DQC STUDY OF THE NITROXIDE BIRADICALS USED IN DNP

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 最近发现，氮氧双自由基在低浓度的DNP中是有效的，这是一种长期用于提高核磁共振信噪比的方法。麻省理工学院的现代DNP实验是基于140或250 GHz回旋源照射氮氧化物，导致信号增强高达400。基本的物理过程被描述为一个三自旋过程，其中两个电子自旋以核频率间隔。双自由基的使用是一种新的方法，它是一种基于顺磁物种的旧技术，顺磁物种具有相对较高浓度的单电子自旋。在最近的一项研究中，使用了双Tempo n-乙二醇双自由基(n=2、3或4)。当n=2，电子自旋为5~10 mm时，增强作用最大。服务请求的目的有两个：1)为几个长度较短的氮氧基提供距离，范围从10到18埃；2)获得氮氧基HF张量的相互取向。由于较弱的B1，鹿的实际短距离极限约为17-20A。另一方面，具有30G或更大B1值的DQC可用于测量较短的距离。我们将DQC应用于DMSO和甘油-水溶液中的BTnE双自由基。此外，还研究了刚性结构的另外三个双根。这些药物包括BTXA、BTOX和BTUrea。BTOX和BTXA DQC给出了清晰的偶极光谱，由此可以很容易地推断距离。BTnE具有更强的柔韧性，其偶极谱未被分辨。虽然DQC确实允许在所有情况下确定距离，但距离的范围从11到16°，并且在W波段连续波-ESR光谱在浸渍溶剂中报告的距离的误差范围内。这项研究将继续获得2D-DQC谱，以确定HF张量的取向。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. It was recently found that nitroxide biradicals are efficient in low concentrations in DNP, a method that has long been used to improve SNR in NMR. The modern DNP experiment at MIT is based on irradiation of nitroxides with 140 or 250 GHz gyrotron sources, leading to signal enhancements of up to 400. The underlying physics is described by a three spin process, with the two electron spins spaced at the nuclear frequency. The use of biradicals is a new approach to an old technique based on paramagnetic species bearing a single electron spin in relatively high concentration. In a recent study bis-TEMPO n-ethyleneglycol (BTnE) biradicals (n=2, 3, or 4) were employed. The largest enhancement was observed for n=2 with 5 to 10 mM of electron spins. The purpose of the service request was two-fold: 1) to provide distances for several nitroxide biradicals of short length, ranging from 10 to 18 A; 2) to obtain mutual orientations of nitroxide hf tensors. A practical short distance limit for DEER is ca. 17-20 A, due to weak B1. On the other hand, DQC featuring B1 of 30 G or greater could be used to measure shorter distances. We applied DQC to BTnE biradicals in DMSO and glycerol-water solutions. Also, three other biradicals of rigid structure were studied. These include BTXA, BTOX, and BTUrea. BTOX and BTXA DQC gave clearly resolved dipolar spectra, from which the distances were easily inferred. BTnE proved to be more flexible, and its dipolar spectra were unresolved. The distances ranged from 11 to 16 ¿ and were well within the margin of error for the distances reported by W-band CW-ESR spectroscopy in perduterated solvents, although DQC did allow determination of distances in all cases. The study will be continued to obtain 2D-DQC spectra in order to determine the orientation of the hf tensors.