Photo-Induced Reactions of Biomolecular Ions in Gas Phase

1.用激光光耗尽光谱研究了氨化铵自由基NH_4(NH_3)_n的电子光谱。为了了解气相中生物分子离子的结构、微观水化机理以及水合作用对生物反应的影响，我们研制了电喷雾电离串联质谱仪，研究了生物分子团簇离子的光诱导反应。(1)研究了多电荷细胞色素c离子的光诱导反应。在低电荷态时，光致电离占主导地位，其产额随电荷的增加而迅速下降。库仑势的模型计算表明多肽链的结构是完全拉长的。(2)我们发展了通过改进电喷雾电离来产生水合生物分子团簇离子的方法。(3)我们研究了含有氨基酸和多肽的水合团簇离子的亚稳态分解，利用蒸发系综模型确定了团簇的增量溶剂结合能和内能。根据这些结果，我们发现电荷的离域与结合能有关。(4)研究了[Fe(III)-原卟啉]^+(氯化血红素^+)离子与水、吡啶和甲醇的光诱导反应。碎片离子的质谱图表明，除了溶剂分子的挥发外，还发生了羧甲基的β裂解。β裂解反应的产率强烈地依赖于激发能和溶剂分子的数量。(5)研究了含有色氨酸和甘氨酸的溶剂化团簇离子的光解离。观察到-NH_3和-COOH基团的裂解，它们与团簇离子中的能量弛豫有关。

1.Electronic spectra of ammoniated ammonium radicals, NH_4(NH_3)_n, are investigated with a laser photodepletion spectroscopy. A drastic decrease of the excitation energy is observed, which is ascribed to the spontaneous ionization of NH_4 in ammonia clusters.2.In order to understand structure of biomolecular ions in the gas phase, mechanisms of microscopic hydrations, and role of hydrations for biological reactions, we develop a tandem mass spectrometer with electrospray ionization, and study the photo-induced reactions of biomolecular cluster ions.(1)Photo-induced reactions of multiply-charged cytochrome c ions are investigated. Photoionization is found to be the dominant process for the lower charged states and its yield decrease rapidly with increasing the charge. Model calculations of the Coulomb potential suggest that the structure of the polypeptide chain is completely elongated.(2)We develop the method to produce hydrated biomolecular cluster ions by improving electrospray ionization.(3)We examine the metastable decomposition of hydrated cluster ions containing amino acids and peptides to determine the incremental solvent binding energies and internal energies for the clusters using evaporative ensemble model. From these results, we find out that delocalization of the charge correlate with the binding energy.(4)Photo-induced reactions of [Fe(III)-protoporphyrin]^+ (hemin^+) ions solvated with water, pyridine, and methanol are investigated. The mass spectra of the fragment ions show the β-cleavage of carboxymethyl groups in addition to the evaporation of solvent molecules. Yield of the β-cleavage reaction is found to depend strongly on the excitation energy and the number of solvent molecules.(5)Photodissociations of solvated cluster ions containing tryptophan and glyciltryptophan are examined. Cleavages of -NH_3 and -COOH groups are observed, which are correlated with energy relaxation in the cluster ions.