Silk fibroin spectra

Monti, P., Taddei, P., Freddi, G., Asakura, T., and Tsukada, M. (2001). Raman spectroscopic characterization of Bombyx mori silk fibroin Raman spectrum of silk I. J. Raman Spectrosc. 32, 103—107. 

Fig. 8.9. Ranges of

Fig. 23.9. (A) quadrupole echo spectrum of (A) an oriented block and (B) unaligned silk fibroin fiber of [2,2- H2]Gly-labeled samples.

Figure 23.9(A) shows the quadrupole echo spectrum of an oriented block of [2,2- H2]Gly labeled silk fibroin fibers when the fiber axis was set parallel to the magnetic field direction. The quadrupole echo spectrum, Fig. 23.9(B), of unaligned [2,2- H2]Gly labeled silk fibroin fiber is also observed as a powder pattern. Both spectra are split into doublets, which give the value of the quadrupole splitting, Avq as 117.8 kHz for the [2,2- H2]Gly site the values are the same in each case. The full rigid-lattice width of about 126 kHz should be observed when the motion is frozen [72]. Thus, it is concluded that the motion of the methylene groups of the Gly residue is almost frozen at room temperature, which is in agreement with the prediction from the intermolecular hydrogen bonding network in the silk fibroin backbone chain with an antiparallel /3-sheet conformation.

The quadrupole splitting, Ai q of 117.8 kHz observed for the oriented block of [2,2- H2]Gly labeled silk fibroin fiber is the same as the value in the spectrum of an unaligned sample as shown in Fig. 23.9(B). Therefore, if the latter quadrupole splitting is used to provide a value of the proportionality constant, (3/4)e qQ/h, which describes the relationship between the quadrupole splitting and the angle CD (the angle of the C H bond vector of Gly relative to the fiber axis) > CD is calculated as 90°. By taking into account an... 

The solid-state NMR spectrum of an oriented block of the [3,3,3- HsjAla labeled silk fibroin fiber was also observed. The quadrupole splitting, Avq, is 39.8 kHz and is the same as the value in the spectrum of the unaligned sample. This is the same as the case of the [2,2- H2]Gly labeled silk fibroin fiber. The smaller value of the quadrupole splitting for the Ala site indicates the presence of three-fold fast rotation about the Ca-C/3 axis [50, 72]. This... 

A restricted (<, ifi) region for Gly in the Ramachandran map (-180° > 0°, 0° > i/r> 180°) was obtained as the overlap of each region obtained experimentally from the NH, NC, CN, and CO bond orientations as described above. The quadrupole echo spectrum of the oriented [2,2- HaJGly labeled silk fibroin fiber yields an angle, 0 = 90 2°, for the C H2 bond vector of Gly residue relative to the fiber axis. A further narrow... 

Fig. 3. Proton-noise-decoupled - C NMR spectrum of B. mori silk fibroin in aqueous solution (8.7 w/v%). The carbonyl resonance region was expanded and inserted in the figure.

Figure 4 shows the C NMR spectrum of the liquid silk from S.c. ricini mature larva.-" The spectrum of S.c. ricini liquid silk is sharp, indicating very rapid segmental motion of the main chain characterized by a very small correlation time on the order of 10 " s at room temperature (as in the case of B. mori silk fibroin). Assignment was performed by reference to chemical shift data of the pentapeptides, Gly-Gly-X-Gly-Gly, where X equals the specified residue.- "- and the amino acid composition. Solution - C and N NMR studies of S.c. ricini silk fibroin in aqueous solution indicate that about 70% of Ala residues form a-helices while, the conformation of the other Ala residues is random coil." - - ... 

Fig. 11. Plots of ln(A/() — A/,) vs. T of dried B. mori silk fibroin powder at —120, —80, 0, and 130°C, where A/o is the equilibrium amplitude of the fully relaxed spectrum, is the amplitude of a partially relaxed spectrum, and r is the delay time between the 180° and 90° pulses.

The dynamics of B. mori silk fibroin membrane and powder insolubilized with methanol in the swollen state were measured and high-resolution C NMR spectra of the silk fibroin membrane treated with methanol in water are shown in Fig. 30 together with the spectrum of the silk fibroin aqueous solution... 

The ESR spectra were analyzed quantitatively and the fraction of the fast (t. = 10 ), slow (r,. = 10 ), and very slow = I0 ") motions of the spin-label site (Tyr side-chain) were determined. A model is proposed for the heterogeneous structure of the swollen silk fibroin membrane. The ESR spectrum was complex, indicating the heterogeneous structure of the swollen membrane. 

Fig. 33. An example of ESR sp trum simulation. The ESR spectrum of spin-labeled silk fibroin membrane treated with methanol for 24 h was simulated by assuming the spectra of fast, slow, and very slow components corresponding to rotational correlation times of 10, 10, and 10 s, respectively. The fraction of fast, slow, and very slow...

The observed CD pattern of silk fibroin at low concentration - 0.1%, may indicate that die predominant structure is random coilAmordered However, there is residual negative ellipticity value at - 220 nm which may suggest contributi(Mi(s) fiom some ordered structure(s). It may be noted that the typical CD spectrum attributed to random coil/unordered structure has moderate positive ell city value at - 218 nm. Interestingly,... 

To check the impact of silk fibroin on the fluorescence emission of the fluorescent molecules, the one-photon fluorescence spectra of the powder of 4NF, 8NF, and of their functionalized silks were acquired under the same conditions. The results showed that 4NF fibers had strong fluorescent emission, while the emission from the 4NF powder was hardly detectable (Figure 7.6b). The fluorescence plots of the 8NF solution, 8NF fibers, and the powders exhibit a mono tonic bathochromic shift in the order of 8NF solution < 8NF fibers < 8NF powder. The emission spectrum... 

---