Journal of magnetic resonance最新文献_第6页

A mathematical model of NMR transverse relaxation for pore size distribution estimation in porous media 多孔介质中孔径分布估计的核磁共振横向弛豫数学模型

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-06-23 DOI: 10.1016/j.jmr.2025.107922

S. Morales-Chávez , M.A. Valdez-Grijalva , M.A. Díaz-Viera , E. Lucas-Oliveira , T.J. Bonagamba

Nuclear Magnetic Resonance (NMR) is a widely useful technique for studying porous media. Of particular interest are transverse relaxation times (

T_{2}

), which are often associated with pore size when surface relaxation is the dominant mechanism. Under specific physical assumptions, a distribution of

T_{2}

can be used to infer the pore size distribution (PSD). However, in real porous rocks, a combination of diffusion and relaxation mechanisms complicates this interpretation. Despite recent advancements in industrial applications, conventional models frequently rely on simplifying assumptions, particularly when pore size is considered in the fast diffusion regime. This results in the neglect of transverse bulk relaxation (

T_{2 B}

) effects, leading to underestimations of pore sizes. To address this, numerical methods, particularly the Finite Element Method (FEM), offer flexibility in modeling symmetric geometries while significantly reducing computational complexity. This paper presents a mathematical NMR model and numerical implementation based on FEM to simulate transverse magnetization signals for a PSD, validated with semi-analytical solutions and applied to synthetic and real samples, such as Berea sandstone. Additionally, a change of variable in the Inverse Laplace Transform (ILT) model is introduced for the direct PSD estimation, demonstrating a strong agreement between experimental and simulated data.

核磁共振（NMR）是一种广泛应用于多孔介质研究的技术。特别令人感兴趣的是横向弛豫时间（T2），当表面弛豫是主要机制时，它通常与孔径有关。在特定的物理假设下，可以利用T2的分布来推断孔隙尺寸分布（PSD）。然而，在真实的多孔岩石中，扩散和松弛机制的结合使这种解释复杂化。尽管最近在工业应用中取得了进展，但传统模型经常依赖于简化的假设，特别是在考虑快速扩散状态下的孔径时。这导致忽略了横向体松弛（T2B）效应，从而导致孔隙尺寸的低估。为了解决这个问题，数值方法，特别是有限元法（FEM），在对称几何建模方面提供了灵活性，同时显著降低了计算复杂性。本文提出了一个核磁共振数学模型和基于FEM的数值实现，用于模拟PSD的横向磁化信号，并通过半解析解进行了验证，并应用于合成样品和实际样品，如Berea砂岩。此外，引入了拉普拉斯逆变换（ILT）模型中的变量变化来直接估计PSD，证明了实验数据和模拟数据之间的强烈一致性。

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引用次数: 0

Accurate image reconstruction from reduced data in pulsed electron paramagnetic resonance imaging 脉冲电子顺磁共振成像中简化数据的精确图像重建

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-06-23 DOI: 10.1016/j.jmr.2025.107920

Zheng Zhang , Boris Epel , Buxin Chen , Dan Xia , Emil Y. Sidky , Howard Halpern , Xiaochuan Pan

Objective:

We investigate and develop algorithms for reconstructing effective probe-density images, and then for obtaining oxygen-concentration images, from data of a subject collected at sparse views (SVs) or over a limited-angular range (LAR) for possibly achieving fast pulsed electron paramagnetic resonance imaging (EPRI). We refer to the effective probe-density image simply as the EPR image in the work.

Methods:

The reconstruction problem of EPR images from SV or LAR data in pulsed EPRI is formulated as an optimization program that includes a constraint either on the total variation (TV) or on the directional-TVs (DTVs) of the EPR image. Two algorithms, referred to as TV and DTV algorithms, are developed then for reconstruction of EPR images, respectively, from SV and LAR data through solving the respective optimization programs. Oxygen-concentration image is estimated subsequently from the EPR images reconstructed.

Results:

Using numerical studies with simulated data of a digital phantom and also with real data of a physical phantom and a mouse model, we demonstrate the potential of the TV and DTV algorithms that yield, respectively, from SV and LAR data, numerically accurate EPR and oxygen-concentration images.

Conclusion:

The TV and DTV algorithms developed can yield numerically accurate EPR and oxygen-concentration images, respectively, from SV and LAR data in pulsed EPRI.

Significance:

The work may yield insights into the design of scans with minimized scanning time, thus potentially enabling basic and preclinical in vivo studies with fast pulsed EPRI.

目的：研究和开发从稀疏视图（SVs）或有限角范围（LAR）采集的受试者数据中重建有效探针密度图像，然后获得氧浓度图像的算法，从而可能实现快速脉冲电子顺磁共振成像（EPRI）。在本文中，我们将有效探针密度图像简称为EPR图像。方法：将脉冲EPRI中SV或LAR数据的EPR图像重建问题制定为一个优化程序，该程序包括对EPR图像的总变差（TV）或方向电视（dtv）的约束。然后，通过求解各自的优化程序，分别开发了两种算法，即TV和DTV算法，用于从SV和LAR数据重建EPR图像。随后从重构的EPR图像中估计氧浓度图像。结果：通过对数字幻影的模拟数据以及物理幻影和小鼠模型的真实数据进行数值研究，我们展示了TV和DTV算法的潜力，分别从SV和LAR数据产生数值精确的EPR和氧浓度图像。结论：所开发的TV和DTV算法可以分别从脉冲EPRI的SV和LAR数据中获得数值精确的EPR和氧浓度图像。意义：这项工作可能会对最小化扫描时间的扫描设计产生见解，从而有可能实现快速脉冲EPRI的基础和临床前体内研究。

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引用次数: 0

Using solid-state MRI and a double-tuned RF coil to quantify bone matrix and mineral densities in rat bones 使用固态MRI和双调谐射频线圈量化大鼠骨骼中的骨基质和矿物质密度

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-06-20 DOI: 10.1016/j.jmr.2025.107925

Victor B. Kassey , Matthias Walle , Diana Yeritsyan , Daniel V. Kassey , Yaotang Wu , Brian D. Snyder , Edward K. Rodriguez , Jerome L. Ackerman , Ara Nazarian

Quantitative information on the composition of bone, specifically the content of calcium phosphate mineral and organic matrix, is essential for accurate diagnosis of metabolic bone diseases such as osteoporosis, osteomalacia, and renal osteodystrophy, as well as for differentiating among these conditions. Conventional MRI fails to provide this information because these substances are solid and, therefore, yield no signal in conventional MRI scans, which typically employ spin or gradient echoes. In this report, we show how phosphorus and proton solid-state MRI yield the desired compositional information in bone specimens with ZTE and WASPI pulse sequences, respectively, coupled with the use of a two-port double-tuned solenoidal RF coil.

Electrical network simulations and construction details of the RF coil are detailed. Electrical performance was simulated using QUCS software to find the circuit component values that minimize reflected power and maximize interport isolation. Phantoms of known composition, as well as ex vivo femurs from normal, low bone density, and vitamin D-deficient rats, were included in the study. A simple correction for B₁ inhomogeneity was applied to achieve quantitative accuracy in the image intensity values.

Bone matrix and mineral densities derived from MRI strongly correlated (R² = 0.84) with chemical analysis, demonstrating the ability to measure compositional differences relevant to osteoporosis and osteomalacia.

骨组成的定量信息，特别是磷酸钙矿物和有机基质的含量，对于准确诊断代谢性骨疾病（如骨质疏松症、骨软化症和肾性骨营养不良）以及区分这些疾病至关重要。传统的MRI无法提供这些信息，因为这些物质是固体的，因此在传统的MRI扫描中无法产生信号，而传统的MRI扫描通常使用自旋或梯度回波。在本报告中，我们展示了磷和质子固态MRI如何分别使用ZTE和WASPI脉冲序列在骨标本中产生所需的成分信息，并结合使用双端口双调谐螺线管射频线圈。详细介绍了射频线圈的电气网络仿真和结构细节。利用QUCS软件对电路的电气性能进行了模拟，以找出使反射功率最小和使接口隔离最大化的电路元件值。已知成分的幻影，以及正常、低骨密度和维生素d缺乏大鼠的离体股骨，都被纳入研究。对B1非均匀性进行了简单的校正，以实现图像强度值的定量精度。MRI得出的骨基质和矿物质密度与化学分析高度相关（R2 = 0.84），证明了测量骨质疏松症和骨软化症相关成分差异的能力。

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引用次数: 0

Circuit design for broadband decoupling in multi-coil multi-nuclear applications 多线圈多核应用中宽带去耦电路设计

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-06-18 DOI: 10.1016/j.jmr.2025.107924

Joseph Busher , Edith Touchet-Valle , Jacob Degitz , Mary P. McDougall

The wealth of information available from multinuclear magnetic resonance imaging and spectroscopy is largely untapped in the clinical setting. This is due to a multitude of challenges in the pipeline ranging from acquisition strategies, hardware design, processing, and interpretation/analysis. As a small part of addressing these challenges, this work presents a straightforward approach for broadband decoupling between coils. This circuit was created with the implementation of a series PIN diode and was evaluated on the bench and experimentally for ¹H, ³¹P and ²³Na at 3 T. Individual coils were single-tuned with this decoupling network and stacked to enable a switched triple-tuned coil. These coils were evaluated in various purposefully coupled configurations and compared to a narrowband trap active detuning network to demonstrate potential modularity of this design. Narrowband trapped coils showed drops in SNR when combined with other coils, presumably due to coupling between receiver elements tuned to different frequencies. This broadband decoupling behavior was shown to be independent of positioning through coils oriented to be nearly perfectly geometrically coupled and the addition of a three-element array of the same size. This configuration was validated on a post-mortem pig to verify the losses of the network did not prohibit its use for preclinical imaging and spectroscopy applications. Although losses were incurred as a result of the broadband decoupling network, it enabled a modular design that can be adapted to a given study without significant compromise of the signal integrity and could eliminate the need for certain custom coils for multi-nuclear studies.

从多核磁共振成像和光谱学中获得的丰富信息在临床环境中很大程度上尚未得到开发。这是由于在获取策略、硬件设计、处理和解释/分析等方面存在大量挑战。作为解决这些挑战的一小部分，这项工作提出了一种直接的线圈间宽带解耦方法。该电路是通过实现串联PIN二极管创建的，并在3t下对1H， 31P和23Na进行了台架和实验评估，单个线圈使用该去耦网络进行单调谐，并堆叠以启用开关三调谐线圈。这些线圈在各种有目的的耦合配置下进行了评估，并与窄带陷阱有源失谐网络进行了比较，以证明该设计的潜在模块化。窄带捕获线圈与其他线圈组合时显示信噪比下降，可能是由于调谐到不同频率的接收器元件之间的耦合。这种宽带去耦行为被证明与定位无关，通过线圈定向成几乎完美的几何耦合和添加相同尺寸的三元阵列。该配置在死后的猪身上进行了验证，以验证网络的损失不会阻止其用于临床前成像和光谱应用。尽管宽带解耦网络造成了损耗，但它实现了模块化设计，可以适应给定的研究，而不会显著损害信号完整性，并且可以消除对多核研究中某些定制线圈的需求。

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引用次数: 0

Probe design for high sensitivity proton-detected solid-state NMR 高灵敏度质子探测固态核磁共振探针设计

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-06-09 DOI: 10.1016/j.jmr.2025.107919

Collin G. Borcik , Lauren E. Price , John P. Heinrich , John A. Stringer , Chad M. Rienstra

Proton (¹H) detection methodologies in solid-state NMR (SSNMR) have revolutionized the field allowing for probing of new frontiers in determining the structure and dynamics within biological systems and materials. While approaches that maximally leverage the high gyromagnetic ratio of ¹H detection have enhanced sensitivity and resolution of SSNMR experiments, the radiofrequency (rf) circuit of magic-angle spinning (MAS) probes is not well optimized for ¹H detection, limiting the overall signal-to-noise ratio (SNR). Rather, SSNMR probes have historically been optimized for lower gamma nuclei such as ¹³C and below. Here we present a design with an inner coil for proton (¹H) to maximize ¹H sensitivity. Optimizing the ¹H channel resulted in a 1.33–2-fold increase in SNR with ¹H detection in a one-dimensional experiment. An outer coil is tuned to the ¹³C and ¹⁵N frequencies, with excellent B₁ homogeneity on all three channels. Using this design, we find that the sensitivity scales better than the theoretical expectations from 600 MHz to 750 MHz, due to a combination of the improved rf efficiency and B₁ homogeneity. We also demonstrate these improvements on a model protein system (GB1) with a 4D experiment collected in less than a day.

固态核磁共振（SSNMR）中的质子（1H）检测方法已经彻底改变了该领域，允许在确定生物系统和材料的结构和动力学方面探索新的前沿。虽然最大限度地利用1H检测的高回旋磁比的方法提高了SSNMR实验的灵敏度和分辨率，但魔角旋转（MAS）探头的射频（rf）电路并未很好地优化用于1H检测，限制了整体信噪比（SNR）。相反，ssmr探测器历来针对低γ核（如13C及以下）进行了优化。在这里，我们提出了一个内部线圈的质子（1H）的设计，以最大限度地提高1H的灵敏度。在一维实验中，优化1H通道使1H检测的信噪比提高1.33 - 2倍。外线圈调谐到13C和15N频率，在所有三个频道上都具有出色的B1均匀性。使用这种设计，我们发现在600 MHz到750 MHz范围内，由于改进的射频效率和B1均匀性的结合，灵敏度的尺度优于理论预期。我们还在不到一天的时间内收集了4D实验，在模型蛋白质系统（GB1）上展示了这些改进。

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引用次数: 0

Design and characterization of a tunable open TE011 resonator for Q-band pulse EPR experiments 用于q波段脉冲EPR实验的可调谐开放式TE011谐振腔的设计与表征

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-06-08 DOI: 10.1016/j.jmr.2025.107921

Kyle Jorgensen, Alexey Silakov

Electron Paramagnetic Resonance (EPR) is an important technique for the investigation of the structure and function of metalloproteins and enzymes. The variety of questions in this line of research requires versatile instrumentation. In this work, we explored the utility of the open resonator concept for a general-use highly tunable TE₀₁₁ resonator design at Q-band frequencies (≈ 34 GHz). Using proof-of-concept calculations, we establish a viable range of critical parameters compatible with the desired instrument specifications. We then present the resonator design, targeting ease of execution and handling. Experimental characterization of the built resonator shows high tunability. Specifically, we show that the resonator can be critically coupled and overcoupled with a three-fold change in the bandwidth using a matching short. We also show that the resonator can be incorporated with frequency tuning by means of movable axial plungers, allowing it to work with a wide range of samples using relatively narrow-bandwidth microwave instrumentation. Furthermore, because of its high tunability, the resonator is very tolerant of manufacturing imperfections, which makes it affordable and easy to execute with minimal tooling. We also discuss the long-term use of the resonator in our research, highlighting its versatility.

电子顺磁共振（EPR）是研究金属蛋白和酶的结构和功能的重要技术。这条研究路线中各种各样的问题需要多种多样的仪器。在这项工作中，我们探索了开放谐振器概念在q波段（≈34 GHz）通用高可调谐TE011谐振器设计中的实用性。使用概念验证计算，我们建立了与所需仪器规格兼容的可行关键参数范围。然后，我们提出了谐振器的设计，目标是易于执行和处理。实验结果表明，该谐振器具有较高的可调性。具体地说，我们证明了谐振器可以在使用匹配短路的带宽变化三倍的情况下进行临界耦合和过耦合。我们还表明，谐振器可以通过可移动的轴向柱塞与频率调谐相结合，使其能够使用相对窄带宽的微波仪器处理大范围的样品。此外，由于其高可调性，谐振器对制造缺陷的容忍度非常高，这使得它价格合理，并且易于使用最少的工具执行。我们还在研究中讨论了谐振器的长期使用，突出了它的多功能性。

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引用次数: 0

Reduction of radiofrequency induced implant heating via flexible metasurface shielding at 7 T 通过柔性超表面屏蔽在7 T下减少射频诱导的植入物加热

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-06-02 DOI: 10.1016/j.jmr.2025.107918

Paul S. Jacobs , Wyger M. Brink , Pradnya Narvekar , Neil E. Wilson , Anshuman Swain , Neeraj Panchal , Samir Mehta , Mark A. Elliott , Ravinder Reddy

Passive implanted devices are commonly contraindicated at ultra-high field MRI due to the risk of radiofrequency heating. Mitigation of this risk has come in many forms, such as modifying implant materials or creating novel radiofrequency coils. These methods require substantial involvement from manufacturers and may not benefit patients with existing implants. In this study, a tailored metasurface design is demonstrated to improve implant safety at 7 T by shielding the local B₁⁺ field. A prototype metasurface was designed and implemented with a unit cell size of 15 mm using discrete capacitors of 30 pF values. Phantom and human body model simulations were used to validate differences in the SAR distribution with and without the metasurface. Fiber optic temperature probes were used to measure temperature increase across two representative orthopedic screws placed inside a tissue mimicking phantom during a high-SAR sequence. Phantom and in-vivo imaging were performed to assess the metasurface effect on image quality. With the metasurface, an average maximum temperature decrease of 0.50 °C or 34.9 % near the implant was observed. RF field simulations yielded similar decreases in SAR for the phantom (40.7 %) and substantial decreases for the in-vivo leg model (97 %). Phantom image SNR showed a global 8.5 % decrease with the metasurface while in-vivo images showed a 4.8 % decrease in SNR, with the region in its immediate vicinity experiencing substantial signal drop. These results demonstrate the feasibility of a metasurface designed to substantially reduce local RF induced heating with only minor degradation of image quality. Future work will focus on refinement of the metasurface design and further in-vivo testing.

由于射频加热的风险，被动式植入装置通常禁止在超高场MRI中使用。减轻这种风险的方法有很多，比如修改植入材料或制造新型射频线圈。这些方法需要制造商的大量参与，并且可能对现有植入物的患者没有好处。在这项研究中，量身定制的超表面设计被证明可以通过屏蔽局部B1+场来提高7 T时种植体的安全性。设计并实现了一个原型超表面，其单元尺寸为15 mm，使用30 pF值的分立电容器。通过模拟和人体模型模拟来验证有和没有超表面时SAR分布的差异。在高sar序列中，使用光纤温度探头测量放置在模拟组织内的两个具有代表性的骨科螺钉的温度升高。幻影和活体成像评估超表面效应对图像质量的影响。在超表面下，种植体附近的平均最高温度下降了0.50°C或34.9%。射频场模拟对假体的SAR也有类似的降低（40.7%），对活体腿模型的SAR也有明显的降低（97%）。幻影图像的信噪比在超表面上整体下降了8.5%，而活体图像的信噪比下降了4.8%，其邻近区域的信号明显下降。这些结果证明了设计一种超表面的可行性，该超表面可以大大减少局部射频引起的加热，而图像质量只有轻微的下降。未来的工作将集中在改进超表面设计和进一步的体内测试上。

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引用次数: 0

Finite element modeling of Rb-129Xe spin-exchange optical pumping and optimized Rb source distribution 铷- 129xe自旋交换光泵浦的有限元建模及优化铷源分布

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-05-30 DOI: 10.1016/j.jmr.2025.107889

Jimmy E. Ball, Jim M. Wild, Graham Norquay

Rubidium (Rb) vapor density (

[Rb]

) is a key parameter in xenon-129 polarization (

P_{Xe}

) build up in spin-exchange optical pumping. In practice,

[Rb]

within the cell often falls below saturation levels and is spatially heterogeneous leading to system underperformance. In this study, finite element modeling was performed to investigate the role of Rb source distribution in heterogeneous in-cell

[Rb]

, and to optimize a Rb presaturator to achieve homogeneous

[Rb]

and reduce the flow rate dependence of

[Rb]

. Lower than expected

P_{Xe}

in previous iterations of our polarizer can be attributed to sub-saturation

[Rb]

due to the small surface area of the Rb source in the main cell body and the absence of upstream Rb vapor presaturation, leading to lower than desired

P_{Xe}

. We found that increasing the surface area of the Rb source in the main cell body does not effectively reduce

[Rb]

heterogeneity. Instead, achieving a more uniform distribution of

[Rb]

necessitates the use of a sufficiently long presaturator at a given gas flow rate, increasing

P_{Xe}

. We also report discrepancy between modeled and experimentally measured laser absorption, highlighting limitations of the existing optical pumping model and suggesting directions for future model revisions and the investigation of currently unexplored areas.

铷（Rb）蒸气密度（[Rb]）是自旋交换光泵浦中氙-129极化（PXe）形成的关键参数。实际上，单元内的[Rb]通常低于饱和水平，并且在空间上不均匀，导致系统性能不佳。本研究通过有限元建模研究了Rb源分布在非均质胞内[Rb]中的作用，并对Rb预饱和器进行了优化，以实现均匀[Rb]并降低对[Rb]流量的依赖。在我们之前的偏振器迭代中，低于预期的PXe可归因于亚饱和[Rb]，这是由于主胞体中Rb源的小表面积和上游Rb蒸气压力的缺乏，导致PXe低于预期。我们发现，增加主细胞体Rb源的表面积并不能有效降低[Rb]的异质性。相反，要实现[Rb]的更均匀分布，就需要在给定的气体流速下使用足够长的预热器，从而增加PXe。我们还报告了模型和实验测量的激光吸收之间的差异，突出了现有光泵模型的局限性，并为未来的模型修订和目前未开发区域的研究提出了方向。

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引用次数: 0

Probing rare and short-lived conformational states in nucleic acids using off-resonance carbonyl and guanidino carbon R1ρ relaxation dispersion 利用非共振羰基和鸟嘌呤碳R1ρ弛豫色散探测核酸的稀有和短寿命构象态

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-05-29 DOI: 10.1016/j.jmr.2025.107910

Supriya Pratihar , Yeongjoon Lee , Ainan Geng , Shibani Bhattacharya , Hashim M. Al-Hashimi

Chemical exchange-based NMR techniques provide powerful approaches for characterizing lowly-populated and short-lived conformational states in nucleic acids. Among possible probes, the nucleobase carbonyl and guanidino carbons stand out due to the sensitivity of their chemical shifts to hydrogen bonding and keto–enol tautomerization. However, chemical exchange measurements targeting these carbon nuclei have not yet been reported in studies of nucleic acids. Here, we present an experiment for measuring off-resonance R_1ρ relaxation dispersion for guanine-C2, guanine-C6, thymine/uracil-C2, and thymine/uracil-C4 carbons in uniformly ¹³C/¹⁵N labeled nucleic acids. We demonstrate the utility of the experiment by characterizing chemical exchange in a G•T mismatch in duplex DNA between a dominant wobble conformation and two lowly-populated, short-lived, and rapidly interconverting Watson–Crick-like tautomeric states (G^enol•T ⇌ G•T^enol) implicated in DNA replicative errors. The population and exchange rate deduced from the guanine-C6, guanine-C2, and thymine-C4 off-resonance R_1ρ relaxation dispersion profiles were in excellent agreement with counterparts obtained from R_1ρ measurements on proton-bound carbon and nitrogen nuclei. The carbon chemical shifts of the minor state were downfield shifted relative to the wobble ground state, consistent with (G)C6 = O···HO-C4(T^enol) and (G^enol)C6-OH···O=C4(T) hydrogen bonding in the Watson-Crick-like tautomeric state. As a second application, we did not detect any exchange contribution to uracil-C2 and uracil-C4 R_1ρ profiles measured for a U·U mismatch in RNA, consistent with isomerization between two alternative wobble conformations occurring on the sub-microsecond timescale. These results establish carbonyl and guanidino carbons as valuable probes for chemical exchange measurements of micro-to-millisecond motions in nucleic acids.

基于化学交换的核磁共振技术为表征核酸中低密度和短寿命的构象状态提供了强有力的方法。在可能的探针中，核碱基羰基和胍基碳因其化学转变对氢键和酮-烯醇互变异构的敏感性而脱颖而出。然而，针对这些碳核的化学交换测量尚未在核酸研究中报道。在这里，我们提出了一个实验测量非共振R1ρ弛豫色散的鸟嘌呤- c2，鸟嘌呤- c6，胸腺嘧啶/尿嘧啶- c2和胸腺嘧啶/尿嘧啶- c4碳在均匀13C/15N标记的核酸。我们通过表征双工DNA中G•T不匹配的化学交换，在一个主要的摆动构象和两个低密度的、短寿命的、快速相互转换的沃森-克里克样互变异构态（Genol•T + G•Tenol）之间进行了实验，证明了该实验的效用。从鸟嘌呤- c6、鸟嘌呤- c2和胸腺嘧啶- c4非共振R1ρ弛豫色散谱中得到的居群和交换率与质子结合碳核和氮核的R1ρ测量结果非常吻合。次要态的碳化学位移相对于摆动基态向下移动，与(G)C6 = O··O-C4（Tenol）和（Genol）C6- oh··O=C4(T)在沃森-克里克样互变异构态中的氢键一致。作为第二个应用，我们没有检测到任何交换对uracil-C2和uracil-C4 R1ρ谱的贡献，用于测量RNA中的U·U错配，这与发生在亚微秒时间尺度上的两种可选摆动构象之间的异构化一致。这些结果建立了羰基和胍基碳作为有价值的探针的化学交换测量的微至毫秒运动的核酸。

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引用次数: 0

Effects of insufficient 31P pulse amplitudes on 13C-detected 31P13C rotational-echo double-resonance measurements in solid state NMR 固态核磁共振中31P脉冲幅值不足对13c检测31P13C旋转回波双共振测量的影响

IF 2 3区化学 Q3 BIOCHEMICAL RESEARCH METHODS

Journal of magnetic resonance

Pub Date : 2025-05-28 DOI: 10.1016/j.jmr.2025.107908

Motahareh G. Larimi, Robert Tycko

We investigate the effects of insufficient ³¹P pulse amplitudes on ¹³C-detected ³¹P¹³C Rotational-Echo Double-Resonance (REDOR) measurements in a 17.5 T magnetic field. Experimental REDOR data on two compounds show that normalized REDOR difference signals

Δ S / S_{0}

are suppressed when the amplitudes of ³¹P π pulse trains are not very large compared with the ³¹P chemical shift anisotropies. This behavior is explained theoretically by an analysis of the effects of imperfections in π pulse rotations due to the orientation-dependent and time-dependent resonance offsets under magic-angle spinning in REDOR measurements. We show that effects of the same pulse imperfections can be observed directly by measurements of an effective relaxation time

{T_{1}}^{eff}

for longitudinal ³¹P spin polarization under identical π pulse trains.

我们研究了在17.5 T磁场中，31P脉冲幅度不足对13c探测到的31P13C旋转回波双共振（REDOR）测量的影响。两种化合物的实验REDOR数据表明，当31P π脉冲序列的幅度不是很大时，归一化REDOR差分信号ΔS/S0被抑制。从理论上解释了这种行为，分析了在REDOR测量中，由于魔角旋转下的方向相关和时间相关的共振偏移，π脉冲旋转中的缺陷的影响。通过测量相同π脉冲序列下纵向31P自旋极化的有效弛豫时间T1eff，可以直接观察到相同脉冲缺陷的影响。

引用次数: 0