The influence of l-aspartic acid on calcium carbonate nucleation and growth revealed by in situ liquid phase TEM

Abstract

In situ transmission electron microscopy has permitted the study of nanomaterials in liquid environments with high spatial and temporal resolutions, allowing chemical reaction visualization in real time. The aim of this work is to better understand how L-aspartic acid (L-Asp), the most abundant amino acid of proteins related to calcium carbonate biomineralization, influences the early stages of calcium carbonate nucleation and growth. Understanding organic–inorganic interactions at the nanoscale level may contribute to nanotechnological applications such as the development of nanodevices for drug delivery. From the in situ liquid phase transmission electron microscopy technique, the formation of organic vesicle-like structures that attracted calcium-rich materials was observed. Calcium carbonate crystals were formed mainly associated with these vesicle-like structures, and the time for crystal formation and Ca²⁺ ion consumption was higher when compared to that in in situ assays without L-Asp. By using molecular dynamics simulation, we confirmed that the carboxyl sites of L-Asp have strong interaction with calcium ions in solution and will form coordinated bonds. Such interactions seem to limit the calcium carbonate crystal growth and decrease the formation rate by decreasing calcium diffusion in solution as observed in samples with L-Asp.