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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Fluorescein Excited-State Proton Exchange Reactions: Nanosecond Emission Kinetics and Correlation with Steady-State Fluorescence Intensity
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Fluorescein Excited-State Proton Exchange Reactions: Nanosecond Emission Kinetics and Correlation with Steady-State Fluorescence Intensity

机译：荧光素激发态质子交换反应：纳秒发射动力学及其与稳态荧光强度的相关性

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摘要

Fluorescein is a complex fluorophore that can exist in one or more of four different prototropic forms (cati neutral, dianion. and monoanion) depending on pH. In the pH range 6-10. only the dianion and monan forms are important. In a previous article, we showed by steady-state fluorescein measurements that an exci fluorescein molecule displays excited-state proton transfer reactions which interconvert the monoanion dianion forms. However, we found that these reactions can occur only in the presence of a suitable pro:donor-acceptor buffer such as phosphate buffer. Assuming that, at 1 M phosphate buffer concentration, excited-state proton exchange reaction of fluorescein rapidly equilibrates during the lifetime of fluoresct we were able to fit quantitatively steady-state fluorescence intensity vs pH titration graphs to a relativ simple reaction model. In this article, we use nanosecond emission (decay time) methods to study the excit state proton reactions of tluorescein in the pH range 6-10 and in the presence of a phosphate bul concentration. Fluorescein is a challenging fluorophore for the study of excited-state proton reactions becai of the strong overlap of the absorption and emission spectra of the monoanion and dianion forms of fluoresct However by recording nanosecond emission graphs and using methods of analysis of high precision, have been able to test kinetic mechanisms and evaluate the specific rate constants for the excited-state proi reactions as well as the lifetimes of the monoanion and dianion. Using these values for lifetimes and r constants, we discuss the process of equilibration in the excited-state and derive expressions which allow to predict how quickly the excited-state reactions can reach equilibrium. Moreover, we use the above kine and spectral parameters to calculate steady-state fluorescence intensity F5 vs pH at 1 M phosphate buf concentration and compare this theoretically calculated graph with the experimental graph.
机译：荧光素是一种复杂的荧光团，可以根据pH值以四种不同的质子形式（阳离子中性，二价阴离子和一价阴离子）中的一种或多种存在。在pH范围6-10。只有二​​价阴离子和莫南形式很重要。在上一篇文章中，我们通过稳态荧光素测量显示，激发态荧光素分子显示出激发态质子转移反应，该反应互变单阴离子二价阴离子形式。但是，我们发现这些反应只能在合适的前体：供体-受体缓冲液（例如磷酸盐缓冲液）存在下发生。假设在1 M磷酸盐缓冲液浓度下，荧光素的激发态质子交换反应在荧光寿命期间迅速达到平衡，我们能够将稳态荧光强度与pH滴定图定量地拟合到相对简单的反应模型中。在本文中，我们使用纳秒发射（衰减时间）方法来研究在6至10的pH范围内和存在磷酸盐bul浓度的情况下，丁香酚素的激发态质子反应。荧光素是研究激发态质子反应的具有挑战性的荧光团，因为荧光的单阴离子和二阴离子形式的吸收光谱和发射光谱有很强的重叠。然而，通过记录纳秒发射图和使用高精度分析方法，已经有了能够测试动力学机制并评估激发态proi反应的比速率常数以及一价阴离子和二价阴离子的寿命。使用这些值作为寿命和r常数，我们讨论了激发态的平衡过程，并导出了表达式，这些表达式可以预测激发态反应可以多快达到平衡。此外，我们使用上述运动场和光谱参数来计算在1 M磷酸盐buf浓度下稳态荧光强度F5与pH的关系，并将此理论计算图与实验图进行比较。

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