Aluminium speciation studies in biological fluids. Part 8. A quantitative investigation of Al(III)–amino acid complex equilibria and assessment of their potential implications for aluminium metabolism and toxicity

Study of Al3+ interaction with AMP, ADP and ATP in aqueous solution

The interaction of Al³⁺ and nucleotide ligands, namely adenosine-5'-monophosphate, (AMP), adenosine-5'-diphosphate, (ADP), adenosine-5'-triphosphate, (ATP), has been studied in aqueous solution at T = 298.15 K and I = 0.15 mol L^-1 in NaCl (only for Al³⁺-ATP system at I = 0.1 mol L^-1). Formation constants and speciation models for the species formed are discussed on the basis of potentiometric results. The speciation models found for the three systems include ML and ML₂ species in all the cases, and for Al³⁺-ADP and ATP systems, MLH, MLOH and ML₂OH species as well. The formation constant value for ML species shows the trend, AMP < ADP < ATP. ¹H NMR spectroscopy was also employed for the study of Al³⁺-ATP system. The ¹H NMR results are in agreement with the speciation model obtained from analysis of potentiometric titration data, confirming the stabilities of the main species. Enthalpy change values were obtained by titration calorimetry; for the main Al³⁺-ATP species (at T = 298.15 K and I = 0.1 mol L^-1 in NaCl), they resulted always higher than zero, as typical for hard-hard interactions. The dependence of formation constants on ionic strength over the range I = 0.1 to 1 mol L^-1 in NaCl is also reported for Al³⁺-ATP system. The sequestering ability of the nucleotides under study towards Al³⁺ was also evaluated by the empirical parameter pL_0.5.

An integrated experimental and theoretical investigation of the vibrational modes and molecular structure of a chelate, tetraaqua cysteine aluminum(III)

The complex formed by Al(3+) and cysteine in aqueous solution has been studied by potentiometry, Raman spectroscopy and DFT calculations (DFT:B3LYP/6-311++G(∗∗)). Atomic charges, frontier molecular orbitals, electrostatic potential contour surface, electrostatic potential map and donor-acceptor second order perturbative energies were examined. The [Al(Cys)(H2O)4](2+) complex adopts a distorted octahedral geometry. Cysteine should act as a bidentate ligand through the oxygen of the carboxylate and the nitrogen of the amino group. The molecule has high HOMO-LUMO energy gap, intense intramolecular charge transfer and positive electrostatic potential.

Cisplatin administration influences on toxic and non-essential element metabolism in rats

Nowadays several papers deal with the effectiveness and side effects of metal complexes, especially cisplatin, in cancer therapy. The excretion of essential metal elements from the body is a serious problem in the treatment, but there are no data concerning the distribution and metabolism of toxic and nonessential elements. Therefore our aim was to study the concentration of some of these elements after treatment with cisplatin. Male Wistar rats (n=20, 175-190 g) were randomly divided into 2 groups (n=10/group). The control group received 1% (w/v) methyl cellulose at 10 mL/kg body weight, p.o. by gastric gavage twice daily for 14 days, while cisplatin was injected i.p. in a single dose of 6.5 mg/kg body weight. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used for measuring Al, B, Ba, Cr, Li, Ni, Pb, Pt, Sb, Si, Sn, Sr and V content in plasma, liver and kidney. Liver total scavenger capacity, diene conjugate content and malondialdehyde concentration were also determined. Cisplatin elevated the free radical reactions in the liver, although redox balance did not change significantly. According to the study it seems that the metabolism of Al, Ba, Cr, Ni, Pb, Sr were changed by the effect of cisplatin, and the most notable alterations were found for Al and Pb. Therefore, besides the toxic effect of and free radical induction by Pt, the side effects of increased levels of other toxic and non-essential elements have to be taken into consideration.

Ion-exchange and potentiometric characterization of Al–cystine and Al–cysteine complexes

The interaction between aluminium and cysteine and cystine was evaluated by means of ion-exchange experiments and potentiometry. Ion-exchange experiments included other ligands with affinity for aluminium and two kinds of resins, either a Na+ -form or an Al3+ -form exchanger. The ability of the ligands to keep aluminium in solution in the presence of the Na+ exchanger or to withdraw it from the Al3+ -form resin was evaluated. Aluminium quantification was carried out by either graphite-furnace or flame atomic absorption spectrometry. Aluminium extraction isotherms were linearised using the Scatchard plot, and stability constants were obtained from the curves' slopes. The experiments showed that the ability of the ligands to withdraw aluminium from the Al3+ -form resin increased following the order cysteine < oxalate < citrate = cystine < nitrilotriacetic acid < ethylenediaminetetraacetic acid. Potentiometric titrations, carried out in aqueous solution with constant ionic strength and temperature, showed that the predominant species in solution have a metal-ligand proportion of 1:1 for both amino acids. The main species are Al(OH)3L, with log K of 6.2 for cysteine, and AlL and Al(OH)L, with log K of 10.3 and 1.7, respectively, for cystine. Stability constants obtained from the Scatchard plots showed a linear correlation with the stability constants obtained by potentiometry for cystine and cysteine in this work and those collected from the literature for the other ligands. These results show that cysteine and cystine extract and maintain aluminium in solution, which may explain elevated concentrations of aluminium in parenteral nutrition solutions containing these amino acids.

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.

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.