Silica deposition induced by isolated aluminum ions bound on chelate resin as a model compound of the surface of microbes.

To elucidate the mechanism of silica biodeposition in hot spring water, which is induced by Al(3+) ions bound to the surface of microbes, a chelate resin (Chelex 100) was used as a model compound of the surface of microbes. No silicic acid was adsorbed on the Na type Chelex 100, whereas silicic acids were significantly adsorbed to the Al type Chelex 100. In the Al type Chelex 100, the Al(3+) ions were present as 1:1 tridentate complex with iminodiacetate (IDA) group. After adsorption of silicic acid to Al type Chelex 100, a IDA-Al-O-Si-(OH)(3) site formed. The site acted as a template for the successive adsorption of silicic acids to form silica sheets around Al type Chelex 100 particles. In conclusion, Al(3+) ions bound to the surface of microbes play a key role as a trigger for the biodeposition of silica in hot spring water.

Formation conditions and stability of a toxic tridecameric Al polymer under a soil environment.

It is important to study the formation conditions and the stability of the tridecameric Al polymer (Keggin-type Al(13) polycation, [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+), known as Al(13)) due to its strong toxicity to living organisms of a soil environment. In order to examine the pH range where toxic Al(13) can exist in aqueous solution, (27)Al NMR spectra for sample solutions containing Al(3+) ions with various pH (pH 3.5-6.1) were measured. The results show that the peak due to Al(13) (peak due to 4-coordinated Al around 63 ppm) appeared at pH 3.6-5.7 and the peak intensity was relatively high at pH 4.1-4.8, suggesting that Al(13) can be formed at pH 3.6-5.7, while it can exist dominantly at pH 4.1-4.8. It was also found that Al(13) can stably adsorb onto a chelate resin, Chelex 100, by weak electrostatic interaction. The Chelex 100, with iminodiacetate groups, served as a model compound for surfaces of microbes covered with carboxyl groups and for surfaces of soil particles covered with humic substances having many carboxyl groups. Additionally, decomposition of Al(13) did not occur even after adsorption, and its pH stability range was wide compared to that in aqueous solution.