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.

Microwave-assisted synthesis and mesomorphic investigations of p-substituted aroylhydrazones and their nickel(II) and copper(II) complexes

Abstract: The present study is focused on the development of green microwave process for the synthesis of mesogenic substituted aroylhydrazones and their nickel(II) and copper(II) complexes. The compounds have been synthesised by microwave-assisted as well as thermal methods for comparison purpose. The compounds were structurally characterised by using suitable spectroscopic techniques. The mesomorphic properties were studied by differential scanning calorimetric analysis and polarising optical microscopy. The stable molecular structures of the mesogenic methylidenehydrazinato-nickel(II) complex have been obtained by density functional theoretical method to understand the structural origin responsible for the mesomorphic property.

DFT study of hydrogen bond bridging mode of pyridine and diazenes in water environment

Abstract: Optimized geometries and vibrational spectra of pyridine (Py), pyridazine (Py1,2), pyrimidine (Py1,3), pyrazine (Py1,4) and their complexes with water molecules have been calculated with a view to look into the strength of hydrogen bonds, binding energies and vibrational wavenumbers of hydrogen bond bridging modes. The counterpoise corrected binding energies for different complexes are also calculated. The results of DFT calculations have been used to draw the potential energy curve and to calculate the amplitude of stretching vibration of hydrogen bond bridging modes. The three types of hydrogen bonds: N…HO, O…HO, and O…HC have been studied. The relative hydrogen bond strengths and vibrational wavenumbers of these bridging modes have been explained in terms of redistribution of electronic charges on individual atoms.

Concentration‐dependent surface‐enhanced Raman scattering and molecular dynamic study of dimethyl formamide

Abstract: A concentration-dependent Raman study of dimethyl formamide (DMF) in Ag nanocolloidal solution was carried out in order to observe the effect of concentration on the surface enhancement mechanism. The Raman spectra in the region 900–2200 cm−1 comprising four prominent Raman modes were measured experimentally and analyzed at five different concentrations: 1, 3, 5, 7, 10 mM, and in neat DMF. In order to find the possible configurations of DMF + Ag complexes, density functional theory (DFT) calculations were carried out taking one, three and five Ag atom clusters. The Raman spectra of unconjugated DMF, DMF + Ag and DMF + 3Ag complexes were calculated theoretically to assign the vibrational modes under consideration more accurately and to understand the wavenumber shift and change in intensity observed in experimental measurements. Water present in the colloidal solution may also conjugate with DMF and its complexes with Ag. In order to see the influence of water on the wavenumber shift and intensity changes, we have also obtained the optimized structures and Raman modes of DMF + water and DMF + water + Ag complexes. Good agreement between the experimental and theoretical wavenumber shifts has been obtained by using B3LYP functional theory and CEP-31G basis set for the DMF + Ag complex. The experimental results suggest that the SERS enhancement is concentration-dependent. The concentration-dependent linewidth shows the existence of the phenomena of motional narrowing and diffusion dynamics in the colloidal solution. Copyright © 2007 John Wiley & Sons, Ltd.

Surface-enhanced Raman spectroscopy (SERS): progress and trends

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.

Solar-driven reforming of lignocellulose to H 2 with a CdS/CdO x photocatalyst

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).

Organic Photoreceptors for Imaging Systems

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.

Assessing Genetic Risks: Implications for Health and Social Policy

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 …