Large Molecular Weight Nitroxide Biradicals Providing Efficient Dynamic Nuclear Polarization at Temperatures up to 200 K

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• 作者：Alexandre Zagdoun ; Gilles Casano ; Olivier Ouari ; Martin Schwarzw盲lder ; Aaron J. Rossini ; Fabien Aussenac ; Maxim Yulikov ; Gunnar Jeschke ; Christophe Cop茅ret ; Anne Lesage ; Paul Tordo ; Lyndon Emsley
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：August 28, 2013
• 年：2013
• 卷：135
• 期：34
• 页码：12790-12797
• 全文大小：416K
• 年卷期：v.135,no.34(August 28, 2013)
• ISSN：1520-5126

文摘

A series of seven functionalized nitroxide biradicals (the bTbK biradical and six derivatives) are investigated as exogenous polarization sources for dynamic nuclear polarization (DNP) solid-state NMR at 9.4 T and with ca. 100 K sample temperatures. The impact of electron relaxation times on the DNP enhancement (蔚) is examined, and we observe that longer inversion recovery and phase memory relaxation times provide larger 蔚. All radicals are tested in both bulk 1,1,2,2-tetrachloroethane solutions and in mesoporous materials, and the difference in 蔚 between the two cases is discussed. The impact of the sample temperature and magic angle spinning frequency on 蔚 is investigated for several radicals each characterized by a range of electron relaxation times. In particular, TEKPol, a bulky derivative of bTbK with a molecular weight of 905 g路mol^鈥?, is presented. Its high-saturation factor makes it a very efficient polarizing agent for DNP, yielding unprecedented proton enhancements of over 200 in both bulk and materials samples at 9.4 T and 100 K. TEKPol also yields encouraging enhancements of 33 at 180 K and 12 at 200 K, suggesting that with the continued improvement of radicals large 蔚 may be obtained at higher temperatures.