Shobhana K. Menon

Solvent extraction, separation of uranium (VI) with crown ether

A solvent extraction separation of uranium with a new crown hydroxamic acid 5, 14-N, N′-hydroxyphenyl-4, 15-dioxo-1,5,14,18-tetraaza hexacosane (NHDTAHA) in the presence of cerium, thorium and lanthanides is described. The uranium is extracted with chloroform solution of NHDTAHA and the extract is directly used for GS-AAS measurements. The detection limit is 0.01 ppm with a sensitivity of 20 ng/0.005 absorbance of uranium. The extraction constants of uranium crown hydroxamic acid complexes are determined. The selectivity factors (Kuranyl/Kn+M) for uranium crown hyrdoxamate evaluated by comparing the Kuranyl with the stability constants for competing metal cations (Kn+M) and anions (KnA−) and were found to be remarkably large. Uranium is preconcentrated and also determined spectrophotometrically. The molar absorptivity is 1.0×104 l−1 mol−1 per cm at 390 nm and system obeys Beer’s law in the range 2.0–30 ppm of uranium. Uranium has been determined in standard and environmental samples.

Polymer supported calix[6]arene hydroxamic acid, a novel chelating resin

Abstract A new polymer-supported calix[6]arene hydroxamic acid has been synthesised by reacting the acid chloride 37,38,39,40,41,42 hexahydroxy 1,8,13,19,25,31 hexacarboxy calix[6]arene with poly(styrene β-hydroxylamine). The synthesised resin was characterised by elemental analysis, FT-IR and mass spectra. Physicochemical properties viz. swelling, wet-density, void-volume, exchange capacity etc. were determined. The resin has 4.46 mmol/g exchange capacity for rare elements. The resin was used for the chromatographic separation of U(VI), Th(IV) and Ce(IV) by the judicious adjustment of pH 4.0, 6.0 and 7.5, respectively. The thorium and cerium were eluted with 0.1 M HCl while uranium was eluted with 2 M HCl. These rare elements were preconcentrated and determined in the presence of each other, monazite sand and environmental samples.

Fullerene derivatized s-triazine analogues as antimicrobial agents.

A series of novel fullerene derivatives bearing s-triazine moiety have been synthesized by adopting 1,3 dipolar cycloaddition reaction of C(60) and azomethine ylides generated from the corresponding Schiff bases of 2,4,6 trisubstituted s-triazine. All the compounds synthesized were characterized by elemental analysis, FT-IR, (1)H NMR, (13)C NMR and FAB-MS. The compounds were then screened for their antibacterial activity against both gram-positive (Staphylococcus aureus, Bacillus subtilis, Bacillus pumilis) and gram-negative (Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae) bacteria by disc diffusion method. All the compounds were found to be active against these strains at very low concentration and were comparable to standard drug ciprofloxacin.

Removal of Fluoride from Aqueous Solution by CaO Nanoparticles

Abstract Colloidal particles of CaO were synthesized by the sol-gel method. The particle morphology was characterized by FT-IR, TGA, DTA, and TEM analysis. The ability of the CaO nanoparticles for removal of fluoride from aqueous solution through adsorption has been investigated. All the experiments were carried out by batch mode. The effect of various parameters viz. contact time, pH effect (pH 2–10), adsorbent dose (0.01–0.1 g/100 ml), initial fluoride concentration (10–100 mg/l) and competitive ions has been investigated to determine the adsorption capacity of CaO nanoparticles. Almost complete removal (98%) of fluoride was obtained within 30 minutes at an optimum adsorbent dose of 0.6 g/L for initial fluoride concentration of 100 mg/L. The adsorption isotherm was also studied to find the nature of adsorbate-adsorbent interaction.

Chelating polycalixarene for the chromatographic separation of Ga(III), In(III) and Tl(III)

Abstract A chelating polycalixarene has been synthesised by introducing the hydroxamate chelating group into the calixarene units and its analytical applications studied. The synthesised polycalixarene is used for the sorption and chromatographic separation of group 13 metal ions, Ga(III), In(III) and Tl(III). For the quantitative sorption and recovery of Ga(III), In(III) and Tl(III), the optimum pH and eluants are pH 3.5–4.0 and 2 M HCl for Ga(III), pH 5.5–6.0 and 0.5 M HCl for In(III) and pH 7.0–7.5 and 1 M HCl for Tl(III). The t1/2 values for Ga(III), In(III) and Tl(III) were determined. The effects of various electrolytes such as NaCl, NaNO3, Na2SO4, NH4Cl, NH4NO3, CH3COONa and sodium tartarate on the sorption of the metals were studied.

Ultrasensitive and specific detection of dimethoate using a p-sulphonato-calix[4]resorcinarene functionalized silver nanoprobe in aqueous solution

We demonstrate a facile strategy for preparing highly stable silver nanoprobe modified p-sulphonato-calix[4]resorcinarene in aqueous media. We also report the efficient and selective sensing properties of the novel assembly for organophosphorus insecticides and its great potential for application to real-time in situ detection of organophosphorus pesticides in waste water.

Fluorescence switch on-off-on receptor constructed of quinoline allied calix[4]arene for selective recognition of Cu2+ from blood serum and F- from industrial waste water.

A novel PET with ICT based substituted calix[4]arene fluroionophore was synthesized and used for detection of Cu(2+) and F(-) by emission spectra. The detection limit of the synthesized receptor was found to be 4.16 nM for Cu(2+) and 2.15 nM for F(-). Moreover, this probe has been applied for recognition of Cu(2+) in blood serum and F(-) from waste water.

Azo calix[4]arene based neodymium(III)-selective PVC membrane sensor

We found that the PVC membrane, containing azo calix[4]arene is a suitable ionophore, exhibited a Nernstian response for neodymium (Nd(3+)) ions (with slope of 19.8±0.2 mV decade(-1) for the triply charged ion) over a wide linear range of 4.0×10(-8) to 1.0×10(-1) mol L(-1) with a detection limit 1.0×10(-8) mol L(-1), a relatively fast response time, in the whole concentration range (<10 s), and a considerable life time at least for four months in the pH range of 4.0-8.0. Furthermore, the electrode revealed high selectivity with respect to all the common alkali, alkaline earth, transition and heavy metal ions, including the members of the lanthanide family other than Nd(3+). Concerning its applications, it was effectively employed for the determination of neodymium ions in industrial waste water as well as in lake water.

Fullerene Isoniazid Conjugate – A Tuberculostat with Increased Lipophilicity: Synthesis and Evaluation of Antimycobacterial Activity

A fullerene–isoniazid conjugate has been synthesized by 1, 3 dipolar cycloaddition reaction of fullerene (C60) with isonicotinic acid (4‐formyl‐benzylidene) hydrazide and N‐methylglycine. The identity and purity of the compound was confirmed by elemental analysis, 1H NMR, 13C NMR and MALDI‐TOF mass spectral analysis. Stable water suspension, in which the particles of the synthesized conjugate were made to aggregate in nanosize, was successfully tested for antimycobacterial activity against Mycobacterium avium and strains of Mycobacterium tuberculosis– H37Rv & H6/99 at concentration as low as 0.50 μg/mL.

A smart and rapid colorimetric method for the detection of codeine sulphate, using unmodified gold nanoprobe

Driven by the need to detect narcotics, we designed a “smart” system for the rapid detection and quantification of codeine sulphate levels using a smartphone, which allows simple, portable, on-spot, rapid and ultrasensitive nanoaggregation colorimetric detection (a lower detection limit of 0.9 μM) using the unique properties of citrate-stabilized gold nanoparticles (AuNPs) as a probe.