Belton, David J. and Deschaume, Olivier and Patwardhan, Siddharth V. and Perry, Carole C. (2010) A solution study of silica sondensation and speciation with relevance to in vitro investigations of biosilicification. Journal of Physical Chemistry B, 114 (31). pp. 9947-9955. ISSN 1520-6106Full text not available in this repository. (Request a copy from the Strathclyde author)
Requiring mild synthesis conditions and possessing a high level of organization and functionality, biosilicas constitute a source of wonder and inspiration for both materials scientists and biologists. In order to understand how such biomaterials are formed and to apply this knowledge to the generation of novel bioinspired materials, a detailed study of the materials, as formed under biologically relevant conditions, is required. In this contribution, data from a detailed study of silica speciation and condensation using a model bioinspired silica precursor (silicon catechol complex, SCC) is presented The silicon complex quickly and controllably dissociates under neutral pH conditions to well-defined, metastable solutions of orthosilicic acid The formation of silicomolybdous (blue) complexes was used to monitor and study different stages of silicic acid condensation In parallel, the rates of silicomolybdic (yellow) complex formation, with mathematical modeling of the species present, was used to follow the solution speciation of polysilicic acids. The results obtained from the two assays correlate well. Monomeric Oleic acid, trimeric silicic acids, and different classes of oligomenc polysilicic acids and silica nuclei can be identified and their periods of stability during the early stages of silica condensation measured For experiments performed at a range of temperatures (273-323 K), an activation energy of 77 kJ.mol(-1) was obtained for the formation of trimers. The activation energies for the forward and reverse condensation reactions for addition of monomers to polysilicic acids (273-293 +/- 1 K) were 55.0 and 58.6 kJ.mol(-1), respectively. For temperatures above 293 K, these energies were reduced to 6 1 and 7.3 kJ.mol(-1), indicating a probable change in the prevailing condensation mechanism The impact of pH on the rates of condensation were measured There was a direct correlation between the apparent third-order rate constant for trimer formation and pH (4.7-6.9 +/- 0.1) while values for the reversible first-order rates reached a plateau at circumneutral pH. These different behaviors are discussed with reference to the generally accepted mechanism for silica condensation in which anionic silicate solution species are central to the condensation process. The results presented in this paper support the use of precursors such as silicon catecholate complexes in the study of biosilicification in vitro Further detailed experimentation is needed to increase our understanding of specific biomolecule silica interactions that ultimately generate the complex, finely detailed siliceous structures we observe in the world around us.
|Keywords:||dilute aqeous solution, colloidal silica, spectrophotometric determination, acid polymerization, amorphous silica, biogenic silica, sodium-silicate, amino acids, neutral ph, degrees c, Chemical engineering, Materials Chemistry, Surfaces, Coatings and Films, Physical and Theoretical Chemistry|
|Subjects:||Technology > Chemical engineering|
|Department:||Faculty of Engineering > Chemical and Process Engineering|
|Depositing user:||Pure Administrator|
|Date Deposited:||15 Jun 2011 09:30|
|Last modified:||04 May 2016 18:45|