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Ranjan K. Singh

Bio: Ranjan K. Singh is an academic researcher from Banaras Hindu University. The author has contributed to research in topics: Raman spectroscopy & Liquid crystal. The author has an hindex of 20, co-authored 134 publications receiving 1465 citations. Previous affiliations of Ranjan K. Singh include Schiller International University & University of Würzburg.


Papers
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Journal ArticleDOI
TL;DR: In this article, a density functional theory (DFT) at the B3LYP/6-31++G(d,p) level was employed to obtain the optimized geometries and vibrational spectra of several pyridine(Py)−water(W) complexes with stoichiometric ratios ranging from 2:1 (Py2W) to 1:3 (PyW3).
Abstract: Density functional theory (DFT) at the B3LYP/6-31++G(d,p) level was employed to obtain the optimized geometries and vibrational spectra of several pyridine(Py)−water(W) complexes with stoichiometric ratios ranging from 2:1 (Py2W) to 1:3 (PyW3). The harmonic vibrational wavenumbers of pyridine ring modes and the fundamental modes of water were calculated in order to examine the influence of hydrogen bonding on the normal modes of both pyridine and water upon complexation. The Raman spectra in the wavenumber region 960−1060 cm-1 covering the ring modes ν1 and ν12 of pyridine (in Wilson's notation) as a function of pyridine mole fraction were recorded. The integrated Raman intensities in the isotropic components of the spectra were used to determine the relative concentration of “free” pyridine molecules in close neighborhood with other Py−W complexes. The combination of both experimental wavenumbers yielding the overall shift induced by the entirety of hydrogen-bonded complexes in the mixture and the DFT-de...

148 citations

Journal ArticleDOI
TL;DR: In this paper, the structural, morphological, and optical properties of Co-doped ZnO nanoparticles (NPs) prepared by a sol-gel method before and after dense electronic excitations caused by swift heavy ion irradiation have been reported.
Abstract: In the present study, the structural, morphological, and optical properties of Co-doped ZnO nanoparticles (NPs) prepared by a sol–gel method before and after dense electronic excitations caused by swift heavy ion irradiation have been reported The pristine and ZnO:Co NPs were irradiated by using a 200 MeV Ag15+ ion beam at a fluence of 5 × 1012 ions per cm2 Structural characterization has been performed using X-ray diffraction (XRD) with Rietveld refinement It shows that the samples are of single phase; grain size and tensile strain has been increased in the ion-irradiated samples Room temperature Raman spectroscopy measurements show that microscopic structural disorders reduce the translational symmetry giving rise to local distortions in the lattice Atomic force microscopic (AFM) studies show prominent grain boundaries and suggest that roughness of the irradiated surfaces increases strongly compared to their pristine counterparts Optical absorption and photoluminescence (PL) studies also reflect the dopant incorporation and swift heavy ion (SHI) irradiation effect on the nanoparticles UV-Vis absorption measurement has been utilized to estimate the optical bandgap of pristine and irradiated ZnO and Co-doped ZnO nanoparticles Enhancement in the PL intensity has been observed in the irradiated samples with respect to their pristine counterparts which can be explained on the basis of the increase of different defect states and Zn–O bonds on the surfaces of the irradiated nanoparticles arising from surface modification Grain boundaries have played an important role in the optical properties (absorption and PL)

71 citations

Journal ArticleDOI
TL;DR: The results indicate that aqueous solubility and stability of Curcumin can be achieved by preparing its quantum dots and demonstrates that by sizing down the particle size has not only enhanced its antimicrobial properties but it has also shown its antibiofilm activities.
Abstract: Bacterial biofilm has been reported to be associated with more than 80 percent of bacterial infections. Curcumin, a hydrophobic polyphenol compound, has anti-quorum sensing activity apart from having anti-microbial action. However, its use is limited by its poor aqueous solubility and rapid degradation. In this study, we attempted to prepare quantum dots of the drug curcumin in order to achieve enhanced solubility and stability and investigated for its antimicrobial and antibiofilm activity. We utilized a newer two-step bottom up wet milling approach to prepare Curcumin Quantum Dots (CurQDs) using acetone as a primary solvent. Minimum inhibitory concentration against select gram-positive and gram-negative bacteria was performed. The antibiofilm assay was performed at first using 96-well tissue culture plate and subsequently validated by Confocal Laser Scanning Microscopy. Further, biofilm matrix protein was isolated using formaldehyde sludge and TCA/Acetone precipitation method. Protein extracted was incubated with varying concentration of Curcumin quantum dots for 4 hrs and was subjected to SDS-PAGE. Molecular docking study was performed to observe interaction between curcumin and phenol soluble modulins as well as curli proteins. The biophysical evidences obtained from TEM, SEM, UV-VIS, fluorescence, Raman spectroscopy and zeta potential analysis confirmed the formation of curcumin quantum dots with increased stability and solubility. The MICs of curcumin quantum dots, as observed against both select gram positive and negative bacterial isolates, was observed to be significantly lower than native curcumin particles. On TCP assay, Curcumin observed to be having antibiofilm as well as biofilm degrading activity. Results of SDS-PAGE and molecular docking have shown interaction between biofilm matrix proteins and curcumin. The results indicate that aqueous solubility and stability of Curcumin can be achieved by preparing its quantum dots. The study also demonstrates that by sizing down the particle size has not only enhanced its antimicrobial properties but it has also shown its antibiofilm activities. Further, study is needed to elucidate the exact nature of interaction between curcumin and biofilm matrix proteins.

63 citations

Journal ArticleDOI
TL;DR: In this article, the authors developed a simple, sensitive, label-free and real time detection method for mercuric ions (Hg2+) in water using liquid crystals (LCs).
Abstract: We developed a simple, sensitive, label-free and real time detection method for mercuric ions (Hg2+) in water using liquid crystals (LCs). In this system, newly synthesized amphiphilic potassium N-methyl-N-dodecyldithiocarbamate (MeDTC) was doped in 4-cyano-4′-pentyl biphenyl (5CB) LC, which align LC molecules at aqueous interface and polar head group of the amphiphile acts as mecuric ion specific chelating ligand. When this sensor system was incubated in the aqueous solution containing Hg2+ ions, a dark to bright transition of the image of LCs was observed. This was caused due to rapid and stable complex formation between dithiocarbamate chelating group of MeDTC with Hg2+ ions at aqueous interface, which disrupted the orientation of LCs giving bright texture. The limit of detection of the system for aqueous Hg2+ ion is 0.5 μM. This sensor did not respond to other metal ions like Pb2+, Cd2+, Cu2+, Zn2+, Na+, Mg2+ and Ca2+, which are common environmental interference in water. We also demonstrated that this sensor is capable of detecting Hg2+ ions in real water samples (tap water). The very simple and effective procedure reported here should facilitate the development of real time, portable and reliable LC based sensor for mercury pollution control.

58 citations

Journal ArticleDOI
TL;DR: In this article, an experimental and theoretical study on hydrogen-bonding between pyrimidine and water as the H-donor was performed by using polarization-resolved linear Raman spectroscopy with the pyridine ring breathing mode ν1 as a marker band.
Abstract: We present an experimental and a theoretical study on hydrogen-bonding between pyrimidine and water as the H-donor. The degree of hydrogen-bonding in this binary system varies with mixture composition. This was monitored experimentally by polarization-resolved linear Raman spectroscopy with the pyrimidine ring breathing mode ν1 as a marker band. A subsequent quantitative line shape analysis of the isotropic Raman intensity for 24 pyrimidine/water mixtures clearly revealed a splitting into three spectral components upon dilution with water. The two additional peaks have been assigned to distinct groups of hydrogen-bonded species that differ in the number of pyrimidine nitrogen atoms (N) involved in hydrogen-bonding to water hydrogen atoms (H). From the integrated Raman intensities for “free” and “hydrogen-bonded” pyrimidine, a concentration profile for these species was established. Our assignments and interpretations are supported by quantum mechanical calculations of structures and by vibrational spectra...

51 citations


Cited by
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Journal ArticleDOI
TL;DR: The limit of sensitivity in SERS is introduced in the context of single-molecule spectroscopy and the calculation of the ‘real’ enhancement factor, which illustrates the broad applications of this powerful technique.
Abstract: Surface-enhanced Raman spectroscopy (SERS) combines molecular fingerprint specificity with potential single-molecule sensitivity. Therefore, the SERS technique is an attractive tool for sensing molecules in trace amounts within the field of chemical and biochemical analytics. Since SERS is an ongoing topic, which can be illustrated by the increased annual number of publications within the last few years, this review reflects the progress and trends in SERS research in approximately the last three years. The main reason why the SERS technique has not been established as a routine analytic technique, despite its high specificity and sensitivity, is due to the low reproducibility of the SERS signal. Thus, this review is dominated by the discussion of the various concepts for generating powerful, reproducible, SERS-active surfaces. Furthermore, the limit of sensitivity in SERS is introduced in the context of single-molecule spectroscopy and the calculation of the 'real' enhancement factor. In order to shed more light onto the underlying molecular processes of SERS, the theoretical description of SERS spectra is also a growing research field and will be summarized here. In addition, the recording of SERS spectra is affected by a number of parameters, such as laser power, integration time, and analyte concentration. To benefit from synergies, SERS is combined with other methods, such as scanning probe microscopy and microfluidics, which illustrates the broad applications of this powerful technique.

706 citations

Journal ArticleDOI
TL;DR: In this paper, the authors presented an Austrian Federal Ministry of Science, Research and Economy and National Foundation for Research, Technology and Development (NFthis paper ) supported by the OMV Group, the EPSRC (DTA studentships for D.W. and T.E.O.), the World Premier Institute Research Center Initiative (WPI), MEXT, Japan (to K.L., GAN 701192 - VSHER), the German Research Foundation (to M.F.
Abstract: This work was supported by the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy and the National Foundation for Research, Technology and Development), the OMV Group (to E.R.), the EPSRC (DTA studentships for D.W.W. and T.E.R), the Isaac Newton Trust, the German Research Foundation (to M.F.K.), the World Premier Institute Research Center Initiative (WPI), MEXT, Japan (to K.L.O.) and a Marie Curie Research fellowship (to K.H.L., GAN 701192 - VSHER).

383 citations

Reference BookDOI
08 Oct 2018
TL;DR: Xerographic photoreceptors charge acceptance and dark discharge photoinduced discharge photogeneration theories photogengeneration in organic solids charge transport theories charge transport in polymers and related materials experimental techniques photoreceptor preparation photoresceptors fatigue summary and future requirements.
Abstract: Xerographic photoreceptors charge acceptance and dark discharge photoinduced discharge photogeneration theories photogeneration in organic solids charge transport theories charge transport in polymers and related materials experimental techniques photoreceptor preparation photoreceptors fatigue summary and future requirements.

378 citations

Journal ArticleDOI
26 Nov 1994-BMJ
TL;DR: In the future of all-conquering genetic technology, who should be screened for what and by whom?
Abstract: Ed Lori B Andrews, Jane E Fullarton, Neil A Holtzman, Arno G Motulsky National Academy Press, £28.95, pp 338 ISBN 0-309-04798-6 Genetic screening tends to serve as a flypaper on which our hovering fears of a Brave New World alight and stick. In the future of all-conquering genetic technology, who should be screened for what and by whom? Here is a dense report, compiled by a committee of the great and the good, with hundreds of recommendations for action and inaction. How much …

332 citations

Journal ArticleDOI
01 May 2019-Talanta
TL;DR: CQDs, their structure, and PL characteristics are introduced and recent advances of the application of CQDs in biotechnology, sensors, and CL is comprehensively discussed.

286 citations