Hydroxyaluminosilicates (HAS)

 

We were the first to demonstrate that silicic acid (Si(OH)4) protected against aluminium toxicity (Birchall, Exley et al., (1989) Nature 338, 146-148) and that hydroxyaluminosilicates (HAS) were sufficiently stable to prevent aluminium toxicity in fish in acid waters (Exley et al., (1997) J Theoret Biol 189, 133-139). We have since identified two discrete forms of HAS which we have called HASA and HASB and we have determined their structures and how they are formed.

Hydroxyaluminosilicate structures (left); biological availability and solid phase, HASA and HASB self aggregation (right)

HAS Formation

Schematic showing pH-dependent formation and stability of Al(OH)3(s), HASA and HASB with particular reference to their abilities to carry charge, their pH of minimum solubility and their aggregation towards filterable sizes. From Exley (2012).

To find out more, check out the following references:

  1. Birchall JD, Exley C, Chappell JS & Phillips MJ (1989) Acute toxicity of aluminium to fish eliminated in silicon-rich acid waters. Nature, 338, 146-148.
  2. Birchall JD & Exley C (1992) Silicon and the bioavailability of aluminium. Metal Compounds in Environment and Life, 4, 411-418.
  3. Exley C & Birchall JD (1992) Hydroxyaluminosilicate formation in solutions of low total aluminium concentration. Polyhedron, 11, 1901-1907.
  4. Exley C & Birchall JD (1993) A mechanism of hydroxyaluminosilicate formation. Polyhedron, 12, 1007-1017.
  5. Exley C, Tollervey A, Gray G, Roberts S & Birchall JD (1993) Silicon, aluminium and the biological availability of phosphorus in algae. Proceedings of the Royal Society of London Series B 253, 93-99.
  6. Exley C & Birchall JD (1995) Comment on "An assessment of complex formation between aluminium and silicic acid in acidic solutions". Geochimica Cosmochimica Acta 59, 5, 1017-1018.
  7. Exley C & Birchall JD (1995) Comment on " An assessment of complex formation between aluminium and silicic acid in acidic solutions". Geochimica Cosmochimica Acta 59, 5, 1017-1018.
  8. Exley C & Birchall JD (1996) Silicic acid and the biological availability of aluminium. European Journal of Soil Science 47, 137.
  9. Exley C, Pinnegar JK & Taylor H (1997) Hydroxyaluminosilicates and acute aluminium toxicity in fish. Journal of Theoretical Biology 189, 133-139.
  10. Exley C (1998) Silicon in life: A bioinorganic solution to bioorganic essentiality. Journal of Inorganic Biochemistry 69, 139-144.
  11. Doucet FJ, Schneider C, Bones SJ, Kretchmer A, Moss I, Tekely P & Exley C (2001) The formation of hydroxyaluminosilicates of geochemical and biological significance. Geochimica Cosmochimica Acta 65, 2461-2467.
  12. Schneider C & Exley C (2001) Silicic acid (Si(OH)4) is a significant influence upon the atomic absorption signal of aluminium measured by graphite furnace atomic absorption spectrometry (GFAAS). Journal of Inorganic Biochemistry 87, 45-50.
  13. Doucet FJ, Rotov ME & Exley C (2001) Direct and indirect identification of the formation of hydroxyaluminosilicates (HAS) in acidic solutions. Journal of Inorganic Biochemistry 87, 71-79.
  14. Exley C, Schneider C & Doucet FJ (2002) The reaction of aluminium with silicic acid in acidic solution: An important mechanism in controlling the biological availability of aluminium ? Coordination Chemistry Reviews 228, 127-135.
  15. Exley C (2003) A biogeochemical cycle for aluminium ? Journal of Inorganic Biochemistry, 97, 1-7.
  16. Schneider C, Doucet F, Strekopytov S & Exley C (2004) The solubility of an hydroxyaluminosilicate. Polyhedron 23, 3185-3191.
  17. Strekopytov S & Exley C (2005) The formation, precipitation and structural characterisation of hydroxyaluminosilicates formed in the presence of fluoride and phosphate. Polyhedron 24, 1585-1592.
  18. Strekopytov S & Exley C (2006) Thermal analyses of aluminium hydroxide and hydroxyaluminosilicates. Polyhedron 25, 1707-1713.
  19. Strekopytov S, Jarry E & Exley C (2006) Further insight into the mechanism of formation of hydroxyaluminosilicates. Polyhedron 25, 3399-3404.
  20. Exley C (2007) The solubility of hydroxyaluminosilicates and the biological availability of aluminium. In; Thermodynamics, Solubility and Environmental Issues (Ed. Letcher TM), Elsevier Science, Amsterdam, The Netherlands. p 315-325.
  21. Exley C (2012) Reflections upon and recent insight into the mechanism of formation of hydroxyaluminosilicates and the therapeutic potential of silicic acid. Coordination Chemistry Reviews 256, 82-88.