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High-resolution solution (13)C-NMR and CD studies of Bombyx mori silk fibroin revealed the presence of an ordered secondary structure 3(10)-helix, in hexafluoro-iso-propanol (HFIP). The solid-state structure of the silk fibroin film prepared by drying it gently from the HFIP solution still keep the structure, 3(10)-helix, which was studied with high-resolution solid state (13)C-NMR. The structural transition from the 3(10)-helix to silk II structure, heterogeneous structure including antiparallel beta-sheet, occurred during the artificial spinning from the HFIP solution. The wide-angle x-ray diffraction and differential scanning calorimetry thermograms of the artificial spinning fiber after postspinning treatments were observed together with the stress-strain curves. The results emphasize that the molecular structures, controlled morphology, and mechanical properties of the protein-based synthetic polymers can be modulated for enhancing biocompatibility.

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The self-diffusion coefficients (D) of rodlike poly(n-alkyl l-glutamate)s having n-dodecyl side chains in the thermotropic liquid crystalline state were measured as a function of the main-chain length [molecular weight (M w) of 7000, 30 000, and 130 000, which correspond to the main-chain lengths (L) of ca. 30, 200, and 890 Å, respectively)] within the temperature range from 50 to 80 °C by means of the pulse field-gradient spin-echo 1H NMR method to elucidate the diffusional behavior of the polypeptides in the thermotropic liquid crystalline state. From the experimental results, it was found that at temperatures above the melting point of side-chain crystallites in poly(n-alkyl l-glutamate) the polypeptide forms the thermotropic liquid crystalline state, and then the isotropic diffusion coefficients (D iso) of the rodlike polypeptides are decreased with an increase in the main-chain length. The diffusion process was analyzed by the Kirkwood theory of diffusion process for rodlike polymers. The diffusion coefficients of poly(l-glutamates) in the directions parallel (D ∥) and perpendicular (D ⊥) to the α-helical axis were determined, and the D ∥ value was found to be larger than the D ⊥ value.

The self-diffusion coefficients (D) and H1 spin–spin relaxation times (T2) of poly(γ-oleyl L-glutamate)(POLLG) with long oleyl side chains and poly(γ-n-octadecyl L-glutamate)(POLG) with n-alkyl side chains have been measured by the pulse field-gradient spin-echo H1 nuclear magnetic resonance (NMR) method and the Carr–Purcell/Meiboom–Gill (CPMG) H1 NMR method, respectively, over a wide range of temperatures from 30 to 80 °C, in order to elucidate the dynamic behavior of polypeptides in the thermotropic liquid crystalline state, which take the α-helical conformation. From these experiments, it was found that the diffusion coefficients of POLLG and POLG chains in the thermotropic liquid crystalline state at 60 °C are 9.97×10−7 and 3.53×10−7 cm2/s, respectively, and the former diffuses faster than the latter. The diffusion coefficients of POLG in the directions parallel (D∥) and perpendicular (D⊥) to the α-helical chain axis were determined over a wide range of temperatures, and the D∥ value was found to be much larger than the D⊥ value. Further, from the H1 T2 experiments, it was suggested that the mobility of the side chains relates closely to the diffusion process.

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