Publications by authors named "Satyajit Saha"

7 Publications

  • Page 1 of 1

Design and Development of Axially Chiral Bis(naphthofuran) Luminogens as Fluorescent Probes for Cell Imaging.

Chemistry 2021 Mar 25;27(17):5470-5482. Epub 2021 Feb 25.

Department of Speciality Chemicals Technology, Institute of Chemical Technology (ICT), Mumbai, 400019, India.

Designing chiral AIEgens without aggregation-induced emission (AIE)-active molecules externally tagged to the chiral scaffold remains a long-standing challenge for the scientific community. The inherent aggregation-caused quenching phenomenon associated with the axially chiral (R)-[1,1'-binaphthalene]-2,2'-diol ((R)-BINOL) scaffold, together with its marginal Stokes shift, limits its application as a chiral AIE-active material. Here, in our effort to design chiral luminogens, we have developed a design strategy in which 2-substituted furans, when appropriately fused with the BINOL scaffold, will generate solid-state emissive materials with high thermal and photostability as well as colour-tunable properties. The excellent biocompatibility, together with the high fluorescence quantum yield and large Stokes shift, of one of the luminogens stimulated us to investigate its cell-imaging potential. The luminogen was observed to be well internalised and uniformly dispersed within the cytoplasm of MDA-MB-231 cancer cells, showing high fluorescence intensity.
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http://dx.doi.org/10.1002/chem.202004942DOI Listing
March 2021

Characterization of zinc oxide nanocrystals with different morphology for application in ultraviolet-light photocatalytic performances on rhodamine B.

Luminescence 2021 Feb 16;36(1):149-162. Epub 2020 Aug 16.

Department of Physics, Vidyasagar University, Paschim Medinipur, West Bengal, India.

ZnO nanostructures of different morphology (nanorods, nano-leaf, nanotubes) were favourably grown using a chemical precipitation process. The prepared ZnO nanostructures were characterized systematically using absorption spectroscopy, emission spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared studies. XRD results showed the hexagonal wurtzite phase of the synthesized ZnO nanostructures. Structural properties such as average crystallite size, lattice constants, volume of the unit cell, atomic fraction, and structural bonds were also studied. The optical band gap of the synthesized ZnO nanocrystals varied from 3.52 eV to 3.69 eV with high quantum yield of the blue emission (~420 nm). Urbach energy for ZnO nanocrystals was calculated to be 0.702 eV, 0.901 eV, and 0.993 eV for nanorods, nano-leaf, and tube like ZnO crystals, respectively. Morphology of the fabricated nanostructures was investigated using SEM. Photocatalytic degradation of rhodamine B (Rh B) in solution under UV irradiation was explored with different ZnO morphology. Photocatalytic experiments showed that ZnO nano-leaf had a higher degradation rate of photocatalytic activity of photodegrading Rh B compared with the other tube shape and rods shape nanostructures. The Rh B dye degraded considerably by ∼79.05%, 74.41%, and 69.8% within 120 min in the presence of the as-fabricated fern nano-leaf, nanotubes, and nanorods of the ZnO nanocrystals at room temperature.
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http://dx.doi.org/10.1002/bio.3930DOI Listing
February 2021

Directing group assisted nucleophilic substitution of propargylic alcohols via o-quinone methide intermediates: Brønsted acid catalyzed, highly enantio- and diastereoselective synthesis of 7-alkynyl-12a-acetamido-substituted benzoxanthenes.

Org Lett 2015 Feb 22;17(3):648-51. Epub 2015 Jan 22.

Institute of Organic Chemistry, University of Leipzig , Johannisallee 29, D-04103 Leipzig, Germany.

BINOL-based, chiral phosphoric acids catalyze the substitution of 1-(o-hydroxyphenyl)propargylic alcohols with enamides to furnish 7-alkynyl-12a-acetamido-substituted benzo[c]xanthenes and related heterocycles in a one-pot operation with excellent diastereo- and enantioselectivity. Ambient reaction temperature, operationally simple reaction conditions, low catalyst loading, high yields, and excellent stereocontrol are attractive features of this process and make it a highly practical and versatile transformation.
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http://dx.doi.org/10.1021/ol503662gDOI Listing
February 2015

Chiral Brønsted acid-catalyzed Friedel-Crafts alkylation of electron-rich arenes with in situ-generated ortho-quinone methides: highly enantioselective synthesis of diarylindolylmethanes and triarylmethanes.

Chem Commun (Camb) 2015 Jan;51(8):1461-4

Institut für Organische Chemie, Universität Leipzig, Johannisallee 29, D-4103 Leipzig, Germany.

We disclose herein a highly enantioselective protocol for the Brønsted acid-catalyzed addition of indoles and phenols to in situ-generated ortho-quinone methides which deliver broadly substituted diarylindolylmethanes and triarylmethanes, respectively, in a one-pot reaction under very mild conditions. A chiral phosphoric acid catalyst has been developed for this process serving to convert the starting ortho-hydroxybenzhydryl alcohols into the reactive ortho-quinone methides and to control the enantioselectivity of the carbon-carbon bond-forming event via hydrogen-bonding.
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http://dx.doi.org/10.1039/c4cc08559kDOI Listing
January 2015

Brønsted acid-catalyzed, highly enantioselective addition of enamides to in situ-generated ortho-quinone methides: a domino approach to complex acetamidotetrahydroxanthenes.

Chemistry 2015 Feb 8;21(6):2348-52. Epub 2014 Dec 8.

Institut für Organische Chemie, Universität Leipzig, Johannisallee 29, 04103 Leipzig (Germany).

The highly enantioselective conjugate addition of enamides and enecarbamates to in situ-generated ortho-quinone methides, upon subsequent N,O-acetalization, gives rise to acetamido-substituted tetrahydroxanthenes with generally excellent enantio- and diastereoselectivities. A chiral BINOL-based phosphoric acid catalyst controls the enantioselectivity of the carbon-carbon bond-forming event. The products are readily converted into other xanthene-based heterocycles.
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http://dx.doi.org/10.1002/chem.201406044DOI Listing
February 2015

Enantioselective organocatalytic Biginelli reaction: dependence of the catalyst on sterics, hydrogen bonding, and reinforced chirality.

J Org Chem 2011 Jan 30;76(2):396-402. Epub 2010 Dec 30.

Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

From a systematic investigation involving the synthesis of a series of catalysts and screening studies, the organocatalyst 16, which is sterically hindered, contains a strong hydrogen-bonding site, and is endowed with reinforced chirality, is shown to promote the Biginelli cyclocondensation of aromatic as well as aliphatic aldehydes with ethyl acetoacetate and urea in a remarkably high enantioselectivity (ee ca. 94-99%).
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http://dx.doi.org/10.1021/jo101717mDOI Listing
January 2011

Intramolecular O-H...O hydrogen-bond-mediated reversal in the partitioning of conformationally restricted triplet 1,4-biradicals and amplification of diastereodifferentiation in their lifetimes.

J Am Chem Soc 2008 Oct 17;130(41):13608-17. Epub 2008 Sep 17.

Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India.

The photoreactivity and nanosecond transient phenomena have been investigated for a rationally designed set of ketones 4-9 in order to gain comprehensive insights concerning the influence of intramolecular hydrogen bonding on (i) the lifetimes of triplet 1,4-biradicals and (ii) the partitioning of the latter between cyclization and elimination. Comparisons of the photochemical results and lifetime data for the biradicals of ketones 6 versus 8 and 7 versus 9 revealed a remarkable influence of hydrogen bonding when superimposed upon steric factors: while 6 and 7 yielded cyclobutanols in poor yields, cyclization was found to be overwhelmingly predominant for 8-anti and moderately so for 9-anti, with a high stereoselectivity in the formation of cyclobutanols (>95% for 8-anti). The diastereochemistry in the case of 8 permitted the occurrence of fragmentation or cyclization almost exclusively (>90% cyclization for 8-anti and >75% elimination for 8-syn). Significantly, the intramolecular hydrogen bonding in the biradicals of 8 and 9 was found to reverse their partitioning between cyclization and elimination compared with the behavior of the biradicals of ketones 3; the ketones 8-anti and 9-anti underwent cyclization in benzene, predominantly leading to cyclobutanols with syn stereochemistry between the C2 and C3 substituents. In accordance with photoproduct profiles, an unprecedented approximately 2-fold difference in the lifetimes of the intermediate diastereomeric triplet biradicals of ketones 8 in nonpolar solvents (e.g., tau(syn) = 123 ns and tau(anti) = 235 ns in cyclohexane) was observed via nanosecond laser flash photolysis, while no such difference in lifetimes was found for the triplet biradicals of acetoxy ketones 9. The intriguing diastereodifferentiation in the lifetimes of the diastereomeric triplet 1,4-biradicals of 8 and the product profiles of ketones 6, 7, and 9 are best reconciled via a unified mechanistic picture in which superposition of steric factors over varying magnitudes of O-H...O hydrogen bonding selectively facilitates a particular pathway. In particular, the diastereodifferentiation in the photochemical outcomes for the diastereomers of ketone 8 and in the lifetimes of their triplet biradicals can be understood on the basis of rapid deactivation of the 8-syn triplet biradical via fragmentation and slow cyclization of the 8-anti triplet biradical from chair- and twist-boat-like hydrogen-bonded conformations, respectively. The photolysis in polar aprotic solvents such as DMSO and pyridine was found to reverse the chemoselectivity, yielding reactivity paralleling that of ketones 3, for which the steric factors between the C2 and C3 substituents control the photochemical outcome.
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http://dx.doi.org/10.1021/ja8032179DOI Listing
October 2008
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