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Project Progress

Macroscopic biominerals (bones, teeth, seashells, etc.) can be a very direct signature for the presence of life. The formation of these macroscopic materials ultimately begins at the nanoscale, where the nucelation and initial growth of inorganic materials is controlled by a protein template. As part of the ABRC biomineralization thrust a collaboration (Douglas and Parise groups) has developed to investigate how the hard-soft interface (organic-mineral) influence the characteristics of the biomineral. This influence occurs at the gross level of particle morphology but also at more subtle levels of mineral orientation, polymorph selection, and influences to the electronic structure of the mineral. Molecular processes of metal-ligand cluster assembly in biology (metal sulfide and metal oxide clusters) may have parallels in the early events in biomineral nucleation. A major focus of research in this thrust area is on precisely how the initial stages of inorganic mineral formation occur at protein surfaces. We have applied a variety of physical techniques including mass spectrometry, high-energy X-ray diffraction, theoretical simulations, analytical ultracentrifugation and light scattering to probe this process of protein-directed mineral formation and growth. By using techniques that can address this process at a variety of spatial and temporal scales, we hope to understand how biology has combined the versatility and evolvability of soft polymeric materials with the often-superior material properties of inorganic materials to enable the emergence of complex life. We have strong evidence that the structural and electronic properties of protein-templated nanoparticles are significantly different from materials with the same composition synthesized without a protein template.

In particular, total X-ray scattering studies have shown that Mn oxide nanoparticles grown inside a hollow protein cage (ferritin) adopt a structure similar to chalcophanite, a layered manganese oxyhydroxide, while nanoparticles grown in the absence of protein show an inverse spinel structure similar to hausmannite. Extensive studies of Fe oxide nanoparticles have shown that materials grown within a protein cage show smaller crystalline domains than their bulk counterparts, suggesting that crystallinity may be limited by the presence of multiple adjacent nucleation sites.