Browsing by Author "K. Ramesh"

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Chemical elicitors- a mitigation strategy for maximize crop yields under abiotic stress
(Elsevier, 2023) Ch L.N. Manikanta; P. Ratnakumar; R. Manasa; Brij B. Pandey; P.R. Vaikuntapu; Akankhya Guru; Arti Guhey; R. Beena; K. Ramesh; Yogeshwar Singh
Plants in their innate environment are challenged by several abiotic stresses viz., extremes of water and temperatures in general and in certain specified environments, salinity, heavy metal, and UV radiations either alone or in combination leading to crop yield penalty worldwide. Breeding approaches either through conventional or non-conventional have significantly contributed to the development of stress tolerant varieties, but not for unforeseen combination of multiple stresses. Therefore, there is a necessity to achieve long term protection to manage stresses. One such promising strategy is the application of low molecular weight chemical elicitors for tapping the innate potential of crops through activation of several defense-related genes and accumulation of phytoalexins. These chemical elicitors are either a natural or synthetic compounds known to act at very low concentrations as messenger molecules activating the signaling pathway via binding to the receptor molecules. This chapter is an attempt to provide an insight into the potential role, classification, and mode of action of the major chemical elicitors as a mitigating strategy against abiotic stress for sustainable yields. © 2023 Elsevier Inc. All rights reserved.
Cobalt oxide decorated zirconium oxide immobilized multiwalled carbon nanotubes as scaffolds for supercapacitors and the CO2 reduction reaction
(Elsevier Ltd, 2021) Dharmendra Kumar Yadav; Fatin Saiha Omar; Mamta Yadav; Xian Liang Ho; Malcolm E. Tessensohn; K. Ramesh; S. Ramesh; Richard D. Webster; Vellaichamy Ganesan
In the field of renewable energy research, the development of materials for use as highly efficient supercapacitors and designing electrocatalytic materials for the reduction of CO2 to produce useful chemicals are envisaged as two important sustainable routes. However, developing stable, selective, and efficient materials for these purposes is a highly challenging task requiring numerous design attempts. In this work, cobalt oxide decorated zirconium oxide immobilized multiwalled carbon nanotubes (MWCNTs-ZrO2-Co3O4) is reported as a catalyst and battery electrode material for the electrochemical reduction of CO2 and supercapacitor applications, respectively. The MWCNTs-ZrO2-Co3O4 electrode assembled for the supercapacitor shows a specific capacity of 258.9 C/g at a current density of 1.0 A/g. The MWCNTs-ZrO2-Co3O4 and activated carbon (AC) based asymmetric supercapacitor (MWCNTs-ZrO2-Co3O4//AC) displays specific energy in the range of 8.9 Wh/kg (at 837.2 W/kg) to 6.23 Wh/kg (at 1674.4 W/kg). The device, MWCNTs-ZrO2-Co3O4//AC displays high cycling stability with 97% capacity retention after 7000 cycles at a current density of 1.0 A/g. In the electrocatalytic reduction of CO2, the MWCNTs-ZrO2-Co3O4 scaffold produces selectively formic acid during the electrolysis at -1.1 V (vs. Ag/AgCl) in 0.1 M aqueous KCl solution. These results indicate that MWCNTs-ZrO2-Co3O4 can serve as a bifunctional material. © 2021 Elsevier Ltd
Dendrimer like star polymer based on β-cyclodextrin with ABC type miktoarms
(Royal Society of Chemistry, 2016) Kranthikumar Tungala; Pubali Adhikary; Venkanna Azmeera; Krishna Kumar; K. Ramesh; S. Krishnamoorthi
The present article reports the synthesis and self aggregation study of a novel dendrimer like star polymer based on β-cyclodextrin (β-CD), in which the primary alcoholic arms of β-CD have been linked to ABC type miktoarm star polymers. Initially, 6-heptaazido-6-deoxy-β-cyclodextrin (7N3-β-CD) has been clicked with alkyne terminated poly(methyl methacrylate) (alkynyl-PMMA-Br), which has been synthesized through atom transfer radical polymerization technique. Subsequently, azidation has been done in order to prepare β-CD(PMMA-N3)7. Parallelly, an amphiphilic block copolymer (alkynyl-PDLL-b-PNIPAAm), having an alkyne end group, has been synthesized by employing a mikto functional initiator having alcohol, xanthate and alkyne functionalities, in ring opening polymerization (ROP) of d,l-lactide (DLL) from -OH end, and reversible addition-fragmentation chain-transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAAm) from xanthate end. Then, the desired star polymer has been synthesized by the click reaction between β-CD(PMMA-N3)7 and alkynyl-PDLL-b-PNIPAAm. The polymers have been characterized by 1H NMR, and gel permeation chromatography. Self aggregation of the star polymers has been investigated by 1H NMR and fluorescence spectroscopy. Size of the micelles formed has been analyzed by dynamic light scattering and transmission electron microscopic techniques. © 2016 The Royal Society of Chemistry.
Enhanced catalytic and antibacterial activities of silver nanoparticles immobilized on poly(N-vinyl pyrrolidone)-grafted graphene oxide
(Royal Society of Chemistry, 2015) Shikha Singh; Ravi Kumar Gundampati; Kheyanath Mitra; K. Ramesh; Medicherla V. Jagannadham; Nira Misra; Biswajit Ray
Poly(N-vinyl pyrrolidone) (PNVP)-grafted graphene oxide (GO) (GO-PNVP) has been synthesized using a GO-based macro-RAFT agent prepared via click reaction of alkyne-terminated RAFT agent (S)-2-(propynyl propionate)-(o-ethyl xanthate) and azide-functionalized GO (GO-N3). FTIR, XPS, Raman, TGA and DSC studies confirmed its formation. Silver nanoparticles are then immobilized on GO-PNVP and GO via in situ reduction of silver nitrate in the presence and absence of glucose at 40 and 95 °C, respectively. FT-IR, UV-Vis, XRD, SEM and TGA studies supported the incorporation of silver (Ag) nanoparticles. Ag nanoparticles immobilized on GO-PNVP are small, spherical and narrowly distributed (homogenous, monodisperse) compared to GO. These nanocomposites are explored as catalysts for the reduction of p-nitrophenol into p-aminophenol and also as antibacterial agents towards Gram(+) S. aureus and Gram(-) E. coli bacteria. Ag nanoparticle immobilized GO-PNVP showed efficient catalytic activity and excellent reusability along with an excellent antibacterial activity. Hence, grafting of PNVP enhances the catalytic and antibacterial properties of GO. © 2015 The Royal Society of Chemistry.
Self-assembly of Novel Poly(d,l-Lactide-co-Glycolide)-b-Poly(N-Vinylpyrrolidone) (PLGA-b-PNVP) Amphiphilic Diblock Copolymers
(Springer Verlag, 2016) K. Ramesh; Shikha Singh; Kheyanath Mitra; Dipankar Chattopadhyay; Nira Misra; Biswajit Ray
Alkyne-terminated poly(d,l-lactide-co-glycolide) (PLGA) has been synthesized via ROP at room temperature. Amphiphilic PLGA-b-poly(N-vinylpyrrolidone) (PNVP) block copolymers have been synthesized via alkyne-azide click reaction of it with azide-terminated PNVPs prepared by RAFT polymerization of NVP using an azide-terminated RAFT agent. 1H NMR and gel permeation chromatography (GPC) confirmed the formation of block copolymers. Self-assembly of these block copolymers was confirmed by fluorescence study using pyrene as a probe and supported by 1H NMR, DLS and TEM studies. Hydrophobic drug doxorubicin was successfully encapsulated at the micellar core of PLGA46-b-PNVP89 with drug-loading content (DLC) and drug-loading efficiency (DLE) of 10.8 and 43.2 %, respectively. Sustained drug release of these drug-loaded micelles was observed at both pH of 6.4 and 7.4. Faster drug release was observed at pH 6.4. Such PLGA-b-PNVP amphiphilic block copolymer may find extensive application in sustained drug delivery, specifically in antitumor drug delivery. © 2015, Springer-Verlag Berlin Heidelberg.
Self-assembly, doxorubicin-loading and antibacterial activity of well-defined ABA-type amphiphilic poly(N-vinylpyrrolidone)-b-poly(d,l-lactide)-b-poly(N-vinyl pyrrolidone) triblock copolymers
(Royal Society of Chemistry, 2016) K. Ramesh; Ravi Kumar Gundampati; Shikha Singh; Kheyanath Mitra; Ankita Shukla; Medicherla V. Jagannadham; Dipankar Chattopadhyay; Nira Misra; Biswajit Ray
A series of ABA type well-defined amphiphilic poly(N-vinylpyrrolidone) (PNVP)-b-poly(d,l-lactide)-b-PNVP triblock copolymers have been synthesized via the combination of ring opening polymerization and xanthate-mediated reversible addition-fragmentation chain transfer polymerization, and analyzed by 1H NMR spectroscopy and gel permeation chromatography. Aggregation properties of these amphiphilic triblock copolymers have been revealed by fluorescence spectroscopy, transmission electron microscopy and dynamic light scattering, and supported by 1H NMR spectroscopy. Doxorubicin (DOX) has successfully been loaded into the block copolymer micelles with a loading efficiency of 37.5%. DOX-loaded PNVP51-b-PDLLA48-b-PNVP51 block copolymer showed sustained release within 36 h. Antibacterial properties of DOX-loaded micelles have been found to be significantly effective with respect to free DOX in terms of minimum inhibitory concentration, disk diffusion assay, growth curve, bacterial reduction and enzymatic assay based on in vitro studies. © 2016 The Royal Society of Chemistry.
Synthesis and self-assembly properties of well-defined four-arm star poly(ε-caprolactone)-b-poly(N-vinylpyrrolidone) amphiphilic block copolymers
(2013) Avnish Kumar Mishra; K. Ramesh; Tapas Kumar Paira; Divesh N. Srivastava; Tarun Kumar Mandal; Nira Misra; Biswajit Ray
Well-defined amphiphilic four-arm star diblock copolymers of poly(ε-caprolactone) (PCL) and poly(N-vinylpyrrolidone) (PNVP) have successfully been synthesized by combining the ring-opening polymerization (ROP) of ε-caprolactone (CL) and xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinylpyrrolidone (NVP). The resulting block copolymer shows the formation of spherical micelles in water as revealed by transmission electron microscopy (TEM) and supported by light-scattering study. The critical micellar concentration (cmc) value of the micelle increases with the increase in the PNVP block length. Hydrodynamic diameter distribution of the micelles decreases with the increase in the PNVP block length. The effective hydrodynamic ratio (R h) remains almost constant over the angles of scattering measurements above the corresponding cmc value. The usefulness of the synthesized star amphiphilic block copolymers was checked by the successful synthesis of silver nanoparticles. Graphical abstract: Well-defined four-arm star poly(ε-caprolactone)-b-poly(N-vinylpyrrolidone) amphiphilic block copolymers are prepared by the combination of ring opening polymerization and xanthate-mediated reversible addition-fragmentation chain transfer polymerization and their self-assembly properties are studied using 1H NMR, fluorescence spectroscopy, dynamic light scattering, and TEM. [Figure not available: see fulltext.] © 2013 Springer-Verlag Berlin Heidelberg.
Synthesis of ABA-type double hydrophilic amphiphilic PU-based block copolymers of poly(N-Vinylpyrrolidone) and poly(N-isopropylacrylamide) via click chemistry
(Bellwether Publishing, Ltd., 2021) Niraj Kumar Vishwakarma; Vijay Kumar Patel; Payel Mitra; K. Ramesh; Kheyanath Mitra; Sambhav Vishwakarma; Krishnendu Acharya; Nira Misra; Pralay Maiti; Biswajit Ray
Double hydrophilic ABA-type amphiphilic polyurethane (PU)-based poly(N-vinylpyrrolidone) (PNVP)-b-PU-b-PNVP and poly(N-isopropylacrylamide) (PNIPAM)-b-PU-b-PNIPAM triblock copolymers have successfully been synthesized via the combination of the step-growth polymerization, reversible addition-fragmentation chain transfer (RAFT) polymerization and azide-alkyne click reaction. All polymers are characterized by 1H NMR, FTIR, and gel permeation chromatography. The cmcs of PNVP-b-PU-b-PNVP block copolymers increase with increase in PNVP block length: 0.0019 mg/mL for PNVP39-b-PU-b-PNVP39 and 0.005 mg/mL for PNVP68-b-PU-b-PNVP68. The iron-chelating ability and the reducing power of PNVP68-b-PU-b-PNVP68 are superior to that of PNVP owing to the presence of urethane moiety of PU block in copolymer. The LCST of PNIPAM-b-PU-b-PNIPAM are lower than that of PNIPAM (33 °C): 23.5 and 25.5 °C for PNIPAM42-b-PU-b-PNIPAM42 and PNIPAM66-b-PU-b-PNIPAM66, respectively. © 2020 Taylor & Francis Group, LLC.
Synthesis of fluorescence poly(N -vinylpyrrolidone) via click chemistry using azide-terminated xanthate mediator (S)-2-(4-azidobutyl propionate)-(O -ethyl xanthate)
(Taylor and Francis Inc., 2016) Vijay Kumar Patel; Niraj Kumar Vishwakarma; Shikha Singh; Kheyanath Mitra; K. Ramesh; Nira Mishra; Biswajit Ray
Azide-terminated xanthate RAFT agent (S)-2-(4-azidobutyl propionate)-(O-ethyl xanthate) has been synthesized and used for the controlled radical polymerization of N-vinylpyrrolidone (NVP). Kinetics study showed the pesudo first-order kinetics along with gradual increase in molecular weight (Mn) of the resulted polymer up to 69% conversion. Chain-end analysis of the resulted polymer by 1H NMR showed the presence of the fragments of xanthate mediator at both chain ends. Successful chain extension has also been performed via the click reaction of alkyne-terminated PNVP with azide-terminated PNVP. Moreover, fluorescence pyrene-tagged PNVP has successfully been made via the click reaction of alkyne-functionalized pyrene with azide-terminated PNVP. © 2016 Copyright Taylor & Francis Group, LLC.
Synthesis of well-defined amphiphilic poly(d,l-lactide)-b-poly(N- vinylpyrrolidone) block copolymers using ROP and xanthate-mediated RAFT polymerization
(Elsevier Ltd, 2012) K. Ramesh; Avnish Kumar Mishra; Vijay Kumar Patel; Niraj Kumar Vishwakarma; Chandra Sekhar Biswas; Tapas Kumar Paira; Tarun Kumar Mandal; Pralay Maiti; Nira Misra; Biswajit Ray
Well-defined amphiphilic poly(d,l-lactide)-b-poly(N-vinylpyrrolidone) (PDLLA-b-PNVP) block copolymers were successfully prepared using ring-opening polymerization (ROP) and xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization. Synthesized PDLLA-b-PNVP block copolymers were characterized by 1H NMR spectroscopy and GPC. Spherical micelles of ∼30.2 nm diameter were formed from the aqueous solution of amphiphilic diblock copolymer PDLLA42-b-PNVP63 as revealed by TEM and supported by 1H NMR and light scattering. The critical micelle concentration value of the block copolymers, determined by fluorescence spectroscopy using pyrene as probe, increased with the increase in the chain length of PNVP block. The average hydrodynamic radius (Rh) of the micelles remained almost constant above the cmc value over the angles of scattering measurement. Thermal properties of these block copolymers were studied by TGA, DTA and DSC. Crystalline properties of these block copolymers were studied by WXRD. © 2012 Elsevier Ltd. All rights reserved.
Tadpole-shaped β-cyclodextrin-tagged poly(N-vinylpyrrolidone): Synthesis, characterization and studies of its complexation with phenolphthalein and anti tumor activities
(Royal Society of Chemistry, 2015) Niraj Kumar Vishwakarma; Vijay Kumar Patel; Sumit Kumar Hira; K. Ramesh; Prateek Srivastava; Kheyanath Mitra; Shikha Singh; Dipankar Chattopadhyay; Pralay Maiti; Nira Misra; Partha Pratim Manna; Biswajit Ray
Tadpole-shaped β-cyclodextrin-tagged poly(N-vinylpyrrolidone) (β-CD-PNVP) has been synthesised via the click reaction of alkyne-terminated PNVP and azide-functionalized β-CD. The formed polymer is characterized by 1H NMR, FTIR, and TGA study. The complexing ability of such a polymer with phenolphthalein is considerably lower with respect to that with β-CD alone. Doxorubicin (DOX)-loaded β-CD-PNVP (DOX-β-CD-PNVP) exhibits higher tumoricidal activity against a panel of tumor cell lines derived from sarcoma (U2-OS) and carcinomas (MCF-7 and HEPG2), causing significant lysis of tumor cells compared to free DOX. The formulation also demonstrates significantly higher uptake by the tumor cells and enhances apoptosis compared to free DOX. This journal is © The Royal Society of Chemistry.