Silicic acid condensation under the influence of water-soluble polymers: from biology to new materials

Abstract

Silicon is among the most abundant elements on the Earth. It occurs in many minerals and plays an important role in several biochemical processes. Some living organisms use silicon dioxide as a substrate for building elements of their bodies. Unicellular diatom algae build frustules from silicon dioxide. The skeleton of siliceous sponges is a silicaprotein composite. Similarly, rice hulls which protect seeds, contain silica as an important component. The living organisms assimilate silicon from the environment in the form of silicic acid. However, the biochemical mechanisms involved in the transformation of silicic acid to solid siliceous materials are still poorly understood.Evidently, condensation of silicic acid in the living organisms proceeds under control of biopolymers and it is important to know how various types of polymers influence the condensation. Bio-inspired chemistry involving the interaction between polymeric silicic acid and functional polymers results in interesting composite materials, including nanoparticles and bulk materials. This review contains a brief description of the mechanism of silicic acid condensation in aqueous medium and also includes a discussion on various precursors of silicic acid. The main focus of the review is on the influence of polymers bearing nitrogen and oxygen-containing functional groups on silicic acid condensation starting from monomer to three-dimensional polymer. Influence of molecular weight of the organic polymer on the condensation and structure of the resulting product is also elaborated. The biological importance of the obtained data and strategies for novel applications of the synthesized composite materials are described in the concluding section of the review. The biomimetic condensation processes open up new vistas for development of novel materials and applications in the biomedical and process industries.

Polymeric Amines and Ampholytes Derived from Poly(acryloyl chloride): Synthesis, Influence on Silicic Acid Condensation and Interaction with Nucleic Acid

“…These results may be attributed to the formation of an inter-polymeric complex in the polymer-PSA system. Precipitation of these systems often depends on the acid-base ratio and an excess of amine units can result in soluble non-stoichiometric complexes as discussed in our review [32]. Introduction of acidic carboxylic units into the polymer chain equalized the acid-base ratio and the polymer-PSA complex became insoluble.…”

“…This anomaly can be attributed to the coating of the siliceous nanoparticles with an organic polymer that led to a decrease in the formation of micro-and mesopores. Condensation of silicic acid in the presence of polymeric amines often results in composite nanoparticles that are stable in aqueous solutions [32,40]. We studied the formation of the composite nanoparticles at a decreased polymer concentration (0.4 g·L −1 ) with the objective to obtain soluble products with a high silica content.…”

“…Condensation of silicic acid at pH 7 proceeded mainly as an S N 2 reaction between the -Si-OH and -Si-O − moieties [33]. Silanol anions arose from the primary PSA particles as Si(OH) 4 is a very weak acid (pK = 9-10) [21,32] in comparison to PSA (pK 0 = 6-7). Interaction between PSA (including primary oligomers) and polyamine chain increased the amount of silanol anions (-SiO − + HN-) and an acceleration in condensation was observed.…”

Iodine‐loaded poly(silicic acid) gellan nanocomposite mucoadhesive film for antibacterial application

“…It is produced in situ using several precursors/inorganic silicates, such as sodium silicates, potassium silicates, by acidification technique and cation exchange resin. 17 Silicic acid has the property of complexation with releasing the proton at pH 10. Silicic acid is used for lowering the atmospheric carbon dioxide.…”

Unusual Polyamines from Baikalian Diatoms

“…The role of LCPAs and silaffins in the synthesis of diatom frustules is unclear, but at least two hypotheses exist: the self‐organization of these compounds may work as a matrix for the condensation of silicic acid, or they may take part in the intracellular transport of silica precursors . In spite of this uncertainty, the discovery of LCPAs and silaffins has inspired works devoted to silicic acid condensation under the action of polyamines and complex amine‐containing polymers . Synthetic LCPAs and their analogs are applied to simulate the processes in vital cells and to synthesize new siliceous and composite materials.…”