Browsing by Author "Ambika Srivastava"

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BF3·Et2O Catalysed 4-Aryl-3-phenyl-benzopyrones, Pro-SERMs, and Their Characterization
(Hindawi Limited, 2015) Ambika Srivastava; Pooja Singh; Rajesh Kumar
We have synthesized the novel 4-(4-hydroxy-benzyl)-3-phenyl-chromen-2-one which is a precursor of SERMs with a smaller number of steps and good yield. Two methodologies for the synthesis have been worked out. Anhydrous BF3·Et2O catalyzed reaction was found to be selective for product formation while anhydrous AlCl3, FeCl3, and SnCl4 catalyzed ones were nonselective. © 2015 Ambika Srivastava et al.
Comparative study of thermal degradation behavior of graft copolymers of polysaccharides and vinyl monomers
(2012) Arti Srivastava; Vivek Mishra; Pooja Singh; Ambika Srivastava; Rajesh Kumar
The thermal degradation of graft copolymers of both polysaccharides (guar gum and xanthan gum) showed gradual decrease in mass loss. Pure guar gum degraded about 95% but pure xanthan gum degraded about 76% up to 1173.15 K, while graft copolymers of guar gum and xanthan gum degraded only 65-76% up to 1173.15 K. Acrylic acid grafted guar gum and xanthan gum showing two-step degradation with formation of anhydride and ketonic linkage during heating, same pattern of degradation was found for xanthan gum-g-methacrylic acid. Guar gum-g-acrylamide degraded in single step and xanthan gum-g-acrylamide started to degrade above 448.15 K and it is a two-stage process and imparts thermal stability due to the formation of imide linkage with evolution NH 3. Guar gum-g-methacrylamide degraded in three steps due to the loss of NH 3 and CO 2 successively. 4-vinyl pyridine grafted both polysaccharides show single step degradation due to loss of pyridine pendent. N-vinyl formamide grafted guar gum and xanthan gum started to degrade at about 427.15 K, showed two-stage degradation process with the evolution of CO and NH 3 molecules while guar gum-g-(N-vinyl-2-pyrrolidone) degraded into two steps by the loss of pyrrolidone nucleus. Gum-g-2-acrylamido-2-methyl-1- propane sulfonic acid (AMPS) showed two-step degradation processes in two successive degradation steps, while xanthan gum-g-AMPS has started degradation at about 427.15 K and completed in five degradation steps. Overall, it was found that the grafted polysaccharides are thermally more stable than pure polysaccharides. © 2011 Akadémiai Kiadó, Budapest, Hungary.
Coumarin-based polymer and its silver nanocomposite as advanced antibacterial agents: Synthetic path, kinetics of polymerization, and applications
(2012) Ambika Srivastava; Vivek Mishra; Pooja Singh; Rajesh Kumar
A novel polymer bearing coumarin pendants of 4-allyloxy-2H-chromen-2-one (ACO) was synthesized by atom transfer radical polymerization (ATRP) in toluene at 110°C using 2-Bromoisobutyryl bromide (BIBB), Cu (I) Br, and 2,2'-bipyridyl (bpy) as initiator, catalyst, and ligand, respectively. The most appropriate molar concentration ratio of [ACO]: [BIBB]: [Cu (I) Br]: [bpy] was found to be 40: 1: 1: 2 for controlled polymerization. Successful chain extension polymerization of poly (4-allyloxy-2H-chromen-2-one) (PACO) confirms the livingness of the process. The activation energy (E a) (76.26 kJ mol -1) and enthalpy of activation (ΔH) (73.07 kJ mol -1) were in good agreement to each other proving the feasibility of the reaction and negative value of entropy of activation (ΔS) (-320 J mol -1 K -1) supported the highly restricted movement of reacting species in transition state during polymerization. Initial polymer decomposition temperature of PACO was found to be 130°C. SEM analysis revealed that polymer surface is not smooth with pointed rod like shapes. The polymer/Ag nanocomposite was synthesized and examined in view of antibacterial effect against Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Proteus mirabilis, and Klebsiella pneumonae. PACO and its Ag nanocomposite (PACON) have been found to be active selectively against bacterial pathogen E. fecalis with minimum inhibitory concentration of 50 and 32 μg mL -1, respectively. Copyright © 2012 Wiley Periodicals, Inc.
Indole-based polymer and its silver nanocomposite as advanced antibacterial agents: Synthetic path, kinetics of polymerization and applications
(2013) Ambika Srivastava; Pooja Singh; Rajesh Kumar; Satish Kumar Verma; Ravindra Nath Kharwar
Atom transfer radical polymerization of 1-allylindole-3-carbaldehyde (AIC) was studied by employing 2-bromoisobutyryl bromide as initiator in toluene. It led to controlled radical polymerization of AIC, with an increase of molecular weight along with the conversion of the monomer, and a relatively narrow molar mass distribution was obtained, as determined by gel permeation chromatography. The living nature of poly(1-allylindole-3-carbaldehyde) (PAIC) was confirmed by the chain extension polymerization whereas 1H NMR analysis showed that the major population of PAIC retained the chain-end functional group. PAIC and its silver nanocomposite were found to be biologically active against some tested bacterial pathogens. Minimum inhibitory concentration tests revealed that PAIC exhibited antibacterial activity against Staphylococcus aureus, Proteus mirabilis and Klebsiella pneumonae whereas PAIC/Ag nanocomposite showed antibacterial activity against Enterococcus faecalis and K. pneumonae. © 2012 Society of Chemical Industry.
Nanoporous well-defined reversible addition-fragmentation chain transfer polymer of N-acrylamido-l-tryptophan: Synthesis and characterization
(John Wiley and Sons Ltd, 2014) Pooja Singh; Ambika Srivastava; Rajesh Kumar
A nanoporous polymer with a chiral pendant chain of N-acrylamido-l-tryptophan was synthesized through a reversible addition-fragmentation chain transfer polymerization process using a dithiobenzoate derivative as chain transfer agent. The polymerization exhibited the usual characteristics of living processes, though slow polymerization rate and low percentage conversion for a chain extension experiment were observed. Depending on the monomer/chain transfer agent ratio, poly(N-acrylamido-l-tryptophan) with number-average molecular weights between 640 and 4340 gmol-1 and molar mass dispersities between 1.10 and 1.24 was obtained, as evidenced from gel permeation chromatography. Scanning electron microscopy images indicated that the polymer was porous. Nitrogen adsorption analysis of the polymer evidenced the presence of mesopores (2-19 nm) associated with micropores (0.45-2 nm) according to the Barrett-Joyner-Halenda method with a specific Brunauer-Emmett-Teller surface area of 22.98 m2g-1. © 2013 Society of Chemical Industry.
Pyrazolo-fused quinoline analogues: Synthesis of 1H-pyrazolo [3, 4-b] quinolines and 3-amino-1H-pyrazolo [3, 4-b] quinolines from 3-formyl and 3-cyano-2-chloroquinolines
(2006) Ambika Srivastava; Mrityunjay K. Singh; R.M. Singh
Stepwise synthesis of 1H-pyrazolo [3, 4-b] quinolines 6 has been described from the reactions of 2-chloro-3-formylquinolines 1 with ethyleneglycol and hydrazine hydrate reagents in sequence followed by hydrolysis with BiCl 3. However, 3-amino-1H-pyrazolo[3, 4-b]quinolines 7 have been synthesized from 2-chloro-3-cyanoquinolines 2 with excess of hydrazine hydrate in one step. The functional group manipulation of amino group in compounds 7 has also been studied.
Synthesis & characterization of tri arm Indole based ATRP Polymer and antibacterial study with its silver nanocomposite
(Springer Science and Business Media B.V., 2022) Ambika Srivastava; Shere Afgan; Paramjeet Yadav; Rajesh Kumar; Arti Srivastava; Ravindra Nath Kharwar
Hyperbranched poly (tris (1-allyl-1H-indol-3-yl) methane -co- 2-propionyloxy ethyl acrylate [Poly (TAIM-co-PEA)] was prepared by self-condensing vinyl copolymerization (SCVCP) of tris (1-allyl-1H-indol-3-yl) methane (TAIM) with 2-(2-bromopropionyloxy) ethyl acrylate (BPEA) via ATRP using the equimolar amount of TAIM and BPEA. In this hyperbranched polymer matrix, silver nanoparticles [Poly (TAIM-co-PEA)]N were prepared using a reductive method. The resultant polymer [Poly (TAIM-co-PEA)] and its silver nanocomposite [Poly (TAIM-co-PEA)]N were characterized by FTIR, 1H NMR, GPC, UV-visible, and TEM. The synthesized polymer has a nanopore size distribution centred at approximately 1.76 nm. Thermal stability of hyperbranched polymer [Poly (TAIM-co-PEA)] and its silver nanocomposite [Poly (TAIM-co-PEA)]N was studied by TGA/DTA and DSC. Antibacterial activity of porous polymer [Poly (TAIM-co-PEA)] and its silver nanocomposite [Poly (TAIM-co-PEA)]N was active against E. fecalis, E. coli, and K. pneumonae bacteria. © 2022, The Polymer Society, Taipei.
Synthesis and characterization of nano micelles of poly(N-acrylamidohexanoic acid)-b-poly(N-vinylcaprolactam) via RAFT process: Solubilizing and releasing of hydrophobic molecules
(Elsevier Ltd, 2015) Pooja Singh; Ambika Srivastava; Rajesh Kumar
RAFT polymerization at 70 °C in 1,4-dioxane with a trithiocarbonate as a CTA is used to synthesize well-defined poly(N-acrylamidohexanoic acid) with pre-determined molecular weight, narrow molar mass dispersity and precise chain end structure. Amphiphilic block copolymers of N-acrylamidohexanoic acid with N-vinylcaprolactam is synthesized and characterized by 1H NMR, FTIR and GPC. The micelles formed by poly(N-acrylamidohexanoic acid)-b-poly(N-vinylcaprolactam) block copolymer in aqueous solution are characterized by UV-visible spectroscopy of 1-pyrenecarboxaldehyde (1-PyCHO) probe, light scattering and TEM analysis. The critical micelle concentration value of the block copolymers, determined by UV-visible spectroscopy increased with the increase in the chain length of PVCL block. 1-PyCHO is encapsulated into the core of micelles via dialysis method. Loading of 5.3 wt % is observed and the micelles containing 1-PyCHO exhibit a sustained release profile. The results indicate that the PNAHA-b-PVCL micelles may be a potential drug delivery carrier for hydrophobic molecules. © 2014 Elsevier Ltd. All rights reserved.
Synthesis of amphiphilic poly(N-vinylcaprolactam) using ATRP protocol and antibacterial study of its silver nanocomposite
(2012) Pooja Singh; Ambika Srivastava; Rajesh Kumar
Atom transfer radical polymerization (ATRP) of N-vinylcaprolactam (NVCL) was studied by uisng ethyl-2-bromoisobutyrate (EIB) as initiator in 1,4-dioxane. It led to controlled radical polymerization of NVCL, with the molecular weight increased along with the conversion of monomer and a relatively narrow molecular weight distribution could be obtained, as determined by gel permeation chromatography. 1H NMR showed that the major population of poly(N-vinylcaprolactam) (PVCL) retained the chain-end functional group. The living nature of the ATRP for NVCL was confirmed by the experiments of PVCL chain extension. PVCL was further investigated for its ability to form micelles in aqueous media. Self-assembling of the amphiphilic PVCL leads to the formation of their micellar aggregates in aqueous media which was confirmed by transmission electron microscope. The critical micelle concentration value was calculated from the photophysical changes of Pyrene-1-Carboxaldehyde by UV absorption studies and was found to be 0.0320 mg/mL. The polymer nanocomposite was synthesized and examined in view of antibacterial effect against Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Proteus mirabilis, and Klebsiella pneumonae. It was found that polymer nanocomposite possess strong antibacterial activity against Enterococcus faecalis with minimum inhibitory concentration value of 32 μg/mL. © 2012 Wiley Periodicals, Inc.
Thiophene-fused quinoline analogues: Facile synthesis of 3-amino-2-cyanothieno [2, 3-b] quinolines from 2-chloro-3-cyanoquinolines
(2005) Ambika Srivastava; Atish Chandra; R.M. Singh
Starting from 2-chloro-3-cyanoquinolines and chloroacetonitrile, a series of 3-amino-2-cyanothieno [2, 3-b] quinoline derivatives have been prepared and characterized spectroscopically. The validity and presence of amino group in products are further evaluated from different routes.
Vilsmeier-Haack reagent: A facile synthesis of 2-chloro-3-formylquinolines from N-arylacetamides and transformation into different functionalities
(2005) Ambika Srivastava; R.M. Singh
A simple and regioselective synthesis of 2-chloro-3-formylquinolines through Vilsmeier-Haack cyclisation of N-arylacetamides has been reported. The cyclisation is facilitated by N-arylacetamides bearing electron donating groups at m-position. However, yields of quinolines having electron donating groups are good in all cases. Further, the nucleophilic substitution reaction of the quinolines is also investigated. Similarly, the formyl group in the quinolines is subjected to further transformation into cyano (CAN-NH3) and alkoxycarbonyl (NIS-K2CO3/alcohols) groups to afford corresponding 3-cyano and 3-alkoxycarbonylquinolines, respectively.