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: Excited state & Catalysis. The organization has 3867 authors who have published 10457 publications receiving 220098 citations.

Permanganate–oxalic acid as a redox initiator in aqueous media. Part II. Kinetics and degree of polymerization

Abstract: The rate of polymerization of aqueous methyl methacrylate under nitrogen at 32°C. is proportional to the first power of catalyst (MnO4−) concentration (0.633 to 15.83 × 10−5 mole/l.) at fixed concentrations of the activator (0.8 × 10−2 mole/l.) and monomer (6.204 × 10−2 mole/l.), independent of activator concentration over a wide range (0.50 to 0.0625 × 10−2 mole/l.), and proportional to the first power of monomer concentration within the range (0.94 to 7.52 × 10−2 mole/l.) at fixed concentrations of the catalyst (3.16 × 10−6 mole/l.) and the activator (0.8 × 10−2 mole/l.). The initial rate of polymerization attains a maximum value at 45°C., but falls with further rise in temperature. The rate of polymerisation is depressed by agitation after initiation, salts and organic solvents, and is accelerated by MnSO4 and complexing agent like NaF (only at low monomer concentration), and in presence of peptizers like sodium cetyl sulfate or cetyltrimethylammonium bromide. The separating phase in the absence of peptizers is a course coagulum, and possibly a steady state with respect to radicals is not attained at high catalyst concentration. Injection of catalyst late in a run increases both the rate of polymerization and yield in unpeptized systems and does the reverse in peptized systems. The molecular weight of the polymers increases in the course of a run and is also affected by change of catalyst concentration but not by activator concentration in the range where the rate of polymerization is independent of activator concentration.

Cobalt doped γ-Fe2O3 nanoparticles: synthesis and magnetic properties

Abstract: We demonstrate here the wet chemical synthesis of cobalt doped γ-Fe2O3 nanoparticles and the subsequent effect on magnetic properties with the variation in dopant concentration. It is observed that cobalt can be homogeneously doped into the γ-Fe2O3 lattice up to 5 mol% without any appreciable change in the particle size ( nm). Further increase in cobalt concentration (10 mol% here) resulted in an increase in particle size ( nm) due to possible adsorption of a cobalt layer on the surface of γ-Fe2O3 nanoparticles rather than complete doping in the iron oxide lattice. The ac susceptibility measurements revealed an increase in blocking temperature (TB) with percentage variation in cobalt doping (2–10%), indicating substitution of Fe3+ ions by Co2+ ions in the γ-Fe2O3 lattice. The dc magnetization measurements showed an increase in saturation magnetization only up to 5%, beyond which it significantly diminished. The reduction in saturation magnetization is attributed to the contribution from surface anisotropy in cobalt coated γ-Fe2O3 nanoparticles.

Ag NPs decorated on a COF in the presence of DBU as an efficient catalytic system for the synthesis of tetramic acids via CO2 fixation into propargylic amines at atmospheric pressure.

Abstract: CO2 fixation reactions by inserting it in reactive organic compounds are very challenging for the utilization of this abundant and harmful gas present in air and thus to mitigate this greenhouse gas responsible for global warming. This can be achieved by appropriate design of functionalized porous nanocatalysts having high surface areas and porosity and good CO2 uptake capacity. Herein, we first report the decoration of silver nanoparticles (NPs) over the surface of a covalent organic framework (COF) material TpPa-1 synthesized through the polycondensation of 2,4,6-triformylphloroglucinol (TFP) and p-phenylenediamine. The resulting material Ag@TpPa-1 was thoroughly characterized by N2 adsorption/desorption, powder X-ray diffraction (PXRD), FE-SEM, TEM, UV-Vis, FT IR and thermogravimetric techniques. This Ag NP decorated porous COF in the presence of DBU exhibited excellent catalytic activity for the synthesis of tetramic acids from a variety of propargylic amine derivatives at 60 °C under atmospheric pressure of carbon dioxide via formation of oxazolidinones, where CO2 acts as a C1 reagent. The Ag@TpPa-1 catalyst exhibited excellent recycling efficiency for the synthesis of tetramic acid with no leaching of Ag from the catalyst surface.

Horndeski theories confront the Gravity Probe B experiment

Abstract: In this work we have investigated various properties of a spinning gyroscope in the context of Horndeski theories. In particular, we have focused on two specific situations---(a) when the gyroscope follows a geodesic trajectory and (b) when it is endowed with an acceleration. In both these cases, besides developing the basic formalism, we have also applied the same to understand the motion of a spinning gyroscope in various static and spherically symmetric spacetimes pertaining to Horndeski theories. Starting with the Schwarzschild de Sitter spacetime as a warm up exercise, we have presented our results for two charged Galileon black holes as well as for a black hole in scalar coupled Einstein-Gauss-Bonnet gravity. In all these cases we have shown that the spinning gyroscope can be used to distinguish black holes from naked singularities. Moreover, using the numerical estimation of the geodetic precession from the Gravity Probe B experiment, we have constrained the gauge/scalar charge of the black holes in these Horndeski theories. Implications are also discussed.