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.

Reversible association of thermoresponsive gold nanoparticles: polyelectrolyte effect on the lower critical solution temperature of poly(vinyl methyl ether).

Abstract: Thermoresponsive gold nanoparticles (GNPs) have been prepared by the borohydride reduction of gold salt in the presence of water-soluble polymer, poly(vinyl methyl ether) (PVME). The PVME-coated GNPs (PVME-GNPs) have been assembled into large aggregates in the presence of polyelectrolytes, viz., poly(sodium-4 styrene sulfonate) and sodium salt of carboxymethylcellulose at low pH by raising the solution temperature from 20 to 40 degrees C. Increase of temperature triggers the interparticle association due to hydrophobic interaction of pendent methyl group of the surface adsorbed PVME. This assembly process is reversible with respect to temperature and pH of the medium and was studied by monitoring the change in surface plasmon resonance band of PVME-GNPs. Three-dimensional assemblies of various architectures, depending on the concentration of polyelectrolytes, were observed through transmission electron microscopy. A mechanistic model has been suggested for the reversible assembly formation that suits well with the experimental observations. The changes in optical properties of the PVME-GNPs due to their aggregation/disaggregation enabled us to use it as an effective tool to monitor the change in lower critical solution temperature (LCST) of PVME in the presence of polyelectrolytes due to interpolymer complexation at low pH. This result agrees well with the variation of LCST of pure aqueous PVME solution in the presence of polyelectrolytes measured by conventional turbidimetric technique.

Concerted Proton–Electron Transfer in Electrocatalytic O2 Reduction by Iron Porphyrin Complexes: Axial Ligands Tuning H/D Isotope Effect

Abstract: The electrochemical O2 reduction by thiolate- and imidazole-bound iron porphyrin complexes and H/D isotope effects on 4e– (determined by rotating disc electrochemistry) and 2e– (determined by rotating ring disc electrochemistry) O2 reduction rates are investigated. The results indicate that a thiolate axial ligand shows an H/D isotope effect greater than 18 and 47 for the 4e– and 2e– O2 reductions, respectively. Alternatively, an imidazole axial ligand results in H/D isotope effects of 1.04 and 4.7 for the 4e– and 2e– O2 reduction, respectively. The catalytic O2 reduction mechanism is investigated in situ with resonance Raman coupled with rotating disc electrochemistry. The data indicate that the rate-determining step changes from O–O bond heterolysis of FeIII–OOH species for a thiolate axial ligand to an O–O bond heterolysis of an FeII–OOH for an imidazole axial ligand.

Improved mechanical and electronic properties of co-assembled folic acid gel with aniline and polyaniline.

Abstract: Co-assembled folic acid (F) gel with aniline (ANI) (ANI:F = 1:2, w/w) is produced at 2% (w/v) concentration in water/DMSO (1:1, v/v) mixture. The gel is rigid and on polymerization of the gel pieces in aqueous ammonium persulfate solution co-assembled folic acid - polyaniline (F-PANI) gel is formed. Both the co-assembled F-ANI and F-PANI gels have fibrillar network morphology, the fiber diameter and its degree of branching increase significantly from those of F gel. WAXS pattern indicates co-assembled structure with the F fiber at the core and ANI/PANI at its outer surface and the co-assembly is occurring in both F-ANI and F-PANI systems through noncovalent interaction of H-bonding and π stacking processes between the components. FTIR and UV–vis spectra characterize the doped PANI formation and the MALDI mass spectrometry indicates the degree of polymerization of polyaniline in the range 24-653. The rheological experiments support the signature of gel formation in the co-assembled state and the storage (G...

Charge disproportionate molecular redox for discrete memristive and memcapacitive switching

Abstract: Electronic symmetry breaking by charge disproportionation results in multifaceted changes in the electronic, magnetic and optical properties of a material, triggering ferroelectricity, metal/insulator transition and colossal magnetoresistance. Yet, charge disproportionation lacks technological relevance because it occurs only under specific physical conditions of high or low temperature or high pressure. Here we demonstrate a voltage-triggered charge disproportionation in thin molecular films of a metal–organic complex occurring in ambient conditions. This provides a technologically relevant molecular route for simultaneous realization of a ternary memristor and a binary memcapacitor, scalable down to a device area of 60 nm2. Supported by mathematical modelling, our results establish that multiple memristive states can be functionally non-volatile, yet discrete—a combination perceived as theoretically prohibited. Our device could be used as a binary or ternary memristor, a binary memcapacitor or both concomitantly, and unlike the existing ‘continuous state’ memristors, its discrete states are optimal for high-density, ultra-low-energy digital computing. Charge disproportionation in thin molecular films of a metal–organic complex enables the realization of a ternary memristor and binary memcapacitor.