Raman Spectroscopic Evidence for Side-Chain Unfolding in Spider Dragline Silk under Tensile Deformation

In-situ Ramanspectra were collected on the N. clavipes spider dragline silk under a tensile deformation rate of 15mm/min. The most prominent features on the spectra were due to those bands near 1100 cm-1, which present as a sensitive probe to structural changes associated with side-chains of silk peptide. A downshift of Raman bands at 1095 cm-1 and 1089 cm-1 was detected with increasing strain. Furthermore, an increase in the intensity of the Raman band at 1062 cm-1 due to the vibration of trans structure without lateral coupling was prominent at certain strain levels. This was interpreted in terms of a morphology transition from the random configuration to the trans conformation modulated by the reorganization of the hydrogen bonding among the side-chain.