甲酸对丝素蛋白结晶结构转变的影响

Effect of formic acid on the crystalline structure transformation of silk protein

结晶结构是丝素蛋白材料表征的重要内容,对丝素蛋白结晶结构的认识和调控是制备高性能材料的基础。甲酸作为一种可溶解蚕丝的优良溶剂,所制备的再生丝素蛋白材料具有优异的性能,其根源与甲酸对丝素蛋白具有促结晶的作用有关。文章对比分析了基于氯化钙-甲酸溶剂溶制再生丝素蛋白膜与基于三元溶剂溶制再生丝素蛋白膜的结晶结构差异,并利用α-糜蛋白酶从基于三元溶剂制备的丝素蛋白水溶液中分离出高结晶部分和低结晶部分,随后分别利用甲酸和乙醇对分离所得高结晶部分和低结晶部分进行处理,对比分析了乙醇和甲酸对其结晶结构转变的影响。结果表明,相对于乙醇处理,甲酸具有更显著的促丝素蛋白结晶的作用,更有利于丝素蛋白从无规卷曲或Silk I结晶态转变为SilkⅡ结晶态。

As a natural polymer protein,silk fibroin,with its excellent biocompatibility,controllable biodegradability,non-toxicity and low immunogenicity,has a wide range of applications in the fields of biomedical engineering materials,flexible wearable sensor devices,food and pharmaceuticals,and fine chemicals.In these engineering applications,silk fibroin is required to have certain mechanical properties and biomedical engineering application performance,and these properties and performance are closely related to the crystalline structure of silk fibroin protein,and the regulation of its mechanical properties can be realized by modulating the crystalline morphology or crystalline structure parameters in silk fibroin protein materials to meet the needs of biomedical engineering applications.The regulation of the crystalline structure of silk fibroin protein materials can be realized by adopting different solvent solutions and post-treatment processes.The silk fibroin protein material prepared by dissolving the aqueous solution of degummed silk with a ternary solvent(a solvent system consisting of calcium chloride,ethanol and water with molar ratio of 1 ∶2 ∶8) exhibits water solubility,low crystallinity,and is of the Silk I or amorphous mainly crystalline structure.It needs to be post-treated with a certain concentration of ethanol to realize the regulation of its crystalline structure,so as to achieve certain mechanical properties and water stability of the material.On the other hand,the silk fibroin primary material prepared with formic acid as solvent has a highly crystalline structure of Silk II and does not require any post-treatment.This suggests that formic acid also has the effect of promoting the crystallization of silk fibroin proteins,but there are few reports on the study of formic acid promoting the crystallization of silk fibroin proteins.To illustrate the effect of formic acid on the crystalline structure of silk fibroin proteins and the role of formic acid in promoting the crystallization of silk fibroin proteins,firstly,the silk fibroin membranes were prepared by using the ternary solvent and calcium chloride-formic acid as solvents,respectively,and the membranes prepared on the basis of the ternary solvent were subjected to the post-treatment of ethanol and the secondary dissolution of formic acid to reform the membranes.Then,the secondary structure and the crystalline structure of the membrane materials prepared were comparatively analyzed by using the FTIR and XRD test and analysis methods,and the effects of different preparation schemes on the crystalline structure of the resulting silk fibroin membranes were illustrated.Further,by utilizing the ability of α-chymotrypsin to separate the aqueous solution of silk fibroin protein into a highly crystalline fraction(precipitate) and a lowly crystalline fraction(dry matter of the supernatant),the aqueous solution of silk fibroin protein prepared based on the ternary solvent was treated by using α-chymotrypsin to obtain the highly crystalline fraction of silk fibroin protein and the lowly crystalline fraction of silk fibroin protein,respectively.Then,the two were subjected to the secondary solubilization of formic acid and the treatment of ethanol,respectively.Furthermore,the secondary structure and crystalline structure transformation of the high crystalline fraction and low crystalline fraction of silk fibroin protein after the secondary dissolution of formic acid and ethanol treatment,respectively,were comparatively analyzed by FTIR and XRD tests.The article investigated the potential ways in which silk fibroin proteins can behave in a crystalline manner by analyzing the crystalline transitions of two silk fibroin materials with very different crystalline properties,discussed the effect of formic acid on the crystalline structure of silk fibroin proteins,and compared formic acid in its pro-crystallization behavior of silk fibroin proteins with that of ethanol.Formic acid is found to have a more significant pro-crystallization effect on silk fibroin proteins relative to ethanol treatment,and is more favorable to the transformation of silk fibroin proteins from the randomly curled or Silk I crystalline state to the Silk II crystalline state.Especially for the low crystalline fraction of silk fibroin,formic acid also regenerates the crystalline structure.Formic acid is an excellent solvent for silk fibroin protein,through which formic acid can not only dissolve the degummed silk,but also has the effect of prompting the crystallization of silk fibroin protein.In the preparation of engineering materials,with the help of formic acid's role in promoting the crystallization of silk fibroin protein,the crystalline structure of the silk fibroin protein material can be regulated to meet the needs of biomedical engineering applications.Nevertheless,since formic acid has high volatility and strong corrosiveness,it is a focus of future research to give full play to the advantages of formic acid,such as exploring the use of formic acid vapor to treat silk fibroin materials or the use of formic acid and water replacement technology.