The H-chains of SF contain twelve hydrophobic, crystalline domains where the amino acids are present in a repetitive sequence composed essentially of glycine (≈43–46%), alanine (≈25–30%), and serine (≈12%), along with some tyrosine (≈5%), valine, and threonine. The L-H complex binds a glycoprotein P25 chain in a 6:1 ratio. The inner part of the fiber is silk fibroin (SF), which is composed of light (L) and heavy (H) polypeptide chains linked at the C-terminus by a disulfide bond. Sericin removal is required to allow continuous and smooth filament reeling and to achieve the desired luster and touch in silk textiles. This (water-soluble) layer is usually removed during the industrial processing of silk fibers in a step called “degumming”, which is usually done by heating the cocoons with hot water under pressure or by boiling them in an alkaline (Na 2CO 3), soap, or synthetic detergent solution. 20–30% of the structure of the cocoon depending on environmental/growing conditions. The outer filament (silk sericin) is a sticky, hydrophilic glycoprotein that represents ca. mori), is composed of two concentric filaments, in addition to small amounts of pigment, wax, and carbohydrates see Figure 1.
Natural silk fiber, e.g., that secreted by the domesticated silk worm species Bombyx mori ( B. Using DOE, we were able to predict values of SF-m% this is satisfactory and important because it results in economy of labor, time, and material. The order of SF dissolution is BuMeImAcO-DMSO > C 3OMeImAcO-DMSO this was attributed to the formation of intramolecular H-bonding between the ether oxygen in the side chain of the latter IL and the relatively acidic hydrogens of the imidazolium cation. Using BuMeImAcO, AlBzMe 2NAcO, and molecular dynamics simulations, we attribute the difference in IL efficiency to stronger SF-IL hydrogen bonding with the former IL, which is coupled with the difference in the molecular volumes and the rigidity of the phenyl ring of the latter IL. The resulting regression coefficients showed that the dissolution of SF in BuMeImAcO-DMSO and C 3OMeImAcO-DMSO is more sensitive to variation of T than of χ DMSO the inverse is observed for the quaternary ammonium ILs. We successfully employed a second-order polynomial to fit the biopolymer dissolution data. We used design of experiments (DOE) to determine the dependence of mass fraction of dissolved SF (SF-m%) on T and χ DMSO. The ILs included BuMeImAcO, C 3OMeImAcO, AlBzMe 2NAcO, and Bu 4NAcO see the names and structures below. We studied the dependence of dissolution of silk fibroin (SF) in mixtures of DMSO with ionic liquids (ILs) on the temperature ( T = 40 to 80 ☌) and DMSO mole fraction ( χ DMSO = 0.5 to 0.9).
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