Diastereoisomers of l-proline-linked trityl-nitroxide biradicals: synthesis and effect of chiral configurations on exchange interactions.
Diastereoisomers of l-proline-linked trityl-nitroxide biradicals: synthesis and effect of chiral configurations on exchange interactions.
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L-脯氨酸连接的三苯甲基氮氧双自由基的非对映异构体：手性构型的合成及其对交换相互作用的影响
DOI：
10.1039/c8sc00969d
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发表时间：
2018-05-21
期刊：
影响因子：
8.4
通讯作者：
Liu Y
中科院分区：
文献类型：
--
作者：
Zhai W;Feng Y;Liu H;Rockenbauer A;Mance D;Li S;Song Y;Baldus M;Liu Y
两个自由基部分的手性构型是控制三苯甲基-硝基氧双自由基的交换作用和DNP性质的关键因素。有机双自由基的交换（J）相互作用是控制其物理化学性质和潜在应用的关键因素，并且可以通过改变连接体的性质来调节。在本工作中，我们首次证明了自由基部分的手性构型对三苯甲基-氮氧自由基（TN）双自由基J值的影响。通过外消旋（R/S）氮氧自由基与外消旋（M/P）三苯甲基自由基vial-proline偶联，合成并纯化了TN双自由基的四种非对映异构体（TNT 1，TNT 2，TNL 1和TNL 2）。通过比较实验和计算的电子圆二色谱（ECD）光谱，将这些非对映异构体的绝对构型指定为TNT 1的（M，S，S）、TNT 2的（P，S，S）、TNL 1的（M，S，R）和TNL 2的（P，S，R）。电子顺磁共振（EPR）结果表明，氮氧部分取代三苯甲基部分是控制交换作用的主要构型，室温下的J值顺序为TNT 1（252 G）> TNT 2（127 G）> TNL 2（33 G）> TNL 1（14 G）.此外，在氮氧部分具有S构型的TNL 1/TNL 2的J值由于其柔性连接体而随温度和溶剂极性而变化，而TNT 1/TNT 2的J值由于其连接体的刚性而对这两个因素几乎不敏感。在800 MHz的动态核极化（DNP）条件下，TNT 1，2和TNL 1，2在冻结状态下的不同交换作用导致了强烈不同的高场动态核极化（DNP）增强，TNT 1，2的ε = 7，TNL 1，2的ε = 40。
The chiral configuration of the two radical parts is a crucial factor controlling the exchange interactions and DNP properties of trityl-nitroxide biradicals. The exchange (J) interaction of organic biradicals is a crucial factor controlling their physiochemical properties and potential applications and can be modulated by changing the nature of the linker. In the present work, we for the first time demonstrate the effect of chiral configurations of radical parts on the J values of trityl-nitroxide (TN) biradicals. Four diastereoisomers (TNT1, TNT2, TNL1 and TNL2) of TN biradicals were synthesized and purified by the conjugation of a racemic (R/S) nitroxide with the racemic (M/P) trityl radical vial-proline. The absolute configurations of these diastereoisomers were assigned by comparing experimental and calculated electronic circular dichroism (ECD) spectra as (M, S, S) for TNT1, (P, S, S) for TNT2, (M, S, R) for TNL1 and (P, S, R) for TNL2. Electron paramagnetic resonance (EPR) results showed that the configuration of the nitroxide part instead of the trityl part is dominant in controlling the exchange interactions and the order of the J values at room temperature is TNT1 (252 G) > TNT2 (127 G) ≫ TNL2 (33 G) > TNL1 (14 G). Moreover, the J values of TNL1/TNL2 with the S configuration in the nitroxide part vary with temperature and the polarity of solvents due to their flexible linker, whereas the J values of TNT1/TNT2 are almost insensitive to these two factors due to the rigidity of their linkers. The distinct exchange interactions between TNT1,2 and TNL1,2 in the frozen state led to strongly different high-field dynamic nuclear polarization (DNP) enhancements with ε = 7 for TNT1,2 and 40 for TNL1,2 under 800 MHz DNP conditions.
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影响因子：
15
作者：
Kiesewetter, Matthew K.;Corzilius, Bjoern;Smith, Albert A.;Griffin, Robert G.;Swager, Timothy M.
通讯作者：
Swager, Timothy M.
影响因子：
18.3
作者：
Ni, Qing Zhe;Daviso, Eugenio;Can, Thach V.;Markhasin, Evgeny;Jawla, Sudheer K.;Swager, Timothy M.;Temkin, Richard J.;Herzfeld, Judith;Griffin, Robert G.
通讯作者：
Griffin, Robert G.
影响因子：
3.6
作者：
Gallagher, Nolan M.;Olankitwanit, Arnon;Rajca, Andrzej
通讯作者：
Rajca, Andrzej
影响因子：
4.4
作者：
Hu, Kan-Nian;Bajaj, Vikram S.;Griffin, Robert G.
通讯作者：
Griffin, Robert G.
影响因子：
2.9
作者：
Legenzov, Eric A.;Sims, Stephen J.;Kao, Joseph P. Y.
通讯作者：
Kao, Joseph P. Y.