Influence of organic solvents on the structural and thermal characteristics of silk protein from the web of Orthaga exvi
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ORIGINAL ARTICLE
Influence of organic solvents on the structural and thermal characteristics of silk protein from the web of Orthaga exvinacea Hampson (Lepidoptera: Pyralidae) Sajitha Narayanan 1 & Mankadath Gokuldas 1
Received: 7 June 2016 / Accepted: 12 August 2016 / Published online: 22 August 2016 # Springer-Verlag Berlin Heidelberg 2016
Abstract The silk protein from the web of Orthaga exvinacea was isolated, purified, and casted into films. This film was treated separately with methanol, acetone, ethyl acetate, and isopropyl alcohol in 50 % concentration for about 30 min. The treated films were thus dried in a desiccator and subjected to FTIR and TG-DTA analysis. The structural studies revealed that the organic solvents induce conformatory changes in the protein film, especially the most sensitive amide I (1650 cm−1) band. This band had shifted to lower wavenumber (1633–1636 cm −1). Furthermore, the conformatory characteristics associated with amide I band also changed from random coil to βsheet. Generally, β-sheet contributes strength to the protein film. Among the treated films, film treated with acetone showed much thermal stability. Moreover, the film treated with methanol had shown two different temperatures of maximum degradation. It is concluded that in addition to β-sheet content, various other factors such as various processing conditions and structural organization of protein may influence the stability of the films.
Keywords FTIR . Orthaga exvinacea . Silk protein . TG-DTA . Silk film . Silken web
Electronic supplementary material The online version of this article (doi:10.1007/s12154-016-0158-4) contains supplementary material, which is available to authorized users. * Sajitha Narayanan [email protected]
1
Insect Physiology and Biochemistry Laboratory, Department of Zoology, University of Calicut, Kerala, India 673 635
Introduction Silk, a common textile fiber, is produced by various silkworms. Moths belonging to different species are actively involved in the production of silk. Silk filaments obtained from the cocoons of silk moths consist of two different proteins. The core of the filament is formed by a fibrous protein, fibroin. Fibroin is a structural protein, characteristically rich in glycine, alanine, and serine [1]. Another protein, sericin, forms a sticky layer around the fibroin filament [2, 3]. Silk fibroin is a textile commodity dating back several centuries. Before the invention of synthetic materials, silk sutures were used in surgery. Decades of research on silk fibroin has manifested in applications of this material in various fields, such as biomedical [4], tissue engineering [5], and cosmetics. The insolubility of fibroin in water is owing to the presence of highly hydrophobic amino acid residues [6]. Different processing methods for silk fibers and proteins have extended its utility to fields other than textiles. It was reported that the dispersion of silk fiber readily occurs in a solvent containing bivalent ions [7, 8]. However, the pure solution of silk fibroin
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