Beena Mathew

Metal complexes of poly(acrylic acid) : synthesis, characterization and thermogravimetric studies

Abstract Thermogravimetric studies of the sodium salt of poly(acrylic acid), its modified sodium salt and its various metal complexes were made. The thermal stabilities of the various systems decreased in the order: poly(acrylic acid) > Ni(II) > Co(II) > Zn(II) > Fe(III) > Cu(II) > polymeric sodium salt. The higher thermal stabilities of the polymer-metal complexes result from the development of stable ring structures in the polymer matrix upon coordination with metal ions. The metal-ion complexation of carboxylate ligands of linear poly(acrylic acid), optimization of the complexation conditions and infra-red and ultraviolet-visible spectrometric characterizations are also illustrated.

Microwave assisted facile green synthesis of silver and gold nanocatalysts using the leaf extract of Aerva lanata.

Herein, we report a simple microwave assisted method for the green synthesis of silver and gold nanoparticles by the reduction of aqueous metal salt solutions using leaf extract of the medicinal plant Aerva lanata. UV-vis., FTIR, XRD, and HR-TEM studies were conducted to assure the formation of nanoparticles. XRD studies clearly confirmed the crystalline nature of the synthesized nanoparticles. From the HR-TEM images, the silver nanoparticles (AgNPs) were found to be more or less spherical and gold nanoparticles (AuNPs) were observed to be of different morphology with an average diameter of 18.62nm for silver and 17.97nm for gold nanoparticles. In order to evaluate the effect of microwave heating upon rate of formation, the synthesis was also conducted under ambient condition without the assistance of microwave radiation and the former method was found to be much faster than the later. The synthesized nanoparticles were used as nanocatalysts in the reduction of 4-nitrophenol to 4-aminophenol by NaBH4.

Polymer-metal complexes of amino functionalized divinylbenzene-crosslinked polyacrylamides

Abstract The complexation of amino functions supported on polyacrylamides with 2–20 mol% of divinylbenzene (DVB) crosslinks was investigated towards Co(II), Ni(II), Cu(II), Zn(II) and Hg(II) ions. With increasing extent of DVB-crosslinking, the metal ion intake decreased in the order: Hg(II) >> Cu(II) > Zn(II) > Ni(II) > Co(II). The polymeric ligand and the derived metal complexes were characterized by their typical i.r. absorptions and from the e.s.r. spectra. The i.r. absorptions of the polymeric ligands were shifted by complexation. The e.s.r. parameters suggested the distorted tetragonal geometry of the Cu(II) complexes. The change in surface morphology on complexation was followed by scanning electron microscopy. The thermal stability varied with the incorporation of metal ions. The activation energy values and the extent of crosslinking in Cu(II) complexes fit into the general equation for a cubic polynomial. The time-course and kinetics of complexation and the adsorption characteristics of complexation were also followed. The swelling characteristics varied with the extent of crosslinking, and the extent of swelling was lower for the complexed resins. The complexed resins can be recycled several times, and the Cu(II)-desorbed resin showed specificity to the Cu(II) ion in the presence of other metal ions.

Crosslinked polystyrene-supported dithiocarbamates as metal complexing agents

Dithiocarbamate functions were introduced into divinylbenzene (DVB)-crosslinked polystyrene matrices in different structural environments and their complexation behaviour with various metal ions was investigated. The reactions involved introduction of the amino functionality into the polystyrene matrix through a number of different heterogeneous amination procedures. These aminopolystyrene derivatives which contain the amino functions in different steric environments were converted to the respective dithiocarbamates by reaction with carbondisulphide in the presence of alkali. The metal complexing ability of the resulting insoluble polystyrene-dithiocarbamates was investigated towards Fe(III), Ni(II), Cu(II) and Zn(II) ions. The structural factors characteristic of the polymer matrix like the molecular character and extent of crosslinking were found to exert influence on the metal complexing ability. The spectral characterization and the relative thermal stabilities of the complexes were also investigated.

Divinylbenzene-crosslinked polyacrylamide-supported dithiocarbamates as metal complexing agents

SummaryDithiocarbamate (DTC) functions were incorporated into divinylbenzene-crosslinked (2–20 mole %) polyacrylamides by a two-step polymer-analogous reaction. The complexations of these resins with DTC functions in different structural environments were investigated towards Co(II), Ni(II), Cu(II), Zn(II) and Hg(II) by batch equilibration technique. The metal ion intake decreased with the extent of the DVB content in the order Hg(II)>>Cu(II)>Zn(II)>Ni(II)>Co(II). The time-course on complexation, swelling behaviours of the uncomplexed and complexed resins, recyclability, IR and thermogravimetric characterisation of the complexes were carried out. The swelling of the resins decreased on complexation with metal ions and the thermal stability increased.

Indigofera tinctoria leaf extract mediated green synthesis of silver and gold nanoparticles and assessment of their anticancer, antimicrobial, antioxidant and catalytic properties

Abstract This study reports the synthesis of noble metal nanoparticles, namely silver and gold from their respective salt by leaf extract of a medicinal plant Indigofera tinctoria. This leaf extract plays a dual role as stabilizing and reducing agent for the formation of nanoparticles. The synthesized silver and gold nanoparticles were characterized by UV-vis. spectroscopy, FTIR spectroscopy, XRD, TEM, EDX and AFM analysis. All these techniques confirm the formation of crystalline nanoparticles. The cytotoxic effect of I. tinctoria leaf extract and the nanoparticles were studied on lung cancer cell line A549. It was shown that the cell viability decreases with increasing concentration and nanoparticles has more toxic effect on cancer cell than the pure leaf extract. IC50 value of I. tinctoria leaf extract, AuNP and AgNP respectively, are 71.92 ± 0.76 μg/ml, 59.33 ± 0.57 μg/ml and 56.62 ± 0.86 μg/ml. Antimicrobial activities were tested against both bacterial and fungal strains by agar well diffusion method. The synthesized nanoparticles show high antimicrobial activities towards all tested microbial strains with varying degree. The antioxidant activities of synthesized nanoparticles were analysed by using DPPH method and found that nanoparticles show higher antioxidant activities than the leaf extract. Outstanding catalytic activities of nanoparticles were demonstrated by employing the reduction reactions of o/p-niroanilines by NaBH4.

Design of EGDMA‐Crosslinked Theophylline Imprinted Polymer with High Specificity and Selectivity

An attempt has been made to design theophylline selective polymers with maximum selectivity and specificity, and to relate the rebinding capacity of the polymers with the degree of crosslinking, as well as with the template‐monomer ratio. The theophylline imprinted and non‐imprinted polymers based on methacrylic acid as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking agent (35–80 mol%) were prepared. The developed imprinted polymers were characterized by FT‐IR, 1H and 13C‐NMR spectra. Equilibrium binding of theophylline by the imprinted and non‐imprinted polymers were investigated and optimized the conditions. Imprinted polymers showed specific binding of the template theophylline. Selectivity of the imprinted polymers was investigated towards caffeine and nicotine. Imprinted polymers showed specific and selective binding of theophylline, which varied with the degree of EGDMA crosslinking. Equilibrium rebinding experiments proved that imprinted polymer with moderate (70%) crosslinking with 1∶2 template‐functional monomer ratio is ideal with maximum specificity and selectivity.

Microwave assisted green synthesis of silver nanoparticles using leaf extract of elephantopus scaber and its environmental and biological applications

Abstract The fabrication of spherical silver nanoparticles using the phytoreducing agent Elephantopus scaber is reported here. Irradiation of the reaction mixture under a domestic microwave oven enabled the formation of stable silver nanoparticles and was confirmed by UV-vis spectral portrait. Chemical components inherent in the aqueous leaf extract which reduces the monovalent silver were identified by FT-IR spectroscopy. The crystal structure of the synthesized nanoparticles was established as face centred cube by the powder XRD analysis. The TEM images suggest an average particle size of 37.86 nm to the silver nanoparticles. The prepared silver nanocatalysts can successfully reduce various organic nitro compounds, namely, 4-nitrophenol, 2-nitroaniline and 4-nitroaniline. The environmental pollution caused by dyes like eosin Y is effectively wiped off within a short span of time using the prepared nanocatalysts. The free radical quenching efficacy of the plant extract and the silver nanoparticles were checked by employing DPPH assay bestowing ascorbic acid reference. The potential of the nanoparticles as antimicrobials against six human disease causing pathogens were tested through the well diffusion pathway. The newly developed silver nanoparticles produced IC50 value 15.68 ± 0.15 μg/mL on human skin carcinoma cells, A375 and 65.49 ± 0.40 μg/mL on fibroblast cells, L929 when the cytotoxicity is studied employing MTT assay. Elephantopus scaber showed IC50 value 50.55 ± 0.17 μg/mL against A375 cells. Graphical Abstract

Microwave-assisted facile green synthesis of silver nanoparticles and spectroscopic investigation of the catalytic activity

Silver nanoparticles have been successfully synthesized in aqueous medium by a green, rapid and cost-efficient synthetic approach based on microwave irradiation. In this study, iota-carrageenan (I-carrageenan) is used both as reducing and stabilizing agent. The formation of nanoparticles is determined using UV–vis, Fourier transform infrared (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray (EDX) and high-resolution-transmission electron microscopic (HR-TEM) analysis. Transmission electron microscopic (TEM) images show that the nanoparticles are of spherical shape with an average diameter of 18.2 nm. I-carrageenan-stabilized silver nanoparticles show outstanding catalytic activity for the reduction of 4-nitrophenol in the presence of NaBH4 in aqueous medium. The reaction follows pseudo-first-order kinetics and the reaction rate increases with the increase in amount of the catalyst. The study of the temperature dependence of reaction rate gives activation energy of 42.81 kJ mol−1. The synthesized silver nanoparticles are anticipated to be a promising material for pollution abatement.

Thermogravimetric studies of the metal complexes of polyacrylamide-supported amines: effect of the variables of macromolecular structure on thermal stability

Abstract The thermal decomposition behaviour of metal complexes of amino functions supported on crosslinked polyacrylamides in different structural environments is followed. The phenomenological and kinetic aspects of the TG curves are investigated. The integral and approximation methods are used for the evaluation of the kinetic parameters. The thermal stabilities of the Cu(II) complexes of aminopolyacrylamides with 2–20 mol.% of DVB crosslinks and 4–20 mol.% of NNMBA crosslinks varied with the extent of crosslinking. The activation energy of decomposition decreases with crosslinking, reaches a minimum, and then increases. The relation between the activation energy and the extent of crosslinking fits into the general equation for a cubic polynomial. The thermal stabilities of the Cu(II) complexes of aminopolyacrylamides with DVB crosslinks are lower than the NNMBA-crosslinked system. This is due to the increased strain energy in the DVB crosslinking points. The thermal stabilities of the amino resins with 4% DVB crosslinks and 2% TTEGDA crosslinks varied with the extent of incorporation of the different metal ions, as well as the unsaturated coordination in the complex.