Abstract: Infrared absorption spectra of sodium phosphate glasses, Na2O=30–50 mol%, have been studied in the region of 400–2000 cm−1. Spectra were analyzed to determine the relative intensity of the IR bands responsible for the different phosphate units. Spectral analyses has shown that the substitution of P2O5 by Na2O influences the intermediate range order of the glass matrix. Increasing Na2O content leads to a gradual degradation of the phosphate ring type structures, with consequent depolymerization causing compaction of the glass matrix. Analyses of IR spectra illustrates the reorganization effects of Na2O in the phosphate matrix.

Abstract: Using laboratory, animal, and human in situ caries models, investigators have shown that casein phosphopeptide amorphous calcium phosphate complexes (CPP-ACP) exhibit an anticariogenic activity. The casein phosphopeptides (CPP) are produced from a tryptic digest of the milk protein casein by aggregation with calcium phosphate and purification by ultrafiltration. The CPP have a remarkable ability to stabilize calcium phosphate in solution and substantially increase the level of calcium phosphate in dental plaque. Through their multiple phosphoseryl residues, the CPP bind to forming clusters of amorphous calcium phosphate (ACP) in metastable solution, preventing their growth to the critical size required for nucleation and precipitation. The proposed mechanism of anticariogenicity for the CPP-ACP is that they localize ACP in dental plaque, which buffers the free calcium and phosphate lon activities, thereby helping to maintain a state of supersaturation with respect to tooth enamel depressing demineralization and enhancing remineralization. The CPP-ACP, unlike fluoride, can be added to sugar-containing foods and therefore have commercial potential as an additive to foods as well as to toothpastes and mouthwashes for the control of dental caries.

Abstract: Plastids of nongreen tissues import carbon as a source of biosynthetic pathways and energy. Within plastids, carbon can be used in the biosynthesis of starch or as a substrate for the oxidative pentose phosphate pathway, for example. We have used maize endosperm to purify a plastidic glucose 6-phosphate/phosphate translocator (GPT). The corresponding cDNA was isolated from maize endosperm as well as from tissues of pea roots and potato tubers. Analysis of the primary sequences of the cDNAs revealed that the GPT proteins have a high degree of identity with each other but share only approximately 38% identical amino acids with members of both the triose phosphate/phosphate translocator (TPT) and the phosphoenolpyruvate/phosphate translocator (PPT) families. Thus, the GPTs represent a third group of plastidic phosphate antiporters. All three classes of phosphate translocator genes show differential patterns of expression. Whereas the TPT gene is predominantly present in tissues that perform photosynthetic carbon metabolism and the PPT gene appears to be ubiquitously expressed, the expression of the GPT gene is mainly restricted to heterotrophic tissues. Expression of the coding region of the GPT in transformed yeast cells and subsequent transport experiments with the purified protein demonstrated that the GPT protein mediates a 1:1 exchange of glucose 6-phosphate mainly with inorganic phosphate and triose phosphates. Glucose 6-phosphate imported via the GPT can thus be used either for starch biosynthesis, during which process inorganic phosphate is released, or as a substrate for the oxidative pentose phosphate pathway, yielding triose phosphates.

Abstract: We have cloned a gene involved in starch metabolism that was identified by the ability of its product to bind to potato starch granules. Reduction in the protein level of transgenic potatoes leads to a reduction in the phosphate content of the starch. The complementary result is obtained when the protein is expressed in Escherichia coli, as this leads to an increased phosphate content of the glycogen. It is possible that this protein is responsible for the incorporation of phosphate into starch-like glucans, a process that is not understood at the biochemical level. The reduced phosphate content in potato starch has some secondary effects on its degradability, as the respective plants show a starch excess phenotype in leaves and a reduction in cold-sweetening in tubers.

Abstract: Summary Organic acids have been implicated in many soil-forming and rhizosphere processes, but their fate in soil is poorly understood. We examined the sorption of four simple short-chain organic acids (citric, oxalic, malic and acetic) in five acid soils and on synthetic iron hydroxide (ferrihydrite). The results for both soils and ferrihydrite indicated that the sorption depended on concentration in the following order of strength: phosphate >> oxalate > citrate > malate >> acetate. The sorption reactions in soil were shown to be little influenced by pH, whereas for ferrihydrite, sorption of all ligands increased strongly with decreasing pH. The sorption of organic anions onto ferrihydrite was influenced to a lesser extent by the presence of metal cations in solution. From the results we calculated that when organic acids enter solution they rapidly become sorbed onto the soil's exchange complex (> 80% within 10 min), and we believe that this sorption will greatly diminish their effectiveness to mobilize nutrients from the rhizosphere.

Abstract: The change in potential during repassivation of titanium in artificial bioliquids was examined, and the regenerated surface oxide film on titanium was characterized using X-ray photoelectron spectroscopy and Auger electron spectroscopy to elucidate the repassivation reaction of titanium in a biological system. The repassivation rate in Hanks' solution was slower than that in saline and was not influenced by the pH of the solution. This indicates that more titanium ions dissolve in a biological system than hitherto was predicted when the surface film is destroyed. Phosphate ions are taken up preferentially in the surface film during regeneration, and the film consists of titanium oxide and titanium oxyhydroxide containing titanium phosphate. Calcium ions and phosphate ions are adsorbed by the film after regeneration, and calcium phosphate or calcium titanium phosphate is formed at the outermost surface. Ions constituting Hanks' solution other than calcium and phosphate were absent from the surface oxide.

Abstract: Thermally processed hydroxyapatite coatings used on dental implants and hip prostheses for enhanced fixation may typically consist of a number of chemical and structural phases. These phases affect coating performance and tissue attachment. Hydroxyapatite was plasma sprayed to examine the phase evolution during processing. Coatings were examined with X-ray diffraction and elemental analysis. Results indicate that phase transformations are produced by (a) preferential removal of hydroxyl and phosphate leading to a change in melt composition, and (b) the high cooling rate due to the thermal spray process. Hydroxyl group removal promotes the amorphous phase and oxyapatite. Further heating produces a less viscous melt facilitating decomposition of hydroxyapatite to tricalcium and tetracalcium phosphate. Phosphate removal during flight produces a more calcium-rich melt preferring tetracalcium phosphate and calcium oxide formation. A proposed model shows the phase location within the lamellae of these coatings. Coating processes must thus prevent removal of hydroxide and phosphate during processing to maximize the hydroxyapatite content.

Abstract: This study was designed to investigate the in vivo biodegration and biocompatibility of a poly(propylene fumarate) (PPF)-based orthopedic biomaterial. The effects of varying the PPF to N-vinyl pyrrolidinone ratio and PPF to β-tricalcium phosphate content were studied. The composite mechanical properties and local tissue interactions were analyzed over 12 weeks. An initial increase in both compressive modulus and strength was seen for composite formulations that incorporated β-tricalcium phosphate. The samples incorporating a higher PPF to N-vinyl pyrrolidinone ratio reached a maximal compressive strength of 7.7 MPa and a maximal compressive modulus of 191.4 MPa at 3 weeks. The lower PPF to N-vinyl pyrrolidinone ratio samples gained a maximum compressive strength of 7.5 MPa initially and a compressive modulus of 134.0 MPa at 1 week. At 6 weeks, all samples for formulations incorporating β-tricalcium phosphate crumbled upon removal and were not mechanically tested. Samples that did not incorporate β-tricalcium phosphate were very weak and insufficient for bone replacement at the 4-day time point and beyond. Tissue interactions resulted in a mild inflammatory response at the initial time points and mature fibrous encapsulation by 12 weeks. © 1998 John Wiley & Sons, Inc. J. Biomed Mater Res, 41, 1–7, 1998.

Abstract: Native microflora present in the alkaline vertisols and two phosphate-solubilizing bacteria (PSB) isolated from soil using conventional screening media could not release phosphorus from alkaline Indian vertisol soils supplemented with carbon and nitrogen sources. The two PSBs could solubilize both rock phosphate and di-calcium phosphate in unbuffered media but failed to solubilize rock phosphate in buffered media. The organic acids secreted by these PSBs were 20-50 times less than that required to solubilize phosphorus from alkaline soil.

Abstract: not available for EP1114005Abstract of corresponding document: WO0006518The invention provides a set gypsum-containing product having increased resistance to permanent deformation and a method for preparing it comprising forming a mixture of a calcium sulfate material, water, and an appropriate amount of one or more enhancing materials chosen from condensed phosphoric acids, each of which comprises 2 or more phosphoric acid units; and salts or ions of condensed phosphates, each of which comprises 2 or more phosphate units. The mixture is then maintained under conditions sufficient for the calcium sulfate material to form a set gypsum material.

Abstract: myo-Inositol hexaphosphate, the salt of myo-inositol hexaphosphoric acid (IP6), is a common constituent of many plant foods, such as cereals and legumes. IP6 interacts with mineral elements, influencing their bioavailability. Processed foods contain a mixture of different inositol phosphates, i.e., IP6 and its degradation products with five or less phosphate groups (IP5-IP1). The interaction of the lower inositol phosphates with mineral elements is not well-known. In this study, the interaction between metal ions (Cu2+, Zn2+, and Cd2+) and isolated fractions of inositol phosphates with 6, 5, 4 and 3 phosphate groups (IP6-IP3) was investigated by using a potentiometric technique. The study was performed at pH 3-7, which is the pH range in the upper part of the duodenum, where mineral absorption takes place. The inositol phosphate fractions studied had a pronounced binding capacity between pH 5 and 7. Thus, mineral complex formation with lower inositol phosphates is likely to occur in the duodenum, which would be important from a nutritional point of view. The mineral binding capacity as calculated per phosphate group was similar for IP6, IP5, IP4, and IP3, but the binding strength was lower for the lower inositol phosphates (IP4 and IP3). At increasing pH, within the range (pH 3-7), the metal complex formation generally began in the order copper, zinc, cadmium for all inositol phosphates indicating the same order of binding strength, i.e., Cu>Zn>Cd. For IP6 the difference was small between Cu and Zn. (Less)

Abstract: A strong positive relationship between the molar P/Fe ratio in fresh hydrothermal Fe ferrihydrite precipitates and seawater-dissolved phosphate has been demonstrated using samples from the Atlantic and Pacific Oceans. We ascribe this relationship to scavenging of dissolved phosphate from seawater during the formation of hydrothermal Fe-rich particles above hydrothermal vents. In contrast, molar V/Fe ratios in hydrothermal particles are inversely correlated with dissolved phosphate. These results indicate that inter-ocean variations in dissolved phosphate control the P/Fe and V/Fe ratios in hydrothermal Fe precipitates, one of the precursors of metalliferous sediment.

Abstract: Reactivities of eight phosphate diesters each coordinated to a dinuclear Co(III) complex were investigated ([Co2(tacn)2(OH)2{O2P(OR)2}]3+; tacn = 1,4,7-triazacyclononane). Four of the complexes were coordinated by substituted phenyl methyl phosphates (substituent m-F, p-NO2 (1a); p-NO2 (1b); m-NO2 (1c); unsubstituted (1d)) and two by substituted phenyl 2-hydroxypropyl phosphates (substituent p-NO2 (2a); unsubstituted (2b)). Reactivities of dialkyl phosphates coordinated to the dinuclear Co(III) complex (1,2-propylene phosphate (3); dimethyl phosphate (4)) were also investigated. Hydrolysis of the phosphate diesters in 1a to 1d takes place by intramolecular oxide attack on the bridging phosphate while hydrolysis of 3 principally takes place by intermolecular hydroxide attack on the bridging phosphate. The diester in 2a cleaves by intramolecular oxide attack while that in 2b cleaves by intramolecular transesterification. Dimethyl phosphate dissociates from 4 without any observable cleavage of the diester. T...

Abstract: The synthesis, structure, and acid function of solid phosphoric acid (SPA) catalyst were studied in detail. 31P and 29Si MAS NMR and X-ray powder diffraction identified the following crystalline silicon phosphate phases in SPA: Si5O(PO4)6, hexagonal-SiP2O7, Si(HPO4)2·H2O, and SiHP3O10. The acidity of SPA is due to a liquid or glassy solution of phosphoric acid oligomers supported on the silicon phosphate phases. 15N MAS NMR of adsorbed pyridine-15N and 13C MAS NMR of adsorbed acetone-2-13C showed Bronsted acid sites and no Lewis acid sites. 1H→15N→31P and 1H→13C→31P double cross polarization MAS NMR of the probe molecules provided a rare opportunity to use NMR to unambiguously localize chemisorption sites; the probe molecules are complexed to phosphoric acid and pyrophosphoric acid but not to the silicon phosphate phases. In situ NMR of the oligomerization of propene on SPA suggests that propene quantitatively reacts with phosphoric acid and its oligomers to form isopropyl phosphate, and formation of thi...

Abstract: The adsorption of citrate on hydroxyapatite (HA) has been studied at 25°C, pH 6 and 8, and at 37°C, pH 8 The experimental results agree with the Langmuir adsorption model at low citrate concentrations, with similar values of the affinity coefficient K The amount adsorbed Q decreases with the increase of pH and the rise in temperature However, the fraction of sites occupied on the HA surface is the same at both values of pH On the other hand, the desorption is higher at pH 8 and zeta potential values of suspensions prepared from HA preadsorbed with citrate are negative and decrease with the rise of pH The adsorption takes place by ionic exchange of phosphate by citrate ions at the solid-solution interface, caused by a higher affinity of citrate than phosphate species for the Ca-sites on the HA surface To explain experimental data we propose a model where citrate species interact in different ways: cit 3− interacts weakly in a bidentate manner (1 citrate per 2 Ca sites), whereas the Hcit 2− interaction is stronger (1 citrate per 1 Ca site) than the previous one, possibly due to certain resonance between a monodentate (using 1 -COO − group) and a surface–chelate interaction (using 2 -COO − groups)

Abstract: Dicalcium phosphate dihydrate (DCPD) was hydrolysed in water and in 1 M Na2HPO4 solution at temperatures from 25-60 degrees C. Hydrolysis was incomplete in water. At 25 degrees C, DCPD partially hydrolysed to hydroxyapatite (HAp). Formation of HAp is indicative of incongruent DCPD dissolution. At the higher temperatures, hydrolysis to HAp was more extensive and was accompanied by the formation of anhydrous dicalcium phosphate (DCP). Both of these processes are endothermic. When hydrolysis was carried out in 1 M Na2HPO4 solution, heat absorption was greater at any given temperature than for hydrolysis in water. Complete hydrolysis to HAp occurred in this solution. The hydrolysis of DCPD to HAp in sodium phosphate solution was also endothermic. The complete conversion of DCPD to HAp in sodium phosphate solution would not be expected if the only effect of this solution was to cause DCPD dissolution to become congruent. Because of the buffering capacity of a dibasic sodium phosphate solution, DCPD hydrolysed completely to HAp. Complete conversion to HAp was accompanied by the conversion of dibasic sodium phosphate to monobasic sodium phosphate. The formation of DCP was not observed indicating that the sodium phosphate solution precluded the DCPD-to-DCP dehydration reaction. In addition to affecting the extent of hydrolysis, reaction in the sodium phosphate solution also caused a morphological change in the HAp which formed. HAp formed by hydrolysis in water was needle-like to globular while that formed in the sodium phosphate solution exhibited a florette-like morphology.

Abstract: The widespread occurrence of soil Pb contamination requires a good understanding of the factors controlling Pb solubility. Pb solubility will often be controlled by phosphates, which are used to reduce environmental risks of Pb-contaminated soils. The solubility equilibria of two different synthetic lead phosphate minerals were determined electrochemically across a wide range of pH and Pb and phosphate concentrations. The resulting chemical equilibrium data could not be explained by standard solubility equations, although a simple empirical regression explained the data very well. The same lead phosphate mineral was then added to two different soils which were equilibrated across a pH range 4−8. Differential pulse anodic stripping voltammetry was used to determine the ASV-labile Pb in the extracted soil solutions, and the free Pb2+ ion activity was calculated. The free Pb2+ activity in the soil solutions followed the expected pH relationship, highest solubility at low pH and gradual decrease with increasi...

Abstract: Laboratory growth experiments were conducted to investigate the oxygen isotope effects associated with bacterial metabolism of phosphatic compounds commonly available in nature. The observed oxygen isotope fractionations suggest complex patterns of exchange between dissolved inorganic phosphate (P i ) and water, and significant circulation of P i between intracellular and extracellular locations with extensive recycling of the dissolved P i pool, even at high concentrations of dissolved P i . Results of these experiments also support current models for bacterial utilization of phosphate. These results have important implications for the use of delta 18 O values of dissolved P i to trace sources of P, and bear on integrity of original oxygen isotope compositions of biogenic and sedimentary apatite minerals that have been subjected to processes of recrystallization and diagenesis. SEM images of laboratory synthesized apatite minerals show that similar textural features may be produced by microbially mediated and abiotic reactions, and that spheroidal structures may be produced by processes of dissolution as well as precipitation. The interpretation of certain mineral structures as microbial in origin solely on the basis of morphological and textural features may be misleading.

Abstract: Crystalline hydroxyapatite (HAP) is generally considered to be the final, stable product in the precipitation of calcium and phosphate ions from neutral to basic solutions. However, over the broad range of solution conditions in which precipitation occurs spontaneously, unstable amorphous products precede the appearance of the HAP phase. These amorphous calcium phosphates (ACPs) are unique among calcium phosphate salts in that they lack the long-range, periodic atomic scale order of crystalline materials. Although this uniqueness has been the subject of considerable interest, of greater relevance to understanding the dynamics of HAP formation by spontaneous precipitation is the instability of these solids in solution. Above pH 9, ACPs convert directly into HAP. However, in the 7 9 pH range, ACPs are the immediate precursors to octacalcium phosphate (OCP) like phases that, in turn, convert to stable HAP. These transformation processes and the possible role they play in biological calcification, more than anything else, raises the importance of the ACPs above being merely laboratory curiosities and places them in the mainstream of calcium phosphate chemistry. This chapter will cover the preparation and properties of the ACPs, their thermodynamic and kinetic relationship to crystalline calcium phosphates, especially OCP and RAP, the controversy surrounding their true structural nature, and their putative presence and role in vivo.