Complexes of aluminium(III) with glucose-6-phosphate in aqueous solutions

The interaction of aluminium(III) with glucose-6-phosphate (GP: LH2) in aqueous solutions has been studied from pH 1 to pH 8, by pH-potentiometry and multinuclear (31P, 27Al, 13C) NMR spectroscopy. Various mononuclear species (MLH2, MLH, ML, ML2H, ML2 and MLH(-3)) and dinuclear complexes M2L2H-n (n=1-4) are formed in the system. NMR clearly indicates that GP is already bound to Al(III) at pH 1. The potentiometric speciation results are confirmed and completed by spectroscopic experiments. Many peaks are observed in the 31P NMR spectra suggesting the formation of isomeric species. An attempt to assign the signals to the corresponding complexes is made, allowing a discussion about their structure. Interestingly enough no metal ion-induced deprotonation and coordination of the alcoholic-OH functions have been observed.     

Metal ion-induced conformational changes of phosphorylated fragments of human neurofilament (NF-M) protein.

The NF-M subunit of human neurofilaments has a C-terminal repeating 13-mer sequence. The 13-mer (Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly) (NF-M13) and 17-mer (Glu-Glu-Lys-Gly)-(NF-M13) sequences were synthesized, as were both the mono- and diphosphorylated Ser species. Circular dichroism (c.d.) studies and c.d. titrations with Al3+ and Ca2+ were performed. The conformation of the phosphorylated and unphosphorylated material was random in water. Deconvolution of the c.d. spectra, in trifluoroethanol, of the untitrated samples yielded a high content of unordered structure, similar to the poly-L-proline II structure. Titration of the phosphorylated species with Al3+ or Ca2+ caused a surprising conformational change to occur, yielding a high content of beta-pleated sheet structure. A mechanism of metal binding to the phosphofragments is proposed which may be relevant to the formation of neurofibrillary tangles in Alzheimer's disease.     

Aluminium speciation in the Vienne river on its upstream catchment (Limousin region, France)

The aim of this study was to investigate the speciation of aluminium in the river Vienne on its upstream catchment (Limousin region, France) over a period of seven years (May 1998-September 2004) in order to assess harmful effects on aquatic life. Two sampling points were selected: the first at 4 km from the spring (Peyrelevade), and the second one at 89 km from the spring (Royères). The aluminium speciation was computed with Mineql+ 4.5 speciation software. Organic matter and phosphorous play a major role in aluminium speciation. If we consider the free aluminium ion (Al3+) as being the only toxic form of aluminium, the concentrations of toxic forms recorded at Peyrelevade and Royères were always below the toxic values for fish. However, if the sum of the concentrations of Al3+, Al(OH)2+, Al(OH)2+ and Al(OH)4- is taken into consideration, the concentration of aluminium recorded may have adverse effects on aquatic life in the upstream catchment of the river Vienne. Al(OH)4- is the major contributor to the concentration in toxic aluminium recorded. In general, Al(OH)4- forms appears in water during the summer with water alkalinisation due to an increase in photosynthetic activities.     

Complexation of labile aluminium species by chelating resins Iontosorb--a new method for Al environmental risk assessment

The utilization of chelating ion-exchange by the method based on binding strength and kinetic discrimination for aluminium fractionation was studied. Two chelating cellulose resins, Iontosorb Oxin (IO) and Iontosorb Salicyl (IS), were used for the determination of quickly reacting labile aluminium species. The possibilities of aluminium fractionation on these chelating resins were investigated by a solid phase extraction technique. The study of the pH (2.5-6.0) influence on the Al complexation by both resins indicates that at low pH the IS has lower sorption capacity but better adsorptive kinetic properties than IO. The optimal resin complexation time for reactive Al species was experimentally found after aluminium sorption study at pH 4.0 in synthetic solutions containing some inorganic and organic ligands, which simulate the composition of analysed acid soil and water samples. The negative influence of sulphate and iron on the Al complexation by IS resin was found and investigated. The flame atomic absorption spectrometry was used for the aluminium quantification.     

Chemical speciation of aluminium in beers

ABSTRACT

Details of analyses of a range of lagers for aluminium and for silica are presented. These permit an estimation of the total levels of aluminium as beer is diluted by saliva and intestinal fluids. These data are combined with databases of formation constants and solubility products and the MINEIR speciation program to calculate the chemical speciation of aluminium from beer through to excretion. Bioavailable species are assumed to be [Al citrate]⁰ and/or [Al phosphate]⁰ but other than a noticeable presence in the small intestine—from which uptake is limited there is not a significant species concentration. With normal kidney action any small traces entering the blood are rapidly cleared.     

Aluminium speciation in the presence of wheat root cell walls: a wet chemical study

Hydrolysis of Al³⁺ was performed in the presence of isolated root cell walls from a series of wheat cultivars (Triticum aestivum L.) known to have differential tolerance to Al contamination. Aluminium speciation was dependent on the cell wall concentration. At low cell wall concentrations, significant amounts of the very toxic Al₁₃ species were formed. At higher cell wall concentrations, formation of the tridecamer was hindered or completely inhibited. The sensitive wheat cultivars displayed a higher affinity for aluminium than the tolerant cultivars. A possible Al tolerance mechanism based on cell wall permeability is discussed.     

Soil Solution Chemistry Controlling the Field Distribution of Melica ciliata L.

Germination, establishment and growth of Melica ciliata L.,an 'acidifuge' species of rocky habitats in Europe, were studiedexperimentally and related to chemical properties of the soilsolution, including pH, base cation composition, Al concentrationand speciation, and Mn concentration. M. ciliata failed to establishin acid leptite soil. However, it was able to grow in solutionat pH 3·6 and exhibited vigorous growth at pH 3·9,a typical soil solution pH of leptite sites, which Melica isunable to colonize. Higher concentrations of Mn than those measuredin any leptite soil solutions did not influence growth. Exposureto 0·037 mmol l^-1 (1 mg l^-1) of Al³⁺, a concentrationusually exceeded in the soil solution of leptite sites, severelyretarded root growth. Speciation technique applied to Al insoil solutions obtained by centrifugation demonstrated a closerelationship between H⁺ and Al concentrations and, in particular,between H⁺ and free ionic (quickly reacting) Al species. Soilsolution concentrations of free ionic Al proved to be < 0·002mmol l^-1 in sites lacking Melica , but often > 0·10mmol l^-1 in site lacking Metalica . It is concluded that theinability of M. ciliata to establish in acid soils is not primarilydue to the high H⁺ concentration but to the high soil solutionconcentrations of Al, especially free Al ionic species at lowsoil pH.Copyright 1993, 1999 Academic Press Melica ciliata, distribution, soil solution, pH, aluminium speciation, manganese, base cations, iron     

The kinetics and mechanisms of the reactions of aluminium(III) with gallic acid, gallic acid methyl ester and adrenaline

The kinetics and mechanisms of the reactions of gallic acid, gallic acid methyl ester and adrenaline with aluminium(III) have been investigated in aqueous solution at 25 degrees C and an ionic strength of 0.5 M. A mechanism has been proposed which accounts satisfactorily for the kinetic data. This is consistent with a mechanism in which complex formation takes place almost exclusively by reaction of [Al(H2O)5OH]2+ with the ligands. [Al(H2O)5OH]2+ reacts with gallic acid, gallic acid methyl ester and adrenaline with rate constants of 1145, 1330 and 316 M(-1) s(-1) respectively. These data together with the equilibrium data enable the rate constants for reaction of [Al(H2O)6]3+ with both gallic acid and gallic acid methyl ester to be calculated. In view of the dissociative nature of water exchange on [Al(H2O)6]3+ and [Al(H2O)5(OH)]2+ the complex formation rate constants are discussed in terms of the Eigen-Wilkins-Tamm mechanism. The overall mechanisms have been validated using global analysis. The results are compared with previously published data on the complex formation reactions of aluminium(III). In addition, the rate constants and mechanisms for replacement of maltol by gallic acid methyl ester and diethylenetriaminepentaacetic acid (dtpa) have been investigated.     

Chemical speciation of binary complexes of L-valine with Co(II), Ni(II) and Cu(II) in propylene glycol-water mixtures

Abstract

Chemical speciation of Co(II), Ni(II) and Cu(II) complexes of L-valine in 0.0-60.0% v/v propylene glycol-water mixtures at an ionic strength of 0.16 mol L^-1 and 303.0 K was studied pH-metrically. Models containing different number of species were refined by using the computer program MINIQUAD75. The number of species in the models was chosen based on exhaustive modelling. The best-fit chemical models were arrived at based on statistical parameters. The formation and distribution of different species with varying pH were represented in the form of distribution diagrams. Influence of the solvent on the speciation was discussed based on the dielectric constant of the medium.     

Computer simulation of the distribution of aluminum speciation in soil solutions in equilibrium with the mineral phase imogolite.

The speciation of aluminum (Al) is a critical issue when evaluating the environmental and biological significance of elevated Al concentrations in soil solutions caused by acidic precipitation. Numerous studies have revealed that, with increased concentrations of silica acid in soil, the activity of Al species in soil solutions is greatly modified by SiO(4)(2-). However, thus far there has been little thorough theoretical modeling of this subject. This paper reports a computer simulation of the distribution of Al speciation in soil solutions in equilibrium with the mineral phase imogolite based on a chemical equilibrium calculation. The unique characteristic associated with imogolite reported by previous researchers can be explained theoretically by the proposed model. The dissolved silica has a remarkable influence on Al speciation: increasing concentrations of silica acid may effectively inhibit the formation of polymeric alumino-hydroxo species, and, furthermore, detoxify Al toxicity to plants.     

Electrostatic interactions between hyaluronan and proteins at pH 4: how do they modulate hyaluronidase activity

Hyaluronan (HA) hydrolysis catalyzed by hyaluronidase (HAase) is inhibited at low HAase over HA ratio and low ionic strength, because HA forms electrostatic complexes with HAase, which is unable to catalyze hydrolysis. Bovine serum albumin (BSA) was used as a model to study the HA-protein electrostatic complexes at pH 4. At low ionic strength, there is formation of (i) neutral insoluble complexes at the phase separation and (ii) small positively-charged or large negatively-charged soluble complexes whether BSA or HA is in excess. According to the ionic strength, different types of complex are formed. Assays for HA and BSA led to the determination of the stoichiometry of these complexes. HAase was also shown to form the various types of complex with HA at low ionic strength. Finally, we showed that at 0 and 150 mmol L(-1) NaCl, BSA competes with HAase in forming complexes with HA and thus induces HAase release resulting in a large increase in the hydrolysis rate. These results, in addition to data in the literature, show that HA-protein complexes, which can exist under numerous and varied conditions of pH, ionic strength and protein over HA ratio, might control the in vivo HAase activity.     

Study of the stability of aluminium trimeric clusters in aqueous solutions

Ab initio molecular dynamics (AIMD) based on density functional theory has been used to study small aluminium–oxygen complexes in water. Such Al–O clusters have been seen in several recent mass spectrometry studies. In this study, we have focused on trimeric Al–O clusters. The initial very compact trimeric Al–O structures opened up and formed linear Al–O chains. The typical Al–O coordination number in these chain structures was 5. We have performed long (up to 200 ps) AIMD simulations and these chain structures are stable on the nanosecond time scale. We have also studied the reactivity of the Al–O dimer and solvated Al. We found a formation path for the trimeric cluster, which has a action barrier (0.04 eV) and a reaction free energy of ? 0.55 eV. This suggests that the association of a dimer and a monomer Al–O species is fast and thermodynamically a very favourable process.     

A key role of aluminium in phosphorus availability,food web structure,and plankton dynamics in strongly acidified lakes

We studied extracellular acid phosphatase activity (AcPA) of planktonic microorganisms, aluminium (Al) speciation, and phosphorus (P) cycling in three atmospherically acidified (pH of 4.5–5.1) mountain forest lakes: ?ertovo jezero (CT), Prá?ilské jezero (PR), and Ple?né jezero (PL) in the Bohemian Forest (?umava, Böhmerwald). Microorganisms dominated pelagic food webs of the lakes and crustacean zooplankton were important only in PR, with the lowest Al concentrations (193 µg L^?1) due to 3–4 times lower terrestrial input. The lakes differed substantially in Al speciation, i.e., in the proportion of ionic and particulate forms, with the highest proportion of ionic Al in the most acid CT (pH = 4.5). The P concentration in the inlet of PL (mean: 22.9 µg L^?1) was about five times higher than in CT and PR (3.9 and 5.1 µg L^?1, respectively). Average total biomass of planktonic microorganisms in PL (593 µg C L^?1) was, however, only ～2-times higher than in CT and PR (235 and 272 µg C L^?1, respectively). Enormous AcPA (means: 2.17–6.82 µmol L^?1 h^?1) and high planktonic C : P ratios suggested severe P limitation of the plankton in all lakes. Comparing 1998 and 2003 seasons, we observed changes in water composition (pH and Al speciation) leading to a significant increase in phytoplankton biomass in the lakes. The increase in the seston C : P ratio during the same time, however, indicates a progressive P deficiency of the lakes. The terrestrial Al inputs, together with in-lake processes controlling the formation of particulate Al, reduced P availability for planktonic microorganisms and were responsible for the differences in AcPA. At pH < 5, moreover, ionic Al forms caused inhibition of extracellular phosphatases. We postulate that both particulate and ionic Al forms affect P availability (i.e., inhibition of extracellular phosphatases and inactivation of P), specifically shape the plankton composition in the lakes and affect plankton recovery from the acid stress.     

Evaluation of the speciation status of aluminium(III) ions in isolated osteoarthritic knee-joint synovial fluid

High field 1H NMR spectroscopy demonstrated that the equilibration of added Al(III) ions in osteoarthritic (OA) knee-joint synovial fluid (SF) resulted in its complexation by citrate and, to a much lesser extent, tyrosine and histidine. The ability of these ligands, together with inorganic phosphate, to compete for the available Al(III) in terms of (1) thermodynamic equilibrium constants for the formation of their complexes and (2) their SF concentrations was probed through the use of computer speciation calculations, which considered low-molecular-mass binary and ternary Al(III) species, the predominant Al(III) plasma transport protein transferrin, and also relevant hydrolysis and precipitation processes. It was found that, at relatively low added Al(III) concentrations, citrate species were more favoured, whilst phosphate species became dominant at higher levels. The significance of these findings with regard to the in vivo corrosion of aluminium-containing metal alloy joint prostheses (e.g., TiAlV alloys) is discussed.     

Model studies of the precipitation of silica in the presence of aluminium; implications for biology and industry

The unique chemical affinity between the oxides of silicon and aluminium has been cited as a potential route for the amelioration of the detrimental effects of aluminium in the environment and in biological systems. A greater understanding of silicon-aluminium interactions may assist in this endeavour and also provide a means of overcoming silica fouling problems encountered by industry which are exacerbated by the presence of aluminium. It is also conceivable that this increased knowledge may demonstrate a positive use for aluminium in the processing of the silicon dioxide phase. In this study we report the effect of aluminium ions, derived from aluminium chloride, on silicic acid species obtained from potassium catecholato complexes of silicon at circumneutral pH at the molar ratios 1000Si:Al, 100Si:Al and 50Si:Al. Silica and low levels of aluminium-rich silica materials were formed with Si:Al ratios of about 3.5:1 comparable with the element ratios detected in senile plaques and aluminium-rich scale. A kinetic study showed that aluminium in the reaction medium slowed down the rate of formation of one of the silica species formed early in the condensation process, e.g. trimers, but increased the rate at which silicic acid was removed from sub 1 nm diameter particles. The materials precipitated in the presence of aluminium were composed of smaller particles and aggregates with smaller pores (Si100:Al and Si50:Al systems) or larger pores (Si1000:Al) compared to the control. The nature of the interactions responsible for these differences is discussed. The effects described here demonstrate the ability of silica and aluminium to interact under conditions such as those found in biological systems. That silica reacts with aluminium in the presence of catechol supports the protective role assigned to silicon.     

Oil formation from glucose with formic acid and cobalt catalyst in hot-compressed water

Liquefaction of glucose into oil was examined in hot-compressed water at 300 degrees C and 30 or 60 min in a tumbling batch reactor. The effects of alkali (KHCO(3)), a hydrogenating agent (HCO(2)H), and a cobalt catalyst (Co(3)O(4)) were studied. Also the combinations of these additives were investigated. HCO(2)H and KHCO(3) showed a positive effect on oil formation. Co(3)O(4) was found to be an advantageous additive as well, increasing the oil formation from glucose, but the stability of this catalyst under reaction conditions was quite low.     

A study in the adsorption of Fe(2+) and NO(3)(-) on pine needles based hydrogels

Novel supports for use as cation and anion adsorbents were prepared from lignocellulosics using pine needles and their carboxymethylated forms by network/hydrogel formation with acrylamide and N,N-methylene bisacrylamide. The hydrogels thus prepared were further functionalized by partial alkaline hydrolysis with 0.5 N NaOH and were characterized by FTIR, SEM and nitrogen analysis. Adsorption of Fe(2+) on these hydrogels was carried as a function of time, temperature, pH and ionic strength. The hydrogel having the maximum adsorption capacity was loaded with Fe(2+) at the conditions those afforded maximum uptake and was used as novel anionic adsorbent for NO(3)(-). The water uptake capacities and biodegradability of the hydrogels before and after the ion loading was studied to evaluate the possible end-uses of these hydrogels as alternate materials in the removal of ionic species from water.     

Speciation study of the anti-inflammatory drug tenoxicam (Htenox) with Cu(II): X-ray crystal structure of [Cu(tenox)(2)(py)(2)].EtOH

A speciation study was carried out in aqueous solution of the anti-inflammatory drug tenoxicam (Htenox), under quasi-physiological conditions (temperature of 37 degrees C and ionic strength 0.15 M NaCl) in order to determine the acidity constants from spectrophotometric studies, the pK(a) values found being pK(1)=1.143+/-0.008 and pK(2)=4.970+/-0.004. Subsequently, the spectrophotometrical speciation of the different complexes of Cu(II) with the drug was performed under the same conditions of temperature and ionic strength, observing the formation of Cu(Htenox)(2)(2+) with log beta(212)=20.05+/-0.01, Cu(tenox)(2) with log beta(012)=13.6+/-0.1, Cu(Htenox)(2+) with log beta(111)=10.52+/-0.08, as well as Cu(tenox)(+) with log beta(011)=7.0+/-0.2, all of them in solution, and solid species Cu(tenox)(2)(s) with an estimated value of log beta(012)(s) approximately 18.7. The crystalline structure of the complex [Cu(tenox)(2)(py)(2)]. EtOH, was also determined, and it was observed that tenoxicam employs the oxygen of the amide group and the pyridyl nitrogen to bond to the cation.     

Magnesium uptake by Al-stressed maize plants with special emphasis on cation interactions at root exchange sites

As aluminium (Al) severely inhibits magnesium (Mg) uptake by many plant species, Mg uptake and Mg-Al interactions in maize (Zea mays L.) were studied in a series of short and long-term experiments. A relationship between Mg uptake and the degree of Mg saturation of exchange or binding sites of the root apoplast (root-CEC) was studied by growing plants in solutions containing: (i) different concentrations of Al, calcium (Ca) and hydrogen (H) ions; and (ii) a number of organic complexes of Al. In short-term experiments, Ca had little effect on the Mg nutrition of maize plants. However, with increasing concentrations of Al and H ions in nutrient solution, there was a decrease in both the degree of Mg saturation of root-CEC and Mg uptake. Effects of pH on cation (H, Al, Mg, Ca) binding at the root apoplasm were pronounced and complicated because of a simultaneous change of H ion concentration, effective root-CEC and Al speciation. The behaviour of Al as organic Al complexes differed from that supplied as aluminium chloride (AlCl₃). In the presence of organo-Al complexes, less Mg was replaced from apoplastic binding sites and Mg uptake was inhibited less severely than with AlCl₃. In a long-term experiment, Al-citrate, in contrast with AlCl₃, was not phytotoxic to maize, expressed by the lack of any inhibition of shoot biomass production.     

Interactions of aluminium(III) with glycerolphosphates and glycerophosphorylcholine

The complexation of aluminium(III) with glycerol-1-phosphate (G1P) and glycerol-2-phosphate (G2P) in aqueous solutions has been studied as a function of pH, by pH-potentiometry, 31P NMR spectroscopy and ESI mass spectrometry. Various mononuclear complexes (MLH(2)(3+), MLH(2+), ML(+), ML(2)H, ML(2)(-)) and polynuclear species (M(3)L(3)H(-1)(2+), M(3)L(2)H(-n)((n-5)-) with n=5, 6, 7, M(2)L(2)H(-1)(+) ) are formed in the system where the full protonated ligands are noted LH(2). NMR experiments clearly show that G1P and G2P already interact with Al(III) at pH 1. The potentiometric results are confirmed by ESI measurements and 31P NMR studies. No metal ion-induced deprotonation and coordination of the alcoholic-OH functions seem to occur during the complexation. The situation is very different for the glycerophosphorylcholine ligand (GPC identical with LH). Only the complex ML(3+) is formed in aqueous solution with a relatively low formation constant (K=5 at 37 degrees C). This species is clearly identified in 31P and 27Al NMR spectra. The complexation study as a function of the temperature allowed us to determine the thermodynamic parameters of the complex formation. The complexation is not governed by the reaction enthalpy that is found to be positive but by the entropy that is largely positive.