In the permanent quest for new materials adapted for specific applications, materials scientists need to establish relationships between the structure and the properties of the material in its end-use solid form. In other words, they need to access the structure of materials to the atomic scale. Unfortunately, in their final form, functional materials often exist as very small particles, for which no general and reliable structure-determination technique exists. Moreover, these materials are often employed in their crystalline form. However, controlling the outcome of crystallization is still out of reach because the mechanisms underlying the formation of a crystal remain essentially unknown. This scientific gap has major consequences for polymorphic materials (i.e. that can crystallize in different forms), as each polymorph has different properties. With no knowledge of the crystallization mechanisms, the outcome of crystallization cannot be controlled, which in turn prevents to control the material’s properties.
Overall, the lack of a general and reliable method for atomic-level structural analysis of polymorphic molecular solids not only prevents accurate characterization of the final powder structure, but also limits the ability to observe the structural changes occurring during the formation of the end-use solid form, hence hampering the ability to control how a specific polymorph is produced.
The aim of STRUCTURE is to develop innovative experimental methods for structure determination of molecular solids based on sensitivity-enhanced solid-state nuclear magnetic resonance (NMR), to:
a) access the atomic-level structure of solid, sub-um sized particles or agglomerates that are currently difficult or impossible to characterize using standard techniques;
b) investigate crystallizing solutions with time at an atomic level and decipher the structural process leading to the formation of a specific polymorph.
STRUCTURE introduced new experimental NMR methods to tackle structure determination in challenging solid samples, whose structure might evolve with time. Results were obtained on the characterization of the structure and the morphology of powdered polymorphic molecular solids relevant for pharmaceutics. STRUCTURE also introduced hyperpolarized-NMR methods to study the temporal evolution of a crystallizing solution at the atomic scale. These methods enabled the stabilization, detection and characterization of transient species forming during crystallization from solution, both in the bulk and under confinement.
The results obtained by STRUCTURE mark a significant stride towards bridging a longstanding scientific gap by offering new experimental tools to look into the mechanistic aspects of the formation and transformation of a solid at the atomic scale — an area of ongoing debate in the scientific literature. Looking ahead, the application of these methods might open new pathways towards mastering the control of material properties through deliberate manipulation of the crystallization process. The implications of these discoveries extend beyond this project, opening up new horizons in materials science and setting the stage for advancements that could redefine the landscape of solid material control and design.
