Synthesis And Stimuli-Responsive Properties Of Ionic Poly(L-Cysteine)s Derivative

Stimuli-responsive polymers are promising materials toward a wide range of applications,such as sensing and detection applications,and biomedical applications.They are able to respond to various external triggers,such as temperature,pH,light redox,and so on.Recently,stimuli-responsive polypeptides with responsiveness to temperature,pH,light,and redox have gained increasing attention due to their great potential in biotechnological and biomedical applications.In this dissertation,we have designed and synthesized two series of poly(L-cysteine)derivatives and investigated their stimuli-responsive properties.A homopolypeptide,namely poly(S-(2-carboxylethyl)-L-cysteine)(PCELC),with pH and redox dual responsiveness was prepared by ring-opening polymerization of S-(2-(methoxycarbonyl)ethyl)-L-cysteine based N-carboxyanhydride(MCELC-NCA)and subsequent hydrolysis.The pH-induced solution phase transition of PCELC was at pH =～4.50 as revealed by DLS and UV-vis spectroscopy.The thioether linkages of PCELC can be readily oxidized by H2O2 at 40 ℃ yielding PCELCox with sulfoxide and sulfone linkages as revealed by 1H NMR and FTIR.PCELCox also showed pH responsiveness with the variation of polymer aggregation sizes,but without solution phase separation.PCELCox can be partially reduced by 3-mercaptopropionic acid as suggested by 1H NMR and FTIR analysis.The pH-induced solution phase transition behavior of the reduction product(i.e.,PCELCre)was different from that of the as-prepared PCELC.Moreover,PCELC can be used as a pH and oxidation dual responsive stabilizer to control the aggregation of single-walled carbon nanotubes(SWCNTs)in aqueous solution.Poly(L-cysteine)bearing imidazoliumsalts,namely poly(S-(2-(3-(N-butylimidazolium tetrafluoroborate)propoxycarbonyl)ethyl)-L-cysteine)(P(ImBF4)LC)was synthesized by ring-opening polymerization of S-(2-(3-chloropropoxy carbonyl)ethyl)-L-cysteine based N-carboxyanhydride(CPLC-NCA),nucleophilic substitution of poly(S-(2-(3-chloropropoxy-carbonyl)ethyl)-L-cysteine)(PCPLC),and subsequent ion-exchange reaction.FTIR and CD analysis revealed the presence of β-sheet conformation of P(ImBF4)LC in the solid-state and aqueous solution,respectively.P(ImBF4)LC with low degree of polymerization(DP = 10)was able to show a distinct upper critical solution temperature(UCST)-type phase behavior at a low critical concentration(1.6 mg mL-1)in water.Variable-temperature UV-vis spectroscopy results revealed that the UCST-type solution phase transition temperature(Tpt)of P(ImBF4)LC in aqueous solutions increased with increasing of polymer concentration,NaI or NaBF4 concentration,whereas it decreased by addition of NaCl.