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141.
142.
Spiroketals are widely found as substructures of many naturally occurring compounds from diverse sources including plants, animals as well as microbes. Naturally occurring spiroketals are biologically active and most of them are chiral molecules. This article aims at reviewing the asymmetric synthesis of biologically active spiroketals for last 10 years (1998-2007). 相似文献
143.
Gold nanocomposite of Polyaniline was prepared by chemical synthesis method and its thin film was made by drop casting. The Schottky junction of thin film was fabricated with aluminium metal. TGA analysis of the sample showed good stability. Current density-voltage characteristics of the junction showed good rectifying nature. The diode ideality factor is greater than unity. The junction showed good sensitivity to CO2 gas with decrease of forward current. The response time of the junction to CO2 showed good repeatability and recovery time is about 52 s. 相似文献
144.
Partha Pratim Saikia 《Tetrahedron letters》2008,49(46):6508-6511
An efficient and practical one-pot protocol for the reduction of β-nitro alcohols to their corresponding N-(tert-butoxycarbonyl) amino alcohols using Zn-NH4Cl in aqueous methanol is described. Other reducible groups such as ketones and isolated double bonds remained intact. This methodology allows a short synthesis of (−)-β-conhydrine to be achieved. 相似文献
145.
Verma RS Padalia RC Saikia D Chanotiya CS Chauhan A Krishna B 《Natural product research》2012,26(13):1257-1260
Essential oil isolated from the inflorescences of Capillipedium parviflorum (R. Br.) Stapf., collected from Kumaon region of Western Himalaya, India, was investigated by GC and GC-MS. A total of 45 constituents representing 99.0% of the essential oil were identified. The major components of this oil were 4-undecanone (33.2%), 4-undecanol (29.7%), 4-nonanol (13.9%), α-muurolol (5.3%), 4-tridecanone (3.6%), methyl-2-oxo-nonanoate (3.1%), trans-2-hexenyl butanoate (1.1%) and 1-tetradecanol (1.0%). The antimicrobial activity of the essential oil was determined against eight Gram-positive and Gram-negative bacterial strains, as well as two fungal strains. The bioassay showed that the essential oil possessed good antibacterial activity. 相似文献
146.
Abhijit Banik Paramartha Gogoi Monali Dutta Saikia 《Journal of inclusion phenomena and macrocyclic chemistry》2012,72(3-4):449-458
The interaction of naproxen with β-cyclodextrin and its derivatives (hosts) as well as polymer has been studied using UV Visible (UV–Vis), Fourier Transform Infrared (FTIR), Nuclear Magnetic Resonance (NMR) spectroscopy and Scanning electron microscopy (SEM). In this paper, the solid inclusion complexes were prepared by freeze drying method. The formation constants of the complexes were determined by UV–Vis method. The adsorption properties of naproxen with β-Cyclodextrin bonded silica stationary phase (CDS) were studied for an in-depth understanding of the host–guest interaction. The inclusion process involving naproxen and hosts was investigated by using the PM3 quantum–mechanical semiempirical method. The stabilization energy values obtained from the semiempirical calculation showed the same relation with the formation constant values determined by UV–Vis spectroscopy. 相似文献
147.
Kokil Saikia Biswajit Deb Bibek Jyoti Borah Podma Pollov Sarmah Dipak Kumar Dutta 《Journal of organometallic chemistry》2012,696(26):4293-4297
New palladium complexes of the type [PdCl2(η2–P∩P)] (1a,1b) and [PdCl2(η2–P∩S)] (1c,1d) have been synthesised by the reaction of PdCl2 with P,P and P,S type bidentate ligands in 1:1 mol ratio, where, P∩P = 9,9–dimethyl-4,5-bis(diphenylphosphanyl) xanthene {Xantphos}(a) or bis(2-diphenylphosphanylphenyl)ether{DPEphos}(b); P∩S = 9,9-dimethyl-4,5-bis(diphenyl -phosphanyl) xanthenemonosulfide {Xantphos(S)}(c) or bis(2-diphenylphosphanyl phenyl) ether monosulfide {DPEphos(S)}(d). The complexes are characterized by elemental analyses, mass spectrometry, 1H, 13C and 31P NMR spectroscopy together with the single crystal X-ray structure determination of 1a and 1d. The palladium atom in all the complexes occupies the centre of a slightly distorted square planar environment formed by a P atom, a P/S atom and two Cl atoms. The catalytic activities of 1a–1d investigated for Suzuki–Miyaura cross-coupling reactions at room temperature exhibit higher yield of the coupling products than catalysed by PdCl2 itself. Among 1a–1d, the palladium complexes of bidentate phosphine (1a, 1b) show higher efficacy than their monosulfide analogues (1c, 1d). However, the recycling experiments with the catalysts for a selected coupling reaction between 4-bromobenzonitrile and phenylboronic acid exhibit that 1c and 1d are more efficient than 1a and 1b, which may be due to the donor effect of the P,S ligands during catalytic reaction. 相似文献
148.
A rapid and efficient method has been developed for the synthesis of vicinal bromoazide directly from olefin using N-bromosuccinimide (NBS) and trimethylsilyl azide (TMSN3) as the bromine and azide sources, respectively, without any catalyst in acetonitrile as solvent. The rate of reaction is remarkably fast in acetonitrile without catalyst to produce bromoazides in high yield. 相似文献
149.
Ionic liquid‐derived polyoxometalate salts [mdsim]3[PM12O40] (where M = W and Mo) of two heteropolyacids H3PW12O40.nH2O and H3PMo12O40.nH2O were synthesized using 2‐methyl‐1,3‐disulfoimidazolium chloride ([mdsim][Cl]) ionic liquid and the corresponding heteropolyacids. Three equivalents of [mdsim][Cl] were treated with the respective Keggin‐structured heteropolyacids (one equivalent) in aqueous medium at room temperature to afford the water‐stable ionic polyoxometalates as acidic solids. They were completely characterized using spectroscopic and other analytical techniques including thermal analysis and Hammett acidity studies. The inherent Brønsted acidic properties of ─SO3H group of these polyoxometalate salts were studied for the nitration of aromatic compounds with 69% HNO3 at normal temperature and 80°C without use of any external concentrated sulfuric acid. These strongly acidic polyoxometalates display good recyclability and efficient reusability. 相似文献
150.
Sajid Saikia Animesh Ghosh Angshuman Nag 《Angewandte Chemie (International ed. in English)》2023,62(33):e202307689
A phosphor emitting both white light and broad near-infrared (NIR) radiation can simultaneously provide visual inspection and early signs of rotting of food products. The broad NIR emission is absorbed by the vibrational overtones of water molecules present in food items, providing the non-invasive image contrast to assess the food freshness. Here we design a phosphor, namely, Cr3+-Bi3+-codoped Cs2Ag0.6Na0.4InCl6, that simultaneously emit warm white light and broad NIR (1000 nm) radiation with quantum yield 27 %. This dual emitter is designed by combining the features of s2-electron (Bi3+) and d3-electron (Cr3+) doping in a weak crystal field of the halide perovskite host. excitation of Bi3+, using a commercial 370 nm ultraviolet light-emitting-diodes (UV-LED), yields both the emissions. A fraction of the excited Bi3+ dopants emit the warm white light, and the other fraction transfers its energy non-radiatively to Cr3+. Then the Cr3+ de-excites emitting broad NIR emission. Temperature dependent (6.4–300 K) photoluminescence in combination with Tanabe-Sugano diagram show that the Cr3+ experiences a weak crystal field ( =2.2), yielding the NIR emission. As a proof of concept, we fabricated a panel containing 122 phosphor-converted LEDs, demonstrating its capability to inspect food products. 相似文献