Faculty of Chemistry, Adam Mickiewicz University, 60-780, Poznań, Grunwaldzka 6, Poland.
Org Biomol Chem. 2010 Dec 21;8(24):5511-8. doi: 10.1039/c0ob00288g. Epub 2010 Oct 19.
Protonation of gossypol Schiff bases (S1 and S2), possessing different numbers of basic N-atoms, was studied using potentiometric, spectroscopic, ESI MS and PM5 methods. Titration of S1 and S2 with HClO(4), monitored by the FT-IR and (1)H NMR, indicated that the change from the enamine-enamine into the protonated imine-imine tautomeric form occurs at different Schiff base-H(+) ratio. The FT-IR and PM5 results show that for S1 the first protonation step occurs at Schiff base moiety whereas for S2 it is realised at N-atom of the morpholine. The formation of N(+)-HO hydrogen bond between morpholine moieties within S2 contributes to high pK(a(ACN)) = 22.65.
质子化的棉酚席夫碱（S1 和 S2），具有不同数量的碱性 N 原子，使用电位滴定法、光谱法、ESI-MS 和 PM5 方法进行了研究。用 HClO(4)滴定 S1 和 S2，通过 FT-IR 和 (1)H NMR 进行监测，表明从烯胺-烯胺到质子化的亚胺-亚胺互变异构形式的变化发生在不同的席夫碱-H(+)比。FT-IR 和 PM5 的结果表明，对于 S1，第一步质子化发生在席夫碱部分，而对于 S2，它发生在吗啉氮原子上。S2 中吗啉部分之间形成的 N(+)-HO 氢键有助于高 pK(a(ACN))=22.65。
