Shibu G. Pillai

Molecular octopus: octa functionalized calix[4]resorcinarene-hydroxamic acid [C4RAHA] for selective extraction, separation and preconcentration of U(VI)

A solvent extraction separation of uranium, in the presence of thorium, cerium and lanthanides with a new calix[4]resorcinarene bearing eight hydroxamic acid groups (C4RAHA) is described. Quantitative extraction of uranium is possible in ethyl acetate solution of C4RAHA at pH 8.0. The lambda(max) and molar absorptivity (varepsilon) for uranium is 356nm and 8352Lmol(-1)cm(-1). The Binding ratio of uranium with C4RAHA as evaluated by Jobs method is 4:1. The system obeys Beers law over the range 0.075-6.0mugml(-1) of uranium with Sandell sensitivity 0.0284mugcm(-2). A preconcentration factor of 142 was achieved by directly aspirating the extract for GF-AAS measurements. The two-phase stability constant evaluated at 25 degrees C for uranium is 15.91. The complexation is characterized by favorable enthalpy and entropy changes. A liquid membrane transport study of uranium was carried out from source to the receiving phase under controlled conditions and a mechanism of transport is proposed. Uranium has been determined in standard and environmental samples.

Solid-phase extractive preconcentration and separation of lanthanum(III) and cerium(III) using a polymer-supported chelating calix [4] arene resin

In the present paper, solid-phase extractive preconcentration and separation of lanthanum(III) and cerium(III) using calix[4]arene-o-vanillinsemicarbazone immobilized on a polymeric matrix, a Merrifield peptide resin, is proposed. The diamino derivative of calix[4]arene was first diazotized and coupled with o-vanillinsemicarbazone to obtain a new “upper-rim” functionalized calix[4]arene-o-vanillinsemicarbazone. It was then covalently linked to the Merrifield peptide resin and characterized by FT-IR and elemental analysis. Quantitative studies were carried out by spectrophotometry and ICP-AES with a relative standard deviation of 1.7%. Various physicochemical parameters like pH, concentration of eluting agents, flow rate, total sorption capacity, metal-ligand stoichiometry, exchange kinetics, preconcentration factor, distribution coefficient, breakthrough capacity, resin stability, and effect of electrolytes and associated metal ions have been studied. The uptake and stripping of these metal ions on the resin was fast, indicating a better accessibility of La(III) and Ce(III) towards the chelating sites. Detection limits corresponded to three times the standard deviation of the blank (3σB) and amounted to 3.05 and 6.86 µg/L, along with preconcentration factors of 153 and 133 for La(III) and Ce(III), respectively. The robustness of the procedure is demonstrated by the recoveries obtained (>97.5%) for La(III) and Ce(III) in the presence of several cations and anions. The proposed method was satisfactorily applied to the separation of La(III) and Ce(III) from each other and also from U(VI) and Th(IV) by sequential acidic elution and varying pH. The validity of the method was tested by analyzing these metal ions in monazite sand and standard geological materials.

Merrifield resin supported chelate forming calix[4]arene-o-vanillinthiosemicarbazone resin employed for the separation, preconcentration and trace determination of Cr(VI), As(III) and Tl(I) in water samples

Abstract Calix[4]arene based polymer supported chelating resin 8 has been synthesized by covalently linking calix[4]arene‐o‐vanillinthiosemicarbazone via its ‘lower rim’ to Merrifield resin and was characterized by FT‐IR, 1H‐NMR and elemental analysis. Resin 8 was competently used to separate and preconcentrate toxic metal ions Cr(VI), As(III) and Tl(I) in a column prior to their determination by UV‐Visible and GF‐AAS with R.S.D. between 1.0–1.4%. Various physico‐chemical parameters like pH, concentration of eluting agents, flow rate, total sorption capacity, metal‐ligand stoichiometry, exchange kinetics, preconcentration factor, distribution coefficient, breakthrough capacity, resin stability, effect of electrolytes, and associated metal ions have been studied. Detection limits (3σB) of 5.83, 8.48 and 5.56 µg L−1, along with preconcentration factors of 117, 90 and 105 for Cr(VI), As(III) and Tl(I) respectively were achieved. Resin 8 was successfully applied to the separation and trace determination of Cr(VI), As(III) and Tl(I) from natural water samples of Ahmedabad city and the standard environmental, biological and geological reference materials.

Octafunctionalized calix[4]resorcinarene-N-fenil-acetohydroxamic acid for the separation, preconcentration and transport studies of cerium(IV)

A new method for liquid-liquid extraction, separation and preconcentration of cerium(IV) with a calix[4]resorcinarene acid derivative [C4RAHA] is reported. Cerium was extracted at pH 9 in ethyl acetate and recovered from monazite sands in the presence of thorium, uranium, lanthanum and large number of cations and anions. Cerium(IV) forms yellow coloured complex, lmax 381 nm, molar absorptivity 1.06 ´ 104 L mol-1cm-1 and obeys Beers law over the range 0.4-15 mg mL-1. The metal ligand ratio for cerium (IV) was found to be 4:1 (M:L). Transport studies were carried out in a three phase system across a liquid membrane containing C4RAHA. For ICP OES measurements, the extract can be directly aspirated, which enhances the sensitivity 25-fold and the limits for estimation are 5-150 µg L-1 of cerium. The method was applied for the determination of cerium in standard geological samples, monazite sand and sea water samples.

Supervanadophile: Complexation, preconcentration and transport studies of vanadium by octa functionalized calix[4]resorcinarene-hydroxamic acid

A new octa functionalized calix[4]resorcinarene bearing eight hydroxamic acid groups (OFCHA) has been synthesized and its analytical properties have been investigated. To elucidate the structure of the compound, elemental analysis, FT-IR and 1H NMR spectral data have been used. The compound showed high affinity and selectivity for vanadium(V) in presence of large quantities of associated metal ions. The complexation of vanadium(V) with OFCHA has a 4:1 metal: ligand stoichiometry as evaluated by Job’s plot. A spectrophotometric method is proposed for the extractive determination of vanadium(V) in an acidic medium in the presence of diversified matrix, and verified by ICP-AES. Under the optimum condition of acidity, solvent, interfering ions and OFCHA concentration, the molar absorptivity of the complex is 5630 l mol-1 cm-1 at 495 nm. The system obeys Beer’s law over the range 0.125–8.75 μg ml-1 of vanadium(V) with Sandell sensitivity 0.009 μg cm-2. The preconcentration factor and overall stability constant evaluated at 25 °C were 142 and 14.18, respectively. The complexation is characterized by favorable enthalpy and entropy changes. Liquid membrane transport studies of vanadium(V) were carried out from source to the receiving phase under controlled conditions and a mechanism for transport is suggested. To check the validity of the proposed method, vanadium is determined in environmental, biological samples and some standard reference materials from NIST and BCS.

Synthesis of Calix[4]resorcinarene Based Dyes and its Application in Dyeing of Fibres

Four new ʻupper rimʼ azocalix[4]resorcinarene have been synthesized by coupling calix[4]resorcinarene with different diazotized aromatic compounds of sulphanilic acid, anthranilic acid, o-aminophenol and p-aminobenzoic acid. The prepared compounds were characterized based on m.p., elemental analysis, FT-IR, 1H-NMR. These dyes have been used for the dyeing of textile fibres like cotton and wool. Their fastness properties such as fastness to sunlight, water, washings, and perspiration have also been studied. The synthesized dyes have been employed for computerized colour strength determination through colour matching with known standards. Their L, A*, B* values as well as the colour difference values such as ∆L, ∆A*, ∆B*, ∆C and ∆H have also been reported.