The evolution of biomineral prenucleation species: Real-time

The classic and long-standing nucleation-and-growth theory (CNT) that describes the formation of crystals from liquid solutions was recently challenged by the observation of stable and soluble pre- nucleation species (PNS) prior to the formation of many solid materials. This suggests non-classical crystallization pathways (NCP) as a key route towards various biological and chemical architectures. However, the quasi-absence of structural and dynamical data related to PNS obscures the rationalization of NCP despite its importance in so-called biomineralization processes. Biomineralization denotes the ability of living organisms to produce solid materials. For such process, for example in bone formation events, precursors of crystallization nuclei emerge within milliseconds when calcium and phosphate ions meet in solution. These species, which appear at the beginning of the crystallization process, are to be characterized analytically in the project and observed with high- resolution methods in order to comprehensively describe biominerals and their underlying chemical processes with new insights and technologies. Biomineralization processes are ideal candidates to tackle this shortcoming as biominerals (in particular calcium phosphate) form via PNS intermediates. However, methods providing the time resolution required for the study of such out-of-equilibrium chemical processes are lacking. This project aims to develop original real-time NMR methods to describe transient species in the frame of NCP, including PNS, at the atomistic level during biomineral crystallization. This will be realized through an innovative combination of hyperpolarized liquid and solid-state nuclear magnetic resonance (NMR) approaches, complemented with cutting-edge computational techniques. PNS are solute species described as highly dynamic nanometric ionic entities that spontaneously form in solution preceding the nucleation of solid phases. Throughout precipitation, they are rate-limiting entities constituted of loosely coordinated ions in dynamic equilibrium with the corresponding free solvated species. Recently, PNS have been categorized into two types3 , denoted here as (i) type 1 PNS, which are stable or metastable in solution and only participate in precipitation upon receiving further stimuli, and (ii) type 2 PNS, which appear transiently during the onset of the phase separation event and which are notoriously challenging to detect and characterize due to their limited lifetimes. Due to the aging of the population and the increase in bone pathologies, understanding bone and calcium phosphate biomineralization is becoming a major challenge. The RealTimeNMR project will provide fundamental knowledge on the early stages of biomineral nucleation to understand their formation mechanisms better and rethink the synthesis strategy of biomimetic biomaterials. The project aims to push the knowledge limits of chemistry of life, where biomineralization is a central process.