Solution structural studies of the Ag(I)-DNA complex.

We report equilibrium dialysis and electric dichroism studies of the two strong complexes (I and II) of silver ion with DNA. Cooperative conversion of DNA to the stronger type I complex results in a 9% length decrease, and a structure in which intercalated ethidium is perpendicular to the helix axis. Upon addition of more Ag+ to form the type II complex, the DNA length reverts to its original value and bound ethidium once again becomes tilted from the plane perpendicular to the helix axis. In both type I and type II Ag (I) - DNA complexes, ethidium binding is mildly cooperative. We interpret the results in terms of a sequence of silver-induced cooperative switches of DNA from its B-form structure with propeller twisted base pairs to a structure with flat base pairs in the type I complex, and back again to propellered base pairs in the type II complex.     

The ionic relations of Porphyra purpurea(Roth) C.Ag. (Rhodophyta, Bangiales)

Abstract Radioisotope equilibration techniques have been used to determine the intracellular concentration of K⁺, Na⁺ and Cl_?, together with the unidirectional ion fluxes across the plasmalemma of Porphyra purpurea. Influx and efflux of ⁴²K⁺, ²⁴Na⁺ and ³⁶C1^? are biphasic, the rapid, initial uptake and loss of tracer from individual thalli being attributable to desorption from extracellular regions. Cellular fluxes are slower and monophasic, cells discriminating in favour of K⁺ and Cl^? and against Na⁺. A comparison between the equilibrium potential of individual ion species and the measured membrane potential demonstrates that there is an active component of K⁺ and Cl^? influx and Na⁺ efflux. ‘Active’ uptake and ‘passive’ loss of K⁺ and Cl^? are reduced when plants are kept in darkness, suggesting that a fraction of the transport of K⁺ and Cl^? may be due to ‘exchange diffusion’ (K⁺/K⁺ and Cl^?/Cl^?antiport).     

Acrochaetium botryocarpum (Harv.) J. Ag. (Rhodophyta) in Southern Australia

The morphology, ecology, cytology and systematics of Acrochaetium botryocarpum (Harv.) J. Ag. have been studied. This species occurs throughout the year in southern Australia and grows on a variety of hosts. The variable appearance of the prostrate system results from the effect of the substratum upon its morphology. Plants reach a height of 6 mm; cells of the erect filaments contain a single chromoplast with a variable number of pyrenoids. Tetrasporangial plants occur mainly in winter and sexual plants occur mainly in spring and early summer; the two generations are isomorphic. Stages of fertilisation have been observed and photographed. Acrochaetium polyrhizum (Harv.) J. Ag. is referred to the synonomy of A. botryocarpum, and A. codicolum Brg., A. grande (Levr.) De Toni fil. and A. rhizoideum (Drew) Sm. are regarded as probable synonyms. This study of A. botryocarpum indicates that host specificity, substrate relations, form of spermatangia and immediate post-fertilisation activity may not be as reliable as formerly thought for making taxonomic distinctions within the Acrochaetium-Rhodochorton complex.     

Preparation,structure and properties of dicyano silver complexes of the M(en)3Ag2(CN)4 and M(en)2Ag2(CN)4 type

Complexes of the M(en)₃Ag₂(CN)₄ (M = Ni, Zn, Cd) and M(en)₂Ag₂(CN)₄ (M = Ni, Cu, Zn, Cd) type were prepared and identified by elemental analysis, infrared spectroscopy, measurement of magnetic susceptibility, and X-ray powder diffractometry. The crystal structures of Ni(en)₃Ag₂(CN)₄ (I) and Zn(en)₂Ag₂(CN)₄ (II) were determined by the method of monocrystal structure analysis. Complex I crystallizes in the space group C2/c, a = 1.2639(5), b = 1.3739(4), c = 1.2494(4) nm, β = 113.25(4)°, D_m = 1.86(1), D_c = 1.86 gcm⁻³ Z = 4, R = 0.0429. The crystal structure of I consists of complex cations [Ni(en)₃]²⁺ and complex anions [Ag(CN)₂]⁻. Complex II crystallizes in the space group I2/m, a = 0.9150(3), b = 1.3308(4), c = 0.6442(2) nm, β = 95.80(3)°, D_m = 2.14(1), D_c = 2.15 gcm⁻³, Z = 2, R = 0.0334. Its crystal structure consists of infinite, positively charged chains of the [-NCAgCNZn- (en)₂]_nⁿ⁺ type and isolated [Ag(CN)₂]⁻ anions. The atoms of Ag are positioned parallely to the z axis and the AgAg distance is equal to 0.3221(2) nm.     

Interaction and coordination geometries for Ag(I) in the two metal sites of hemocyanin.

111Ag(I) perturbed angular correlations of gamma-rays (PAC) has been used to investigate the binuclear metal site of 111Ag(I)-substituted Carcinus aestuarii deoxyhemocyanin. The studies have shown that apo-hemocyanin is able to bind 2 mol of Ag(I) per mol of protein and that the binding is specific for the metal ion sites. The PAC spectra show pronounced changes when the stoichiometry of Ag(I) to protein is increased from 0.1 to 2.0. These changes have been interpreted as evidence of interactions between the two sites in terms of a structural destabilization of the first occupied site caused by the occupation of the second site. The experimental data for the Ag(I)-substituted metal sites do not agree well with the three-coordinated structure found in the Cu(I) holo-protein. However, if a water molecule is included as a coordinating ligand in the Ag(I) metal site a successful interpretation of the experimental data can be obtained.     

Photosynthetic production of hydrogen peroxide by Ulva rigida C. Ag. (Chlorophyta)

Production of hydrogen peroxide has been found in Ulva rigida (Chlorophyta). The formation of H₂O₂ was light dependent with a production of 1.2 mol·g FW^–1·h^–1 in sea water (pH 8.2) at an irradiance of 700 mol photons m^–2·s^–1. The excretion was also pH dependent: in pH 6.5 the production was not detectable (< 5 nmol·g FW^–1·h^–1) but at pH 9.0 the production was 5.0 mol·g FW^–1·h^–1. The production of H₂O₂ was totally inhibited by 3-(3,4-dichlorophenyl)-1,1 dimethylurea (DCMU). The ability of U. rigida growing in tanks (7501) under a natural light regime to excrete H₂O₂ was checked and found to be seven times higher at 08.00 hours than other times of the day. The H₂O₂ concentration in the cultivation tank (density: 2 g FW·l^–1) reached the highest value (3 M) at 11.00 hours. Photosynthesis was not influenced by H₂O₂ formation. The H₂O₂ is suggested to come from the Mehler reaction (pseudocyclic photophosphorylation). With an oxygen evolution of 120 mmol·g FW^–1·h^–1 at pH 8.2 and 90 mmol·g FW^–1·h^–1 at pH 9.0, 0.5% and 2.7% of the electrons were used for extracellular H₂O₂ production. The H₂O₂ production is sufficiently high to be of physiological and ecological significance, and is suggested to be a part of the defence against epi and endophytes.Abbreviations ACL artificial, continuous light - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - GNL greenhouse - LDC Luminol-dependent chemiluminescence - SOD Superoxide dismutase This investigation was supported by SAREC (Swedish Agency for Research Cooperation with Developing Countries), Hierta-Retzius Foundation, Marianne and Marcus Wallenberg Foundation, the Swedish Environmental Protection Board, and CICYT Spain.     

Solute Regulation in the Euryhaline Marine Alga Enteromorpha prolifera (O. F. Mull) J. Ag.

Young, A. J., Collins, J. C. and Russell, G. 1987. Solute regulationin the euryhaline marine alga Enteromorpha prolifera (O. F.Mll) J. Ag.—J. exp. Bot. 38: 1298–1308. The physiological basis for salt tolerance has been studiedin the euryhaline alga Enteromorpha prolifera. Levels of inorganicions and organic (compatible) solutes have been measured. K⁺makes the major contribution towards the internal osmotic potentialof the cell, while Cl^– and, in particular, Na⁺ contentsare low. Levels of the organic solute ß-dimethylsulphonio-propionate(DMSP) are high but are fairly insensitive to changes in theexternal salinity. Levels of amino-acids, calcium, phosphateand sulphate contribute relatively little towards the internalosmotic potential of the alga. As salinity is altered there are marked changes in the tissuewater content and volume. These changes directly affect theconcentration of the osmotic solutes within the cell. In diluteseawaters there is an increase in turgor as there is littlechange in the internal solute content of the cell compared tovalues in normal sea water. Inorganic ions, in particular K⁺,and organic solutes are accumulated in concentrated seawaters,although concentrations greater than 2·00 x seawaterresult in a reduction in the internal osmotic potential of thecell, mainly through loss of K⁺. Key words: Enteromorpha, salinity, osmoregulation     

On possible existence of pseudobinary mixed valence fluorides of Ag(I) / Ag(II): a DFT study

The DFT calculations performed within local density approximation disclose conceivable existence of two novel mixed–valence Ag(I)/Ag(II) fluorides, Ag₂F₃, i.e., Ag(I)Ag(II)F₃ and Ag₃F₄, i.e., Ag(I)₂Ag(II)F₄. Ag₂F₃ is predicted to crystallize in three equally stable NaCuF₃–, KAgF₃–, or CuTeO₃–type structures, while Ag₃F₄ should be isostructural to Na₂CuF₄. The calculated vibration-corrected energies of formation at 0 K of Ag₂F₃ and Ag₃F₄ (in their most stable polytypes) from binary fluorides are negative but small (respectively, –0.09 eV and –0.21 eV per formula unit). Formation of Ag₃F₅ (which, in fact, is a mixed valence Ag(I)/Ag(III) salt) from binary fluorides is much less likely, since the energy of formation is quite positive of about a quarter eV. The predicted volumes per formula unit for all forms of Ag₂F₃ are larger and that for K₂CuF₄–type Ag₃F₄ is smaller than the sum of volumes of the corresponding binary fluorides; Ag₂F₃ should not form at high pressure conditions due to a decomposition to the binary constituents. Ag₂F₃ and Ag₃F₄ should exhibit genuine mixed– and not intermediate–valence with quite different coordination spheres of Ag(I) and Ag(II). Nevertheless, they should not be electric insulators. Ag₂F₃ is predicted to be a metallic ferrimagnet with a magnetic superexchange coupling constant, J, of –2 meV while Ag₃F₄ should be a metallic ferromagnet with J of +52 meV. Since Ag₂F₃ and Ag₃F₄ are at the verge of thermodynamic stability, a handful of exothermic reactions have been proposed which could yield these as yet unknown compounds.     

Recovery and development of parasexual fusion products inEnteromorpha linza (L.) J. Ag. (Ulvales,Chlorophyta)

Newly released zoospores fromEnteromorpha linza (L.) J. Ag. lack significant cellulose cell wall material and are suitable for treatment as protoplasts in a parasexual fusion process using high pH-Ca^{+ +}, PEG and centrifugation. Treated zoospores settled on glass cover slips within 3 h and were examined microscopically at 1000 ×. Presumptive fusion products were identified by their larger size and presence of twin chloroplasts and eyespots. Unfused zoospores adjacent to fusion cells were killed by 2–3 min exposure to blue light (410–490 nm) from a high pressure mercury illuminator. Unexposed fusion cells developed into uniseriate germlings within 10 days at which stage they could be readily identified at 60 × with a dissecting microscope and isolated by micropipette. Ten-day germlings from both unfused zoospores and fusion cells were stained with the DNA-localizing fluorochrome hydroethidine and relative nuclear DNA content determined with epi-(incident) UV illumination. All germlings were found to be uninucleate. Germlings from unfused zoospores had haploid nuclei with 1N = 10 and 1C and 2C levels of DNA, while germlings from fusion cells had diploid nuclei with 2N = 20 and 2C and 4C levels of DNA. These result are interpreted as evidence of karyogamy following parasexual zoospore fusions. Isolated diploid germlings, cultured for 10 weeks were found to conserve their 2N chromosome complements and elevated levels of nuclear DNA. Although most diploid germlings were morphologically similar to haploid control plants, some exhibited ‘gigas’ characteristics, including larger cells, chloroplasts, and nuclei. These results are discussed in terms of unique phenotypes that result when nuclear and organellar genes are combined in different ways.     

Toxic effects of Ag(I) and Hg(II) on Candida albicans and C. maltosa: a flow cytometric evaluation

The effects of Ag(I) and Hg(II) on membrane potential and integrity of cells of Candida albicans and C. maltosa were determined with a flow cytometric procedure that employed an anionic membrane potential-sensitive dye, bis-(1,3-dibutylbarbituric acid) trimethine oxonol, and a membrane integrity indicator, propidium iodide. The membrane potentials of cells of both species were reduced rapidly within 15 min of exposure to Ag(I). No threshold dose for Hg(II) existed, and cells of both species lost membrane potential gradually in Hg(II) solutions. Cells of both species lost membrane integrity more rapidly in Ag(I) solutions than in Hg(II) solutions. In Ag(I) solutions, the decrease in the numbers of cells recoverable in culture occurred at a rate similar to the rate of cell depolarization and membrane permeabilization. In Hg(II) solutions, loss of cell recoverability preceded the loss of membrane potential and membrane integrity. C. albicans, in contrast to C. maltosa, showed no loss of membrane integrity after exposure to Hg(II) solutions for 1 h. Different rates of binding of Ag(I) and Hg(II) between the two species suggest that the two ions target different primary sites.     

Toxic Effects of Ag(I) and Hg(II) on Candida albicans and C. maltosa: a Flow Cytometric Evaluation

The effects of Ag(I) and Hg(II) on membrane potential and integrity of cells of Candida albicans and C. maltosa were determined with a flow cytometric procedure that employed an anionic membrane potential-sensitive dye, bis-(1,3-dibutylbarbituric acid) trimethine oxonol, and a membrane integrity indicator, propidium iodide. The membrane potentials of cells of both species were reduced rapidly within 15 min of exposure to Ag(I). No threshold dose for Hg(II) existed, and cells of both species lost membrane potential gradually in Hg(II) solutions. Cells of both species lost membrane integrity more rapidly in Ag(I) solutions than in Hg(II) solutions. In Ag(I) solutions, the decrease in the numbers of cells recoverable in culture occurred at a rate similar to the rate of cell depolarization and membrane permeabilization. In Hg(II) solutions, loss of cell recoverability preceded the loss of membrane potential and membrane integrity. C. albicans, in contrast to C. maltosa, showed no loss of membrane integrity after exposure to Hg(II) solutions for 1 h. Different rates of binding of Ag(I) and Hg(II) between the two species suggest that the two ions target different primary sites.     

Syntheses and structures of Ag(I) compounds containing btp ligands

Four new Ag(I) complexes with three different modes of structures were obtained by varying the counteranions , and their structures characterized by single-crystal X-ray diffraction analysis. Compounds 1, 2, and 3 crystalize in the C-centered monoclinic space group C2/m. Compound 4 crystalizes in the monoclinic space group P2₁/c. The crystal structures of these complexes show that the complexes 1, 2, and 3 form ligand-supported dinuclear rings, and the dinuclear units of 1 and 3 are further linked by anions to form one-dimensional polymer, while the complex 4 forms an one-dimensional zigzag chain. The structural differences between 1, 2, 3, and 4 show the influences of the counteranions on the structures of the complexes.     

Luminescence and photoreactivity of Ag(8-quinolinol)(8-quinolinolate)

The complex Ag(8-quinolinol)(8-quinolinolate) shows an IL fluorescence while an IL phosphorescence does not appear. The IL triplet is deactivated to a reactive LMCT state. A subsequent photoredox reaction leads to generation of elemental silver.     

The Effects of Salinity upon Galactosyl-Glycerol Content and Concentration of the Marine Red Alga Porphyra purpurea (Roth) C.Ag.

Changes in the major alcohol-soluble, low molecular weight carbohydratesof P. purpurea, O--D-galactopyranosyl-(1-2)-glycerol (‘floridoside’)and O--D-galactopyranosyl-(1-1)-glycerol (‘isofloridoside’),have been examined in response to salinity variation. ‘Floridoside’is shown to vary in absolute amount, increasing in hypersalineand decreasing in hyposaline media. ‘Isofloridoside’content per cell does not change in a similar manner. Responsesare almost identical under light or dark conditions, ‘floridoside’changes being complete within 24 h. Decreasing the externalwater potential using ionic and non-ionic solutes has the sameeffect upon galactosyl-glycerol content. The amount of ‘floridoside’synthesized, and degraded under hypersaline and hyposaline conditionsrespectively is shown to be insufficient to restore cell volumeto its original value. It is therefore suggested that the primaryfunction of ‘floridoside’ increases in concentratedsea-waters is that of a compatible solute, serving to protectthe cell during periods when the external salt content is increaseddramatically.