Different Concentrations Of Phosphate Research Articles

Effect of electrolyte composition on the surface characteristics of plasma electrolytic oxidation coatings over Ti[sbnd]40Nb alloy

The present work aims to develop corrosion-resistant and cytocompatible coatings on Ti40Nb alloy by the plasma electrolytic oxidation (PEO) process. Usually, PEO coatings on niobium substrate with superior surface characteristics are obtained using a silicate-based electrolyte system, and a phosphate-based electrolyte system is used for titanium substrate. Till date, electrolyte system composition is not optimised for the PEO coatings on Ti40Nb alloys. To study the influence of electrolyte composition on PEO coating properties over Ti40Nb alloy, three different concentrations of phosphate and silicate (75:25, 50:50, and 25:75) and a fixed amount of KOH were used, and their surface characteristics and corrosion properties were evaluated in this study. We found that coatings formed with an equal proportion of phosphate and silicate in an electrolyte system are dense, compact, thick and corrosion-resistant. A coating aimed for high bioactivity is also developed by adding hydroxyapatite (HA) nanoparticles to an equal proportion (50:50) electrolyte system. After the successful development of the PEO coatings over Ti40Nb alloy, its phase composition, surface morphological features, wettability, scratch resistance, and corrosion properties are examined. The cell viability and live/dead cell morphology of L-929 fibroblast cells were evaluated for untreated Ti40Nb alloy, PEO-treated Ti40Nb alloy, and Ti40Nb alloy PEO-treated with hydroxyapatite nanoparticles. All surface-modified samples exhibited better corrosion resistance than the untreated alloy. Ti40Nb alloy PEO treated with phosphate: silicate electrolyte system (50:50) exhibited better scratch resistance, higher wettability, bioactivity, favourable chemical composition, and surface morphological features than the other ratios of phosphate and silicate (25:75 and 75:25). Meanwhile, Ti40Nb alloy PEO treated with hydroxyapatite nanoparticles addition showed better cytocompatibility than without HA addition.

Dual-electrolyte fabrication of micro arc oxidation coatings on Ta–12W alloy with enhanced wear resistance

Electrolyte systems are crucial for the micro-arc oxidation (MAO) process. In this paper, we have prepared MAO coatings on Ta–12W alloy in alkali electrolytes with different concentrations of phosphate and aluminate. The effect of the electrolyte on the composition, morphology, and microstructure of the coating is investigated in detail. It is found that the growth of the coating in phosphate is dominated by the oxidation of the substrate, with numerous crater-like pores on the surface. However, aluminate can greatly promote the growth rate of the coating through the deposition effect of aluminum compounds, along with the pancake-like structure and protrusions on the surface. The characterization of the phase structure demonstrates that in the phosphate system, the outer layer of the coating is well crystallized and contains large-sized Ta2O5 crystals, while the aluminate favors the formation of coatings with an inner nanocrystalline layer and an outer amorphous layer. The growth process of MAO coatings in different electrolytes is also discussed. Moreover, the wear resistance of the coating is evaluated and the corresponding wear behavior is studied. The results suggest that the coatings prepared in the dual-electrolyte exhibit superior wear resistance, with the wear rate much lower than that of the substrate.

A Study on the Effect of Nitrate and Phosphate Concentrations on the Production of Mycosporine-Like Amino Acids by Chlorella Vulgaris.

Cyanobacteria can produce compounds absorbing ultraviolet irradiation. Mycosporine like amino acids (MAAs) are some of these important metabolites, which can be potentially considered as a sunscreen agent in the pharmaceutical and cosmetic industry. Different factors have been reported that can affect the biosynthesis of MAA. In this study, the influence of different concentrations of phosphate and nitrate under different environmental conditions on MAA production by Chlorella vulgaris was investigated using an experimental design method, in order to enhance MAAs production in this specious. A 23 full factorial design (FFD) using Design-Expert v7.0.0 software was used to optimize simultaneously all the three factors of nitrate and phosphate concentration and condition of incubation environment on the MAA production by this species of C. vulgaris. Two milliliter of organism stock were grown in 200 mL BG11 medium and after 21 days, the biomasses of all samples were separated. Then, the MAA was extracted from dried biomass using methanol extraction. The extracts were analyzed by reverse-phase high performance liquid chromatography (RP-HPLC). After complete analysis, four samples were then cultured at the optimized conditions and analyzed by liquid chromatohraphy coupled to mass spectrometry (LC/MS). The results showed that this microalga could produce compounds with λmax of 330 nm and a retention time of about 2 min. According to the central composite analysis, phosphate at 0.51 g.L-1 and nitrate at 2.5 g.L-1 can be considered as the optimum concentrations, resulting to the preferable conditions concerning the culture in germinator. Based on LC/MSS analysis, the major compound had a m/z of 332 at the optimum condition. Thus, this species is expected to have the capability of MAA production (maybe Shinorine) or one of its glycosylated derivatives.

Phosphate and methionine affect cadmium uptake in valerian (Valeriana officinalis L.)

This study investigated the effects of exogenous methionine (Met) and different phosphate (PO4) concentrations on Cd uptake and translocation in Valeriana officinalis L. Seedlings were grown in nutrient solutions with three different concentrations of phosphate (900, 1200, and 1500 μM) for two weeks, then exposed for 4 days to 10 μM Cd, either in presence or absence of 400 μM methionine. The Met treatment decreased root Cd accumulation by up to 40%, while it enhanced Cd uptake into the shoots by 50%. In absence of Met, shoot Cd uptake was not affected by the level of phosphate application, although root Cd contents increased. The latter effect was entirely due to increased apoplastic Cd binding. In presence of Met, the Cd accumulation of both plant parts showed trends to increase with increasing phosphate level. In contrast to the treatments without Met, however, the phosphate effect on root Cd was due to increased symplastic root Cd allocation. The results suggest that the effects of Met on Cd uptake were due to the formation of mobile Cd-Met complexes, reducing phosphate-promoted Cd-retention in the apoplast and enhancing Cd transfer into the root symplast. Irrespective of the treatment, shoot Cd accumulation showed a close linear relationship to shoot mass, suggesting that convective transport with the transpirational water stream was the rate-governing uptake process. The results indicate that methionine supplementation could reduce Cd accumulation in valerian roots, which are the parts of this plant harvested for medicinal purposes, in Cd-contaminated soil, while phosphate would enhance it.

Roles of defects and linker exchange in phosphate adsorption on UiO-66 type metal organic frameworks: Influence of phosphate concentration

Recently, UiO-66 type metal organic frameworks (MOFs) have been studied as adsorbents for phosphate removal from wastewater; however, the adsorption mechanism with different concentrations of phosphate, especially the roles of defects and linker exchange, are not entirely clear. In this work, the phosphate adsorption mechanism in HCl-UiO-66 and HCl-NH2-UiO-66 were examined by testing the relationship between the adsorbed phosphate and released linker in the adsorption process. Adsorption kinetics studies (3.0 mM phosphate solution) and adsorption isotherm analyses (0.3–6.0 mM phosphate solution) revealed highly linear relationships (R2 = 0.8949–0.9978) between the adsorbed phosphate and released linker for both adsorbents. Further analysis showed that when the adsorbed phosphate was lower than 0.56 mmol/g for HCl-UiO-66 and 0.51 mmol/g for HCl-NH2-UiO-66, phosphate was preferentially adsorbed on the defect sites in the MOFs with no linker release. However, when the adsorbed phosphate exceeded these levels, the defects were saturated by phosphate and linker exchange became the major adsorption mechanism. Based on density functional theory calculations, the obtained strengths of the linkers (H2BDC: Terephthalic acid; NH2-H2BDC: 2-Aminoterephthalic Acid; NO2-H2BDC: 2-Nitroterephthalic Acid) and phosphate species as Lewis bases fall in the order, PO43- > HPO42- > NH2-BDC2- > BDC2- > H2PO4- > NO2-BDC2- > H3PO4, which clearly evidences why linkers can be exchanged by phosphate. Given the propensity for ligand exchange and the resulting structural destabilization, UiO-66 type MOFs is not suggested as ideal adsorbents for phosphate removal from wastewater with high phosphate concentrations.

Fatty Acid Content and Profile of the Novel Strain of Coccomyxa elongata (Trebouxiophyceae, Chlorophyta) Cultivated at Reduced Nitrogen and Phosphorus Concentrations.

A novel freshwater strain of Coccomyxa elongata (MZ-Ch64) was isolated from the Zaporizhia region, Ukraine. The identification was based on the phylogenetic analysis of SSU rDNA gene and ITS1-5.8S rDNA-ITS2 region and predicted secondary structure of the ITS2. Phylogenetic analysis placed this strain in the Coccomyxa group, within the class Trebouxiophyceae. The novel strain MZ-Ch64 formed a strongly supported lineage closest with C.elongata. The MZ-Ch64 strain differed from the morphological description of the species by the sizeof vegetative cells and absence of small mucilaginous caps at one end of the cell. A number of experiments with different concentrations of phosphate and nitrate were conducted to evaluate changes in the resulting fatty acid profiles and biomass productivity. The fatty acid profile and total fatty acids varied significantly under different nutrient deficiencies. The dominant fatty acid during cultivation on standard BBM medium, as well as in phosphorus-depleted conditions, was oleic acid (to 48.0%-54.6% of total fatty acids). Absence of nitrogen alone, and absence of both nitrogen and phosphorus, led to an increase of palmitic acid (to 24.7%-25.6%), cis-7-hexadecenoic acid (to 14.8%) and α-linolenic acid (to 9.1%-10.1%) in comparison with the control sample. The greatest variation was found for oleic acid (31.9%-54.6%). Thus, this strain can be considered as a potential producer of oleic acid or cis-7-hexadecenoic and α-linolenic acids for biotechnological applications.

Postprandial adjustments in renal phosphate excretion do not involve a gut-derived phosphaturic factor.

What is the central question of this study? Does a previously hypothesized signalling mechanism, believed to detect postprandial increases in intestinal phosphate and that can stimulate the kidneys to rapidly excrete phosphate, operate under physiological conditions? What is the main finding and its importance? Contrary to earlier reports, rapid signalling between the small intestine and kidney mediated by a gut-derived phosphaturic factor in response to a physiological intestinal phosphate load is not supported by the present findings; moreover, hyperphosphataemia and increased parathyroid hormone concentrations are likely to be the underlying factors responsible for the phosphaturia following a supraphysiological intestinal phosphate load. To date, the role of the small intestine in the regulation of postprandial phosphate homeostasis has remained unclear and controversial. Previous studies have proposed the presence of a gut-derived phosphaturic factor that acts independently of changes in plasma phosphate concentration or parathyroid hormone (PTH) concentration; however, these early studies used duodenal luminal phosphate concentrations in the molar range, and therefore, the physiological relevance of this is uncertain. In the present study, we used both in vivo and in vitro approaches to investigate the presence of this putative 'intestinal phosphatonin'. Instillation of 1.3m phosphate into the duodenum rapidly induced phosphaturia, but in contrast to previous reports, this was associated with significant hyperphosphataemia and elevated PTH concentration; however, there was not the expected decrease in abundance of the renal sodium-phosphate cotransporter NaPi-IIa. Instillation of a physiological (10mm) phosphate load had no effect on plasma phosphate concentration, PTH concentration or phosphate excretion. Moreover, phosphate uptake by opossum kidney cells was unaffected after incubation with serosal fluid collected from intestinal segments perfused with different concentrations of phosphate. Taken together, these findings do not support the concept of a gut-derived phosphaturic factor that can mediate rapid signalling between the gut and kidney, leading to increased urinary phosphate excretion, as part of normal phosphate homeostasis.

Effects of phosphate and citric acid on Pb adsorption by red soil colloids

There are abundant organic acids in rhizospheric soil, which may interfere in the reaction between phosphate and heavy metals. Effects of phosphate on Pb2+ adsorption by red soil colloids(Ultisol) were studied in the presence of citric acid (Cit) through batch equilibrium experiments, Zeta potential and X‐ray diffraction (XRD) analyses. Results showed that in the presence of different concentrations of phosphate (P), the peak‐like curves of Pb2+ sorption was moved up even disappeared. When the Langmuir equation was used to model isothermal adsorption curve of Pb2+, the adsorption reaction constant (K), the maximum adsorption quantity (Xm) of several treatments were both in a decreasing order of 1.0 mmol/L P > 1.0 mmol/L P + 0.5 mmol/L Cit > 0.5 mmol/L Cit. Under the influence of citric acid, the Pb2+ adsorption amount increased at pH < 4.5, and then decreased gradually with pH increase. The order of Zeta potential reduction was: 1 mmol/L P + 0.5 mmol/L Cit > 0.5 mmol/L Cit > 1 mmol/L P, which were different from that of the Pb2+ adsorption amount, suggesting that the adsorption of Pb2+ was not only an electrical adsorption in the presence of P. XRD patterns proved that occurrence of pyromorphite for the treatment with 1.0 mmol/L P addition, whereas no lead phosphate peak was detected in other treatments. The mechanism of Pb2+ adsorbed in red soil colloids with addition of phosphate was primary formation of pyromorphite‐like compounds. However, 0.5 mmol/L Cit inhibited the formation of pyromorphite. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 969–974, 2016

Multitechnique Investigation of the pH Dependence of Phosphate Induced Transformations of ZnO Nanoparticles

In order to properly evaluate the ecological and human health risks of ZnO manufactured nanomaterials (MNMs) released to the environment, it is critical to understand the likely transformation products in various environments, such as soils, surface and ground waters, and wastewater treatment processes. To address this knowledge gap, we examined the transformation of 30 nm ZnO MNMs in the presence of different concentrations of phosphate as a function of time and pH using a variety of orthogonal analytical techniques. The data reveal that ZnO MNMs react with phosphate at various concentrations and transform into two distinct morphological/structural phases: a micrometer scale crystalline zinc phosphate phase (hopeite-like) and a nanoscale phase that likely consists of a ZnO core with an amorphous Zn3(PO4)2 shell. The P species composition was also pH dependent, with 82% occurring as hopeite-like P at pH 6 while only 15% occurred as hopeite-like P at pH 8. These results highlight how reactions of ZnO MNMs with phosphate are influenced by environmental variables, including pH, and may ultimately result in structurally and morphologically heterogeneous end products.

The influence of phosphorus availability and Laccaria bicolor symbiosis on phosphate acquisition, antioxidant enzyme activity, and rhizospheric carbon flux in Populus tremuloides

Many forest tree species are dependent on their symbiotic interaction with ectomycorrhizal (ECM) fungi for phosphorus (P) uptake from forest soils where P availability is often limited. The ECM fungal association benefits the host plant under P limitation through enhanced soil exploration and increased P acquisition by mycorrhizas. To study the P starvation response (PSR) and its modification by ECM fungi in Populus tremuloides, a comparison was made between nonmycorrhizal (NM) and mycorrhizal with Laccaria bicolor (Myc) seedlings grown under different concentrations of phosphate (Pi) in sand culture. Although differences in growth between NM and Myc plants were small, Myc plants were more effective at acquiring P from low Pi treatments, with significantly lower k m values for root and leaf P accumulation. Pi limitation significantly increased the activity of catalase, ascorbate peroxidase, and guaiacol-dependent peroxidase in leaves and roots to greater extents in NM than Myc P. tremuloides. Phosphoenolpyruvate carboxylase activity also increased in NM plants under P limitation, but was unchanged in Myc plants. Formate, citrate, malonate, lactate, malate, and oxalate and total organic carbon exudation by roots was stimulated by P limitation to a greater extent in NM than Myc plants. Colonization by L. bicolor reduced the solution Pi concentration thresholds where PSR physiological changes occurred, indicating that enhanced Pi acquisition by P. tremuloides colonized by L. bicolor altered host P homeostasis and plant stress responses to P limitation. Understanding these plant-symbiont interactions facilitates the selection of more P-efficient forest trees and strategies for tree plantation production on marginal soils.

Specific responses to nitrogen and phosphorus enrichment in cyanobacteria: Factors influencing changes in species dominance along eutrophic gradients

Anthropogenic eutrophication is a worldwide problem, causing proliferation of cyanobacterial masses, some of which may be toxic. However, little is known about whether the response to nutrient enrichment differs among cyanobacterial species. To address this issue, distinct patterns in growth and competitive response of benthic cyanobacteria under N and P nutrient regimes were studied. Nine cyanobacterial species, collected from Guadarrama river biofilms at several locations with different nutrient concentrations, were isolated and used for a series of N and P enrichment bioassays. In competition experiments with a mixture of all nine species, a great predominance of certain cyanobacteria over others was noted at high nutrient conditions, while under low nutrient conditions some others dominated. On the basis of these results four selected strains were subjected to a gradient of different concentrations of phosphate, nitrate and ammonium, in independent bioassays, both in monocultures and mixed cultures. Depending on the concentration of N and P, stimulation or inhibition of growth was observed. Some species grew better, dominating at high nutrient concentrations, while higher yields were recorded for others under low nutrient regimes, dominating in these conditions. Results from this study clarify previously published field observations, whereby a group of species occurred mostly in downstream nutrient-rich locations, while other was typical of upstream oligotrophic conditions. Our findings concerning differential growth in relation to nutrient concentrations may be useful for environmental management, because they help us predict which cyanobacteria may be expected to occur under certain conditions.

Aqueous phosphate removal using nanoscale zero-valent iron

Nanoscale zero-valent iron (NZVI) particles have been used for the remediation of a wide variety of contaminants. NZVI particles have high reactivity because of high reactive surface area. In this study, NZVI slurry was successfully used for phosphate removal and recovery. Batch studies conducted using different concentrations of phosphate (1, 5, and 10 mg PO4 3−-P/L with 400 mg NZVI/L) removed ~96 to 100 % phosphate in 30 min. Efficacy of the NZVI in phosphate removal was found to 13.9 times higher than micro-ZVI (MZVI) particles with same NZVI and MZVI surface area concentrations used in batch reactors. Ionic strength, sulfate, nitrate, and humic substances present in the water affected in phosphate removal by NZVI but they may not have any practical significance in phosphate removal in the field. Phosphate recovery batch study indicated that better recovery is achieved at higher pH and it decreased with lowering of the pH of the aqueous solution. Maximum phosphate recovery of ~78 % was achieved in 30 min at pH 12. The successful rapid removal of phosphate by NZVI from aqueous solution is expected to have great ramification for cleaning up nutrient rich waters.

The inhibitory degree between Skeletonema costatum and dinoflagllate Prorocentrum donghaiense at different concentrations of phosphate and nitrate/phosphate ratios

Interactions between Skeletonema costatum (S. costatum) and Prorocentrum donghaiense (P. donghaiiense) were investigated using bi-algal cultures at different concentrations of phosphate (PO4-P) and nitrate/phosphate (N/P) ratios. Experiments were conducted under P-limited conditions and the Lotka-Volterra mathematical model was used to simulate the growth of S. costatum and P. donghaiense in the bi-algal cultures. Both of these two species were inhibited significantly in bi-algal culture. The results of the simulation showed that the inhibitory degree of S. costaum by P. donghaiense was high when the concentration of PO4-P was low (0.1 μmolL−1/2 d), but that of P. donghaiense by S. costaum was high with increased PO4-P supply (0.6 μmolL−1/2 d). At low concentration of PO4-P (0.1 μmolL−1/2 d), or high concentration of PO4-P (0.6 μmolL−1/2 d) with high N/P ratio (160), the interactions between S. costatum and P. donghaiense were dependent on the initial cell densities of both species. At high concentration of PO4-P (0.6 μmolL−1/2 d) with low N/P ratio (25 or 80), S. costatum exhibited a survival strategy superior to that of P. donghaiense. The degree of inhibition of P. donghaiense by S. costaum increased with elevated N/P ratio when the medium was supplemented with concentration 0.1 μmolL−1/2 d of PO4-P. The degree of inhibition to P. donghaiense by S. costaum increased with elevated N/P ratio at low concentration of PO4-P (0.1 μmolL−1/2 d). This trend was conversed at high concentration of PO4-P (0.6 μmolL−1/2 d). However, the degree of inhibition of S. costaum by P. donghaiense increased with the increased N/P ratio at different PO4-P concentrations (0.1 μmolL−1/2 d and 0.6 μmolL−1/2 d). These results suggested that both phosphate concentration and N/P ratio affected the competition between S. costaum and P. donghaiense: P. donghaiense is more competitive in environments with low phosphate or high N/P ratio and the influence of N/P ratio on the competition was more significant with lower phosphate concentration.

The inhibitory degree between Skeletonema costatum and dinoflagllate Prorocentrum donghaiense at different concentrations of phosphate and nitrate/phosphate ratios

The inhibitory degree between Skeletonema costatum and dinoflagllate Prorocentrum donghaiense at different concentrations of phosphate and nitrate/phosphate ratios

Effects of different photoperiods and concentrations of phosphate on the growth of the cyanobacterium Cylindrospermopsis raciborskii (Woloszynska)

The freshwater cyanobacterium, Cylindrospermopsis raciborskii is potentially toxic and widely distributed in tropical and sub-tropical regions. This species is highly abundant throughout the Anzali Lagoon during the months of July and August. The effects of four different photoperiods (L/D 12:12, 10:14, 14:10, 8:16) as well as three different concentrations of phosphate (2 fold, 3 fold and half of the main culture) on growth rates of C. raciborskii were studied. C. raciborskii , isolated from water samples collected from the Anzali Lagoon, was cultured in Zehnder 8 media (using Z 8 without a nitrogen source) under light intensity of 3000 Lux at 25 + 2°C. A control group cultured with the main culture medium was also used. This experiment was carried out for 25 days. Inoculants and C. raciborskii cells were counted every other day throughout the experiment period using a Neubauer chamber and specific growth rates (SGR) and cell division rates (G) were estimated. The maximum growth rate (8x10 6 ± 5 cells ml -1 ) was observed at 12 L:12 D photoperiod followed by 14 L:10 D, 10 L:14 D and 8 L:16 D. The results obtained in the present study especially with 14 L:10 D and 12 L:12 D were in complete agreement with general growth pattern of C. raciborskii observed in warmer months with rather longer daytime in tropical and subtropical areas. The maximum growth rates were observed in the group treated with 2 fold PO 4 concentration. The strategy of growth in this species may depend on nitrogen fixation, when other algae were nitrogen limited and fast PO 4 uptake even if very low concentration is available. Key words: Cyanobacteria, Cylindrospermopsis raciborskii, Anzali Lagoon, photoperiod, phosphate, growthrate.

High phosphate diet reduces atherosclerosis formation in apolipoprotein E-deficient mice

Although higher serum phosphate level is a risk factor for cardiovascular diseases in general population as well as chronic kidney disease patients, it has not been clarified whether higher phosphate can affect atherosclerotic plaque formation. In this study, we investigated the effect of prolonged-intake of different concentrations of phosphate on atherosclerosis formation using apolipoprotein E-deficient mice. Apolipoprotein E-deficient mice were fed with high fat diet including 0.6%, 1.2% or 1.8% phosphate. After 20-week treatment, atherosclerotic plaque formation in aorta in 1.8% phosphate diet group was unexpectedly less than that in the other groups. To elucidate mechanisms of suppression of plaque formation by high phosphate diet, we hypothesized that high phosphate diet may modify a profile of monocytes/macrophages suppressing plaque formation. We confirmed that elevated peripheral monocytes (CD11b+, F4/80+ cell numbers) in apolipoprotein E-deficient mice were decreased by feeding with 1.8% P diet. In addition, ex vivo study indicated that high dose of phosphate induced macrophage apoptosis. These observations suggest that excess phosphate intake decreased atherosclerosis formation, at least in part, by changing the profile of peripheral monocytes or inducing apoptosis of macrophages in apolipoprotein E-deficient mice.

Stability of Continuous Renal Replacement Therapy Solutions After Phosphate Addition: An Experimental Study

The incidence of hypophosphatemia is high in critically ill children on continuous renal replacement therapy (CRRT) and the addition of phosphate supplements to the replacement and dialysis fluids reduces the frequency of hypophosphatemia. The objective of this study was to determine the in vitro stability of the CRRT solutions after phosphate addition. Three different concentrations of phosphate, 2.5, 4.6 and 7.7 mg/dL, in the replacement and dialysis fluids were analyzed. The pH, glucose, total calcium, phosphate, and magnesium were determined before adding the phosphate and at 2, 24, and 48 h after its addition. The bags were macroscopically observed for possible precipitation. After addition of the phosphate, its concentration remained stable and there were no significant changes in the concentrations of the other components. There were no visible signs of precipitation up to 48 h. The addition of phosphate to the CRRT fluids at concentrations of up to 7.7 mg/dL does not cause problems with precipitation or instability of the mixture.

The methodology and results of determination of inorganic arsenic species in mobile fractions of tsunami deposits by a hyphenated technique of HPLC-HG-AAS

A method of extraction has been proposed for the determination of inorganic species of As(III) and As(V) in the exchangeable fraction of sediments left by the 2004 tsunami. The method combines the fractionation of solid samples with speciation analysis by high performance liquid chromatography with hydride generation and atomic absorption spectrometry (HPLC-HG-AAS). The proposed extraction liquid is a phosphate buffer of Na2HPO4 and KH2PO4, with different concentrations of phosphate ranging from 5 to 50 mmol L−1. This method has been tested for different masses of samples as well as for different times of extraction, pH, temperature, and the presence or absence of mixing. The optimum conditions of extraction have been obtained by the use of buffer (50 mmol L−1 under pH from 5.8 to 6.2) at 80°C. The new technique was applied for the analysis of tsunami deposits left on land and sampled shortly after the tsunami (2005) and after the first (2006) and second rainy seasons (2007). The obtained results show that the exchangeable fraction of tsunami deposits was enriched in arsenic in comparison to reference soil samples. The major changes after the rainy seasons were not in the total concentration of inorganic As species, but in the ratio of As(III) to As(V). More toxic As(III) was removed from the deposits or oxidised, and after two years was hardly detectable in the tsunami deposits.

Membrane phospholipids as a phosphate reserve: the dynamic nature of phospholipid‐to‐digalactosyl diacylglycerol exchange in higher plants

It is well established that phosphate deficiency induces the replacement of membrane phospholipid with non-phosphorous lipids in extra-plastidial membranes (e.g. plasma membrane, tonoplast, mitochondria). The predominant replacement lipid is digalactosyl diacylglycerol (DGDG). This paper reports that the phospholipid-to-DGDG replacement is reversible, and that when oat seedlings are re-supplied with radio-labelled phosphate, it is initially recovered primarily in phosphatidylcholine (PC). Within 2 d, the shoot contains more than half of the lipid-associated radiolabel, reflecting phosphate translocation. Oat was also cultivated in different concentrations of phosphate and the DGDG/PC ratio in roots and phospholipase activities in isolated plasma membranes was assayed after different times of cultivation. The DGDG/PC ratio in root tissue correlated more closely with plasma membrane-localized phospholipase D, yielding phosphatidic acid (PA), than with plasma membrane-localized PA phosphatase, the activity that results in a decreased proportion of phospolipids. The lipid degradation data did not reflect a significant involvement of phospholipase C, although a putative phospholipase C analogue, non-specific phospholipase C4 (NPC4), was present in oat roots. The correlation between increased phospholipase D activity and DGDG/PC ratio is consistent with a model where phospholipid-to-DGDG replacement involves formation of PA that readily is removed from the plasma membrane for further degradation elsewhere.

Effects of Geometric Isomerism and Anions on the Kinetics and Mechanism of the Stepwise Formation of Long-Range DNA Interstrand Cross-Links by Dinuclear Platinum Antitumor Complexes

Reported herein is a detailed study of the kinetics and mechanism of formation of a 1,4-GG interstrand cross-link by the dinuclear platinum anticancer compound [15N][{cis-PtCl(NH3)2}2{mu-NH2(CH2)6NH2}]2+ (1,1/c,c (1)). The reaction of [15N]1 with 5'-{d(ATATGTACATAT)2} (I) has been studied by [1H,15N] HSQC NMR spectroscopy in the presence of different concentrations of phosphate. In contrast with the geometric trans isomer (1,1/t,t), there was no evidence for an electrostatic preassociation of 1,1/c,c with the polyanionic DNA surface, and the pseudo-first-order rate constant for the aquation of [(15)N]1 was actually slightly higher (rather than lower) than that in the absence of DNA. When phosphate is absent, the overall rate of formation of the cross-link is quite similar for the two geometric isomers, occurring slightly faster for 1,1/t,t. A major difference in the DNA binding pathways is the observation of phosphate-bound intermediates only in the case of 1,1/c,c. 15 mM phosphate causes a dramatic slowing in the overall rate of formation of DNA interstrand cross-links due to both the slow formation and slow closure of the phosphate-bound monofunctional adduct. A comparison of the molecular models of the bifunctional adducts of the two isomers shows that helical distortion is minimal and globally the structures of the 1,4 interstrand cross-links are quite similar. The effect of carrier ligand was investigated by similar studies of the ethylenediamine derivative [15N]1-en. A pKa value of 5.43 was determined for the [15N]1,1/c,c-en diaquated species. The rate of reaction of [15N]1-en with duplex I is similar to that of 1,1/c,c and the overall conformation of the final adduct appears to be similar. The significance of these results to the development of "second-generation" polynuclear platinum clinical candidates based on the 1,1/c,c chelate (dach) series is discussed.