Fractal-like R5 assembly promote the condensation of silicic acid into silica particles

Levena Gascoigne; Jose Rodrigo Magana; Dylan Luke Atkins; Christian C M Sproncken; Berta Gumi-Audenis; Sandra M C Schoenmakers; Deborah Wakeham; Erica J Wanless; Ilja Karina Voets

doi:10.1016/j.jcis.2021.04.030

Fractal-like R5 assembly promote the condensation of silicic acid into silica particles

J Colloid Interface Sci. 2021 Sep 15:598:206-212. doi: 10.1016/j.jcis.2021.04.030. Epub 2021 Apr 15.

Authors

Levena Gascoigne¹, Jose Rodrigo Magana², Dylan Luke Atkins², Christian C M Sproncken², Berta Gumi-Audenis², Sandra M C Schoenmakers³, Deborah Wakeham⁴, Erica J Wanless⁵, Ilja Karina Voets⁶

Affiliations

¹ Laboratory of Self-Organizing Soft Matter & Institute for Complex Molecular Systems, Eindhoven University of Technology, Department of Chemical Engineering and Chemistry, De Zaale, 5612 AZ Eindhoven the Netherlands; School of Environmental and Life Sciences, University of Newcastle, University Drive, Callaghan, NSW 2308, Australia. Electronic address: l.c.gascoigne@tue.nl.
² Laboratory of Self-Organizing Soft Matter & Institute for Complex Molecular Systems, Eindhoven University of Technology, Department of Chemical Engineering and Chemistry, De Zaale, 5612 AZ Eindhoven the Netherlands.
³ Institute for Complex Molecular Systems, Eindhoven University of Technology, Department of Chemical Engineering and Chemistry, De Zaale, 5612 AZ Eindhoven the Netherlands.
⁴ Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation (ANSTO), New Illawarra Rd, Lucas Heights, NSW 2234, Australia.
⁵ School of Environmental and Life Sciences, University of Newcastle, University Drive, Callaghan, NSW 2308, Australia.
⁶ Laboratory of Self-Organizing Soft Matter & Institute for Complex Molecular Systems, Eindhoven University of Technology, Department of Chemical Engineering and Chemistry, De Zaale, 5612 AZ Eindhoven the Netherlands. Electronic address: i.voets@tue.nl.

PMID: 33905996
DOI: 10.1016/j.jcis.2021.04.030

Abstract

Hypothesis: Despite advances in understanding the R5 (SSKKSGSYSGKSGSKRRIL) peptide-driven bio-silica process, there remains significant discrepancies regarding the physicochemical characterization and the self-assembling mechanistic driving forces of the supramolecular R5 template. This paper investigates the self-assembly of R5 as a function of monovalent (sodium chloride) and multivalent salt (phosphate) to determine if assembly is phosphate ion concentration dependent. Additionally, we hypothesize that the assembled R5 aggregates do not resemble a micelle or unimer structure as proposed in current literature.

Experiments: R5 peptides were synthesized, and aggregates evaluated for their size, morphology, and association state as a function of salt and ionic strength concentration via dynamic and static light scattering, small angle X-ray and neutron scattering and cryogenic transmission electron microscopy. Furthermore, we compare the proposed R5 template to precipitated silica by scanning electron microscopy.

Findings: R5 peptides assemble into large aggregates due to multivalence bridging and the decrease in electrostatic repulsion due to ionic strength. We elucidate the structure of R5 aggregates as mass-fractals composed of small spherical aggregates. Moreover, we discover that phosphate ions not only have a significant role in driving the growth of the R5 scaffold, but additionally in driving the polycondensation of silicic acid during the bio-silification process via electrostatic interactions.

Keywords: Biomineralization; Peptides; Self-assembly; Silaffin; Silica; Supramolecular chemistry; Template synthesis.