|Ph.D Student||Ben-Shir Irina|
|Subject||Investigation of Inorganic-Bioorganic Interfaces by Solid|
|Department||Department of Chemistry||Supervisor||Professor Asher Schmidt|
|Full Thesis text|
Molecular level characterization of the interfacial interactions and the structural and dynamical state of surface-bound and matrix-occluded molecules was obtained by solids NMR. Such interactions are of fundamental scientific and technological importance in vast fields, e.g. catalysis, biomimetics and biomineralization.
We show that small amino acids with non-polar sidechains, Gly and L-Ala, loaded onto SBA-15 and MCM-41 mesoporous silicas adsorb using a general pattern of interactions. However, the binding geometry, stoichiometry, strength, dynamics and effect of water and temperature depend on the surfaces molecular characteristics. Being able to identify accurately all binding characteristics we show how the surface details determine its functionality/reactivity. Such understanding is critical for rational functional surface design.
Organisms synthesize materials at ambient conditions resulting in optimized functional properties (mechanical, optical) through a process known as biomineralization. The resulting materials are mostly hierarchical inorganic-bioorganic composites where the interfaces determine their properties. We have targeted to unravel the finest molecular details of the interfacial interactions, whether buried or at exposed surfaces, in a biogenic and synthetic model systems.
For the aragonitic shell of Perna canaliculus (bivalve) we observe their highly ordered crystalline aragonite with minor inter-crystalline bioorganic layers. We identify the small fraction of disordered interfacial carbonates characterized as disordered aragonite. These were found to divide to two classes: exposed, solvent accessible interfacial carbonates, interact primarily with bioorganics; buried, solvent inaccessible, interact exclusively with spatially separated water and bicarbonates. Whether this molecular description of biogenic interfaces is abundant, and how it correlates with the shell properties will be the subject of future study.
Similar goals were addressed for the in vitro model of CaCO3 precipitated in the presence of Asp and Glu, two amino acids implicated in biomineralization due to their calcium binding. The precipitates formed crystalline vaterite, occluding small amount (<1%) of amino acid. The immediate surrounding shell (<5%) consisted of disordered interfacial carbonates and water. The interfacial interactions with the amino groups was by carbonates identified as disordered calcite, while disordered vaterite (DV) carbonates were inferred to interact with the carboxylate groups. Unexpected thermal stability was found for these interfacial interactions.
In this work, a solids NMR toolbox to directly identify the bioorganic-inorganic interfaces was devised, and its application for the three classes of systems demonstrates NMR's unique capability to provide comprehensive insight on the structure of composite materials.