Important role of the CH/pi hydrogen bond in the enhancement of CD amplitude of 1,3-diene steroids
Important role of the CH/pi hydrogen bond in the enhancement of CD amplitude of 1,3-diene steroids
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CH/pi氢键在增强1,3-二烯类固醇CD振幅中的重要作用
DOI：
10.1039/c2nj40955k
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
and Motohiro Nishio
中科院分区：
文献类型：
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作者：
Osamu Takahashi;Yuji Kohno;Kazuyoshi Ueda;and Motohiro Nishio
已知在甾体1，3-二烯的10和5位桥头碳上引入甲基会影响在约100 ℃的π-π* 跃迁的Cotton效应。260 nm。因此，5α-雌甾-1，3-二烯-17 β-醇的圆二色性（CD）曲线的正号在5α-雄甾-1，3-二烯-17 β-醇中变为负值，尽管二烯发色团的螺旋方向实际上保持不变。为了研究甲基取代对1，3-二烯甾体CD的影响，我们在M06-2X/6-311++G（d，p）//MP2/6- 31 G（d，p）水平上进行了含时密度泛函理论（TD-DFT）计算.结果表明，用甲基取代桥头氢对π-π* 跃迁CD谱的符号和振幅有很大影响。我们认为，甲基取代引起的CD曲线的变化源于二烯π-系统和与其同烯丙基的CH 3基团之间的CH/π氢键。
Introduction of methyl group(s) at bridgehead carbons at positions 10 and 5 of steroidal 1,3-dienes has been known to influence the Cotton effect of the π–π* transition at ca. 260 nm. Thus the positive sign of the circular dichroism (CD) curve of 5α-estra-1,3-dien-17β-ol becomes negative in 5α-androsta-1,3-dien-17β-ol, even though the helical sense of the diene chromophore remains practically unchanged. In order to investigate the effect of methyl substitution on the CD of 1,3-diene steroids, we carried out time dependent density functional theory (TD-DFT) calculations at the M06-2X/6-311++G(d,p)//MP2/6-31G(d,p) level. It has been shown that replacement of the bridgehead hydrogen by a methyl group greatly influenced the sign and amplitude of CD spectra of the π–π* transition. We suggest that the change in the CD curves by methyl substitution originates from CH/π hydrogen bonds between the diene π-system and a CH3 group homoallylic to it.