Phase Separation of Oppositely Charged Polymers Regulates Bioinspired Silicification

Abstract

In nature, simple organisms evolved mechanisms to form intricate biosilica nanostructures, far exceeding current synthetic manufacturing. Based on the properties of extracted biomacromolecules, polycation-polyanion pairs were suggested as moderators of biosilica formation. However, the chemical principles of this polymer-induced silicification remain unclear. Here, we used a biomimetic polycation-polyanion system to study polymer-induced silicification. We demonstrate that it is the polymer phase separation process, rather than silica-polymer interactions, which controls silica precipitation. Since ionic strength controls this electrostatic phase separation, it can be used to tune the morphology and structure of the precipitates. In situ cryo electron microscopy highlights the pivotal role of the hydrated polymer condensates in this process. These results pave the road for developing nanoscale morphologies of bioinspired silica based on the chemistry of liquid-liquid phase separation.

Lysozyme is Sterically Trapped Within the Silica Cage in Bioinspired Silica–Lysozyme Composites: A Multi-Technique Understanding of Elusive Protein–Material Interactions

“…When longer mixing times are used, the contribution from this proton pool to the Q 4 sites increases (Figure S9). The proton pool at a higher chemical shift is broad and overlaps with the H N proton pool as obtained from the { 1 H}− 13 C HETCOR (see Figure S10, Table S8). If D 2 O is used for rehydration, the 1 H peak corresponding to amides is reduced (due to D/H exchange) in the traces of the 13 C NMR spectra but not abolished.…”

“…A representative high-resolution 1 H NMR spectrum of lysozyme in solution is given alongside with the 1 H trace from the { 1 H}− 13 C HETCOR. We observe that, at low contact times, 13 C receives magnetization from the closest protein protons and, at longer times, from more distant protons on neighboring bonded atoms (e.g., blue trace shows higher polarization of Cα by H N at 1500 μs). In the { 1 H}− 29 Si HETCOR (integration regions are shown in Figure S7), Q 4 29 Si sites receive magnetization mainly from silanols, whereas Q 3 29 Si sites also receive magnetization from the protons at higher chemical shift values.…”

“…We have therefore proceeded with the solid-state NMR characterization (see details in the Supporting Information and Table S1). Observation of the protein resonances is possible through 13 C MAS NMR spectra (Figure 1). These were first acquired for the freeze-dried sample.…”

“…A direct correlation of 13 C MAS NMR signals from the protein to 29 Si MAS NMR signals from the matrix would enable us to reveal an intimate contact between the two components. 65,66 However, detection of such correlation is necessarily limited since both the 13 C nuclei in the protein and the 29 Si nuclei in silica are in natural abundance (1.1% 13 C and 4.7% 29 Si) in the complex, reducing the probability of a coupled 13 C− 29 Si spin pair to 1 in 2000. 65 Therefore, we have chosen to work on the comparison of the 1 H traces and to discriminate among the protons that act as polarization sources for the heteronuclear sites.…”

“…One possibility for further sorting this out is to find out whether the carbon nuclei in the protein and the silicon nuclei in the silica matrix are getting polarized by the same proton source(s) or not. Therefore, the HETCOR experiments were repeated with 13 C as the target nucleus, still on the dry sample. The 1 H− 13 C correlation spectra are common for a protein sample where maximal transfer is observed at a shorter mixing time of 150 μs for the directly bonded 1 H− 13 C spin pairs such as alpha protons (Hα)-alpha carbons (Cα) and at longer times for carbonyl (C′) carbons polarized by amide protons (H N ) and Hα (Figure 5).…”