Influence Of Phosphate Concentration Research Articles

The Influence of Phosphate Concentration on the Spectral Properties of Thulium Ions in Fluorophosphate Glasses

The Judd–Ofelt parameters of thulium ions in fluorophosphate glasses with different phosphate component concentrations are calculated. It is shown that the Ωt parameters of glasses with Ba(PO3)2 concentrations up to 10 mol % are close to the corresponding parameters of fluoride glasses and sharply increase with increasing phosphate concentration. The spectral-luminescent parameters of glasses are analyzed within the Judd–Ofelt theory. The spontaneous transition probabilities, branching ratios (β), and radiative lifetimes (τrad) for different excited states of Tm3+ are determined. It is found that glasses with low phosphate concentrations are characterized by a high radiative lifetime of the excited 3F4 laser level. It is shown that the glasses under study have a typical broad flat gain spectrum, which makes them promising for developing broadband amplifiers.

Influence of phosphate concentration on amine, amide, and hydroxyl CEST contrast.

To evaluate the influence of phosphate on amine, amide, and hydroxyl CEST contrast using Bloch-McConnell simulations applied to physical phantom data. Phantom solutions of 4 representative metabolites with exchangeable protons-glycine (α-amine protons), Cr (η-amine protons), egg white protein (amide protons), and glucose (hydroxyl protons)-were prepared at different pH levels (5.6 to 8.9) and phosphate concentrations (5 to 80 mM). CEST images of the phantom were collected with CEST-EPI sequence at 3 tesla. The CEST data were then fitted to full Bloch-McConnell equation simulations to estimate the exchange rate constants. With the fitted parameters, simulations were performed to evaluate the intracellular and extracellular contributions of CEST signals in normal brain tissue and brain tumors, as well as in dynamic glucose-enhanced experiments. The exchange rates of α-amine and hydroxyl protons were found to be highly dependent on both pH and phosphate concentrations, whereas the exchange rates of η-amine and amide protons were pH-dependent, albeit not catalyzed by phosphate. With phosphate being predominantly intracellular, CEST contrast of α-amine exhibited a higher sensitivity to changes in the extracellular microenvironment. Simulations of dynamic glucose-enhanced signals demonstrated that the contrast between normal and tumor tissue was mostly due to the extracellular CEST effect. The proton exchange rates in some metabolites can be greatly catalyzed by the presence of phosphate at physiological concentrations, which substantially alters the CEST contrast. Catalytic agents should be considered as confounding factors in future CEST-MRI research. This new dimension may also benefit the development of novel phosphate-sensitive imaging methods.

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.

Optical Characterization of Nano- and Microcrystals of EuPO₄ Created by One-Step Synthesis of Antimony-Germanate-Silicate Glass Modified by P₂O₅.

Technology of active glass-ceramics (GC) is an important part of luminescent materials engineering. The classic method to obtain GC is based on annealing of parent glass in proper temperature and different time periods. Generally, only the bulk materials are investigated as a starting host for further applications. However, the effect of an additional heat-treatment process on emission and structural properties during GC processing is omitted. Here, we focus on the possibility of obtaining transparent glass-ceramic doped with europium ions directly with a melt-quenching method. The influence of phosphate concentration (up to 10 mol %) on the inversion symmetry of local environment of Eu3+ ions in antimony-germanate-silicate (SGS) glass has been investigated. The Stark splitting of luminescence spectra and the local asymmetry ratio estimated by relation of (5D0→7F2)/(5D0→7F1) transitions in fabricated glass confirms higher local symmetry around Eu3+ ions. Based on XRD and SEM/EDX measurements, the EuPO4 nano- and microcrystals with monoclinic geometry were determined. Therefore, in our experiment, we confirmed possibility of one-step approach to fabricate crystalline structures (glass-ceramic) in Eu–doped SGS glass without additional annealing process.

Application of Central Composite Design for the Determination of Exfoliating Agents in Cosmetics by Capillary Electrophoresis with Electroosmotic Flow Modulation

Multivariate analysis within central composite design is applied to simplify an optimization procedure and explore the interactions among experimental parameters in analytical chemistry. In this study, central composite design was used to identify the optimal capillary electrophoresis conditions with electroosmotic flow modulation to determine seven exfoliating agents in cosmetics. The influence of phosphate concentration, cetyltrimethylammonium bromide concentration, and methanol percentage on the response was evaluated by the use of the chromatographic exponential function to simultaneously investigate the resolution and separation under sixteen sets of capillary electrophoresis conditions. The optimized conditions were 150 mM phosphate solution (pH = 7) containing 0.5 mM cetyltrimethylammonium bromide, 3 mM γ-cyclodextrin, and 25% methanol as the running buffer. To shorten the analysis time, an electroosmotic flow modulating agent (cetyltrimethylammonium bromide) was added to the separation buffer. Calibration plots were linear (r ≧ 0.998) with high precision and accuracy in the homemade cosmetic matrix. The exfoliating agents in two commercial cosmetic products were determined using the optimized conditions, and the results correlated well with results obtained by high-performance liquid chromatography–mass spectrometry.

Adsorption of Arsenic on MgAl Layered Double Hydroxide

Groundwater in the Eastern Croatia, as well in the South-eastern Hungary, contains relatively high concentrations of arsenic that can cause chronic toxicity to humans. Therefore, the aim to find an effective composite adsorbent that can be applied for arsenic water remediation by introducing it in the groundwater treatment is very important. The presented results were obtained using layered double hydroxide (LDH) as a sorbing system. MgAl LDH samples with a Mg:Al molar ratio of 2:1 were synthesized. Adsorption of arsenic anions from groundwater samples from Eastern Croatia, as well as adsorption of model aquatic arsenic sample solutions, on MgAl layered double hydroxide was investigated. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for determination of arsenic concentration after adsorption. It was shown that in both cases the adsorption process could be interpreted in terms of Kroeker adsorption isotherm regardless to the presence of other ions in the groundwater. Additionally, the influence of phosphate concentration on adsorption of model arsenic samples was examined and it was shown that (at least in examined range of arsenic and phosphate concentration) there is no significant influence of phosphate on adsorption of arsenic.

Artificial enzymes based on cyclodextrin with phenol as the catalytic group

β-Cyclodextrin containing one or two N-linked ortho-N-acetylaminophenols has been synthesized and tested for their properties as artificial glycosidases. Four different para-nitrophenyl glycosides were used as substrates and kcat/kuncat values of up to 381 were found for the di-functionalized products, whereas the mono derivative showed up to 47 times rate enhancement. The optimum pH for the catalysis was found to be approximately pH 8 and the influence of phosphate concentration was investigated.

Phosphate uptake from water on a Surfactant-Modified Zeolite and Ca-zeolites

The phosphate adsorption kinetics are determined in batch-wise (noted B) and fixed-bed column (noted C) experiments on a Surfactant-Modified Zeolite (SMZ) and various Ca-zeolites. The influence of phosphate concentration (0.08 or 0.8 mmol/L), presence of NO3−, HCO3−, SO42− and Cl− competing anions (individual concentration = 0.8 meq/L) and flow rate Q (1–30 mL/min) is studied. Preliminary experiments lead to the selection of the most efficient Ca-LTA and SMZ samples for the subsequent studies. In B experiments, the nature of the used system does not influence the equilibrium removal rate R (≈80%) but affects the adsorption kinetics. The equilibrium times are shorter on SMZ than on Ca-LTA, increasing with the phosphate concentration and the presence of competing anions, respectively in the ~0.5–6 or ~3–24 h ranges. In C experiments, the phosphate uptake performances on SMZ are higher than in the corresponding B experiments, with in particular higher final q/qm values. The deterioration of the performances on SMZ in presence of competing anions or with increase of Q is due to the effect of the slow phosphate ion-exchange kinetics and the short used contact time. For similar reasons, sorption on Ca-LTA is lower than on SMZ. For instance, with a 0.8 mmol/L phosphate concentration and a 10 mL/min flow rate, the time-decreasing R values become close to 50 and 10% after filtration of 10 bed-volumes respectively in presence of SMZ and Ca-LTA. Globally, SMZ is clearly more efficient than Ca-LTA, being furthermore a versatile and easily regenerable material.

Influence of Phosphate Concentration on Plasma Electrolytic Oxidation of AZ80 Magnesium Alloy in Alkaline Aluminate Solution

Plasma electrolytic oxidation of AZ80 magnesium alloy in alkaline aluminate electrolytes develops MgAl 2 O 4 -based highly crystalline oxide coatings with the morphology changing largely with phosphate concentration in electrolyte. The thickness of the coatings increases with phosphate concentration from 5 μm in phosphate-free electrolyte to ∼70μm in the electrolyte containing 0.1 mol·dm -3 phosphate after anodizing for 900 s. The formation of the latter thick coating is associated with intense sparking during anodizing. The thick coatings formed in the electrolytes containing 0.075 and 0.1 mol·dm -3 phosphate are highly cracked. In contrast, the coating formed in the electrolyte containing 0.05 mol·dm -3 phosphate is relatively uniform, showing the highest corrosion protection in 0.5 mol·dm -3 NaCl solution. The coatings consist of two layers, comprising an outer thick layer with high concentration of aluminum and an inner thin magnesium-rich layer.

Promotion by phosphate of Fe(III)- and Cu(II)-catalyzed autoxidation of fructose

Although the oxidative destruction of glucose and fructose has been studied by several investigators over the past century, the mechanism by which phosphate promotes these oxidation reactions is not known. A wide range of oxidation products have been used to monitor the oxidation of sugars and free radicals have been shown to be involved. The influence of phosphate concentration on the rate of production of free radicals and several sugar oxidation products has been studied. It was found that fructose is much more susceptible to autoxidation than glucose, galactose, or sucrose. The promotion of sugar oxidation by phosphate was found to be iron dependent. Addition of the iron chelators, diethylenetriaminepentaacetic acid (DTPA) and desferrioxamine completely suppressed the oxidation reactions, even at high concentrations of phosphate. Formaldehyde was positively identified as a product of fructose oxidation by HPLC analysis of its acetylacetone adduct. A mechanism is proposed in which phosphate cleaves the oxo bridges of the iron(III)–fructose complex, based on UV spectral analysis and magnetic susceptibility measurements, and thereby catalyzes the autoxidation of fructose.

Influence of phosphate concentration and reaction temperature when using the molybdenum blue method for determination of phosphate in water

The formation rate in water of the blue phosphoantimonylmolybdenum complex declines both with decreasing phosphate concentration (studied range 5–500 μg PO 4-P l −1) and decreasing reaction temperature (studied range + 1 to + 21°C). At + 15°C, only solutions containing ≥ 50 μg PO 4-P l −1 reached full colour expression within 5 min, and at + 10°C all tested concentrations needed a longer reaction time. At temperatures below + 15°C, not even a reaction time of 10 min is always sufficient for complete colour development. For instance, at + 7°C, maximum absorbance level is reached in 10 min only at concentrations ≥ 250 μg PO 4-P l −1, whereas a solution of 5 μg PO 4-P l −1 requires about 30 min. Slow formation rate of the coloured complex is a possible, insidious source of under-estimation, particularly when determining low concentrations of phosphate.

Combined nitrogen and phosphorus removal in a full-scale continuous up-flow sand filter

An attractive method for post-denitrification may be the use of sand filters. In this paper, a description and evaluation are given of full scale studies of the use of a continuous sand filter for the combined removal of suspended solids, phosphorus and nitrogen. Experiments were performed using methanol as a carbon source for denitrification and ferric chloride for an improved phosphorus removal. The studied continuous sand filter was a DynaSand filter marketed by Nordic Water Products AB. The filter has a surface area of 4.7 m2 and a maximum possible bed height of 6 m. The bed consisted of sand with 1.2-2 mm grain size. The tested bed heights were 3.5-4.8 m, and the hydraulic load varied between 5.4 and 24.5 m/h. The effluent from the Loudden treatment plant in Stockholm was supplied to the filter. Influent nitrate concentrations up to 20 mg N/l were tested and they decreased to 0.5-2 mg N/l. The methanol dosage was controlled by the measurement of nitrate continuously in the effluent by a dr Lange meter. The denitrification rate followed a half order reaction down to low values of nitrate. Results showed that an effluent concentration of 0.15 mg P/l could easily be obtained. It was found that the influence of phosphate concentration is small on the denitrification rate if the phosphate concentration is above 0.1 mg P/l. The reject has a low sludge index which is favourable if the reject is returned to a sedimentation basin. The emission of nitrous gas (N2O) is very low. The installation makes it possible to use space efficiently, since polishing, phosphorus removal and denitrification can take place in the same unit. Already the phosphorus removal process reduces the need for process volume by 80% compared to a conventional process with flocculation and sedimentation basins.

Influence of phosphate concentration on the respiratory activity of Azotobacter vinelandii

AbstractAzotobacter vinelandii was grown in batch cultures supplied with ammonia as an N‐source and phosphate at limiting concentration. After phosphate depletion the respiratory rate was affected in a characteristic way. The oxygen consumption during growth and the phase following growth was substantially higher than in cultures amply supplied with phosphate. It is suggested that phosphate limitation impairs the oxidative phosphorylation and stimulates the substrate phosphorylation which leads to a higher degree of respiratory NAD(P)H oxidation due to changes in the branched electron transport system.

Influence of phosphate concentration on the respiratory activity ofAzotobacter vinelandii

Influence of phosphate concentration on the respiratory activity ofAzotobacter vinelandii

The influence of phosphate concentration on the kinetics of uptake by maize roots

In an experiment with native maize roots depending on different phosphorus concentration in the external solution (0.001 … 50 mM P), the multiphasic character of the kinetics of phosphate uptake has been stated. The single phases are characterized by the different values of Km and Vmax. In the wide range of concentrations the isotherm of the phosphate uptake has five evident phases. The character of kinetics for the uptake of phosphate is analogical to the kinetics of the enzymatic reactions described by the Michaelis-Menten equation. On the other hand the linear dependence for the inactivated root was determined,i.e. the uptake of phosphate versus different phosphorus concentration in the external solution.