Journal of magnetic resonance最新文献_第3页

Computationally efficient 4D spectral-spatial EPR imaging 计算效率高的四维光谱空间EPR成像。

IF 1.9 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-10-06 DOI: 10.1016/j.jmr.2025.107980

Mark Tseytlin , Oxana Tseytlin

Four-dimensional spectral–spatial imaging (4D SSI) enables noninvasive mapping of spin probes and their microenvironments. Despite its demonstrated utility, 4D SSI remains constrained by substantial computational demands, including large data volumes, the iterative nature of reconstruction algorithms, and significant requirements for memory and computational resources. These resource demands scale cubically with the size of the imaged object. To address these limitations, a set of computational strategies has been developed to improve reconstruction efficiency without compromising image fidelity. These include the use of filtered back projection (FBP) to generate an initial spin concentration map, which serves both as an initial guess for further iterations and as a mask to exclude non-signal voxels. Eliminating these empty voxels significantly reduces the problem size, thereby lowering memory usage and computation time. Additional acceleration is achieved by transforming the 4D reconstruction into a reduced 2D problem, minimizing redundant computation through precomputed values, and employing a compact look-up table for spectral fitting. The resulting workflow, implemented in MATLAB with performance-critical routines compiled as C-based MEX functions, achieves iteration times as low as one minute. Numerical phantom simulations and experimental data from physical phantoms confirm that convergence is substantially improved by excluding non-signal voxels. Among all evaluated approaches, the FBP-based masking of non-signal voxels and the use of a lookup table proved most effective in accelerating algorithm convergence. These improvements enable scalable and computationally efficient 4D SSI suitable for high-resolution, larger-animal preclinical studies and future clinical imaging applications.

四维光谱空间成像（4D SSI）能够对自旋探针及其微环境进行无创测绘。尽管已经证明了它的实用性，但4D SSI仍然受到大量计算需求的限制，包括大数据量、重建算法的迭代性以及对内存和计算资源的大量需求。这些资源需求与成像对象的大小成三次比例。为了解决这些限制，已经开发了一套计算策略来提高重建效率而不影响图像保真度。其中包括使用滤波后投影（FBP）来生成初始自旋浓度图，该图既可以作为进一步迭代的初始猜测，也可以作为排除非信号体素的掩模。消除这些空体素大大减少了问题的大小，从而降低了内存使用和计算时间。通过将四维重建转换为简化的二维问题，通过预计算值减少冗余计算，并采用紧凑的查找表进行光谱拟合，可以实现额外的加速。由此产生的工作流在MATLAB中实现，并将性能关键例程编译为基于c的MEX函数，迭代时间低至一分钟。数值幻影模拟和物理幻影的实验数据证实，通过排除非信号体素，收敛性大大提高。在所有评估的方法中，基于fbp的非信号体素掩蔽和查找表的使用被证明在加速算法收敛方面是最有效的。这些改进使4D SSI适用于高分辨率、更大的动物临床前研究和未来的临床成像应用。

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引用次数: 0

Measuring reliable electron spin coherence times with dynamical decoupling sequences that use selective mw pulses 使用选择性毫瓦脉冲的动态解耦序列测量可靠的电子自旋相干时间。

IF 1.9 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-10-06 DOI: 10.1016/j.jmr.2025.107981

George Mitrikas , Rania Giourtsidou

Dynamical decoupling methods like the Carr-Purcell-Meiboom-Gill (CPMG) or XY4- and XY8-based sequences play a key role in the measurement of reliable electron spin coherence times as they help to disentangle different sources of decoherence. Although these methods are mainly evaluated for their robustness and ability to mitigate pulse imperfections, to date little attention has been paid to the selectivity of the microwave pulses (mw), which is a factor that affects the determination of

T_{2}

in two ways: first, unwanted stimulated echoes, which decay with

T_{1}

, overlap with desired refocused echoes, resulting in overestimated values of

T_{2}

. Second, under selective mw excitation, the amplitude of the different refocused echoes shows an additional time decay even in the absence of relaxation processes. Here, we investigate the characteristics of CPMG, XY4 and XY8-based sequences by performing numerical simulations for a two-level spin system. Using the Liouville space representation of the spin state, we introduce relaxation effects in the simulations. We show that our numerical calculations reproduce well all the features of the experimental echoes and allow for the accurate determination of

T_{2}

times without the need to perform tedious phase-cycle protocols to eliminate unwanted signals.

动态解耦方法，如carr - purcell - meiboomm - gill （CPMG）或基于XY4-和xy8的序列，在可靠的电子自旋相干时间测量中起着关键作用，因为它们有助于解开不同的退相干源。虽然这些方法主要是通过鲁棒性和减轻脉冲缺陷的能力来评估的，但迄今为止，人们很少关注微波脉冲的选择性（mw），这是影响T2测定的一个因素，主要有两个方面：首先，不需要的受激发回波，随着T1衰减，与期望的重聚焦回波重叠，导致T2值高估。其次，在选择性毫微米激励下，即使在没有弛豫过程的情况下，不同重聚焦回波的振幅也表现出额外的时间衰减。本文通过对两能级自旋系统的数值模拟，研究了CPMG、XY4和xy8序列的特性。利用自旋态的刘维尔空间表示，我们在模拟中引入了弛豫效应。我们表明，我们的数值计算可以很好地再现实验回波的所有特征，并允许准确确定T2时间，而无需执行繁琐的相位周期协议来消除不需要的信号。

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引用次数: 0

15N optimal control pulses: an efficient approach to enhance heteronuclear-detected NMR experiments at high magnetic fields 15N最优控制脉冲：一种在高磁场下增强异核探测核磁共振实验的有效方法。

IF 1.9 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-10-04 DOI: 10.1016/j.jmr.2025.107972

Marco Schiavina , David Joseph , Christian Griesinger , Isabella C. Felli , Roberta Pierattelli

Carbon-13 detected Nuclear Magnetic Resonance (NMR) experiments have become a well-established and powerful tool for investigating a wide variety of biomolecular systems, offering unique insights into structure and dynamics. High field NMR spectrometers offer unprecedented resolution, particularly when working at 1.2 GHz, which is crucial in general and particularly important for samples with crowded NMR spectra. However, operating at such high fields introduces new challenges, including the need for efficient spin manipulations across broad frequency ranges while adhering to the power limitations of modern probes. Optimal control (OC) theory offers a powerful framework for designing Radio-Frequency (RF) pulses that achieve desired spin manipulations with high efficiency, even under strict experimental constraints. In this work, we focus on the implementation of OC-designed ¹⁵N pulses to enhance the performance of ¹³C-detected experiments at 1.2 GHz. Specifically, we demonstrate how these pulses improve both excitation bandwidth and signal sensitivity. The approach is validated using a small, well-folded protein and a more challenging intrinsically disordered protein (IDP) dissolved in a high-salt buffer as commonly required for IDPs' stability. Our results show that ¹⁵N OC pulses provide clear benefits across sample types and conditions, confirming their utility as a robust solution for bandwidth-limited NMR experiments at the highest available magnetic fields.

碳-13检测核磁共振（NMR）实验已经成为研究各种生物分子系统的一种成熟而强大的工具，提供了对结构和动力学的独特见解。高场核磁共振光谱仪提供了前所未有的分辨率，特别是当工作在1.2 GHz时，这在一般情况下是至关重要的，对于具有拥挤核磁共振光谱的样品尤其重要。然而，在如此高的磁场下工作带来了新的挑战，包括需要在宽频率范围内进行有效的自旋操作，同时坚持现代探针的功率限制。最优控制（OC）理论为设计射频（RF）脉冲提供了一个强大的框架，即使在严格的实验约束下，也能高效地实现所需的自旋操纵。在这项工作中，我们专注于实现oc设计的15N脉冲，以提高1.2 GHz下13c检测实验的性能。具体来说，我们演示了这些脉冲如何提高激励带宽和信号灵敏度。该方法使用小的、折叠良好的蛋白质和溶解在高盐缓冲液中的更具挑战性的内在无序蛋白（IDP）进行了验证，这通常是IDP稳定性所必需的。我们的研究结果表明，15N OC脉冲在样品类型和条件下都有明显的优势，证实了它们作为在最高可用磁场下带宽有限的核磁共振实验的强大解决方案的实用性。

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引用次数: 0

Passive shimming performance in 3 T MRI systems: Influence of shim parameters under varying magnet field distributions 3t MRI系统的被动摆振性能：不同磁场分布下摆振参数的影响。

IF 1.9 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-09-27 DOI: 10.1016/j.jmr.2025.107969

Jinhao Liu , Miutian Wang , Wenchen Wang , Yaohui Wang , Wenhui Yang , Weimin Wang , Feng Liu

This study proposes a simple and computationally efficient method to optimize the structural design parameters of passive shimming slots, aiming to improve magnetic field homogeneity in cryogen-free 3 T/200 mm superconducting magnets used across diverse application environments. The proposed method combines Latin Hypercube Sampling (LHS), utilizing over 300 sampled configurations, with a linear programming (LP)-based optimization framework to explore high-dimensional design spaces while adhering to structural constraints. The method was applied to four distinct magnets, each characterized by unique field inhomogeneity patterns resulting from manufacturing and assembly variations. Through harmonic decomposition, system-specific sensitivities were identified and effectively mitigated using customized passive shimming strategies tailored to each magnet. The optimization process achieved substantial improvements in magnetic field homogeneity, with peak-to-peak (PP) values enhanced to 12.16, 10.04, 27.28, and 54.59 parts per million (ppm) for Magnets 1 to 4, respectively. Correspondingly, the root-mean-square error (RMSE) homogeneity improved to 2.28, 1.98, 5.07, and 9.68 ppm. Furthermore, the magnitudes of all harmonic terms were reduced by 1-2 orders of magnitude, with suppression levels exceeding 90%, while minimizing the use of ferromagnetic materials. The practical feasibility of the proposed strategy was validated on-site: Magnet 1 successfully delivered high-quality animal MRI imaging with excellent signal-to-noise ratios (SNRs), and the remaining magnets are currently undergoing final calibration and delivery. This work presents a robust and scalable optimization framework for precise and resource-efficient passive shimming, offering valuable guidance for future magnet design, customization, and deployment in biomedical and industrial applications.

本研究提出了一种简单且计算效率高的方法来优化被动调光槽的结构设计参数，旨在改善不同应用环境下无低温3t / 200mm超导磁体的磁场均匀性。该方法将拉丁超立方体采样（LHS）与基于线性规划（LP）的优化框架相结合，利用300多个采样配置来探索高维设计空间，同时坚持结构约束。该方法应用于四种不同的磁体，每个磁体都具有独特的磁场不均匀性模式，这是由制造和组装变化引起的。通过谐波分解，确定了系统特定的灵敏度，并使用针对每个磁体量身定制的被动摆振策略有效地减轻了灵敏度。优化过程显著改善了磁场均匀性，磁体1至4的峰对峰（PP）值分别提高到12.16、10.04、27.28和54.59 ppm。相应的，均方根误差（RMSE）均匀性提高到2.28、1.98、5.07和9.68 ppm。此外，所有谐波项的幅度降低了1-2个数量级，抑制水平超过90%，同时最大限度地减少了铁磁材料的使用。现场验证了所提出策略的实际可行性：磁体1成功提供了高质量的动物MRI成像，具有优异的信噪比（SNRs），其余磁体目前正在进行最后的校准和交付。这项工作为精确和资源高效的被动摆振提供了一个强大的可扩展优化框架，为未来磁体的设计、定制和部署在生物医学和工业应用中提供了有价值的指导。

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引用次数: 0

NMR of chemical exchange: Revisited 核磁共振化学交换：重访

IF 1.9 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-09-24 DOI: 10.1016/j.jmr.2025.107968

Janez Stepišnik , Aleš Mohorič

Nuclear magnetic resonance is a powerful technique for examining chemical exchange in liquids by observing how molecular structures evolve. The Carr-Purcell-Meiboom-Gill technique, one of key NMR methods, enables the detection of molecular conformation fluctuations and their influence on observed chemical shifts. This study proposes how NMR measurements of chemical exchange processes can be interpreted using a molecular conformation fluctuation spectrum framework together with chemical Langevin equations. Experimental results obtained for sucrose solutions support the proposed approach, revealing insights into chemical exchange dynamics and spectral line behavior.

核磁共振是一种强大的技术，通过观察分子结构的演变来检测液体中的化学交换。Carr-Purcell-Meiboom-Gill技术是核磁共振的关键方法之一，可以检测分子构象波动及其对观察到的化学位移的影响。本研究提出了如何利用分子构象波动谱框架和化学朗之万方程来解释化学交换过程的核磁共振测量。蔗糖溶液的实验结果支持该方法，揭示了化学交换动力学和谱线行为。

引用次数: 0

Separate and detailed characterization of signal and noise at low resonance frequencies 分离和详细表征信号和噪声在低共振频率

IF 1.9 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-09-22 DOI: 10.1016/j.jmr.2025.107956

A. Guinness , Alec A. Beaton , John M. Franck

When developing or deploying a Nuclear Magnetic Resonance (NMR) spectrometer, especially for Overhauser Dynamic Nuclear Polarization (ODNP) or other experiments that require low-volume low-field measurements, the ability to mitigate noise and to quantitatively predict signal amplitude prove crucial. A quantitative treatment allows separate analysis of signal and noise and independent optimization of each. In particular, the results here emphasize that clarity and insight come from (1) characterizing the spectral distribution of the noise, and (2) integrating elements of theory and notation originally developed for Electron Spin Resonance (ESR) spectroscopy. Specifically, the spectral noise density “fingerprint spectrum” identifies sources of electromagnetic interference (EMI) and definitively confirms which actions do and do not mitigate the EMI, while the quantitative ratio (

Λ

) of

B_{1}

to the square root of the power on the transmission line provides a useful focal point that simplifies the prediction of signal intensity and that decomposes into a few simple but exact factors. Thus, this article provides a relatively comprehensive overview of signal and noise in low-field NMR instruments. The protocol/toolkit introduced here should apply to a wide range of instruments, and give most spectroscopists the freedom to systematically design sensitive NMR hardware even in cases where it must be integrated with multiple other hardware modules (e.g., an existing ESR system), or where other requirements constrain the design of the NMR hardware. It enables a systematic approach to instrument design and optimization. For the specific X-band ODNP design demonstrated here (and utilized in other laboratories), it facilitates a reduction of the noise power by more than an order of magnitude, and accurately predicts the signal amplitude from measurements of the nutation frequency. Finally, it introduces reasoning to exactly determine the field distribution factor (

η^{'}

, essentially, a more specific definition of the filling factor) experimentally from

Λ

and thus identifies the inefficient distribution of fields in the hairpin loop probe as the main remaining bottleneck for the improvement of low-field, low-volume ODNP signal-to-noise ratio (SNR).

在开发或部署核磁共振（NMR）光谱仪时，特别是对于需要小体积低场测量的Overhauser动态核极化（ODNP）或其他实验，减轻噪声和定量预测信号幅度的能力至关重要。定量处理允许信号和噪声的独立分析和各自的独立优化。特别是，这里的结果强调了清晰度和洞察力来自(1)表征噪声的光谱分布，以及(2)整合最初为电子自旋共振（ESR）光谱开发的理论和符号元素。具体来说，频谱噪声密度“指纹频谱”识别电磁干扰（EMI）的来源，并明确确认哪些行为会减轻EMI，哪些不会减轻EMI，而B1与传传线上功率的平方根的定量比（Λ）提供了一个有用的焦点，简化了信号强度的预测，并分解为几个简单但精确的因素。因此，本文对低场核磁共振仪器中的信号和噪声进行了较为全面的概述。这里介绍的协议/工具包应该适用于广泛的仪器，并给予大多数光谱学家系统地设计敏感核磁共振硬件的自由，即使在它必须与多个其他硬件模块集成的情况下（例如，现有的ESR系统），或者在其他要求限制核磁共振硬件设计的情况下。它使仪器设计和优化的系统方法。对于这里演示的特定x波段ODNP设计（并在其他实验室中使用），它有助于将噪声功率降低一个数量级以上，并从章动频率的测量中准确预测信号幅度。最后，引入推理，从Λ实验中精确确定场分布因子（η′，本质上是填充因子的更具体定义），从而确定发卡环探针中场的低效分布是提高低场，小体积ODNP信噪比（SNR）的主要瓶颈。

{"title":"Separate and detailed characterization of signal and noise at low resonance frequencies","authors":"A. Guinness , Alec A. Beaton , John M. Franck","doi":"10.1016/j.jmr.2025.107956","DOIUrl":"10.1016/j.jmr.2025.107956","url":null,"abstract":"<div><div>When developing or deploying a Nuclear Magnetic Resonance (NMR) spectrometer, especially for Overhauser Dynamic Nuclear Polarization (ODNP) or other experiments that require low-volume low-field measurements, the ability to mitigate noise and to quantitatively predict signal amplitude prove crucial. A quantitative treatment allows separate analysis of signal and noise and independent optimization of each. In particular, the results here emphasize that clarity and insight come from (1) characterizing the spectral distribution of the noise, and (2) integrating elements of theory and notation originally developed for Electron Spin Resonance (ESR) spectroscopy. Specifically, the spectral noise density “fingerprint spectrum” identifies sources of electromagnetic interference (EMI) and definitively confirms which actions do and do not mitigate the EMI, while the quantitative ratio (<span><math><mi>Λ</mi></math></span>) of <span><math><msub><mrow><mi>B</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> to the square root of the power on the transmission line provides a useful focal point that simplifies the prediction of signal intensity and that decomposes into a few simple but exact factors. Thus, this article provides a relatively comprehensive overview of signal and noise in low-field NMR instruments. The protocol/toolkit introduced here should apply to a wide range of instruments, and give most spectroscopists the freedom to systematically design sensitive NMR hardware even in cases where it must be integrated with multiple other hardware modules (<em>e.g.</em>, an existing ESR system), or where other requirements constrain the design of the NMR hardware. It enables a systematic approach to instrument design and optimization. For the specific X-band ODNP design demonstrated here (and utilized in other laboratories), it facilitates a reduction of the noise power by more than an order of magnitude, and accurately predicts the signal amplitude from measurements of the nutation frequency. Finally, it introduces reasoning to exactly determine the field distribution factor (<span><math><msup><mrow><mi>η</mi></mrow><mrow><mo>′</mo></mrow></msup></math></span>, essentially, a more specific definition of the filling factor) experimentally from <span><math><mi>Λ</mi></math></span> and thus identifies the inefficient distribution of fields in the hairpin loop probe as the main remaining bottleneck for the improvement of low-field, low-volume ODNP signal-to-noise ratio (SNR).</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"381 ","pages":"Article 107956"},"PeriodicalIF":1.9,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145120051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

A simple algorithm to suppress diagonal peaks in high-resolution homonuclear chemical shift correlation NMR spectra 一种抑制高分辨率同核化学位移相关核磁共振谱对角峰的简单算法。

IF 1.9 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-09-13 DOI: 10.1016/j.jmr.2025.107967

Shengyu Zhang , Jhinuk Saha , Yuchen Li , Xinhua Peng , Ryan P. McGlinchey , Ayyalusamy Ramamoorthy , Riqiang Fu

Previous experimental strategies aimed at completely suppressing diagonal peaks in NMR homonuclear correlation spectra often resulted in reduced sensitivity for cross peaks. In this work, we report a spectral shearing approach that transforms diagonal peaks along the diagonal axis of a homonuclear correlation spectrum into a zero-frequency line in the indirect dimension. This allows for effective extraction and substantial suppression of diagonal peaks using a recently proposed data processing algorithm based on quadrature-detected spin-echo diagonal peak suppression. Since the shearing process only rearranges the positions of cross peaks without affecting their intensities, the sensitivity of cross peaks is fully preserved while diagonal peaks are significantly reduced. The effectiveness of this method is demonstrated using uniformly ¹³C,¹⁵N labeled α-synuclein amyloid fibrils and aquaporin Z membrane protein samples.

以往旨在完全抑制核磁共振同核相关谱对角峰的实验策略往往导致交叉峰灵敏度降低。在这项工作中，我们报告了一种光谱剪切方法，该方法将沿同核相关谱对角线轴的对角峰转换为间接维的零频率线。使用最近提出的基于正交检测自旋回波对角峰抑制的数据处理算法，这允许有效地提取和大量抑制对角峰。由于剪切过程只是重新排列了交叉峰的位置，而不影响其强度，因此交叉峰的灵敏度得到了充分的保留，而对角峰的灵敏度明显降低。用13C、15N标记的α-突触核蛋白淀粉样原纤维和水通道蛋白Z膜蛋白样品证明了该方法的有效性。

引用次数: 0

Residual motion artifact removal enables dynamic μMRI of a behaving Pachnoda marginata 残馀运动伪影的去除，使动态μMRI的行为Pachnoda边缘

IF 1.9 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-09-04 DOI: 10.1016/j.jmr.2025.107954

Ajmal Chenakkara , Mazin Jouda , Ulrike Wallrabe , Jan G. Korvink

Microscopic magnetic resonance imaging, also referred to as

μ

MRI, is a non-invasive imaging modality ideal for studying small live model organisms. However,

μ

MRI raw data acquisition is inherently sequential and slow in comparison to the biomechanics timescale of the behaving organism, leading to motion artifacts upon image reconstruction. Recently, we have developed an integrated spherical treadmill with a prospectively triggered k-space acquisition technique to provide position consistency for studying live, behaving insect using

μ

MRI. Despite this advancement, behaving insects on the treadmill still exhibited motion artifacts due to tethered locomotion being coupled with internal organ dynamics. Here, we are addressing the large-scale non-rigid nature of the abdominal motion of the behaving insect by developing a fully retrospective gating strategy using the motion information obtained from an in-situ computer vision system. Residual motion artifacts persisting after gating are effectively managed through a deep learning technique. We trained a U-Net-based deep convolutional neural network using pairs of simulated motion-corrupted and motion-free images as a supervised image-to-image translation problem. Our results demonstrate that combining retrospective gated

μ

MRI reconstruction with a deep learning residual motion compensation technique can significantly reduce the motional artifacts, thereby paving the way for the non-invasive dynamic imaging studies of behaving organisms with 117

μ

m in-plane resolution.

显微磁共振成像，也被称为μMRI，是一种非侵入性的成像方式，非常适合研究小型活模式生物。然而，与行为生物体的生物力学时间尺度相比，μMRI原始数据采集固有的顺序和缓慢，导致图像重建时的运动伪影。最近，我们开发了一种集成的球形跑步机，该跑步机具有前瞻性触发k空间采集技术，为使用μMRI研究活昆虫提供位置一致性。尽管有了这一进展，但在跑步机上活动的昆虫仍然表现出运动伪影，因为系绳运动与内部器官动力学相结合。在这里，我们通过使用从原位计算机视觉系统获得的运动信息开发一个完全回顾性的门控策略，来解决行为昆虫腹部运动的大规模非刚性性质。通过深度学习技术有效地处理门控后持续存在的残余运动伪影。我们训练了一个基于u - net的深度卷积神经网络，使用对模拟的运动损坏和无运动的图像作为监督图像到图像的翻译问题。我们的研究结果表明，将回溯门控μMRI重建与深度学习残余运动补偿技术相结合可以显著减少运动伪影，从而为117 μm平面内分辨率的行为生物的无创动态成像研究铺平了道路。

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引用次数: 0

Significant acceleration of solid-state NMR simulations via three-angle powder averaging 通过三角度粉末平均显著加速固态核磁共振模拟

IF 1.9 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-08-30 DOI: 10.1016/j.jmr.2025.107966

Elijah Burlinson , Frédéric A. Perras

The anisotropic frequency shifts imparted onto the NMR resonance frequency depend on the spherical angular coordinates that describe the orientations of the NMR interaction tensors with respect to the applied magnetic field direction. Experiments performed using magic-angle spinning, however, gain a dependence on a third angle: the rotor phase γ. Traditionally, a carousel average is performed to integrate over γ, which leads to a slow convergence of intensities without contributing to the underlying powder patterns. Herein, we show an order of magnitude acceleration in computation time may be obtained by including the γ-averaging into the main powder average to eliminate redundant calculation of resonance frequencies.

传递到核磁共振共振频率上的各向异性频移取决于描述核磁共振相互作用张量相对于外加磁场方向的方向的球角坐标。然而，使用魔角旋转进行的实验获得了对第三个角度的依赖：转子相位γ。传统上，对γ进行旋转平均积分，导致强度缓慢收敛，而不会影响潜在的粉末图案。通过在主粉末平均中加入γ-平均来消除共振频率的冗余计算，可以在计算时间上得到一个数量级的加速。

引用次数: 0

Revealing the sensitivity of methyl tunneling towards local environment changes with quantum-rotor EPR spectroscopy 利用量子转子EPR光谱揭示甲基隧穿对局部环境变化的敏感性

IF 1.9 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-08-26 DOI: 10.1016/j.jmr.2025.107943

Andrea Eggeling, Janne Soetbeer, Gunnar Jeschke

Methyl rotors have potential as local environment probes because their rotation barrier is sensitive to hindering interactions with the nearby surrounding. Quantum-rotor electron paramagnetic resonance (EPR) measurements allow access to this local environment information of the methyl rotor if it is coupled to an electron spin. This is the case for commonly used nitroxide-based spin-labels, where electron spin echo envelope modulation (ESEEM) signals exhibit two contributions on different time scales at low temperatures. The slower decaying contribution is related to matrix-driven nuclear pair ESEEM while the faster contribution originates from methyl tunneling of the electron spin-coupled methyl rotors. The tunneling ESEEM contribution contains local environment information in terms of a distribution of the rotation barrier, which can be quantified using the methyl quantum rotor model. Here, we study the sensitivity of the tunneling behavior towards changes in the rotors’ surrounding by systematically investigating the two-pulse ESEEM signal of nitroxide spin probes containing two pairs of geminal methyl groups in different biologically-relevant matrix compositions. We find that the nitroxide ring structure of these probes strongly impacts the rotation barrier of the observed methyl rotors whereas the matrix surrounding does not affect the underlying rotation barrier distribution. These insights are crucial for designing nitroxide-based spin-labels as local environments probes in combination with site-directed spin-labeling for protein structure elucidation.

甲基转子具有作为局部环境探针的潜力，因为它们的旋转势垒对阻碍与周围环境的相互作用很敏感。量子转子电子顺磁共振（EPR）测量允许访问这个甲基转子的局部环境信息，如果它是耦合到一个电子自旋。这是常用的基于氮氧化物的自旋标签的情况，其中电子自旋回波包络调制（ESEEM）信号在低温下的不同时间尺度上表现出两种贡献。较慢的衰减贡献与基质驱动的核对ESEEM有关，而较快的衰减贡献来自电子自旋耦合甲基转子的甲基隧穿。隧道效应的ESEEM贡献包含了旋转势垒分布的局部环境信息，这些信息可以使用甲基量子转子模型进行量化。在这里，我们通过系统地研究含有两对双甲基的氮氧化物自旋探针在不同生物相关基质组成中的双脉冲ESEEM信号，来研究隧道行为对转子周围变化的敏感性。我们发现这些探针的氮氧化物环结构强烈影响观察到的甲基转子的旋转势垒，而周围的基质不影响底层的旋转势垒分布。这些见解对于设计基于氮氧化物的自旋标记作为局部环境探针与位点定向自旋标记相结合用于蛋白质结构阐明至关重要。

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引用次数: 0