Browsing by Author "Rajni Kant"

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A dinuclear copper(i) thiodiacetate complex as an efficient and reusable 'click' catalyst for the synthesis of glycoconjugates
(Royal Society of Chemistry, 2017) Neha Sareen; Anoop S. Singh; Vinod K. Tiwari; Rajni Kant; Subrato Bhattacharya
We report herein the facile synthesis and structural characterization of a highly stable dinuclear Cu(i) complex, [(PPh3)2Cu(μ-tda)Cu(PPh3)2]·6H2O 1 (tda = thiodiacetate anion), in which the Cu-Cu distance is 7.197 Å. This "pre-formed" complex serves as an extremely efficient and recyclable homogeneous catalyst (2 mol%, 30 min) for CuAAC in dichloromethane solvent. The synthesis of a variety of glycoconjugates under ambient conditions is successfully achieved using 1 as a catalyst. The products are obtained in high yields and very short reaction times while complying with the "click protocols". A simpler procedure solely involving the mixing of substrates with 1 (i.e. base free and solvent free) gave the corresponding glycoconjugate in 10 min using 2 mol% of the catalyst. © The Royal Society of Chemistry 2017.
CRISPR/Cas12a-Based Detection Platform for Early and Rapid Diagnosis of Scrub Typhus
(Multidisciplinary Digital Publishing Institute (MDPI), 2023) Pooja Bhardwaj; Nikita Shrikant Nanaware; Sthita Pragnya Behera; Smita Kulkarni; Hirawati Deval; Rajesh Kumar; Gaurav Raj Dwivedi; Rajni Kant; Rajeev Singh
Orientia tsutsugamushi is responsible for causing scrub typhus (ST) and is the leading cause of acute encephalitis syndrome (AES) in AES patients. A rapid and sensitive method to detect scrub typhus on-site is essential for the timely deployment of control measures. In the current study, we developed a rapid, sensitive, and instrument-free lateral flow assay (LFA) detection method based on CRISPR/Cas12a technology for diagnosing ST (named LoCIST). The method is completed in three steps: first, harnessing the ability of recombinase polymerase for isothermal amplification of the target gene; second, CRISPR/Cas12a-based recognition of the target; and third, end-point detection by LFA. The detection limit of LoCIST was found to be one gene copy of ST genomic DNA per reaction, and the process was complete within an hour. In 81 clinical samples, the assay showed no cross-reactivity with other rickettsial DNA and was 100% consistent with PCR detection of ST. LoCIST demonstrated 97.6% sensitivity and 100% specificity. Overall, the LoCIST offers a novel alternative for the portable, simple, sensitive, and specific detection of ST, and it may help prevent and control AES outbreaks due to ST. In conclusion, LoCIST does not require specialized equipment and poses a potential for future applications as a point-of-care diagnostic. © 2023 by the authors.
Indium(III) and organotin(IV) 2-(methoxycarbonyl)benzenethiolates: Synthesis, structure and properties
(Elsevier B.V., 2022) Krishna Kumar; Priyanka Tiwari; Srikanta Moharana; Rajni Kant; Subrato Bhattacharya
Two compounds In(mts)3, 1 and triphenyltin(mts), 2 [where mts = 2-(methoxycarbonyl) ben- zenethiolate] were synthesized and characterized. Both the compounds crystallize in the monoclinic system; 1 with space group P21/c and 2 with space group P21/n. Molecule 1 has a distorted trigonal bipyramidal geometry around the In(III) center. In the case of 1, out of the three mts ligands, two bind (S and O) bidentately while the third one binds mainly through its S atom, whereas 2 has a tetrahedral geometry around Sn(IV) center in which the mts ligand is bonded through its S atom only. Hirshfeld analyses were carried out to understand the nature of weak interactions responsible for the deviation from the ideal geometry of both compounds. Quantum chemical calculations were carried out at the DFT level using B3LYP functional in order to get the optimized geometry and vibrational frequencies. Natural bond orbital analyses (NBO) were performed to explore hyper-conjugative interaction energies, HOMO-LUMO, and various inter and intramolecular transitions. The thermodynamic profiles and electrostatic potential surfaces of the compounds have been investigated. Bulk properties such as dielectric loss/constant and AC conductivities have also been explored. © 2022 Elsevier B.V.
Molecular docking study of conformational polymorph: Building block of crystal chemistry
(Hindawi Publishing Corporation, 2013) Rashmi Dubey; Ashish Kumar Tewari; Ved Prakash Singh; Praveen Singh; Jawahar Singh Dangi; Carmen Puerta; Pedro Valerga; Rajni Kant
Two conformational polymorphs of novel 2-[2-(3-cyano-4,6-dimethyl-2-oxo-2H- pyridin-1-yl)-ethoxy]-4,6-dimethyl nicotinonitrile have been developed. The crystal structure of both polymorphs (1a and 1b) seems to be stabilized by weak interactions. A difference was observed in the packing of both polymorphs. Polymorph 1b has a better binding affinity with the cyclooxygenase (COX-2) receptor than the standard (Nimesulide). © 2013 Rashmi Dubey et al.
Phylogenetic and immunological investigations of complete TSA56 ORF of Orientia tsutsugamushi present in acute encephalitis syndrome cases from eastern Uttar Pradesh, India
(Springer Science and Business Media Deutschland GmbH, 2023) Pooja Bhardwaj; Sthita Pragnya Behera; Nikita Nanaware; Kamran Zaman; Hirawati Deval; Rajni Kant; Smita Kulkarni; Rajesh Kumar; Gaurav Raj Dwivedi; Rajeev Singh
Scrub typhus (ST) caused by Orientia tsutsugamushi (OT), has long been known to cause acute encephalitis syndrome (AES) and acute febrile illness (AFI). The immunodominant 56 kDa protein of OT, which is encoded by the 56 kDa gene (1600 bp encoding 516–541 amino acids) is a commonly studied antigen for genotype and serotype assignment. Previous studies from India have utilized partial type specific antigen (TSA) 56 kDa sequences for OT strain characterisation. On the other hand, understanding the antigenic diversity of current OT strains, is critical for developing specific diagnostic tests and vaccines against ST. As a result, the current study analyses antigenic variants using the entire TSA56 ORF of OT from AES cases. Phylogenetic investigation using complete TSA56 ORF sequences revealed Karp and Gilliam were the circulating predominant strains of OT. Furthermore, Immuno-informatical analysis demonstrated that the majority of high-binding affinity CD4 TCEs against the most prevalent Indian human leukocyte antigen alleles were present in the S-VDIII/IV and S-VDIV spacer regions of TSA56 ORF. TSA56 conserved spacer is crucial for OT immunological response investigations. Further, the pathophysiological effects of spacer domains in ST require further investigation. Furthermore, the characterization of the TSA56 spacer region of the OT from different parts of India is critical for developing region-specific ST diagnostic assays and vaccines. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Structural studies on thiosalicylate complexes of Zn(II) & Hg(II). First insight into Zn(II)-thiosalicylate complex as potential antibacterial, antibiofilm and anti-tumour agent
(Elsevier S.A., 2020) Mousumi Nayak; Ashish Kumar Singh; Pradyot Prakash; Rajni Kant; Subrato Bhattacharya
Thiosalicylato complexes of Zn(II) and Hg(II), [Zn(SC6H4CO2)(TMEDA)]2 (1) and [TMEDA-H2][Hg(SC6H4CO2)2] (2) where (TMEDA = N,N,N',N'-tetramethylethylenediamine) have been synthesized and characterized by spectral and single crystal X-ray analyses. Thiosalicylate opted different binding modes; in 1 all three binding sites are used whereas in 2 bonding of the ligands are mainly through S atoms, however, Hg-O distances indicate the existence of significant Hg…O interactions. Bonding features have been explained on the basis of DFT calculations. Electronic absorption and emission spectral properties of both complexes have been studied. Electronic transitions have been calculated by TDDFT method and the results are consistent with the experimental spectra. We further have evaluated anti-bacterial, anti-biofilm and anti-tumour activities of 1 in addition to its cytotoxicity profile. It has been found to be highly effective against Escherichia coli, Klebsiella pneumoniae, Methicillin sensitive Staphylococcus aureus, Methicillin resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa clinical as well as reference strains. Interestingly, complex 1 has been found to be more potent than earlier reported Au(III) as well as Pt(II) thiosalicylate complexes. The effect of complex 1 on 72 h old biofilms of S. Aureus (MDR isolate 3) has been investigated by confocal laser scanning microscopy which revealed its bactericidal activities at the concentration as low as 0.125 µg/mL possibly by membrane alterations as evident by clear propidium iodide (PI) uptake. However, its antibiofilm activity is possibly due to interactions with biofilm matrix constituents. © 2019 Elsevier B.V.
Synthesis and structural characterization of Cd(II) complexes based on acetylene dicarboxylate: A 1-D polymer as a precursor to CdO nanoparticles
(Elsevier B.V., 2022) Neha Sareen; Krishna Kumar; Rajni Kant; Somenath Garai; Subrato Bhattacharya
Two new compounds, [Cd(adc)(L)(H2O)3]2 (1), [Cd(adc)(bipy)2.H2O]n (2) (Where L = N, N′-bis-pyridin-4-ylmethylenehydrazine, adc = acetylene dicarboxylate and bipy = 2,2’-bipyridine) have been isolated in good yields and structurally characterized by IR, single-crystal X-ray diffraction, and thermogravimetric analysis. Direct thermolysis of complex 2 at 500 °C for 1 h under an ambient atmosphere yielded CdO nanoparticles. The nanoparticles were characterized for their size and structure by powder X-ray diffraction, scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (TEM). TEM images show the formation of nanorods as well as nanospheres. The optical band gap determined by the optical absorption method was found to be 3.8 eV. © 2022 Elsevier B.V.
Synthesis and structural studies of Cu(i) methylthiosalicylate complexes and their catalytic application in thiol-yne click reaction
(Royal Society of Chemistry, 2022) Krishna Kumar; Priyanka Tiwari; Rajni Kant; Subrato Bhattacharya
Three complexes of Cu(i), [Cu(PPh3)2(mts)] (1), [Cu(dppf)(mts)] (2) and [Cu(dppe)(mts)]2 (3) (mts = methylthiosalicylate; dppf = diphenylphosphinoferrocene; dppe = diphenylphosphinoethane), have been synthesized and characterized. Complexes 1 and 2 are monomeric, while 3 has a dimeric structure. The coordination geometry around Cu(i) in these complexes are trigonal pyramidal/distorted tetrahedral. The catalytic activities of the complexes towards hydrothiolation of alkynes (via thiol-yne click reaction) have been studied. Out of these three complexes, 2 has been found to be an efficient catalyst for the synthesis of unsymmetrical vinyl sulfide. The desired vinyl sulfides are obtained in good to excellent yields, with up to >99% Z stereoselectivity in one case. This protocol tolerates a wide variety of functional groups or substrates, is palladium-free, and does not require the use of expensive or air-sensitive additives. The scope and versatility of the method have been successfully demonstrated with a few examples. © 2022 The Royal Society of Chemistry.