This study is focused on the Raman spectroscopic analysis of degummed silk fibroin (SF) fibers and regenerated Bombyx mori silk fibroin films: a correlation was found between some spectral features related to the methylene deformation modes and the molecular orientation of the samples.
Polarized Raman spectra on SF fibers were used to obtain the orientation distribution function of carbonyl groups along the protein backbone. The variation of the intensity ratio of 1400/1450 cm−1 for the peaks attributed to the wagging and bending deformation modes of CH2 groups with respect to the angular orientation of the fiber was measured and quantitatively correlated with the orientation distribution function of the carbonyl groups.
Unpolarized Raman spectra were measured for regenerated silk fibroin films and lyophilized solutions. The variation of the intensity ratio of 1415/1455 cm−1, which is related to the deformation modes of CH2 groups in SF regenerated materials, was qualitatively related to the microstructural orientation of the samples observed by scanning electron microscopy (SEM), and to the presence of Silk I phase as suggested by the analysis of samples obtained in different casting conditions and also by the measurements on mechanically deformed films.
The results obtained showed the utility of the spectroscopic intensity ratio of 1400/1450 cm−1 for the rapid assessment of molecular orientation in silk fibers, which could be useful for quality and process control of regenerated silk-based textiles. Moreover, the qualitative dependence of the intensity ratio of 1415/1455 cm−1 was found to be sensitive to both the microstructural orientation and Silk I content of regenerated silk fibroin films, suggesting a possible correlation of this Raman marker of the Silk I phase with the degree of molecular order brought about by this polymorph. Copyright © 2006 John Wiley & Sons, Ltd.