13C CP-MAS spectra of different silk fibers. a) Recombinant CT domain and b) 4RepCT from Euprosthenops australis (E.a.), in fiber form. c) Araneus gemmoides (A.g.), Argiope argentata (A.ar), Argiope aurantia (A.au), Latrodectus Hesperus (L.h.), and Nephila clavipes (N.c.) Creager et al.. Reprinted with permission from Creager, M. S., Jenkins, J. E., Thagard-Yeaman, L. A., Brooks, A. E., Jones, J. A., Lewis, R. V., Holland, G. P., & Yarger, J. L. (2010). Solid-state NMR comparison of various spiders’ dragline silk fiber. Biomacromolecules, 11(8). https://doi.org/10.1021/bm100399x. Copyright 2021 American Chemical Society.



METHODS
Dry fiber samples for 13C natural abundance ssNMR experiments were packed into 4.0 mm zirconia MAS rotors and a few microliters of water was added to hydrate the sample. Kel-f inserts (vol. 30 uL) with sealing plug and screws were used to keep sample wet during the experiments. Solid-state NMR experiments were performed on samples of CT fibers (sample I) and 4RepCT fibers (sample II) using a Bruker Avance III HD 500 MHz NMR spectrometer equipped with a 4.0 mm MAS probe (Bruker Biospin). The 13C CP-MAS NMR experiments were performed at a spinning rate of 9 kHz with a sample temperature of 298 K, 1H 90deg pulse length of 3.3 us, a 2.0 ms contact time, a recycle delay of 2.5 s, and an applied Spinal-64 decoupling78 on 1H at 75.8 kHz.


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