Synthesis,Characterization, Antibacterial Properties,and In Vitro Studies of Selenium and Strontium Co-Substituted Hydroxyapatite

In this study, as a measure to enhance the antimicrobial activity of biomaterials, the selenium ions have been substituted into hydroxyapatite (HA) at different concentration levels. To balance the potential cytotoxic effects of selenite ions (SeO₃²⁻) in HA, strontium (Sr²⁺) was co-substituted at the same concentration. Selenium and strontium-substituted hydroxyapatites (Se-Sr-HA) at equal molar ratios of x Se/(Se + P) and x Sr/(Sr + Ca) at (x = 0, 0.01, 0.03, 0.05, 0.1, and 0.2) were synthesized via the wet precipitation route and sintered at 900 °C. The effect of the two-ion concentration on morphology, surface charge, composition, antibacterial ability, and cell viability were studied. X-ray diffraction verified the phase purity and confirmed the substitution of selenium and strontium ions. Acellular in vitro bioactivity tests revealed that Se-Sr-HA was highly bioactive compared to pure HA. Se-Sr-HA samples showed excellent antibacterial activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus carnosus) bacterial strains. In vitro cell–material interaction, using human osteosarcoma cells MG-63 studied by WST-8 assay, showed that Se-HA has a cytotoxic effect; however, the co-substitution of strontium in Se-HA offsets the negative impact of selenium and enhanced the biological properties of HA. Hence, the prepared samples are a suitable choice for antibacterial coatings and bone filler applications.     

Uptake of Se(IV/VI) oxyanions by hardened cement paste and cement minerals: An X-ray absorption spectroscopy study

The uptake of selenate (Se^VIO₄²⁻) or selenite (Se^IVO₃²⁻) by hardened cement paste (HCP) and important constituents of the cement matrix such as calcium silicate hydrate (C-S-H), portlandite (CH), ettringite (AFt) and monosulfate (AFm) was investigated using X-ray absorption spectroscopy (XAS). The XAS measurements were conducted on samples with Se loadings ranging between 1200 and 8800 ppm. X-ray absorption near edge structure (XANES) spectroscopy shows that redox reactions do not influence uptake processes in the cementitious systems. The EXAFS (extended X-ray absorption fine structure) spectra of Se(IV) and Se(VI) bound to CH, AFt, AFm and C-S-H are similar to those of SeO₄²⁻ and SeO₃²⁻ in solution, indicating a “solution-like” coordination environment upon uptake by the cement minerals. Similarly, the spectra of Se(IV)- and Se(VI)-treated HCP samples reveal the absence of backscattering atoms at short distances. These results suggest that the coordination sphere of the SeO₄²⁻ and SeO₃²⁻ entities is maintained upon immobilization by HCP and cement minerals and non-specific interactions dominate at the given Se loadings.     

Adsorption of selenite and selenate ions onto thiourea‐formaldehyde resin

In the present work, thiourea‐formaldehyde (TUF) chelating resin was synthesized and used in the adsorptions of selenite (SeO) and selenate (SeO) ions. The effects of initial acidity and initial selenium concentrations on the adsorptions were examined by batch technique. The synthesized resin was applied to the elemental analysis to determine its composition. FT‐IR spectra and SEM/EDS were also recorded before and after selenite adsorption. It was found that selenite and selenate ions were adsorbed onto TUF resin at strong acidic conditions (3–5M HCl). The adsorption capacities of the resin were calculated as 833.3 mg g^?1 TUF resin for selenite ions and 526.3 mg g^?1 TUF resin for selenate. All the adsorption data obtained for both selenite and selenate ions fitted well to the Langmuir isotherm. It was seen that the adsorption mechanisms in the both adsorptions were governed by the reduction of selenite or selenate to elemental selenium, Se⁰. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Surface Characterization and Biocompatibility of Selenium‐Doped Hydroxyapatite Coating on Titanium Alloy

Selenium‐doped hydroxyapatite (HA) was biomimetically coated on Ti6Al4V plates with the aim of combining the anticancer and antibacterial properties of selenium with the biocompatibility and bioactivity of HA. For the coating process, the composition of 1.5 × SBF (solution with ion concentrations at 1.5 times that of simulated body fluid, SBF) was modified to include 0.15 mM selenate (SeO₄^2?) ion. The selenium‐doped HA coating was characterized by several methods, such as scanning electron microscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy. The cytotoxicity of selenium on osteoblast and osteosarcoma cells was determined. The coating was shown to inhibit the growth of Staphylococcus epidermidis.     

Slow-release selenium fertilizers to correct selenium deficiency in grazing sheep in Western Australia

A slow-release selenium (Se) fertilizer was tested under grazing conditions with merino sheep, in a mediterranean environment on a lateritic podzolic and a non-calcic brown soil in Western Australia. The experimental site was located 80 km east of Perth, Western Australia. Some sheep were maintained on the pasture for 4 yr and other low selenium sheep were introduced at various times over 5 yr to distinguish carryover effects within the sheep from those in the pasture/soil. A single application of the slow-release Se fertilizer based on BaSeO₄ at 10 g Se ha^–1, maintained adequate Se concentration in the blood to prevent subclinical Se deficiency for 4 yr. A single application of Na₂SeO₄ fertilizer applied at the same rate was effective for only 15 mo. The difference in solubility between the quick (Na₂SeO₄) and the slow-release form (BaSeO₄) of Se allows alternative management strategies. The quick-release form could be used annually in smaller quantities (2–3 g Se ha^–1) where pastures are rotated with crops that do not require Se. The slow-release form at higher application rates (10 g Se ha^–1) is more suited to long-term pasture areas which would therefore require infrequent applications of Se. Slow-release Se fertilizers that are controlled by dissolution are well adapted to the mediterranean environment where crop growth is restricted to the cool wet winter months and there is very little soil moisture or plant growth during the summer.     

Studies of the reduction mechanism of selenium dioxide and its impact on the microstructure of manganese electrodeposit

The influence of selenium dioxide (SeO₂) on the microstructure and electrodeposition of manganese coatings obtained from a sulfate based neutral solution was investigated by material characterization methods and electrochemical techniques. The crystal structure and surface morphology of these coatings were studied by scanning electron microscopy (SEM) and powder X-ray diffraction spectroscopy (XRD), respectively. The SEM and XRD data showed that SeO₂ could effectively accelerate phase transformation, and facilitate leveled and fine grain growth. The electrochemical results indicated that SeO₂ could inhibit hydrogen evolution reaction and promote manganese deposition. The action of selenium dioxide in manganese deposition was found to be a reduction and adsorption mechanism. The process could be explained as following: First, Se (IV) was reduced to Se (0), and part of Se (0) future reduce to selenide, which then combined with the remainder Se (0) forming a complicate compound (multi-selenium ions).     

Synthesis and Characterization of Cadmium Selenide (CdSe) Nanoparticles Using Trigonal Selenium (t-Se) Nanorods as Selenium Source

Cadmium selenide (CdSe) nanoparticles were synthesized through colloidal method in aqueous medium using the reaction intermediates selenium nanorods as selenium source. Trigonal selenium nanorods (t-Se) were synthesized in water by the reduction method in the presence of sodium borohydride at 60?°C using sodium selenite (Na₂SeO₃) as selenium source. These selenium nanorods were further utilized to synthesis cadmium selenide nanoparticles at 100?°C in water. The synthesized nanorods and nanoparticles were characterized using XRD, SEM, TEM and XPS analysis. X-ray diffraction (XRD) analysis shown that the nanorods possess trigonal phase while the nanoparticles possess a cubic zinc blende structure. Scanning electron microscope (SEM) analysis of the prepared hexagonal shaped nanorods reveals the diameter of the nanorods are about 150 nm. Transmission electron microscopy (TEM) analysis shows the size of the synthesized CdSe nanoparticles are about 4–8 nm. X-ray photoelectron spectroscopy (XPS) analysis illustrates the presence of respective elements Cd, Se with its corresponding oxidation states. The activity of nano selenium rods in aqueous solution during the conversion of cadmium selenide nanoparticles was discussed.     

Thermodynamic evaluation of the compounds of gold, silver, and other trace elements formed upon the combustion of brown coal

The thermodynamically most probable main compounds of Ag, Au, Ge, Se, Sr, U, and ash-forming elements formed upon the combustion of brown coal, which was close in the composition of organic and mineral matter to coal from the Nazarovskoe deposit of the Kansk-Achinsk Basin, were determined. According to the experimental data, silver (in the form of AgO(g)) and gold (in the form of Au(g)) quantitatively passed into a gas phase at temperatures higher than 200 and 1179°C, respectively; selenium passed into a gas phase in the form of SeO₂(g) at t = 800–1000°C and in the form of SeO₂(g) and SeO(g) at t ≥ 1000°C. The SeO(g): SeO₂(g) ratio increased with temperature. Germanium formed gaseous GeO(g) and GeO₂ at t ≥ 1000°C, and the amount of the former dramatically increased with temperature.     

Solid‐State NMR Study of Mn2+ for Ca2+ Substitution in Thermally Processed Hydroxyapatites

In the present study calcium hydroxyapatites enriched at 0.08 wt% in Mn²⁺ ions (Mn–HA) and their unsubstituted forms (HA) were synthesized using the same standard wet chemical route. Mn‐HA and HA were both calcined at 800°C to give Mn‐HAc and HAc, respectively or sintered at 1250°C, to give Mn‐HAs and HAs, respectively. The influence of the heat treatment on physicochemical properties of Mn‐HA was investigated using powder X‐ray diffraction (PXRD), scanning, and transmission electron microscopy (SEM and TEM), and solid‐state nuclear magnetic resonance (ssNMR). Mn‐HAc and Mn‐HAs were compared to each other and to HAc and HAs, respectively. Assignment of the proton ssNMR peaks from high‐temperature‐treated apatites has been revised. It was found that Mn–HAc and HAc were nanocrystalline, while Mn‐HAs and HAs comprised micrometer sized, partially fused particles (SEM and TEM). PXRD and ssNMR demonstrated that the incorporation of Mn²⁺ into the crystal lattice of hydroxyapatite significantly facilitates its dehydroxylation and decomposition to oxyhydroxyapatite during calcination at 800°C, and induces its transformation to tetracalcium phosphate (TTCP) and alpha‐tricalcium phosphate (α‐TCP) at 1250°C. Contamination by CaO has also been detected. The ¹H→³¹P NMR cross‐polarization experiments have indicated that the Mn²⁺ ions preferentially occupied the Ca(I) position in the crystallographic unit cell of Mn‐HAc. In Mn‐HAs, the Mn²⁺ ions were evenly distributed between the Ca(I) and Ca(II) positions.     

Selenium fractions in selenate-fertilized field soils of Finland

Depending on the soil environment, selenium (Se) can exist as several species differing greatly in bioavailability. Characterization of soil Se reserves is thus necessary in assessing the nutritional supply of this essential element. In low-Se areas, Se fertilization is an option for securing adequate Se nutrition. Fertilization is, however, challenged by the unknown fate of the residual Se. In this study, we aimed to clarify the Se status of selenate-fertilized field soils by fractionating soil Se into five pools: salt-soluble (KCl), adsorbed (KH₂PO₄/K₂HPO₄), organically associated (NaOH), elemental (Na₂SO₃) and recalcitrant Se (NaOCl). Changes induced in these fractions by repeated application of low selenate doses were examined by comparing samples collected from the same locations in 1992 and 2004. The distribution of Se among the five fractions was relatively similar in all soils. On average, 1% of the amount of Se acquired was salt-soluble, 17% adsorbed, 39% organically associated, 14% elemental and 29% recalcitrant organic Se or metal selenides. The added Se was distributed among several fractions, leading to a relatively small change in each fraction. However, in mineral soils (n = 5), a significant increase in soil Se concentration was found between 1992 and 2004 in adsorbed, organically associated and recalcitrant Se, as well as in the total amount of Se acquired as a sum of the fractions. Our findings provide the first field-scale experimental support for the theoretical assumption of accumulation of residual selenate in acidic mineral soil in insoluble form.     

Crystal structure analysis of selenium-doped hydroxyapatite samples and their thermal stability

The aim of this study is to obtain more information about the fine crystal structure of selenium-doped hydroxyapatite (Se-HA) and investigate the effect of Se doping on the thermal stability of HA. Se-HA samples with different Se/P ratios were synthesized by the chemical precipitation method. The physicochemical properties of the powders were characterized by X-ray fluorescence spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The results indicate that selenite and a small amount of carbonate co-incorporate into the well-crystallized samples by substituting for phosphate groups. Rietveld refinement was performed to further analyze the crystal structure and determine the crystal structure model of the Se-HA samples. Se incorporation leads to an increase of the a lattice parameter and a decrease of the c lattice parameter of the crystal lattice. The thermal stability of the Se-HA powders during sintering is also discussed. Doping the HA structure with a small amount of selenium improves the thermal stability of HA. Compared with HA, the Se-HA samples with Se/P ≤ 0.05 doping are more stable after heat treatment without any impurities, which makes these materials promising for bone repair materials.     

Microstructure and <Emphasis Type="Italic">in vitro</Emphasis> Bioactivity of Silicon-Substituted Hydroxyapatite

Silicon-substituted hydroxyapatite has shown superior biological performance compared to its stoichiometric counterpart both in vitro and in vivo. In the present study, single-phase silicon-substituted hydroxyapatite was successfully synthesized by the precipitation method. Chemical composition, crystalline phase, microstructure, and morphology of the materials were characterized by XRF, XRD, FT-IR, solid-state NMR and SEM. The results showed that hydroxyapatite kept its original structure with silicon up to a level of 0.9 wt%. The precipitation method was proved to be an efficient way to synthesize single-phase silicon-substituted hydroxyapatite. Solid-state NMR combined with other techniques gave direct evidence for the isomorphous substitution of PO₄ ^3- by SiO₄ ^4- in the hydroxyapatite structure. Silicon-substituted hydroxyapatite showed better bioactivity than stoichiometric hydroxyapatite in the in vitro bioactivity experiment. The higher the silicon content in the hydroxyapatite structure, the better the in vitro bioactivity. The enhanced bioactivity of silicon-substituted hydroxyapatite over pure hydroxyapatite has been attributed to the effect of silicate ions in accelerating dissolution.     

Counterion motions and thermal ordering effects in perfluorosulfonate ionomers probed by solid-state NMR

Perfluorosulfonate ionomers (PFSIs) neutralized by tetraalkylammonium ions have been investigated using variable temperature ¹H and ¹³C solid-state NMR (ssNMR) spectroscopy to probe the thermally induced properties of tetraalkylammonium ions at temperatures near the α-relaxations. Tetramethylammonium (TMA⁺), tetraethylammonium (TEA⁺), tetrapropylammonium (TPA⁺) and tetrabutylammonium (TBA⁺) ions have been incorporated in our study for the systematic control of ionic interactions within PFSIs according to the chain-length of ammonium ions. ¹³C static ssNMR results show that bulkier TPA⁺ and TBA⁺ ions undergo molecular tumbling motions near or above the α-relaxation temperature of the corresponding PFSI ionomers, with jumping rates of κ ≈ 1 kHz. Moreover, the results of ¹H spin-lattice (T₁) relaxation time measurements suggest that smaller TMA⁺ ions in the PFSI exhibit a thermally induced ordering effect as the sample temperature approaches the α-relaxation temperature of TMA⁺-PFSI. This ordering phenomenon is also supported by the results from small-angle X-ray scattering.     

Deposition of selenium thin layers on gold surfaces from sulphuric acid media: Studies using electrochemical quartz crystal microbalance, cyclic voltammetry and AFM

In this paper we report here new considerations about the relationship between the mass and charge variations (m/z relationship) in underpotential deposition (UPD), bulk deposition and also in the H₂Se formation reaction. Nanogravimetric experiments were able to show the adsorption of H₂SeO₃ on the AuO surface prior to the voltammetric sweep and that, after the AuO reduction, 0.40 monolayer of H₂SeO₃ remains adsorbed on the newly reduced Au surface, which was enough to gives rise to the UPD layer. The UPD results indicate that the maximum coverage with Se_ads on polycrystalline gold surface corresponds to approximately 0.40 monolayer, in good agreement with charge density results. The cyclic voltammetry experiments demonstrated that the amount of bulk Se obtained during the potential scan to approximately 2 Se monolayers, which was further confirmed by electrochemical quartz crystal microbalance (EQCM) measurements that pointed out a mass variation corresponding of 3 monolayers of Se. In addition, the Se thin films were obtained by chronoamperometric experiments, where the Au electrode was polarized at +0.10 V during different times in 1.0 M H₂SO₄ + 1.0 mM SeO₂. The topologic aspects of the electrodeposits were observed in Atomic Force Microscope (AFM) measurements. Finally, in highly negative potential polarizations, the H₂Se formation was analyzed by voltammetric and nanogravimetric measurements. These finding brings a new light on the selenium electrodeposition and point up to a proposed electrochemical model for molecule controlled surface engineering.     

Stannous chloride—an effective reducing agent for the removal of selenium(IV) from acidic solution

BACKGROUND: Selenium removal from aqueous solutions can be a significant industrial problem, particularly in the metallurgical industry. In order to evaluate new reducing agents for this application, the reduction of selenious acid (H₂SeO₃) species with stannous ions (Sn²⁺) from weakly acidic sulfate solutions containing 300 mg L^?1 of selenium at 23 °C was studied. RESULTS: At initial pH values < 1.3 and molar ratio ≥ 2, less than 0.5 µg L^?1 of selenium(IV) remained in solution after reduction. The reductive precipitation reaction started as soon as the stannous ions were added to the selenium‐bearing solution and was completed in less than 5 min. The reaction products, characterized using X‐ray diffraction, electron microscopy, particle and surface area measurements, X‐ray photoelectron spectroscopy and chemical analysis, were composed of approximately equal amounts of tin selenide and tin dioxide. In addition to tin selenide a minor amount of selenium(IV) was found to be removed via adsorption on the tin dioxide formed in situ. Tests with a complex industrial solution also resulted in full and stable selenium precipitation. CONCLUSION: Stannous ions were found to be very effective in removing selenious ions from synthetic and industrial solutions, producing very stable precipitates. Copyright © 2012 Society of Chemical Industry     

Electrochemical formation of nanometric layers of tin selenides on Ti surface

Photoelectrically active tin selenide coatings of nanometric thickness were manufactured by electrodeposition from separate solutions of Sn and Se precursors. Sn was deposited from acidic SnSO₄ electrolytes and Se was deposited from H₂SeO₃ solutions. Fine-grained Sn coatings were deposited at potential φ = −0.3 V with 100% current efficiency. Se coatings were formed at two potentials: φ = −0.5 V, forming Se⁰, and φ = −0.85 V, forming Se²⁻ ions. After the Sn coating was immersed into H₂SeO₃ solution, small quantities (∼2 at.%) of SnSe were formed and SeO₃²⁻ was adsorbed on the surface. A short-time deposition of Se at φ = −0.5 V passivated the surface, so no Sn dissolution is observed upon anodic polarization. XPS and Auger data indicated that under those conditions 20 at.% of Se⁰ and only 2 at.% of SnSe were formed. Thickening of Sn and Se layers led to formation of larger quantities of Se⁰ (75 at.%) and SnSe (4-5 at.%) on the surface, whereas deeper layers contained up to 10 times more of SnSe phase. Upon deposition of Se at φ = −0.85 V, new SnSe₂ phase was formed and the quantity of SnSe phase is increased and that of Se⁰ was reduced. All coatings formed exhibited photoelectric properties.     

Comparison of Selenium Nanoparticles and Sodium Selenite on the Alleviation of Early Atherosclerosis by Inhibiting Endothelial Dysfunction and Inflammation in Apolipoprotein E-Deficient Mice

Atherosclerosis and related cardiovascular diseases represent the greatest threats to human health, worldwide. Previous animal studies showed that selenium nanoparticles (SeNPs) and Na₂SeO₃ might have anti-atherosclerotic activity, but the underlying mechanisms are poorly elucidated. This study compared the anti-atherosclerotic activity of SeNPs stabilized with chitosan (CS-SeNPs) and Na₂SeO₃ and the related mechanism in a high-fat-diet-fed apolipoprotein E-deficient mouse model of atherosclerosis. The results showed that oral administration of both CS-SeNPs and Na₂SeO₃ (40 μg Se/kg/day) for 10 weeks significantly reduced atherosclerotic lesions in mouse aortae. Mechanistically, CS-SeNPs and Na₂SeO₃ not only alleviated vascular endothelial dysfunction, as evidenced by the increase of serum nitric oxide level and the decrease of aortic adhesion molecule expression, but also vascular inflammation, as evidenced by the decrease of macrophage recruitment as well as the expression of proinflammatory molecules. Importantly, these results were replicated within in-vivo experiments on the cultured human endothelial cell line EA.hy926. Overall, CS-SeNPs had a comparable effect with Na₂SeO₃ but might have more potential in atherosclerosis prevention due to its lower toxicity. Together, these results provide more insights into the mechanisms of selenium against atherosclerosis and further highlight the potential of selenium supplementation as a therapeutic strategy for atherosclerosis.     

High cell density fermentation of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> GS2 for selenium-enriched yeast production

This paper describes a fed-batch fermentation protocol about production of selenium-enriched yeast. Saccharomyces cerevisiae GS2 was selected because of its high tolerance to selenium. The strain GS2 was tested and 122±0.5 g·l ⁻¹ dry cell weight was obtained after 30 h cultivation through feed back control of feed rate of glucose according to the concentration of ethanol and dissolved oxygen. Furthermore, the optimal pattern of Na₂SeO₃ addition was 9 mg Na₂SeO₃ against 1 g DCW at late exponential phase. With the combination of glucose feeding and Na₂SeO₃ addition, the final dry cell biomass reached 102±0.4 g·l ⁻¹ and a Se uptake level of 2,020±13 mg·Kg⁻¹ was achieved in a 5 l fermentor after 38 h cultivation.     

Electrolytic manganese metal from chloride electrolytes. II. Effect of additives

Results of beaker scale and large laboratory scale experiments on the deposition of manganese from chloride electrolytes using selenium based additives are reported. High cathode efficiencies (85–90%) were obtained at moderate selenium levels (0.03–0.06 gl^–1). Selenium pick-up in the deposit was lower when selenium was added as the selenate [Se(VI)].A cost/benefit analysis of selenium additions is presented.     

Effect of multi-ions doping on the properties of carbonated hydroxyapatite bioceramic

The effect of multi-ions (Mg²⁺, SiO₄^4-, Zn²⁺, Cu²⁺) doping on the properties of carbonated hydroxyapatite (CHA) prepared by a wet chemical method has been investigated. Different combinations of ions were doped into the CHA and the as-synthesized compacts were sintered at 900?°C prior to body characterization. It was found that regardless of ions doping, the lattice structure of the CHA was not disrupted. In addition, secondary phases were not detected for all the multi-ions doped samples. The XRD and FTIR results further confirmed the presences of a B-Type CHA in the sintered samples. The XRD analysis revealed that the lattice parameters (c/a ratio) increased with dopant addition and resulted in a smaller crystallite size. The FESEM examination also showed the presences of smaller grain size for the multi-ions doped CHA samples thus indicating that the doping was beneficial in suppressing grain coarsening in carbonated hydroxyapatite.