Indian Association for the Cultivation of Science

About: Indian Association for the Cultivation of Science is a education organization based out in Kolkata, India. It is known for research contribution in the topics: Catalysis & Excited state. The organization has 3867 authors who have published 10457 publications receiving 220098 citations.

Superior activity of structurally deprived enzyme-carbon nanotube hybrids in cationic reverse micelles.

Abstract: In the present work, we report the superior activity of hydrophobically adsorbed enzymes onto single-walled carbon nanotubes (SWNTs) in the reverse micelles of cationic surfactants. Horseradish peroxidase and soybean peroxidase adsorbed onto SWNTs endure a notable loss in secondary structure and catalytic activity. This structurally and functionally deformed enzyme-SWNT when confined in CTAB reverse micelles showed approximately 7-9-fold enhancement in activity compared to that was in water and also importantly approximately 1500-3500 times higher activity than that of the enzymes in aqueous-organic biphasic mixtures. The activation observed for this nanobiocomposite is due to the (i) possible localization of enzyme-SWNT hybrid at the micellar interface; (ii) facile transport of substrates across the microscopic interface of reverse micelles; and (iii) greater local concentration of substrates at the augmented interfacial space in the presence of SWNT. This interfacial localization of the SWNT-protein hybrid was tested using FITC-tagged protein (BSA) by fluorescence spectroscopy. FTIR and CD spectroscopy established that the enzyme notably loses its native structure as it gets adsorbed onto the CNTs. However, this loss in the secondary structure is neither aggravated nor recovered when the enzyme-SWNT resides at the reverse micellar interface. So, localization of the surface-active peroxidase-CNT hybrids at the interface is the main reason for significant enzyme activation. The generality of the activation of the enzyme-CNT hybrid by reverse micelles was tested using amphiphiles with varying headgroup sizes, where an overall enhancement in activity was observed with an increase in headgroup size. Activation of this nanobiocomposite would find utmost importance in material science as the activity of structurally deprived enzyme in reverse micelles surpassed (approximately 1.7-fold) even the activity of the native enzyme in water.

Echoes from braneworld black holes

Abstract: The holographic interpretation of the Randall-Sundrum model based on the adaptation of the $\mathrm{AdS}/\mathrm{CFT}$ correspondence to the braneworld scenario states that the black holes localized on the brane are quantum corrected. This can be better understood from the fact that the classical ${\mathrm{AdS}}_{5}$ bulk dynamics is dual to gravity coupled with conformal field theory (CFT) on the four-dimensional brane. Based on the backreaction of the CFT on the classical black hole geometry, localized on the brane, it is expected that there exist possible near-horizon modifications. This may result in the black hole horizon becoming partially reflective, thus giving rise to echoes in the ringdown signal in gravitational wave observations. In this paper, we investigate the existence of such echoes in the ringdown phase of a black hole localized on the brane, carrying a negative tidal charge, and establish the layout for future investigation of higher-dimensional effects in the ringdown signal. Confirmed detections of echoes at the current levels of instrumental sensitivity can constrain the dimensionless value of tidal charge to $|Q|\ensuremath{\lesssim}{M}^{2}$.

Annealing CsPbX3 (X = Cl and Br) Perovskite Nanocrystals at High Reaction Temperatures: Phase Change and Its Prevention

Abstract: Annealing perovskite nanocrystals at high reaction temperature changes their crystal phase, shape, and optical properties. Carrying out reactions between 180 and 250 °C, the impact of thermal annealing for CsPbCl3 and CsPbBr3 nanocrystals in a reaction flask was investigated here. At higher temperature, a phase change was observed instantly, which could not be trapped even with ice-bath cooling. Interestingly, using a calculated amount of preformed alkylammonium halides as dual passivating agents, the nanocrystals of both CsPbCl3 and CsPbBr3 could even be stabilized for hours of annealing at 250 °C. CsPbCl3, which was reported to be a poor emissive nanocrystal in comparison to CsPbBr3, could sustain even more than 5 h of annealing at 250 °C and recorded ∼51% absolutely quantum yield. Details of the interface chemistry and the role of the used dual passivating agent for providing thermal stability are studied and reported in this Letter.