Thursday, September 11, 2008, Condensed Matter Seminar, Pulak Dutta, Dept. Physics & Astronomy, Northwestern University, Evanston IL, "Biometric Crystal Growth at Organic-Inorganic Interfaces," 4:30 PM, Doherty Hall A310, CMU

Abstract

During the growth of shells, bones and other biominerals, organic molecules control the inorganic crystal shapes, sizes, orientations and arrangements. This results in the assembly of nanocomposite materials with tailored mechanical, chemical, optical and/or magnetic properties. How molecules grow oriented crystals is "the big mystery of biomineralization...organisms know how to do it; we do not yet know how they know."1 In addition to fundamental interest, understanding what happens at the organic-mineral interface may lead to biomimetic methods for creating novel materials, and to strategies for growing or inhibiting the growth of biominerals in vivo (e.g. bones, kidney stones).

We are using grazing-incidence X-ray diffraction to study nucleation under floating lipid monolayers, a system that simulates aspects of the biomineralization process. X-rays allow us to see both the organic and inorganic structures in situ during nucleation, and the resulting evidence contradicts widespread assumptions about the role of organic molecules in biomineralization. I will argue that the small amounts of organic sulfates found within shells, rather than the ubiquitous acid groups, are responsible for the oriented growth of calcite crystals. Crystal morphology and shape can be varied using apparently quite distinct methods, but these may just be different ways to vary the interfacial energy (surface tension).

1. K. M. Towe, Science 311, 1554 (2006)