6 Cocoon Silk: From Mesoscopic Materials Design …
273
Fig. 6.18 Raman spectroscopy for characterizing secondary structure and polarized Raman spectra
to measure orientation in silk materials. a Image of Raman spectroscopy. b Raman band decomposition of amide I region (1580–1740 cm −1 ) of isotropic spectra for Samia cynthia ricini (S. c.
ricini) silk fibers. Reproduced with permission [55]. Copyright 2006, American Chemical Society.
Polarized Raman spectra of the coagulated film and c The I xx and I zz curve are nearly the same.
d Polarized spectra of the fibroin fiber of B. mori silk. The I xx and I zz curve are significantly distinct.
c, d Reproduced with permission [50]. Copyright 2004, American Chemical Society
alanine sequences, the AG and GGA sequence motifs might also be incorporated
into the β-sheets [56].
In addition to the molecular conformation, polarized Raman spectra have recently
been adopted to compare the molecular orientation within SF materials [57]. In a
typical polarized Raman spectroscopy measurement, the intensity I ij refers to the
intensity measured when the incident beam is polarized in the i direction and the
scattered light is polarized in the j direction, where i, j = x, y, or z are the axes
associated with the laboratory frame. The polarized spectra in the amide I region of
both the regenerated SF film and cocoon silk fiber are presented in Fig. 6.18c and d,
respectively [57]. For the SF film, the intensity of the amide I band in the xx and zz
spectra is equal, implying that the sample is isotropic. However, the intensity of the
amide I band is much weaker in the zz spectrum of the cocoon silk compared to that in
the xx spectrum, which is consistent with the high orientation of the peptide groups.
Specifically, this is attributed to the fact that the carbonyl groups within the SF and
SF films are mostly oriented along the x axis and are randomly distributed. In this
way, by measuring the ratio of the intensity of I xx and I zz , the molecular orientation
can be quantitatively measured [57].
273
Fig. 6.18 Raman spectroscopy for characterizing secondary structure and polarized Raman spectra
to measure orientation in silk materials. a Image of Raman spectroscopy. b Raman band decomposition of amide I region (1580–1740 cm −1 ) of isotropic spectra for Samia cynthia ricini (S. c.
ricini) silk fibers. Reproduced with permission [55]. Copyright 2006, American Chemical Society.
Polarized Raman spectra of the coagulated film and c The I xx and I zz curve are nearly the same.
d Polarized spectra of the fibroin fiber of B. mori silk. The I xx and I zz curve are significantly distinct.
c, d Reproduced with permission [50]. Copyright 2004, American Chemical Society
alanine sequences, the AG and GGA sequence motifs might also be incorporated
into the β-sheets [56].
In addition to the molecular conformation, polarized Raman spectra have recently
been adopted to compare the molecular orientation within SF materials [57]. In a
typical polarized Raman spectroscopy measurement, the intensity I ij refers to the
intensity measured when the incident beam is polarized in the i direction and the
scattered light is polarized in the j direction, where i, j = x, y, or z are the axes
associated with the laboratory frame. The polarized spectra in the amide I region of
both the regenerated SF film and cocoon silk fiber are presented in Fig. 6.18c and d,
respectively [57]. For the SF film, the intensity of the amide I band in the xx and zz
spectra is equal, implying that the sample is isotropic. However, the intensity of the
amide I band is much weaker in the zz spectrum of the cocoon silk compared to that in
the xx spectrum, which is consistent with the high orientation of the peptide groups.
Specifically, this is attributed to the fact that the carbonyl groups within the SF and
SF films are mostly oriented along the x axis and are randomly distributed. In this
way, by measuring the ratio of the intensity of I xx and I zz , the molecular orientation
can be quantitatively measured [57].