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Onoabedje E.A.,University of Nigeria | Okoro U.C.,University of Nigeria | Sarkar A.,India Association for the Cultivation of Science | Knight D.W.,University of Cardiff
Journal of Sulfur Chemistry | Year: 2016

New alkynyl derivatives of phenothiazine and phenoxazine were obtained via Sonogashira cross-coupling reactions. This was achieved by first synthesizing the intermediates 6-chloro-5H-benzo[a]phenothiazin-5-one, 6-chloro-5H-benzo[a]phenoxazin-5-one and 6-chloro-5H-naphtho[2,1-b]pyrido[2,3-e][1,4]oxazin-5-one by anhydrous base-catalyzed condensations between 2,3-dichloro-1,4-naphthoquinone and 2-aminothiophenol, 2-aminophenol and 2-aminopyridinol, respectively .The cross-couplings of these electron-rich chlorophenothiazine and chlorophenoxazine intermediates with terminal alkynes, employing 4 mol% Pd and 7 mol% XPhos in the presence of base in acetonitrile at 80°C, afforded the highly colored alkynylated derivatives in good yields. These reaction conditions allowed the incorporation of both unprotected N-H and carbonyl groups. Structural assignments were established by spectroscopic (UV, IR, 1H and 13Cnmr), ms and elemental analytical data. © 2016 Taylor & Francis Source

Majumdar D.,India Association for the Cultivation of Science | Saha S.K.,India Association for the Cultivation of Science
Applied Physics Letters | Year: 2010

Long range charge delocalization usually inhibits ferroelectric response in conjugated polymers. We observe remarkable ferroelectric response (remnant polarization 2.8 μC cm-2) in polyaniline (PANI) nanotubes synthesized by oxidative polymerization technique in methanol medium using anodic alumina (AAO) template. Ferroelectricity in PANI nanotubes arises due to spontaneous polarization caused by hydrogen bonds, created due to charge transfer between methanol molecule and aligned polymer chain. Due to directional growth along the AAO nanochannel, PANI chains are well-aligned and all these dipoles associated with hydrogen bonds are arranged in regular order-exhibiting exceptional ferroelectric response. However, such effect is absent in bulk PANI. © 2010 American Institute of Physics. Source

Sau S.,Bose Institute of India | Sau S.,University of Texas at Austin | Sutradhar S.,India Association for the Cultivation of Science | Paul R.,India Association for the Cultivation of Science | Sinha P.,Bose Institute of India
PLoS ONE | Year: 2014

In the budding yeast, centromeres stay clustered near the spindle pole bodies (SPBs) through most of the cell cycle. This SPB-centromere proximity requires microtubules and functional kinetochores, which are protein complexes formed on the centromeres and capable of binding microtubules. The clustering is suggested by earlier studies to depend also on protein-protein interactions between SPB and kinetochore components. Previously it has been shown that the absence of non-essential kinetochore proteins of the Ctf19 complex weakens kinetochore-microtubule interaction, but whether this compromised interaction affects centromere/kinetochore positioning inside the nucleus is unknown. We found that in G1 and in late anaphase, SPB-centromere proximity was disturbed in mutant cells lacking Ctf19 complex members,Chl4p and/or Ctf19p, whose centromeres lay further away from their SPBs than those of the wild-type cells. We unequivocally show that the SPB-centromere proximity and distances are not dependent on physical interactions between SPB and kinetochore components, but involve microtubule-dependent forces only. Further insight on the positional difference between wildtype and mutant kinetochores was gained by generating computational models governed by (1) independently regulated, but constant kinetochore microtubule (kMT) dynamics, (2) poleward tension on kinetochore and the antagonistic polar ejection force and (3) length and force dependent kMT dynamics. Numerical data obtained from the third model concurs with experimental results and suggests that the absence of Chl4p and/or Ctf19p increases the penetration depth of a growing kMT inside the kinetochore and increases the rescue frequency of a depolymerizing kMT. Both the processes result in increased distance between SPB and centromere. © 2014 Sau et al. Source

Bera M.,India Association for the Cultivation of Science | Ghosh T.K.,India Association for the Cultivation of Science | Akhuli B.,India Association for the Cultivation of Science | Ghosh P.,India Association for the Cultivation of Science
Journal of Molecular Catalysis A: Chemical | Year: 2015

Tris(2-aminoethyl)-amine, TREN based tris-ureas (1a-1d) and tris-thiourea (1e) have been explored towards a wide range of catalytic Michael addition reactions. These tris-ureas, 1a-1d efficiently catalyze the addition reaction of β-nitro styrenes (2a-2d) with various nucleophiles such as β-ketoesters (3a-3c), 1,3-dicarbonyl compound (3d), a cyanoester (3e) and a nitroester (3f) under ambient conditions to produce corresponding nitro alkanes in high yields. Pentafluorophenyl attached tris-urea, 1d is found to be the most effective catalyst in the series that yields 78-98% products conversion. In case of the reaction between β-nitro styrenes and malononitrile (3g) in presence of 1d, 2-amino-5-nitro-4,6-diphenylcyclohex-1-ene-1,3,3-tricarbonitriles are also isolated as a minor product along with the corresponding Michael adduct. The added advantage of bridge-head nitrogen center in tris-urea organocatalysts, 1a-1d has been established by studying analogous benzene platform based tris-ureas (1f, 1g, 1h) in similar experimental conditions. Furthermore, a plausible reaction mechanism has also been established based on in-situ 1H NMR kinetic studies. © 2015 Elsevier B.V. Source

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