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首页> 外文期刊>Chemistry: A European journal >Optical, Redox, and DNA-Binding Properties of Phenanthridinium Chromophores: Elucidating the Role of the Phenyl Substituent for Fluorescence Enhancement of Ethidium in the Presence of DNA
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Optical, Redox, and DNA-Binding Properties of Phenanthridinium Chromophores: Elucidating the Role of the Phenyl Substituent for Fluorescence Enhancement of Ethidium in the Presence of DNA

机译：菲鎓发色团的光学，氧化还原和DNA结合特性：阐明苯基取代基在DNA的存在下对荧光增强乙啶的作用

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摘要

The phenanthridinium chromophores 5-ethyl-6-phenylphenanthridinium (1), 5-ethyl-6-methylphenanthridinium (2), 3,8-diamino-5-ethyl-6-methylphenanthridinium (3), and 3,8-diamino-5-ethyl-6-(4-N,N-diethylaminophenyl)phenanthridinium (4) were characterized by their optical and redox properties. All dyes were applied in titration experiments with a random-sequence 17mer DNA duplex and their binding affinities were determined. The results were compared to well-known ethidium bromide (E). In general, this set of data allows the influence of substituents in positions 3, 6, and 8 on the optical properties of E to be elucidated. Especially, compound 4 was used to compare the weak electron-donating character of the phenyl substituent at position 6 of E with the more electron-donating 4-N,N-diethylaminophenyl group. Analysis of all of the measurements revealed two pairs of chromophores. The first pair, consisting of 1 and 2, lacks the amino groups in positions 3 and 8, and, as a result, these dyes exhibit clearly altered optical and electrochemical properties compared with E. In the presence of DNA, a significant fluorescence quenching was observed. Their binding affinity to DNA is reduced by nearly one order of magnitude. The electronic effect of the phenyl group in position 6 on this type of dye is rather small. The properties of the second set, 3 and 4, are similar to E due to the presence of the two strongly electron-donating amino groups in positions 3 and 8. However, in contrast to 1 and 2, the electron-donating character of the substituent in position 6 of 3 and 4 is critical. The binding, as well as the fluorescence enhancement, is clearly related to the electron-donating effect of this substituent. Accordingly, compound 4 shows the strongest binding affinity and the strongest fluorescence enhancement. Quantum chemical calculations reveal a general mechanism related to the twisted intramolecular charge transfer (TICT) model. Accordingly, an increase of the twist angle between the phenyl ring in position 6 and the phenanthridinium core opens a nonradiative channel in the excited state that depends on the electron-donating character of the phenyl group. Access to this channel is hindered upon binding to DNA.
机译：菲啶发色团5-乙基-6-苯基菲啶鎓（1），5-乙基-6-甲基菲啶鎓（2），3,8-二氨基-5-乙基-6-甲基菲啶鎓（3）和3,8-二氨基-5 -乙基-6-（4-N，N-二乙基氨基苯基）菲啶鎓（4）的特征在于其光学和氧化还原特性。所有染料均用于具有随机序列17mer DNA双链体的滴定实验中，并确定了它们的结合亲和力。将结果与众所周知的溴化乙锭（E）进行比较。通常，该组数据可以阐明3、6和8位上的取代基对E的光学性质的影响。特别是，化合物4用于比较E的6位上的苯基取代基的弱供电子特性与供电子较多的4-N，N-二乙基氨基苯基。所有测量结果的分析揭示了两对生色团。第一对由1和2组成，在3和8位上缺少氨基，因此，这些染料与E相比具有明显改变的光学和电化学性质。在DNA的存在下，显着的荧光猝灭观测到的。它们与DNA的结合亲和力降低了近一个数量级。第6位上的苯基对这类染料的电子效应很小。第二组3和4的性质与E相似，这是由于在3和8位上存在两个强供电子氨基。但是，与1和2相比，第二组的给电子特性3和4的6位上的取代基至关重要。结合以及荧光增强显然与该取代基的给电子作用有关。因此，化合物4显示出最强的结合亲和力和最强的荧光增强。量子化学计算揭示了与扭曲的分子内电荷转移（TICT）模型有关的一般机制。因此，位置6上的苯环和菲啶核之间的扭转角的增加打开了激发态的非辐射通道，该非辐射通道取决于苯基的供电子特性。与DNA结合后，无法进入该通道。

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