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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >The Photophysical Properties of 6-Azaindole
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The Photophysical Properties of 6-Azaindole

机译：6-氮杂吲哚的光物理性质

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The biosynthetic incorporation of tryptophan analogues into proteins using plasmid expression systems has been shown to offer advantages in fluorescence spectroscopic studies of the molecular details of the interacting segments of protein-protein complexes. There are two underlying concepts of this approach. The first is based on a close structural similarity between the analogue and the native tryptophan. The second is that the analogue has an extended red absorbance permitting the selective excitation in the presence of tryptophan. The reported intense absorbance band of 6-azatryptophan at 325 nm would appear to offer a unique opportunity of using this analogue in such studies. In this work, we present the photophysical characterization of the excited state behavior of 6-azatryptophan through a complete study of the cognate indole moiety 6-azaindole. It was found that the absorbance at 320 nm for 6-azaindole and 325 nm for 6-azatryptophan was due to the protonated form in which both ring nitrogens are protonated. The protonation equilibrium for 6-azaindole had a pK_a value of 8. The fluorescence of 6-azaindole was centered at 380 nm. It was found that the neutral form of 6-azaindole was nonfluorescent in nonpolar solvents. In aqueous solution at pH values between 6.5 and 10, the fluorescence maximum of 6-azaindole remained at 380 nm, and the intensity decreased as the pH increased. Above pH 10, there was increased fluorescence on the low-energy side of the spectrum until at pH 14 the fluorescence spectrum showed a single maximum at 440 nm. The observations of the collective experiments in a variety of solvent conditions and pH values, including time-resolved fluorescence measurements, permitted a consistent assignment of each of the fluorescence species together with a rationalization of the excited-state processes that result from the excitation of either the protonated form or the neutral N1-H tautomer. The 440 nm fluorescence was attributed to the fluorescence from the excited state of the N6-H tautomer, a species that formed from the protonated excited state molecule that had previously been formed from initial excitation of the N1-H ground state. The work reports determinations of the excited-state pK_a values of each of the three species. The relative energy values of each of the groundstate molecules and excited-state species could be estimated. The relevance of the photophysics of 6-azaindole to protein structural studies was demonstrated by the biosynthetic incorporation of 6-azatryptophan into the Y99W mutant of rat calmodulin and the observation of 6-azaindole fluorescence from this protein.
机译：已经证明使用质粒表达系统将色氨酸类似物生物合成掺入蛋白质中，在蛋白质-蛋白质复合物相互作用部分的分子细节的荧光光谱研究中具有优势。此方法有两个基本概念。第一种是基于类似物与天然色氨酸之间的紧密结构相似性。第二个是类似物具有扩展的红色吸光度，允许在色氨酸存在下进行选择性激发。所报道的6-氮杂色氨酸在325 nm处的强吸收带似乎为在此类研究中使用该类似物提供了独特的机会。在这项工作中，我们通过对同源吲哚部分6-氮杂吲哚的完整研究，介绍了6-氮杂色氨酸的激发态行为的光物理特征。发现6-氮杂吲哚在320nm处的吸光度和6-氮杂色氨酸在325nm处的吸光度是由于两个环氮均被质子化的质子化形式。 6-氮杂吲哚的质子平衡的pK_a值为8。6-氮杂吲哚的荧光以380nm为中心。发现6-氮杂吲哚的中性形式在非极性溶剂中是非荧光的。在pH值介于6.5和10之间的水溶液中，6-氮杂吲哚的荧光最大值保持在380 nm，并且强度随着pH的增加而降低。高于pH 10时，光谱的低能侧荧光增加，直到在pH 14时，荧光光谱在440 nm处显示一个最大值。在各种溶剂条件和pH值（包括时间分辨的荧光测量）下进行的集体实验的观察结果，使得每种荧光物质的分配都一致，并且合理化了由任一种激发产生的激发态过程质子化形式或中性N1-H互变异构体。 440 nm的荧光归因于N6-H互变异构体激发态的荧光，N6-H互变异构体是由质子化的激发态分子形成的，该分子先前是由N1-H基态的初始激发形成的。这项工作报告了对这三种物质的激发态pK_a值的测定。可以估计每个基态分子和激发态物质的相对能量值。通过将6-氮杂色氨酸生物合成掺入大鼠钙调蛋白的Y99W突变体并观察到该蛋白质中的6-氮杂吲哚荧光，证明了6-氮杂吲哚的光物理性质与蛋白质结构研究的相关性。

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