EXCITED-STATE CHEMISTRY OF AROMATIC AMINO-ACIDS AND RELATED PEPTIDES .3. TRYPTOPHAN
EXCITED-STATE CHEMISTRY OF AROMATIC AMINO-ACIDS AND RELATED PEPTIDES .3. TRYPTOPHAN
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DOI：
10.1021/ja00843a004
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发表时间：
1975-01-01
影响因子：
15
通讯作者：
HAYON, E
中科院分区：
文献类型：
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作者：
BENT, DV;HAYON, E
利用频率为 265 nm 的四倍频钕激光发出的持续时间约为 3.6-15 纳秒的单脉冲以及动态吸收分光光度法技术，对水中吲哚、色氨酸和肽衍生物的光物理和光化学进行了详细研究。检查了以下化合物；吲哚、吲哚-3-丙酸、N-甲基吲哚、色氨酸、色胺、N-甲基色氨酸、'-乙酰色氨酸、色氨酰甘氨酸和甘氨酰色氨酰甘氨酸。测定了这些化合物的三重态-三重态吸收光谱和三重态寿命。在所有情况下，TT 吸收最大值均位于 450±10 nm 处。中性溶液中的寿命范围为 11 至 16 毫秒。对于色氨酸、色胺和 Try-Gly，还观察到寿命较短的瞬态 (Tj)，Xmax~ 450 nm 和~ 20-45 纳秒。 T i 瞬态暂时建议为三重态。它们不是寿命较长的三重态的前体，并且仅当分子中存在末端 NHj+ 基团时才能观察到。在 Trp 中，pH 10 时未观察到 Ti。三重态被氧 (kq~ 5 X 109 M~ 1 sec-1) 和二硫化物 RSSR (kq~ 4-6 X 109/-1 sec-1) 有效猝灭。 RSSR 化合物的猝灭机制是通过电子转移过程发生的，并形成 RSSR·-自由基阴离子。发现吲哚和色氨酸衍生物的光电离以相对高的量子产率发生。在中性溶液中，观察到Xmax~720 nm的eaq-和Xmax~550 nm的阳离子自由基。阳离子自由基的寿命约为 10-6 秒，并衰变产生中性吲哚自由基。在碱性溶液中，由于与 OH 离子反应，其寿命较短，而在酸性溶液中，阳离子自由基的寿命为几百微秒。研究了三线态产率和光电离过程对 pH、温度和 265 nm 光强度的依赖性。结论是，在所研究的条件下，吲哚的光电离通过来自较高激发单线态和/或振动激发最低单线态的主要单光子过程发生。对于色氨酸，大约 10% 的 eaq 产物是由最低激发单线态的衰变形成的。这些结果与酪氨酸和苯丙氨酸的类似研究结果进行了比较。讨论了蛋白质中色氨酸光电离的可能影响。
Using single pulses of~ 3.6-15 nsec duration from a frequency quadrupled neodymium laser emitting at 265 nm, and the technique of kinetic absorption spectrophotometry, a detailed study of the photophysics and photochemistryof indole, tryptophan, and peptide derivatives in water has been carried out. The following compounds were examined; indole, in-dole-3-propionic acid, TV-methylindole, tryptophan, tryptamine, N-methyltryptophan,'-acetyltryptophan, tryptophanylgly-cine, and glycyltryptophanylglycine. The triplet-triplet absorption spectra and lifetimesof the triplet states of these com-pounds were determined. The TT absorption maximum is at 450±10 nm in all cases. The lifetimes in neutral solution range from~ 11 to 16 Msec. With Trp, tryptamine, and Try-Gly, shorter lived transients (Tj) with Xmax~ 450 nm and~ 20-45 nsec are observed in addition. The T i transients are tentatively suggested to be triplet states. They are not precursors of the longer lived triplet states, and are observed only when a terminal NHj+ group is present in the molecule. Ti is not observed at pH 10 in Trp. The triplet states are effectively quenched by oxygen (kq~ 5 X 109 M~ 1 sec-1) and by disulfides RSSR (kq~ 4-6 X 109/-1 sec-1). The quenching mechanism with RSSR compounds is shown to occur via an electron transfer process, with the formationof the RSSR·-radical anion. The photoionization of indoles and tryptophan derivatives is found to occur with a relatively high quantum yield. In neutral solution, eaq-with Xmax~ 720 nm and the cation radical with Xmax~ 550 nm are observed. The cation radical has a lifetime of~ 10-6 sec and decays to give the neutral indole radical. In alkaline solutions it is shorter lived due to reaction with OH-ions, while in acid solutions the cation radical has a lifetime of a few hundred microseconds. The dependence upon pH, temperature, and 265-nm light intensity of the yields of the triplet states andthe photoionization processes were examined. It is concluded that the photoionization of the indoles occurs, under the conditions studied, via a predominantly monophotonic process from a higher excited singlet state and/or a vibrationally excited lowest singlet state. With Trp,~ 10% of the eaq-produced are formed from the decay of the lowest excited singlet state. These results are compared with those of a similar study with tyrosineand phenylalanine. The possible implications of the photoionizationof Trp in proteins are discussed.