Studies on electron transfer reactions: reduction of heteropoly 11-tungstophosphovanadate(V) by <Emphasis Type="SmallCaps">l</Emphasis>-cysteine and thioglycolic acid in aqueous acid medium

The rates of the electron transfer reaction of l-cysteine and thioglycolic acid with the polyoxometalate, [PV^VW₁₁O₄₀]⁴⁻, have been measured spectrophotometrically in aqueous acid medium. The polyoxometalate oxidizes cysteine to cystine and thioglycolic acid to dithioglycolic acid and gets reduced to heteropoly blue, [PV^IVW₁₁O₄₀]⁵⁻. The order of the reaction with respect to oxidant is one, whereas the reaction shows second order dependence on the substrates. The rate–pH profile shows that both the unionized and ionized thiol groups of the substrates are active species involved in electron transfer. A suitable mechanism has been proposed for the title reaction based on the results of kinetic studies.     

Efficient and effective heuristics for the coordinated capacitated lot-size problem

Coordinating procurement decisions for a family of products that share a constrained resource, such as an ocean shipping container, is an important managerial problem. However due to the problem’s difficult mathematical properties, efficient and effective solution procedures for the problem have eluded researchers. This paper proposes two heuristics, for the capacitated, coordinated dynamic demand lot-size problem with deterministic but time-varying demand. In addition to inventory holding costs, the problem assumes a joint setup cost each time any member of the product family is replenished and an individual item setup cost for each item type replenished. The objective is to meet all customer demand without backorders at minimum total cost. We propose a six-phase heuristic (SPH) and a simulated annealing meta-heuristic (SAM). The SPH begins by assuming that each customer demand is met by a unique replenishment and then it seeks to iteratively maximize the net savings associated with order consolidation. Using SPH to find a starting solution, the SAM orchestrates escaping local solutions and exploring other areas of the solution state space that are randomly generated in an annealing search process. The results of extensive computational experiments document the effectiveness and efficiency of the heuristics. Over a wide range of problem parameter values, the SPH and SAM find solutions with an average optimality gap of 1.53% and 0.47% in an average time of 0.023 CPU seconds and 0.32 CPU seconds, respectively. The heuristics are strong candidates for application as stand alone solvers or as an upper bounding procedure within an optimization based algorithm. The procedures are currently being tested as a solver in the procurement software suite of a nationally recognized procurement software provider.     

Ion chromatographic determination of trace level phosphorus in purified quartz

Trace levels of phosphorus in purified quartz are determined by ion chromatography. In situ reagent purification, matrix digestion and oxidation of phosphorus to orthophosphate ion are carried out simultaneously in a vapour phase digestion (VPD) assembly using a mixture of HF, HNO3 and H2O2. A drastic reduction (475 times) in phosphate blank from reagents (HF/H2O2) was achieved in the VPD through in situ purification of the reagent. The residues remaining after volatilisation (solvent/matrix), mostly consisting of insoluble phosphate/fluoride salts of divalent and trivalent cations, were solubilised by ion-exchange dissolution. Phosphate was analysed on the IonPac AS17 column with suppressed conductivity detection. The results of the ion chromatography (IC) method were compared with a spectrophotometric method. Accuracy was evaluated by analysing a certified reference material (silicon, NIST 57a). The method detection limit was 0.05 microg g(-1).     

DNA binding and antimicrobial studies of some polyethyleneimine-copper(II) complex samples containing 1,10-phenanthroline and l-theronine as co-ligands

The polymer–copper(II) complex samples, [Cu(phen)(l-Thr)(BPEI)]ClO₄ · 2H₂O (l-Thr = l-theronine, phen = 1,10-phenanthroline and BPEI = branched polyethyleneimine), with varying degrees of copper(II) chelate content in the polymer chain, were prepared by ligand substitution method in water–ethanol medium and characterized by Infra-red, UV–Vis, EPR spectral and elemental analysis methods. The binding of these complex samples with calf thymus DNA (CT-DNA) has been investigated by absorption spectroscopy and emission spectroscopy and gel electrophoresis techniques. The experimental results indicate that the polymer–copper(II) complex is an avid DNA binder and the binding constant increased with the increase in amount of copper(II) chelate content in the polymer chain. Besides the electrostatic interaction between a negatively charged DNA molecule and a positively charged polymer–copper(II) complex molecule, other binding modes, such as van der Waals interaction, hydrogen bonding and partial intercalation binding modes may also exist in this system. A sample of polymer–copper(II) complex was tested for its antibacterial and antifungal activity and it was found to have good antibacterial and antifungal activities.     

Feature extraction from spectral and other data by the principal components and discriminant function techniques

Principal component analysis is applied to the interpretation of ¹³C-n.m.r. spectra and to the resolution of mass spectral data. A procedure is given for determining the relative amounts of pure components, with and without the use of pure mass lines, in mass spectra of mixtures. The use of the Fisher discriminant method in combination with the principal components technique is demonstrated in the treatment of trace element data on hair for environmental purposes. The importance of feature generation and selection is emphasized.     

A rapid ultrasound-assisted thiourea extraction method for the determination of inorganic and methyl mercury in biological and environmental samples by CVAAS

A rapid ultrasound-assisted extraction procedure for the determination of total mercury, inorganic and methyl mercury (MM) in various environmental matrices (animal tissues, samples of plant origin and coal fly ash) has been developed. The mercury contents were estimated by cold vapour atomic absorption spectrometry (CVAAS). Inorganic mercury (IM) was determined using SnCl₂ as reducing agent whereas total mercury was determined after oxidation of methyl mercury through UV irradiation. Operational parameters such as extractant composition (HNO₃ and thiourea), sonication time and sonication amplitude found to be different for different matrices and were optimized using IAEA-350 (Fish homogenate), IM and MM loaded moss and NIST-1633b (Coal fly ash) to get quantitative extraction of total mercury. The method was further validated through the analysis of additional certified reference materials (RM): NRCC-DORM2 (Dogfish muscle), NRCC-DOLT1 (Dogfish liver) and IAEA-336 (Lichen). Quantitative recovery of total Hg was achieved using mixtures of 5% HNO₃ and 0.02% thiourea, 10% HNO₃ and 0.02% thiourea, 20% HNO₃ and 0.2% thiourea for fish tissues, plant matrices and coal fly ash samples, respectively. The results obtained were in close agreement with certified values with an overall precision in the range of 5-15%. The proposed ultrasound-assisted extraction procedure significantly reduces the time required for sample treatment for the extraction of Hg species. The extracted mercury species are very stable even after 24 h of sonication. Closed microwave digestion was also used for comparison purposes. The proposed method was applied for the determination of Hg in field samples of lichens, mosses, coal fly ash and coal samples     

Speciation of Cr(III) and Cr(VI) in waters using immobilized moss and determination by ICP-MS and FAAS

The possibility of using moss (Funaria hygrometrica), immobilized in a polysilicate matrix as substrate for speciation of Cr(III) and Cr(VI) in various water samples has been investigated. Experiments were performed to optimize conditions such as pH, amount of sorbent and flow rate, to achieve the quantitative separation of Cr(III) and Cr(VI). During all the steps of the separation process, Cr(III) was selectively sorbed on the column of immobilized moss in the pH range of 4-8 while, Cr(VI) was found to remain in solution. The retained Cr(III) was subsequently eluted with 10 ml of 2 mol l⁻¹ HNO₃. A pre-concentration factor of about 20 was achieved for Cr(III) when, 200 ml of water was passed. The immobilized moss was packed in a home made mini-column and incorporated in flow injection system for obtaining calibration plots for both Cr(III) and Cr(VI) at low ppb levels that were compared with the plots obtained without column. After separation, the chromium (Cr) species were determined by inductively coupled plasma mass spectrometry (ICP-MS) and flame atomic absorption spectrometry (FAAS). The sorption capacity of the immobilized moss was found to be ∼11.5 mg g⁻¹ for Cr(III). The effect of various interfering ions has also been studied. The proposed method was applied successfully for the determination of Cr(III) and Cr(VI) in spiked and real wastewater samples and recoveries were found to be >95%.     

Graphite furnace atomic absorption spectrometric (GFAAS) determination of Cu, Cd, Cr, Mn, Ni and Pb in tellurium metal using precipitation and ion-exchange procedures

 Two independent procedures have been developed for the determination of Cd, Cu, Ni, Mn, Cr and Pb in high-purity tellurium by GFAAS. In the first, tellurium is precipitated as TeO₂ in the presence of EDTA at pH 4.5±0.2 to remove of 99.4% of tellurium as tellurium dioxide. The supernatant is analysed for impurities. In the second procedure, the trace impurities are preconcentrated on a Chelex-100 resin column at pH 9.4±0.2, and eluted by two column volumes of 2 mol/L HNO₃. In this case a matrix separation coefficient (k_s) of 1500 is achieved. The analyses are carried out by GFAAS. The relative standard deviations of the analyte concentrations in the samples are 4–8%. Separation of the matrix and recovery of the analytes are essentially complete as confirmed by standard addition of the analytes to the matrix. Received: 30 July 1996/Revised: 7 November 1996/Accepted: 13 November 1996     

Synthesis,spectral, redox and antimicrobial activities of Schiff base complexes derived from 1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one and acetoacetanilide

Novel terdentate neutral complexes of Cu^II, Ni^II, Co^II, Mn^II, Zn^II, Cd^II, Hg^II, VO^II, ZrO^II and UO₂ ^II have been prepared using a Schiff base derived from 1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one (4-aminoantipyrine) and acetoacetanilide. The structural features of the chelates have been confirmed by microanalytical data, i.r., u.v.–vis., ¹H-n.m.r., e.s.r. and mass spectral techniques. Electronic absorption and i.r. spectra of the complexes indicate an octahedral geometry around the central metal ion, except for the VO^II and ZrO^II complexes which show square pyramidal geometry. The monomeric and neutral nature of the complexes are confirmed from their magnetic susceptibility and low conductance values. The cyclic voltammogram of the copper complex in MeCN at 300 K shows a quasi-reversible peak for the couple Cu^II/Cu^III at Ep_c = 0.47 and Ep_a = 0.61 V versus Ag/AgCl and two irreversible peaks for Cu^II Cu^I and Cu^I Cu⁰ reduction at Ep_c = –0.63 and – 0.89 V respectively. The e.s.r. spectra of copper and vanadyl complexes in DMSO solution at 300 K and 77 K were recorded and their salient features are reported. The molecular orbital coefficients (², ²) were calculated for complexes. The antimicrobial activity of the ligand and its complexes have been extensively studied on microorganisms such as Staphylococcus aureus, Klebsiela pneumoniae, Bacillus subtillis, Escherichia coli, Citrobacter ferundii and Salmonella typhi. Most of the complexes have higher activities than that of the free ligand.     

Measurement of the ground state 2n pickup probability for 28Si+68Zn and its role in sub-barrier fusion enhancement

The ground state and excited state transfer yields for the 2-neutron pickup channel in the ²⁸Si+⁶⁸Zn system have been measured explicitly. The recoil mass separator at the nuclear Science Centre, New Delhi was used for the measurement. A NaI(T1) detector was used for detecting the deexcitation γ’s from the transfer products. The kinematic coincidence technique was employed for the transfer measurement. Simplified coupled channels calculations show that out of all transfer channels the major contribution to the sub-barrier enhancement comes from the ground state 2 neutron pickup channel with a ground state Q-value of+1.83 MeV.