Stimuli-Responsive Zwitterionic Block Copolypeptides: Poly(N-isopropylacrylamide)-block-poly(lysine-co-glutamic acid)

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• 作者：Jingguo Li ; Tao Wang ; Dalin Wu ; Xiuqiang Zhang ; Jiatao Yan ; Song Du ; Yifei Guo ; Jintao Wang ; Afang Zhang
• 刊名：Biomacromolecules
• 出版年：2008
• 出版时间：October 13, 2008
• 年：2008
• 卷：9
• 期：10
• 页码：2670-2676
• 全文大小：262K
• 年卷期：v.9,no.10(October 13, 2008)
• ISSN：1526-4602

文摘

Synthesis of novel zwitterionic block copolypeptides, poly(N-isopropylacrylamide)-block-poly(l-glutamic acid-co-l-lysine) [PNiPAM_n(PLG_x-co-PLLys_y)_m, where n is the number-average degree of polymerization (DP_n) of PNiPAM block, x and y are the mole fraction of glutamic acid and lysine residues, respectively, and m is the total DP_n of the peptide block], and their stimuli-responsiveness to temperature and pH variation in aqueous solutions are described. Initiated with the amino-terminated poly(N-isopropylacrylamide) (PNiPAM_n-NH₂), ring-opening polymerization (ROP) of a mixture of γ-benzyl-l-glutamate N-carboxyanhydride (BLG-NCA), and Boc-l-lysine N-carboxyanhydride (BLLys-NCA) afforded the block copolypeptides PNiPAM_n(PBLG_x-co-PBLLys_y)_m, with a poly(N-isopropylacrylamide) block together with a random copolypeptide block, which was then deprotected with HBr/trifluoroacetic acid into the double hydrophilic block copolypeptides, PNiPAM_n(PLG_x-co-PLLys_y)_m. Their block ratios and lengths, as well as the amino acid residue ratios in the random copolypeptide block are varied (n = 360, x = 0.4−0.5, y = 0.4−0.6, and m = 220−252). The secondary structures of the copolypeptides in aqueous solution at different pH conditions were examined. Phase transitions in aqueous solutions induced by both pH and temperature variation were investigated by ¹H NMR spectroscopy. The transitions induced by temperature were also explored by turbidity measurements using UV/vis spectroscopy for their lower critical aggregation temperature (LCAT) determination. Furthermore, these aggregation processes were followed by dynamic light scattering measurements.