Browsing by Author "Monalisha Nayak"

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Detection of a Neurotoxin Quinolinic Acid at Ultra-Trace Amount: SERS and DFT Study
(John Wiley and Sons Ltd, 2025) Monalisha Nayak; Chandan Bhai Patel; Om Prakash; Ashish Kumar Singh; Ranjan Kumar Singh
The presence of quinolinic acid (QA) below 100 nM is a normal condition while its increased amount may cause variety of neurodegenerative diseases. The precise detection of QA in trace amounts (nanomolar) is crucial to control its toxic effects. In the present study, the SERS-based detection of QA and its interaction at varying concentrations in human serum is carried out using silver nanoparticle substrates. The analysis of conformational dynamics of QA across different concentrations ranging from 10−3 to 10−9 M has been done. The adsorption mechanism between QA and silver nanoparticles has been studied using DFT, and the detection of QA up to nanomolar concentration is achieved. A significant shift in the SERS spectra of QA is observed between 10−4 and 10−5 M concentration, attributed to changes in adsorption geometry with varying pH and conformational change from zwitterionic QA → neutral QA. These findings are supported by UV–visible spectra, pH measurements, and DFT calculations. © 2025 John Wiley & Sons Ltd.
Effect of different synthesis parameters on the structural, morphological and optical properties of hydrothermally synthesized tungsten diselenide (WSe2) nanostructures: Experimental and theoretical validation
(Elsevier Ltd, 2025) Sushmita Seth; Biplab Mondal; Monalisha Nayak; Satyendra Prakash Pal
In this study, tungsten diselenide (WSe2) nanostructures were synthesized via a hydrothermal route using sodium tungstate dihydrate (Na2WO4.2H2O) and selenium (Se) powder as precursors. Particular attention was given to the influence of synthesis parameters, namely reaction temperature and growth duration, as these play a decisive role in crystallite size, morphology, and the presence of impurities. To systematically evaluate their impact, WSe2 samples were prepared under different conditions and examined for structural, morphological, and optical variations. The as-synthesized samples were characterized by using X-ray diffraction (XRD), Raman spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray Analysis (EDAX), High Resolution Transmission Electron Microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Ultraviolet-Visible (UV-Vis) spectroscopy and Photoluminescence (PL) spectroscopy. The bonding structure and the vibrational modes of Raman spectrum were validated by Density Functional Theory (DFT) calculation using the B3LYP/LANL2DZ mode. The XRD and Raman spectroscopy measurements confirmed the formation of the hexagonal phase (2H-WSe2). The morphology transitioned from aggregated particles to flake-like nanostructures with increasing temperature, while reaction time influenced the crystal refinement and stacking. A significant decrement in the value of the energy band gap for most pure exfoliated WSe2 was observed from the UV-Vis absorption spectra. PL spectra revealed indirect and excitonic transitions with emission peaks in the near-IR region (∼1.3 and ∼1.5 eV). Further, the PL spectra of exfoliated bulk WSe2 exhibited a clear blue-shift of the emission peak, indicating effective material thinning from multilayered to few-layered WSe2. These optical properties indicate a possible optoelectronic potential of WSe2. © 2025 Elsevier Ltd
Monitoring the temperature-induced phase transition in a calamitic liquid crystal MABAB-12 via temperature-dependent Raman and DFT study
(Taylor and Francis Ltd., 2025) Sunny Shukla; Monalisha Nayak; Sachin Kumar Singh; Chandan Bhai Patel; Ranjan Kumar Singh
The calamitic liquid crystal methyl 4-(4’-12-alkoxybenzylideneamino) benzoate (MABAB-12) containing a Schiff base as linking group has been synthesised. Mesomorphic properties and phase transition temperatures were probed through temperature-dependent Raman spectroscopy and analysed using density functional theory (DFT). Analysis of Raman marker bands of C-H in-plane bending, C=C stretching of phenyl rings and C=N stretching of the linker gives evidence of phase transitions. To understand the molecular changes more clearly, an in situ Raman measurement of C-H in-plane bending has also been performed. The temperature-dependent Raman study of MABAB-12 reveals the intra-molecular rotation-induced coplanarity of phenyl rings during the Cr→SmA transition. As a result of intra-molecular rotation, significant charge transfer from the phenyl rings to the linking group is observed. Rotational conformational analysis of MABAB-12 has also been performed through density functional theory (DFT), which also supports induced coplanarity of phenyl rings at the Cr→SmA transition. The analysis of Raman spectra reveals the melting of the hitherto rigid core. © 2025 Informa UK Limited, trading as Taylor & Francis Group.
Spectroscopic study of coordination of Cu2+ with liquid crystal HBDBA: An investigation at ultra trace level
(Elsevier B.V., 2024) Chandan Bhai Patel; Monalisha Nayak; Satyabratt Pandey; Om Prakash; Sachin K. Singh; Ranjan K. Singh
The present work describes the synthesis and characterization of a copper complex with a liquid crystal compound called N-(o-hydroxybenzylidene)-N'-(4-n-alkoxybenzylidene) azines (HBDBA). The FTIR/ Raman spectroscopy and DFT calculations were employed to confirm the coordination of Cu2+ ion with HBDBA. On complex formation several changes in the Raman and FTIR spectra were observed. The linewidth and peak position of few Raman/ IR bands changed and few new bands in the Raman and IR spectra appeared. The experimentally observed bands of HBDBA molecule and its Cu2+- complex are assigned with the help of DFT. In the next part a concentration-dependent study has been done to detect ultra-trace amount (∼10–8 M) of Cu2+ ion binding with HBDBA using Raman and fluorescence spectroscopy. The result suggests that HBDBA can be used to detect Cu2+ ions in trace amount. © 2024
Unveiling the Influence of Glutathione in Suppressing the Conversion of Aspirin to Salicylic Acid: A Fluorescence and DFT Study
(Springer, 2024) Monalisha Nayak; Chandan Bhai Patel; Anurag Mishra; Ranjana Singh; Ranjan K. Singh
Aspirin is a commonly used nonsteroidal anti-inflammatory drug, associated with many adverse effects. The adverse effects of aspirin such as tinnitus, Reye’s syndrome and gastrointestinal bleeding are caused due to conversion of aspirin into its active metabolite salicylic acid after oral intake. Glutathione is a naturally occurring antioxidant produced by the liver and nerve cells in the central nervous system. It helps to metabolize toxins, break down free radicles, and support immune function. This study aims to investigate and explore the possibility of inhibiting aspirin to salicylic acid conversion in presence of glutathione at a molecular level using spectroscopic techniques such as UV–Visible absorption, time-Resolved and time-dependent fluorescence and theoretical DFT/ TD-DFT calculations. The results of steady state fluorescence spectroscopy and time-dependent fluorescence indicated that the aspirin to salicylic acid conversion is considerably inhibited in presence of glutathione. Further, the results presented here might have significant clinical implications for individuals with variations in glutathione level. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024.