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.

A mechanistic and kinetic study of the formation of metal nanoparticles by using synthetic tyrosine-based oligopeptides

Abstract: Synthetic oligopeptides containing redox-active tyrosine residues have been employed to prepare gold and silver nanoparticles. In this reduction process an electron from the tyrosinate ion of the peptide is transferred to the metal ion at basic pH through the formation of a tyrosyl radical, which is eventually converted to its dityrosine form during the reaction. This reaction mechanism was confirmed from UV-visible, fluorescence, and EPR spectroscopy and was found to be pH-dependent. Transmission electron microscopy measurement shows that the average size and the monodispersity of gold nanoparticles increase as the number of tyrosine residues in the peptide increases. The kinetic study, based on spectrophotometric measurements of the surface plasmon resonance optical property, shows that the rate of formation of gold nanoparticles was much faster at higher pH than at lower pH and was also dependent on the number of tyrosine residues present in the peptide. The dityrosine form of the peptide was found to retain reducing properties like those of tyrosine in basic medium.

Pd-grafted porous metal–organic framework material as an efficient and reusable heterogeneous catalyst for C–C coupling reactions in water

Abstract: Palladium nanoparticles (Pd NPs) have been grafted at the surfaces of a Co-containing metal–organic framework material MCoS-1. The Pd NPs grafted material Pd(0)/MCoS-1 has been characterized by HR TEM, XPS and EPR spectroscopic analyses. Pd(0)/MCoS-1 showed excellent catalytic activities in Suzuki–Miyaura cross-coupling reaction for the synthesis of a diverse range of biaryl organics in water. Sonogashira cross-coupling between terminal alkynes and aryl halides has also been carried out over this Pd-nanocatalyst in water without the addition of any Cu co-catalyst. In both reactions the catalyst is easily recoverable and can be reused for several times without appreciable loss of catalytic activity. No evidence of the leaching of Pd from the catalyst during the course of reaction has been observed, suggesting true heterogeneity in our catalytic systems.

Enhanced catalytic performance by copper nanoparticle–graphene based composite

Abstract: A graphene based composite with copper nanoparticles (Cu–G) has been synthesized and used as catalyst for N-arylation and O-arylation. The structure and composition of the nanocomposite have been characterized by TEM, AFM, Raman and XPS. The catalytic activity of the Cu–G has been tested for the N-arylation of N–H heterocycles using arylboronic acids and the O-arylation of phenols using aryl halides. The catalytic N-arylation produces N-aryl heterocyles and the catalytic O-arylation produces diaryl ethers, under mild reaction conditions with excellent yields and selectivities. The developed catalyst is air-stable, inexpensive, easy to prepare, easy to recover by simple filtration and can be reused without appreciable loss of activity.

Intergranular Magnetoresistance in Sr 2 FeMoO 6 from a Magnetic Tunnel Barrier Mechanism across Grain Boundaries

Abstract: We present magnetization (M) and magnetoresistance (MR) data for a series of ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ samples with independent control on antisite defect and grain-boundary densities, which reveal several unexpected features, including a novel switching-like behavior of MR with M. These, in conjunction with model calculations, establish that the MR in ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ is dominantly controlled by a new mechanism, derived from the magnetic polarization of grain-boundary regions acting like spin valves, leading to behavior qualitatively different from that usually encountered in tunneling MR. We show that a simple and useful experimental signature for the presence of this spin-valve-type MR (SVMR) is a wider hysteresis in MR compared to that in M.

Au Nanoparticle-Based Surface Energy Transfer Probe for Conformational Changes of BSA Protein

Abstract: In the present study, Au nanoparticle based surface energy transfer (SET) has been used to measure conformational changes in proteins. A significant photoluminescence (PL) quenching (91−97%) of tryptophan intensities of bovine serum albumin (BSA) protein is observed in the presence of Au nanoparticles, and the measured distances (r) between the donor (tryptophan) and the acceptor (Au nanoparticle) are 27.0, 22.9, and 25.7 A for E, N, and B forms of BSA protein, respectively. Results indicate that Au nanoparticle quenches BSA fluorescence mainly through a static quenching mechanism. Analysis suggests that binding constant and bound/unbound ratio varies with changing the conformation of protein. The PL quenching of dye varies from 47.2 to 86.6% with changing the conformation of protein without changing the radiative rate of dye. The measured distances (d) between the donor (dye) and the acceptor (Au nanoparticle) are 116.5, 76.1, and 86.4 A for E, N, and B forms of BSA protein, respectively, using the effic...