Effect of the ortho Modification of Azobenzene on the Photoregulatory Efficiency of DNA Hybridization and the Thermal Stability of its cis Form
Effect of the ortho Modification of Azobenzene on the Photoregulatory Efficiency of DNA Hybridization and the Thermal Stability of its cis Form
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DOI：
10.1002/chem.200902789
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发表时间：
2010-01-01
影响因子：
4.3
通讯作者：
Asanuma, Hiroyuki
中科院分区：
文献类型：
--
作者：
Nishioka, Hidenori;Liang, Xingguo;Asanuma, Hiroyuki
我们合成了各种偶氮苯甲基化在其邻位相对于偶氮键更有效的光调控的DNA杂交。光调节效率，从T-M（Δ T-M）的变化引起的反式-顺式异构化评价，显着改善所有邻位改性偶氮苯相比，非改性偶氮苯由于更稳定的反式和更不稳定的顺式形式。在所合成的偶氮苯中，4-羧基-2 '，6'-二甲基偶氮苯（2 '，6-Me-Azo）的Δ T-m最大，其中2个邻位苯环上的羧基被甲基化，而新合成的2，6-Me-Azo在另一个苯环的两个邻位上具有两个甲基的（4-羧基-2，6-二甲基偶氮苯）显示出Δ T-m的适度改善。核磁共振光谱分析和计算机模拟都表明，2 '，6'-Me-Azo上的两个甲基位于相邻碱基对的亚氨基质子附近;这些甲基通过反式形式的堆积相互作用稳定DNA双链体，并通过顺式形式的空间位阻使DNA双链体不稳定。此外，cis-2 '，6'-Me-Azo的热稳定性也有很大提高，而cis-2，6-Me-Azo的热稳定性没有提高。溶剂对顺式异构体半衰期的影响表明，所有改性偶氮苯的顺式到反式异构化是通过转化途径进行的。2 '，6'-Me-Azo而不是2，6-Me-Azo在顺式形式下的热稳定性的改善归因于由于氮原子的π轨道的孤对电子与远端苯环上的甲基之间的空间位阻而导致的反转过程的延迟。
We synthesized various azobenzenes methylated at their ortho positions with respect to the azo bond for more effective photoregulation of DNA hybridization. Photoregulatory efficiency, evaluated from the change of T-m (Delta T-m) induced by trans-cis isomerization, was significantly improved for all ortho-modified azobenzenes compared with non-modified azobenzene due to the more stabilized trans form and the more destabilized cis form. Among the synthesized azobenzenes, 4-carboxy-2',6'-dimethylazobenzene (2',6-Me-Azo), in which two ortho positions of the distal benzene ring with respect to carboxyl group were methylated, exhibited the largest Delta T-m, whereas the newly synthesized 2,6-Me-Azo (4-carboxy-2,6-dimethylazobenzene), which possesses two methyl groups on the two ortho positions of the other benzene ring, showed moderate improvement of Delta T-m. Both NMR spectroscopic analysis and computer modeling revealed that the two methyl groups on 2',6'-Me-Azo were located near the imino protons of adjacent base pairs; these stabilized the DNA duplex by stacking interactions in the trans form and destabilized the DNA duplex by steric hindrance in the cis form. In addition, the thermal stability of cis-2',6'-Me-Azo was also greatly improved, but not that of cis-2,6-Me-Azo. Solvent effects on the half-life of the cis form demonstrated that cis-to-trans isomerization of all the modified azobenzenes proceeded through an inversion route. Improved thermal stability of 2',6'-Me-Azo but not 2,6-Me-Azo in the cis form was attributed to the retardation of the inversion process due to steric hindrance between lone pair electrons of the pi orbital of the nitrogen atom and the methyl group on the distal benzene ring.