Solid State NMR Molecular Level Elucidation of Inorganic-Bioorganic Interfaces
Written by Ira Ben-Shir
Ira Ben-Shir, Shifi Kababya, and Asher Schmidt
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel
The molecular interfaces between bioorganics and inorganics play key role in diverse scientific and technological research areas ranging from nanoelectronics and biomimetics, through biomineralization, to medical applications like drug delivery and implant coating. However, the physical and chemical basis of surface recognition by biomolecules still remains unclear. Elucidation of the interfacial interactions and of the structural and dynamical state of the surface bound molecules is of prime fundamental scientific importance. Likewise, these details are essential when the design of new functional interfaces is sought.Our aim is to establish atomic level Solid State NMR characterization of the binding of bioorganic molecules to inorganic surfaces as function of the hydration level and temperature. The model system chosen for this study is alanine (specifically 15N and 13C labeled) loaded onto SBA-15 mesoporous silica with high surface area (840 m2/g). Inter- and intra-molecular dipolar recoupling NMR techniques (REDOR, SLF) were employed. 29Si{15N} and 15N{29Si} REDOR NMR revealed intermolecular interactions between the alanine ammonium moiety to silica surface species, and served to infer the interaction stoichiometry and geometry. These REDOR measurements provide for the first time direct observation of the surface and amino acid interacting species in such systems with 29Si at natural abundance. The dynamic states of the alanine molecules is identified by 15N{13C} REDOR NMR, showing fast averaging of the intramolecular 13C1--15N dipolar interaction. At the lowest hydration state we identify a single population of surface bound alanine molecules that undergo small amplitude, anisotropic reorientation while anchored via their ammonium moiety. At increased hydration level, two additional populations are quantified: surface bound alanine with large amplitude anisotropic motion, and isotropic reorienting alanines. 15N{1H3} SLF with PMLG5 identifies the interacting moiety as –NH3+. Current work focuses on determining the dynamic details and to extend our characterization to heptapeptides with high surface affinity.
