¹³C and ²7Al NMR study of complexation between aluminium ion and simple dicarboxylic acids under an acidic condition: new peak assignments of ²7Al NMR spectra of mixed solutions of Al³âº and simple dicarboxylic acids.

Due to a consideration of Al detoxicification by simple carboxylic acid, the interaction between aluminium ion (Al³âº) and three dicarboxylic acids (oxalic acid (OX), malonic acid (MA) and succinic acid (SU)) under an acidic condition was investigated using ¹³C and ²7Al NMR techniques. Based on deconvolution of the ²7Al NMR spectra and quantitative ¹³C NMR spectra, the structure of each complex was elucidated. Especially, we focused on the peak assignments of ²7Al NMR spectra by combining of the results of quantitative ¹³C NMR spectra. In the OX system, the peak at 16 ppm in the ²7Al NMR spectrum originates from Al(OX)3³â» and Al(OX)2⁻, and the ratio of each complex depends on the OX/Al molar ratio. In the MA system, the three complexes (Al(MA)2⁻, Al(MA)3³â» and Al(MA)⁺) are represented in the peak at 2 ppm in the ²7Al NMR spectrum. The assignment of peaks in the ²7Al NMR spectra in this study differs from those described in previous papers.

Quantification method of size distribution of polysilicic acid in supersaturated silicic acid solution.

In order to estimate the absolute size distribution of polysilicic acid particles in geothermal waters, the distribution coefficient (K(av)) of gel permeation chromatography (GPC) for polysilicic acid particles and the hydrodynamic radius for the same polysilicic acid particles from Dynamic Light Scattering (DLS) are combined to quantify the particle size. From the combination, a quantitative relationship between the K(av) from GPC and the hydrodynamic radius for polysilicic acid from DLS was built up. Using this relationship, the change in particle size of polysilicic acid formed during the polymerization of silicic acid at pH 8 and 9 (initial silicic acid concentration: 800 ppm as SiO2) was examined. The result showed that polysilicic acid grew to 500 and 1000 nm by 5 h at pH 9 and 8, respectively. It was found that aluminum affects the growth of polysilicic acid particles, and that the effect depends on the pH. The proposed method in this study has been proved to be valid to measure the size of polysilicic acid during the polymerization of silicic acid in solutions with relatively low silicic acid concentration, such as geothermal water.

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.

Interaction between Al3+ and acrylic acid and polyacrylic acid in acidic aqueous solution: a model experiment for the behavior of Al3+ in acidified soil solution.

From the viewpoint of the phytotoxicity and mobility of Al(3+) released from soil minerals due to soil acidification, the interaction between Al(3+) and acrylic acid (AA) and polyacrylic acid (PAA) as a model compound of fulvic acid was investigated. The interaction was examined at pH 3 so as to avoid the hydrolysis of Al(3+). The interaction between Al(3+) and AA was weak. However, the interaction between Al(3+) and PAA was strong and depended on the initial (COOH in PAA)/Al molar ratio (R(P)) of the solution. For the range of 1/R(P), the interaction between Al(3+) and PAA can be divided into three categories: (1) 1:1 Al-PAA-complex (an Al(3+) combines to a carboxyl group), (2) intermolecular Al-PAA-complex (an Al(3+) combines to more than 2 carboxyl groups of other Al-PAA-complexes) in addition to the 1:1 Al-PAA-complex and (3) precipitation of intermolecular complexes. In conclusion, R(P) is an important factor affecting the behavior of Al(3+) in acidic soil solution.