Water dependent structural changes of silk from Bombyx mori gland to fibre as evidenced by Raman and IR spectroscopies

• Published in: Vibrational spectroscopy 2014-07, Vol.73, p.79-89
• Main Authors: Percot, Aline, Colomban, Philippe, Paris, Céline, Dinh, Hung Manh, Wojcieszak, Marine, Mauchamp, Bernard
• Format: Article
• Language: English
• Subjects: Amorphous materials; Araneae; ATR-FTIR; Backbone; Bombyx mori; Conformation; Fibre; Gland; Infrared spectroscopy; Life Sciences; Moisture content; Raman; Silk; Spectroscopy; Water
• ISSN: 0924-2031; 1873-3697
• DOI: 10.1016/j.vibspec.2014.05.004

•ATR FTIR showed the deshydration of Bombyx mori gland in less than 30 min.•Fibroin organisation was studied along the Bombyx mori gland in the quasi in vivo hydrated state and changes were pointed out in the middle part by micro Raman spectroscopy and by DSC.•Fibroin organisation/orientation was characterized in the dried gland and in the spun fibre, and highlighted the crucial role of remaining “bound” water. DSC, attenuated total reflexion infrared (ATR-FTIR), and Raman microspectroscopy were used for the first time in a close to in vivo environment to study ready-to-spin Bombyx mori silkworms. The aim was to understand the change of the fibroin backbone organisation from the gland to the fibre. Raman shifts of the Amide I components reveal a strong change of organisation in the middle part of the hydrated gland, as anticipated previously measured modifications of salts concentrations and pH. Series of bands characteristics of the fully hydrated silk disappear, as observed for spider silk, despite the different aminoacid sequence. Confirmation is obtained from IR spectra taking into account the superimposed water component. The change of the silk–water interaction in the central part of the gland, from a hydrophobic to hydrophilic behaviour, is related to the water content decrease along the gland. pH sensitive carboxylate side chains markers confirm the modification. Fibroin organisation was also studied in the dried gland and in the spun fibre. The fibre extrusion by orients the fibroin chains along the fibre axis, with intercalated water molecules, leading to a material with specific mechanical properties, compared to the amorphous dried gland.