Molecular conformation and liquid structure of 2-propanol through neutron diffraction

The neutron diffraction data analysis of deuterated liquid 2-propanol at room temperature to define its molecular conformation is presented. 2-Propanol being a large molecule with twelve atomic sites, the conformation analysis is tricky and an improved method of data analysis is given. The intermolecular structural correlations, i.e., hydrogen-bonded liquid structure, can be modelled accurately to extract the nature of the average hydrogen-bonded molecular association in liquid state at room temperature. Like other alcohols these are mostly hexamer ring chain (HRC) clusters. The cluster analysis of recent X-ray data available in the literature also support the same liquid structure.     

Synthesis and characterization of water-soluble carbon nanotubes from mustard soot

Carbon nanotubes (CNT) has been synthesized by pyrolysing mustard oil using an oil lamp. It was made water-soluble (wsCNT) through oxidative treatment by dilute nitric acid and was characterized by SEM, AFM, XRD, Raman and FTIR spectroscopy. The synthesized wsCNT showed the presence of several junctions and defects in it. The presence of curved graphene structure (sp²) with frequent sp³ hybridized carbon is found to be responsible for the observed defects. These defects along with the presence of di- and tri-podal junctions showed interesting magnetic properties of carbon radicals formed by spin frustration. This trapped carbon radical showed ESR signal in aqueous solution and was very stable even under drastic treatment by strong oxidizing or reducing agents. Oxidative acid treatment of CNT introduced several carboxylic acid group functionalities in wsCNT along with the nicking of the CNT at different lengths with varied molecular weight. To evaluate molecular weights of these wsCNTs, an innovative method like gel electrophoresis using high molecular weight DNA as marker was introduced.     

Anisotropy of the electron momentum distribution in Bi2Sr2CaCu2O8+δ superconductor studied by positron annihilation

The temperature dependent (30-300 K) Doppler broadening of the positron annihilated γ-radiation measurement has been investigated on single crystalline Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) high T_c superconducting samples along two different crystallographic orientations. It has been observed that throughout the temperature range the electron momentum distribution has a larger value along the crystallographic c-axis than in the a-b plane. The temperature dependent Doppler broadened positron annihilation γ-radiation lineshape analysis shows a step like increase of S-parameter at the temperature region 92-116 K.     

Algebraic approach to anomalous sigma models

Anomalous σ-models in 1+1 and 1+3 dimensions are analysed using purely algebraic methods. We find, in the 1+1 dimensional example, a current algebra containing an arbitrary parameter which is compatible with the Wess-Zumino anomaly and anon-vanishing curvature. The consistency of the algebra is checked by means of a consistency condition and the Jacobi identity. In the 1+3 dimensional case, however, the conventional (anomalous) current algebra with a vanishing curvature is reproduced.     

Spectroscopic studies of microenvironment dictated structural forms of piroxicam and meloxicam

Long acting non-steroidal anti-inflammatory drugs (NSAIDs) belonging to the oxicam group have attracted special interest because of their diverse biological functions. In this study we present the influence of microenvironment on the spectral properties of two oxicam drugs viz. piroxicam and meloxicam. For the two drugs, a high energy shift of the UV absorption maxima was observed with increasing drug concentrations both in protic solvent like ethanol and aprotic solvent like dimethyl sulfoxide (DMSO). Studies involving variation of percentage volume of water as well as pH, using absorption and steady state fluorescence spectroscopy, allow us to identify the principal species present at different concentrations of the drugs. It is found that even trace quantity of water present in the solvent becomes significant at low concentration of the drug making the water/drug ratio sufficiently large to support the formation of anion. As the concentration of the drug increases, the number of water molecules available per drug molecule decreases and most of the drug molecules face a relatively apolar environment in which zwitterionic/neutral species become predominant. This results in a concentration-dependent high-energy shift of the absorption maximum. This study demonstrates how microenvironments of these drugs guide the nature of the predominant form present in solution.     

Transient response of hot electrons in narrow-gap semiconductors at low temperatures in the presence of a longitudinal quantizing magnetic field

Transient response of hot electrons in narrow-gap semiconductors to a step electric field in the presence of a longitudinal quantizing magnetic field has been studied at low temperatures using displaced Maxwellian distribution. The energy and momentum balance equations are used assuming acoustic phonon scattering via deformation potential responsible for the energy relaxation and elastic acoustic phonon scattering together with ionized impurity scattering for momentum relaxation. The calculations for the variation of drift velocity and electron temperature as functions of time are made for n-Hg_0.8Cd_0.2 Te in the extreme quantum limit at 1.5 K and 4.2 K. The momentum and energy relaxation times are found to be of the same order of magnitudes as with the experimental values. The magnetic field and lattice temperature dependences of the relaxation rates have been investigated.One of the authors, Suchandra Bhaumik, acknowledges the Council of Scientific and Industrial Research (New Delhi) for financial support.