Photochemistry of cationic synthetic polyamino acid -dye systems

光致变色多肽因其与生物过程中的光调节有关而代表了一个有趣的系统，并且似乎有希望成为光敏聚合物材料。目前，关于各种中性和阴离子多肽的光谱和光致变色性质已经有了相当多的了解。然而，人们对阳离子偶氮芳香多肽知之甚少。在这个项目中，我们研究了阳离子偶氮芳香氨基酸（赖氨酸及其低级同系物）、寡肽（精氨酸肽）、多肽（α -聚赖氨酸及其低级同系物和-聚赖氨酸）以及阳离子乙烯基聚合物（聚乙烯胺和聚烯丙胺）的合成和可逆光致变色性能。利用吸收光谱、荧光光谱和圆二色光谱研究了上述偶氮芳香族化合物在六氟-2-丙醇（HFIP）等溶剂中的光化学性质。在手性条件下，由于偶氮芳基的光异构化作用，二色带在可见光波段的光显色性随辐照时间的变化基本可逆。在240 nm以下的负二向色带中，侧链较长的阳离子偶氮芳香多肽的主结构为α -螺旋结构，侧链较短的为β -结构。偶氮芳香多肽的光化学行为表现出可逆的二向色性特征。研究了两种偶氮几何构象在hfip -水等混合溶剂中因偶极矩不同而引起的光刺激溶解度变化。由于阳离子偶氮芳香族聚赖氨酸同源物有可能作为光反应系统，我们将研究范围扩大到天然光敏色素模型肽的合成和光感觉系统的制备。

Photochromic polypeptides represent interesting systems because of their relevance to the photoregulation in biological processes and seem to have promise as photosensitive polymeric materials. Currently considerable knowledge is available regarding the spectral and photochromic properties of various neutral and anionic polypeptides. However, little is known about cationic azo aromatic polypeptides. In this project we studied the synthesis and reversible photochromic properties of cationic azo aromatic amino acids (lysine and its lower homologs), oligopeptides (arginine peptide), and polypeptides (alpha-polylysine and its lower homologs, and -polylysine), together with cationic vinyl polymers (polyvinylamine and polyallylamine).The photochemical properties of the azo aromatic compounds described above was investigated by absorption, fluorescence, and circular dichroism spectroscopy in solvents such as hexafluoro-2-propanol (HFIP). When chiral, the photochromism of the dichroic band in the visible wavelength region was mostly reversible as a function of irradiation time at different wavelengths due to the trans-cis photoisomerization of the azo aromatic moieties. The negative dichroic bands below 240 nm, the backbone conformations of the cationic azo aromatic polypeptides with longer side chains take an alpha-helix, while those with shorter a beta-structure. The photochemical behaviors of the beta-structure azo aromatic polypeptides exhibit the characteristic reversible dichroic photochromism. The photo-stimulated solubility changes due to the different dipole moments of two azo geometric conformers were examined in such mixed solvents as HFIP-water.Since cationic azo aromatic polylysine homologs may have promise as photoresponsive systems, we extent our study to synthesize the natural phytochrome model peptides and to prepare the photosensory systems.