Dynamic Nuclear Polarization (DNP) is a wide-spread technique for sensitivity enhancement of MAS NMR. During a typical MAS DNP experiment, several mechanisms resulting in polarization transfer may be active at the same time. One such mechanism which is most commonly active but up to now mostly disregarded is SCREAM-DNP (Specific Cross Relaxation Enhancement by Active Motions under DNP). This effect is generally observed in direct DNP experiments if molecular dynamics are supporting heteronuclear cross relaxation similar to the nuclear Overhauser effect. We investigate this effect for the CH₃ groups of all methyl-bearing amino acids (i.e., alanine, valine, leucine, isoleucine, threonine, and methionine). At the typical DNP temperature of ∼110 K the three-fold reorientation dynamics are still active, and efficient SCREAM-DNP is observed. We discuss variations in enhancement factors obtained by this effect in context of sample temperature and sterical hindrance of the methyl group. Next to the direct transfer to the methyl carbon, we also find evidence for much weaker transfer from the methyl protons directly to other carbons in the amino acid molecule and succeed to correlate build-up dynamics with the CH dipole coupling which is modulated by the CH₃ orientation. Besides methyl dynamics we also identify ring dynamics within proline as a source of SCREAM-DNP. Our results are the first step towards utilization of this effect as a specific probing techniqueusing methyl groups in protein systems.

动态核极化法（DNP）是一种用于增强MAS NMR灵敏度的广泛技术。在典型的MAS DNP实验中，导致极化转移的几种机制可能同时处于活动状态。一种这样的机构，它是最常用的活性，但到现在为止大多忽略是SCREAM-DNP（小号pecific ç罗斯- [R elaxation é nhancement由甲莫如中号DNP下otions）。如果分子动力学支持异核交叉弛豫（类似于核Overhauser效应），则通常在直接DNP实验中观察到此效应。我们调查了所有含甲基氨基酸的CH ₃基团（即，丙氨酸，缬氨酸，亮氨酸，异亮氨酸，苏氨酸和蛋氨酸）。在约110 K的典型DNP温度下，三重重新定向动力学仍然有效，并且观察到有效的SCREAM-DNP。我们讨论了在样品温度和甲基的空间位阻的背景下，通过这种效应获得的增强因子的变化。除了直接转移到甲基碳之外，我们还发现从甲基质子直接转移到氨基酸分子中其他碳的弱得多的证据，并且成功地将积累动力学与C H偶极偶合相关，后者由C H偶极子调节。通道₃方向。除甲基动力学外，我们还将脯氨酸内的环动力学确定为SCREAM-DNP的来源。我们的结果是利用这种效应作为在蛋白质系统中使用甲基的一种特殊探测技术的第一步。