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Shiv Nadar University

(SoNS) School of Natural Sciences

Detailed 27Al and 63Cu nuclear magnetic resonance (NMR) experiments have been performed in between 4.5 and 295 K on a polycrystalline sample of CeCu3Al2 which has a Kondo temperature ∼11K. The NMR spectral features and Knight shift measurements show that in this compound, Cu occupy both c and g lattice sites, while Al occupy only the g sites. From the temperature dependence of Knight shift (K), the hyperfine fields for 63Cu and 27Al at the g sites have been estimated as 2.02(5) and 1.67(5)kOe/$\mu$B, respectively and that for 63Cu at c sites as -3.83(5)kOe/$\mu$B. Nuclear spin-lattice relaxation time (T1) measurements indicate that though the relaxation process is governed by fluctuations of magnetic interaction, nuclear quadrupolar interaction also has a significant contribution, especially towards relaxation of 63Cu in both c and g sites. For 27Al, K and T 1 have yielded the effective 4f-spin correlation rate 1/$\tau$4f. The behavior of its temperature dependence indicates that at low temperatures in CeCu3Al2, the valence state of cerium might not be stable. {\textcopyright} 2010 Elsevier B.V. All rights reserved.

World University root node

Physics

Physica B: Condensed Matter

27Al and 63Cu NMR studies on intermetallic Kondo compound CeCu3Al2

Research on structure and magnetic properties of polynuclear metal complexes to understand the structural and chemical factors governing the electronic exchange coupling mediated by multi-atom bridging ligands is of growing interest. Hydrothermal treatment of Ni(NO3) 2{\textperiodcentered}6H2O with N-(4-carboxyphenyl)iminodiacetic acid [N-4(H3CPIDA)] at 150 °C yielded a 3D coordination polymer of general formula [Ni3{N-4(CPIDA)}2(H2O) 3]{\textperiodcentered}6H2O (1). An analogous network of general formula [Co3{N-3(CPIDA)}2(H2O) 3]{\textperiodcentered}3H2O (2) was synthesized using N-(3-carboxyphenyl)iminodiacetic acid [N-3(H3CPIDA)] in combination with Co(NO3)2{\textperiodcentered}6H2O under identical reaction condition. Both the complexes contain trinuclear secondary building unit and crystallized in monoclinic system with space groups C2/c (1) and P21/c (2), respectively. Variable temperature magnetic characterization of these complexes in the temperature range of 2-300 K indicated the presence of overall ferromagnetic and antiferromagnetic behavior for 1 and 2, respectively. Density functional theory calculations (B3LYP functional) were performed for further insight on the trinuclear units to provide a qualitative theoretical interpretation on the overall magnetic behavior of the complexes 1 and 2. {\textcopyright} 2010 Elsevier B.V. All rights reserved.

Chemistry

Inorganica Chimica Acta

Synthesis, crystal structures and magnetic behavior of two 3D coordination polymers using N-(4/3-carboxyphenyl)iminodiacetic acids as bridging ligands

The effect of interfacial hydrogen bonding on the behavior of the freezing/melting processes in two organic liquids, namely, ethylene glycol [(CH2OH)2] and isopropanol [CH3CH(OH)CH 3], confined in nanopores of ZSM-5 zeolite has been investigated using the positron annihilation spectroscopy (PAS) and nuclear magnetic resonance (NMR) techniques. Both liquids have intermolecular hydrogen bonding and feel attractive interaction toward the surface of the confining wall, resulting in an increase in the freezing/melting temperature while confined in nanopores. This observation differs from our earlier report on the behavior of benzene confined in ZSM-5 as well as in silica pores wherein a depression in freezing temperature was seen due to a weakly attractive/repulsive interaction between benzene and the pore surface. The measured S parameter, o-Ps lifetime and intensity profiles across the freezing point of ethylene glycol confined in ZSM-5 are seen to be different from those of isopropanol, signifying the difference in the behavior of phase transition in these two liquids under confinement. It is to be noted that, unlike isopropanol, ethylene glycol has strong intramolecular hydrogen bonding. This causes the difference in the fluid-wall interfacial interaction between ethylene glycol and isopropanol within the confinement. The phase-transition behavior of these two confined liquids was also investigated using the NMR technique by studying the spin-spin relaxation time (T2). The T2 process in ethylene glycol is expressed as a sum of at least two distinct components exhibiting Gaussian decay, whereas in isopropanol, T2 is expressed as a sum of three components showing Lorentzian decay. The transitions from one component to another were seen to be consistent with the positron annihilation spectroscopic observation. {\textcopyright} 2010 American Chemical Society.

Journal of Physical Chemistry C

Effect of interfacial hydrogen bonding on the freezing/melting behavior of nanoconfined liquids

This article delineates preliminary results obtained from three newly set up very low frequency (VLF) radio receiver observation stations at low latitude Indian sites Allahabad (16.49°N), Nainital (20.48°N) and Varanasi (15.41°N), during 2007. These stations were set up by collaboration between the Indian Institute of Geomagnetism, Mumbai and Stanford University, USA under the International Heliophysical Year 2007/United Nations Basic Space Science Initiative (UNBSSI) program. VLF stations are part of Atmospheric Weather Electromagnetic System for Observation, Modeling and Education (AWESOME) network being operated globally to study the ionosphere and the magnetosphere with the help of electromagnetic waves in extremely low frequency (ELF) and VLF bands. The new set up of VLF receiver is a marked improvement over the traditional recording and analysis systems in India. It provides additional facilities to study the VLF phenomena at low latitudes which were not studied earlier, like direction finding of events like whistlers, emissions, etc. and D-region ionospheric perturbation caused by the geophysical phenomena such as solar flares, lightning induced electron precipitations, cosmic gamma ray flares, terrestrial gamma rays flares, geomagnetic storm effect, etc. Simultaneous observation at multiple sites will provide opportunity to study in more detail the application of ELF/VLF data as earthquake precursors. Some of the initial results obtained from the preliminary analysis are presented to show the probing potentiality of ELF/VLF waves in ionosphere/magnetosphere studies.

Life Sciences

Current Science

Initial results from AWESOME VLF receivers: Set up in low latitude Indian regions under IHY2007/UNBSSI program

Genetic variability, heritability and genetic advance as per cent of mean for 14 characters in 7 elite and diverse genotypes of chilli (Capsicum annuum L.) were studied. The phenotypic coefficient of variation was higher than the respective genotypic coefficient of variation for all the 14 characters under study. Considerable amounts of GCV and PCV were observed for capsaicin content, number of fruits per plant, fruit length, fruit diameter, leaf area and total fresh yield per plant indicating the existence of greater diversity for these characters. Heritability, in broad sense, was found appreciably high (&gt;90%) for the characters: number of primary branches, leaf area, fruit length, number of fruits per plant, total fresh yield per plant and the total dry yield per plant. High heritability estimates have been found to be helpful in making selection of superior genotypes on the basis of phenotypic performance with respect to quantitative characters. High heritability coupled with high degree of genetic advance was noted for total fresh yield per plant, number of fruits per plant and ascorbic acid content in both, the F1s and parents. High heritability coupled with high genetic advance and genetic coefficient of variation reflects that the above characters are under the control of additive gene effects, and could be relied upon for yield improvement.

Vegetos

Genetic Architecture in the improvement of Chilli (Capsicum annuum L.) Crops

K-antigen capsule synthesis is an important virulence determinant of the oral anaerobe Porphyromonas gingivalis. We previously reported that the locus required for synthesis of this surface polysaccharide in strain W83 (TIGR identification PG0106 to PG0120) is transcribed as a large (∼16.7-kb) polycistronic message. Through sequence analysis, we have now identified a 77-bp inverted repeat located upstream (206 bp) of the start codon of PG0106 that is capable of forming a large hairpin structure. Further sequence analysis just upstream and downstream of the capsule synthesis genes revealed the presence of two genes oriented in the same direction as the operon that are predicted to encode DNA binding proteins: PG0104, which is highly similar (57%) to DNA topoisomerase III, and PG0121, which has high similarity (72%) to DNA binding protein HU (β-subunit). In this report, we show that these two genes, as well as the 77-bp inverted repeat region, are cotranscribed with the capsule synthesis genes, resulting in a large transcript that is ∼19.4 kb (based on annotation). We also show that a PG0121 recombinant protein is a nonspecific DNA binding protein with strong affinity to the hairpin structure, in vitro, and that transcript levels of the capsule synthesis genes are downregulated in a PG0121 deletion mutant. Furthermore, we show that this decrease in transcript levels corresponds to a decrease in the amount of polysaccharide produced. Interestingly, expression analysis of another polysaccharide synthesis locus (PG1136 to PG1143) encoding genes involved in synthesis of a surface-associated phosphorylated branched mannan (APS) indicated that this locus is also downregulated in the PG0121 mutant. Altogether our data indicate that HU protein modulates expression of surface polysaccharides in P. gingivalis strain W83. Copyright © 2010, American Society for Microbiology. All Rights Reserved.

Fulltext

Journal of Bacteriology

HU protein affects transcription of surface polysaccharide synthesis genes in Porphyromonas gingivalis

L 139 a NMR study was performed in grain-aligned (c→|| H→0) sample of LaCoPO and polycrystalline LaFePO. Knight shift is isotropic and temperature independent in LaFePO. It is strongly temperature dependent and anisotropic in LaCoPO. The spin-lattice relaxation rate in LaCoPO clearly reveals the existence of three-dimensional spin fluctuations both in the paramagnetic and ferromagnetic state over and above the dominant two-dimensional spin fluctuations in the paramagnetic state, observed earlier from P 31 NMR measurements in the same oriented sample. The spin fluctuation parameters in LaCoPO determined from L 139 a NMR relaxation and magnetization data, using the self-consistent renormalization theory, are in close agreement and follow the universal Rhodes-Wohlfarth curve. {\textcopyright} 2010 The American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Electron spin dynamics in grain-aligned LaCoPO: An itinerant ferromagnet

Systematic evolution of the 400 nm electroluminescence (EL) with increasing flash lamp annealing (FLA) temperature from 800 to 1100 °C in an Er-doped Ge-rich metal-oxide semiconductor structure is presented. No significant change in the 1535 nm Er EL is observed with increasing FLA temperature. Enhancement of the 400 nm EL decay time with rising FLA temperature is found to be associated with recrystallization of the damaged Ge clusters in the absence of Ge outdiffusion. The 400 nm EL quenching with continuous charge injection process is also discussed within the device operation time. © 2010 American Institute of Physics.

Journal of Applied Physics

Controlling blue-violet electroluminescence of Ge-rich Er-doped SiO 2 layers by millisecond annealing using flash lamps

The anisotropy of the electronic interactions between fullerenes in crystalline solids was examined using a confocal fluorescence microscope by probing the polarization of the fluorescence emission arising from fullerene excimer-like emitting states. Crystals of C60 obtained by vacuum-sublimation or from chloroform solution exhibited no or little polarization (p = 0 or 0.11, respectively), as expected from the high symmetry of the C60 fcc lattice or the low degree of anisotropy induced by included solvent molecules. The use of hydrogen-bonding to supramolecularly control interfullerene electronic interactions was explored using a fullerene derivative (1) combining a solubilizing 3,4-di-tert-butylbenzene group and a barbituric acid hydrogen-bonding (H-B) moiety. The crystal structure of 1 establishes the existence of fullerene H-B tapes along which interfullerene electronic interactions are expected to be large. In agreement with this, we observe very strong polarization of the fullerene excimer-like emission (p = 0.78), indicative of a high degree of anisotropy in the fullerene interactions. The charge-carrier mobility of 1 as determined from OFET devices was found to be lower than that of C60 (1.2 × 10-4 vs 1.2 × 10-2 cm2/s V), which is rationalized on the basis of the reduced dimensionality of 1 as a wire-like semiconductor and variations in the morphology of the device active layer revealed by AFM measurments. © 2010 American Chemical Society.

Journal of the American Chemical Society

Self-assembly of supramolecular fullerene ribbons via hydrogen-bonding interactions and their impact on fullerene electronic interactions and charge carrier mobility

Two coumarin derived dyes (compounds La and L) have been synthesized in high yields by Schiff base condensation. On probing with a femtosecond laser, none of these compounds show any two-photon activity in the wavelength range, 760-860 nm. However, La in presence of Zn(II) and L in presence of Mg(II), exhibit large two-photon absorption as well as emission in the same wavelength range. Theoretical calculations at the B3LYP functional with 6-31G and LanL2DZ mixed basis set under DFT formalism support experimental results. © 2010 Elsevier B.V. All rights reserved.

Coumarin derived chromophores in the donor-acceptor-donor format that gives fluorescence enhancement and large two-photon activity in presence of specific metal ions