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Hofmaier M, Urban B, Lentz S, Borkner CB, Scheibel T, Fery A, Müller M. Dichroic Fourier Transform Infrared Spectroscopy Characterization of the β-Sheet Orientation in Spider Silk Films on Silicon Substrates. J Phys Chem B 2021; 125:1061-1071. [PMID: 33433229 DOI: 10.1021/acs.jpcb.0c09395] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Orientation analysis of the β-sheet structure within films of the established recombinant spider silk protein eADF4(C16) was performed using a concept based on dichroic transmission- and attenuated total reflection-Fourier transform infrared spectroscopy, lineshape analysis, assignment of amide I components to specific vibration modes, and transition dipole moment directions of β-sheet structures. Based on the experimental dichroic ratio R, the order parameter S of β-sheet structures was calculated with respect to uniaxial orientation. Films of eADF4(C16) were deposited on untexturized (Si) and unidirectionally scratched silicon substrates (Si-sc) and post-treated with MeOH vapor. Freshly cast thin and thick eADF4(C16) films out of hexafluoroisopropanol featured β-sheet contents of ≈6%, which increased to >30% after MeOH post-treatment in dependence of time. Pseudo-first order folding kinetics were obtained, suggesting a transition from an unfolded to a folded state. In MeOH post-treated thin films with diameters in the nanometer range, a significant orientation of β-sheets was obtained regardless of the texturization of the silicon substrate (Si, Si-sc). This was rationalized by dichroic ratios of the amide I component at 1696 cm-1 assigned to the (0, π) mode of antiparallel β-sheet structures, whose transition dipole moment M is located in parallel to both β-sheet plane and chain direction. The calculated high molecular order parameter S ≈ 0.40 suggested vertically (out-of-plane) oriented antiparallel β-sheet stacks with tilt angles of γ ≈ 39° to the surface normal. Microscale (thick) films, in contrast, revealed low order parameters S ≈ 0. Scanning force microscopy on thin eADF4 films at silicon substrates showed dewetted polymer film structures rather at the micro-scale. These findings give new insights in the role of the β-sheet crystallite orientation for the mechanical properties of spider silk materials.
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Affiliation(s)
- Mirjam Hofmaier
- Institute of Physical Chemistry and Polymer Physics, Leibniz Institute of Polymer Research Dresden (IPF), Hohe Strasse 6, D-01069 Dresden, Germany.,Chair of Macromolecular Chemistry, Technical University of Dresden (TUD), Mommsenstraße 4, D-01062 Dresden, Germany
| | - Birgit Urban
- Institute of Physical Chemistry and Polymer Physics, Leibniz Institute of Polymer Research Dresden (IPF), Hohe Strasse 6, D-01069 Dresden, Germany
| | - Sarah Lentz
- Chair of Biomaterials, University of Bayreuth, Prof.-Rüdiger-Bormann-Str. 1, D-95447 Bayreuth, Germany
| | - Christian B Borkner
- Chair of Biomaterials, University of Bayreuth, Prof.-Rüdiger-Bormann-Str. 1, D-95447 Bayreuth, Germany
| | - Thomas Scheibel
- Chair of Biomaterials, University of Bayreuth, Prof.-Rüdiger-Bormann-Str. 1, D-95447 Bayreuth, Germany
| | - Andreas Fery
- Institute of Physical Chemistry and Polymer Physics, Leibniz Institute of Polymer Research Dresden (IPF), Hohe Strasse 6, D-01069 Dresden, Germany.,Chair of Physical Chemistry of Polymeric Materials, Technical University Dresden (TUD), D-01069 Dresden, Germany
| | - Martin Müller
- Institute of Physical Chemistry and Polymer Physics, Leibniz Institute of Polymer Research Dresden (IPF), Hohe Strasse 6, D-01069 Dresden, Germany.,Chair of Macromolecular Chemistry, Technical University of Dresden (TUD), Mommsenstraße 4, D-01062 Dresden, Germany
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