期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 24, 期 51, 页码 13485-13494出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201801251
关键词
dynamic nuclear polarization; magic angle spinning; NMR spectroscopy; radicals; water-soluble
资金
- Icelandic Research Fund [141062051]
- University of Icelandic Research Fund
- Deutsche Forschungsgemeinschaft (DFG) through Emmy Noether grant [CO802/2-1]
- BMRZ
- Deutsche Forschungsgemeinschaft [SFB 740, SFB 1078]
Nitroxide biradicals are very efficient polarizing agents in magic angle spinning (MAS) cross effect (CE) dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR). Many recently synthesized, new radicals show superior DNP-efficiency in organic solvents but suffer from insufficient solubility in water or glycerol/water for biological applications. We report DNP efficiencies for two new radicals, the water-soluble bcTol-M and cyolyl-TOTAPOL, and include a comparison with three known biradicals, TOTAPOL, bcTol, and AMUPol. They differ by linker groups, featuring either a 3-aminopropane-1,2-diol or a urea tether, or by the structure of the alkyl substituents that flank the nitroxide groups. For evaluating their performances, we measured both signal enhancements epsilon and DNP-enhanced sensitivity kappa, and compared the results to electron spin relaxation data recorded at the same magnetic field strength (9.4 T). In our study, differences in DNP efficiency correlate with changes in the nuclear polarization dynamics rather than electron relaxation. The ratios of their individual epsilon and kappa differ by up to 20%, which is explained by starkly different nuclear polarization build-up rates. For the radicals compared here empirically, using proline standard solutions, the new radical bcTol-M performs best while being most soluble in water/glycerol mixtures.
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