Crystal structure of [1,4-bis[1-(3,5-dichlorophenolato-2-ylmethyl)-ylpropylamino-kappa2N,O]piperazine-kappa2N,N']cobalt(II).

The X-ray crystal structure of the title complex, Co(Cl2bprpi) is described. In this complex the Co(II) center displays a distorted octahedral coordination geometry. The piperazine ring exhibits boat conformation, forming chelate rings and capping the Co atom. The N2-Col-N3 angle is 69.41(15) degrees, extremely smaller than 90 degrees. Because the small angle causes a large steric hindrance, the piperazine ring can be effective as an ion size-recognition site. The molecular structure is stabilized by intramolecular N-H...O hydrogen bonds and Cl...H contacts.     

Direct analysis of solid samples by atomic absorption spectrometry, following preconcentration of trace elements from seawater with 8-hydroxyquinoline

Summary 8-Hydroxyquinoline (8-HOQ) was used for the preconcentration of Cd, Cu, Mn, Pb and Zn from seawater prior to their determination by graphite furnace atomic absorption spectrometry using an inner miniature cup for solid sampling technique. The metal ions in seawater were precipitated quantitatively in the pH range 7–8.5 with 8-HOQ alone. The precipitate thus formed was directly analysed by an atomic absorption spectrometer equipped with a specially deviced graphite furnace and miniature cup. The present method was confirmed to be highly reliable for analysis of seawater. Detection limits (3_b) for Cd(II), Cu(II), Mn(II), Pb(II) and Zn(II) are 1.4, 10, 5, 10, and 6 ng l^–1, respectively, for the analysis of a 400-ml portion of seawater samples. Corresponding precision of 6–14% is typical for determination 5-fold above the detection limits.

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Direkte Analyse von Feststoffproben durch AAS nach Anreicherung von Spurenelementen aus Meerwasser mit 8-Hydroxychinolin

     

Determination of manganese in iron and steels by u.h.f. plasma-torch emission spectrometry

The determination of manganese in iron and steels by u.h.f. plasma torch spectrometry is described. The intensity of the Mn II 257.16-nm ion line decreased with increasing concentration of iron, whereas the intensity of the Mn I 403.07-nm atom line increased; only the Mn I 279.48-nm atom line showed constant intensity as the concentration of iron increased. This behavior can be explained in terms of plasma temperature. The effects of acids were examined; the influence of small amounts of diverse elements was depressed by a large amount of iron. A simple and rapid method for the determination of manganese in iron and steels was established, the relative standard deviation being 2.6 % for 0.10 % Mn.     

Synthesis, structures and reactions of cyclometallated gold complexes containing (2-diphenylarsino-n-methyl)phenyl (n = 5, 6)

Reaction of (C6H3-2-AsPh2-n-Me)Li (n = 5 or 6) with [AuBr(AsPh3)] at -78 degrees C gives the corresponding cyclometallated gold(I) complexes [Au2[(mu-C6H3-n-Me)AsPh2]2] [n = 5, (1); n = 6, (9)]. 1 undergoes oxidative addition with halogens and with dibenzoyl peroxide to give digold(II) complexes [Au2X2[(mu-C6H3-5-Me)AsPh2]2] [X = Cl (2a), Br (2b), I (2c) and O2CPh (3)] containing a metal-metal bond between the 5d9 metal centres. Reaction of 2a with AgO2CMe or of 3 with C6F5Li gives the corresponding digold(II) complexes in which X = O2CMe (4) and C6F5 (6), respectively. The Au-Au distances increase in the order 4 < 2a < 2b < 2c < 6, following the covalent binding tendency of the axial ligand. Like the analogous phosphine complexes, 2a-2c and 6 in solution rearrange to form C-C coupled digold(I) complexes [Au2X2[mu-2,2-Ph2As(5,5-Me2C6H3C6H3)AsPh2]] [X = Cl (5a), X = Br (5b), X = I (5c) and C6F5 (7)] in which the gold atoms are linearly coordinated by As and X. In contrast, the products of oxidative additions to 9 depend markedly on the halogens. Reaction of 9 with chlorine gives the gold(I)-gold(III) complex, [ClAu[mu-2-Ph2As(C6H3-6-Me)]AuCl[(6-MeC6H3)-2-AsPh2]-kappa2As,C] (10), which contains a four-membered chelate ring, Ph2As(C6H3-6-Me), in the coordination sphere of the gold(III) atom. When 10 is heated, the ring is cleaved, the product being the digold(I) complex [ClAu[mu-2-Ph2As(C6H3-6-Me)]Au[AsPh2(2-Cl-3-Me-C6H3)]] (11). Reaction of 9 with bromine at 50 degrees C gives a monobromo digold(I) complex (12), which is similar to 11 except that the 2-position of the substituted aromatic ring bears hydrogen instead halogen. Reaction of 9 with iodine gives a mixture of a free tertiary arsine, (2-I-3-MeC6H3)AsPh2 (13), a digold diiodo compound (14) analogous to 11, and a gold(I)-gold(III) zwitterionic complex [I2Au(III)[(mu-C6H3-2-AsPh2-6-Me)]2Au(I)] (15) in which the bridging units are arranged head-to-head between the metal atoms. The structures of 2a-2c and 4-15 have been determined by single-crystal X-ray diffraction analysis. The different behaviour of 1 and 9 toward halogens mirrors that of their phosphine analogues; the 6-methyl substituent blocks C-C coupling of the aryl residues in the initially formed oxidative addition product. In the case of 9, the greater lability of the Au-As bond in the initial oxidative addition product may account for the more complex behaviour of this system compared with that of its phosphine analogue.     

Green polymers from Geobacillus thermodenitrificans DSM465--candidates for molecularly imprinted materials

Novel molecular recognition materials were prepared from water soluble proteins from thermophile G. thermodenitrificans DSM465 by an alternative molecular imprinting method. Water soluble proteins from G. thermodenitrificans DSM465 were converted into the molecularly imprinted materials by adopting 9-EA as a print molecule. The molecularly imprinted protein membranes recognized As in preference to Gs. The adsorption isotherms led to the conclusion that molecular recognition sites toward As were constructed by the presence of 9-EA during the membrane preparation process. The affinity constant between As and the molecular recognition site thus constructed was determined to be 1.75 x 10(5) mol(-1) dm(3). The results obtained in the present study suggest that water soluble proteins from G. thermodenitrificans DSM465 is one of environmentally-friendly 'green' polymers to be converted into molecular recognition materials by applying an alternative molecular imprinting method.     

Enantioselective synthesis mediated by chiral crystal of achiral hippuric acid in conjunction with asymmetric autocatalysis

Enantiomorphous crystals composed of achiral hippuric acid, i.e., naturally occurring N-benzoylglycine, have been used successfully as chiral inducers in enantioselective synthesis in combination with asymmetric autocatalysis to afford the product with extremely high enantiomeric excess.     

Synaptic inhibition and γ-aminobutyric acid in the mammalian central nervous system

Signal transmission through synapses connecting two neurons is mediated by release of neurotransmitter from the presynaptic axon terminals and activation of its receptor at the postsynaptic neurons. γ-Aminobutyric acid (GABA), non-protein amino acid formed by decarboxylation of glutamic acid, is a principal neurotransmitter at inhibitory synapses of vertebrate and invertebrate nervous system. On one hand glutamic acid serves as a principal excitatory neurotransmitter. This article reviews GABA researches on; (1) synaptic inhibition by membrane hyperpolarization, (2) exclusive localization in inhibitory neurons, (3) release from inhibitory neurons, (4) excitatory action at developmental stage, (5) phenotype of GABA-deficient mouse produced by gene-targeting, (6) developmental adjustment of neural network and (7) neurological/psychiatric disorder. In the end, GABA functions in simple nervous system and plants, and non-amino acid neurotransmitters were supplemented.