Time-Dependent Solution Speciation of the AlIII−Citrate System: Potentiometric and NMR Studies

Abstract

Time-dependent potentiometric and NMR spectroscopic measurements were carried out in the Al III −citric acid system in an equimolar solution and at an excess of ligand in order to monitor the changes in speciation as a function of time. In fresh solutions, the mononuclear 1:1 species [AlLH] + , [AlL], [AlLH −1 ] − and [AlLH −2 ] 2− and the 1:2 complexes [AlL 2 ] 3− , [AlL 2 H −1 ] 4− and [AlL 2 H −2 ] 5− are formed. In agreement with earlier findings (Inorg. Chem . 1988, 27, 2565), these complexes are converted to a large extent into a thermodynamically more stable trinuclear species as the solutions age. Depending on the composition of the initially formed mono- [a]

Nanoparticles for Enhanced Oil Recovery: Influence of pH on Aluminum-Cross-linked Partially Hydrolyzed Polyacrylamide-Investigation by Rheology and NMR

“…At pH 3.85, a complicated pattern resembling the trinuclear complex specie is observed. This is in agreement with previous observations. ,, In fact, a trinuclear complex was observed even below this pH. , Around this pH a bis-ligand complex, [Al(Cit) 2 ] 3– is reported by Bodor and co-workers at molar concentration of 0.25 M Al and 1.0 M Cit . However, we did not observe this complex, probably because of the low concentration as well as low ratio of Cit-to-Al used here (0.7 mM Al and 1.1 mM Cit).…”

“…Furthermore, molecular exchange between aluminum-bound and unbound citrate (intermolecular ligand exchange) and within bound citrate (intramolecular ligand exchange) results in line broadening. Speciation of AlCit complexes as a function of pH has been studied extensively. − Öhman showed that primarily mononuclear AlCit complexes are formed in dilute solutions, that is, citrate concentrations in the order of 10 –6 M, whereas polynuclear complexes are the dominating species for semidilute solutions with concentrations about 10 –3 M . The concentration of aluminum and citrate used in the present work is 0.7 and 1.1 mM, respectively, suggesting that polynuclear complexes are the dominating complexes formed for AlCit at these conditions.…”

Nanoparticles for Enhanced Oil Recovery: Influence of pH on Aluminum-Cross-linked Partially Hydrolyzed Polyacrylamide-Investigation by Rheology and NMR

“…At pH 3.85, a complicated pattern resembling the trinuclear complex specie is observed. This is in agreement with previous observations. ,, In fact, a trinuclear complex was observed even below this pH. , Around this pH a bis-ligand complex, [Al(Cit) 2 ] 3– is reported by Bodor and co-workers at molar concentration of 0.25 M Al and 1.0 M Cit . However, we did not observe this complex, probably because of the low concentration as well as low ratio of Cit-to-Al used here (0.7 mM Al and 1.1 mM Cit).…”

“…Furthermore, molecular exchange between aluminum-bound and unbound citrate (intermolecular ligand exchange) and within bound citrate (intramolecular ligand exchange) results in line broadening. Speciation of AlCit complexes as a function of pH has been studied extensively. − Öhman showed that primarily mononuclear AlCit complexes are formed in dilute solutions, that is, citrate concentrations in the order of 10 –6 M, whereas polynuclear complexes are the dominating species for semidilute solutions with concentrations about 10 –3 M . The concentration of aluminum and citrate used in the present work is 0.7 and 1.1 mM, respectively, suggesting that polynuclear complexes are the dominating complexes formed for AlCit at these conditions.…”

Speciation of AlIII in Blood Serum − The AlIII−Citrate−Phosphate Ternary System

“…The time course of the pH changes proved to be dependent on the starting pH of the samples: starting at pH < 5.6, the hydrogen ion concentration increases with time, while above this pH it decreases. Similar behaviour was observed for the binary Al III −citrate system16 and was explained in terms of the slow oligomerization of the mononuclear complexes with formation of the trinuclear species [Al 3 (AH −1 ) 3 OH] 4− . While the oligomerization of the semi‐protonated mononuclear complexes is accompanied by the release of protons in the acidic pH range, at basic pH the mixed hydroxo species oligomerize with the liberation of hydroxide ions 16.…”

Aluminum speciation in biological environments. The deprotonation of free and aluminum bound citrate in aqueous solution

“…However, the aging of the solution led to a thermodynamically more stable [Al 3 Á(OH)(LH À1 ) 3 ] À4 compound. Similar results were achieved by time-dependent potentiometric and NMR spectroscopic measurements, 27 finding that various species with 1 :…”

Nanoparticles for Enhanced Oil Recovery: Influence of pH on Aluminum-Cross-linked Partially Hydrolyzed Polyacrylamide-Investigation by Rheology and NMR

“…At pH 3.85, a complicated pattern resembling the trinuclear complex specie is observed. This is in agreement with previous observations. ,, In fact, a trinuclear complex was observed even below this pH. , Around this pH a bis-ligand complex, [Al(Cit) 2 ] 3– is reported by Bodor and co-workers at molar concentration of 0.25 M Al and 1.0 M Cit . However, we did not observe this complex, probably because of the low concentration as well as low ratio of Cit-to-Al used here (0.7 mM Al and 1.1 mM Cit).…”

“…Furthermore, molecular exchange between aluminum-bound and unbound citrate (intermolecular ligand exchange) and within bound citrate (intramolecular ligand exchange) results in line broadening. Speciation of AlCit complexes as a function of pH has been studied extensively. − Öhman showed that primarily mononuclear AlCit complexes are formed in dilute solutions, that is, citrate concentrations in the order of 10 –6 M, whereas polynuclear complexes are the dominating species for semidilute solutions with concentrations about 10 –3 M . The concentration of aluminum and citrate used in the present work is 0.7 and 1.1 mM, respectively, suggesting that polynuclear complexes are the dominating complexes formed for AlCit at these conditions.…”

Speciation of AlIII in Blood Serum − The AlIII−Citrate−Phosphate Ternary System

“…The time course of the pH changes proved to be dependent on the starting pH of the samples: starting at pH < 5.6, the hydrogen ion concentration increases with time, while above this pH it decreases. Similar behaviour was observed for the binary Al III −citrate system16 and was explained in terms of the slow oligomerization of the mononuclear complexes with formation of the trinuclear species [Al 3 (AH −1 ) 3 OH] 4− . While the oligomerization of the semi‐protonated mononuclear complexes is accompanied by the release of protons in the acidic pH range, at basic pH the mixed hydroxo species oligomerize with the liberation of hydroxide ions 16.…”

Aluminum speciation in biological environments. The deprotonation of free and aluminum bound citrate in aqueous solution

“…However, the aging of the solution led to a thermodynamically more stable [Al 3 Á(OH)(LH À1 ) 3 ] À4 compound. Similar results were achieved by time-dependent potentiometric and NMR spectroscopic measurements, 27 finding that various species with 1 :…”

Nanoparticles for Enhanced Oil Recovery: Influence of pH on Aluminum-Cross-linked Partially Hydrolyzed Polyacrylamide-Investigation by Rheology and NMR

“…At pH 3.85, a complicated pattern resembling the trinuclear complex specie is observed. This is in agreement with previous observations. ,, In fact, a trinuclear complex was observed even below this pH. , Around this pH a bis-ligand complex, [Al(Cit) 2 ] 3– is reported by Bodor and co-workers at molar concentration of 0.25 M Al and 1.0 M Cit . However, we did not observe this complex, probably because of the low concentration as well as low ratio of Cit-to-Al used here (0.7 mM Al and 1.1 mM Cit).…”

“…Furthermore, molecular exchange between aluminum-bound and unbound citrate (intermolecular ligand exchange) and within bound citrate (intramolecular ligand exchange) results in line broadening. Speciation of AlCit complexes as a function of pH has been studied extensively. − Öhman showed that primarily mononuclear AlCit complexes are formed in dilute solutions, that is, citrate concentrations in the order of 10 –6 M, whereas polynuclear complexes are the dominating species for semidilute solutions with concentrations about 10 –3 M . The concentration of aluminum and citrate used in the present work is 0.7 and 1.1 mM, respectively, suggesting that polynuclear complexes are the dominating complexes formed for AlCit at these conditions.…”

Speciation of AlIII in Blood Serum − The AlIII−Citrate−Phosphate Ternary System

“…The time course of the pH changes proved to be dependent on the starting pH of the samples: starting at pH < 5.6, the hydrogen ion concentration increases with time, while above this pH it decreases. Similar behaviour was observed for the binary Al III −citrate system16 and was explained in terms of the slow oligomerization of the mononuclear complexes with formation of the trinuclear species [Al 3 (AH −1 ) 3 OH] 4− . While the oligomerization of the semi‐protonated mononuclear complexes is accompanied by the release of protons in the acidic pH range, at basic pH the mixed hydroxo species oligomerize with the liberation of hydroxide ions 16.…”

Aluminum speciation in biological environments. The deprotonation of free and aluminum bound citrate in aqueous solution

“…However, the aging of the solution led to a thermodynamically more stable [Al 3 Á(OH)(LH À1 ) 3 ] À4 compound. Similar results were achieved by time-dependent potentiometric and NMR spectroscopic measurements, 27 finding that various species with 1 :…”