The Study On The Structure And Fabrication Of Rhodamine Modified Silkworm Silk

In recent years, silkworm silk, as a new environmentally friendly and biodegradable polymer material, has gained widespread interests in researchers. There is a long history to obtain intrinsically/colored silk by feeding method. However, it is difficult to develop due to the limitation of measurement technology. Recently, some researchers have made fluorescent dyes to infiltrate into silk by feeding method. It brings new process to obtain luminescent silk and has a important applications in the fields of medicine. But, feeding method is just at its beginning. In the paper, five similar fluorescent dyes were taken into account and we successfully got the luminescent silks. By wide-angle X-ray diffraction(WAXD), X-ray diffraction(XRD), FTIR micro-spectroscopy(M-FTIR) and flurescence spectroscopy, we have further studied the the factors of dyes structure, content and feeding method that affect the fibroin, including the amount in fibroin, structure change, mechanical properties, and crystalline performance. At the same time, we compare the structure and performance of the fibroin of feeding method and dyeing method. The main results are as follows:(1) By comparing the amount in silk fibroin of five similar fluorescent dyes (sodium fluorescein, rhodamine110, rhodamine B, rhodamine101salt, acridine orange), we found that there’s almost no fluorescein sodium in silk. Great solubility of fluorescein sodium made it directly excepted out of body. Although Rhodamine110can enter into silk gland, it is difficult to enter into the hydrophobic region of the fibroin globule. Most Rhodamine110which is in silk gland can form intermolecular forces and very little Rhodamine110can enter into hydrophobic region of fibroin globule, so the amount of Rhodamine110in sericin is four times than in sericin. Referred to the Rodamine B and Rodamine101inner salt, the amount of dyes in silk are most concentrated in the silk fibroin. The amount of Rodamine101inner salt is ten times than in sericin and the amount of Rodamine B in fibroin is just four times than in sericin, so we think that Rodamine101inner salt within this structure can easier access into silk fibroin. Acridine orange has no hydrophilic group, and it is difficult to enter into silk gland. Although the amount of acridine orange in silk is very small, the amount of acridine orange in fibroin is more than in sericin.(2) We get the conclusion that two conditions may affect fluorescent functional molecules into silk. Firstly, the fluorescent functional molecules should have a hydrophilic group, this will ensure that substances can enter the gland with body fluids. Secondly, the fluorescent functional molecules should have a hydrophobic group which have some group can form hydrogen bonds with fibroin micelles.(3) By FTIR, we found that the addition of fluorescent dyes would affect the structure of fibroin by the feeding method. The addition of Rhodamine110by feeding method may inhibit the formation of hydrogen bond between fibroins. However, the addition of Rhodamine B by feeding method can be conducive to the formation of inter-molecular hydrogen bond between fibroins, making the absorption peak of amide III band shifts to lower wavenumber. Besides these, the addition of Rhodamine B can inhibit the random coil turn to β-sheet conformation, so the amount of β-sheet conformation is decreased. Similar to Rhodamine B, the addition of Rodamine101inner salt can be conducive to the formation of inter-molecular hydrogen bonding between fibroins. There is no change in fibroin when we add acridine orange into the feeds.(4) When add these fluorescent dyes into feeds, the silk fibroin have lower crystallinity. Adding Rhodamine B and acridine orange into feeds, the silk fibroin have smaller spacings. Besides theses, the addition of these fluorescent dyes can lead the tensile strength and modulus decrease. (5) We also studied the difference between fibroin of feeding method and dyeing method. In feeding method, with the increase of Rhodamine B, the intensity of crystalline diffraction peak in silk fibroin is reduced, and the high-level crystalline diffraction peaks gradually disappear, the cell parameters and paracrystalline parameter decreased. It means the addition of Rhodamine B by feeding method can lead crystallinity and crystallite size decrease. The presence of hydrogen bond between the silk fibroin fibers and Rhodamine B, making the spacing become smaller, the regularity of the crystal become better, crystals align more closely and get more perfect.