Research On The Process And Mechanism Of Dissolving Keratin By Ionic Liquids

Wool keratin is a kind of naturally abundant fibrous protein which exhibits excellent biocompatibility and mechanical properties within wide temperature range and unfolds beyond high limits.These properties have led to the remarkable development of keratin-based materials with applications in biodegradable materials,biomedicine and other functional materials.Achieving the dissolution of keratin is premise to use it,however,complicated disulfide bond network in keratin is an obstacle for its dissolution by traditional solvents.In recent years,applying ionic liquids(ILs)to dissolve keratin has aroused the attention of researchers.It has potentially broad application to use ILs extracting keratin or serve ILs as dissolving medium to further prepare keratin-based composite materials.The foundation to screen and design functional ILs dissolving keratin is to fully clarify dissolution mechanism of keratin in ILs,especially ILs' effects on disulfide bond.Further,solubility of keratin in ILs and properties of regenerated keratin could be manipulated by changing types of cations and anions or dissolution conditions,the rule of these dissolution variables' effects on properties of regenerated keratin would provide basic date for optimizing keratin dissolution parameters.Finally,ILs recycling is the bottle neck for ILs' industrial application,water is often used as antisolvent to regenerate keratin from IL/keratin solution,the large-scale recycling of ILs from these solution is urgently to be dealt with.The breakage of disulfide bonds is the key point for keratin dissolution in ILs.In this study,the method,combining experiments,spectrum characterization and molecular simulation,was used to investigate interaction mechanism and structure activity relationship for the dissolution of keratin in ILs.These would supply scientific foundation for designing efficient ILs to dissolve keratin and accelerating its industrial utilization.The innovative results of the dissertation are as follows.(1)Oxidized glutathione(GSSG)was chosen as the disulfide bond-containing model compound to investigate the change of disulfide bond in ILs.After GSSG regenerating from ILs,the molecular weight of GSSG was decreased and H2S was detected,implying that ILs could induce the reductive cleavage of disulfide bond.What'more,14 kinds of ILs,1-butyl-3-methylimidazolium halide([Bmim]Cl/[Bmim]Br),1?ethyl-3-methylimidazolium chloride([Emim]Cl),1-hexyl-3-methylimidazolium chloride([Hmim]Cl),1-butyl-pyridinium chloride([BPy]Cl),tetrabutylphosphonium chloride([P4444]Cl),tetrabutyl-ammonium chloride([N4444]Cl),1-allyl-3-methylimidazolium chloride([Amim]Cl),1-butyl-3-methylimidazolium acetate([Bmim]OAc,[Emim]OAc),1-ethyl-3-methylimidazolium dimethylphosphate([Emim]DMP),1-ethyl-3-methylimidazolium diethylphosphate([Emim]DEP),1?butyl-3-methylimidazolium dibutylphosphate([Bmim]DBP),and 1-butyl-3-methylimidazolium dihydrogen phosphate([Bmim]H2PO4),were used to investigate the influence of ILs types on the disulfide bond content and properties of the regenerate wool keratin.During the dissolution process,H2S was also detected,and these ILs showed differentiated capability to cleave disulfide bonds.Imidazolium-based acetate could cleavage 90%of disulfide in keratin while quaternary ammonium and phosphonium ILs had nearly no capability to cleave disulfide bond.13C-NMR was used to analysis keratin's secondary structure distribution,the less content of a-helix structure,more content of ?-sheet and disordered structure and less recovery percentage of keratin were observed with increasing disulfide bond cleaving ability of ILs.Through molecular simulation,it can also be found that the ILs' ability of cleaving disulfide bond was closely linked with interaction energy between cystine and ILs and the distribution density of ILs around cystine.(2)Under same dissolution condition,different cations and anions in ILs can lead to varied cleaving ability of disulfide bond in keratin.For[Bmim]+-based ILs,the order of the ability to cleave-S-S-followed:[OAc]->Cl->Br->[DBP]->[H2PO4]-.For the ILs incorporating[Emim]+ cation,the order was[OAc]->Cl->[DEP]->[DMP]-.The effectiveness of the cations in cleaving disulfide bond was found to be[Emim]+>[Amim]+ ?[Bmim]+>[Hmim]+>[BPy]+>[P4444]+>[N4444]+.Further,the side chain lengths of imidazole cation have little effect on the ILs' disulfide bonds cleaving ability.In addition,the effects of dissolution temperature,time and atmosphere on disulfide bond,cystine,sulphur content and degree of crystallinity were studied.With dissolution time and temperature rising,the content of disulfide bond,cystine and sulfur in regenerated keratin decreased.And the dissolution of keratin under N2 could reduce the cleavage of disulfide bond.Either rising dissolution temperature or increasing dissolution time could lead to the decrease of degree of crystallinity of regenerated keratin,however,temperature's effect was more obvious.(3)Water molecule could interact with ILs to form hydrogen bond,molecular dynamic simulation found that the interaction energy between cation and anion in ILs decreased with water content increasing,which could reduce ILs' capability to cleave disulfide bond and increase its dissolution time for wool keratin.To guarantee the ILs'dissolving ability for wool keratin,the water content in ILs should be less than 0.8(mole ratio,H2O/IL).Finally,fall-film evaporator was developed to recycle ILs,and the water content can be reduced to 4000 ppm after evaporating,which could still efficiently dissolve keratin.