Phosphate-containing Solutions Research Articles

The Capture of Cadmium from Solution during the Replacement of Calcite by Apatite.

The capture of cadmium (Cd) from phosphate-containing solutions during the replacement of CaCO3 by phosphate phases such as hydroxylapatite (HAP) and tricalcium phosphate (TCP) has been studied under high and low temperature and pressure conditions using atomic force microscopy, scanning electron microscopy equipped with an X-ray spectrometer and a backscattered electron detector, Raman spectroscopy, and microprobe analysis. Starting with cubes of Carrara Marble (polycrystalline calcite) and single crystals of calcite, a new solid phosphate phase was observed to incorporate Cd from solution, formed under different pressure and temperature conditions tested. Results showed that Cd precipitated in a new phase on the surface of all samples tested. In Carrara Marble, pseudomorphic replacement of CaCO3 is restricted possibly due to kinetic limitation caused by the adsorption of Cd complexes formed in solution at reactive surface sites and the variation of fluid composition inside the sample. However, on the sample surface, this kinetic limitation is less influential, so the new phase could incorporate higher amounts of Cd faster. Furthermore, this reaction at room temperature was found to have similar and/or better Cd-uptake efficiency as HAP and CaCO3 in pure Cd solution through the precipitation of Cd-containing phosphate crystals on the sample surface. Both reactions were able to capture Cd in the precipitating phase structure and could provide a mechanism for simultaneous Cd and phosphate removal from solutions contaminated with both, in industrial or natural settings.

Electrochemical properties of hydroxyapatite immobilization material for potential cytosensor fabrication

Aim: The biorecognition unit of an electrochemical biosensor requires molecules that are immobilised to serve as a bridge between the recognition unit and the transducing surface. Unique materials that enhance immobilisation of biorecognition molecules and improve electrochemical signal transduction are important in overcoming challenges based on the sensitivity of biosensors. In this regard, the electrochemical properties (EPs) of hydroxyapatite (HAp) material for the direct immobilisation of cells was investigated. Methods: Snail shell HAp (SHAp) material was synthesised from Achatina achatina snail shells and phosphate-containing solutions. The SHAp material was characterised using X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy to determine the structural configuration, after which it was blended with a conductive polymer [poly(3,4-ethylenedioxythiophene): poly-4-styrene sulfonate (PEDOT: PSS)] to improve the electrochemical responses. The SHAp/PEDOT: PSS blend was used to modify a screen-printed carbon electrode (SPCE) by drop-casting, followed by seeding of pheochromocytoma (PC 12) and human embryonic kidney (HEK)-293T cells on the modified SPCE to record the EP using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Red blood cells (RBCs) were used as a control. Results: The CV analysis showed lower peak currents for HEK 293T (50 µA) and PC 12 (120 µA) compared to the RBC (230 µA). Also, the EIS showed impedance values of 0.70 for HEK 293T, 0.62 for PC 12, and 0.52 mΩ for RBC. The findings indicate that SHAp/PEDOT: PSS enables the differentiation of cell proliferation signals through voltammetric and impedimetric measurements. Conclusions: The unique current and impedance differences among the cells could serve as potential markers for rapid cell detection.

Recovering struvite from livestock wastewater by fluidized-bed homogeneous crystallization as a pre-treatment process to sludge co-digestion

Livestock wastewater can contain high levels of phosphates and trace amounts of various ionic species harming the environment and human health. These ions can be successfully removed from livestock effluent and recovered in a non-toxic crystal form via crystallization. The fluidized bed homogeneous crystallization (FBHC) technology is a cutting-edge pretreatment method that removes phosphate and ammonium by crystallizing struvite. The findings demonstrated a 37% removal for ammonium solutions alone, 38% with copper, 35% with zinc, and 33% when copper and zinc were present, while the crystallization efficiency was achieved at 35%, 33% with copper, 28% with zinc, and 26% with copper and zinc. For phosphate-containing solutions, 95% was removed, 81% with copper, 96% with zinc, and 88% with copper and zinc. Similarly, crystallization efficiency was attained at 87%, 60% with copper, 94% with zinc, and 81% when copper and zinc were combined with phosphates. For ammonium solutions, copper and zinc reduced the removal and crystallization efficiency at constant pH and increased at increasing pH. For phosphate solutions, the removal and crystallization efficiencies increased at increasing pH. However, zinc ions resulted in the highest removal, and crystallization efficiency for phosphate solutions was attained. Based on SEM, EDS, XRD, and XPS analyses, the peaks revealed the presence of struvite in the form of magnesium ammonium phosphate.

A simplified protocol of regional citrate anticoagulation with phosphate-containing solutions in infants and children treated with continuous kidney replacement therapy.

Regional citrate anticoagulation (RCA) is the preferred modality of anticoagulation used in continuous kidney replacement therapy (CKRT) in adults and less extensively in children. Potential metabolic complications limit widespread use in infants, neonates, and in children with liver failure. We report our experience with a simplified protocol in 50 critically ill children, infants, and neonates, some of them with liver failure, with commercially available solutions containing phosphorous and higher concentration of potassium and magnesium. RCA allowed attainment of a mean filter lifetime of 54.5 ± 18.2h, 42.5% of circuits lasted more than 70h, and scheduled change was the most frequent cause of CKRT interruption. Patient Ca++ and circuit Ca++ were maintained in the target range with mean values of 1.15 ± 0.13mmol/l and 0.38 ± 0.07mmol/l, respectively. No session had to be stopped because of metabolic complications. The most frequent complications were hyponatremia, hypomagnesemia, and metabolic acidosis mostly related to primary disease and critical illness. No session had to be stopped because of citrate accumulation (CA). Transitory CA occurred in 6 patients and was managed without requiring RCA interruption. No patients with liver failure presented CA episodes. In our experience, RCA with commercially available solutions was easily applied and managed in critically ill children, even in patients with low weight or with liver failure. Solutions containing phosphate and higher concentrations of magnesium and potassium allowed reduction of metabolic derangement during CKRT. Prolonged filter life was ensured with no detrimental effects on patients and reduced staff workload. A higher resolution version of the Graphical abstract is available as Supplementary information.

How Chemical Nature of Fixed Groups of Anion-Exchange Membranes Affects the Performance of Electrodialysis of Phosphate-Containing Solutions?

Innovative ion exchange membranes have become commercially available in recent years. However, information about their structural and transport characteristics is often extremely insufficient. To address this issue, homogeneous anion exchange membranes with the trade names ASE, CJMA-3 and CJMA-6 have been investigated in NaxH(3-x)PO4 solutions with pH 4.4 ± 0.1, 6.6 and 10.0 ± 0.2, as well as NaCl solutions with pH 5.5 ± 0.1. Using IR spectroscopy and processing the concentration dependences of the electrical conductivity of these membranes in NaCl solutions, it was shown that ASE has a highly cross-linked aromatic matrix and mainly contains quaternary ammonium groups. Other membranes have a less cross-linked aliphatic matrix based on polyvinylidene fluoride (CJMA-3) or polyolefin (CJMA-6) and contain quaternary amines (CJMA-3) or a mixture of strongly basic (quaternary) and weakly basic (secondary) amines (CJMA-6). As expected, in dilute solutions of NaCl, the conductivity of membranes increases with an increase in their ion-exchange capacity: CJMA-6 < CJMA-3 << ASE. Weakly basic amines appear to form bound species with proton-containing phosphoric acid anions. This phenomenon causes a decrease in the electrical conductivity of CJMA-6 membranes compared to other studied membranes in phosphate-containing solutions. In addition, the formation of the neutral and negatively charged bound species suppresses the generation of protons by the "acid dissociation" mechanism. Moreover, when the membrane is operated in overlimiting current modes and/or in alkaline solutions, a bipolar junction is formed at the CJMA- 6/depleted solution interface. The CJMA-6 current-voltage curve becomes similar to the well-known curves for bipolar membranes, and water splitting intensifies in underlimiting and overlimiting modes. As a result, energy consumption for electrodialysis recovery of phosphates from aqueous solutions almost doubles when using the CJMA-6 membrane compared to the CJMA-3 membrane.

Formation of environmentally friendly protective Ce2O3-CeO2 conversion coatings on Al, modified by phosphate layers: chemical and electrochemical characterization

Conversion ceria coatings were deposited on substrates of Al-1050 in a solution containing CeCl3×7H2O and CuCl2×2H2O. The post-treatment of as deposited coatings was realized in phosphate-containing solutions: 0.08 M Na3PO4 or 0.22 M NH4H2PO4. The XPS characterization of the surface of samples was carried out on an AXIS Supra electronspectrometer (KratosAnalytical Ltd.). The electrochemical investigations and determination of the basic corrosion parameters (Ecor, icor, Epit, EOCP, Rp, CR, etc.) for the studied systems were carried out on a Gamry Interface 1000 (EISSFR Analyzer EIS300). Based on the XPS investigations, it was ascertained that there is a substantial influence of the “pretreatment” and “post-treatment” operations on the chemical composition and chemical state of the elements on the samples` surface. It is expressed by a strong decrease in the concentration of Аl2O3 and Ce2O3+CeO2 components in the ceria coatings at the expense of formation of AlPO4 and AlOOH, CePO4, as well as PO3-, P2O5 and P4O10 compounds with Al and Се. The comparison of the results of Rp values and concentrations of Ce3+/Се4+, Al and P shows that the changes in Rp and quantity of Се4+ and P on the surface of the studied samples are directly related. The supposed and proved formation of low-soluble corrosion products on the surface of the studied systems and accomplished synergic effect of protective action by the formed cerium and aluminum oxides/phosphates layers determine the increase of the Rp and decrease of icor and CR, respectively. It was also concluded that the mixed conversion layers are a more effective barrier for the chloride ions diffusion to the metal surface and increase the corrosion resistance of Al 1050 to pitting and general corrosion.

Contrasting Trivalent Lanthanide and Actinide Complexation by Polyoxometalates via Solution-State NMR.

Deciphering the solution chemistry and speciation of actinides is inherently difficult due to radioactivity, rarity, and cost constraints, especially for transplutonium elements. In this context, the development of new chelating platforms for actinides and associated spectroscopic techniques is particularly important. In this study, we investigate a relatively overlooked class of chelators for actinide binding, namely, polyoxometalates (POMs). We provide the first NMR measurements on americium-POM and curium-POM complexes, using one-dimensional (1D) 31P NMR, variable-temperature NMR, and spin-lattice relaxation time (T1) experiments. The proposed POM-NMR approach allows for the study of trivalent f-elements even when only microgram amounts are available and in phosphate-containing solutions where f-elements are typically insoluble. The solution-state speciation of trivalent americium, curium, plus multiple lanthanide ions (La3+, Nd3+, Sm3+, Eu3+, Yb3+, and Lu3+), in the presence of the model POM ligand PW11O397- was elucidated and revealed the concurrent formation of two stable complexes, [MIII(PW11O39)(H2O)x]4- and [MIII(PW11O39)2]11-. Interconversion reaction constants, reaction enthalpies, and reaction entropies were derived from the NMR data. The NMR results also provide experimental evidence of the weakly paramagnetic nature of the Am3+ and Cm3+ ions in solution. Furthermore, the study reveals a previously unnoticed periodicity break along the f-element series with the reversal of T1 relaxation times of the 1:1 and 1:2 complexes and the preferential formation of the long T1 species for the early lanthanides versus the short T1 species for the late lanthanides, americium, and curium. Given the broad variety of POM ligands that exist, with many of them containing NMR-active nuclei, the combined POM-NMR approach reported here opens a new avenue to investigate difficult-to-study elements such as heavy actinides and other radionuclides.

Effect of Pulsed Electric Field on the Electrodialysis Performance of Phosphate-Containing Solutions.

A comparative analysis of mass transfer characteristics and energy consumption was carried out for the electrodialysis recovery of PV from of NaH2PO4 solutions and multicomponent (0.045 M NaxH(3-x)PO4, 0.02 M KCl, 0.045 M KOH, 0.028 M CaCl2, and 0.012 M MgCl2, pH 6.0 ± 0.1) solution in conventional continuous current (CC) and pulsed electric field (PEF) modes. The advantages of using PEF in comparison with CC mode are shown to increase the current efficiency and reduce energy consumption, as well as reduce scaling on heterogeneous anion-exchange membranes. It has been shown that PEF contributes to the suppression of the "acid dissociation" phenomenon, which is specific for anion-exchange membranes in phosphate-containing solutions. Pulse and pause lapse 0.1 s-0.1 s and duty cycle 1/2 were found to be optimal among the studied PEF parameters.

Association of Phosphate-Containing versus Phosphate-Free Solutions on Ventilator Days in Patients Requiring Continuous Kidney Replacement Therapy.

Hypophosphatemia is commonly observed in patients receiving continuous KRT. Patients who develop hypophosphatemia may be at risk of respiratory and neuromuscular dysfunction and therefore subject to prolongation of ventilator support. We evaluated the association of phosphate-containing versus phosphate-free continuous KRT solutions with ventilator dependence in critically ill patients receiving continuous KRT. Our study was a single-center, retrospective, pre-post cohort study of adult patients receiving continuous KRT and mechanical ventilation during their intensive care unit stay. Zero-inflated negative binomial regression with and without propensity score matching was used to model our primary outcome: ventilator-free days at 28 days. Intensive care unit and hospital lengths of stay as well as hospital mortality were analyzed with a t test or a chi-squared test, as appropriate. We identified 992 eligible patients, of whom 649 (65%) received phosphate-containing solutions and 343 (35%) received phosphate-free solutions. In multivariable models, patients receiving phosphate-containing continuous KRT solutions had 12% (95% confidence interval, 0.17 to 0.47) more ventilator-free days at 28 days. Patients exposed to phosphate-containing versus phosphate-free solutions had 17% (95% confidence interval, -0.08 to -0.30) fewer days in the intensive care unit and 20% (95% confidence interval, - 0.12 to -0.32) fewer days in the hospital. Concordant results were observed for ventilator-free days at 28 days in the propensity score matched analysis. There was no difference in hospital mortality between the groups. The use of phosphate-containing versus phosphate-free continuous KRT solutions was independently associated with fewer ventilator days and shorter stay in the intensive care unit.

ZnO Transducers for Photoluminescence-Based Biosensors: A Review

Zinc oxide (ZnO) is a wide bandgap semiconductor material that has been widely explored for countless applications, including in biosensing. Among its interesting properties, its remarkable photoluminescence (PL), which typically exhibits an intense signal at room temperature (RT), arises as an extremely appealing alternative transduction approach due to the high sensitivity of its surface properties, providing high sensitivity and selectivity to the sensors relying on luminescence output. Therefore, even though not widely explored, in recent years some studies have been devoted to the use of the PL features of ZnO as an optical transducer for detection and quantification of specific analytes. Hence, in the present paper, we revised the works that have been published in the last few years concerning the use of ZnO nanostructures as the transducer element in different types of PL-based biosensors, namely enzymatic and immunosensors, towards the detection of analytes relevant for health and environment, like antibiotics, glucose, bacteria, virus or even tumor biomarkers. A comprehensive discussion on the possible physical mechanisms that rule the optical sensing response is also provided, as well as a warning regarding the effect that the buffer solution may play on the sensing experiments, as it was seen that the use of phosphate-containing solutions significantly affects the stability of the ZnO nanostructures, which may conduct to misleading interpretations of the sensing results and unreliable conclusions.

Investigation of Causes of Low Current Efficiency in Electrodialysis of Phosphate-Containing Solutions

Investigation of Causes of Low Current Efficiency in Electrodialysis of Phosphate-Containing Solutions

Effect of platelet-poor plasma additive on the formation of biocompatible calcium phosphates

Biocompatible calcium phosphates were synthesized by mixing calcium- and phosphate-containing solutions in medium with various pH value, which contained up to 6 vol.% of platelet-poor plasma (PPP). Depending on the pH of precipitation medium, the influence of PPP components favored the formation of calcium-deficient hydroxyapatites with varying composition. In neutral medium, dicalcium phosphate dihydrate (DCPD) was the predominant phase but the buffering properties of PPP favored formation up to 24 wt.% of apatitic tricalcium phosphate. In alkaline medium, negatively charged surface of the PPP component macromolecules inhibited Ca2+ diffusion, which in turn lowered the Ca/P molar ratio of the formed hydroxyapatite from 1.67 to 1.62. After soaking in simulated body fluid (SBF), DCPD underwent hydrolysis yielding 29 wt.% of octacalcium phosphate and 19 wt.% of apatitic tricalcium phosphate and hydrolyzed DCPD/PPP sample contained 9 wt.% and 42 wt.% of octacalcium phosphate and apatitic tricalcium phosphate. Calcium-deficient hydroxyapatite in HA/PPP sample consumed the ions of SBF with an increase of its Ca/P molar ratio from 1.62 up to 1.66. In both cases, the Ca/P molar ratio of the calcium phosphates increased, indicating the apatite forming ability of the obtained calcium phosphates. Obtained results seem to be promising in development of new generation of hybrid composites based on calcium phosphates and blood components.

Detection of Ru potential metallodrug in human urine by MALDI-TOF mass spectrometry: Validation and options to enhance the sensitivity

We studied the possibility of detection of [Ru(η5-C5H5)(PPh3)2Cl] (abbreviated by RuCp) complex as a model system for Ru-based metallodrugs in human urine by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) without previous purification or removal of inorganic salts. Inorganic salts might prevent the detection of RuCp by MALDI-TOF MS, most likely through the increased number and intensity of background/organic matrix signals. This problem might be overcome by the acquisition of matrix-free spectra and the addition of nanoparticles, such as carbon dots, to the urine solution. Our results suggest that RuCp is easily detectable by MALDI-TOF MS in all acquisition conditions, with the CHCA matrix being the best for acquisition in phosphate-containing solutions, whereas in urine, DHB and matrix-free approach demonstrated the highest sensitivity, precision, and reproducibility. The sensitivity of matrix-free MALDI detection of RuCp could be increased by the addition of carbon dots to the urine. Based on theoretical calculations for all matrix/analyte combinations, the model for the interaction of RuCp with carbon dots was established, and higher sensitivity explained.

Effect of a nanocomposite containing ostrich eggshell on calvarium healing in the rabbit: a pathologic study

The aim of the current study was to determine effect of a nanocomposite containing ostrich eggshell (NCOE) on the calvarium healing in the rabbit. Fresh ostrich eggshell was ground (300-500 μm), treated in phosphate-containing solutions and sterilized by gamma irradiation. Fifteen New Zealand white adult male rabbits were used. Four full-thickness skull defects were created in the calvarium. The first defect kept unfilled (control). The second defect was filled with autograft bone. The third defect was filled using NCOE. The fourth defect was filled with mixture of the autograft+NCOE bone. At 30, 60 and 90 days after surgery animals were euthanized and tissue specimens were collected and stained with hematoxylin eosin and trichrome staining method. Microsections were examined toassess the extent and intensity of inflammation, calvarium formation status and foreign body reaction. According to the results, filling defect significantly increased in NCOE-treated rabbits compared to the control group at 30 and 60 days post-surgery (P&lt;0.05). There a statistically significant difference between experimental groups compared to the control group at 30 and 60 days post-surgery (P&lt;0.05) while no statistically significant differences were observed among autograft, NCOE, autograft+NCOE (P&gt;0.05). Also, absorb material significantly decreased in NCOE and autograft+NCOE groups compared to the control group at 60 days post-surgery (P&lt;0.05). The filling defect significantly increased in autograft, NCOE and NCOE+autograft groups compared to the control group at 90 days post-surgery (P&lt;0.05). There was no significant difference on inflammation and absorb material among the groups at 90 days post-surgery (P&gt;0.05). These results suggested NCOE+autograft has improved the rate of calvarium healing in rabbits.

Hypophosphatemia in critically ill patients with acute kidney injury on renal replacement therapies.

Hypophosphatemia is a common but often underestimated electrolyte derangement among intensive care unit (ICU) patients. Low phosphate levels can lead to cellular dysfunction with potentially relevant clinical manifestations (e.g., muscle weakness, respiratory failure, lethargy, confusion, arrhythmias). In critically ill patients with severe acute kidney injury (AKI) renal replacement therapies (RRTs) represent a well-known risk factor for hypophosphatemia, especially if the most intensive and prolonged modalities of RRT, such as continuous RRT or prolonged intermittent RRT, are used. Currently, no evidence-based specific guidelines are available for the treatment of hypophosphatemia in the critically ill; however, considering the potentially negative impact of hypophosphatemia on morbidity and mortality, strategies aimed at reducing its incidence and severity should be timely implemented in the ICUs. In the clinical setting of critically ill patients on RRT, the most appropriate strategy could be to anticipate the onset of RRT-related hypophosphatemia by implementing the use of phosphate-containing solutions for RRT through specifically designed protocols. The present review is aimed at summarizing the most relevant evidence concerning epidemiology, prognostic impact, prevention and treatment of hypophosphatemia in critically ill patients with AKI on RRT, with a specific focus on RRT-induced hypophosphatemia.

Solubility-pH profile of desipramine hydrochloride in saline phosphate buffer: Enhanced solubility due to drug-buffer aggregates

Although solubility-pH data for desipramine hydrochloride (DsHCl) have been reported previously, the aim of the present study was to critically examine the aqueous solubility-pH behavior of DsHCl in buffer-free and buffered solutions, in the presence of physiologically-relevant chloride concentration, using experimental practices recommended in the recently-published “white paper” (Avdeef et al., 2016). The computer program pDISOL-X was used to design the structured experiments (pH-RSF method), to process the data, and to refine the equilibrium constants. Low-to-high and high-to-low pH assays (using HCl, H3PO4, or NaOH to adjust pH) were performed on phosphate-buffered (0.12‑0.15 M) saturated solutions of DsHCl in the pH 1.3–11.6 range. After equilibration (stirring 6 h, followed by 18 h stir-free sedimentation), filtration or centrifugation was used for phase separation. Concentration was measured using HPLC with UV/VIS detection. The 2:1 drug-phosphate solubility product (Ksp2:1 = [DsH+]2[HPO42−]) was determined from data in the pH 4–9 region. The free base of desipramine was prepared and used to determine the Ksp1:1 ([DsH+][H2PO4−]) in chloride-free acidified suspension. In addition, phosphate-free titrations were conducted to determine the intrinsic solubility, S0, and the 1:1 drug-chloride solubility product, KspDsHCl = [DsH+][Cl−]. Under the assay conditions, only the phosphate-free solutions showed some supersaturation near pHmax 8.0. In phosphate-containing solutions, pHmax was indicated at higher pH (8.8–9.6). Oils mixed with solids were observed to form in alkaline solutions (pH > 11). Notably, soluble drug-phosphate complexes appeared to form below pH 3.9 and above pHmax in saturated phosphate‑containing saline solutions. This was indicated by the systematic pH shift to higher values in the log S-pH curve in alkaline solution than expected from the Henderson-Hasselbalch equation. For pH < 3.9, saturated phosphate-containing saline solutions exhibited elevated solubility, with drug-hydrochloride as the sole precipitate. Salt solubility products, intrinsic solubility, and complexation constants, which rationalized the data, were determined. Elemental, thermogravimetric (TGA), differential scanning calorimetric (DSC), and powder X-ray diffraction (PXRD) analyses were used to characterize the precipitates isolated from suspensions at different pH.

Growth dynamics of vaterite in relation to the physico-chemical properties of its precursor, amorphous calcium carbonate, in the Ca-CO3-PO4system

Vaterite is one of three non-hydrate calcium carbonate crystalline polymorphs and is formed as an initial phase under pseudo-biological conditions. However, biological hard tissues that use vaterite are rare; the reason for vaterite rarely appearing in vivo is still unclear. There is consensus that, in phosphate-containing solutions, vaterite barely forms and amorphous calcium carbonate (ACC), the precursor of crystalline calcium carbonate and considered as aggregation of growth unit of vaterite, is stabilized. In this study, to clarify the biomineralization process, we investigated how phosphate acts as an inhibitor of vaterite growth. We measured vaterite growth rates in situ and estimated the essential crystal growth parameter, edge free energy, in the Ca-CO3-PO4 system in relation to the physico-chemical properties of ACC. The effects of PO4 on the ACC structure and dynamics were also observed.

Effects of Silicate, Phosphate, and Calcium on the Stability of Aldopentoses.

Ribose is an important constituent of RNA: ribose connects RNA bases and forms a strand of sugar phosphates. Accumulation of ribose on prebiotic Earth was difficult because of its low stability. Improvement in the yield of ribose by the introduction of borate or silicate in a formose-like reaction has been proposed. The effects of borates have been further analyzed and confirmed in subsequent studies. Nonetheless, the effects of silicates and phosphates remain unclear. In the present study, we incubated aldopentoses in a highly alkaline aqueous solution at a moderate temperature to determine the effects of silicate or phosphate on the degradation rates of ribose and its isomeric aldopentoses. The formation of a complex of silicate (or phosphate) with ribose was also analyzed in experiments with (29)Si and (31)P nuclear magnetic resonance (NMR). We found that silicate or phosphate complexes of ribose were not detectable under our experimental conditions. The stability of ribose and lyxose improved after addition of 40-fold molar excess (relative to a pentose) of sodium silicate or sodium phosphate to the alkaline solution. The stability was not improved further when an 80-fold molar excess of sodium silicate or sodium phosphate was added. Calcium was removed from these solutions by precipitation of calcium salts. The drop in Ca(2+) concentration might have improved the stability of ribose and lyxose, which are susceptible to aldol addition. The improvement of ribose stability by the removal of Ca(2+) and by addition of silicate or phosphate was far smaller than the improvement by borate. Furthermore, all aldopentoses showed similar stability in silicate- and phosphate-containing solutions. These results clearly show that selective stabilization of ribose by borate cannot be replaced by the effects of silicate or phosphate; this finding points to the importance of borate in prebiotic RNA formation.

Impact of acids on the structure and composition of Linde Type A zeolites for use in reverse osmosis membranes for recovery of urine-containing wastewaters

On the International Space Station (ISS) there are low pH, urine containing wastewaters that need to be recycled. We evaluated the effects of synthetic ISS wastewater on Linde Type A (LTA) zeolites to assess their applicability in membrane separations to produce potable water. Specifically, we studied the impact of the four acid-producing components found in the wastewater: chromium(VI) oxide, potassium phosphate monobasic, sodium phosphate monobasic dihydrate and sulfuric acid. We characterized effects of the acids on crystal structure, bonding, surface morphology and solid phase composition of the LTA zeolites. After 24h of exposure to synthetic wastewater brine (pH 1.94), the zeolites sustained some damage with extensive structural degradation occurring after 128h. The crystal structure of the LTA particles completely degraded in all acid-type solutions with a pH below 1 and in phosphate solutions with a pH below 5. The structural degradation resulted from the removal of aluminum from the zeolite framework. Additionally, we observed that phosphate caused changes in bonding of the zeolite, through removal of silicon from the framework and formation of aluminum phosphate precipitates. Ultimately, we found that the presence of acidic anions (specifically dihydrogen phosphate anions that catalyzed aluminum and silicon removal), rather than pH, was the most significant factor causing degradation of LTA in dihydrogen phosphate-containing solutions. Our results indicate that Linde Type A zeolites are inappropriate for use with low-pH, dihydrogen phosphate containing solutions.

Preparation and properties of calcium-silicate filled resins for dental restoration. Part I: chemical-physical characterization and apatite-forming ability

Objective. The aim of this study was to measure dimensional changes due to hygroscopic expansion and the bioactivity of two experimental methacrylate-based dental adhesives either incorporating Bioglass® 45S5 (3-E&RA/BG) or MTA (3-E&RA/WMTA). Materials and methods. 3-E&RA/BG, 3-E&RA/WMTA and a control filler-free resin blend (3-E&RA) were formulated from commercially available monomers. Water sorption (WS) and solubility (SL) behaviour were evaluated by weighing material disks at noted intervals; the relationship between degree of hydration and the glass transition temperature (Tg) was investigated by using differential scanning calorimetry (DSC). In vitro apatite-forming ability as a function of soaking time in phosphate-containing solutions was also determined. Kruskal-Wallis analysis of variance (ANOVA) was used to evaluate differences between groups for maximum WS, SL, net water uptake and the percentage change in Tg values. Post-ANOVA pair-wise comparisons were conducted using Mann-Whitney-U tests. Results. 3-E&RA/BG and 3-E&RA/WMTA exhibited values of maximum WS and net water uptake that were significantly higher when compared to 3-E&RA. However, no statistically significant differences were observed in terms of SL between all the adhesives. The addition of the Bioglass® 45S5 and MTA to the 3-E&RA showed no reduction of the Tg after 60 days of storage in deionized water. ATR Fourier Transform Infrared Spectroscopy (ATR-FTIR) of the filled resin disks soaked in DPBS for 60 days showed the presence of carbonate ions in different chemical phases. Conclusion. Dentine bonding agents comprising calcium-silicates are not inert materials in a simulated oral environment and apatite formation may occur in the intra-oral conditions. Clinical significance. A bioactive dental material which forms apatite on the surface would have several benefits including closure of gaps forming at the resin–dentine interface and potentially better bond strength over time (less degradation of bond).