Photostability of amino acids: photodissociation dynamics of phenylalanine chromophores.
Photostability of amino acids: photodissociation dynamics of phenylalanine chromophores.
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DOI：
10.1039/b925338f
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发表时间：
2010-05
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通讯作者：
Chien-Ming Tseng;Ming-Fu Lin;Yi Lin Yang;Yu-Chieh Ho;C. Ni;Jia-Lin Chang
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作者：
Chien-Ming Tseng;Ming-Fu Lin;Yi Lin Yang;Yu-Chieh Ho;C. Ni;Jia-Lin Chang
苯酚、咪唑和吲哚的激发态上氢原子消除的理论预测，以及氨基酸酪氨酸、组氨酸和色氨酸各自的生色团，以及实验观察对理论预测的证实，对于解释氨基酸在紫外光照射下的光稳定性有很大的影响。另一方面，对另一种芳香族氨基酸苯丙氨酸的激发态光解动力学还没有进行理论预测。本工作利用多质量离子成像技术，在248 nm和193 nm的分子束中研究了苯乙胺、N-甲基苯乙胺和N-乙酰苯丙氨酸甲酯等多种苯丙氨酸发色团的光解动力学。这些化合物的主要解离通道是C-C键断裂。然而，苯乙胺的光碎片平动能分布包含两个组分。慢分量对应于内转换后基态表面的解离，快分量对应于具有大出射势垒的激发态的解离。基态解离和激发态解离之间的竞争随着生色团尺寸的增大而变化。对于大的生色团，解离前的基态的内部转换成为主要的非辐射过程。这项研究揭示了这些氨基酸生色团的大小依赖的光稳定性。
The theoretical prediction of H atom elimination on the excited state of phenol, imidazole and indole, the respective chromophores for the amino acids tyrosine, histidine and tryptophan, and the confirmation of theoretical prediction by experimental observations have a great impact on the explanation of photostability of amino acids upon irradiation with UV photons. On the other hand, no theoretical prediction of the excited state photodissociation dynamics has been made on the other aromatic amino acid, phenylalanine. In this work, photodissociation dynamics for various phenylalanine chromophores, including, phenylethylamine, N-methyl-phenylethylamine, and N-acetyl phenylalanine methyl ester was investigated in a molecular beam at 248 and 193 nm using multimass ion imaging techniques. The major dissociation channel for these compounds is the C-C bond cleavage. However, the photofragment translational energy distribution of phenylethylamine contains two components. The slow component corresponds to the dissociation on the ground state surface after internal conversion, and the fast component represents the dissociation from an excited state with a large exit barrier. The competition between the dissociation on the ground state and on the excited state changes as the size of chromophores increases. Internal conversion to the ground state prior to dissociation becomes the major nonradiative process for large chromophores. This study reveals the size-dependent photostability for these amino acid chromophores.