The efficacy of dynamic nuclear polarization (DNP) surface-enhanced NMR spectroscopy (SENS) is reviewed for alumina, silica, and ordered mesoporous carbon (OMC) materials, with vastly different surface areas, as a function of the biradical concentration. Importantly, our studies show that the use of a “one-size-fits-all” biradical concentration should be avoided when performing DNP SENS experiments and instead an optimal concentration should be selected as appropriate for the type of material studied as well as its surface area. In general, materials with greater surface areas require higher radical concentrations for best possible DNP performance. This result is explained with the use of a thermodynamic model wherein radical-surface interactions are expected to lead to an increase in the local concentration of the polarizing agent at the surface. We also show, using plane-wave density functional theory calculations, that weak radical-surface interactions are the cause of the poor performance of DNP SENS for carbonaceous materials.

审查了动态核极化（DNP）表面增强NMR光谱（SENS）对氧化铝，二氧化硅和有序介孔碳（OMC）材料的功效，该材料具有很大不同的表面积，是双自由基浓度的函数。重要的是，我们的研究表明，进行DNP SENS实验时应避免使用“一刀切”的双自由基浓度，而应根据所研究材料的类型及其表面选择合适的最佳浓度区域。通常，具有更大表面积的材料需要更高的自由基浓度才能获得最佳的DNP性能。使用热力学模型解释了该结果，其中预期自由基与表面的相互作用会导致表面上偏振剂的局部浓度增加。