Microsecond Exchange Processes Studied by Two-Dimensional ESR at 95 GHz.
Microsecond Exchange Processes Studied by Two-Dimensional ESR at 95 GHz.
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DOI：
10.1021/jacs.0c09469
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发表时间：
2020-12-23
影响因子：
15
通讯作者：
Freed JH
中科院分区：
文献类型：
--
作者：
Dzikovski B;Khramtsov VV;Chandrasekaran S;Dunnam C;Shah M;Freed JH
二维交换核磁共振技术通常研究包括构象变化、质子化/去质子化和结合平衡在内的交换过程，其中关于具有不同核磁共振位移的环境之间的核交换信息是通过交叉峰的发展来获得的。2D核磁共振能够实时研究毫秒和较慢的交换过程，而2D-Eldor(二维电子-电子双共振)形式的2D ESR具有在纳秒到微秒实时尺度上进行此类研究的潜力。以前在ESR中已经看到由于化学交换导致的交叉峰发展，但对于大多数常见的ESR探针，如在典型ESR频率下研究的氮氧化物，这是不可能的，因为与核磁共振不同，交换状态产生的ESR信号在各自的线宽内不能彼此分辨。但在95 GHz下，由于g因子分辨率的提高，在许多情况下都有可能解决这些问题。在ACERT发生的95 GHz仪器开发现在使这样的研究成为可能。我们在两个研究中展示了这些新的能力：(A)水溶液中对pH敏感的咪唑啉自旋标记的质子化/去质子化过程，其中交换态的交换速率和布居比分别由缓冲溶液的浓度和pH控制，以及(B)多层脂泡中氮氧自由基在极性(水)和非极性(磷脂)环境之间的分配，其中交叉峰的发展源于两相之间的氮氧自由基交换。这项工作是观察和分析涉及氮氧化物自旋标记的化学交换过程中产生的交叉峰的第一个例子。
Exchange processes which include conformational change, protonation/deprotonation, and binding equilibria are routinely studied by 2D exchange NMR techniques, where information about the exchange of nuclei between environments with different NMR shifts is obtained from the development of cross-peaks. Whereas 2D NMR enables the real time study of millisecond and slower exchange processes, 2D ESR in the form of 2D-ELDOR (two-dimensional electron–electron double resonance) has the potential for such studies over the nanosecond to microsecond real time scales. Cross-peak development due to chemical exchange has been seen previously for semiquinones in ESR, but this is not possible for most common ESR probes, such as nitroxides, studied at typical ESR frequencies because, unlike NMR, the exchanging states yield ESR signals that are not resolved from each other within their respective line widths. But at 95 GHz, it becomes possible to resolve them in many cases because of the increased g-factor resolution. The 95 GHz instrumental developments occurring at ACERT now enable such studies. We demonstrate these new capabilities in two studies: (A) the protonation/deprotonation process for a pH-sensitive imidazoline spin label in aqueous solution where the exchange rate and the population ratio of the exchanging states are controlled by the concentration and pH of the buffer solution, respectively, and (B) a nitroxide radical partitioning between polar (aqueous) and nonpolar (phospholipid) environments in multilamellar lipid vesicles, where the cross-peak development arises from the exchange of the nitroxide between the two phases. This work represents the first example of the observation and analysis of cross-peaks arising from chemical exchange processes involving nitroxide spin labels.
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影响因子：
4.4
作者：
Gupta, Pranav;Liang, Zhichun;Freed, Jack H.
通讯作者：
Freed, Jack H.
DOI：
10.1021/acs.jpcb.5b08165
发表时间：
2015-10-22
期刊：
The journal of physical chemistry. B
影响因子：
--
作者：
Dzikovski B;Livshits V;Freed J
通讯作者：
Freed J
影响因子：
16.6
作者：
EIGEN, M
通讯作者：
EIGEN, M
影响因子：
3.4
作者：
Costa, AJ;Shimoyama, Y;Freed, JH
通讯作者：
Freed, JH
影响因子：
2
作者：
Earle, KA;Dzikovski, B;Freed, JH
通讯作者：
Freed, JH