Browsing by Author "Kunwar Vikram"

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Distinct spectral line shifts in the Raman lines’ Stokes and anti-Stokes components with temperature in the liquid crystalline system 4DBA
(Institute of Physics, 2025) Anoop Thomas; Chandan Bhai Patel; Ranjan K Singh; Kunwar Vikram
An anomalous Raman phenomenon (ARP) refers to a scenario in which the Stokes and anti-Stokes frequencies of a Raman mode are different. Here we report that ARP introduces different line shifts in Stokes and anti-Stokes frequencies in 4-Decyloxy Benzoic acid with temperature across two thermally driven structural transitions: the smectic (S) to nematic (N) phase transition at 375 K and the nematic (N) to isotropic (I) transition at 390 K. Four Raman modes near 663, 773, 1128, and 1168 cm−1 shift towards higher frequencies (blueshift) in the Stokes frequency and towards lower frequencies (redshift) in the anti-Stokes frequency with rise in temperature near S to N phase transitions. However, in the isotropic liquid phase, both the Stokes and anti-Stokes components exhibit a redshift as temperature increases, without any noticeable distinct spectral lineshifts. Our studies bring out the importance of phonon band structure in ARP. © 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.
Exploring a solid polymorphism and phase transitions in 4-cyano-4′-pentylbiphenyl (5CB) and rGO-doped 5CB using temperature dependent Raman spectroscopy
(Elsevier B.V., 2025) Ummer Bashir Khoja; Chandan Bhai Patel; Pankaj Kumar Tripathi; Rajesh Kumar; Soni Mishra; Sachin Kumar Singh; Ranjan Kumar Singh; Kunwar Vikram
Raman spectroscopy is used to examine the temperature-dependent phase transition behaviour of the liquid crystalline system 4-cyano-4′-pentylbiphenyl (5CB) and its nanocomposite with reduced graphene oxide (5CB@rGO) over the temperature range of −160 °C to 90 °C. First time, such a broad temperature range study of 5CB and 5CB@rGO has been reported. The structural and intermolecular interaction characteristics of the liquid crystal 5CB and its behaviour in the presence of reduced graphene oxide (rGO) are examined in depth by the temperature-induced Raman spectra and DFT calculations. To assess the phase transitions in 5CB and 5CB@rGO, the significant bands associated with the polar C[tbnd]N group and phenyl rings were thoroughly examined. A new crystal-crystal (solid polymorphism) phase transition is investigated first time, occurring between −120 °C and −100 °C. Another significant new crystal-crystal phase transition in 5CB and 5CB@rGO is also exposed, taking place between −20 °C and −10 °C. Differential scanning calorimeter (DSC) measurements confirm this new phase transition in 5CB and temperature sensitivity fairly matches Raman analysis. To evaluate the structural as well as change in intermolecular interactions in each phase, the detailed DFT study is performed on the 5CB molecule to establish the spectra-structure relation. The detailed spectra-structure correlation is discussed in this study. The spectra-structure correlation and change in spectral parameters are used to investigate the structure and intermolecular interaction of each phase. © 2025 Elsevier B.V.
Facile in-situ synthesis of reduced graphene oxide/TiO2 nanocomposite: a promising material for the degradation of methyl orange
(Taylor and Francis Ltd., 2023) Kunwar Vikram; Rajesh Kumar Srivastava; Amit Raj Singh; K. Ummer; Santosh Kumar; Manish Pratap Singh
Titanium oxide (TiO2) and reduced graphene oxide-TiO2 (r-GO/TiO2) layered nano-composite were synthesized by the one step hydrothermal method. In this study, one step hydrothermal technique is adopted for the facile and in-situ synthesis of r-GO/TiO2 nano-composite. Crystal structure, surface morphology, chemical composition of TiO2 and r-GO/TiO2 layered nano-composite were investigated by Powder XRD, TEM, FT-IR, UV, and Raman spectroscopy. The unique feature of resultant r-GO/TiO2 nano-composite template is intercalation of TiO2 nanoparticles with well dispersion between graphene layers. The synthesized material was investigated for application in photocatalytic activity using UV light irradiation for degradation of methyl orange dye. The result shows that the(r-GO/TiO2) layered nano-composite effectively photodegrade methyl orange, showing almost double photocatalytic activity (∼1.82 times) in comparison to pristine TiO2 and commercially available TiO2 (P25). © 2022 Taylor & Francis Group, LLC.
MoS2-Modified Curcumin Nanostructures: The Novel Theranostic Hybrid Having Potent Antibacterial and Antibiofilm Activities against Multidrug-Resistant Hypervirulent Klebsiella pneumoniae
(American Chemical Society, 2019) Ashish Kumar Singh; Himanshu Mishra; Zeba Firdaus; Shivangi Yadav; Prerana Aditi; Nabarun Nandy; Kavyanjali Sharma; Priyanka Bose; Akhilesh Kumar Pandey; Brijesh Singh Chauhan; Kaushik Neogi; Kunwar Vikram; Anchal Srivastava; Amrita Ghosh Kar; Pradyot Prakash
The recent emergence of hypervirulent clinical variants of Klebsiella pneumoniae (hvKP) causing community-acquired, invasive, metastatic, life-threatening infections of lungs, pleura, prostate, bones, joints, kidneys, spleen, muscles, soft-tissues, skin, eyes, central nervous system (CNS) including extrahepatic abscesses, and primary bacteremia even in healthy individuals has posed stern challenges before the existing treatment modalities. There is therefore an urgent need to look for specific and effective therapeutic alternatives against the said bacterial infection or recurrence. A new type of MoS2-modified curcumin nanostructure has been developed and evaluated as a potential alternative for the treatment of multidrug-resistant isolates. The curcumin quantum particles have been fabricated with MoS2 via a seed-mediated hydrothermal method, and the resulting MoS2-modified curcumin nanostructures (MQCs) have been subsequently tested for their antibacterial and antibiofilm properties against hypervirulent multidrug-resistant Klebsiella pneumoniae isolates. In the present study, we found MQCs inhibiting the bacterial growth at a minimal concentration of 0.0156 μg/mL, while complete inhibition of bacterial growth was evinced at concentration 0.125 μg/mL. Besides, we also investigated their biocompatibility both in vitro and in vivo. MQCs were found to be nontoxic to the SiHa cells at a dose as high as 1024 μg/mL on the basis of the tested adhesion, spreading of the cells, and also on the various serological, biochemical, and histological investigations of the vital organs and blood of the Charles Foster Rat. These results suggest that MQCs have potent antimicrobial activities against hvKP and other drug resistant isolates and therefore may be used as broad spectrum antibacterial and antibiofilm agents. Copyright © 2019 American Chemical Society.