Structural changes of native and regenerated silk fibroin membranes were induced by immersion in water‐methanol solutions and examined as a function of immersion time and methanol concentration. X‐ray diffractometry and infrared spectroscopy data showed that transition from random coil to β‐sheet structure occurred favorably when both native and regenerated silk fibroin membranes were immersed in water‐methanol solutions, regardless of the different immersion time. Only native silk membrane, treated for 2 min with pure methanol, maintained its original amorphous structure, as demonstrated by differential scanning calorimetric (DSC) curves. The degree of displacement, measured by thermomechanical analysis (TMA), was much greater for regenerated than for native silk fibroin membranes. SDS‐PAGE pattern showed that native silk fibroin has a molecular weight of 350, while the regenerated sample is formed by a large number of polypeptides in the range of 200‐50 KD. The amount of acidic and basic amino acids decreased slightly in regenerated silk fibroin. Physical properties of silk membranes treated with water‐methanol solutions are discussed in terms of membrane structure, treatment conditions, and chemical structure of starting material. © 1994 John Wiley & Sons, Inc.

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This study was focused on the conformational characterization of Bombyx mori silk Ðbroin in Ðlm, Ðber and powder form by means of Fourier transform Raman spectroscopy. Native and regenerated silk Ðbroin Ðlms prepared by casting dilute silk Ðbroin solutions (AE1% , w/v) display characteristic conformationally sensitive bands at 1660 cm-1 (amide I), in the range 1276-1244 cm-1 (a complex amide III region with multiple detectable maxima) and at 1107 and 938 cm-1. This spectral pattern can be related to a prevalently random coil conformation, with traces of a-helix. Liquid silk, prepared by casting the silk gland content (Ðbroin concentration 20-25% , w/v), shows almost the same wavenumbers in the amide I and III ranges, while di †erences appear below 1000 cm-1, where three bands at 952, 930 and 867 cm-1 increase in intensity. The spectral di †erences between Ðlms and liquid silk are discussed with a view to identifying possible markers for silk I structure, a crystalline modiÐ-cation of silk Ðbroin. The treatment of both native and regenerated Ðlms with 50% (v/v) methanol solution induces the conformational transition to a b-sheet structure, as demonstrated by the shift of amide I to 1665 cm-1 and the appearance of new maxima at 1262 and 1236 cm-1 (amide III) and at 1084 cm-1. When liquid silk is cast at above 50 ÄC, the prevailing conformation taken by silk Ðbroin is b-sheet, whatever the rate of drying. By comparing the Raman spectra of silk Ðbroin Ðber and powder, both having a b-sheet structure, a di †erence in the tyrosine doublet bands and in the amide I band can be observed. The value of the intensity ratio increases in I 853 /I 830 (R tyr ) the powder while amide I shifts to lower wavenumbers, suggesting that the hydrogen bonds involving the tyrosil residues are weaker in the powder than in the Ðber.

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Structural changes of tussah (Antheraea pernyi) silk fibroin films treated with different water‐methanol solutions at 20°C were studied as a function of methanol concentration and immersion time. X‐ray diffraction measurements showed that the α‐helix structure, typical of untreated tussah films, did not change for short immersion times (2 min), regardless of methanol concentration. However, crystallization to β‐sheet structure was observed following immersion of tussah films for 30 min in methanol solutions ranging from 20 to 60% (v/v). IR spectra of tussah films untreated and methanol treated for 2 min exhibited strong absorption bands at 1265, 892, and 622 cm−1, typical of the α‐helix conformation. The intensity of the bands assigned to the β‐sheet conformation (1245, 965, and 698 cm−1) increased for the sample treated with 40% methanol for 30 min. Raman spectra of tussah films with α‐helix molecular conformation exhibited strong bands at 1657 (amide I), 1263 (amide III), 1106, 908, 530, and 376 cm−1. Following α → β conformational transition, amide I and III bands shifted to 1668, and to 1241, 1230 cm−1, respectively. The band at 1106 cm−1 disappeared and new bands appeared at 1095 and 1073 cm−1, whereas the intensity of the bands at 530 and 376 cm−1 decreased significantly. ©1995 John Wiley & Sons, Inc.