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

Hypothesis: Despite advances in understanding the R5 (SSKKSGSYSGKSGSKRRIL) peptide-driven biosilica 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 micro-scopy. 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 polycon-densation of silicic acid during the bio-silification process via electrostatic interactions. (c) 2021 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Automated summary

This study investigates the self-assembly of R5 peptides and reveals that they form large aggregates with a mass-fractal structure composed of small spherical aggregates. Additionally, it is discovered that phosphate ions not only drive the growth of the R5 scaffold but also promote the polycondensation of silicic acid through electrostatic interactions during the biosilification process.