Sudeshna Bhattacharya

Detailed spectroscopic investigations to reveal the nature of interaction of anionic porphyrin with calf thymus DNA

The interaction between anionic form of meso-tetrakis(4-carboxyphenyl) porphyrin (TCPP) and calf thymus deoxyribonucleic acid (CT DNA) is investigated by measuring UV-vis absorption, steady-state fluorescence, steady-state fluorescence anisotropy, time-resolved fluorescence, resonance light scattering (RLS), FT-IR and circular dichroism (CD) spectra along with the help of atomic force microscopy (AFM) under Tris-Borate-EDTA (TBE) buffer solution of pH 8.3. The static mode of fluorescence quenching of porphyrin by calf thymus deoxyribonucleic acid indicates the formation of a ground-state complex. The formation of ground-state complex is a spontaneous molecular interaction procedure in which outside groove binding through hydrogen bond or van der Waals force plays a major role. For biomedical application this investigation is very important as here TCPP, i.e. the anionic porphyrin does not bring any changes in the original structure of the CT DNA to selectively cleaving the nucleic acid to destroy the cancer or tumor cells whereas cationic porphyrin makes change in the protein structure significantly during the same process.

Azide-Functionalized Lanthanide-Based Metal–Organic Frameworks Showing Selective CO2 Gas Adsorption and Postsynthetic Cavity Expansion

We report herein selective CO2 gas adsorption by two azide-functionalized lanthanide-based metal-organic frameworks (MOFs). This work also demonstrates that azide-functionalized MOFs can be used for postsynthetic cavity expansion, further corroborated by enhanced gas-sorption data.

Transport properties of CdS nanowire embedded poly(3-hexyl thiophene) nanocomposite

Electrical transport properties of CdS nanowire embedded regioregular poly(3-hexyl thiophene) (P3HT) nanocomposite are investigated and the results are compared with those of the pure P3HT polymer. Both dc and ac conductivities of P3HT and CdS-P3HT nanocomposites show semiconducting nature and conductivity of CdS-P3HT is much less than that of the pure P3HT conducting polymer. The difference in the electrical behavior is attributed to the formation of nanowires in the CdS-P3HT nanocomposite. The dc conductivity data at high and low temperatures are qualitatively consistent with the optical-photon-assisted hopping and variable-range hopping models, respectively. However, the multiphonon-assisted hopping models of small polarons in nonadiabatic regime, which consider strong interactions with electrons with the optical as well as acoustical phonons, are the best to interpret quantitatively the experimental data in the entire temperature range for both P3HT and CdS-P3HT nanocomposites. We observe that the quantum tunneling model of small polarons is consistent with almost every respect of the loss data of P3HT conducting polymer, while for CdS-P3HT nanocomposite the ac conductivity varies with temperature in a different manner, which is explained in terms of simple quantum tunneling model of electrons in contrast to that of pure P3HT conducting polymer.

Effect of Cr doping on the electrical conductivity and Seebeck coefficient in the superconductors obtained from the Bi–Pb–Sr–Ca–Cu–Cr–O-type glassy precursors by annealing

Homogenous (Bi 3 Pb)Sr 3 Ca 3 (Cu 4− n Cr n )O x ( n 4 0 to 0.20) type glassy precursors become high- T c superconductors by annealing at 840 °C. The suppression of T c with increase of Cr concentration supports the pair-breaking mechanism. The feeble semiconducting behavior shown by the doped samples above their respective T c values followed Motts variable range hopping conduction mechanism. Like Ti- and Fe-doped samples, studied earlier, the thermoelectric power (TEP) of the present Cr-containing sample showed small positive peak above T c , which was considered to be associated with the phonon-drag effect. The linear part of the temperature-dependent TEP (above T c ) well fitted the two-band model.

Construction of Co(II) coordination polymers comprising of helical units using a flexible pyrazole based ligand

1H-Pyrazole based molecules are potentially important in crystal engineering because of their ability to play a dual role in metal coordination as well as hydrogen bond formation using an in-built hydrogen bonding site. We report here the construction of a series of coordination polymers using a flexible pyrazole based ditopic ligand and different benzene polycarboxylic acids as auxiliary ligands. For all the structures, hydrogen bonding and π–π stacking were found to be instrumental in bringing additional stability to the self-assembly of these polymeric networks. Furthermore, we have successfully demonstrated the strategy of introducing helicity in the resultant polymeric network using a V-shaped ligand, H2MBP for the present work.

Electrical properties of ion conducting molybdate glasses

The electrical conductivity and conductivity relaxation of xAg2O‐(1−x)MoO3 glasses have been reported in the frequency range of 10Hz−2MHz and temperature range of 183–413K. The dc conductivity and activation energy for the binary silver molybdate glasses have been compared with those of Ag+ ion conducting binary phosphate, borate, and tellurite glasses. The silver molybdate glasses exhibit the highest conductivity and the lowest activation energy of the glasses formed with other glass formers such as phosphate, borate, and tellurite containing the same modifier Ag+ ions. We have analyzed the ac conductivity using the power law and the electric modulus formalisms. We have observed that the concentration of mobile Ag+ ions is not thermally activated and only 10%–25% of the total Ag+ ions contribute to the dynamic processes and are independent of the Ag2O content. We have observed that the conductivity relaxation is highly nonexponential. The motion of Ag+ ions is decoupled more and more from the viscous mot...

Optical and other physical properties of semiconducting cadmium vanadate glasses

The optical and other physical properties of semiconducting xV2O5−(1−x)CdO glasses have been reported in this article. The changes in both density and molar volume indicate structural modification of crystalline V2O5 due to addition of CdO. The glass transition temperatures are observed to decrease with an increase in V2O5 content in the compositions. It has been observed from the analysis of Fourier-transform infrared spectra that the network structure strongly depends upon the V2O5 content in the glass compositions. Introduction of CdO into the V2O5 matrix changes the two-dimensional layer structure of the crystalline V2O5 into a more complicated three-dimensional structure. The fundamental absorption edge for all the glasses is analyzed in terms of the theory proposed by Davis and Mott [E. A. Davis and N. F. Mott, Philos. Mag. 22, 903 (1970)]. The position of absorption edge and, hence, the value of the optical band gap are found to depend on the V2O5 content in the glass compositions.

Broadband conductivity spectra of fast-ion-conducting silver selenite glasses: Dependence on power law and scaling

In this letter we have studied broadband conductivity spectra (10 Hz–3 GHz) of fast-ion-conducting silver selenite glasses of compositions xAgI-(1−x)(yAg2O-(1−y)SeO2). We have observed that the conductivity spectra below 10 MHz are characterized by a power law with exponent less than unity, while the conductivity spectra in the high-frequency range (above 10 MHz) have been adequately explained in the framework of the unified site relaxation model with exponent greater than unity. The scaling of the conductivity spectra indicates that the time-temperature superposition principle is valid in the low-frequency regime, but not in the high-frequency regime.

Design of chiral Co(II)-MOFs and their application in environmental remediation and waste water treatment

The present work reports the construction of new Co-MOFs based on an amide based bispyrazole ligand and different carboxylic acids with potential applications in the sphere of CO2 adsorption and photocatalytic waste water treatment. Four multifunctional MOFs, with a wide variety of dimensionality, porosity and surface characteristics were exploited for this purpose. The unique bis-bidentate nature of the ligand with two chelating compartments along with a semi-rigid backbone leads to some interesting chiral MOFs. Detail self-assembly studies reveals that both helicity as well as local environments around the metal centres are responsible for chirality. A detailed investigation shows the importance of these materials as chiral zeolite analogues for environmental remediation. The much improved photocatalytic degradation of a representative toxic dye molecule highlights the advantages of MOFs over the usual metal oxide based semiconductors as remediation materials. Furthermore, MOFs with an ability to capture CO2 gas, offer a solution to environmental pollutions.

Hopping conduction in zinc vanadate semiconducting glasses

In this paper, we have studied the electrical conductivity for different compositions of the zinc vanadate semiconducting glasses within a wide temperature range. We have analyzed the temperature dependence of the electrical conductivity within the framework of various models for the hopping conduction. We have observed that Mott’s phonon-assisted nearest neighbor hopping model of small polarons is appropriate for describing the conductivity data at high temperatures. We have further observed that at lower temperatures, Mott’s variable range hopping model is operative, while Greaves’ variable range hopping model is valid within the intermediate temperature range. The values of the density of states at the Fermi level, which are obtained from the analysis, are consistent with those for localized states.