Flow injection atomic absorption spectrometery for the standardization of arsenic, lead and mercury in environmental and biological standard reference materials

Results of a thorough study and application of flow injection atomic absorption spectrometry for the determination of As, Pb and Hg in parts per million to sub-parts per billion levels in environmental and biological samples have been described. Various standard reference materials from the National Bureau of Standards, USA, the National Institute of Standards and Technology, USA, the Community Bureau of Reference, Brussels, Belgium and the National Institute for Environmental Studies, Japan and Standard Chinese river sediment were used. By flow injection hydride generation AAS the standard reference materials were analyzed for As and Pb. Mercury was determined by cold vapour flow injection AAS from environmental and biological standard reference materials. The technique is fast, simple and highly sensitive. It takes only 30 s for each analysis from the digested solution. The detection limits of As, Pb and Hg are 1.8 μg L^–1 and 2.0 μg L^–1 and 1.5 μg L^–1, respectively. The results show good agreement with the certified values. Received: 9 May 1996 / Revised: 13 August 1996 / Accepted: 14 August 1996     

A construction of balanced arrays of strengtht and some related incomplete block designs

Summary Saha [6] has shown the equivalence between a ‘tactical system’ (or at-design) and a 2-symbol balanced array (BA) of strengtht. The implicit method of construction of BA in that paper has been generalized herein to that of ans-symbol BA of strengtht. Some BIB and PBIB designs are also constructed from these arrays. Majindar [2], Vanstone [8] and Saha [6] have all shown that the existence of a symmetrical BIBD forv treatments implies the existence of six more BIBD's forv treatments in (v/2) blocks. An analogue of this result has been obtained for a large class of PBIB designs in this paper.     

Induction of Supramolecular Chirality in the Self‐Assemblies of Lipophilic Pyrimidine Derivatives by Choice of the Amino Acid‐Based Chiral Spacer

A new family of supramolecular organogelators, based on chiral amino acid derivatives of 2,4,6‐trichloro‐pyrimidine‐5‐carbaldehyde, has been synthesized. L ‐alanine was incorporated as a spacer between the pyrimidine core and long hydrocarbon tails to compare the effect of chirality and hydrogen bonding to that of the achiral analogue. The role of aromatic moiety on the chiral spacer was also investigated by introducing L ‐phenyl alanine moieties. The presence of intermolecular hydrogen‐bonding leading to the chiral self‐assembly was probed by concentration‐dependent FTIR and UV/Vis spectroscopies, in addition to circular dichroism (CD) studies. Temperature and concentration‐dependent CD spectroscopy ascribed to the formation of β‐sheet‐type H‐bonded networks. The morphology and the arrangements of the molecules in the freeze‐dried gels were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X‐ray diffraction (XRD) techniques. Calculation of the length of each molecular system by energy minimization in its extended conformation and comparison with the small‐angle XRD pattern reveals that this class of gelator molecules adopts a lamellar organization. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) indicate that the solid state phase behavior of these molecules is totally dependent on the choice of their amino acid spacers. Structure‐induced aggregation properties based on the H‐bonding motifs and the packing of the molecule in three dimensions leading to gelation was elucidated by rheological studies. However, viscoelasticity was shown to depend only marginally on the H‐bonding interactions; rather it depends on the packing of the gelators to a greater extent.     

Synthesis, spectroscopic, and structural aspects of two trinuclear cyano-bridged heterometallic complexes

Two new cyano-bridged trinuclear heterometallic complexes [Sr₂(Phen)₄(CF₃CO₂)(H₂O)₃Fe(CN)₆]·2H₂O (1) [Ca₂(Phen)₄(CF₃CO₂)(H₂O)Co(CN)₆]·2H₂O (2) (where Phen=1,10-phenanthroline) have been synthesized and their crystal structures have been determined. The structure of complex (1) features a central [Fe(CN)₆]³⁻ unit that links a monocation, [Sr(Phen)₂(OH₂)(OOCCF₃)]⁺ and a dication, [Sr(Phen)₂(OH₂)₂]²⁺ via two trans cyanide bridges. The complex (2) features a central [Co(CN)₆]³⁻ unit that links two monocations of [Ca(Phen)₂(OH₂)(OOCCF₃)]⁺ (the positions of the trifluoro acetate and water molecules are disordered over two positions) via two trans cyanide bridges. Each metal atom is seven coordinated and achieves pentagonal bipyramidal geometry. Two cocrystallized water molecules are present in both the complexes. The presence of an extensive network of hydrogen bonding imparts the overall stability to both the systems.     

Kinetics and mechanism of the oxidation of some neutralized α-Hydroxy acids by hexachloroiridate(IV)

Summary The kinetics of oxidation of some neutralized -hydroxy acids such as lactic (LA), mandelic (MA), -hydroxyisobutyric (IB) and benzilic (BA) acid by hexachloroiridate(IV) have been studied. The oxidation products are acetaldehyde, benzaldehyde, acetone and benzophenone for the respective reactions, which are first order with respect to each substrate and to iridium(IV). The reaction rate increases with increase in pH and salt concentrations. The temperature influence is quite marked in all these reactions. A mechanism involving the formation of an unstable complex, which decomposesvia a free radical pathway to give the respective reaction products, is proposed.     

Indium(I) iodide-mediated cleavage of diphenyl diselenide. An efficient one-pot procedure for the synthesis of unsymmetrical diorganyl selenides

A simple and efficient procedure has been developed for the synthesis of unsymmetrical diorganyl selenides through a one-pot indium(I) iodide-mediated reaction of alkyl halide and diphenyl diselenide in methylene chloride at room temperature. [reaction: see text]     

Facile synthesis of silver nano particles with highly efficient anti-microbial property

A simple surfactant assisted aqueous solution approach, based on the conventional Tollen’s reaction has been applied for the facile syntheses of silver nano-assembly. Nano particle morphologies strongly depend on the temperature adopted during the synthesis. Two-dimensional (2 D) nano-disks and three-dimensional (3D) nano-globules with “Cauliflower” like morphology were observed. The unique and distinctive feature of the synthesized silver nano particle in solution is its very high anti-microbial activity. This is evident in very low (4 μg/ml) inhibitory concentration (MIC) value for Escherichia coli, Vibrio cholerae, Shigella flexneri, Salmonella typhimurium and three varieties of Staphylococcus aureus. This low MIC value is comparable to that of Penicillin and in the cases of E. coli and S. aureus (ML 422), the MIC value is as low as 2 μg/ml which beats even Penicillin.     

Mixed-spin binuclear nickel(II) complexes in unsymmetrical ligand environments and related mononuclear compounds: electronic and molecular structures in solution and in the solid state

Nickel(II) complexes of three new heterodonor ligands (HL(1), H(2)L(2), and H(3)L(3)) based on 2-aminocyclopent-1-ene-1-dithiocarboxylate have been synthesized, and their crystallographic characterizations are reported. With the pentacoordinating ligands HL(1) and H(3)L(3), the products obtained (1 and 2) are both mononuclear square planar compounds in which one of the pyrazolyl arms of ligand HL(1) and the bridgehead alkoxy oxygen of H(3)L(3) are staying away from coordination in 1 and 2, respectively. The saturated three carbon alkanyl chain in the ligand H(3)L(3) provides enough flexibility to generate tetrahedral distortion (dihedral angle, 22.7 degrees ) in the planarity of 2. Compound 1 displays paramagnetic line-broadening in its (1)H NMR spectrum due to oligomerization in solution. With the unsymmetrical binucleating ligand H(2)L(2), two mixed-spin homodinuclear complexes (3 and 4) have been synthesized using pyrazole and 2-mercaptopyridine as ancillary mu(2)-bridging ligands. Both these complexes have square planar low-spin and spin-triplet nickel(II) centers which display both coordination number and donor set asymmetry in tandem. The compounds have been characterized by (1)H NMR, electronic spectroscopy, and electrochemical studies.     

Studies on radical cyclization of 2,3-epoxy alcohols containing a β-(alkoxy)acrylate moiety using Cp2TiCl

Radical-mediated opening of chiral 2,3-epoxy alcohols, containing suitably positioned β-(alkoxy)acrylate moieties, using Cp₂TiCl triggered intramolecular cyclization to give tetrahydrofuran and tetrahydropyran moieties.     

Total synthesis of stevastelin B3

The total synthesis of stevastelin B3 was achieved using, as a key step, a method developed by us for the synthesis of 2-methyl-1,3-diols by Ti(III)-mediated diastereo- and regioselective opening of trisubstituted 2,3-epoxy alcohols, to carry out the stereoselective construction of its propionate-derived fatty acid segment.