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Preparation of industrially important aluminium oxide, aluminium hydroxide and aluminium salt materials is often based on the hydrolysis of aluminium-ion solutions. [1] One of the frequently employed processes is neutralisation of Al-ion solutions with alkali or acid. [2] A number of reaction conditions affect the structure and properties of the resulting Alcontaining materials, such as pH, temperature, ionic strength, type of anion, etc. [1,2] Better control of materials synthesis through aqueous routes can be obtained by known speciation of Al-ions. The key problem of Al aqueous speciation in solutions with noncomplexing anions (chloride, nitrate, etc.) is the presence of large Al polycations of the Keggin type ± Al 13 -mer (I) and Al 30 -mer (II). [3,4] These polycations are used in a number of material science applications including clay pillaring, [5] preparation of Al 2 O 3 nanoparticles, [6] antiperspirant actives, [7] catalysts, [8] composite materials, [9] etc. The Al 13 -mer has been studied for decades, [10] whereas the structure of the Al 30 -mer has been identified recently. [3,4] Thermodynamic and kinetic data on the Al 30 -mer are not available in the literature.Aim: Preliminary results of a multi-technique study for Al-speciation are presented for model aqueous systems at high temperature and medium Al concentrations for the formation of large aluminium polycations. Information on the reaction pathway may aid in the development of routes to solutions containing single species that can be used in model studies to investigate the effects of aluminium in the environment as well as in the generation of materials from molecular scale precursors.Results and Discussion: The pH-metric titration curves reconstructed from multi-batch measurements (Fig. 2) show all major inflexions characteristic of the analogous systems at room temperature: [11] (1) h < 0.2 ± hydrolysis of Al monomers; (2) 0.2 < h < 2.6 ± formation of Al polycations including Al dimers/trimers, Al 13 -mers and Al 30 -mers; (3) 2.6 < h < 3.0 ± collapse of Al polycations and formation of the metastable colloidal phase of Al hydroxide; (4) h~3.0 ± bulk precipitation of Al hydroxide; (5) h > 3.0 ± gradual dissolution of Al hydroxide with the formation of Al(OH) 4 ± . At prolonged hydrolysis times the early hydrolysis stages (inflexion 1) did not change profoundly. The greatest time-dependent change was observed at stages (3), (4) and (5) in Figure 2. The major inflexion (4) moves to slightly higher hydrolysis ratios (from h~2.8 at 0 h to h~3.0 at 48 h). Other inflexions retained their position during 48 h of experiment. 27 Al solution NMR spectroscopy revealed a number of Al species present in the sample batches. Assignment of the NMR signals and corresponding Al species is given in Table 1. 27 Al solution NMR spectra of the sample solutions of hydrolysed Al-ions (Fig. 3) indicate all species listed in COMMUNICATIONS 836

Speciation diagrams of aluminium ions in aqueous solution (0.2 M) at high temperature (90 degrees C) have been obtained from 48 h time-resolved multi-batch titration experiments monitored by 27Al NMR spectroscopy, potentiometry and dynamic light scattering. The quantitative speciation patterns and kinetic data obtained offer a dynamic picture of the distribution of soluble and insoluble Al species as a function of hydrolysis ratio h(h=[OH-]/[Al3+]) over a very broad range of conditions (-1.0 < or =h < or = 4.0). Monomeric, small oligomeric, tridecameric (the 'Al13-mer') and the recently characterised 30-meric aluminium species (the 'Al30-mer') as well as aluminium hydroxide have been identified and quantified. The Al13-mer species dominates over a relatively broad range of hydrolysis ratios (1.5 < or =h< or = 2.7) during the first 6 h of experiment, but are gradually replaced by Al30-mers at longer reaction times. Kinetic profiles indicate that the formation of the Al30-mer is limited by the disappearance of the Al13 species at mildly acidic conditions. The estimated rate constants of both hydrolytic processes show good internal correlation at h> or = 1.5. The effect of local perturbations leading to the formation of aluminium hydroxide below the electroneutrality point (h= 3.0) has been estimated quantitatively.

In order to understand the possible interactions between silicon species and collagen, the effects of sodium silicate, molecular complexes of silicon and silica nanoparticles on the collagen selfassembly process have been extensively studied at a range of concentrations from ca. 8 6 10 25 to 1 6 10 22 M. The mode of interaction between collagen and 'silicon' appears species dependent. Depending on its concentration, silicate solutions either promote or hinder collagen fibrillogenesis. Low concentrations of a silicate solution promote fibril formation as does the addition of a silicon catecholato complex. The presence of silica nanoparticles and concentrated silicate solutions hinders fibril formation. The data obtained suggest that there may be direct interaction between the various 'Si' containing species and the collagen triple helices as initially formed. The effect of collagen self-assembly on 'silicon' speciation/condensation has also been investigated. These studies showed that collagen modifies the equilibrium distribution of molecular silicon species in solution, but to a much lesser extent than has been observed for other proteins extracted from biosilicifying organisms.

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