Oligo-DNP · Unveiling transient material synthesis in dilute solutions and their solid morphology combining dDNP and MAS-DNP.

Unveiling transient material synthesis in dilute solutions and their solid morphology combining dDNP and MAS-DNP.

Introduction: The problem addressed in this proposal can be summarised by the following questions: What are the early stage processes governing the silicate (compounds based on silicon and oxygen) formation in structural materials? How does the formation proceed under different conditions of concentration, temperature and pH? What is the influence of silicon-based material chemistry in dilute solutions? These questions are all both academic and industrially relevant. Silicates and aluminosilicates (materials where aluminum replaces silicon atoms) comprise most of Earth's crust and mantle, as well as the other terrestrial planets, rocky moons, and asteroids. In the oceans, the simplest form of soluble silica (silicon dioxide), orthosilicic acid, is also present in dilute concentrations (parts per million). It is most likely in this form that silicon is taken up by living organisms. The silicate formation process, which proceeds from monomers to oligomers to particles/gels determines the morphology and reactivity of the silica products and biological control of the silica morphology has generated an interest for novel mechanisms for biomimetic silica synthesis. In vitro orthosilicic acid at concentrations above 1mM and circumneutral pH, undergoes spontaneous condensation to larger silicate oligomers and eventually stable particles will form. The atomic-level processes involved are very difficult to determine, and despite the introduction of a limited number of methods the questions above remain unanswered. Objectives: We've planned to use a combined approach involving nuclear magnetic resonance (NMR) and its parent technique dissolution dynamic nuclear polarisation (dDNP) to achieve both atomic level resolution and the necessary sensitivity to elucidate the early-stage of the nucleation process. NMR provides the atomic level resolution. dDNP is capable to overcome the low signal coming from the low sample volumes used and the fact the nuclear spin species observed have low natural abundance (~4% for 29Si and ~1% for 13C), thus providing the necessary sensitivity. The overall objective was to establish a novel methodology capable to study the nucleation processes at a very initial stage (seconds from the initial reaction), at low concentration (mM) and at an atomic level. The approach used is general and can allow for example the detection of the initial formation of calcium carbonate that is another material widely used in industry as the main component in numerous construction materials, such as cement and limestone aggregates, and can be used as a means of sequestering carbon dioxide (CO2) in reducing CO2 emissions.

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