediates formed during the reaction.

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