Infrared Rheo-Optics of Bombyx Mori Fibroin Film by Dynamic Step-Scan FT-IR Spectroscopy Combined with Digital Signal Processing

Abstract

Recently developed dynamic step-scan FT-IR spectroscopy combined with software-based digital signal processing (DSP) was applied for infrared rheo-optical measurements of isotactic polypropylene and regenerated Bombyx mori silk fibroin film undergoing sinusoidal mechanical strain. Comparative measurements of dynamic infrared spectra of polypropylene film using the DSP-based method and two lock-in amplifiers (LIAs) indicated that a high signal-to-noise ratio (SNR) advantage is attained by the DSP method compared with the LIA method. With the DSP technique, dynamic spectra of Bombyx mori silk fibroin film with high SNR were successfully recorded in the whole mid-infrared region in only 30 min. The dynamic spectra revealed that stress-induced dynamic reorientation in fibroin film is mainly localized in the segment with β-sheet conformation and is almost synchronous with the applied mechanical strain. Two-dimensional (2D) correlation analyses of the dynamic spectra showed that (1) the broad amide I band is resolved into three components whose positions are dependent on secondary structures, (2) the dynamic behavior of tyrosine residues was extracted by separation of the feature due to its aromatic side chains from the broad envelope of the amide I band in the 2D asynchronous map, and (3) the dynamic behavior of the amide A and B modes is the same as that of the amide II mode, when the mechanical strain is applied to fibroin film.

The preparation of regenerated silk fibroin microspheres

“…3, the secondary structure of the silk fibroin in microspheres prepared with a high ethanol-RSF ratio was predominantly the b-sheet structure, with peaks at 1623 cm 21 (amide I) and 1526 cm 21 (amide II), whereas silk I structure was observed in those microspheres obtained with lower ethanol-RSF ratios, with peaks at 1648 cm 21 (amide I) and 1539 cm 21 (amide II). 35,36 In other words, the higher the ethanol-RSF ratio, the more b-sheet structures in the microspheres, which is in accordance with the well-known conformational transition of silk fibroin from random coil and/or helical conformation to b-sheet induced by low dielectric organic solvents, such as methanol and ethanol. 37,38 This means the increase of ethanol concentration favors the b-sheet structure, and results in higher crystallinity in the microspheres at the same freezing temperature and RSF concentration.…”

Paclitaxel‐loaded silk fibroin nanospheres

“…It is also found that the absorption increases with the increase in initial PTX‐loading capacity (curve a − c [PTX] is from 1.5 to 7.5%) that implies the actual drug loading increases correspondingly. In the meantime, the increase of the adsorption at 1630 cm −1 in amide I band with the increase in initial PTX‐loading capacity indicates the increase of the β‐sheet conformation in RSF nanospheres 15, 36–38. It is found that the β‐sheet content in pristine RSF nanospheres is about 16%, but it increases from 20 to 25% in the PTX‐loaded RSF nanospheres (Table I).…”

Dynamic Protein−Water Relationships during β-Sheet Formation

“…The frequency is shown from 1000 to 1800 cm -1 , which contains the most important band regions of amide I, amide II, and amide III. [48][49][50] The IR spectral region within 1700-1500 cm -1 was assigned to the peptide backbone of amide I (1700-1600 cm -1 ) and amide II (1600-1500 cm -1 ) absorptions; the amide III region was from 1350 to 1200 cm -1 . 27,28 The amide I region mainly comes from the CdO stretching vibration (80%) with minor contributions from the NH in-plane bending, the out-of-phase CN stretching vibration, and the CCN deformation.…”