Showing papers on "Phosphorus published in 2003"

New Chiral Phosphorus Ligands for Enantioselective Hydrogenation

Abstract: The increasing demand to produce enantiomerically pure pharmaceuticals, agrochemicals, flavors, and other fine chemicals has advanced the field of asymmetric catalytic technologies.1,2 Among all asymmetric catalytic methods, asymmetric hydrogenation utilizing molecular hydrogen to reduce prochiral olefins, ketones, and imines, have become one of the most efficient methods for constructing chiral compounds.3 The development of homogeneous asymmetric hydrogenation was initiated by Knowles4a and Horner4b in the late 1960s, after the discovery of Wilkinson’s homogeneous hydrogenation catalyst [RhCl(PPh3)3]. By replacing triphenylphosphine of the Wilkinson’s catalystwithresolvedchiralmonophosphines,6Knowles and Horner reported the earliest examples of enantioselective hydrogenation, albeit with poor enantioselectivity. Further exploration by Knowles with an improved monophosphine CAMP provided 88% ee in hydrogenation of dehydroamino acids.7 Later, two breakthroughs were made in asymmetric hydrogenation by Kagan and Knowles, respectively. Kagan reported the first bisphosphine ligand, DIOP, for Rhcatalyzed asymmetric hydrogenation.8 The successful application of DIOP resulted in several significant directions for ligand design in asymmetric hydrogenation. Chelating bisphosphorus ligands could lead to superior enantioselectivity compared to monodentate phosphines. Additionally, P-chiral phosphorus ligands were not necessary for achieving high enantioselectivity, and ligands with backbone chirality could also provide excellent ee’s in asymmetric hydrogenation. Furthermore, C2 symmetry was an important structural feature for developing new efficient chiral ligands. Kagan’s seminal work immediately led to the rapid development of chiral bisphosphorus ligands. Knowles made his significant discovery of a C2-symmetric chelating bisphosphine ligand, DIPAMP.9 Due to its high catalytic efficiency in Rh-catalyzed asymmetric hydrogenation of dehydroamino acids, DIPAMP was quickly employed in the industrial production of L-DOPA.10 The success of practical synthesis of L-DOPA via asymmetric hydrogenation constituted a milestone work and for this work Knowles was awarded the Nobel Prize in 2001.3k This work has enlightened chemists to realize * Corresponding author. 3029 Chem. Rev. 2003, 103, 3029−3069

Role of sediment and internal loading of phosphorus in shallow lakes

Abstract: The sediment plays an important role in the overall nutrient dynamics of shallow lakes. In lakes where the external loading has been reduced, internal phosphorus loading may prevent improvements in lake water quality. At high internal loading, particularly summer concentrations rise, and phosphorus retention can be negative during most of the summer. Internal P loading originates from a pool accumulated in the sediment at high external loading, and significant amounts of phosphorus in lake sediments may be bound to redox-sensitive iron compounds or fixed in more or less labile organic forms. These forms are potentially mobile and may eventually be released to the lake water. Many factors are involved in the release of phosphorus. Particularly the redox sensitive mobilization from the anoxic zone a few millimetres or centimetres below the sediment surface and microbial processes are considered important, but the phosphorus release mechanisms are to a certain extent lake specific. The importance of internal phosphorus loading is highly influenced by the biological structure in the pelagic, and lakes shifting from a turbid to a clearwater state as a result of, for example, biomanipulation may have improved retention considerably. However, internal loading may increase again if the turbid state returns. The recovery period following a phosphorus loading reduction depends on the loading history and the accumulation of phosphorus in the sediment, but in some lakes a negative phosphorus retention continues for decades. Phosphorus can be released from sediment depths as low as 20 cm. The internal loading can be reduced significantly by various restoration methods, such as removal of phosphorus-rich surface layers or by the addition of iron or alum to increase the sediment's sorption capacity.

Simultaneous nitrification, denitrification, and phosphorus removal in a lab-scale sequencing batch reactor.

Abstract: Simultaneous nitrification and denitrification (SND) via the nitrite pathway and anaerobic-anoxic-enhanced biological phosphorus removal (EBPR) are two processes that can significantly reduce the energy and COD demand for nitrogen and phosphorus removal. The combination of these two processes has the potential of achieving simultaneous nitrogen and phosphorus removal with a minimal requirement for COD. A lab-scale sequencing batch reactor (SBR) was operated in alternating anaerobic-aerobic mode with a low dissolved oxygen (DO) concentration (0.5 mg/L) during the aerobic period, and was demonstrated to accomplish nitrification, denitrification, and phosphorus removal. Under anaerobic conditions, COD was taken up and converted to polyhydroxyalkanoates (PHAs), accompanied by phosphorus release. In the subsequent aerobic stage, PHA was oxidized and phosphorus was taken up to <0.5 mg/L by the end of the cycle. Ammonia was also oxidized during the aerobic period, but without accumulation of nitrite or nitrate in the system, indicating the occurrence of simultaneous nitrification and denitrification. However, off-gas analysis showed that the final denitrification product was mainly nitrous oxide (N(2)O), not N(2). Further experimental results demonstrated that nitrogen removal was via nitrite, not nitrate. These experiments also showed that denitrifying glycogen-accumulating organisms (DGAOs), rather than denitrifying polyphosphate-accumulating organisms (DPAOs), were responsible for the denitrification activity.

Phosphorus Limitation of Coastal Ecosystem Processes

Abstract: Primary production in coastal wetlands is conventionally thought to be limited by nitrogen. Although the plant community in a pristine salt marsh was found to be limited primarily by nitrogen availability, the bacterial community in the soil was limited by phosphorus. Hence, in coastal wetlands, and possibly in many ecosystems, individual trophic groups may respond differently to nitrogen and phosphorus loading. Phosphorus limitation of the growth of nitrogen-transforming bacteria will affect carbon fixation, storage, and release mediated by plants, a result that has important implications for ecosystem management.

The Global Phosphorus Cycle

Abstract: Phosphorus is an essential nutrient for all life-forms It is a key player in fundamental biochemical reactions involving genetic material (DNA and RNA) and energy transfer (ATP) and in structural support of organisms provided by membranes (phospholipids) and bone (the biomineral hydroxyapatite) Photosynthetic organisms utilize dissolved phosphorus, carbon, and other essential nutrients to build their tissues using energy from the sun Biological productivity is contingent upon the availability of phosphorus to these simple organisms that constitute the base of the food web in both terrestrial and aquatic systems It begins with a brief overview of the various components of the global phosphorus cycle Estimates of the mass of important phosphorus reservoirs, transport rates (fluxes) between reservoirs Following the overview, various aspects of the global phosphorus cycle are examined in more depth, including a discussion of the most pressing research questions currently being posed and research efforts presently underway to address these questions

Speciation of phosphorus in phosphorus-enriched agricultural soils using X-ray absorption near-edge structure spectroscopy and chemical fractionation.

Abstract: Knowledge of phosphorus (P) species in P-rich soils is useful for assessing P mobility and potential transfer to ground water and surface waters. Soil P was studied using synchrotron X-ray absorption near-edge structure (XANES) spectroscopy (a nondestructive chemical-speciation technique) and sequential chemical fractionation. The objective was to determine the chemical speciation of P in long-term-fertilized, P-rich soils differing in pH, clay, and organic matter contents. Samples of three slightly acidic (pH 5.5-6.2) and two slightly alkaline (pH 7.4-7.6) soils were collected from A or B horizons in two distinct agrosystems in the province of Quebec, Canada. The soils contained between 800 and 2100 mg total P kg(-1). Distinct XANES features for Ca-phosphate mineral standards and for standards of adsorbed phosphate made it possible to differentiate these forms of P in the soil samples. The XANES results indicated that phosphate adsorbed on Fe- or Al-oxide minerals was present in all soils, with a higher proportion in acidic than in slightly alkaline samples. Calcium phosphate also occurred in all soils, regardless of pH. In agreement with chemical fractionation results, XANES data showed that Ca-phosphates were the dominant P forms in one acidic (pH 5.5) and in the two slightly alkaline (pH 7.4-7.6) soil samples. X-ray absorption near-edge structure spectroscopy directly identified certain forms of soil P, while chemical fractionation provided indirect supporting data and gave insights on additional forms of P such as organic pools that were not accounted for by the XANES analyses.

Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory : evaluation of alkaline persulfate digestion as an alternative to Kjeldahl digestion for determination of total and dissolved nitrogen and phosphorus in water

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Why the phosphorus retention of lakes does not necessarily depend on the oxygen supply to their sediment surface

Abstract: In order to improve the trophic state of Lake Sempach, a eutrophied lake in central Switzerland, its external phosphorus (P) load has been decreased and its hypolimnion has been artificially oxygenated to lower the lake-internal P recycling. Based on more than 15 yr of experience, we conclude that the reduction of the external P load resulted in a corresponding decrease of the lake's P concentration. However, contrary to initial expectations, increased hypolimnetic dissolved oxygen concentrations neither (1) reduced the P release from sediments during summer nor (2) resulted in an increased permanent P retention. These observations warrant a reevaluation of the well-accepted management strategy of decreasing the lake internal P cycling by maintaining an aerobic hypolimnion and sediment surface. We hypothesize that oxygenation only results in an increased permanent benthic P burial if, because of the depressed sulfide production, more ferrous phosphate (e.g., vivianite) and less FeS is deposited in the anoxic sediment. Hence, it is not the oxic sediment surface that directly affects the permanent redox-dependent sediment P retention but the molar ratio of the available reactive Fe(II): S 2- : PO 4 in the anoxic sediment. This ratio is driven by the settling rate and the nature of organic matter and particulate iron, as well as the supply of oxygen, nitrate, and sulfate to the sediment.

Chickpea and white lupin rhizosphere carboxylates vary with soil properties and enhance phosphorus uptake

Abstract: Chickpea and white lupin roots are able to exude large amounts of carboxylates, but the resulting concentrations in the rhizosphere vary widely. We grew chickpea in pots in eleven different Western Australian soils, all with low phosphorus concentrations. While final plant mass varied more than two-fold and phosphorus content almost five-fold, there were only minor changes in root morphological traits that potentially enhance phosphorus uptake (e.g., the proportion of plant mass allocated to roots, or the length of roots per unit root mass). In contrast, the concentration of carboxylates (mainly malonate, citrate and malate, extracted using a 0.2 mM CaCl2 solution) varied ten-fold (averaging 2.3 µmol g −1 dry rhizosphere soil, approximately equivalent to a soil solution concentration of 23 mM). Plant phosphorus uptake was positively correlated with the concentration of carboxylates in the rhizosphere, and it was consistently higher in soils with a smaller capacity to sorb phosphorus. Phosphorus content was not correlated with bicarbonate-extractable phosphorus or any other single soil trait. These results suggest that exuded carboxylates increased the availability of phosphorus to the plant, however, the factors that affected root exudation rates are not known. When grown in the same six soils, three commonly used Western Australian chickpea cultivars had very similar rhizosphere carboxylate concentrations (extracted using a 0.2 mM CaCl2 solution), suggesting that there is little genetic variation for this trait in chickpea. Variation in the concentration of carboxylates in the rhizosphere of white lupin did not parallel that of chickpea across the six soils. However, in both species the proportion of citrate decreased and that of malate increased at lower soil pH. We conclude that patterns of variation in root exudates need to be understood to optimise the use of this trait in enhancing crop phosphorus uptake.

Regulation of root elongation under phosphorus stress involves changes in ethylene responsiveness.

Abstract: We characterized the growth of the primary root of Arabidopsis under phosphorus sufficiency (1 mm phosphate) and deficiency (1 μm phosphate), focusing on the role of ethylene We quantified the spatial profile of relative elongation with a novel method based on image processing, as well as the production rates of cortical cells, trichoblasts, and atrichoblasts Phosphorus deficiency moderately decreased the maximal rate of relative elongation, shortened the growth zone, and decreased the production rate of both epidermal cell types but not of cortical cells Inhibiting ethylene production (with aminoethoxyvinyl-glycine) or action (with 1-methylcyclopropene) increased elongation in high phosphorus and decreased it in low phosphorus That these effects were specific to ethylene was confirmed by negating the effect of inhibited ethylene production with simultaneous treatment with an ethylene precursor (1-aminocyclopropane-1-carboxylic acid) Under both phosphorus regimes, ethylene regulated the maximal rate of relative elongation rather than the size of the growth zone In addition, inhibiting ethylene action in high versus low phosphorus elicited opposite responses for the position of root hair initiation and for the production rates of cortex cells and atrichoblasts We conclude that the root system acclimates to phosphorus deficiency by changing the signal transduction pathway connecting ethylene levels to growth and division

Hydrocarbon production from secondarily treated piggery wastewater by the green alga Botryococcus braunii

Abstract: A laboratory study was conducted on the removal of nitrogen and phosphorus from piggery wastewater during growth of Botryococcus braunii UTEX 572, together with measurements of hydrocarbon formation by the alga. The influence was tested of the initial nitrogen and phosphorus concentration on the optimum concentration range for a culture in secondarily treated piggery wastewater. A high cell density (> 7 g L−1 d. wt) was obtained with 510 mg L−1 NO3-N. Growth increased with nitrogen concentration at the basal phosphorus concentration (14 mg P L−1). The growth rate was nearly independent (μ = 0.027 ∼ 0.030 h−1) of the initial phosphate concentration, except under conditions of phosphate deficiency (μ = 0.019 h−1). B. braunii grew well in piggery wastewater pretreated by a membrane bioreactor (MBR) with acidogenic fermentation. A dry cell weight of 8.5 mgL−1 and hydrocarbon level of 0.95 gL−1 were obtained, and nitrate was removed at a rate of 620 mg NL−1. These results indicate that pretreated piggery wastewater provides a good culture medium for the growth and hydrocarbon production by B. braunii.

Hidden sources of phosphorus in the typical American diet: does it matter in nephrology?

Abstract: Elevated serum phosphorus is a major, preventable etiologic factor associated with the increased cardiovascular morbidity and mortality of dialysis patients. An important determinant of serum phosphorus is the dietary intake of this mineral; this makes dietary restriction of phosphorus a cornerstone for the prevention and treatment of hyperphosphatemia. The average daily dietary intake of phosphorus is about 1550 mg for males and 1000 mg for females. In general, foods high in protein are also high in phosphorus. These figures, however, are changing as phosphates are currently being added to a large number of processed foods including meats, cheeses, dressings, beverages, and bakery products. As a result, and depending on the food choices, such additives may increase the phosphorus intake by as a much as 1 g/day. Moreover, nutrient composition tables usually do not include the phosphorus from these additives, resulting in an underestimate of the dietary intake of phosphorus in our patients. Our goal is to convey an understanding of the phosphorus content of the current American diet to better equip nephrologists in their attempt to control hyperphosphatemia.

Physiological roles for aerenchyma in phosphorus-stressed roots.

Abstract: Low phosphorus availability induces the formation of cortical aerenchyma in roots. The adaptive significance of this response is unknown. We hypothesized that aerenchyma may be helpful to low-phosphorus plants by reducing root respiratory and phosphorus requirements, thereby increasing the metabolic efficiency of soil exploration. To test this hypothesis we investigated aerenchyma formation, root respiration and tissue phosphorus concentration in maize and common bean genotypes in response to phosphorus availability and ethylene treatments. Genotypes differed substantially in their ability to form aerenchyma in response to low phosphorus. Aerenchyma formation was disproportionately correlated with reduced root respiration; roots with 30% cross-sectional area as aerenchyma had 70% less respiration than roots without aerenchyma. Aerenchyma formation was also proportionally correlated with reduced root phosphorus concentration. Variation in aerenchyma formation was correlated with root respiration and phosphorus concentration, regardless of whether such variation was caused genetically or by ethylene or phosphorus treatments. Results with isolated roots were confirmed by measurement of whole root respiration of intact maize plants. Our results support the hypothesis that aerenchyma formation reduces the respiratory and phosphorus requirements of soil exploration by roots, and thus, represents a useful adaptation to low phosphorus availability.

Dissolved inorganic phosphorus, dissolved iron, and Trichodesmium in the oligotrophic South China Sea

Abstract: [1] Dissolved inorganic phosphorus (DIP) concentrations in the oligotrophic surface waters of the South China Sea decrease from ∼20 nM in March 2000 to ∼5 nM in July 2000, in response to seasonal water column stratification. These minimum DIP concentrations are one order of magnitude higher than those in the P-limited, iron-replete stratified surface waters of the western North Atlantic, suggesting that the ecosystem in the South China Sea may be limited by bioavailable nitrogen or some trace nutrient rather than DIP. Nutrient enrichment experiments using either nitrate, phosphate or both indicate that nitrogen limits the net growth of phytoplankton in the South China Sea, at least during March and July 2000. The fixed nitrogen limitation may result from the excess phosphate (N:P<16) transported into the South China Sea from the North Pacific relative to microbial population needs, or from iron control of nitrogen fixation. The iron-limited nitrogen fixation hypothesis is supported by the observation of low population densities of Trichodesmium spp. (<48 × 103 trichomes/m3), the putative N2 fixing cyanobacterium, and with low concentrations of dissolved iron (∼0.2–0.3 nM) in the South China Sea surface water. Our results suggest that nitrogen fixation can be limited by available iron even in regions with a high rate of atmospheric dust deposition such as in the South China Sea.

Effect of broadcast manure on runoff phosphorus concentrations over successive rainfall events.

Abstract: Concern over eutrophication has directed attention to manure management effects on phosphorus (P) loss in runoff. This study evaluates the effects of manure application rate and type on runoff P concentrations from two, acidic agricultural soils over successive runoff events. Soils were packed into 100- x 20- x 5-cm runoff boxes and broadcast with three manures (dairy, Bos taurus, layer poultry, Gallus gallus; swine, Sus scrofa) at six rates, from 0 to 150 kg total phosphorus (TP) ha(-1). Simulated rainfall (70 mm h(-1)) was applied until 30 min of runoff was collected 3, 10, and 24 d after manure application. Application rate was related to runoff P (r2 = 0.50-0.98), due to increased concentrations of dissolved reactive phosphorus (DRP) in runoff; as application rate increased, so did the contribution of DRP to runoff TP. Varied concentrations of water-extractable phosphorus (WEP) in manures (2-8 g WEP kg(-1)) resulted in significantly lower DRP concentrations in runoff from dairy manure treatments (0.4-2.2 mg DRP L(-1)) than from poultry (0.3-32.5 mg DRP L(-1)) and swine manure treatments (0.3-22.7 mg DRP L(-1)). Differences in runoff DRP concentrations related to manure type and application rate were diminished by repeated rainfall events, probably as a result of manure P translocation into the soil and removal of applied P by runoff. Differential erosion of broadcast manure caused significant differences in runoff TP concentrations between soils. Results highlight the important, but transient, role of soluble P in manure on runoff P, and point to the interactive effects of management and soils on runoff P losses.

Effectiveness of different precipitated phosphates as phosphorus sources for plants

Abstract: Eleven precipitated phosphates were evaluated as sources of phosphorus (P) for plant growth by comparing their effectiveness with that of monocalcium phosphate, a source of water-soluble P that is generally considered to be fully plant available. The precipitated phosphates comprised struvites recovered from waste water discharges (mainly magnesium ammonium phosphate), laboratory synthesised struvites, a synthetic iron phosphate and a recovered calcium phosphate. Precipitating phosphates in these forms could be a way for removing P from waste water before it is discharged to rivers, so reducing the risk of eutrophication. Application to agricultural land would be one potential use for such phosphates. Evaluation was by pot experiments with a sandy loam soil and with a sandy clay loam soil using perennial ryegrass as the test crop. The soils differed in pH (6.6 and 7.1) and in Olsen P (28 and 11 mg L -1 ). Measured variables were grass dry-matter (DM) yield and grass P concentration which were used to calculate offtake of P in the harvested grass. DM yields of ryegrass and P offtakes given by the synthetic and recovered struvites were not significantly different statistically either between themselves or to MCP applied at the same rate. On this basis these struvites could be used to recycle P to similar soils and the effect of the P on crop yield should be similar to that of MCP

Application of Phoslock TM , an innovative phosphorus binding clay, to two Western Australian waterways: preliminary findings

Abstract: Phoslock™ is a specially modified clay designed to permanently bind phosphorus in those situations where phosphorus (P) release from sediments is a main driver of algal bloom formation. Extensive laboratory and mesocosm trials have demonstrated the effectiveness of Phoslock™ in binding sediment released P using less than a millimetre thickness of clay. Two full-scale applications were undertaken in the summer of 2001/2002 in the impounded riverine section of two estuaries along the coastal plain of south west Western Australia. Both rivers are subject to blue-green algal blooms in the summer months. Phoslock™ applied in a slurry from a small boat reduced dissolved P in the water column to below detection limit in the few hours it took for the clay to settle and substantially reduced P efflux from the sediments during the course of the trial. The effect of P reduction on phytoplankton growth was clearly evident in the phytoplankton dominated Vasse River but was less clear in the alternating phytoplankton to aquatic plant dominated Canning River which is also subject to surface nutrient inputs.

Chiral P,N-ligands with pyridine-nitrogen and phosphorus donor atoms. Syntheses and applications in asymmetric catalysis: Tetrahedron report number 659

Abstract: This account is intended to focus on recent developments in the syntheses and metal-catalysed asymmetric reactions of not only chiral pyridine-phosphines, but also of other chiral P,N-ligands in which the pyridine framework is part of more complex heterocycles, such as quinolines, isoquinolines, phenanthridines, etc. and the phosphorus atom belongs not only to simple phosphine functionalities, but also to other groups, such as phosphites, phosphoramides, etc.

Genetic variation for adventitious rooting in response to low phosphorus availability: Potential utility for phosphorus acquisition from stratified soils

Abstract: We hypothesized that adventitious roots may improve crop adaptation to low-phosphorus soils by enhancing topsoil foraging. In a tropical field study, phosphorus stress stimulated adventitious rooting in two phosphorus-efficient genotypes of common bean (Phaseolus vulgaris L.) but not in two phosphorus-inefficient genotypes. Although phosphorus availability had no consistent effects on the length or biomass of whole root systems, it had differential effects on adventitious, basal, and taproots within root systems in a genotype-dependent manner, resulting in increased allocation to adventitious roots in efficient genotypes. Adventitious roots had greater length per unit biomass than other root types, especially under phosphorus stress. Adventitious roots had less construction cost than basal roots, despite having similar tissue nitrogen content. Phosphorus stress reduced lateral root density, and adventitious roots had less lateral root density than basal roots. Lateral roots formed further from the root tip in adventitious roots compared with basal roots, especially under phosphorus stress. Field results were confirmed in controlled environments in solid and liquid media. Stimulation of adventitious rooting by phosphorus stress tended to be greater in wild genotypes than in cultivated genotypes. We propose that adventitious rooting is a useful adaptation to low phosphorus availability, because adventitious roots explore topsoil horizons more efficiently than other root types.