Swarup Roy

Ecofriendly gold nanoparticles – Lysozyme interaction: Thermodynamical perspectives

In the featured work interaction between biosynthesized gold nanoparticles (GNP) and lysozyme (Lys) has been studied using multi-spectroscopic approach. A moderate association constant (Kapp) of 2.66×104L/mol has been observed indicative of interactive nature. The binding constant (Kb) was 1.99, 6.30 and 31.6×104L/mol at 291, 298 and 305K respectively and the number of binding sites (n) was found to be approximately one. Estimated values of thermodynamic parameters (Enthalpy change, ΔH=141.99kJ/mol, entropy change, ΔS=570J/mol/K, Gibbs free energy change, ΔG=-27.86kJ/mol at 298K) suggest hydrophobic force as the main responsible factor for the Lys-GNP interaction and also the process of interaction is spontaneous. The average binding distance (r=3.06nm) and the critical energy transfer distance (Ro=1.84nm) between GNP and Lys was also evaluated using Försters non-radiative energy transfer (FRET) theory and results clearly indicate that non-radiative type energy transfer is possible. Moreover, the addition of GNP does not show any significant change in the secondary structure of Lys as confirmed from circular dichroism (CD) spectra. Furthermore, NMR spectroscopy also indicates interaction between Lys and GNP. The resulting insight is important for the better understanding of structural nature and thermodynamic aspects of binding between the Lys and GNP.

Fast electrochromic display: tetrathiafulvalene–graphene nanoflake as facilitating materials

A new electrochromic gel (EC-Gel)-based active material has been prepared by using ethyl viologen (EV)–graphene nanoflakes (GNFs)–tetrathiafulvalene (TTF) for a faster and more efficient electrochromism. A prototype flexible electrochromic device has been fabricated by using the above-mentioned EC-Gel as an active layer which shows overall improved coloring efficiency as high as 208 (C cm−2)−1. At the same time, the abovementioned electrochromism shows color switching at a bias of 1.6 V with coloration/bleaching times as low as 0.4 and 0.9 seconds, respectively, which is better in comparison to that of other traditional EC-Gel or non EC-Gel-based electrochromic devices. Redox activity of EV–TTF pair results in such a fast bias induced color switching. Besides acting as an electrolyte, GNFs also facilitate achieving a faster bleaching time by allowing reversing the redox process quickly. The abovementioned facilitation is done by temporarily storing the electrons, which are released by EV during coloring cycle, to be supplied to TTF in the bleaching cycle through ballistic channels in graphene. An in situ UV-Vis spectroscopy establishes a transmission change of ∼45% in its stable state reversibly for more than 2500 cycles when the device is tested under ambient conditions.

Synthesis of Conducting Polypyrrole-Titanium Oxide Nanocomposite: Study of Structural, Optical and Electrical Properties

Optical and electronic properties of hybrid Polypyrrole (Ppy)–Titanium oxide (TiO2) nanocomposite, synthesized using oxidative chemical polymerization method have been investigated here. The synthesized organic–inorganic hybrid materials have been characterized using XRD, FT-IR, FESEM, UV–Vis, Raman, and TGA. Electrical conductance and dielectric behavior of the electrical phenomena of the sample have also been investigated. XRD results demonstrate the amorphous nature of Ppy, however, its composites with TiO2 exhibit crystalline nature. FT-IR spectroscopy reveals the presence of interaction between conducting Ppy and TiO2. UV–Vis study show changes in spectra of Ppy in presence of TiO2 with a slight increase in the band gap. The SEM results reveal encapsulation of TiO2 particles in Ppy matrix and agglomeration of grains have also been observed with evident changes in morphology with increasing percentages of TiO2. TGA data indicates that the composite materials show good thermal stability. Conductance results show that electrical conductivity of Ppy increases upon addition of TiO2. It has also been noticed that the dielectric parameters (dielectric constant, loss tangent) of Ppy vary with addition of TiO2. The resulting insight clearly suggests that by embedding TiO2 in Ppy the electrical properties of the composites can be improved.

Binding affinity of pyrano[3, 2-f]quinoline and DNA: spectroscopic and docking approach

The interaction between pyrano[3, 2-f]quinoline (PQ) and calf thymus DNA (CTDNA) using spectroscopic and molecular modeling approach has been presented here. Apparent association constant (1.05×105 L/mol) calculated from UV-vis specta, indicates a moderate complex formation between CTDNA and PQ. The quenching phenomena as obtained from emission spectra of ethidium bromide (EB)–CTDNA by PQ was found to be a dynamic one and the binding constants found to be 8.64, 9.25, 11.17, 12.03 × 104 L/mol at 293, 300, 308, and 315 K. Thermodynamic parameter enthalpy change (ΔH) and entropy change (ΔS), indicates weak force like van der Walls force and hydrogen bonds having the key role in this binding process. The results of circular dichroism (CD) demonstrate that PQ has not induced characteristic changed in CTDNA. Results achieved from UV absorption and fluorescence spectroscopy indicating the binding mode of PQ with DNA seems to be a nonintercalative binding. The theoretical results as originating from molecular modeling showed that PQ possibly will bind into the hydrophobic region of DNA having docking binding energy = −10.03 kcal/mol and the obtained results are in consonance with the inferences obtained from experimental data. This result is important for the better understanding of pharmaceutical aspects of binding affinity of PQ and CTDNA.

Spectroscopic Evidence of Phosphorous Heterocycle–DNA Interaction and its Verification by Docking Approach

AbstractIn the present work, the interaction of phosphorous heterocycle (PH) with calf thymus DNA (CTDNA) has been studied using spectroscopy and verified by molecular modeling which is found to be in consonance with each other. Apparent association constant (Kapp = 4.77u2009×u2009103 M−u20091), calculated using UV–Vis spectra indicating an adequate complex formation between CTDNA and PH. A dynamic mode of the fluorescence quenching mechanism in case of ethidium bromide (EB)u2009+u2009CTDNA by PH has been observed confirming formation of DNA-PH complex. A moderate binding constants of PH with CTDNAu2009+u2009EB has been observed (2.74u2009×u2009104 M−u20091 at 293xa0K) by means of fluorescence data. Calculated values of thermodynamic parameters enthalpy change (ΔH) and entropy change (ΔS), suggests weak (van der Walls like) force and hydrogen bonds playing the main role in the binding of PH to CTDNA. Furthermore, the results of circular dichroism (CD) reveal that PH does not disturb native conformation of CTDNA. As observed from absorption and fluorescence spectroscopy the binding mode of PH with DNA was indicative of a non-intercalative binding, which was supposed to be a groove binding. The molecular modeling results show that PH is capable of binding DNA having docking binding energy = -7.26 kcalu2009×u2009mol−u20091. Above mentioned experimental results are found to be in consonance with molecular docking simulations and supports the CTDNA-PH binding.n Graphical Abstract

An insight of spirooxindole-annulated thiopyran – DNA interaction: spectroscopic and docking approach of these biological materials

Abstract The interaction of spirooxindole-annulated thiopyran (STP) with calf thymus DNA (CTDNA) has been studied here using spectroscopic and molecular modeling. A static mode of quenching has been observed from the fluorescence quenching mechanism of ethidium bromide (EB)–CTDNA by STP. A moderately strong binding affinity between STP and CTDNA has been observed (3.98, 2.51, 0.79 × 103 L mol−1 at 293, 303 and 313 K) from the fluorimetric data. Thermodynamic parameter, enthalpy change (ΔH) and entropy change (ΔS), suggested van der Walls force and hydrogen bonds played the main role in the binding of STP to CTDNA. Furthermore, circular dichroism (CD) revealed that STP did not disturb native conformation of CTDNA. As observed in the UV absorption and fluorescence spectroscopy the binding mode of STP with DNA was indicative of a non-intercalative binding, which was supposed to be a groove binding. Above mentioned results are found to be in consonance with molecular docking simulations and supports the STP–CTDNA binding with docking binding energy of -11.00 kcal/mol.

Construction of well aligned highly dense Cobalt nanoneedles for efficient device application

Abstract One step morphology transformation has been reported here by the addition of ammonium fluoride. Two different morphologies of the same structure have been reported for Cobalt Oxide nanostructures. Cobalt oxide nanoneedles in which, one is sleazy needles (s-NDs) and other one is erected needles (e-NDs) have been synthesised. Hydrothermal method has been used for the construction of both the nanoneedles structure. Morphological study by SEM attributes conversion of sleazy bowed done shape to well aligned ones, highly dense and sharp nanostructures. Quantitative analysis shows that after addition of ammonium fluoride, randomly distributed network of nanoneedles converts into a surface covered with vertically aligned, sharp and dense nanoneedles.