Single-Residue Sensitivity in Neutron Reflectivity and Resonant X-ray Reflectivity from Langmuir Monolayers of Synthetic Peptides

J. Strzalka,1 S. Satija,2 E. DiMasi,3 I. Kuzmenko,4 T. Gog4 and J. K. Blasie1,4

1 Department of Chemistry, University of Pennsylvania
2Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD
3 National Synchrotron Light Source, Brookhaven National Lab
4 CMC CAT, Advanced Photon Source, Argonne National Lab


Labeling groups with 2H to distinguish them in the scattering length density (SLD) profile constitutes the chief advantage of neutron reflectivity (NR) in studying Langmuir monolayers (LM) of lipids and proteins. Solid phase peptide synthesis (SPPS) permits the labeling of a single residue in a peptide. Recent work demonstrates the sensitivity of NR to single 2H-labeled residues in LM of vectorially oriented alpha-helical bundle peptides. NR requires comparison of isomorphic samples of all-1H and 2H-labeled peptides. Alternately, resonant x-ray reflectivity (RXR) uses only one sample. RXR exploits energy-dependent changes in the scattering factor from heavy atoms to distinguish them within the SLD profile. Peptides may be labeled by SPPS (e.g. Br-Phe), or may have inherent labels (e.g. Fe in heme proteins). As test cases, we studied LM of Br-labeled lipids and peptides with RXR. Both approaches require a model-independent means of obtaining SLD profiles from the reflectivity data. We have applied box-refinement to obtain the gradient SLD profile. This is fit uniquely with a sum of Gaussians and integrated analytically [Blasie et al., PRB 67 224201 (2003)] to provide the SLD profile. Label positions can then be determined to sub-Angstrom accuracy. This work supported by the NIH (GM55876).


A 10-minute platform presentation on this topic was delivered at the March Meeting of the American Physical Society in Montreal, Canada, 22-26 March, 2004, as part of Session A8: Neutron Scattering and Other Studies of Phospholipids.

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2004 American Physical Society Abstract / June 2004 / send comments to strzalka@sas.upenn.edu