Protonation equilibria of Hoechst 33258 in aqueous solution
Protonation equilibria of Hoechst 33258 in aqueous solution
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DOI：
10.1002/hlca.200490296
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发表时间：
2005-01-01
影响因子：
1.8
通讯作者：
Zoete, V
中科院分区：
文献类型：
--
作者：
Ladinig, M;Leupin, W;Zoete, V
双苯并咪唑衍生物 Hoechst 33258 (2'-(4-羟基苯基)-5-(4-甲基哌嗪-1-基)-2,5'-bi-1H-苯并咪唑) 与 DNA 双链体的小沟结合，广泛用作 DNA 的荧光细胞学染色剂。中性化合物 1 是两亲性的，具有四个碱性位点和三个酸性位点。我们通过分光光度滴定测定了所有七个酸度常数，以定义水溶液中从完全质子化的四正离子 1(4+) 到完全去质子化的三阴离子 1(3-) 的物质的 pH 依赖性分布。借助密度泛函计算确定了中间质子化态的结构。计算静电相互作用自由能，以调整 1 分子亚基的酸度常数以适应其在物种 1(4+) 至 1(3-) 中的环境。实验和理论 pK(a) 值非常吻合，但与文献中先前给出的估计值有很大差异。
The bis-benzimidazole derivative Hoechst 33258 (2'-(4-hydroxyphenyl)-5-(4-methylpiperazin-1-yl)-2,5'-bi-1H-benzimidazole) binds to the minor groove of DNA duplexes and is widely used as fluorescent cytological stain for DNA. The neutral compound, 1, is amphiphilic with four basic and three acidic sites. We have determined all seven acidity constants by spectrophotometric titration to define the pH-dependent distribution of species, from the fully protonated tetracation 1(4+) to the fully deprotonated trianion 1(3-), in aqueous solution. The structures of the intermediate protonation states were assigned with the aid of density-functional calculations. Electrostatic interaction free energies were calculated to adjust the acidity constants of the molecular subunits of 1 to their environment in the species 1(4+) to 1(3-). The experimental and theoretical pK(a) values agree well, but they differ substantially from previous estimates given in the literature.