PULSE SEQUENCES FOR PULSED AND FT-ESR: DISTANCE MEASUREMENTS

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。 在过去的几年里，Acert和其他组织开发了几个用于距离测量的新脉冲序列。为了实现ESR在这一领域的潜力，结构生物学的需求需要进一步的发展。这在RNA的研究中是必不可少的，因为它的大小可能会对该方法造成负担，以及对于大的水溶性蛋白质及其络合物。由于需要较长的驰豫时间来确定超过40°的距离，因此报告自旋标记被放置在分子的外表面，在那里它们完全暴露在水溶液介质中。在这种情况下，D2O的使用增加了T2‘S，但仍然存在由体系中的残余质子，特别是蛋白质中的残余质子引起的驰豫过程，以及一些光谱扩散机制，导致在时间上具有二次到三次定律的驰豫。抑制这种类型的扩散需要多次重新聚焦。为了增加DQC方法中的上限距离，我们修改了6脉冲序列中信号的获取方式。我们称之为双量子滤波重聚焦一次回波(DQF-RPE)的方法是基于标准的6脉冲DQC脉冲序列，但信号的捕获方式不同。这使得更好地抑制二次弛豫，并允许在10？S的时间尺度上采集DQC信号。这使得测量70？in RNA的距离成为可能。更长的距离或质子化的溶剂需要更多的重新聚焦脉冲，这对于有限宽度的脉冲来说是一项艰巨的任务。其他进展包括实现具有小相位步长的脉冲序列，用于多量子相干分离，以及提高相位循环的有效性和更好地抑制不想要的相干路径。在2D-Eldor和ESR-显微镜的新方法的背景下，正在开发多脉冲序列能力。仪器的开发在相关项目中进行了描述。描述了DQF-RPE在26b.p.《华尔街日报》刊登了《核糖核酸》。化学。SoC。

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. Several new pulse sequences for distance measurements were developed over the last few years at ACERT and by other groups. The demands of structural biology require their further development in order to realize the potential of ESR in this field. This is essential in the study of RNA, which can tax the method due to its large size, and for large water-soluble proteins and their complexes. Since long relaxation times are necessary to determine distances exceeding 40¿, the reporter spin labels are placed on the outer molecular surfaces where they are fully exposed to the aqueous solvent medium. In this case the use of D2O increases T2's but there are still relaxation processes caused by residual protons in the system, in particular those of the protein, and by a number of spectral diffusion mechanisms, which result in relaxation with a quadratic to cubic law in time. Suppression of this type of diffusion requires multiple refocusing. To increase the upper range of distances in the DQC method, we modified the way the signal in the 6-pulse sequence was acquired. The method that we call double-quantum filtered refocused primary echo (DQF-RPE) is based on standard 6-pulse DQC pulse sequence, but the signal is acquired differently. This results in better suppression of quadratic relaxation and permits DQC signal acquisition on a time-scale of 10 ?s. This made it possible to measure a distance of 70¿ in RNA. Longer distances or protonated solvents require a larger number of refocusing pulses, which is a formidable task for pulses of finite width. Other developments include implementation of pulse sequences with small phase steps for multiple-quantum coherence separation and for increasing the effectiveness of phase cycling and better suppression of unwanted coherence pathways. Multiple-pulse sequence capability is being developed in the context of new methods of 2D-ELDOR and ESR-microscopy. The instrumentation development is described in related projects. A short communication describing application of DQF-RPE to 26 b.p. RNA is in press in J. Am. Chem. Soc.