Surface-grafting of phosphates onto a polymer for potential biomimetic functionalization of biomaterials

In the human body, phosphate groups play important roles in signaling and the biological functions of proteins and peptides. Despite the importance of phosphate groups, polymer surfaces have not been directly grafted with phosphate groups by chemical reactions because the usual organic solvents used to graft phosphate groups can dissolve or swell polymers. We focused this study on grafting phosphate groups onto a poly(ethylene-co-acrylic acid) (PEAA) surface in an aqueous solution. O-phospho L-serine and O-phosphoethanolamine were grafted on PEAA surfaces to introduce phosphate groups by activating carboxylic acid groups of PEAA using N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) in an aqueous environment. X-ray photoelectron spectroscopy (XPS) was used to elucidate the process by which surface grafting occurs and the process that the phosphate group is cleaved into a phosphate ion and a hydrolyzed molecule at high pH. It was found that under appropriate reaction conditions the phosphate groups could be successfully grafted on the polymer surfaces. The phosphate-grafted polymer surfaces showed lower water contact angles than the initial polymer surfaces likely due to their highly mobile and hydrophilic phosphate side groups. This work demonstrates a technique to successfully graft phosphate groups onto organic polymer surfaces in a biocompatible aqueous environment, which may open new avenues to functionalizing synthetic polymeric and natural macromolecule derived biomaterials.     

Proton interaction in phosphate adsorption onto goethite

The adsorption of phosphate on goethite is generally modeled by assuming a simple ligand exchange reaction with surface hydroxyl groups. This study investigates the binding forms of phosphate on goethite by evaluating the proton interaction and surface charge change during phosphate adsorption. It is found that OH(-) release stoichiometry increases with phosphate coverage, which suggests that different mechanisms predominate at different phosphate loadings. It demonstrates that surface binding changes from monodentate complexation to bidentate complexation with increasing surface phosphate coverage. The net OH(-) release accompanying this transformation is best interpreted with a 2pK(a) multisite model.     

Paramagnetic cobalt(II) as a probe for kinetic and NMR relaxation studies of phosphate binding and the catalytic mechanism of Streptomyces dinuclear aminopeptidase

Phosphate was proposed to be a bridging ligand in the structure 1xjo.pdb of Streptomyces dizinc aminopeptidase (sAP), which prompted further studies of phosphate binding to this enzyme. Phosphate inhibits sAP and its Co(2+)-substituted derivatives in a noncompetitive manner from pH 6.0 to 9.0, with strongest inhibition observed at lower pHs (K(i) = 0.6, 8.2, and 9.1 mM for ZnZn-, CoCo-, and CoZn-sAP, respectively, at pH 6.0), which indicates that phosphate does not compete with substrate binding to the dinuclear active site and that monobasic phosphate has a higher binding affinity. The inhibition K(i)-pH profiles for phosphate inhibition of both the native and the Co(2+)-substituted derivatives reveal a similar pK(a) around 7.0, reflecting that phosphate binding is not affected by the metal centers of different Lewis acidities. Modification of ZnZn- and CoCo-sAP with the arginine-specific reagent phenylglyoxal reveals a significant weakening in phosphate and substrate binding by showing approximately a 10-fold increase in the dissociation constant K(i) for phosphate binding and approximately 4-8-fold increase in K(m). The catalysis is also influenced by the modification as reflected by a significant decrease in k(cat) in both cases. Furthermore, phosphate and the transition-state inhibitor 1-aminobutyl phosphonate can protect arginine from the modification, strongly suggesting that Arg202 near the active site is involved in phosphate binding and in stabilizing the transition state. The effect on (31)P NMR relaxation of phosphate caused by the paramagnetic metal center in Co(2+)-substituted derivatives of sAP has been measured, which reveals that only one phosphate is bound to sAP with the Co(2+)-(31)P distance in the range of 4.1-4.3 A. The (1)H NMR relaxation of the bulk water signal in the CoCo-sAP sample remains unchanged in the presence of phosphate, further indicating that phosphate may not bind to the active-site metals to displace any metal-bound water/hydroxide. These results strongly support that the phosphate binding site is Arg202 and that this residue plays an important role in the action of sAP.     

Adsorption of phosphate from seawater on calcined MgMn-layered double hydroxides

Adsorptive properties of MgMn-3-300 (MgMn-type layered double hydroxide with Mg/Mn mole ratio of 3, calcined at 300 degrees C) for phosphate were investigated in phosphate-enriched seawater with a concentration of 0.30 mg-P/dm3. It showed the highest phosphate uptake from the seawater among the inorganic adsorbents studied (hydrotalcite, calcined hydrotalcite, activated magnesia, hydrous aluminum oxide, manganese oxide (delta-MnO2)). The phosphate uptake by MgMn-3-300 reached 7.3 mg-P/g at an adsorbent/solution ratio of 0.05 g/2 dm3. The analyses of the uptakes of other constituents (Na+, K+, Ca(+, Cl-, and SO(2-)4) of seawater showed that the adsorbent had a markedly high selectivity for the adsorption of phosphate ions. Effects of initial phosphate concentration, temperature, pH, and salinity on phosphate uptake were investigated in detail by a batch method. The phosphate uptake increased slightly with an increase in the adsorption temperature. The adsorption isotherm followed Freundlich's equation with constants of logK(F)=1.25 and 1/n=0.65, indicating that it could effectively remove phosphate even from a solution of markedly low phosphate concentration as well as with large numbers of coexisting ions. The pH dependence showed a maximum phosphate uptake around pH 8.5. The pH dependence curve suggested that selective phosphate adsorption progresses mainly by the ion exchange of HPO(2-)4. The study on the effect of salinity suggested the presence of two kinds of adsorption sites in the adsorbent: one nonspecific site with weak interaction and one specific site with strong interaction. The effective desorption of phosphate could be achieved using a mixed solution of 5 M NaCl + 0.1 M NaOH (1 M = 1 mol/dm3), with negligible dissolution of adsorbent. The adsorbent had high chemical stability against the adsorption/desorption cycle; it kept a good phosphate uptake even after the repetition of the seventh cycle.     

Phosphate oxygen isotope analysis on microsamples of bioapatite: removal of organic contamination and minimization of sample size

Modern and fossil teeth record seasonal information on climate, diet, and migration through stable isotope compositions in enamel and dentine. Climatic signals such as seasonal variation in meteoric water isotopic composition can be recovered through a microscale histology-based sampling and isotopic analysis of enamel phosphate oxygen. The phosphate moiety in bioapatite is particularly resistant to post mortem diagenesis. In order to determine the phosphate oxygen isotope composition of enamel, phosphate must be chemically purified from other oxygen sources in the enamel lattice and matrix, mainly hydroxyl and carbonate ions, and trace quantities of organics.We present a wet chemical technique for purifying phosphate from microsampled enamel and dentine. This technique uses a sodium hypochlorite oxidation step to remove interferences from residual organic constituents of the enamel and/or dentine scaffold, isolates phosphate as relatively large and easily manipulated Ag(3)PO(4) crystals by using a strongly buffered, moderate-temperature microprecipitation, and preserves the oxygen isotope composition of the initial tooth phosphate. The reproducibility of phosphate oxygen isotope compositions thus determined (measured as delta(18)O, V-SMOW scale) is typically 0.2-0.3 per thousand (1 s.d.) on samples as small as 300 microg of enamel or dentine, a considerable improvement over available techniques for analyses of bioapatite phosphate oxygen.     

超声萃取/气相色谱-串联质谱法同时测定纺织品中6种禁用有机磷阻燃剂

以丙酮为萃取溶剂,建立了超声萃取/气相色谱-串联质谱同时测定纺织品中6种禁用有机磷阻燃剂的分析方法.6种禁用有机磷阻燃剂三-(1-氮杂环丙基)氧化膦( TEPA)、三-(2-氯乙基)磷酸酯(TCEP)、三-(2,3-二氯丙基)磷酸酯(TDCP)、二-(2,3-二溴丙基)磷酸酯(DDBPP)、三-(邻甲苯基)磷酸酯(TO...     

An unprecedented uranyl phosphate framework in the structure of [(UO2)3(PO4)O(OH)(H2O)2](H2O)

The new uranyl phosphate [(UO2)3(PO4)O(OH)(H2O)2](H2O) (1) with an unprecedented framework structure has been synthesized at 150 and 185 degrees C. The structure (tetragonal, P4(2)/mbc, a = 14.015(1) A, c = 13.083(2) A, V = 2575.6(4) A(3), Z = 8) contains uranyl phosphate chains composed of uranyl pentagonal and hexagonal bipyramids and phosphate tetrahedra linked by sharing of polyhedral edges. The uranyl phosphate chains are aligned both along [100] and [010] and are linked into a novel framework structure involving channels along [001]. Topologically identical chains occur linked into sheets in more than a dozen uranyl phosphate minerals, but these chains have never been observed in opposing orientations and linked into a framework as in 1.     

Biological Removal of Phosphate at Low Concentrations Using Recombinant Escherichia coli Expressing Phosphate-Binding Protein in Periplasmic Space

During wastewater treatment, phosphate removal is an important and challenging process; thus, diverse technologies, including those derived from biological means, have been devised for efficient phosphate removal. Although conventional biological methods are effective in decreasing wastewater phosphate levels to ~1 mg/L, long periods of microbial adaptation are required for effective phosphate removal, and the removal efficiency of these methods is relatively poor at lower phosphate concentrations. In the present work, we constructed a recombinant Escherichia coli with periplasmic-expressed phosphate-binding protein (PBP) and investigated its biological removal ability for low phosphate levels. We found that the PBP-expressing recombinant E. coli cells showed efficient (> 94 %) removal of phosphate at low concentrations (0.2–1.0 mg/L) in a treated cell mass-dependent manner. Collectively, we propose that our PBP-expressing recombinant whole-cell system could be successfully used during wastewater treatment for the biological removal of low concentrations of phosphate.     

A multifaceted phosphate tether: application to the C1-C14 subunit of dolabelides A-D

A phosphate tether approach to the C1-14 subunit of dolabelide is described. The phosphate tether serves a multifaceted role mediating several processes, including (i) diastereotopic differentiation via RCM, (ii) selective CM by imparting Type III behavior to the exocyclic olefin, (iii) regioselective hydrogenation, and (iv) regioselective Pd(0)-catalyzed reductive opening of the bicyclic phosphate. Overall, this strategy uses orthogonal protecting- and leaving-group properties innate to phosphate esters to rapidly assembly the titled subunit.     

Formation of calcium phosphates in gelatin with a novel diffusion system

The present paper demonstrated a novel and simple diffusion system to precipitate calcium phosphates in gelatin gel. In this system, a gelatin cup was specially used as the membrane separating reservoirs of calcium and phosphate ions. Relative to the conventional diffusion system, the novel one in our experiment decreased the time required for the deposition from 5-7 days to 20 h and increased the amount of the precipitated mineral phases significantly. The influence of pH values and concentrations of calcium and phosphate solutions buffered with Tris-HCl and NaOH, respectively, was investigated. The results showed that precipitation of the mineral phase at low pH values (7 for calcium and 11 for phosphate) and concentrations (200 mM for calcium and 15 mM for phosphate) resulted in the formation of plate-like octacalcium phosphate (OCP) crystals. With increasing the pH values of calcium and phosphate solutions to 8 and 12, respectively, spherical amorphous calcium phosphate (ACP) particles were obtained uniquely. Furthermore, flower-like hydroxyapatite (HAP) aggregates composed of many nano-sized needles were formed from the solutions with high pH values (8 for calcium and 12 for phosphate) and concentrations (500 mM for calcium and 37.5 mM for phosphate). The novel diffusion system is proposed to play an important role in both studying the process of biological mineralization and synthesizing calcium phosphates in different forms.     

Preparation and properties of uniform colloidal metal phosphates IV. Cadmium-, nickel-, and manganese(II)-phosphates

Colloidal dispersions of uniform spherical particles of cadmium phosphate, nickel basic phosphate, and manganese (II) phosphate were prepared by aging at elevated temperatures metal salt solutions and phosphoric acid or sodium dihydrogen phosphate in the presence of urea and sodium dodecyl sulfate. Uniform spheres were obtained only if urea and the surfactant were added within a given range of concentrations.The spherical particles were amorphous as prepared. Cadmium phosphate and nickel basic phosphate particles crystallized when calcined at appropriate temperatures. Manganese (II) phosphate particles underwent a phase transformation to crystalline plate-like solids when aged in doubly distilled water at room temperature.Supported by NFS grant CHE-8619509.Part of M. S. Thesis by L.L.S.     

Selective adsorption of phosphate from seawater and wastewater by amorphous zirconium hydroxide

Phosphate adsorption from single electrolyte (NaH2PO4), phosphate-enriched seawater, and model wastewater was studied using amorphous zirconium hydroxide, ZrO(OH)2(Na2O)0.05 1.5H2O, as an adsorbent. Batch experiments were carried out to investigate the adsorption of phosphate. The effect of pH on phosphate adsorption from seawater showed that the uptake of phosphate increased with an increase in pH up to 6, and then decreased sharply with a further increase in pH of the solution. The equilibrium data of phosphate adsorption were followed with a Freundlich isotherm. The uptake of phosphate at the adsorbent/solution ratio 0.05 g/2 L was 10 and 17 mg-P/g for the phosphate-enriched seawater and the model wastewater, respectively. A much higher adsorptivity toward phosphate ions in seawater was observed on ZrO(OH)2(Na2O)0.05 1.5H(2)O than on other representative adsorbents based on layered double hydroxides of Mg(II)-Al(III), Mg(II)-Fe(III), and Ni(II)-Fe(III). The effective desorption of phosphate ions on ZrO(OH)2(Na2O)0.05 1.5H2O could be achieved using a 0.1 M NaOH solution. The usefulness of experimental data for practical applications in removing phosphate in seawater and wastewater is discussed.     

ATR-IR spectroscopic studies of the influence of phosphate buffer on adsorption of immunoglobulin G to TiO2

In situ attenuated total reflectance infrared (ATR-IR) spectroscopy has been applied to the study of the influence of phosphate on the extent of protein adsorption onto TiO₂. Immunoglobulin G (Ig.G) was adsorbed onto a TiO₂ sol–gel film from solutions containing phosphate or NaCl. Monitoring of the amide II absorbance (v=1545 cm⁻¹) confirmed reduced protein adsorption from the phosphate containing solution. In situ ATR-IR spectroscopy was also used to study phosphate induced desorption of Ig.G. Solutions containing various phosphate concentrations were passed over a TiO₂ film with Ig.G adsorbed to it. As the concentration of phosphate increased the amide II absorbance decreased confirming the removal of bound Ig.G from the TiO₂ surface. As the amide II absorbance decreased the phosphate absorbance (v=1080 cm⁻¹) increased suggesting accumulation of phosphate at the TiO₂ surface. Not all of the bound protein could be displaced from the TiO₂ surface by phosphate suggesting the presence of weakly and strongly bound Ig.G.     

Better bioactive ceramics through sol-gel process

Bioactive glasses and glass ceramics need to be capable of growing a calcium phosphate layer at their surfaces in physiological environment in order to bond with living bone. Sol-gel prepared silica (silica gel) and titania (titania gel) are efficient calcium phosphate absorbents. Both gels extract calcium and phosphate from surrounding physiological and other calcium phosphate solutions and form a calcium phosphate at their surfaces in return. Thus, they can integrate with bone. Under the same condition, however, silica and titania, as both prepared through a conventional high temperature process, are unable to transfer calcium and phosphate from the solutions to obtain a calcium phosphate at their surfaces. Therefore, it is concluded that using inorganic or metal organic precursors, sol-gel process can yield bioactive materials with a high bioactivity.     

Estimation of organophosphoric acid triesters in soft polyurethane foam using a concentrated sulfuric acid dissolution technique and gas chromatography with flame photometric detection.

A concentrated sulfuric acid dissolution technique and a GC method are described for the estimation of tributyl phosphate, tris(2-chloroethyl) phosphate, tris(chloropropyl) phosphate, tris(1,3-dichloro-2-propyl) phosphate, triphenyl phosphate and tris(butoxyethyl) phosphate in soft polyurethane foam. A soft polyurethane foam sample containing organophosphoric acid triesters was dissolved in concentrated sulfuric acid. The solution was added to water, where only the polyurethane was separated out. The pH of the solution was adjusted, and organophosphoric acid triesters were extracted with toluene. After purification, the compounds were determined by GC. The detection limits of the organophosphoric acid triesters were 0.3 - 0.9 microg g(-1). The recoveries of the organophosphoric acid triesters from a 0.05 g sample of soft polyurethane foam were 80.0 - 90.0%, when the spiked amounts were 0.25 - 1 microg. The compounds were detected from soft polyurethane foam at the level of 0.4 - 23.3 microg g(-1).     

The mechanism of the acid-catalyzed decomposition of the farnesyl phosphates

The rates and (in some cases) products of the acid-catalyzed decomposition of (Z,E)- and (E,E)-farnesyl phosphate, (Z,E)- and (E,E) - 1,1 - dideutereofarnesyl phosphate, (Z)- and (E) - 6,7,10,11 - tetrahydrofarnesyl phosphate, and t-butyl phosphate have been studied in an attempt to determine whether (Z,E)-farnesyl phosphate ionizes with intramolecular assistance from the C-6/C-7 double bond or via an unassisted process leading to a simple allylic cation. Data in support of both possibilities are adduced, but it is concluded, primarily on the basis of the secondary deuterium kinetic isotope effects, that the ionization involves little, if any, assistance from the double bond.     

Activation of acyl phosphate monoesters by lanthanide ions: enhanced reactivity of benzoyl methyl phosphate

Acyl phosphate monoesters are intermediates in many biochemical acylation reactions, such as those involving aminoacyl adenylates. Benzoyl methyl phosphate, a typical acyl phosphate monoester, is slowly hydrolyzed in neutral solutions but reacts rapidly with amines. Since biochemical processes of acyl phosphate monoesters involve accelerated reactions with oxygen-centered nucleophiles, we sought catalysts for hydrolysis and methanolysis of benzoyl methyl phosphate to mimic the biochemical outcome. Lanthanide ions are particularly effective catalysts, accelerating reactions much more than comparable levels of magnesium ion. Detailed kinetic analysis of the hydrolysis reactions reveals formation of a 1:1 complex, followed by rapid reaction with a nucleophile. The hydroxide-dependent hydrolysis rate in the europium complex is about 10(5) times that of free substrate with hydroxide. A mechanism that accounts for the data and observed behavior involves bidentate coordination of the metal ion by the acyl phosphate through phosphate and carbonyl oxygens, lowering the energy of the tetrahedral addition intermediate and the associated transition states. The dependence of the metal ion catalyzed process on the concentration of hydroxide ion is consistent with coordinated hydroxide acting as a nucleophile. The reaction of benzoyl methyl phosphate with methanol to form methyl benzoate and methyl phosphate is 30 000 times more rapid in the presence of 0.0001 M lanthanum triflate (in the absence of the metal ion k(obs) = 2.1 x 10(-7) s(-1), at 25 degrees C). Thus, the combination of acyl phosphate esters and lanthanide salts appears to be a promising method for biomimetic acylation of hydroxyl groups.     

Phosphate uptake by TiO2: batch studies and NMR spectroscopic evidence for multisite adsorption

Systematic studies, combining batch experiments with NMR spectroscopic methods, are carried out for phosphate sorption on titanium dioxide (TiO(2)). It is found that phosphate sorption on TiO(2) decreases with increasing pH, whereas the phosphate uptake by TiO(2) increases with increasing ionic strength of the solution. In I ≤ 0.1 M, the sorption sharply increases and reaches a near maximum and then followed by little changes showing Langmuir-type behavior, whereas in I = 0.7 M, non-Langmuirian uptake becomes evident as equilibrium phosphate concentrations increase in solution. The sorption of phosphate on TiO(2) is rapid and mostly irreversible at pH 4.5 and 7.0. At pH 9.0, however, the phosphate sorption is initially reversible and followed by resorption of phosphate on TiO(2) at the system re-equilibration. (31)P{(1)H} cross-polarization and magic angle spinning (CP/MAS) NMR spectra contain at least four main peaks which appear similar in position and width under all adsorption conditions, but vary in intensity with surface loading. The spectral characteristics of these peaks, including cross-polarization dynamics and chemical shift anisotropy obtained from spinning sideband analysis, suggest that they arise from distinct inner-sphere adsorption complexes, most of which are protonated. These results indicate that uptake of phosphate by TiO(2) occurs by formation of several types of surface complexes.     

High-precision determination of 18O/16O ratios of silver phosphate by EA-pyrolysis-IRMS continuous flow technique

A high-precision, and rapid on-line method for oxygen isotope analysis of silver phosphate is presented. The technique uses high-temperature elemental analyzer (EA)-pyrolysis interfaced in continuous flow (CF) mode to an isotopic ratio mass spectrometer (IRMS). Calibration curves were generated by synthesizing silver phosphate with a 13 per thousand spread in delta(18)O values. Calibration materials were obtained by reacting dissolved potassium dihydrogen phosphate (KH(2)PO(4)) with water samples of various oxygen isotope compositions at 373 K. Validity of the method was tested by comparing the on-line results with those obtained by classical off-line sample preparation and dual inlet isotope measurement. In addition, silver phosphate precipitates were prepared from a collection of biogenic apatites with known delta(18)O values ranging from 12.8 to 29.9 per thousand (V-SMOW). Reproducibility of +/- 0.2 per thousand was obtained by the EA-Py-CF-IRMS method for sample sizes in the range 400-500 microg. Both natural and synthetic samples are remarkably well correlated with conventional (18)O/(16)O determinations. Silver phosphate is a very stable material and easy to degas and, thus, could be considered as a good candidate to become a reference material for the determination of (18)O/(16)O ratios of phosphate by high-temperature pyrolysis.     

Kinetics and energetics of phosphate sorption in a multi-component Al(III)-Fe(III) hydr(oxide) sorbent system

Multi-component Al-Fe hydr(oxides) are ubiquituous in soil and aquatic environments, where they exhibit biogeochemical controls on nutrients and contaminants. Although, sorption on single-component Al and Fe hydr(oxides) have been extensively studied, limited studies have been done on their multi-component counterparts. In this study, effects of Al/Fe content on the kinetics and energetics of phosphate sorption in a poorly-crystalline co-precipitated mixed Al-Fe hydr(oxide) system were investigated using a combination of traditional batch techniques and flow adsorption calorimetry. Differences in Al/Fe content was found to influence the structural development and anion exchange capacity of the hydr(oxides) and subsequently their phosphate sorption characteristics. Higher structural development decreased phosphate sorption, while higher AEC was associated with increased phosphate sorption, initial sorption rate, and smaller losses in sorption with increasing pH. Results from flow adsorption calorimetry indicated that at pH 4.8 phosphate sorption: (i) occurred irreversibly on anion exchange sites, with a loss of 1.9 moles of AEC per mole of phosphate sorbed, and (ii) was exothermic, with molar heats of adsorption between -25 and -39 kJmol(-1). Molar heats of adsorption were ten times that for anion exchange and independent of hydr(oxide) composition with the amount of energy evolved being directly proportional to the quantity of phosphate sorbed.