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Arora R.,University of DelhiDelhi | Kakkar R.,University of DelhiDelhi
Computational and Theoretical Chemistry | Year: 2017

The mechanism of the Wolff rearrangement of some deprotonated diazocarbonyl compounds has been studied using density functional calculations, for both the gas and aqueous phases. The anionic rearrangement of the deprotonated analogues proceeds in a similar manner to the neutral counterparts. In the gas phase, the syn and anti conformers form the deprotonated ketene product concertedly. In certain analogues, the reaction of the anti conformer occurs non-concertedly, involving a deprotonated carbene-like intermediate. The migratory aptitude is similar to that in the neutral rearrangement, except that methoxy and amino substituents exchange positions. © 2017 Elsevier B.V.

Gupta Y.,University of DelhiDelhi | Gupta Y.,University of Delhi | Arun P.,University of DelhiDelhi
Materials Chemistry and Physics | Year: 2017

The sensitivity of tin sulphide thin films and in turn their ability to generate charge carriers on exposure to light is intimately connected to the residual strain in the film resulting from film fabrication. These strains lead to the formation of traps within the band-gap of the films which upon excitation releases trapped charge carriers for conduction. © 2017 Elsevier B.V.

Kalimuthu V.,University of DelhiDelhi | Kalimuthu V.,Pondicherry University | Rath S.,University of DelhiDelhi
Materials Letters | Year: 2017

Porous silicon (pSi) coated with gold (Au) was synthesized by a one-step electrochemical etching process without any post treatment. The porous nature was confirmed by scanning electron microscopy (SEM) as well as Raman and photoluminescence spectroscopy. The surface enhanced Raman spectroscopic (SERS) sensing performance of Au-coated pSi (Au-pSi) was compared with uncoated pSi by using rhodamine 6G dye as the analyte. The bio-sensing performance of Au-pSi was evaluated using bovine serum albumin (BSA) protein as the analyte. The Au-pSi shown better sensitivity for R6G and BSA as compared to pSi. © 2017 Elsevier B.V.

Gupta A.,University of DelhiDelhi | Dutta S.,Solid State Physics Laboratory | Tandon R.P.,University of DelhiDelhi
Journal of Magnetism and Magnetic Materials | Year: 2017

Integration of ferrite thin films of CoFe2O4 with silicon was an essential step for the development of magnetic and microwave micro-electro-mechanical system (MEMS) devices. This paper reports about the integration of Zn and Mn co-doped CoFe2O4 (Co0.6Zn0.4Fe1.7Mn0.3O4) thin films on silicon wafer surface. The films were deposited by spin coating technique and subsequently annealed at 600 °C (thickness ∼200 nm) and 700 °C (thickness ∼150 nm). Higher values of in plane remanance ratio (33–35%) compared to out of planes (5–13.5%) ones indicate the in plane orientation of the easy axis of magnetization driven by the shape anisotropy of the thin film structure. Upon rise in annealing temperature, coercivity for longitudinal Kerr hysteresis loop increases from 164 Oe to 227 Oe and that for the transverse hysteresis Kerr loop increases from 244 Oe to 586 Oe. © 2017 Elsevier B.V.

Vijayarangamuthu K.,University of DelhiDelhi | Rath S.,University of DelhiDelhi
International Journal of Applied Ceramic Technology | Year: 2015

Sensing of low concentrations of two nitroaromatic compounds, 1,2-dinitrotoluene and 2-nitrophenol, is presented. The sensing mechanism is based on surface-enhanced Raman scattering (SERS) using nanostructured tin oxide as the SERS-active substrate. The SnOx nanostructures are synthesized by a simple solgel method and doped with Ag and Au. The Raman signal of a low concentration of the analyte, otherwise extremely weak, becomes significant when the analytes are attached to these substrates. Doping of SnOx nanopowders with Ag and Au leads to a further increase in the Raman intensities. This study demonstrates the scope of ceramic-metal nanocomposites as convenient solid-state SERS sensors for low-level detection. © 2014 The American Ceramic Society.

Yadav A.,University of DelhiDelhi | Mathur P.,University of DelhiDelhi
Inorganica Chimica Acta | Year: 2015

Abstract Copper(II) complexes of a N-octylated bisbenzimidazolyl ligand are synthesized and characterized. These complexes carry out the oxidative dealkylation of 2,4,6-tri-tertbutylphenol (TTBP) using molecular oxygen to 2,6-ditertbutylbenzoquinone and 4,6-di-tertbutylbenzoquinone. The oxidation proceeds via a phenoxyl radical species detected spectrophotometrically, and by EPR. A reactive copper(II)-dioxygen species is involved that carries out the oxidation reaction. A comparison of the rates of formation of the 4,6-di-tert-butylbenzoquinone versus 2,6-di-tert-butylbenzoquinone suggests that alternative pathway may exist for the formation of the para-quinone derivative. Isolation of an intermediate 4,4′-peroxybis(2,4,6-tri-tert-butylcyclohexa-2,5-dienone species and its structural characterization supports the above contention. © 2015 Elsevier B.V.

Bandyopadhyay B.,University of DelhiDelhi | Schleicher D.R.G.,University of Concepción
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

The reionization of helium describes the transition from its singly ionized state to a doubly ionized state in the intergalactic medium. This process is important for the thermal evolution of the intergalactic medium and influences the mean free path of photons with energies above 54.4 eV. While it is well known that helium reionization is mostly driven by the contribution of energetic quasars at z<6, we study here how helium reionization proceeds if there is an additional contribution due to the annihilation of dark matter. We explore the effects of different dark matter profiles for the dark matter clumping factor, which can significantly enhance the annihilation rate at late times. We find that the presence of dark matter annihilation enhances the He++ abundance at early stages where it would be zero within the standard model, and it can further increase during structure formation, reflecting the increase of the dark matter clumping factor. The latter is, however, degenerate with the buildup of the quasar contribution, and we therefore expect no significant changes at late times. We expect that future studies of the He+ Lyman α forest may help to assess whether the evolution is consistent with the contribution from quasars alone, or if an additional component may be required. © 2015 American Physical Society.

Rani P.,University of DelhiDelhi | Biswas P.,University of DelhiDelhi
Journal of Physical Chemistry B | Year: 2015

Hydration water dynamics around globular proteins have attracted considerable attention in the past decades. This work investigates the hydration water dynamics around partially/fully intrinsically disordered proteins and compares it to that of the globular proteins via molecular dynamics simulations. The translational diffusion of the hydration water is examined by evaluating the mean-square displacement and the velocity autocorrelation function, while the rotational diffusion is probed through the dipole-dipole time correlation function. The results reveal that the translational and rotational motions of water molecules at the surface of intrinsically disordered proteins/regions are less restricted as compared to those around globular proteins/ordered regions, which is reflected in their higher diffusion coefficient and lower orientational relaxation time. The restricted mobility of hydration water in the vicinity of the protein leads to a sublinear diffusion in a heterogeneous interface. A positive correlation between the mean number of hydrogen bonds and the diffusion coefficient of hydration water implies higher mobility of water molecules at the surface of disordered proteins, which is due to their higher number of hydrogen bonds. Enhanced hydration water mobility around disordered proteins/regions is also related to their higher hydration capacity, low hydrophobicity, and increased internal protein motions. Thus, we generalize that the intrinsically disordered proteins/regions are associated with higher hydration water mobility as compared to globular protein/ordered regions, which may help to elucidate their varied functional specificity. © 2015 American Chemical Society.

Kotla S.K.R.,University of DelhiDelhi | Choudhary D.,University of DelhiDelhi | Tiwari R.K.,Chapman University | Verma A.K.,University of DelhiDelhi | Verma A.K.,Jawaharlal Nehru UniversityDelhi
Tetrahedron Letters | Year: 2015

Abstract The Rh(III)-catalyzed oxidative coupling of 2-aryl-imidazopyridines with internal alkynes via double C-H activation has been described. This approach provides straightforward access to highly functionalized polycyclic imidazopyridines in good to excellent yields. © 2015 Elsevier Ltd.

Lumb S.,University of Delhi | Munjal D.,University of DelhiDelhi | Prasad V.,University of DelhiDelhi
Physica Scripta | Year: 2015

Exponential cosine screened Coulomb potential (ECSCP) has been widely used in various branches of physics e.g., solid-state physics, nuclear physics and plasma physics. The atomic photoionization processes under plasma shielding can serve as an efficient tool for study of plasma properties in various environments ranging from nano-scale devices to astrophysical objects. In the present study, ECSCP has been used to characterize a dense quantum plasma and its effect on the spectrum of an atom encaged in a spherical box has been investigated. The work has further been extended to study the response of such a system to a periodic laser field. Photoexcitation and ionization probabilities of the system have been studied as a function of applied laser field parameters using the non-perturbative Floquet technique. As the Floquet method requires exact energy values and oscillator strengths, the spectrum of confined system has been calculated using Bernstein-polynomial method. The variation of energy spectrum and oscillator strengths with screening as well as confinement parameters has also been explored. © 2015 The Royal Swedish Academy of Sciences.

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