Carbon (13C) and nitrogen (15 N) translocation in a maize-striga hermonthica association

The translocation of C and N in a maize-Striga hermonthica association was investigated at three rates of nitrogen application in a glasshouse experiment. The objectives were to measure the transfer of C and N from maize to S. hermonthica and to determine whether the amount of N in the growing medium affected the proportions of C and N transferred. Young plants of maize were labelled in a (CO2)-C-13 atmosphere and leaf tips were immersed in ((NH4)-N-15)(2)SO4 Solution. The Striga x N interaction was not significant for any of the responses measured. Total dry matter for infected maize was significantly smaller than for uninfected maize from 43 to 99 days after planting, but N application increased total dry matter at all sampling times. Infected maize plants partitioned 39-45 % of their total dry matter to the roots compared with 28-31 % for Uninfected maize. Dry matter of S. hermonthica was not affected by the rate of N applied. S. hermonthica derived 100 % of its carbon from maize before emergence, decreasing to 22-59 % thereafter; the corresponding values for nitrogen were up to 59 % pre-emergence and Lip to 100 % after emergence. The relative proportions of nitrogen depleted from the host (up to 10 %) were greater than those of carbon (maximum 1.2 %) at all times of sampling after emergence of the parasite. The results show that the parasite was more dependent on the host for nitrogen than for carbon.

Thermodynamic analysis of ferrous ion binding to Escherichia coli ferritin EcFtnA

Iron oxidation in the bacterial ferritin EcFtnA from Escherichia coli shows marked differences from its homologue human H-chain ferritin (HuHF). While the amino acid residues that constitute the dinuclear center in these proteins are highly conserved, EcFtnA has a third iron-binding site (C site) in close proximity to the dinuclear center that is seemingly responsible for these differences. Here, we describe the first thermodynamic study of Fe2+ binding to EcFtnA and its variants to determine the location of the primary ferrous ion-binding sites on the protein and to better understand the role of the third C site in iron binding. Isothermal titration calorimetric analyses of the wild-type protein reveal the presence of two main classes of binding sites in the pH range of 6.5-7.5, ascribed to Fe2+ binding, first at the A and then the B sites. Site-directed mutagenesis of ligands in the A, B, or C sites affects the apparent Fe2+-binding stoichiometries at the unaltered sites. The data imply some degree of inter- and intrasubunit negative cooperative interaction between sites. Unlike HuHF where only the A site initially binds Fe2+, both A and B sites in EcFtnA bind Fe2+, implying a role for the C site in influencing the binding of Fe2+ at the B site of the di-iron center of EcFtnA. The ITC equations describing a binding model for three classes of independent binding sites are reported here for the first time.

De novo alanine synthesis by bacteroids of Mesorhizobium loti is not required for nitrogen transfer in the determinate nodules of Lotus corniculatus

Deletion of both alanine dehydrogenase genes (aldA) in Mesorhizobium loti resulted in the loss of AldA enzyme activity from cultured bacteria and bacteroids but had no effect on the symbiotic performance of Lotus corniculatus plants. Thus, neither indeterminate pea nodules nor determinate L. corniculatus nodules export alanine as the sole nitrogen secretion product.

A conserved basic loop in hepatitis C virus p7 protein is required for amantadine-sensitive ion channel activity in mammalian cells but is dispensable for localization to mitochondria

We previously identified the function of the hepatitis C virus (HCV) p7 protein as an ion channel in artificial lipid bilayers and demonstrated that this in vitro activity is inhibited by amantadine. Here we show that the ion channel activity of HCV p7 expressed in mammalian cells can substitute for that of influenza virus M2 in a cell-based assay. This was also the case for the p7 from the related virus, bovine viral diarrhoea virus (BVDV). Moreover, amantadine was shown to abrogate HCV p7 function in this assay at a concentration that specifically inhibits M2. Mutation of a conserved basic loop located between the two predicted trans-membrane alpha helices rendered HCV p7 non-functional as an ion channel. The intracellular localization of p7 was unaffected by this mutation and was found to overlap significantly with membranes associated with mitochondria. Demonstration of p7 ion channel activity in cellular membranes and its inhibition by amantadine affirm the protein as a target for future anti-viral chemotherapy.

Amino-acid cycling drives nitrogen fixation in the legume - Rhizobium symbiosis

The biological reduction of atmospheric N-2 to ammonium (nitrogen fixation) provides about 65% of the biosphere's available nitrogen. Most of this ammonium is contributed by legume rhizobia symbioses(1), which are initiated by the infection of legume hosts by bacteria (rhizobia), resulting in formation of root nodules. Within the nodules, rhizobia are found as bacteroids, which perform the nitrogen fixation: to do this, they obtain sources of carbon and energy from the plant, in the form of dicarboxylic acids(2,3). It has been thought that, in return, bacteroids simply provide the plant with ammonium. But here we show that a more complex amino-acid cycle is essential for symbiotic nitrogen fixation by Rhizobium in pea nodules. The plant provides amino acids to the bacteroids, enabling them to shut down their ammonium assimilation. In return, bacteroids act like plant organelles to cycle amino acids back to the plant for asparagine synthesis. The mutual dependence of this exchange prevents the symbiosis being dominated by the plant, and provides a selective pressure for the evolution of mutualism.

Immobilisation of eta(3)-allyidicarbonyl complexes of Mo-II with bidentate nitrogen ligands within aluminium-pillared clays

Molybdenum(II) complexes [MOX(CO)(2)(eta(3)-allyl)(CH3CN)(2)] (X = Cl or Br) were encapsulated in an aluminium-pillared natural clay or a porous clay heterostructure and allowed to react with bidentate diimine ligands. All the materials obtained were characterised by several solid-state techniques. Powder XRD, and Al-27 and Si-29 MAS NMR were used to investigate the integrity of the pillared clay during the modification treatments. C-13 CP MAS NMR, FTIR, elemental analyses and low-temperature nitrogen adsorption showed that the immobilisation of the precursor complexes was successful as well as the in situ ligand-substitution reaction. The new complex [MoBr(CO)(2)(eta(3)-allyl)(2-aminodipyridyl)] was characterised by single-crystal X-ray diffraction and spectroscopic techniques, and NMR studies were used to investigate its fluxional behaviour in solution. The prepared materials are active for the oxidation of cis-cyclooctene using tert-butyl hydroperoxide as oxidant, though the activity of the isolated complexes is higher. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

Complete filling of zeolite frameworks with polyalkynes formed in situ by transition-metal ion catalysts

We report the use of transition-metal-exchanged zeolites as media for the catalytic formation and encapsulation of both polyethyne and polypropyne, and computer modeling studies on the composites so formed. Alkyne gas was absorbed into the pores of zeolite Y (Faujasite) exchanged with transition-metal cations [Fe(II), Co(II), Cu(II), Ni(II), and Zn(II)]. Ni(II) and Zn(II) were found to be the most efficient for the production of poly-ynes. These cations were also found to be effective in polymer generation when exchanged in zeolites mordenite and beta. The resulting powdered samples were characterized by FTIR, Raman, diffuse reflectance electronic spectroscopy, TEM, and elemental analysis, revealing, nearly complete loading of the zeolite channels for the majority of the samples. Based on the experimental carbon content, we have derived the percentage of channel filling, and the proportion of the channels containing a single polymer chain for mordenite. Experimentally, the channels for Y are close to complete filling for polyethyne (PE) and polypropyne (PP), and this is also true for polyethyne in mordenite. Computer modeling studies using Cerius2 show that the channels of mordenite can only accept a single polymer chain of PP, in which case these channels are also completely filled.

Reactions of silylene with unreactive molecules. 2. nitrogen: gas-phase kinetic and theoretical studies

Time-resolved studies of the reaction of silylene, SiH2, with N-2 have been attempted at 296, 417, and 484 K, using laser flash photolysis to generate and monitor SiH2. No conclusive evidence for reaction could be found even with pressures of N-2 of 500 Torr. This enables us to set upper limits of ca. 3 x 10(-15) cm(3) molecule(-1) s(-1) for the second-order rate constants. A lower limit for the activation energy, E-a, of ca. 47 kJ mol(-1) is also derived. Ab initio calculations at the G3 level indicate that the only SiH2N2 species of lower energy than the separated reactants is the H2Si...N-2 donor-acceptor (ylid) species with a relative enthalpy of -26 kJ mol(-1), insufficient for observation of reaction under the experimental conditions. Ten bound species on the SiH2N2 surface were found and their energies calculated as well as those of the potential dissociation products: HSiN + NH((3)Sigma(-)) and HNSi + NH((3)Sigma(-)). Additionally two of the transition states involving cyclic-SiH2N2 (siladiazirine) were explored. It appears that siladiazirine is neither thermodynamically nor kinetically stable. The findings indicate that Si-N-d bonds (where N-d is double-bonded nitrogen) are not particularly strong. An unexpected cyclic intermediate was found in the isomerization of silaisocyanamide to silacyanamide.

Separation of Ba-137m from Cs-137 using new ion exchanger Na-2(H2O)(4)(H3O)[Al(OH)(6)Mo6O18]

A new polyoxometalate of chemical formula, Na-2(H2O)(4)(H3O)[Al(OH)(6)Mo6O18] (1) containing Anderson type large anion has been synthesized and characterized by single-crystal X-ray structure determination and IR spectroscopic studies. The crystal of 1 is triclinic, spacegroup P-1 with cell dimensions, a = 6.365(9) angstrom, b = 10.37(1) angstrom, c = 10.44(1) angstrom and alpha = 65.41(1), beta = 77.18(1), gamma = 86.58(1) and Z = 1. The compound 1 behaves as an ion exchanger and is stable in thermal, radiation and chemical environments. Radiochemical separation of the short-lived daughter Ba-137m (t(1/2) = 2.50 min) from its long-lived parent Cs-137 using this newly designed and synthesized ion exchanger has been developed.

Influence of a halide ion on ribbons of water pentamer

Reactions of CuF2, CuCl2 center dot 2H(2)O and CuBr2 with 2,2'-dipyridylamine (HDPA) in water at room temperature using Cu: HDPA = 2: 1 mol yield [Cu(HDPA) (H2O)(2)F]F center dot 3H(2)O (1), Cu(HDPA) Cl-2 (2) and [Cu(HDPA) Br-2 (3) respectively. The structures of 2 and 3 are isostructural in spacegroup C-2 with cell dimensions; for 2, a = 14.702(8), b = 7.726(2), c = 4.829(6) angstrom, beta = 96.68(8)degrees and for 3, a = 14.2934(8), b = 7.9057(6), c = 5.1982(5) angstrom, beta = 94.049(7)degrees. In the X-ray crystal structure, the complex 1 is found to contain tapes of water pentamers. Our DFT calculations at the B3LYP/LanL2DZ level show that the reaction Cu(HDPA)X-2 + 2H(2)O = [Cu(HDPA)(H2O)(2)X]X is most exothermic in the gas phase when X- = F-, i.e., the tendency of water uptake is maximum for Cu(HDPA) F-2. It seems that the exothermicities of the aquations of Cu(HDPA) Cl-2 and Cu(HDPA) Br-2 are not sufficient to stabilise the type of ribbons of water observed in 1 and consequently water is eschewed when X- = Cl- or Br-.

An unprecedented mononuclear double helicate with a square planar metal ion

Reactions of the 1:2 condensate (L) of benzil dihydrazone and 1-methyl-2-imidazole carboxaldehyde with Cd(ClO4)(2)center dot xH(2)O and CdI2 yield [CdL2]( ClO4)(2) (1) and LCdI2 (2), respectively. The yellow ligand L, and its yellow complexes 1 and 2 are characterized by NMR and single crystal X-ray diffraction. Though L contains four N-donor centers, 1 is found to be a four-coordinate double helicate with a square planar Cd(II)N-4 core and 2 a spiral coordination polymer with tetrahedral Cd(II)N2I2 moieties. The bidentate nature of L and the occurrence of the square planar coordination of Cd( II) is explained by DFT calculations. (c) 2007 Elsevier B. V. All rights reserved.

Structural studies of lanthanide complexes with tetradentate nitrogen ligands

Complexes have been synthesised with bis(2-pyridine carboxaldehyde) ethylenediimine (1) and bis(2-pyridine carboxaldehyde)propylene-1,3-diimine (2) with all of the available lanthanide trinitrates. Crystal structures were obtained for all but one complex with 1 and for all but one complex with 2. Four distinct structural types were established for 1 but only two for 2, although in all cases the structures contained one ligand bound to the metal in a tetradentate fashion. With 1, the four different structures of the lanthanide(III) nitrate complexes included 11-coordinate [Ln(1)(NO3)(3)(H2O)] for Ln = La; 10 coordinate [Ln(1)(NO3)(3)(H2O)] with one monodentate and two bidentate nitrates for Ln = Ce, then 10-coordinate [Ln(1)(NO3)(3)] for Ln = Pr-Yb with three bidentate nitrates; and 9-coordinate [Ln(1)(NO3)(3)] with one monodentate and two bidentate nitrates for Ln = Lu. On the other hand for 2 only two distinct types of structure are obtained, the first type with Ln = La-Pr and the second type for Ln = Sm-Lu, although all are 10-coordinate with stoichiometry [Ln(2)(NO3)(3)]. The difference between the two types is in the disposition of the ligand relative to the nitrates. With the larger lanthanides La-Pr the ligand is found on one side of the coordination sphere with the three nitrate anions on the other. In these structures, the ligand is folded such that the angle between the two pyridine rings approaches 90degrees, while with the smaller lanthanides Sm-Lu, two nitrates are found on one side of the ligand and one nitrate on the other and the ligand is in an extended conformation such that the two pyridine rings are close to being coplanar. In both series of structures, the Ln-N and Ln-O bond lengths were consistent with the lanthanide contraction though there are significant variations between ostensibly equivalent bonds which are indicative of intramolecular hydrogen bonding and steric crowding in the complexes. (C) 2004 Elsevier B.V. All rights reserved.

QSAR studies of multidentate nitrogen ligands used in lanthanide and actinide extraction processes

Quantitative structure activity relationships (QSARs) have been developed to optimise the choice of nitrogen heterocyclic molecules that can be used to separate the minor actinides such as americium(III) from europium(III) in the aqueous PUREX raffinate of nuclear waste. Experimental data on distribution coefficients and separation factors (SFs) for 47 such ligands have been obtained and show SF values ranging from 0.61 to 100. The ligands were divided into a training set of 36 molecules to develop the QSAR and a test set of 11 molecules to validate the QSAR. Over 1500 molecular descriptors were calculated for each heterocycle and the Genetic Algorithm was used to select the most appropriate for use in multiple regression equations. Equations were developed fitting the separation factors to 6-8 molecular descriptors which gave r(2) values of >0.8 for the training set and values of >0.7 for the test set, thus showing good predictive quality. The descriptors used in the equations were primarily electronic and steric. These equations can be used to predict the separation factors of nitrogen heterocycles not yet synthesised and/or tested and hence obtain the most efficient ligands for lanthanide and actinide separation. (C) 2003 Elsevier B.V. All rights reserved.

An overview and historical look back at the solvent extraction using nitrogen donor ligands to extract and separate An(III) from Ln(III)

The partitioning of minor trivalent actinides (An) from lanthanides (Ln) is one of the challenges in the chemical treatment of nuclear waste. The optimal ligand to carry out the separation of An(III) and Ln(III) using solvent extraction has to meet several important criteria: high selectivity towards the solute, chemical and radiolytic stability, stripping possibilities and recycling of the organic phase, high separation factors and good distribution ratio, to name just a few of them. A chronological line can be drawn along the development of each extraction ligand family and some milestones are emphasized in this overview. Further developments in organic synthesis of extracting ligands are expected.

Nitrogen management is essential to prevent tropical oil palm plantations from causing ground-level ozone pollution

More than half the world's rainforest has been lost to agriculture since the Industrial Revolution. Among the most widespread tropical crops is oil palm (Elaeis guineensis): global production now exceeds 35 million tonnes per year. In Malaysia, for example, 13% of land area is now oil palm plantation, compared with 1% in 1974. There are enormous pressures to increase palm oil production for food, domestic products, and, especially, biofuels. Greater use of palm oil for biofuel production is predicated on the assumption that palm oil is an "environmentally friendly'' fuel feedstock. Here we show, using measurements and models, that oil palm plantations in Malaysia directly emit more oxides of nitrogen and volatile organic compounds than rainforest. These compounds lead to the production of ground-level ozone (O-3), an air pollutant that damages human health, plants, and materials, reduces crop productivity, and has effects on the Earth's climate. Our measurements show that, at present, O-3 concentrations do not differ significantly over rainforest and adjacent oil palm plantation landscapes. However, our model calculations predict that if concentrations of oxides of nitrogen in Borneo are allowed to reach those currently seen over rural North America and Europe, ground-level O-3 concentrations will reach 100 parts per billion (10(9)) volume (ppbv) and exceed levels known to be harmful to human health. Our study provides an early warning of the urgent need to develop policies that manage nitrogen emissions if the detrimental effects of palm oil production on air quality and climate are to be avoided.