AVS 49th International Symposium
    Biomaterials Wednesday Sessions
       Session BI-WeP

Paper BI-WeP14
NEXAFS Characterization of Poly (Amino Acids) at the Carbon, Nitrogen and Oxygen Edges

Wednesday, November 6, 2002, 11:00 am, Room Exhibit Hall B2

Session: Biointerfaces and Surfaces II
Presenter: N.T. Samuel, University of Washington
Authors: N.T. Samuel, University of Washington
D.A. Fischer, National Institute of Standards and Technology
D.G. Castner, University of Washington
Correspondent: Click to Email
Near edge X-ray absorption fine structure (NEXAFS) spectroscopy has established itself as a powerful tool to characterize small molecules at interfaces. Recent developments in instrumentation have made it possible to image polymers and other biological molecules at very high spatial resolution and chemical specificity. In addition, NEXAFS offers the possibility to probe orientation and order in biological molecules at interfaces. Poly(amino acids) represent an important system of model compounds, since amino acids are the building blocks of proteins and peptides. Previous NEXAFS studies were done at the carbon and oxygen edges of individual and di amino acids. However, nitrogen is present in the backbone and some side chains of amino acids. In the present study, sixteen poly-amino acids were spin-cast or deposited as thick films onto silicon substrates. The samples were characterized by x-ray photoelectron spectroscopy (XPS) to ensure that a uniform film was obtained and no contaminants were present. The carbon edge spectra of these samples agrees well with the earlier work on amino acids. The nitrogen edge spectra of the poly(amino acids) exhibits three characteristic peaks, one due to the amide @pi@* resonance and the other two due to C-N @sigma@* resonances. Also, a pre-edge feature was observed that was associated with x-ray beam induced sample degradation. Overall, these poly-amino acids captured the major resonances in peptide and protein NEXAFS spectra. The different information content of NEXAFS and XPS will also be highlighted. These results coupled with previous results from our group indicate that NEXAFS can be used extract information about the orientation and order of biological molecules at interfaces.