Magnesium and strontium interaction with carbonate-containing hydroxyapatite in aqueous medium

Crystallographic and spectroscopic studies were performed on the solid products obtained from magnesium and strontium interaction with carbonate-containing hydroxyapatite under aqueous conditions employing a cyclic pH variation technique. Low concentrations of magnesium and strontium make easier the transformation of carbonate-containing hydroxyapatite into β-tricalcium phosphate by heat treatment. At high concentration magnesium stabilizes the β-tricalcium phosphate crystal structure while the apatite crystal structure is maintained when the Ca/Sr molar ratio decreases. It is suggested that these ions are important in determining the structure of the calcium phosphate deposits in biological tissues during the physiological and pathological local pH variations.     

Studies of strontium biokinetics in humans. Part 2: uptake of strontium from aqueous solutions and labelled foodstuffs

The accidental release of radioactive isotopes of strontium, mainly (90)Sr, into the environment and its transfer into the biosphere results in an internal radiation exposure of the affected population. In order to obtain reliable estimates of the committed dose due to an intake of Sr radionuclides, reliable information on its metabolic behaviour inside the human body is needed, i.e. biokinetic data on fractional uptake from contaminated foodstuffs, distribution to and retention in different organs and tissues of the human body. Such information can be obtained by tracer kinetic investigations. The committed effective dose is dependent on the fractional intestinal absorption of the ingested activity (f(1) value). The International Commission on Radiological Protection in its publication ICRP 67 adopted an f(1) value of 0.3 for adults. This study is aimed at investigating if the value corresponds with the actual uptake from contaminated foodstuffs. Aqueous solutions and contaminated vegetables, i.e. cress and salad (lettuce) were used as test materials. For this purpose, the methodology for intrinsic labelling of foodstuffs described in part 1 was applied. For aqueous solutions, a mean f(1) value of 0.63+/-0.14 (mean +/- SD) was obtained by administering 1 mg of strontium. The uptake of Sr from cress intrinsically labelled with about 1 mg Sr almost corresponds to that from aqueous solutions (f(1)=0.62+/-0.10), but from lettuce it is reduced by a factor of 2 (f(1)=0.27+/-0.08).     

Rheological characterization of schizophyllan aqueous solutions after denaturation-renaturation treatment

Schizophyllan (SPG) with a molecular weight of 2.6x10(6), designated SPG-1, is denatured and then renatured at a concentration of 1.8 wt % by alkalization-neutralization. The prepared denatured-renatured samples (DRSPG-1) are diluted to various concentrations and equilibrated for 10 days before rheological and intrinsic viscosity measurements. When concentration (C(p)) is above 0.75 wt %, DRSPG-1 aqueous systems have weak gel-type rheological properties. However, for 0.28 wt % 相似文献   

Alginate coated loofa sponge discs for the removal of cadmium from aqueous solutions

A biosorbent was prepared by coating the fibrous network of loofa sponge (Luffa cylindrica) with a thin film of calcium alginate. Alginate-coated loofa sponge removed Cd(II) rapidly, reaching equilibrium loading of 124 mg g(-1) in 30 min. Seventy % of equilibrium uptake was achieved in 10 min. In contrast, it took 240 min for alginate beads to reach a loading equilibrium of 88 mg g(-1) under identical conditions. The biosorption behaviour followed the Langmuir adsorption isotherm and the ACLS biosorbent was shown to be highly effective in removing Cd(II) from a 10 mg l(-1) solution in a continuous flow fixed-bed column bioreactor.     

An osmometer for aqueous biopolymer solutions

A sensitive osmometer for the study of the osmotic pressure of aqueous protein solutions is presented. Equilibrium is reached within 1 to 2 h and is reproducible to about 1 N.m-2 (= 0.01 cm H2O). The method allows the determination of dissociation constants of proteins down to 1 x 10(-8) M.     

Alcohol adsorption on softwood lignin from aqueous solutions

Lignin prepared by acid and enzyme hydrolysis of a softwood mixture adsorbs acetone, butanol, and other alcohols while showing only a slight uptake of glucose. Adsorption of butanol is independent of temperature in the range of 30-65 degrees C. The Polanyi theory fits adsorption for the linear alcohols methanol through hexanol with values of AS and Delta(mu) ranging from 2.6 to 26 J mol(-1) K(-1)and -0.8 to -8 kJ/mol. The adsorption capacity is given by Q (g alcohol/g lignin) = KC(*). Where C(*) is the equilibrium alcohol concentration (g/mL), K = epsilon(W)exp (Delta/R), and epsilon(w) is the porosity of the lignin (0.23-0.42 mL/g). The value of the adsorption capacity constant K for n-butanol ranges from 1.3 to 2.7 mL/g on sorbent containing 26-72% lignin, while ethanol is 0.5-0.73, acetone is 0.62-1.0, and glucose is 0.35. Adsorption is shown to occur through combined hydrophobic and hydrophilic interactions of the alkyl and hydroxyl groups, respectively, of the adsorbate with the lignin. Consequently, for the alcohols methanol to hexanol, we present the capacity constant K[=K(R) + K(OH)] as a sum of an alky! adsorption constant (0.1-9.5 mL/g) and a hydrophilic (0.40-0.50 mL/g) contribution. This approach may be applicable to organic acids. Lignin's sorbent properties have potential to moderate product inhibition in the anaerobic acetone-butanol-ethanol (ABE) fermentation.     

Phenol removal from aqueous solutions by peroxidase extracted from horseradish

Horseradish peroxidase (HRP) is one of the most recently used enzymes in the process of enzymatic phenol removal. It has a catalytic ability over a broad range of pH, temperature and contaminant concentrations. In this study we revealed the possibility of successful use the crude peroxidase obtained from horseradish roots for the phenol removal from aqueous solutions in the presence of the low molecular polyethylene glycol (PEG 300) at room temperature (20°C) and pH 7.2. Reaction was monitored by direct measuring of the absorbance changes in a samples taken at certain time intervals from the reaction mixture. At the first time PEG 300 was shown to be a more stabilizing effect on crude HRP and provided a higher phenol removal in comparison with PEG 3350. Crude HRP used in these study demonstrated a greater resistance on phenol and hydrogen peroxide inactivation that allowed a higher phenol removal. The highest phenol removal was achieved when the concentration of PEG 300, phenol and hydrogen peroxide were 300 mg/L, 2.0 and 2.5 mM, respectively.     

Removal of ammonium from aqueous solutions using alkali-modified biochars

Biochars converted from agricultural residuals can effectively remove ammonium from water. This work further improved the sorption ability of biochars to aqueous ammonium through alkali modification. Three modified biochars were prepared from agricultural residuals pre-treated with NaOH solution through low-temperature (300 °C) slow pyrolysis. The modified biochars effectively removed ammonium ions from water under various conditions with relatively fast adsorption kinetics (reached equilibrium within 10 h) and extremely high adsorption capacity (>200 mg/g). The Langmuir maximum capacity of the three modified biochars were between 313.9 and 518.9 mg/g, higher than many other ammonium adsorbents. Although the sorption of ammonium onto the modified biochar was affected by pH and temperature, it was high under all of the tested conditions. Findings from this work indicated that alkali-modified biochars can be used as an alternative adsorbent for the removal of ammonium from wastewater.     

Removal of lead from aqueous solutions by Penicillium biomass

The removal of lead ions from aqueous solutions by adsorption on nonliving Penicillium chrysogenum biomass was studied. Biosorption of the Pb(+2) ion was strongly affected by pH. Within a pH range of 4 to 5, the saturated sorption uptake of Pb(+2) was 116 mg/g dry biomass, higher than that of activated charcoal and some other microorganisms. At pH 4.5, P. chrysogenum biomass exhibited selectivity for Pb(+2) over other metal ions such as Cd(+2), Cu(+2), Zn(+2), and As(+3) Sorption preference for metals decreased in the following order: Pb > Cd > Cu > Zn > As. The sorption uptake of Pb(+2) remained unchanged in the presence of Cu(+2) and As(+3), it decreased in the presence of Zn(+2), and increased in the presence of Cd(+2). (c) 1993 John Wiley & Sons, Inc.     

Mechanisms of neurotransmitter release facilitation in strontium solutions

Mechanisms of neurotransmitter release facilitation were studied using electrophysiological recording of end-plate currents (EPC) and nerve ending (NE) responses after substitution of extracellular Ca ions with Sr ions at the frog neuromuscular junction. The solutions with 0.5 mM concentration of Ca ions (calcium solution) or 1 mM concentration of Sr ions (strontium solution) were used where baseline neurotransmitter release (at low-frequency stimulation) is equal. Decay of paired-pulse facilitation of EPC at calcium solutions with increase of interpulse interval from 5 to 500 ms was well described by three-exponential function consisting of early, first and second components. Facilitation at strontium solutions was significantly diminished due mainly to decrease of early and first components. At the same time, EPC facilitation with rhythmic stimulation (10 or 50 imp/s) at strontium solutions was significantly increased. Also more pronounced decrease of NE response 3rd phase, reflecting potassium currents was detected under rhythmic stimulation of 50 imp/s at strontium solutions comparing to calcium solutions. It was concluded that facilitation sites underlying first and early components had lower affinity to Sr ions than to Ca ions. The enhancement of frequency facilitation at strontium solutions is mediated by two mechanisms: more pronounced broadening of NE action potential and increase of bivalent cation influx due to feebly marked activation of Ca(2+)-dependent potassium current by Sr ions, and slower dynamics of Sr(2+) removal from NE axoplasm comparing to Ca(2+).     

Favorable chitosan/cellulose film combinations for copper removal from aqueous solutions

Three well-formed film combinations of chitosan, in the beta form and cellulose acetate biopolymer, having different proportions, have been synthesized and characterized by X-ray diffraction and infrared spectroscopy. The film having a 1.0/0.50 proportion presented 6.87 mmol of nitrogen atoms per gram of synthesized hybrid, with the highest affinity for adsorbing copper from aqueous solutions at 298+/-1K. The isotherm obtained in this adsorption showed a saturation plateau that corresponds to 1.92 mmol of copper per gram of hybrid. The energetic effects caused by copper ion interaction were determined through calorimetric titration at the solid-liquid interface in aqueous solution and gave a net thermal effect that enabled the calculation of the exothermic enthalpic values and the equilibrium constant. The complete thermodynamic data showed that the system is favored by exothermic enthalpies, negative Gibbs free energies and positive entropies.     

Adsorption of methyl violet from aqueous solutions by the biochars derived from crop residues

The adsorption of methyl violet by the biochars from crop residues was investigated with batch and leaching experiments--adsorption capacity varied with their feedstock in the following order: canola straw char>peanut straw char>soybean straw char>rice hull char. This order was generally consistent with the amount of negative charge of the biochars. Zeta potentials and Fourier transform infrared photoacoustic spectroscopy, combined with adsorption isotherms and effect of ionic strength, indicated that adsorption of methyl violet on biochars involved electrostatic attraction, specific interaction between the dye and carboxylate and phenolic hydroxyl groups on the biochars, and surface precipitation. Leaching experiments showed that 156 g of rice hull char almost completely removed methyl violet from 18.2 L of water containing 1.0 mmol/L of methyl violet. The biochars had high removal efficiency for methyl violet and could be effective adsorbents for removal of methyl violet from wastewater.     

Ion beam treatment of titanium surfaces for enhancing deposition of hydroxyapatite from solution

Surface coating with hydroxyapatite (HA) is a common way to improve the osseointegration of orthopaedic and dental titanium (Ti)-based materials. The main problems with current techniques are changes in composition during heating and poor adhesion to the surface. An alternative method is deposition of HA onto an activated surface out of a solution. The present work studies the surface treatment involving ion implantation of Na into Ti to induce a modification in chemistry and morphology, showing sodium titanate (Na(2)TiO(3)) incorporated within the surface layer with concentration, depth distribution, and morphology depending on the parameters of the ion implantation. Such ion-implanted Ti surfaces actively induce heterogeneous precipitation of HA from a simulated body fluid containing physiological concentrations of calcium and phosphate ions. This is compared with the activation by NaOH etching. The growth of bone forming cells on the pure Na implanted surface is oriented without an increased bone formation. Cell growth on the NaOH etched surface is reduced. After deposition of HA on both surfaces cell the growth pattern was improved.     

Penicillin recovery from aqueous solutions by continuous foam flotation

Summary Penicillin G recovery is investigated in a continuous flotation column in the presence of different collectors which form a complex with penicillin. The performance of the penicillin recovery was investigated as a function of the mole ratio () of collector-to-penicillin and the aliphatic chain length of the collector. At =1 and low penicillin concentrations (e.g., 20 mg·1^-1), high foam liquid concentrations (680 mg·l^-1), low residue concentrations (12 mg·l^-1) and high penicillin separation (56) can be attained. At =4 the separation increases to 150, and 95% of the penicillin can be recovered.Symbols C_p penicillin concentration in feed (mg·l^-1) - C_R penicillin concentration in outlet liquid (mg·l^-1) - C_S penicillin concentration in foam liquid (mg·l^-1) - C_S/C_P penicillin enrichment (-) - C_S/C_R penicillin separation (-) - % Pen in S penicillin yield in foam liquid (%) - VV}_S foam liquid volume flow (ml·min^-1) - VV}_P feed (ml·min^-1) - VV_{N 2} nitrogen flow rate (ml·s^-1) - temperature     

Removal of radioactive strontium from the rat by feeding stable strontium

The effect of administering the stable isotope of strontium (as phos-phate) at different dietary levels to adult rats (fed on a cereal and pulse-based diet containing 0.4% Ca) on the retention of radiostrontium (⁸⁹Sr) and radiocalcium (⁴⁵Ca) in the femur and the whole skeleton was studied for a period up to 6 weeks after an intraperitoneal injection of the two radioisotopes. The ability of strontium to remove⁸⁹Sr under the above dietary conditions was examined. Feeding Sr at 0.5% or 1% levels for 6 weeks had no effect on the skeletal content of⁸⁹Sr or⁴⁵Ca while a dietary regimen of 2% Sr (2000 times the normal content), significantly lowered the⁸⁹Sr and⁴⁵Ca content by about 30% in the femur but not in the whole skeleton. At this Sr level, the urinary excretion of the isotopes increased with a concomitant decrease in their excretion in the faeces. This study underscores the limitations of dietary Sr to mobilise⁸⁹Sr from the bones after it is incorporated in the bone mineral.     

Evaluation of a countercurrent biosorption system for the removal of lead and copper from aqueous solutions

Abstract: An automated bench-scale countercurrent biosorption system (CBS) has been designed for the removal of metals from aqueous effluents. The system has been tested with activated sludge microorganisms as a biosorbent and lead and copper as model metals. Nearly 5 1 of a lead nitrate solution at 100 mg l⁻¹ of lead have been treated down to a final concentration of 0.1 mg l⁻¹ (99.9% removal) by using 4.8 g of dry biosorbent. Under similar conditions, copper chloride solutions at 100 mg 1⁻¹ of copper were treated down to a final concentration of 35–45 mg l^−l representing 60% removal. The advantage of the CBS is to maximize metal concentration in the biosorbent, from which the metal may thereby be recovered if desired. In addition, the CBS minimizes metal concentration in the treated effluent, which is the first objective of the treatment.     

Vibrational circular dichroism of carbohydrate films formed from aqueous solutions

Vibrational circular dichroism (VCD) spectra in the entire 2000-900 cm(-1) region have been recorded, for the first time, for films of carbohydrates prepared from aqueous solutions. Eight different carbohydrates, alpha-D-glucopyranosyl-(1-->4)-D-glucose, cyclomaltohexaose, alpha-D-glucopyranosyl alpha-D-glucopyranoside, beta-D-glucopyranosyl-(1-->6)-D-glucose, beta-D-glucopyranosyl-(1-->4)-D-glucose, D-glucose, and both enantiomers of 6-deoxygalactose and of allose, were investigated. The VCD spectra obtained for films are found to be identical to the corresponding spectra obtained for aqueous solutions of carbohydrates. These measurements demonstrate several advantages of significant importance. The strong infrared absorption of water has prevented, in the past, the pursuit for routine applications of VCD in determining the structures of carbohydrates in aqueous solutions. This limitation is not present for film studies because water solvent is removed in the process of preparing the films. Also, strong infrared absorption of water at 1650 cm(-1) requires the use of very short-pathlength (6 microm) cells for measurements on aqueous solutions. This requirement and concomitant inconveniences (such as laborious assembling of a demountable liquid cell or purchasing an expensive variable pathlength liquid cell) have been eliminated for film measurements. The removal of interfering water absorption in film studies resulted in higher light throughput and better signal-to-noise ratios for VCD measurements. Another point of significance is that the amount of carbohydrate sample required for VCD measurements on films is approximately one to two orders of magnitude smaller than that required for corresponding VCD measurements on aqueous solutions. Since carbohydrate samples can now be studied as films, VCD spectroscopy becomes much more broadly applicable for carbohydrates than previously believed. The present work, in combination with other film measurements in our laboratory, indicate that VCD studies on films can be used more generally, providing a convenient and powerful approach for probing structural information for biologically important compounds.