From biosilicification to tailored materials: Optimizing hydrophobic domains and resistance to protonation of polyamines

Abstract

Considerable research has been directed toward identifying the mechanisms involved in biosilicification to understand and possibly mimic the process for the production of superior silica-based materials while simultaneously minimizing pollution and energy costs. Molecules isolated from diatoms and, most recently sponges, thought to be key to this process contain polyamines with a propylamine backbone and variable levels of methylation. In a chemical approach to understanding the role of amine (especially propylamine) structures in silicification we have explored three key structural features: (i) the degree of polymerization, (ii) the level of amine methylation, and (iii) the size of the amine chain spacers. In this article, we show that there are two factors critical to their function: the ability of the amines to produce microemulsions and the presence of charged and uncharged amine groups within a molecule, with the latter feature helping to catalyze silicic acid condensation by a proton donor/acceptor mechanism. The understanding of amine-silicate interactions obtained from this study has enabled the controlled preparation of hollow and nonporous siliceous materials under mild conditions (circumneutral pH, room temperature, and in all aqueous systems) possibly compatible with the conditions used by biosystems. The ''rules'' identified from our study were further used predictively to modulate the activity of a given amine. We believe that the outcomes of the present contribution will form the basis for an approach to controlling the growth of inorganic materials by using tailor-made organic molecules.bioinspired materials ͉ biosilica ͉ hollow particles T he commercialization of siliceous materials has generated a multibillion pound industry with the value of precipitated silica products alone estimated to have reached 1.4 billion pounds by the year 2006 (1). This value largely depends on the ability to produce silica for specific applications through control of surface chemistry and morphology during the condensation and aggregation process. Industrial processes involved in the production of high-value siliceous materials typically involve harsh conditions of high temperature and acidity or basicity, environmentally damaging waste streams, and often toxic silicate precursors. These processes also generally exert poor chemical and morphological control over the materials produced. In comparison, natural silica production in organisms such as sponges, diatoms, and radiolaria occurs under biologically benign conditions and produces silica of exquisite form and function, all from a monosilicic acid source of only a few parts per million in concentration (2). Considerable research has been directed toward identifying the mechanisms involved in the biosilicification process to understand and possibly mimic the process to allow us to produce superior materials without the attendant pollution and high-energy usage (3, 4).Studies of the processes associated with the formation of siliceous diatom shells (thecae) have i...

An Eco‐Friendly, Tunable and Scalable Method for Producing Porous Functional Nanomaterials Designed Using Molecular Interactions

“…Bioinspired silica was synthesised using pentaethylenehexamine (PEHA) as an additive owing to its high catalytic activity 22. Once synthesised at pH 7, the suspension was treated with acid for 10 min to reach a desired pH value between 7 and 2 (the isoelectric point of silica) 23.…”

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Multifunctional, biocompatible and pH-responsive carbon nanotube- and graphene oxide/tectomer hybrid composites and coatings

“…55 pK = 9.6 for glycine amino acid, however in tectomer assemblies the amino terminal groups are in close vicinity, and it is well-known that protonation of amino groups in polyamines electrostatically suppresses subsequent protonation processes in neighboring groups. [61][62][63] Therefore, at pH 7.4, a significant number of amino terminal groups in tectomer assemblies are deprotonated, which allows extended tectomer formation. On the other hand, under acidic conditions, electrostatic repulsion between neighbouring terminal amino groups, due to strong protonation, leads to tectomer disassembly, and to the formation of vesicular and tubular structures for 2T (Fig.…”

Synthesis of biomimetic polyamines

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