N.L. Abbott

1. University of Wisconsin-Madison Materials Research Science & Engineering Center on Nanostructured Interfaces UW MRSEC DMR-0520527 Juan J. de Pablo, PI IRG 3:Characterization of Material Interfaces Functionalized with Biomolecules using Near Edge X-Ray Fine Structure Spectroscopy N.L. Abbott Whereas many past studies of biomolecules at interfaces have reported on the functional properties of the molecules (e.g., binding affinity or enzymatic activity), few investigations have characterized the surface chemistry leading to the immobilization of biomolecules or the resulting structural states of the immobilized biomolecules. Over the past year, IRG3 has demonstrated that near-edge x-ray absorption fine structure spectroscopy (NEXAFS) can be used to characterize a widely-employed immobilization chemistry that leads to the covalent attachment of biologically relevant oligopeptides to material interfaces. By observing changes in the * and * orbitals of specific nitrogen and carbon atoms (amide, imide, carbonyl), IRG3 was able to follow the sequential reactions leading to immobilization of the oligopeptide. The IRG has also shown that it is possible to use NEXAFS to determine whether the immobilization chemistry results in a preferred the orientation of the oligopeptide at sub-monolayer surfaces densities that are relevant to a range of biomaterials applications. Overall, these new results establish a general methodology based on NEXAFS for characterizing the chemistry of immobilization and the resulting bonding configurations of a wide range of biomolecules on surfaces. These results also establish methods that can be used to optimize procedures for the immobilization of biomolecules on material interfaces, and provide insights into the structural origins of the functional properties of biomolecules at surfaces. Caption: Left column: Schematic illustration of the chemistry used to immobilize an oligopeptide kinase substrate (bottom) on a solid surface. The numbered arrows indicate different bonding configurations of nitrogen that are quantified in the N1s NEXAFS spectra shown in the middle column. The right side data shows the polarization dependence of the N 1s NEXAFS spectra from immobilized Y1173 peptide at normal (90) and grazing (30) angle of incidence. The peptide bond at 401.4 eV shows significant polarization dependence, indicating a preferred orientation of the peptide on the surface.