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.

Nonionic surfactants: a key to enhance the enzyme activity at cationic reverse micellar interface.

Abstract: The primary objective of the present study is to understand how the different nonionic surfactants modify the anisotropic interface of cationic water-in-oil (W/O) microemulsions and thus influences the catalytic efficiency of surface-active enzymes. Activity of Chromobacterium viscosum lipase (CV-lipase) was estimated in several mixed reverse micelles prepared from CTAB and four different nonionic surfactants, Brij-30, Brij-92, Tween-20, and Tween-80/water/isooctane/n-hexanol at different z ([cosurfactant]/[surfactants]) values, pH 6 (20 mM phosphate), 25 degrees C across a varying range of W0 ([water]/[surfactants]) using p-nitrophenyl-n-octanoate as the substrate. Lipase activity in mixed reverse micelles improved maximum up to approximately 200% with increasing content of non-ionic surfactants compared to that in CTAB probably due to the reduced positive charge density as well as plummeted n-hexanol (competitive inhibitor of lipase) content at the interfacial region of cationic W/O microemulsions. The highest activity of lipase was observed in CTAB (10 mM) + Brij-30 (40 mM)/isooctane/n-hexanol)/water system, k2 = 913 +/- 5 cm3 g-1 s-1. Interestingly, this observed activity is even higher than that obtained in sodium bis (2-ethyl-1-hexyl) sulfosuccinate (AOT)/n-heptane reverse micelles, the most popular W/O microemulsion in micellar enzymology. To ascertain the influence of non-ionic surfactants in improving the activity of surface-active enzymes is not limited to lipase only, we have also investigated the catalytic activity of Horseradish peroxidase (HRP) in different mixed W/O microemulsions. Here also following the similar trend as observed for lipase, HRP activity enhanced up to 2.5 fold with increasing concentration of nonionic surfactants. Finally, the enzyme activity was correlated with the change in the microenvironment of mixed reverse micelles by steady-state fluorescence study using 8-anilino-1-napthalenesulphonic acid (ANS) as probe.

A Novel Example of Metal-Mediated Aromatic Thiolation in a Ruthenium Complex. Crystal Structure of RuII(SC6H4NNC6H4N)2†

Abstract: ctc-Ru(L)2(Cl)2, 1 [L = pyridine-2-azobenzene], reacts with EtOCS2K to give an unusual product, 3, where the ortho-carbon atom of the pendant phenyl ring of each L is selectively thiolated. Crystal structure and spectra of compound 3 are reported.

Resonance Energy Transfer from Rhodamine 6G to Gold Nanoparticles by Steady-State and Time-Resolved Spectroscopy

Abstract: In the present study, we found a pronounced effect on the PL and shortening of the overall lifetime of rhodamine 6G (R6G) when interacting with the spherical, shaped, and capped Au NPs, but there are no measured effects on radiative rate of the dye. The observed Forster distances (R0) are 105.75, 170, and 124 A for spherical, shaped, and capped Au nanoparticles, respectively and the distances between the donor and acceptor are 103.56, 194.77, and 134.43 A. However, the distances between the donor and acceptor are 78.26, 99.04, and 88.43 A for spherical, shaped, and capped Au nanoparticles, respectively, using the efficiency of surface energy transfer which follows a 1/d4 distance dependence between donor and acceptor. On the basis of these findings, we may suggest that surface energy transfer process has a more reasonable agreement with experimental finding. The anisotropy decay of R6G with spherical Au nanoparticles is single exponential with correlation time constant of 240 ps. However, the anisotropy d...

Ionic Liquid as Catalyst and Reaction Medium: A Simple, Convenient and Green Procedure for the Synthesis of Thioethers, Thioesters and Dithianes using an Inexpensive Ionic Liquid, [pmIm]Br

Abstract: An easily accessible and inexpensive room temperature ionic liquid, 1-pentyl-3-methylimidazolium bromide, [pmIm]Br efficiently catalyzes the reaction of alkyl halides or acyl halides with thiols without any solvent at room temperature leading to the synthesis of thioethers and thioesters in high yields. This reaction has also been extended for the preparation of dithianes and transthioetherification. The ionic liquid is recovered and recycled for subsequent runs.