Raman spectroscopic characterization of Bombyx mori silk fibroin: Raman spectrum of Silk I

Abstract

This study focuses on the conformational characterization of differently processedBombyx mori silk fibroin samples by Raman spectroscopy. The Raman spectra of silk fibroin film and liquid silk are discussed in comparison with those of the crystalline fractions of Bombyx mori silk fibroin (Cp, chymotryptic precipitate) with Silk I (Silk I-Cp) and Silk II (Silk II-Cp) structures. The complete 1800-200 cm −1 Raman spectrum of Silk I-Cp is reported for the first time. The amide I and amide III modes were found to be scarcely suitable for the spectroscopic characterization of silk fibroin in the Silk I form in the presence of a random coil conformation. Raman marker bands for the Silk I form were identified in other spectral ranges at about 1415, 950, 930, 865, 260 and 230 cm −1 . On the basis of the above findings, the comparison of the Raman spectra of film, liquid silk and Silk I-Cp in the range 1000-800 cm −1 clearly indicates that in addition to random coil, both film and liquid silk contain local domains of Silk I structure; their amount is higher in liquid silk, as indicated by the relative intensity of the bands at about 950, 930 and 865 cm −1 and by the I 1415 /I 1455 intensity ratio.The assignments of the bands at about 1275 and 1107 cm −1 are also discussed. These bands were previously assigned to the presence of a-helical conformation in Bombyx mori silk but, from the results reported, they should rather be attributed to the Silk I form.

Physically Crosslinked Biocompatible Silk‐Fibroin‐Based Hydrogels with High Mechanical Performance

“…According to the literatures, the amide I band around 1659 and 1667 cm −1 are associated to random coil and β-sheet conformations of RSF, respectively. [ 36,37 ] At the very beginning stage of heating, Raman spectra of the RSF/HPMC9 mixture showed a broad and asymmetric peak at amide I band ( Figure 5 b, 0 min), indicating a predominantly random coil conformation along with little amount of other secondary structures of RSF. After 10 min of incubation, the fact that the peak became sharper at amide I band illustrated the conformation of RSF molecules changed from random coil to β-sheet at the initial stage of gelation ( Figure 5 b, 10 min).…”

Vibrational 13C‐cross‐polarization/magic angle spinning NMR spectroscopic and thermal characterization of poly(alanine‐glycine) as model for silk I Bombyx mori fibroin

“…Two prominent bands appeared at 1276 and 1245 cm Ϫ1 in the amide III range, together with other strong bands at 1414, 1107, 954, 928, 864, 263, and 231 cm Ϫ1 , which were recently identified as marker bands for the silk I crystalline modification of silk fibroin. 22 The amide I band of silk I-Cp was very narrow, and that of pAG II broadened at higher wavenumbers. This feature may arise from the presence of different conformational and hydrogen-bonding arrangements, which suggests a higher degree of structural heterogeneity for pAG II.…”

“…19 -22 In an attempt to assign the characteristic Raman vibrational modes of the silk I form of silk fibroin, we used silk I-and silk II-Cp polypeptides. 22 Raman marker bands for the silk I form were identified at about 1415, 1105, 950, 930, 865, 260, and 230 cm…”

Structure of silk by raman spectromicroscopy: From the spinning glands to the fibers

“…Other studies performed on B. mori fibroin samples provided useful band assignments of the silk I conformation (the native form found in the spinning dope) and random coil. 66,67 Model peptides based on the sequence of the B. mori silk fiber have also been investigated to understand the secondary structure adopted by fibroins. 68 The Fermi resonance doublet of the tyrosyl ring at 830/850 cm 21 has often been used to assess the strength of hydrogen bonding of the hydroxyl group of Tyr residues, its ionization state and the hydrophobic/hydrophilic character of its environment.…”