سال:1383 | دوره: | شماره: |تعداد مقالات:11

The selective use of tert-butoxycarbonyl protecting group chemistry has enabled efficient syntheses of multilinked macrocyclic derivatives incorporating tetraaza and aza-thia donor rings. Mixed ring species have also been prepared as well as a dendrimer incoporating nine N2S2-donor macrocyclic sites. The interaction of these species with selected metal ions is discussed. A series of cage molecules with varying cavity sizes has been prepared and their interaction with both (selected) metal ions and small molecules described. The formation of new large molecular squares and catenanes involving self-assembly is also presented.

Metallocavitands are coordination compounds based on rigidified molecular cavities which possess at least one entry. Those in which the metal centre is rigidly held above the entrance are particularly promising for the study of host-guest interactions between metal-bonded substrates and the internal part of a cavity. Such systems also open the way to highly selective intra-cavity reactions. The present review focusses on conical cavities derived from calixarenes and cyclodextrins and examines their possible use as second coordination sphere ligands.

Coordination behaviour of a biologically potent sulphonamide-imine having N?N donor moiety towards the diorgano and triorganotin(IV) have been investigated. The unimolar and bimolar reactions of di-and triorgano-tin(IV) chlorides with monobasic bidentate imine resulted in the formation of colored solids, soluble in DMSO, DMF and MeOH, which have been characterized by elemental analyses, molecular weight determinations and conductance measurements. Structures of the resulting complexes have been proposed using IR, 1H, 13C and 119 Sn NMR spectral studies. All the complexes are monomeric in nature as indicated by their molecular weight determinations. Conductivity measurements in dry DMF show them to be non-electrolytes. The pathogenicity and virulence of certain microbial infections associated with ions of the complexes have been found to be potent and like broad spectrum antibiotics. These results made it desirable to delineate a comparison between the ligand and its metal complexes. Emphasis has been given to the nematicidal properties.

The high yield conversion of aldehydes into their corresponding nitriles using hydroxylamine hydrochloride/ CH3 COCl /charcoal system is presented. We have clearly shown the effectiveness of charcoal in these reactions.

Three new alternative synthetic strategies based on reactions of hydrazonoyl halides 3 with 2-methylthiouracil 2 and treatment of either 2 -pyrimidinyl thiohydrazonates 8 or the diazonium coupling products of active (pyrimidin-2-ylthio)methylene compounds 12 with sodium ethoxide in ethanol are described for the title compounds. The mechanisms and regiochemistry of the studied reactions are discussed

The species of Cr(III) and Cr(VI) in water samples were determined by flow injection on-line preconcentration and separation on two-microcolumn system–derivative flame atomic absorption spectrometry during a collaborative analysis for certification. The Cr(III) and Cr(VI) in water samples were retained on two microcolumns with ion exchange resin and were eluted directly to nebulizer by 15% HNO3 and 8% NH4NO3, respectively. The characteristic concentration (at the sensitivity grade of 2 mV min-1 for 1 min of preconcentration time) for Cr(III) and Cr(VI) were 0.130 and 0.0985 µg l-1, in the order which were 332- and 431-fold better than those of FAAS, and 45- and 47-fold better than those of FI-FAAS, respectively. The relative standard deviations were 3.27% and 3.66% with corresponding detection limits (3?) of 0.244 and 0.235 µg l-1, respectively. The linear ranges of determinations for Cr(III) and Cr(VI) were 0~100 µgm l-1 with correlation coefficients of 0.9984 to 0.9996. The satisfactory recovery of 94.4%~106% for Cr(III) and Cr(VI) could be obtained from water samples.

The microsurface adsorption–spectral correction technique (MSASC) has been applied to investigation of the ternary interaction of 1,5-di(2-hydroxy-5-sulfophenyl)-3-cyanoformazan (DHSPCF) with cetyltrimethylammonium bromide (CTAB) and rare earths Y, Eu, Dy and Yb. The CTAB micelle enriched DHSPCF molecules on its microsurface in monolayers and then sensitized the complexation between rare earths and DHSPCF. The binary aggregate and the ternary complex both were characterized.

Three new pendant arm Schiff-base macrocyclic complexes, [CdLn]2+ (n = 5, 6, 7), have been prepared via cyclocondensation of 2,6-diacetylpyridine with three different branched hexaamines in the presence of Cd(II). The ligands are 15-, 16- and 17-membered pentaaza macrocycles having two 2-aminoethyl pendant arms [L5 = 2,13-dimethyl-6,9-bis(aminoethyl)-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, L6 = 2,14-dimethyl-6,10-bis(aminoethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19),2,13,15,17-pentaene and L7 = 2,15-dimethyl-6,11-bis(aminoethyl)-3,6,11,14,20-pentaazabicyclo[14.3.1]eicosa-1(20),2,14,16,18-pentaene]. All complexes were investigated by IR, 1H and 13C NMR, COSY(H,H) and HETCOR(H,C) spectroscopy and X-ray diffraction. In the solid state structure of each complex the Cd(II) ion is situated centrally within an approximately planar pentaaza macrocyclic ring, binding to the five nitrogen atoms, and also to the two pendant amines which are located on opposite sides of the macrocyclic plane. ab initio HF-MO calculations using a standard 3-21G* basis set have been used to verify that these similar basic structures correspond to energy minima in the gas phase.

Hydroxamic acids, RCONHOH, form highly stable complexes with vanadium(IV) in 1:1, 1:2 and 1:3 molar ratios. The stability constants of the complexes were determined through spectrophotometric and potentiometric methods at various pH and found to be comparable. Acetohydroxamate, benzohydroxamate and salicylhydroxamate were selected for the study. Using the spectrophotometric method, graphical calculations were applied to confirm the results. Potentiometric method associated with computer calculation program BEST was also applied to check the reproducibility of the results.

Ab initio calculations at HF/6-31G* level of theory for geometry optimization and MP2/6-31G*//HF/6-31G* for a single point total energy calculation are reported for the three geometrical isomers of cycloocta-l,5-diene 1-3.

The extraction and preconcentration of a metal complex via surfactant-mediated phase separation was studied. A sensitive, selective and low-cost methodology for the determination of micro amounts of thorium, lanthanum and yttrium ions, using Eriochrome Cyanine R (ECR) with a flotation step prior to spectrophotometric determination was developed. The precipitate in the scum layer was quantitatively collected, stripped with 4 ml of 3% HCl and measured spectrophotometrically at 540 nm for Th(IV) and at 650 nm for both La(III) and Y(III). The stripping of Th(IV), La(III) and Y(III) from the scum layer was carried out in one step with different mineral acids. The stripping efficiency was found to be quantitative in the case of HCl. An excess amount of ECR was used to eliminate the interfering effects of various foreign species. The proposed procedure was applied to the determination of Th(IV), La(III) and Y(III) spiked in natural water samples and in some ore samples. Additionally, the mechanism of flotation of the metal chelate was proposed to be due to a physical interaction between the metal chelate and the oleic acid surfactant through the Van der Waals force.