The dynamics and energetics of matrix assembly and mineralization

Formation of biominerals commonly occurs within the context of an organic matrix composed of proteins, polysaccharides, and other macromolecules. Much has been learned about the structure of matrices and the spatial and molecular relationships between matrix and mineral. Only recently has quantitative study of matrix organization and subsequent mineralization been pursued. Here, we review findings from physical studies of matrix assembly in the system of microbial S-layer proteins and of calcium carbonate nucleation on organic templates composed of organothiol self-assembled monolayers on noble metals. Studies on S-layers reveal the importance of multistage assembly pathways and kinetic traps associated with the conformational transformations required to build the basic oligomeric building blocks of the matrix. Experimental investigations of calcium carbonate nucleation on carboxyl-terminated self-assembled monolayers combined with theoretical analyses demonstrate the applicability of classical concepts of nucleation, even when cluster-aggregation pathways are considered, and reveal the underlying energetic and structural source of matrix control over the process. Taken together, these studies highlight the ways in which matrix assembly and mineralization deviate from our classical concepts of crystallization but clearly demonstrate that the concepts of physical chemistry that date back to the days of Gibbs and Ostwald still serve us well in understanding the nucleation and growth of organic matrices and mineral phases.