Spin-spin interaction and relaxation in two trityl-nitroxide diradicals.
Spin-spin interaction and relaxation in two trityl-nitroxide diradicals.
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DOI：
10.1016/j.jmr.2021.107078
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发表时间：
2021-11
期刊：
影响因子：
--
通讯作者：
Eaton GR
中科院分区：
文献类型：
--
作者：
Moore W;Yao R;Liu Y;Eaton SS;Eaton GR
三甲基氮氧化物在固体动态核极化中显示出巨大的应用前景。为了优化性能，重要的是要了解自旋-自旋相互作用对双自由基弛豫时间的影响。测量了两个三苯基氮氧化物的连续波谱和电子自旋弛豫，这两个氮氧化物的取代基不同，并且具有不同的交换作用J。通过重叠的AB自旋分裂模式分析EPR谱，解释了J对光谱不同区域的影响。对于某些氮核自旋态，即使是中等的J值，相对于三苯基和氮氧化物共振之间的分离也是很大的。在流体溶液的X-带和Q-带的连续波谱中，观察到每个双自由基有两种构象。对于一个双自由基，在293K时，J=15G(83%)和5G(17%)，在80K时，J=27G(67%)和3G(33%)，自旋间距分别为16？和12？对于第二个双自由基，交换作用更强：在293K时，两种构象的J=113G(67%)和59G(33%)，在80K时，J=43G，存在两种构象，自旋间距分别为13和11.5？观察到每个双自由基的两种构象，具有不同的J值，表明它们的交换相互作用依赖于通键轨道相互作用。在80~120K温度范围内，三苯基氮氧自由基的自旋弛豫速率分别为1/T1和1/Tm，与单氮氧自由基相似，但比三叔丁基自由基快。这些观察表明，即使对于相对较小的J值，氮氧化物也非常有效地增强了较慢松弛的三苯基的松弛。
Trityl-nitroxides show substantial promise as polarizing agents in solid state dynamic nuclear polarization. To optimize performance it is important to understand the impact of spin-spin interactions on relaxation times of the diradicals. CW spectra and electron spin relaxation were measured for two trityl-nitroxides that differ in the substituents on the amide linker and have different strengths of the exchange interaction J. Analysis of the EPR spectra in terms of overlapping AB spin-spin splitting patterns explains the impact of J on various regions of the spectra. Even modest values of J are large relative to the separation between trityl and nitroxide resonances for some nitrogen nuclear spin state. Two conformations for each diradical were observed in CW spectra in fluid solution at X-band and Q-band. For one diradical J = 15 G (83%) and 5 G (17%) at 293 K, and J = 27 G (67%) and 3 G (33%) with interspin distances of 16 Å and 12 Å, respectively, at 80 K. For the second diradical the exchange interaction is stronger: the two conformations in fluid solution at 293 K had J = 113 G (67%) and 59 G (33%) and at 80 K the value of J was 43 G and there were two conformations with interspin distances of 13 and 11.5 Å. The observation of two conformations for each diradical, with different values of J, demonstrates the dependence of their exchange interactions on through-bond orbital interactions. X-band values of spin relaxation rates 1/T1 and 1/Tm at 80 to 120 K for the trityl-nitroxides are similar to values for nitroxide mono-radicals, and faster than for trityl radicals. These observations show that even for a relatively small value of J, the nitroxide is very effective in enhancing the relaxation of the more slowly relaxing trityl.
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影响因子：
15
作者：
Michaelis, Vladimir K.;Smith, Albert A.;Corzilius, Bjoern;Haze, Olesya;Swager, Timothy M.;Griffin, Robert G.
通讯作者：
Griffin, Robert G.
影响因子：
0.6
作者：
Eaton, Sandra S.;Woodcock, Lukas B.;Eaton, Gareth R.
通讯作者：
Eaton, Gareth R.
用于生物分子高场动态核极化的高效三苯甲基氮氧双自由基
影响因子：
4.3
作者：
Cai, Xinyi;Paioni, Alessandra Lucini;Liu, Yangping
通讯作者：
Liu, Yangping
影响因子：
2.2
作者：
EATON, SS;MORE, KM;EATON, GR
通讯作者：
EATON, GR
影响因子：
2.2
作者：
LABSKY, J;PILAR, J;LOVY, J
通讯作者：
LOVY, J