Application of dopamine as an electroactive ligand for the determination of aluminum in biological fluids

Acetylcholinesterase inhibition-based biosensor for aluminum(III) chronoamperometric determination in aqueous media

A novel amperometric biosensor for the determination of Al(III) based on the inhibition of the enzyme acetylcholinesterase has been developed. The immobilization of the enzyme was performed on screen-printed carbon electrodes modified with gold nanoparticles. The oxidation signal of acetylthiocholine iodide enzyme substrate was affected by the presence of Al(III) ions leading to a decrease in the amperometric current. The developed system has a detection limit of 2.1 ± 0.1 μM for Al(III). The reproducibility of the method is 8.1% (n = 4). Main interferences include Mo(VI), W(VI) and Hg(II) ions. The developed method was successfully applied to the determination of Al(III) in spiked tap water. The analysis of a certified standard reference material was also carried out. Both results agree with the certified values considering the respective associated uncertainties.

Chronic exposure to aluminum reduces tyrosine hydroxylase expression in the substantia nigra and locomotor performance in rats

Aluminum (Al) is a neurotoxic agent that accumulates in the substantia nigra of patients affected by Parkinson's disease and in other cerebral areas of different neurodegenerative pathologies. Al has been associated with neuronal and glial dysfunctions, and neuronal changes have been suggested to affect several neurotransmitter systems including the dopaminergic system. The present study was designed to evaluate by means of immunohistochemistry using antibodies against tyrosine hydroxylase (TH; the rate-limiting enzyme of dopamine synthesis) the effects of chronic Al exposure (0, 3%) in drinking water during 4 months in adulthood or since intra-uterine age in the substantia nigra. Our results show a significant decrease in the number of cells labeled by the antibody against TH in rats treated with Al compared to controls. The TH-immunoreactive decrease following Al treatment is accentuated in the rat group treated since intrauterine age. In both treated groups, Al exposure induced a significant decrease of locomotor performance. Interestingly, as for TH-immunoreactivity, the decreased locomotor activity was also accentuated in the group treated since intrauterine age. The Al-induced TH alterations may be one of the causes of aluminum-induced neurotoxicity.

Linear scan voltammetric indirect determination of AlIII by the catalytic cathodic response of norepinephrine at the hanging mercury drop electrode

The biological effects of aluminum (Al) have received much attention in recent years. Al is of basic relevance as concern with its reactivity and bioavailability. In this paper, the electrochemical behaviors of norepinephrine (NE) in the absence and presence of Al(III) at the hanging mercury drop electrode have been studied and applied to the practical analysis. Highly selective catalytic cathodic peak of NE is yielded by linear scan voltammetry (LSV) at -1.32 V (vs. SCE). A linear relationship holds between the cathodic peak current and the Al(III) concentration. It has been successfully applied to the determination of Al(III) in real waters and synthetic biological samples with satisfying results, which are in accordance with those obtained by ICP-AES method. The electrochemical properties and the mechanisms of the peaks in the presence and absence of Al(III) have been explored. The results show that they are irreversible adsorptive hydrogen catalytic waves. These studies not only enrich the methods of determining Al, but also lay foundations of further understanding of the mechanisms of neurodementia.

NMR spectra and potentiometry studies of aluminum(III) binding with coenzyme NAD+ in acidic aqueous solutions

Complexation and conformational studies of coenzyme NAD+ with aluminum were conducted in acidic aqueous solutions (pH 2-5) by means of potentiometry as well as multinuclear (1H, 13C, 31P, 27Al) and two-dimensional (1H, 1H-NOESY) NMR spectroscopy. These led to the following results: (1) Al could coordinate with NAD+ through the following binding sites: N7' of adenine and pyrophosphate free oxygen (O(A)1, O(N)1,O(A)2) to form various mononuclear 1:1 (AlLH23+, AlLH2+) and 2:1 (AlL2-) species, and dinuclear 2:2 (Al2L22+) species. (2) The conformations of NAD+ and Al-NAD+ depended on the solvents and different species in the complexes. The results suggest the occurrence of an Al-linked complexation, which causes structural changes at the primary recognition sites and secondary conformational alterations for coenzymes. This finding will help us to understand role of Al in biological enzyme reaction systems.

Multimethod characterization of the interaction of aluminum ion with alpha-ketoglutaric acid in acidic aqueous solutions

It has recently been reported that aluminum plays a very important role in reducing the activity of Krebs-cycle enzymes and glutamate dehydrogenase in rat brain homogenate. Therefore, it is necessary to identify the aluminum binding ability with the pivotal substrate alpha-ketoglutarate in biological systems. The interactions of aluminum with alpha-ketoglutarate were studied with pH-potentiometry, cyclic voltammetry, UV-vis, 1H, 27Al-NMR and Raman spectra multi-analytical techniques in acidic aqueous solution to measure the stoichiometries and stability constants of the complexes and its keto-enol tautomerism. The alpha-ketoglutarate was found to bind Al in a bidentate manner at the carboxylate and carbonyl moieties. The mononuclear 1:1 (AlLH(-1), AIL+, AlHL2+) and 2:1 (AlL2-, AlL2H(-2)3-) species, and dinuclear 2:1 (Al2L4+) species were found in acidic aqueous solution. Meanwhile, Al can promote alpha-KG tautomerize to its enolic-structure compounds in solutions. These findings may help to further understand the influence of Al on GDH enzyme reactions in biological systems.

Potentiometric and multi-NMR studies of aluminum(III) complex with L-glutamate in acidic aqueous solutions

Complex formation studies of L-glutamate with aluminum(III) ion were conducted in acidic aqueous solutions (pH 2.0 - 5.5) by means of pH-metric titration and multinuclear (1H, 13C and 27Al) NMR techniques. The following results were obtained: (1) Al could weakly coordinate with Glu to form various mononuclear 1:1 (AlLH2+, AlL+, AlLH(-1)) species and dinuclear 2:1 (Al2L4+) species in acidic aqueous solutions, which somewhat agreed with previous findings. (2) The multi-NMR spectra of Al-Glu and Al-Asp strongly suggest that, besides negatively charged carboxylate donors (-COO(-), -COO(-)), the amino group of Glu can participate in the binding of Al in the AlL+ and AlLH(-1) species in the case of its deprotonation, which rather agreed with the case of Al-Asp. (3) These tridentate five-+seven-membered joint chelate (-COO(-), -NH2, -COO(-)) complexes exhibit an enhanced stability, which can help to better understand the biological studies that Al-Glu could cross the erythrocyte membrane and the blood-brain barrier (BBB) and be deposited selectively in various brain regions, particularly in the cortex. It will also help to intrinsically understand the Al's role in the biological transamination system, which is a very important process in all living things.