| The applications of enzymes in ecological textile dyeing and finishing have increasingly attracted more attention,especially in textile dyeing,which has become a hot research topic in recent years.Compared with traditional chemical dyes,the enzymatic staining is more advantageous owing to its environmental friendliness and mild dyeing conditions.Hereby,a novel laccase-based catalytic dyeing of protein fibers is presented to provide an alternative for textile dyeing.In this work,the protein fibers were dyed using in situ laccase-based catalytic dyeing.Color properties and morphology of dyed protein fibers were tested.The laccase-based catalytic reaction of two amino acids:tyrosine and tryptophan(the choosen representative monomers)were investigated,and structures and molecular weights of the products were characterized.The colored silk and wool fabrics were analyzed by a series of performance tests.These results were then combined to elucidate the in situ chromogenic mechanism of protein fibers.Furthermore,to improve the color depth and the color spectrum of the protein fibers,tyrosine and tryptophan were introduced as exogenous monomers and used in the laccase-based catalytic dyeing of protein fibers,in which different dyeing colors were obtained.Lastly,the anti-ultraviolet properties of silk fabrics were improved by laccase-based catalytic dyeing in the presence of dopa.The research findings can be summarized as follows.Firstly,silk and wool fabrics were treated with laccase.The effects of laccase treatments on silk,wool and cotton fabrics were then compared.The results showed that the color of silk and wool fabrics were brownish yellow.This demonstrated that the protein fibers were catalyzed by laccase,resulting in fiber coloration.Based on the K/S value,the laccase-catalyzed dyeings of silk and wool fabrics was optimized,and the colored fabrics were evaluated for color performance.The optimal treatment conditions were as follows:laccase dose:1.2 U/mL;pH:5.0;temperature:50?;reaction time:24 h;and bath ratio:50:1.The dry and wet rubbing fastness and the light fastness of the colored silk and wool fabrics were of grades 4-5 and 2-3,respectively.Moreover,the colored silk and wool fabrics obtained from reactions containing weak acid aqueous solution and at different temperatures had excellent color uniformity and color stability,whereas that obtained from a reaction containing strong acid solution and metal ions had poor stability.The Digital Microscope,Optical Microscope,SEM and AFM images showed that the surface of silk fiber was smooth,and the squama layer of wool fiber surface was clear and no attachment was observed;and the appearance was not significantly changed,the colored silk and wool fibers had good levelness and penetration.Secondly,the laccase-catalyzed reactions of representative monomers were monitored,and structures and molecular weights of the oxidative products were characterized.Combined with performance analysis of the colored silk and wool fabrics,the in situ chromogenic mechanism was demonstrated.Analysis of FT-IR,MALDI-TOF MS,and LC-MS showed that tyrosine monomer was catalyzed by laccase and generated phenoxyl and benzene ring-based carbon radicals.The oxidative products were obtained from the intercoupling reaction of the two free radicals as well as the Michael addition reaction of benzene ring-based carbon radicals and the amino group of tyrosine.The oxidative product of tyrosine was a mixture of dimers,trimers,and tetramers(polytyrosine pigment).On the other hand,the oxidative dimeric and trimeric(polytryptophan pigment)products of tryptophan from a reaction catalyzed by laccase were the result of the intercoupling of pyrrole nitrogen radicals and benzene ring-based carbon radicals.When a mixture of tyrosine and tryptophan was catalyzed by laccase,the oxidative products were found to be polytyrosine and polytryptophan pigments.When such mixture was catalyzed in a copolymerization reaction,the products were found to be the copolymers of tyrosine:tryptophan at various ratios:1:1;2:1;and 3:1.Because the colors of polytryptophan pigment is red-brown and that of polytyrosine pigment is brownish yellow,which are the same as that of the colored silk and wool fabrics that was catalyzed by laccase,it can be speculated that the oxidation coupling reaction of tyrosine residues may play a main role in the in situ coloration mechanism.Moreover,the silk and wool fabrics were treated with DMF and then characterized by ATR-IR,XPS,UV-vis,and the acid hydrolysate of silk fabrics were tested by LC-MS.The results showed that the K/S values of the colored silk and wool fabrics were not changed after DMF treatment.Structural analysis of the colored silk and wool fibers by ATR-IR and XPS showed that additional C=O,C-O-C and C-N were observed,and new co-planar conjugate structures were formed between large molecular peptide chains.Additionally,dityrosine and tyrosine-tryptophan structure were observed in LC-MS analysis of silk hydrolysate of acid.According to these results,the in situ chromogenic mechanism of which silk and wool fabrics were dyed via laccase-catalyzed oxidation can be inferred:(i)the conjugate structures were formed between benzene ring and aryl ketone of phenol group of tyrosine residues;(ii)phenol groups of tyrosine residues were then catalyzed to generate phenoxyl radicals and benzene ring-based carbon radicals,a new conjugate structure and ether bond were finally formed in the silk and wool macromolecular peptides by further coupling reaction of the active free radical intermediates,leading to the dyeing of silk and wool fabrics;(iii)imino groups of tryptophan residues were catalyzed to generate nitroxide free radical benzene ring-based carbon radicals,then a new conjugate structure were formed by coupling reaction of the active benzene ring-based carbon radicals;and(iiii)another conjugate structure were formed by coupling reaction of the active benzene ring-based carbon radicals from tyrosine residues and tryptophan residues.Thirdly,in order to enhance the color depth and spectrum of silk and wool fabrics by laccase-based dyeing,tyrosine and tryptophan were introduced as exogenous monomers.Color parameters of the dyed fabrics were examined,and the dyeing effects under different treatment methods were compared.In addition,the color fastness was tested,and the dyeing process was optimized.The surface morphology,horizontal cross-sections and structure of the dyed silk and wool fibers were characterized by Digital Microscope,Optical Microscope,SEM,ATR-IR,and DMF treatment.The dyeing mechanisms of silk and wool fabrics were studied.In the laccase-based catalytic dyeing of silk and wool fabrics in the presence of tyrosine,brownish yellow-color polytyrosine pigments were formed as a result of laccase catalytic reaction,and then dyed the silk and wool fibers.These dyed silk and wool fabrics had good levelness and penetration,the dry friction fastness of grade 4,the fastness to the wet friction of grades 3-4,and the light fastness of grade 3.The optimal process conditions can be summarized as follows:laccase dose:1.8 U/mL;pH:5.0;tyrosine concentration:0.5 g/L;temperature:50?;reaction time:24 h;and bath ratio:50:1.Analysis of the stripping color test of DMF and ATR-IR indicated that phenoxyl and benzene ring-based carbon radicals of polytyrosine formed covalent bonds with those of the silk and wool fibers.Additionally,the amino group of the pigment appeared to be covalently bonded to adjacent carbon of the phenol hydroxyl group of silk and wool fibers via Michael addition reaction.One the other hand,in the laccase-based catalytic dyeing of silk and wool fabrics in the presence of tryptophan,polytryptophan pigments were formed as a result of the laccase catalysis,and then stained the silk and wool fibers to red-brown color.The dyed silk and wool fabrics had the dry friction fastness of grade 4,the fastness to the wet friction of grades 3-4,and the light fastness of grade 3.The optimal process conditions were as follows:laccase dose:1.2 U/mL;pH:5.0;tryptophan concentration:6 g/L;temperature:50?;reaction time:16 h;and bath ratio:50:1.Analysis of the stripping color test of DMF and ATR-IR revealed that pyrrole nitrogen free radicals of polytryptophan formed covalent bonds with phenoxyl and benzene ring-based carbon radicals of the silk and wool fibers;and the amino group of the pigment appeared to be covalently linked with adjacent carbon of phenol hydroxyl group of silk and wool fibers as a result of Michael addition reaction.Finally,in an attempt to enhance anti-ultraviolet performance in silk fabrics dyeing,an exogenous monomer dope was used in the laccase-based catalytic dyeing.The color parameters of the silk fabrics were tested,and the dyeing effects from different treatment methods were compared.The color fastness of the dyed fabric was tested,and the dyeing process was optimized.Characterizations of surface morphology,horizontal cross-sections and structure of the dyed silk fibers were conducted by Digital Microscope,Optical Microscope,SEM,AFM,XPS,ATR-IR,and DMF treatment.The dyeing of silk fibers with dopa melanin was explored.Color of the silk fabric dyed laccase-based catalytic dyeing in the presence of dopa was black.Its UFP value was found to be 100~+,and the light fastness was of grade 5.Analysis of the results from SEM,AFM,and XPS revealed that dopa was catalyzed by laccase to form dopa melanin,which then dyed the silk fiber,causing its surface to become rougher.The dyed silk fibers obtained good levelness and penetration because of infiltration of dopamelanin.The ATR-IR and DMF treatment demonstrated that pyrrole nitrogen free radicals of dopa melanin reacted with phenoxyl and benzene ring-based carbon radicals of the silk fibers to form N-O and C-N covalent bonds.The optimal process conditions were as follows:laccase dose:3 U/m L;pH:5.0;dopa concentration:2 g/L;temperature:50?;time:24 h;and bath ratio:50:1.This article presents the dyeing effect as well as the mechanism of laccase-based dyeing of protein fibers,providing preliminary information,which could be used as a reference for other textile dyeings. |
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