The triplet-state lifetime of indole in aqueous and viscous environments: Significance to the interpretation of room temperature phosphorescence in proteins
The triplet-state lifetime of indole in aqueous and viscous environments: Significance to the interpretation of room temperature phosphorescence in proteins
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DOI：
10.1021/ja016609x
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发表时间：
2002-09-04
影响因子：
15
通讯作者：
Schauerte, JA
中科院分区：
文献类型：
--
作者：
Fischer, CJ;Gafni, A;Schauerte, JA
对蛋白质室温磷光研究的解释需要了解控制完全暴露于溶剂和深埋于蛋白质疏水核心的残基色氨酸三重态寿命的机制。由于色氨酸在溶剂中的表现与游离吲哚在溶液中的表现相似，因此准确测量吲哚在水溶液中的三重态寿命是很重要的。利用光子计数技术和低光通量（J/cm(2)），我们观察到水溶液、脱氧吲哚和几种吲哚衍生物的三态寿命约为40 μ m，与Bent和Hayon先前基于闪光光解的报告（12,us; Bent， D. V.; Hayon， E. J. Am）非常吻合。化学。但比最近观测到的1.2 ms寿命短得多（Strambini, g.b.; Gonnelli, m.j. Am.）。化学。社会科学，1995,17,7646-7651)。然而，我们现在已经能够再现后者的工作者报道的水性吲哚溶液的长寿命，并表明它可能是由吲哚自由基阳离子和溶剂化电子的共轭重组引起的，这是基于对水中吲哚自由基阳离子的研究得出的结论（Bent和Hayon， 1975）。这一点的证据来自磷光发射的快速上升和在无缓冲溶液中相应增强的量子产率的测量。这种物质可以很容易地淬灭，相应的快速上升消失，留下单指数40 μ s衰减，我们认为这是真正的吲哚三重态寿命。这项工作是在室温下蛋白质磷光研究的背景下进行的。
The interpretation of room temperature phosphorescence studies of proteins requires an understanding of the mechanisms governing the tryptophan triplet-state lifetimes of residues fully exposed to solvent and those deeply buried in the hydrophobic core of proteins. Since solvents exposed tryptophans are expected to behave similarly to indole free in solution, it is important to have an accurate measure of the triplet state lifetime of indole in aqueous solution. Using photon counting techniques and low optical fluence (J/cm(2)), we observed the triplet-state lifetime of aqueous, deoxygenated indole and several indole derivatives to be approximately 40 mus, closely matching the previous reports by Bent and Hayon based on flash photolysis (12,us; Bent, D. V.; Hayon, E. J. Am. Chem. Soc. 1975, 97, 2612-2619) but much shorter than the 1.2 ms lifetime observed more recently (Strambini, G. B.; Gonnelli, M. J. Am. Chem. Soc. 1995, 117, 7646-7651). However, we have now been able to reproduce the long lifetime reported by the latter workers for aqueous indole solutions and show that it likely arises from geminate recombination of the indole radical cation and solvated electron, a conclusion based on studies of the indole radical cation in water (Bent and Hayon, 1975). The evidence for this comes from a fast rise in the phosphorescence emission and measurements of a corresponding enhanced quantum yield in unbuffered solutions. This species can be readily quenched, and the corresponding fast rise disappears, leaving a monoexponential 40 mus decay, which we argue is the true indole triplet lifetime. The work is put in the context of room temperature phosphorescence studies of proteins.