d-, l- and d,l-Tryptophan-Based Polyamidoamino Acids: pH-Dependent Structuring and Fluorescent Properties
d-, l- and d,l-Tryptophan-Based Polyamidoamino Acids: pH-Dependent Structuring and Fluorescent Properties
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DOI：
10.3390/polym11030543
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发表时间：
2019-03-22
期刊：
影响因子：
5
通讯作者：
Ranucci, Elisabetta
中科院分区：
文献类型：
--
作者：
Lazzari, Federica;Manfredi, Amedea;Ranucci, Elisabetta
N，N ′-亚甲基双丙烯酰胺与d-、d，l-和l-色氨酸（M-d-Trp，M-d，l-Trp和M-l-Trp）通过加成反应合成了手性聚酰胺氨基酸。从L-色氨酸/甘氨酸混合物制备了L-色氨酸/甘氨酸共聚物M-G-l-Trp（5）、M-G-l-Trp（10）、M-G-l-Trp（20）和M-G-l-Trp（40）。这些聚合物是两性的，具有与母体氨基酸相似的酸碱性质。具有高甘氨酸含量的l-色氨酸/甘氨酸共聚物在pH 2-12范围内是水溶性的。M-G-1-Trp（40）显示出以pH 4.5为中心的溶解度间隙，并且所有色氨酸均聚物仅在pH > 7时可溶。在其溶解度范围内进行动态光散射测量，即2-11 M-G-l-Trp（5）、M-G-l-Trp（10）和M-G-l-Trp（20），以及7-11 M-G-l-Trp（40）、M-d-Trp、M-l-Trp和M-d，l-Trp，M-I-Trp和M-G-I-Trp共聚物均显示pH-1。在200-280 nm波长区间内的依赖圆二色性光谱，揭示了结构化。所有样品都是荧光的。它们的发射光谱是非结构化的，并且如果针对它们的色氨酸含量进行归一化，则在相同的pH下几乎是可重叠的，这提供了只有色氨酸支配光致发光性质的证据。改变pH值在所有情况下诱导的发射波长的最大值归因于由不同的质子化程度引起的吲哚环周围的微环境的修改的轻微移位。
Chiral polyamidoamino acids were obtained by polyaddition of N,N'-methylenebisacrylamide with d-, d,l- and l-tryptophan (M-d-Trp, M-d,l-Trp and M-l-Trp). l-tryptophan/glycine copolymers, M-G-l-Trp(5), M-G-l-Trp(10), M-G-l-Trp(20) and M-G-l-Trp(40,) were prepared from l-tryptophan/glycine mixtures. These polymers were amphoteric, with acid-base properties similar to those of the parent amino acids. The l-tryptophan/glycine copolymers with high glycine content were water soluble in the pH range 2-12. M-G-l-Trp(40) showed a solubility gap centred at pH 4.5 and all tryptophan homopolymers were soluble only at pH > 7. Dynamic light scattering measurements performed in their solubility ranges, namely 2-11 M-G-l-Trp(5), M-G-l-Trp(10) and M-G-l-Trp(20) and 7-11 for M-G-l-Trp(40), M-d-Trp, M-l-Trp and M-d,l-Trp, showed that the size of all samples did not significantly vary with pH. Both M-l-Trp and M-G-l-Trp copolymers showed pH-dependent circular dichroism spectra in the wavelength interval 200-280 nm, revealing structuring. All samples were fluorescent. Their emission spectra were unstructured and, if normalized for their tryptophan content, almost superimposable at the same pH, providing evidence that only tryptophan governed the photoluminescence properties. Changing pH induced in all cases a slight shift of the emission wavelength maximum ascribed to the modification of the microenvironment surrounding the indole ring induced by different protonation degrees.