Exploration of Pb2+ Selective Behavior of Calix[6]arene Ester Derivative

The selective behavior of calix[n]arene ester derivatives in two-phase extraction systems using polarographic technique has been investigated. Calix[4]arene tetraester derivative shows remarkable Na⁺ over Pb²⁺ selectivity; whereas calix[6]arene hexaester derivative shows Pb²⁺ over Na⁺ selectivity. The interference of some selected cations (Na⁺, K⁺, Cu²⁺ and Mg²⁺) were also examined and no significant effect on the selectivity behavior as well as extraction ability of these ionophores was found except Na⁺. The study reveals for the first time that the calix[6]arene hexaester derivative is highly Pb²⁺ selective ionophore and can be employed in the field of sensor as well as separation science and technology. The work also highlights the usefulness of polarographic technique in trace metal determination.     

Synthesis and oxoanions (dichromate/arsenate) sorption study of N-methylglucamine derivative of calix[4]arene immobilized onto poly[(phenyl glycidyl ether)-co-formaldehyde]

The article describes synthesis as well as the evaluation of sorption properties of new N-methylglucamine substituted calix[4]arene and its poly[(phenyl glycidyl ether)-co-formaldehyde] immobilized product. Firstly, 5,17-bis-[(N-methylglucamine)methyl]-25,26,27,28-tetrahydroxy-calix[4]arene (3) was synthesized by the treatment of calix[4]arene with a secondary amine N-methylglucamine and formaldehyde via Mannich reaction. The immobilization of 3 onto poly[(phenyl glycidyl ether)-co-formaldehyde] to form calixarene based polymer (4) was carried out under suitable reaction conditions via nucleophilic substitution reaction. All the new compounds were characterized by a combination of FT-IR, ¹H-NMR spectroscopic and elemental analysis techniques. The sorption studies of 4 reveal that it is an excellent material for the removal of toxic oxoanions especially arsenate from aqueous environment. To understand the selectivity of 4, we also examined the retention of dichromate anions in the presence of Cl^?, NO₃ ^? and SO₄ ^2? anions at pH 1.5.     

An excellent arsenic(V) sorption behavior of p-tert-butylcalix[8]areneoctamide impregnated resin

The present article describes the arsenic(V) extraction behavior of p-tert-butylcalix[8]areneoctamide (3) and of a resin (4) impregnated with 3. Liquid–liquid and solid–liquid (column sorption) extraction studies were carried out to optimize various experimental parameters such as pH, extraction effeciency and column stability. Thermodynamic studies based upon Temkin and Flory-Hugins models reveal that the sorption was spontaneous and exothermic. The values of correlation coefficients (R2) show that Langmuir and Freundlich isotherm models are best fit to describe the sorption equilibrium. Application of 4 to real samples indicates a slight decrease (5-7%) in extraction efficiency of 4 because of high concentration of total dissolved salts (TDS). It is deduced that 4 is highly effective for the removal of arsenic(V) at a wide range of pH and attains a maximum value, i.e. 99% at pH 4. The impregnated resin is easy to synthesize from cheap materials. It is more efficient and easily regenerable as compared to already reported resins.     

Synthesis,characterisation, and antioxidant study of Cr(III)-rutin complex

The article describes the synthesis and characterisation of the Cr(III)-rutin complex along with an estimate of its antioxidant activity. The complex was characterised using elemental analysis, UV-VIS, IR, conductance data, thermal, and gravimetric analyses. In the UV-VIS study, a bathochromic shift of approximately 98 nm indicates the formation of a rutin complex by more than one chelating site. The FT-IR spectra clearly show the formation of the Cr—O bond between rutin and Cr(III) at 494 cm^?1, while the thermal study shows the presence of eight coordinated water molecules in the complex. The gravimetric analysis quantitatively proves the presence of four chloride ions. From these data, the formula of the Cr(III)-rutin complex was deduced as [Cr₂(C₂₇H₂₈O₁₆)(H₂O)₈]Cl₄. Moreover, the antioxidant study of the complex was evaluated by using 2,2′-diphenyl-1-picrylhydrazyl (DPPH) free-radical, ferric-reducing, and phosphomolybdenum assays, which show that the complex has a higher antioxidant activity than rutin.     

Analytical Evaluation of Cu<Superscript>2+</Superscript> Selective Behavior of calix[4]arene Derivative

The present article describes the solvatochromic effect including solvent system selection, time study and a detailed complexation study along with exploration of extraction properties of 5,11,17,23-tetrakis[(diethylamino)methyl]-25,26,27,28-tetrahydroxycalix[4]arene (4) that bears nitrogen atom as a donor group available for chelating metal ions. Complexation properties of 4 toward selected transition metal ions have been investigated by UV-visible and fluorescence spectroscopies. The% efficiency of 4 toward selected transition metal ions was found in order Cu²⁺> Ni²⁺> Hg²⁺> Zn²⁺> Co²⁺> Cd²⁺> Pb²⁺. It has been noticed that 4 is not only proved to be an efficient Cu²⁺ selective chromoionophore but also possesses an effective extraction property for transferring Cu²⁺ ions from an aqueous to dichloromethane layer. The FT-IR spectroscopic method has also been applied for further confirmation of the complexation phenomenon of 4 with Cu²⁺ ion and found adequate.     

Role of substrate,temperature, and hydrogen on the flame synthesis of graphene films

Graphene films are grown in open-atmosphere on metal substrates using a multiple inverse-diffusion flame burner with methane as fuel. Substrate material (i.e. copper, nickel, cobalt, iron, and copper–nickel alloy), along with its temperature and hydrogen treatment, strongly impacts the quality and uniformity of the graphene films. The growth of few-layer graphene (FLG) occurs in the temperature range 750–950 °C for copper and 600–850 °C for nickel and cobalt. For iron, the growth of graphene is not exclusively observed. The variation of graphene quality for different substrates is believed to be due primarily to the difference in carbon solubility between the metals.     

New potential humic acid stationary phase toward drug components: Development of a chemometric‐assisted RP‐HPLC method for the determination of paracetamol and caffeine in tablet formulations

A new humic acid based stationary phase has been used, for the first time, to achieve the separation and quantification of paracetamol and caffeine in pharmaceutical preparations under reversed‐phase high‐performance liquid chromatography conditions. Central composite design was applied as a powerful tool to optimize the most dominant parameters that influence the resolution of reversed‐phase high‐performance liquid chromatography, that is, mobile phase composition (acetonitrile percentage in water), flow rate, and column temperature. The optimum conditions were obtained as 21.69%, 1.5 mL/min, and 15°C, respectively, with the aid of a second‐order quadratic model and desirability function. Under the optimum conditions, the peaks could be baseline separated within 10 min. For the developed reversed‐phase high‐performance liquid chromatography method, the linearity was investigated in the concentration ranges of 2–160 mg/mL (R² = 0.999) for paracetamol and 2–9.9 mg/mL (R² = 0.991) for caffeine. Mean recoveries for paracetamol and caffeine were 95.90 and 95.68%, respectively. The limits of detection and quantification were 4.1 × 10^‐4 and 1.3 × 10^‐3 mg/mL for paracetamol and 1.6 × 10^‐4 and 5.0 × 10^‐4 mg/mL for caffeine. The results showed that the new humic acid based stationary phase is very suitable for the separation of paracetamol and caffeine in pharmaceutical preparations and, thus it can be used effectively in the pharmaceutical industry.     

Synthesis and extraction properties of new ‘proton-switchable’ tri- and tetra-substituted calix[4]arene derivatives bearing pyridinium units

The article describes the syntheses and complexation properties of new calixarene-based extractants, which have been synthesized from 5,11,17,23-tetra-tert-butyl-25,26,27-tris(chlorocarbonylmethoxy)-28-hydroxycalix[4]arene and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(chlorocarbonylmethoxy)calix[4]arene by treatment with isoniazid (isonicotinic acid hydrazide) in the presence of pyridine, respectively. p-tert-Butylcalix[4]arene teraamide was converted to its methyl iodide salt by refluxing with methyl iodide in acetonitrile. In this synthesis it was thought to explore the role of pyridinium sites in the extraction of HCr₂O₇⁻/Cr₂O₇²⁻ anions. The complexing properties of the extractants toward selected alkali/transition metal cations and HCr₂O₇⁻/Cr₂O₇²⁻ anions are reported. It has been observed that both receptors do not extract alkali metal cations but show excellent selectivity toward transition metals. The protonated pyridinium forms of the receptors are effective for transferring the HCr₂O₇⁻/Cr₂O₇²⁻ anions from an aqueous into a dichloromethane layer.     

Determination of glyoxal and methylglyoxal in the serum of diabetic patients by MEKC using stilbenediamine as derivatizing reagent

An analytical method has been developed for the separation of glyoxal (Go), methylglyoxal (MGo), and dimethylglyoxal (DMGo) by MEKC using stilbenediamine (SD) as derivatizing reagent, separation time 6.5 min, SDS as micellar medium at pH 8, and sodium tetraborate (0.1 M) as buffer. Uncoated fused-silica capillary, effective length 50 cm x 75 microm id; applied voltage 20 kV and photodiode array detection, were used. Calibration was linear within 0.02-150 microg/mL with detection limits 3.5-5.8 ng/mL. Go and MGo, observed for diabetic and healthy volunteers, were within 0.098-0.193 microg/mL Go and 0.106-0.245 microg/mL MGo with RSD 1.6-3.5 and 1.7-3.4%, respectively, in diabetics against 0.016-0.046 microg/mL Go and 0.021-0.066 microg/mL MGo with RSDs 1.5-3.5 and 1.4-3.6%, respectively, in healthy volunteers. Go and MGo in diabetics were also measured by standard addition and DMGo as an internal standard. Additives do not contribute significantly to Go and MGo matrix.     

Effect of Metal Substitution in BSCCO Ceramic Superconductors

The fabrication, electrical, and optical properties of ceramic Bi_2-xM_xSr₂Ca₂Cu₃O_y (where M=Al or Ni and x=0.3) superconductors are described. Resistivity measurements reveal that when Al is partially substituted at the bismuth site in the BiSrCaCuO compound, T _c decreases to 77 K and the nickel-substituted compound shows a T _c of 70 K, compared to the undoped ceramic BiSrCaCuO samples with T _c of 85 K. Infrared reflectance measurements, which cover the 50-4000 cm^–1 range, find that the reflectance from the ceramic samples decreases in the metal-doped samples. The observed phonon modes in the infrared conductivity spectra (obtained by Kramers-Kronig analysis) decrease in strength and some features are completely smeared out. Furthermore some of the modes are observed to shift slightly in the frequency on doping, the change in the T _c and vibrational modes is attributed to destabilization of 2223 phase.