Aluminum Fluoride Complexes Research Articles

Use of activated silica sol as a coagulant aid to remove aluminium from water defluoridated by electrocoagulation

Presence of fluorides in drinking water has become a public health problem. Aluminium compounds are popular for defluoridation of water owing to high affinity of fluoride toward aluminium. Use of these compounds may lead to high aluminium concentrations in drinking water. Aluminium is found to be a potential neurotoxicant. Synergistic associations of both aluminium and fluorides in the drinking water supply have been expounded by researchers. Aluminium–fluoride complexes also increase the risk of developing Alzheimer’s disease. Therefore, it is imperative to control the residual aluminium in the water. In the present work, the electrocoagulation process with aluminium electrodes has been used for defluoridation of water. In subsequent steps, activated silica sol has been used as a coagulant aid to remove aluminium from defluoridated water. Taguchi design has been used to develop a statistical model for aluminium removal. The experimental investigations revealed that activated silica sol reduces residual aluminium to a range of 0.003–0.034 mg/L.

The impact of aluminum, fluoride, and aluminum-fluoride complexes in drinking water on chronic kidney disease.

It is suspected that drinking water containing fluoride and aluminum results in negative health effects especially on brain, liver, and kidney. In this investigation, the effect of F, Al, and AlFx complex on chronic kidney disease (CKD) was investigated. Mice were treated either with WHO recommended or slightly higher F and Al levels in drinking water. Treatment solutions contained 0.05-10.0 mg/L of F, 0.08-10.0 mg/L of Al, or 0.07-15 mg/L of AlFx, and the treatment period was 42 weeks. Blood urea level and creatinine levels were investigated as a measure of malfunction of kidneys. Histopathological evaluations of kidney tissues were carried out to assess the extent of damage that F, Al, and AlFx complex could cause. It was demonstrated that the treated drinking water containing F and Al with par with WHO or moderately above the WHO levels or AlFx in low level (0.07-15 mg/L) does not lead to CKD in mice.

On the mechanism of phosphoenolpyruvate synthetase (PEPs) and its inhibition by sodium fluoride: potential magnesium and aluminum fluoride complexes of phosphoryl transfer

Phosphoenolpyruvate synthase (PEPs) catalyzes the conversion of pyruvate to phosphoenolpyruvate (PEP) using a two-step mechanism invoking a phosphorylated-His intermediate. Formation of PEP is an initial step in gluconeogenesis, and PEPs is essential for growth of Escherichia coli on 3-carbon sources such as pyruvate. The production of PEPs has also been linked to bacterial virulence and antibiotic resistance. As such, PEPs is of interest as a target for antibiotic development, and initial investigations of PEPs have indicated inhibition by sodium fluoride. Similar inhibition has been observed in a variety of phospho-transfer enzymes through the formation of metal fluoride complexes within the active site. Herein we quantify the inhibitory capacity of sodium fluoride through a coupled spectrophotometric assay. The observed inhibition provides indirect evidence for the formation of a MgF3(-) complex within the enzyme active site and insight into the phospho-transfer mechanism of PEPs. The effect of AlCl3 on PEPs enzyme activity was also assessed and found to decrease substrate binding and turnover.

Comparison of Three Dimeric 18F-AlF-NOTA-RGD Tracers

RGD peptide-based radiotracers are well established as integrin αvβ3 imaging probes to evaluate tumor angiogenesis or tissue remodeling after ischemia or infarction. In order to optimize the labeling process and pharmacokinetics of the imaging probes, we synthesized three dimeric RGD peptides with or without PEGylation and performed in vivo screening. Radiolabeling was achieved through the reaction of F-18 aluminum-fluoride complex with the cyclic chelator, 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA). Three imaging probes were synthesized as (18)F-AlF-NOTA-E[c(RGDfK)]2, (18)F-AlF-NOTA-PEG4-E[c(RGDfK)]2, and (18)F-AlF-NOTA-E[PEG4-c(RGDfk)]2. The receptor binding affinity was determined by competitive cell binding assay, and the stability was evaluated by mouse serum incubation. Tumor uptake and whole body distribution of the three tracers were compared through direct tissue sampling and PET quantification of U87MG tumor-bearing mice. All three compounds remained intact after 120 min incubation with mouse serum. They all had a rapid and relatively high tracer uptake in U87MG tumors with good target-to-background ratios. Compared with the other two tracers, (18)F-AlF-NOTA-E[PEG4-c(RGDfk)]2 had the highest tumor uptake and the lowest accumulation in the liver. The integrin receptor specificity was confirmed by co-injection of unlabeled dimeric RGD peptide. The rapid one-step radiolabeling strategy by the complexation of (18)F-aluminum fluoride with NOTA-peptide conjugates was successfully applied to synthesize three dimeric RGD peptides. Among the three probes developed, (18)F-AlF-NOTA-E[PEG4-c(RGDfk)]2 with relatively low liver uptake and high tumor accumulation appears to be a promising candidate for further translational research.

The effects of fluoride and aluminum ions on ferrous-iron oxidation and copper sulfide bioleaching with Sulfobacillus thermosulfidooxidans

Microorganisms that grow at high temperatures can improve Fe(II) bio-oxidation and thereby its technological applications, such as bioleaching and H2S removal. Conversely, elements present in industrial growth media, such as fluoride, can inhibit bacterial growth and iron bio-oxidation. In this work, the influence of fluoride on the kinetics of ferrous-iron bio-oxidation with Sulfobacillus thermosulfidooxidans was investigated. The effects of fluoride concentrations (0–0.5mmolL−1) on both iron oxidation and bacterial growth rates were assessed. In addition, the effect of the addition of aluminum, which was intended to complex free fluoride and reduce the concentration of HF through the formation of aluminum–fluoride complexes, was also investigated. The results show that 0.5mmolL−1 NaF completely inhibited bacterial growth within 60h. Nevertheless, fluoride toxicity to S. thermosulfidooxidans was minimized by control of the aluminum–fluoride ratio in the system because, at a 2:1 aluminum–fluoride molar ratio, bacterial growth was similar to that observed in the absence of fluoride ions. Despite a slower bacterial growth rate, fluoride concentrations less than the inhibitory concentration increased the Fe(II) oxidation rate. Successful copper bioleaching (80–100%) from fluoride-containing sulfide ores (1% total fluoride) was demonstrated in the presence of aluminum.

Spectrophotometric Determination of Fluoride in Groundwater Using Resorcin Blue Complexes

New simple and sensitive spectrophotometric determination of fluoride in drinking groundwater has been developed using aluminium-resorcin blue complex. The method is based on the reaction of fluoride with the coloured complex to produce colourless aluminium fluoride complex and releasing of the free ligand. The relationship of the reaction of flu-oride with the complex is sixth-order polynomial function. The reaction reaches equilibrium at fluoride concentration of 0.054 mM. The equilibrium constant (Keq) was calculated as 1.12 × 1014. Beer-Lambert law is obeyed in the range 0.0 - 0.024 mM of fluoride (0.0 - 1.0 mg·L-1). The molar absorptivity at 502 nm is 6.45 × 103 L·mol-1·cm-1. Fluoride concentration higher than 1.0 mg·L-1 can be measured after proper dilution. The sensitivity, detection limit, quantitation limit, and the percentage recovery of 0.75 mg·L-1 fluoride for the method were found to be 0.357 μg·ml-1., 0.07 mg·L-1, 0.2 mg·L-1, and 101.1 respectively.

Effect of aluminum fluoride complexation on fluoride removal by coagulation

Effect of aluminum fluoride complexation on fluoride removal by Al salts coagulation was investigated by a series of batch experiments. Transformation of fluoride species in coagulation was studied by simultaneous determination of free fluoride and total fluoride at different pH and fluoride concentrations. Results showed that aluminum fluoride complexes dominated at low pH and high fluoride concentrations but more complexes did not represent higher fluoride removal. Comparison between coagulation with complexation and adsorption by Al(OH) 3 flocs was conducted and coagulation showed higher fluoride removal efficiency than adsorption in the pH range of 6.0–9.0. Titration test showed that Al F complexes were coprecipitated with less OH − than Al 3+. Characterization of FTIR and XPS also indicated that flocs after complexation was different from Al(OH) 3 flocs with or without fluoride. It was concluded that a new Al F OH coprecipitate formed in coagulation and fluoride was effectively removed by the coprecipitation.

Simultaneous determination of aluminium, aluminium fluoride complexes and iron in groundwater samples by new HPLC–UVVIS method

The paper presents the application of the new HPLC–UVVIS method used in speciation analysis of aluminium form Al3+, aluminium complexes with fluorides and iron in groundwater samples. Based on the obtained results of groundwater samples analysis, the separation of iron in the retention time ≈3.7, was obtained. The conditions of the occurrence of particular aluminium forms based on the speciation analysis and modeling in the Mineql program were presented and confirmed. The influence of pH and ligand concentration on forming complexes was shown. The preliminary study of aluminium complexes with sulfates based on model solutions did not allow for the separation of the above complexes in presented analytical system. The paper presents the possible types of transformation of aluminium hydroxy forms and aluminium sulfate complexes by the reaction of the sample with mobile phase. An indirect method for the determination of aluminium in the form of aluminium sulfate was proposed. The new method was successfully applied in the determination of the following aluminium forms: Al3+, AlF2+, AlF30, AlF4−, AlF2+ and Fe3+.

Determination of aluminium in groundwater samples by GF-AAS, ICP-AES, ICP-MS and modelling of inorganic aluminium complexes

The paper presents the results of aluminium determinations in ground water samples of the Miocene aquifer from the area of the city of Poznań (Poland). The determined aluminium content amounted from <0.0001 to 752.7 μg L(-1). The aluminium determinations were performed using three analytical techniques: graphite furnace atomic absorption spectrometry (GF-AAS), inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). The results of aluminium determinations in groundwater samples for particular analytical techniques were compared. The results were used to identify the ascent of ground water from the Mesozoic aquifer to the Miocene aquifer in the area of the fault graben. Using the Mineql+ program, the modelling of the occurrence of aluminium and the following aluminium complexes: hydroxy, with fluorides and sulphates was performed. The paper presents the results of aluminium determinations in ground water using different analytical techniques as well as the chemical modelling in the Mineql+ program, which was performed for the first time and which enabled the identification of aluminium complexes in the investigated samples. The study confirms the occurrence of aluminium hydroxy complexes and aluminium fluoride complexes in the analysed groundwater samples. Despite the dominance of sulphates and organic matter in the sample, major participation of the complexes with these ligands was not stated based on the modelling.

Speciation analysis of aluminium and aluminium fluoride complexes by HPIC-UVVIS

The study presents a new analytical method for speciation analysis in fractionation of aluminium fluoride complexes and free Al 3+ in soil samples. Aluminium speciation was studied in model solutions and soil extract samples by means of high performance ion chromatography (HPIC) with UV–VIS detection using post-column reaction with tiron for the separation and detection of aluminium fluoride complex and Al 3+ forms during one analysis. The paper presents particular stages of the chromatographic process optimization involving selecting the appropriate eluent strength, type of elution or concentration and quantity of derivatization reagent. HPIC was performed on a bifunctional analytical column Dionex IonPac CS5A. The use of gradient elution and the eluents A: 1 M NH 4Cl and B: water acidified to pH of eluent phase, enabled full separation of fluoride aluminium forms as AlF 2 +, AlF 3 0, AlF 4 − (first signal), AlF 2+ (second signal) and form Al 3+ in a single analytical procedure. The proposed new method HPIC-UVVIS was applied successfully in the quantitative and qualitative analysis of soil samples.

Speciation of aluminium fluoride complexes and Al3+ in soils from the vicinity of an aluminium smelter plant by hyphenated High Performance Ion Chromatography Flame Atomic Absorption Spectrometry technique

Abstract The paper presents a new tool for the determination of inorganic speciation forms of aluminium: AlFn(3 − n)+, and Al3+ by means of the HPIC-FAAS. The proposed method has been successfully used for speciation analysis (qualitative and quantitative) of inorganic aluminium forms AlFn(3 − n)+ in soil samples. In order to isolate the most environmentally available fraction, 5 g of the sample was collected and extracted in deionised water (water soluble fraction) for 1 h using a magnetic stirrer. The determinations in a hyphenated technique system were performed for a number of prepared water extracts. Concentration determinations of particular aluminium forms were performed based on model studies and real samples. The separation of Al species with nominal charge of + 1, + 2, and + 3 required a run time of less than 4 min during a single analysis. Based on the analysis of water extracts of soil, it was obtained that aluminium forms elute in the following order: 1PA (first signal) — AlF2+ and/or AlF4−; 2PA (second signal) — AlF2+ and/or AlF30; 3PA (third signal) — Al3+. In order to confirm the occurrence of these forms a simulation using the Mineql program was conducted. The details of speciation analysis of aluminium fluoride forms by means of an HPIC-FAAS instrument equipped are presented. Interpretation of the speciation analysis of the water soluble fraction of soil samples is proposed, based on the separation during chromatographic run and calculated data by Mineql.

New method for speciation analysis of aluminium fluoride complexes by HPLC–FAAS hyphenated technique

Speciation analysis of aluminium in the presented system of HPLC-FAAS hyphenated technique lasts 4min. Using the bifunctional column in model analysis and using the calculation methods for modelling using the Mineql program enabled the authors to presume that particular forms will be subjected to elution in the following order: (1) AlF(2)(+) and AlF(4)(-), (2) AlF(2+) and AlF(3)(0) and (3) Al(3+). Based on the obtained results for model solutions, the presented method enables the determination of aluminium fluoride complexes and Al(3+) speciation form. The study compares the tendency of occurrence variability of aluminium fluoride complexes and Al(3+) form, determined based on the results obtained using the HPLC-FAAS hyphenated technique with the trend defined based on the Mineql program calculation method. The method was successfully applied to soil samples.

Development of a new analytical method for online simultaneous qualitative determination of aluminium (free aluminium ion, aluminium-fluoride complexes) by HPLC-FAAS

The paper presents a novel method for simultaneous online examination of inorganic forms of aluminium: AlF 2 +, AlF 2+, and Al 3+ by means of the high performance liquid chromatography hyphenated with a detection by the atomic absorption spectrometry with flame atomization (HPLC-FAAS) without post-column reaction. The application of optimization procedure conditions of chromatographic separation of inorganic forms of aluminium was achieved by the analytical column IonPac CS5A (Dionex) with guard column IonPac CG5A (Dionex) and an aqueous ammonium chloride mobile phase, at pH about 3 with gradient elution. The separation of Al forms with nominal charge of 1+, 2+, 3+ required a run time of less than 8 min during a single analysis. The proposed method has been successfully used for the examination of aluminium forms formation AlF n (3− n)+ in environmental samples.

Fluoride complexes of oncogenic Ras mutants to study the Ras-RasGAP interaction

Down-regulation of Ras signalling is mediated by specific GTPase-activating proteins (GAPs), which stimulate the very slow GTPase reaction of Ras by 10(5)-fold. The basic features of the GAP activity involve the stabilisation of both switch regions of Ras in the transition state, and the insertion of an arginine finger. In the case of oncogenic Ras mutations, the features of the active site are disturbed. To understand these features in more detail, we have investigated the effects of oncogenic mutations of Ras and compared the GAP-stimulated GTPase reaction with the ability to form GAP-mediated aluminium or beryllium fluoride complexes. In general we find a correlation between the size of the amino acid at position 12, the GTPase activity and ability to form aluminium fluoride complexes. While Gly12 is very sensitive to even the smallest possible structural change, Gly13 is much less sensitive to steric hindrance, but is sensitive to charge. Oncogenic mutants of Ras defective in the GTPase activity can however form ground-state GppNHp complexes with GAP, which can be mimicked by beryllium fluoride binding. We show that beryllium fluoride complexes are less sensitive to structural changes and report on a state close to but different from the ground state of the GAP-stimulated GTPase reaction.

Inhibition of phosphate uptake in corn roots by aluminum-fluoride complexes.

F forms stable complexes with Al at conditions found in the soil. Fluoroaluminate complexes (AlF(x)) have been widely described as effective analogs of inorganic phosphate (Pi) in Pi-binding sites of several proteins. In this work, we explored the possibility that the phytotoxicity of AlF(x) reflects their activity as Pi analogs. For this purpose, (32)P-labeled phosphate uptake by excised roots and plasma membrane H(+)-ATPase activity were investigated in an Al-tolerant variety of maize (Zea mays L. var. dwarf hybrid), either treated or not with AlF(x). In vitro, AlF(x) competitively inhibited the rate of root phosphate uptake as well as the H(+)-ATPase activity. Conversely, pretreatment of seedlings with AlF(x) in vivo promoted no effect on the H(+)-ATPase activity, whereas a biphasic effect on Pi uptake by roots was observed. Although the initial rate of phosphate uptake by roots was inhibited by AlF(x) pretreatment, this situation changed over the following minutes as the rate of uptake increased and a pronounced stimulation in subsequent (32)Pi uptake was observed. This kinetic behavior suggests a reversible and competitive inhibition of the phosphate transporter by fluoroaluminates. The stimulation of root (32)Pi uptake induced by AlF(x) pretreatment was tentatively interpreted as a phosphate starvation response. This report places AlF(3) and AlF(4)(-) among Al-phytotoxic species and suggests a mechanism of action where the accumulation of Pi-mimicking fluoroaluminates in the soil may affect the phosphate absorption by plants. The biochemical, physiological, and environmental significance of these findings is discussed.

Nod factors stimulate plasma membrane delimited phospholipase C activity in vitro

Nod factors are lipo‐chito‐oligosaccharides secreted by Rhizobium to initiate deformation of root hairs and other changes in host plants. Since Nod factor‐induced changes in intracellular calcium occur in responsive root hairs, we tested if phospholipase C (PLC) activity is stimulated by Nod factors. Plasma membranes were isolated from the nodulation‐competent zone of roots of Vigna unguiculata to assay PLC activity in vitro. Nod factors isolated from Rhizobium sp. NGR234, NodNGR[S] and NodNGR[Ac] significantly increased PLC activity and this increase in activity was inhibited in the presence of the PLC inhibitors, neomycin and U‐73122. The response appears specific as PLC activity was not significantly induced neither by the 4‐sugar, N,N′,N′′,N′′′‐tetracetylchitotetraose (TACT), or the five‐sugar, penta‐N‐acetylchitopentaose (PACT), backbone of Nod factors. The G‐protein activators, GTPγS and the aluminium fluoride complex, had no effect on PLC activity in the presence or absence of NodNGR[S], suggesting that Nod factors act independently of G‐proteins in vitro. However, the combination of oleic acid and TACT mimicked the effect of Nod factors on PLC activity indicating that the presence of the lipid tail may be critical. Also this combination of compounds acted synergistically together to evoke root hair deformation in vivo. Our results indicate that Nod factors can modulate membrane delimited PLC activity and indicate that PLC is likely to be a component of the Nod factor‐signalling pathway.

Speciation of aluminum in rainwater using a fluoride ion-selective electrode and ion-exchange chromatography with fluorometric detection of the aluminum-lumogallion complex.

Soluble aluminum in rainwater was separated into three categories: free aluminum (Al3+), fluoride complexes (sum of AlF2+ and AlF2+), and other forms of aluminum. The free form of the aluminum ion (Al3+) was directly obtained from the separation data of aluminum species according to their charge using gradient elution cation-exchange chromatography. The aluminum fluoride complexes were estimated by combining the data of the free and total fluoride determined using a fluoride ion-selective electrode, with the assumption that 2+ charged aluminum species consisted only of AlF2+. The rest of the aluminum species had a 1+, neutral, or negative charge and mainly consisted of organic complexes. The origin of the organically bound aluminum is discussed. The concentration range of the total dissolved fluoride and aluminum in the rainwater samples was usually in the micromolar to submicromolar range, and the ratio of [T-F]/[T-Al] was found to be between 1 and 4. The speciation of dissolved aluminum into three categories was carried out on the basis of data of 15 rainwater samples collected in the city of Otsu.

Decomplexation of aluminium–fluoride complexes by citrate-based buffers as a function of pH, aluminium and fluoride concentrations

Citrate-based buffers effectively decomplex AlFx complexes, a process which is not only pH-dependent, but also a function of both the fluoride and aluminium concentrations. At 1mg/l fluoride, the lowest concentration examined, the tolerance for Al3+ is relatively high and constant in the pH range 5.5–8. At a pH of 8 and at 100mg/l fluoride, the highest level tested, the tolerance for Al3+ is only about six times lower compared to the tolerance of a 1mg/l fluoride solution. However, at a pH of 5.5, the tolerance for Al3+ decreases about 500 times compared to the tolerance for Al3+ at 1mg/l F−. In other words, at a pH of 5.5, the tolerance for Al3+ decreases rapidly as F− levels increase, whereas the tolerance for Al3+ at a pH of 8 decreases very little towards higher F− levels. The intolerance for aluminium ions was also observed in calibration curves at high levels of Al3+ and low pH. The calibration curves are perfectly linear except in cases where the Al3+/F− ratio is too high (>10). Incomplete decomplexation caused the values of the slopes and intercepts to deviate from the regression values without Al3+. As a result, insufficient fluoride concentrations were measured when standard calibration curves were used without any Al3+ added.

Rate of water exchange between Al(C 2O 4)(H 2O) 4+(aq) complexes and aqueous solutions determined by 17O-NMR spectroscopy

Substitution of an oxalate molecule for two inner-coordination-sphere waters of Al(H 2O) 6 3+(aq) enhances, by a factor of ≈ 10 2, the rate of exchange of water molecules from the innercoordination sphere to the bulk solution. The rate parameters for chemical exchange are: k ex 298 = 109 s −1, ΔH ‡ = 68.9 ± 2.4 kJ/mol, and ΔS ‡ = 25.3 ± 6.7 J/mol/K, measured via dynamic 17O-NMR. This reactivity enhancement of coordinated waters by oxalate results from a change in bonding between Al(III) and oxygens throughout the complex upon ligation by oxalate. A similar process has been proposed to explain ligand-enhanced dissolution of oxide minerals (e.g., Stumm, 1991; Casey and Ludwig, 1995; Phillips et al., 1997) where a stable adsorbate increases the flux of metals from a surface. These new rate coefficients for aluminum-oxalate complexes, along with previous work on aluminum-fluoride complexes, show a correlation with the respective equilibrium constants similar to that obtained by Ludwig et al. (1995, 1996).

Phytotoxicity of aluminium-fluoride complexes and their uptake from solution culture by Avena sativa and Lycopersicon esculentum

Avena sativa (oats) and Lycopersiconesculentum (tomatoes) were grown in dilute nutrientsolutions supplemented with Al only, F only or acombination of both. In solutions containing Al andF, shoot growth was limited when predicted Alr(Al3+, AlOH2+ and Al(OH)\(_2^ + \))activities were < 0.1 μM, activities three orders ofmagnitude lower than the critical value determinedwith Al only. The data suggest that at the activitiesused in these experiments, Alr is most toxic,AlF2+ and AlF\(_2^ + \) are toxic to a lesserextent, and AlF3, AlF\(_4^ - \) and F-are least toxic. Fluoride concentrations in shootsgrown in solutions correlated best with positivelycharged AlF\(_x^{3 - x} \) species (i.e.AlF2+, AlF\(_2^ + \)) and the molar ratio ofF:Al in most plants shoots was about 3:2. However,when activities of positively chargedAlF\(_x^{3 - x} \) species were low (< 50 μM)and theactivity of AlF3 species high (500 μM) the molarratio of F:Al in plant shoots suggested AlF3 wastaken up. These findings are discussed in relation toplant uptake and toxicity. Measured concentrations of Alr and F- insolutions containing Al and F were compared withconcentrations predicted by a computer model(GEOCHEM-PC). The method for measuring F-concentrations, using a non-complexing buffer and Fion-selective electrode, gave good agreement withpredicted F- concentrations. The8-hydroxyquinoline method for measuring Alrconcentrations did not agree with predictedconcentrations, highlighting the limitations of thismethod when measuring Alr in the presence of F ina multi-ligand system with high concentrations of Fand Al.