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Authors
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Hofmaier, M. ; Urban, B. ; Lentz, S. ; Borkner, C.B. ; Scheibel, T. ; Fery, A. ; Müller, M.
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Title
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Dichroic fourier transform infrared spectroscopy characterization of the b-sheet orientation in spider silk films on silicon substrates
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Date
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12.01.2021
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Number
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59183
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Abstract
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Orientation analysis of the ß-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 ß-sheet structures. Based on the experimental dichroic ratio R, the order parameter S of ß-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 ß-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 ß-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, p) mode of antiparallel ß-sheet structures, whose transition dipole moment M is located in parallel to both ß-sheet plane and chain direction. The calculated high molecular order parameter S ˜ 0.40 suggested vertically (out-of-plane) oriented antiparallel ß-sheet stacks with tilt angles of · ˜ 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 ß-sheet crystallite orientation for the mechanical properties of spider silk materials.
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Publisher
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Journal of Physical Chemistry B
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Wikidata
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Citation
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Journal of Physical Chemistry B 125 (2021) 1061-1071
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DOI
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https://doi.org/10.1021/ACS.JPCB.0C09395
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Tags
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