The chemistry of aluminum as related to biology and medicine.
The increasing number of roles discovered for Al3+ in physiological processes demands an understanding of how Al3+ interacts with compounds in biological systems. Al3+ is expected to complex with oxygen donor ligands, especially phosphates, and it does so in soils, in the gastrointestinal tract, and in cells. The stability of Al3+ complexes has generally been misjudged because of lack of recognition that free, aqueous Al3+ is not the dominant form in neutral solutions and that the solubility of Al(OH)3 limits the free Al3+ at the plasma pH 7.4 to less than 10(-11) mol/L. In the presence of inorganic phosphate, the permitted free Al3+ is decreased further, through formation of insoluble aluminum phosphate. This precipitate facilitates the elimination of Al3+ from the body. In contrast, citrate solubilizes Al3+, and an appreciable fraction occurs as a neutral complex that may pass through membranes and provide a vehicle for Al3+ absorption into the body. In the blood plasma the most likely small-molecule complex is that with citrate, while the only competitive protein complex is that with transferrin, a protein built to transport Fe3+ but whose sites are only 30% occupied.
D000535:Aluminum / Q000378:metabolism; D001798:Blood Proteins / Q000378:metabolism; D002021:Buffers; D002412:Cations; D055598:Chemical Phenomena; D002621:Chemistry; D002951:Citrates / Q000378:metabolism; D019343:Citric Acid; D005459:Fluorides / Q000378:metabolism; D006801:Humans; D008670:Metals; D010710:Phosphates / Q000378:metabolism; D011522:Protons; D012995:Solubility
D001798:Blood Proteins; D002021:Buffers; D002412:Cations; D002951:Citrates; D008670:Metals; D010710:Phosphates; D011522:Protons; D019343:Citric Acid; D000535:Aluminum; D005459:Fluorides