The effects of Group 11 transition metals, including gold, on ethylene binding to the ETR1 receptor and growth of Arabidopsis thaliana

It has been previously shown that Cu(I) and the ethylene response antagonist, Ag(I), support ethylene binding to exogenously expressed ETR1 ethylene receptors. Both are Group 11 transition metals that also include gold. We compared the effects of gold ions with those of Cu(I) and Ag(I) on ethylene binding in exogenously expressed ETR1 receptors and on ethylene growth responses in etiolated Arabidopsis seedlings. We find that gold ions also support ethylene binding but, unlike Ag(I), do not block ethylene action on plants. Instead, like Cu(I), gold ions affect seedlings independently of ethylene signaling.     

Limitations of the use of plant material grown in Petri dishes for physiological experiments

Roots of plants growing "aeroponically" (AP) on moistened filter paper in Petri dishes for a few days are fairly often used for physiological experiments (e.g. measurement of root growth), for ion or herbicide uptake tests, before the establishment of hydroponic or aseptic cultures although their hormonal status is markedly different from that of the hydroponic (HP) control. On the 4th day of germination the ethylene production of cucumber (Cucumis sativus L. cv. Budai csemege) roots growing in AP under controlled conditions increased considerably and exhibited a maximum curve, HP roots evolved ethylene much more constantly. The morphological changes in AP roots (e.g. inhibited elongation and swelling of primary roots, and increased formation of root hairs), resembling those caused by exogenously applied ethylene, can be prevented with 10(-5) M Ag+, an inhibitor of ethylene action. In roots of one-week-old AP seedlings, the amount of an acidic inhibitor, which as judged from the Rf values is likely to be abscisic acid (ABA), is about twice as high as in HP seedlings. An elevated ethylene or ABA level of AP roots may result in a reduced elongation of the primary roots. Counteraction of this inhibition by Ag+ suggests that the effect of ethylene is the primary event in the reduction of root length. When using plant material grown in Petri dishes the possibility of similar changes in hormonal status of the roots must be taken into consideration.     

Metal binding to Pseudomonas aeruginosa azurin: a kinetic investigation

The interaction between azurin from Pseudomonas aeruginosa and Ag(I), Cu(II), Hg(II), was investigated as a function of protein state, i.e. apo-, reduced and oxidised azurin. Two different metal binding sites, characterized by two different spectroscopic absorbancies, were detected: one is accessible to Ag(I) and Cu(II) but not to Hg(II); the other one binds Ag(I) and Hg(II) but not copper. When added in stoichiometric amount, Ag(I) shows high affinity for the redox center of apo-azurin, to which it probably binds by the -SH group of Cys112; it can displace Cu(I) from reducedazurin, while it does not bind to the redox center of oxidizedazurin. Kinetic experiments show that Ag(I) binding to the reduced form is four times faster than binding to the apo-form. This result suggests that metal binding requires a conformational rearrangement of the active site of the azurin. Interaction of Ag(I) or Hg(II) ions to the second metal binding site, induces typical changes of UV spectrum and quenching of fluorescence emission.     

Silicon does not mitigate cell death in cultured tobacco BY-2 cells subjected to salinity without ethylene emission

Key message

Silicon induces cell death when ethylene is suppressed in cultured tobacco BY-2 cells. There is a crosstalk between Si and ethylene signaling.

Abstract

Silicon (Si) is beneficial for plant growth. It alleviates both biotic and abiotic stresses in plants. How Si works in plants is still mysterious. This study investigates the mechanism of Si-induced cell death in tobacco BY-2 cell cultures when ethylene is suppressed. Results showed that K₂SiO₃ alleviated the damage of NaCl stress. Si treatment rapidly increased ethylene emission and the expression of ethylene biosynthesis genes. Treatments with Si + Ag and Si + aminooxyacetic acid (AOA, ethylene biosynthesis inhibitor) reduced the cell growth and increased cell damage. The treatment with Si + Ag induced hydrogen peroxide (H₂O₂) generation and ultimately cell death. Some nucleus of BY-2 cells treated with Si + Ag appeared TUNEL positive. The inhibition of H₂O₂ and nitric oxide (NO) production reduced the cell death rate induced by Si + Ag treatment. Si eliminated the up-regulation of alternative pathway by Ag. These data suggest that ethylene plays an important role in Si function in plants. Without ethylene, Si not only failed to enhance plant resistance, but also elevated H₂O₂ generation and further induced cell death in tobacco BY-2 cells.

     

Facile synthesis of Ag nanocubes and Au nanocages

This protocol describes a method for the synthesis of Ag nanocubes and their subsequent conversion into Au nanocages via the galvanic replacement reaction. The Ag nanocubes are prepared by a rapid (reaction time < 15 min), sulfide-mediated polyol method in which Ag(I) is reduced to Ag(0) by ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) and a trace amount of Na(2)S. When the concentration of Ag atoms reaches supersaturation, they agglomerate to form seeds that then grow into Ag nanostructures. The presence of both PVP and Na(2)S facilitate the formation of nanocubes. With this method, Ag nanocubes can be prepared and isolated for use within approximately 3 h. The Ag nanocubes can then serve as sacrificial templates for the preparation of Au nanocages, with a method for their preparation also described herein. The procedure for Au nanocage preparation and isolation requires approximately 5 h.     

Antimicrobial and anticancer activity of tetrahedral, chelated, diphosphine silver(I) complexes: comparison with copper and gold

Tetrahedral, bischelated Ag(I) diphosphine complexes [Ag(P-P)2]NO3, where P-P is Ph2P(CH2)2PPh2 (dppe), Et2P(CH2)2PPh2 (depe), and cis-Ph2P(CH = CH)PPh2 (dppey), are potently cytotoxic to B16 melanoma cells in vitro (IC50 4 microM) and exhibit good activity against ip P388 leukemia in mice. The complex [Ag(dppe)2]NO3 is active against M5076 reticulum cell sarcoma. The antibacterial and antifungal activities of Ag(I) diphosphine and related Cu(I) and Au(I) complexes were assessed. The complexes [Au(dppey)2]Cl, [Au(dppp)2]Cl and (CuCl)2(dppe)3 show modest activity against three of the 12 bacterial strains tested, but all complexes exhibit antifungal activity against three strains of C. albicans in a "defined" medium, [Ag(depe)2]NO3 and [Au(dppp)2]Cl having comparable activity to fungizone. Antifungal activity of the complexes is reduced in Sabouraud's broth medium, and lost altogether for the Ag(I) complexes. Reactions of some of the Ag(I) complexes with glutathione and blood plasma were studied by 31P NMR.     

Coexistence of hepatitis B surface antigen (HBs Ag) and anti-HBs antibodies in chronic hepatitis B virus carriers: influence of "a" determinant variants

In chronic hepatitis B (CHB), the persistence of hepatitis B surface antigen (HBs Ag) is sometimes associated with antibodies (Ab) to HBs (anti-HBs). To assess the hypothesis of the selection of HBs Ag immune escape variants in CHB patients, the variability of the HBV S gene was determined for patients persistently carrying both HBs Ag and anti-HBs antibodies and patients solely positive for HBs Ag. We selected 14 patients who presented both markers (group I) in several consecutive samples and 12 patients positive for HBs Ag only (group II). The HBs Ag-encoding gene was amplified and cloned, and at least 15 clones per patient were sequenced and analyzed. The number of residue changes within the S protein was 2.7 times more frequent for group I than for group II patients and occurred mostly in the "a" determinant of the major hydrophilic region (MHR), with 9.52 versus 2.43 changes per 100 residues (P = 0.009), respectively. Ten patients (71%) from group I, but only three (25%) from group II, presented at least two residue changes in the MHR. The most frequent changes in group I patients were located at positions s145, s129, s126, s144, and s123, as described for immune escape variants. In CHB patients, the coexistence of HBs Ag and anti-HBs Ab is associated with an increase of "a" determinant variability, suggesting a selection of HBV immune escape mutants during chronic carriage. The consequences of this selection process with regard to vaccine efficacy, diagnosis, and clinical evolution remain partially unknown.     

Influence of ethylene produced by soil microorganisms on etiolated pea seedlings

There is indirect evidence that soil microorganisms producing ethylene (C(2)H(4)) can influence plant growth and development, but unequivocal proof is lacking in the literature. A laboratory study was conducted to demonstrate the validity of this speculation. Four experiments were carried out to observe the characteristic "triple" response of etiolated pea seedlings to C(2)H(4) microbially derived from l-methionine as a substrate in the presence or absence of Ag(I), a potent inhibitor of C(2)H(4) action. In two experiments, the combination of l-methionine and Acremonium falciforme (as an inoculum) was used, while in another study the indigenous soil microflora was responsible for C(2)H(4) production. A standardized experiment was conducted with C(2)H(4) gas to compare the contribution of the microflora to plant growth. In all cases, etiolated pea seedlings exhibited the classical triple response, which includes reduction in elongation, swelling of the hypocotyl, and a change in the direction of growth (horizontal). The presence of Ag(I) afforded protection to the pea seedlings against the microbially derived C(2)H(4). This study demonstrates that microbially produced C(2)H(4) in soil can influence plant growth.     

Ethylene Production and Leaflet Abscission of Three Peanut Genotypes Infected with Cercospora arachidicola Hori

Ethylene can induce abscission of leaves and other plant organs. Increased ethylene production by plant tissues can occur after invasion by microorganisms. The fungus Cercospora arachidicola Hori, attacks peanut leaflets and causes defoliation. Our objective was to determine if ethylene was involved in this defoliation. Leaves of three peanut, Arachis sp., genotypes were inoculated with C. arachidicola. Two genotypes, `Tamnut 74' and PI 109839, produced ethylene and were defoliated. The third genotype, PI 276233, a wild species, did not produce ethylene above control levels and was not defoliated. Increase in ethylene production by Tamnut 74 and PI 109839 coincided with appearance of disease symptoms. Tamnut 74 produced the most ethylene, but PI 109839 was equally defoliated. Thus, less overall ethylene production did not necessarily indicate a more resistant genotype in this system unless ethylene production remained at control levels, as it did for PI 276233. Ethylene sufficient to initiate abscission could have been produced by the seventh day after inoculation when it was similar for both Tamnut 74 and PI 109839, but 3 to 4 times control amounts. This occurred before the rapid increase in ethylene production and before disease symptoms were visible. Silver ion, a potent inhibitor of ethylene action, was sprayed at three concentrations on intact Tamnut 74 plants. All rates reduced abscission and 150 mg/liter Ag(I) decreased abscission to below 10%. The data indicate that ethylene produced by peanut leaves in response to C. arachidicola infection initiates abscission and that ethylene action can be blocked by Ag(I) in such a host-pathogen interaction.     

The structure of silver(I) iodide and bromide,and the silver(I) solvate in tetrahydrothiophene solution: An X-ray scattering and raman spectroscopic study

Structures of silver(I) iodide and bromide, and the solvated silver(I) ion are determined in tetrahydrothiophene solution with Large Angle X-ray Scattering (LAXS) technique. In a silver(I) perchlorate tetrahydrothiophene solution, silver(I) is solvated by four tetrahydrothiophene molecules in a regular tetrahedron. The main peak in the radial distribution function corresponds to four AgS distances at 2.526(7) Å. An SS distance at 2.65(2) Å in the solvent bulk is also included in the main peak. This shows that an internal structure exists in the tetrahydrothiophene bulk. Silver(I) iodide and bromide are tetrameric complexes with a stella quadrangula configuration, in saturated solution. The distances in the [AgI(SC₄H₈)]₄ complex are AgI 2.799(4); AgAg, 3.072(6) and II, 4.638(19) Å and in the [AgBr(SC₄H₈)]₄ complex they are AgBr, 2.592(3); AgAg, 2.866(5) and BrBr, 4.25(4) Å. The AgI bond distances in the [AgI(SC₄H₈)]₄ complex is shorter in solution than in the solid solvate. This is because bulk tetrahydrothiophene is a markedly weaker donor than free tetrahydrothiophene due to the sulfursulfur interactions in the bulk, shown to be around 2.65 Å. Raman spectroscopic studies on silver(I) and copper(I) iodide and silver(I) chloride tetrahydrothiophene solutions show that the polymetric structures predominate in concentrated solution and that they disintegrate upon dilution.     

Production and action of ethylene in senescing leaf discs: effect of indoleacetic Acid, kinetin, silver ion, and carbon dioxide

Supraoptimal concentrations of indoleacetic acid (IAA) stimulated ethylene production, which in turn appeared to oppose the senescence-retarding effect of IAA in tobacco leaf discs. Kinetin acted synergistically with IAA in stimulating ethylene production, but it inhibited senescence. Silver ion and CO(2), which are believed to block ethylene binding to its receptor sites, delayed senescence in terms of chlorophyll loss and stimulated ethylene production. Both effects of Ag(+) were considerably greater than those of CO(2). IAA, kinetin, CO(2), and Ag(+), combined, acted to increase ethylene production further. Although this combination increased ethylene production about 160-fold over that of the control, it inhibited senescence. Treatment with 25 mul/l of ethylene in the presence of IAA enhanced chlorophyll loss in leaf discs and inhibited by about 90% the conversion of l-[3,4-(14)C] methionine to (14)C(2)H(4) suggesting autoinhibition of ethylene production.The results suggest that ethylene biosynthesis in leaves is controlled by hormones, especially auxin, and possibly the rate of ethylene production depends, via a feedback control system, on the rates of ethylene binding at its receptor sites.     

The alpha 1/alpha 2 domains of class I HLA molecules confer resistance to natural killing

The expression of transfected HLA class I Ag has previously been shown to protect human target cells from NK-mediated conjugation and cytolysis. In this same system, transfected H-2 class I Ag fail to impart resistance to NK. In this study, we have mapped the portion of the HLA class I molecule involved in this protective effect by exploiting this HLA/H-2 dichotomy. Hybrid class I genes were produced by exon-shuffling between the HLA-B7 and H-2Dp genes, and transfected into the class I Ag-deficient B-lymphoblastoid cell line (B-LCL) C1R. Only those transfectants expressing class I Ag containing the alpha 1 and alpha 2 domains of the HLA molecule are protected from NK, suggesting the "protective epitope" is located within these domains. Since a glycosylation difference exists between HLA and H-2 class I Ag within these domains (i.e., at amino acid residue 176), the role of carbohydrate in the class I protective effect was examined. HLA-B7 mutant genes encoding proteins which either lack the normal carbohydrate addition site at amino acid residue 86 (B7M86-) or possess an additional site at residue 176 (B7M176+) were transfected into C1R. Transfectants expressing either mutant HLA-B7 Ag were protected from NK. Thus, carbohydrate is probably not integral to a class I "protective epitope." The potential for allelic variation in the ability of HLA class I Ag to protect C1R target cells from NK was examined in HLA-A2, A3, B7, and Bw58 transfectants. Although no significant variation exists among the HLA-A3, B7, and Bw58 alleles, HLA-A2 appears unable to protect. Comparison of amino acid sequences suggests a restricted number of residues which may be relevant to the protective effect.     

Synthesis and X-ray crystal structure of [Ag(phendio)<Subscript>2</Subscript>]ClO<Subscript>4</Subscript> (phendio = 1,10-phenanthroline-5,6-dione) and its effects on fungal and mammalian cells

The Cu(II) and Ag(I) complexes, [Cu(phendio)₃](ClO₄)₂4H₂O and [Ag(phendio)₂]ClO₄ (phendio = 1,10-phenanthroline-5,6-dione), are prepared in good yield by reacting phendio with the appropriate metal perchlorate salt. The X-ray crystal structure of the Ag(I) complex shows it to have a pseudo tetrahedral structure. `Metal-free' phendio and the Cu(II) and Ag(I) phendio complexes strongly inhibit the growth of the fungal pathogen Candida albicans, and are more active than their 1,10-phenanthroline analogues. The simple Ag(I) salts, AgCH<sub>3</sub>CO<sub>2</sub>, AgNO<sub>3</sub> and AgClO<sub>4</sub>.H<sub>2</sub>O display superior anti-fungal properties compared to analogous simple Cu(II) and Mn(II) salts, suggesting that the nature of the metal ion strongly influences activity. Exposing C. albicans to `metal-free' phendio, simple Ag(I) salts and [Ag(phendio)₂]ClO₄ causes extensive, non-specific DNA cleavage. `Metal-free' phendio and [Ag(phendio)₂]ClO₄ induce gross distortions in fungal cell morphology and there is evidence for disruption of cell division. Both drugs also exhibit high anti-cancer activity when tested against cultured mammalian cells.     

Impact of Silver(I) on the Metabolism of Shewanella oneidensis

Anaerobic cultures of Shewanella oneidensis MR-1 reduced toxic Ag(I), forming nanoparticles of elemental Ag(0), as confirmed by X-ray diffraction analyses. The addition of 1 to 50 μM Ag(I) had a limited impact on growth, while 100 μM Ag(I) reduced both the doubling time and cell yields. At this higher Ag(I) concentration transmission electron microscopy showed the accumulation of elemental silver particles within the cell, while at lower concentrations the metal was exclusively reduced and precipitated outside the cell wall. Whole organism metabolite fingerprinting, using the method of Fourier transform infrared spectroscopy analysis of cells grown in a range of silver concentrations, confirmed that there were significant physiological changes at 100 μM silver. Principal component-discriminant function analysis scores and loading plots highlighted changes in certain functional groups, notably, lipids, amides I and II, and nucleic acids, as being discriminatory. Molecular analyses confirmed a dramatic drop in cellular yields of both the phospholipid fatty acids and their precursor molecules at high concentrations of silver, suggesting that the structural integrity of the cellular membrane was compromised at high silver concentrations, which was a result of intracellular accumulation of the toxic metal.Silver is an element that has been used widely in industrial processes as diverse as photographic processing, catalysis, mirror production, electroplating, alkaline battery production, and jewelry making (18). It has been known for some time that silver ions and silver-based compounds can be highly toxic to microorganisms, and with increasing concern about pathogenic “superbugs” with high resistance to conventional antibiotics, silver is attracting much interest as a potential biocide (11, 18, 36, 42). Silver has no known physiological functions and can exist in several oxidation states, although it is most commonly encountered in its elemental [Ag(0)] and monovalent [Ag(I)] forms. Although use of nanoscale elemental Ag(0) as a biocide has been increasing, for example, in wound dressings and as an antimicrobial coating on consumer products, little is known about its mode of toxicity. This is despite the surprising ability of actively growing Fe(III)-reducing bacteria such as Geobacter sulfurreducens to precipitate nanoscale Ag(0) particles within and around the cell surface via reduction of Ag(I) (18). Ionic Ag(I), in contrast, has been the focus of more studies on the mode of metal toxicity. Previous research showed that silver ions have antimicrobial activities against a wide diversity of bacteria (19). They have been shown to disrupt the respiratory chain of Escherichia coli (3) and inhibit the exchange of phosphate and its uptake (34). Ag(I) has also been linked to copper metabolism in E. coli, potentially competing with copper binding sites on the cell surface and subsequent copper transport into the cell (8). However, the toxicity of silver is not limited to prokaryotes, as long-term exposure in humans can cause argyria, impaired night vision, and abdominal pain (31, 32, 36). The detailed mechanism of toxicity in prokaryotes or eukaryotes remains to be identified, although it has been proposed that silver ions react with cellular proteins via SH groups (16), leading to the disruption of cellular metabolism.Microbial cells have evolved an extremely diverse range of mechanisms to survive high concentrations of toxic metals. The mechanisms invoked include biosorption, bioaccumulation, special efflux systems, alteration of solubility and toxicity via reduction or oxidation, extracellular complexation or precipitation of metals, and lack of specific metal transport systems (1). For example, for silver ions the bacterial cell wall can be an efficient permeability barrier to block the uptake of metal (21), with additional complexation in the periplasm by specific silver-binding proteins (35). Redox transformations also offer the potential to detoxify Ag(I) ions, e.g., through the reduction to insoluble elemental Ag(0) (30). In addition, the energy-dependent efflux of toxic Ag(I) is perhaps the best-studied resistance mechanism for silver, mediated via ATPases and chemiosmotic cation/protons antiporters (9).Shewanella spp., Gram-negative, dissimilatory metal-reducing bacteria, can use a wide variety of terminal electron acceptors for growth (23, 39), including high oxidation state metals such as Fe(III), Mn(IV), Cr(VI), U(VI), and Au(III) (5, 17, 26, 28, 41). Shewanella species also have the potential to reduce Ag(I), given their similar activities against Au(III), and the reduction of Ag(I) to form nanoscale deposits of Ag(0) within the cell has been documented for other Fe(III)-reducing bacteria (18). This metabolic versatility offers considerable potential for bioremediation applications, for example, via reduction of U(VI) to insoluble U(IV) (5, 17, 26, 28, 41), and the recovery of precious metals such as silver and gold via reductive precipitation. It also offers an interesting model organism to study the metabolism of toxic metals such as silver, including the physiological impact of ionic Ag(I) and nanoscale Ag(0).This paper describes interactions of Shewanella oneidensis MR-1 with various concentrations of Ag(I), including demonstrations of the reduction and deposition of silver nanoparticles under anaerobic conditions. A range of techniques, including X-ray diffraction (XRD) and analytical transmission electron microscopy (TEM), were used to investigate the nature and cellular localization of the precipitates, while Fourier transform infrared (FT-IR) spectroscopy metabolic profiling techniques were used to identify the impact of toxic metal accumulation on the cell. The disruption of membrane integrity was implied by these investigations and confirmed by fatty acid methyl ester (FAME) analysis, which showed a dramatic decrease in the quantities of membrane lipid components.     

Probing structural changes in the α and β domains of copper- and silver-substituted metallothionein by emission spectroscopy and electrospray ionization mass spectrometry

Steady-state emission spectra, excited-state lifetimes, kinetic data, and mass spectroscopic properties are reported for Ag(I)- and mixed Ag(I)/Cu(I)-substituted α and β domains of recombinant human metallothionein (MT1a). Kinetic analysis of the changes in the Cu(I) emission spectra during the stepwise displacement of Cu(I) ions by Ag(I) at room temperature shows that the rate of displacement of Cu(I) is unexpectedly slow. Although the first Ag(I) added results in major changes in the Cu(I)-MT binding site, Cu(I) displacement by Ag(I) does not take place until the addition of the third Ag(I), and is completed by the addition of the seventh Ag(I). The emission from Ag(I) and mixed Cu(I)/Ag(I)-MT species at 77 K shows that the band maxima shift as a function of Ag(I) loading, which can be correlated with shifts in coordination geometry from trigonal to digonal. Two phosphorescence lifetimes were detected for the Ag(I)-substituted α and β domains of MT, which are attributed to the presence of Ag(I) ions in two different environments. The lifetime of Ag(I)-substituted MT was found to be shorter when the Ag(I)-MT species were formed by Ag(I) additions to the Cu(I)-substituted α and β fragments than when the Ag(I)-MT species were formed from the apo-α and apo-β fragments, suggesting the formation of structurally different Ag(I)-MT clusters. Electrospray ionization mass spectrometric studies suggest the metallation reactions of Ag(I) with MT take place in a series of steps to form a series of Ag(I)-substituted MT species. Ag(I)-substituted MT species are not detected until past the addition of 3 mol equiv of Ag(I), suggesting that cluster formation begins only at this point, stabilizing the metallated species sufficiently to survive ionization.     

Ethylene evolution by rust-infected,detached bean (Phaseolus vulgaris L.) leaves susceptible and hypersensitive to Uromyces phaseoli (Pers.) Wint.

Ethylene production in leaves of susceptible and hypersensitive varieties of beans has been followed after inoculation with Uromyces phaseoli. Four different states of ethylene evolution are distinguishable: (1) 13 h after inoculation and concomitant to the penetration of the fungal mycelium through the stomata, all varieties show an outburst of ethylene with significant differences between the three varieties. (2) After 36 h postinoculation, in all three varieties ethylene evolution is scarcely higher than in noninfected leaves. (3) Starting 59 h after inoculation, only in the hypersensitive variety 765 (which shows the lowest ethylene production after 13 h), a second, very strong ethylene outburst is observed. (4) From 125 h after inoculation, significant ethylene production is not observed in any variety. At this time, characteristic symptoms are expressed in susceptible leaves (differentiation of uredosori) and in the hypersensitive variety 765 (large brown necrotic spots); no macroscopic symptoms are observed in the hypersensitive variety 814, which exhibits the strongest ethylene outburst 13 h after inoculation. The capacity for ethylene formation after mechanical wounding (point freezing) is almost identical in healthy leaves of all three varieties. This capacity is still preserved after the first ethylene outburst 36 h after infection.This work was supported by the Deutsche Forschungsgemeinschaft, by the Kleinwanzlebener Saatzucht AG (Einbeck, FRG) and by a NATO fellowship to P.M.     

Synthesis, structure, and catalytic activity of chiral silver(I) and copper(II) complexes with biaryl-based nitrogen-containing ligands

A series of chiral Ag(I) and Cu(II) complexes have been prepared from the reaction between AgX (X = NO₃, PF₆, OTf) or CuX₂ (X = Cl, ClO₄) and chiral biaryl-based N-ligands. The rigidity of the ligand plays an important role in the Ag(I) complex formation. For example, treatment of chiral N₃-ligands 1-3 with half equiv of AgX (X = NO₃, PF₆, OTf) gives the chiral bis-ligated four-coordinated Ag(I) complexes, while ligand 4 affords the two-coordinated Ag(I) complexes. Reaction of AgX with 1 equiv of chiral N₄-ligands 5, 7, 8 and 10 gives the chiral, binuclear double helicate Ag(I) complexes, while chiral mono-nuclear single helicate Ag(I) complexes are obtained with N₄-ligands 6 and 9. Treatment of either N₃-ligand 1 or N₄-ligand 9 or 10 with 1 equiv of CuX₂ (X = Cl, ClO₄) gives the mono-ligated Cu(II) complexes. All the complexes have been characterized by various spectroscopic techniques, and elemental analyses. Seventeen of them have further been confirmed by X-ray diffraction analyses. The Cu(II) complexes do not show catalytic activity for allylation reaction, in contrast to Ag(I) complexes, but they do exhibit catalytic activity for Henry reaction (nitroaldol reaction) that Ag(I) complexes do not.     

Prevention of salt-induced epinasty by α-aminooxyacetic acid and cobalt

Ethylene production in leaf petiole and laminae tissues was stimulated in tomato (Lycopersicon esculentum Mill. cv. UCT5) plants exposed to salinity-stress. At the highest salinity level (250 mM NaCl), rates of ethylene production more than doubled over those observed in non-stressed plants. Correspondingly, petiolar epinasty increased with increasing levels of stress impositions. Both responses were suppressed when either 1 mM -aminooxyacetic acid (AOA), or 100 M Co²⁺ was simultaneously applied. Co²⁺, but not AOA, had a pronounced effect on ethylene production resulting from the application of a saturating dose (2 mM) of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene. This result suggests that ethylene production is dependent upon the activity of ethylene forming enzyme (EFE). The magnitude of ethylene stimulation in leaf petioles was related to the salinity level imposed and to the induction of petiole epinasty. In the absence of stress impositions, epinastic responsiveness to ethylene or its precursor, ACC, might provide a simple, indirect criteria to adjudge salt-sensitivity among plants.Research supported by AID contract II, NEB-1070-A-00-2074-00.