Pub Date : 2025-03-30DOI: 10.1016/j.jmr.2025.107873
Ivan Argatov, Vitaly Kocherbitov
A two-site magnetic exchange model comprising a set of two linear first-order differential Bloch–McConnell equations is considered. The relaxation and exchange behavior is described using a symmetrical form of the general solution derived in the case of longitudinal magnetization for the zero initial conditions. The inverse problem with limited magnetization information has been solved exactly in an analytical explicit form under mild a priori knowledge about the exchange and relaxation parameters.
{"title":"Exact solution of the parameter identification inverse problem for the Bloch–McConnell equations. Longitudinal magnetization","authors":"Ivan Argatov, Vitaly Kocherbitov","doi":"10.1016/j.jmr.2025.107873","DOIUrl":"10.1016/j.jmr.2025.107873","url":null,"abstract":"<div><div>A two-site magnetic exchange model comprising a set of two linear first-order differential Bloch–McConnell equations is considered. The relaxation and exchange behavior is described using a symmetrical form of the general solution derived in the case of longitudinal magnetization for the zero initial conditions. The inverse problem with limited magnetization information has been solved exactly in an analytical explicit form under mild <em>a priori</em> knowledge about the exchange and relaxation parameters.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"375 ","pages":"Article 107873"},"PeriodicalIF":2.0,"publicationDate":"2025-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143760667","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-28DOI: 10.1016/j.jmr.2025.107875
Ke Xu, Jörn Schmedt auf der Günne
Nuclear magnetic resonance (NMR) is a routine method to study chemical exchange in reactions and molecular rearrangements in solution. However, when it comes to exchange of molecular species in liquid-liquid, two phase systems like in phase-transfer catalysis, the rate becomes a function of the surface area between two phases, which means that only persistent emulsions could be studied with standard equipment. Unstable emulsions, which rapidly demix, require a continuous application of shear forces by stirring. Here, a setup is described with which unstable emulsions can be produced and studied in-situ by solution NMR spectroscopy. The setup provides sufficient torque and spinning frequency for generating an unstable two-phase water/oil mixture by rapid stirring. The pneumatically driven stirrer in the probe head was designed using ideas borrowed from magic angle sample spinning and a prototype was produced by 3D printing. As proof of concept, the dynamics in an aniline water emulsion over the phase boundary are studied by regular exchange spectroscopy NMR experiments.
{"title":"Chemical exchange in unstable emulsions","authors":"Ke Xu, Jörn Schmedt auf der Günne","doi":"10.1016/j.jmr.2025.107875","DOIUrl":"10.1016/j.jmr.2025.107875","url":null,"abstract":"<div><div>Nuclear magnetic resonance (NMR) is a routine method to study chemical exchange in reactions and molecular rearrangements in solution. However, when it comes to exchange of molecular species in liquid-liquid, two phase systems like in phase-transfer catalysis, the rate becomes a function of the surface area between two phases, which means that only persistent emulsions could be studied with standard equipment. Unstable emulsions, which rapidly demix, require a continuous application of shear forces by stirring. Here, a setup is described with which unstable emulsions can be produced and studied in-situ by solution NMR spectroscopy. The setup provides sufficient torque and spinning frequency for generating an unstable two-phase water/oil mixture by rapid stirring. The pneumatically driven stirrer in the probe head was designed using ideas borrowed from magic angle sample spinning and a prototype was produced by 3D printing. As proof of concept, the dynamics in an aniline water emulsion over the phase boundary are studied by regular exchange spectroscopy NMR experiments.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"375 ","pages":"Article 107875"},"PeriodicalIF":2.0,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143746888","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-28DOI: 10.1016/j.jmr.2025.107874
Noella D'Souza , Kieren A. Harkins , Cooper Selco , Ushoshi Basumallick , Samantha Breuer , Zhuorui Zhang , Paul Reshetikhin , Marcus Ho , Aniruddha Nayak , Maxwell McAllister , Emanuel Druga , David Marchiori , Ashok Ajoy
Optical dynamic nuclear polarization (DNP) offers an attractive approach to enhancing the sensitivity of nuclear magnetic resonance (NMR) spectroscopy. Efficient, optically-generated electron polarization can be leveraged to operate across a broad range of temperatures and magnetic fields, making it particularly appealing for applications requiring high DNP efficiency or spatial resolution. While a large class of systems hold promise for optical DNP, many candidates display both variable electron polarizability and electron and nuclear T1 relaxation times as functions of magnetic field and temperature. This necessitates tools capable of studying DNP under diverse experimental conditions. To address this, we introduce a cryogenic field cycling instrument that facilitates optical DNP studies across a wide range of magnetic fields (10 mT–9.4 T) and temperatures (∼10 K–300 K) for wide-bore magnets. Continuous cryogen replenishment enables sustained, long-term operation. Additionally, the system supports the ability to manipulate and probe rapidly hyperpolarized (∼60 s) nuclear spins via pulse sequences involving millions of RF pulses. We describe innovations in the device design and demonstrate its operation on a model system of 13C nuclear spins in diamond polarized through optically pumped nitrogen vacancy (NV) centers. We anticipate the use of the instrument for a broad range of optical DNP systems and studies.
光学动态核极化（DNP）是提高核磁共振（NMR）光谱灵敏度的一种有吸引力的方法。利用高效的光学产生的电子极化可以在广泛的温度和磁场范围内工作，这使得它对需要高DNP效率或空间分辨率的应用特别有吸引力。虽然一大类系统有望实现光学DNP，但许多候选系统显示出可变的电子极化率以及电子和核T1弛豫时间作为磁场和温度的函数。这就需要能够在不同实验条件下研究DNP的工具。为了解决这个问题，我们引入了一种低温场循环仪器，该仪器有助于在宽口径磁体的大范围磁场（10 mT-9.4 T）和温度（~ 10 K - 300 K）下进行光学DNP研究。持续的冷冻剂补充可以保证持续、长期的运行。此外，该系统支持通过涉及数百万RF脉冲的脉冲序列操纵和探测快速超极化（~ 60秒）核自旋的能力。我们描述了器件设计上的创新，并在一个通过光泵浦氮空位中心偏振的金刚石13C核自旋模型系统上演示了其操作。我们期望将该仪器用于广泛的光学DNP系统和研究。
{"title":"Cryogenic field-cycling instrument for optical NMR hyperpolarization studies","authors":"Noella D'Souza , Kieren A. Harkins , Cooper Selco , Ushoshi Basumallick , Samantha Breuer , Zhuorui Zhang , Paul Reshetikhin , Marcus Ho , Aniruddha Nayak , Maxwell McAllister , Emanuel Druga , David Marchiori , Ashok Ajoy","doi":"10.1016/j.jmr.2025.107874","DOIUrl":"10.1016/j.jmr.2025.107874","url":null,"abstract":"<div><div>Optical dynamic nuclear polarization (DNP) offers an attractive approach to enhancing the sensitivity of nuclear magnetic resonance (NMR) spectroscopy. Efficient, optically-generated electron polarization can be leveraged to operate across a broad range of temperatures and magnetic fields, making it particularly appealing for applications requiring high DNP efficiency or spatial resolution. While a large class of systems hold promise for optical DNP, many candidates display both variable electron polarizability and electron and nuclear <em>T</em><sub>1</sub> relaxation times as functions of magnetic field and temperature. This necessitates tools capable of studying DNP under diverse experimental conditions. To address this, we introduce a cryogenic field cycling instrument that facilitates optical DNP studies across a wide range of magnetic fields (10 mT–9.4 T) and temperatures (∼10 K–300 K) for wide-bore magnets. Continuous cryogen replenishment enables sustained, long-term operation. Additionally, the system supports the ability to manipulate and probe rapidly hyperpolarized (∼60 s) nuclear spins via pulse sequences involving millions of RF pulses. We describe innovations in the device design and demonstrate its operation on a model system of <sup>13</sup>C nuclear spins in diamond polarized through optically pumped nitrogen vacancy (NV) centers. We anticipate the use of the instrument for a broad range of optical DNP systems and studies.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"375 ","pages":"Article 107874"},"PeriodicalIF":2.0,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143814904","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}
Pub Date : 2025-03-21DOI: 10.1016/j.jmr.2025.107841
Aleksandr Fedotov , Pavel Tikhonov , Viktor Puchnin , Ekaterina Brui , Anatoliy Levchuk , Ayshat Karaeva , Alena Shchelokova , Georgiy Solomakha , Anna Hurshkainen
Wireless radio frequency coils offer an alternative to conventional cable-connected coils due to their compatibility with multiple vendor MRI systems and reduced electromagnetic interaction with the environment of the MRI scanner. However, wireless coils being inductively coupled with a transceiver body coil require manual input power calibration due to the significant increase of a body coil transmit efficiency locally in the region of interest and disturbance of homogeneity complicating routine scanning procedures. This study aims to implement the concept of a wireless receive-only coil for female breast MRI at 1.5T. The approach combines the advantages of wireless coils to increase signal to noise ratio of transceiver body coil in the target region of interest and the ability to perform the automatic reference voltage calibration.
{"title":"A concept of volume wireless receive-only coil for 1.5T MRI","authors":"Aleksandr Fedotov , Pavel Tikhonov , Viktor Puchnin , Ekaterina Brui , Anatoliy Levchuk , Ayshat Karaeva , Alena Shchelokova , Georgiy Solomakha , Anna Hurshkainen","doi":"10.1016/j.jmr.2025.107841","DOIUrl":"10.1016/j.jmr.2025.107841","url":null,"abstract":"<div><div>Wireless radio frequency coils offer an alternative to conventional cable-connected coils due to their compatibility with multiple vendor MRI systems and reduced electromagnetic interaction with the environment of the MRI scanner. However, wireless coils being inductively coupled with a transceiver body coil require manual input power calibration due to the significant increase of a body coil transmit efficiency locally in the region of interest and disturbance of <span><math><msubsup><mrow><mi>B</mi></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math></span> homogeneity complicating routine scanning procedures. This study aims to implement the concept of a wireless receive-only coil for female breast MRI at 1.5T. The approach combines the advantages of wireless coils to increase signal to noise ratio of transceiver body coil in the target region of interest and the ability to perform the automatic reference voltage calibration.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"374 ","pages":"Article 107841"},"PeriodicalIF":2.0,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143716197","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}
Pub Date : 2025-03-18DOI: 10.1016/j.jmr.2025.107866
Selina Eckel , Julian Nagel , Mazin Jouda , Jan Gerrit Korvink , Ahmet Çağrı Ulusoy
In broadband transmission-based electron paramagnetic resonance (EPR) spectrometers, non-resonant planar microwave probes play a key role, but very few systematic explorations of their design space exist. We develop design guidelines for two common types of transmission lines, microstrip and coplanar waveguide, to achieve a high effective microwave magnetic field strength, which ultimately leads to a more sensitive EPR measurement set-up. We compare the optimized transmission line structures and show that the coplanar waveguide achieves a higher simulated effective magnetic field strength. The simulation results are confirmed by EPR measurements up to a microwave frequency of 45 GHz.
{"title":"Design of planar transmission line microwave probes for broadband EPR spectroscopy","authors":"Selina Eckel , Julian Nagel , Mazin Jouda , Jan Gerrit Korvink , Ahmet Çağrı Ulusoy","doi":"10.1016/j.jmr.2025.107866","DOIUrl":"10.1016/j.jmr.2025.107866","url":null,"abstract":"<div><div>In broadband transmission-based electron paramagnetic resonance (EPR) spectrometers, non-resonant planar microwave probes play a key role, but very few systematic explorations of their design space exist. We develop design guidelines for two common types of transmission lines, microstrip and coplanar waveguide, to achieve a high effective microwave magnetic field strength, which ultimately leads to a more sensitive EPR measurement set-up. We compare the optimized transmission line structures and show that the coplanar waveguide achieves a higher simulated effective magnetic field strength. The simulation results are confirmed by EPR measurements up to a microwave frequency of 45<!--> <!-->GHz.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"374 ","pages":"Article 107866"},"PeriodicalIF":2.0,"publicationDate":"2025-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684075","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-11DOI: 10.1016/j.jmr.2025.107863
Yishay Manassen , Michael Averbukh , Zion Hazan , Yahel Tzuriel , Pino Boscolo , Alexander Shnirman , Baruch Horovitz
We detect a single spin nuclear magnetic resonance (NMR) by monitoring the intensity modulations of a selected hyperfine line in the electron spin resonance (ESR) spectrum. We analyse the power spectrum of the corresponding hyperfine intensity and obtain the nuclear magnetic resonance (NMR) spectrum. Our process also demonstrates ionization of a molecule with the bias voltage of a Scanning Tunnelling Microscope (STM), allowing detection of NMR even in molecules that are non-radical in their neutral state. We have observed this phenomenon in four types of molecules: toluene, triphenylphosphine, TEMPO and adenosine triphosphate (ATP) showing NMR of H, 13C, 31P and 14N nuclei. The spectra are detailed and show signatures of the chemical environment, i.e. chemical shifts. A theoretical model to account for these data is outlined.
{"title":"NMR of a single nuclear spin detected by a scanning tunnelling microscope","authors":"Yishay Manassen , Michael Averbukh , Zion Hazan , Yahel Tzuriel , Pino Boscolo , Alexander Shnirman , Baruch Horovitz","doi":"10.1016/j.jmr.2025.107863","DOIUrl":"10.1016/j.jmr.2025.107863","url":null,"abstract":"<div><div>We detect a single spin nuclear magnetic resonance (NMR) by monitoring the intensity modulations of a selected hyperfine line in the electron spin resonance (ESR) spectrum. We analyse the power spectrum of the corresponding hyperfine intensity and obtain the nuclear magnetic resonance (NMR) spectrum. Our process also demonstrates ionization of a molecule with the bias voltage of a Scanning Tunnelling Microscope (STM), allowing detection of NMR even in molecules that are non-radical in their neutral state. We have observed this phenomenon in four types of molecules: toluene, triphenylphosphine, TEMPO and adenosine triphosphate (ATP) showing NMR of <span><math><msup><mrow></mrow><mrow><mn>1</mn></mrow></msup></math></span>H, <sup>13</sup>C, <sup>31</sup>P and <sup>14</sup>N nuclei. The spectra are detailed and show signatures of the chemical environment, i.e. chemical shifts. A theoretical model to account for these data is outlined.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"374 ","pages":"Article 107863"},"PeriodicalIF":2.0,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143628443","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High-field nuclear magnetic resonance (NMR) experiments call for the further development of pulsed magnets with a more practical winding structure and higher magnetic field homogeneity. This study presents the construction method and test results of a high-homogeneity pulsed magnet based on an optimized localized split structure. A winding craft using gap spacers was developed for the precise winding of split-gap transition wires. Magnetic field mapping was achieved in a steady-state low field of 32 mT using a Hall probe, with a measured magnetic field inhomogeneity of 198 ± 19 ppm over 1 cm diameter of spherical volume (DSV). The full-width at half-maximum (FWHM) of NMR spectra was adopted as a means of evaluating the magnetic field homogeneity in the pulsed field. In the optimal position, the measured FWHM is 42.2 ± 2.5 ppm at the low field of 7.7 T over a sample volume of 12.6 mm3. At the high field of 50 T, the FWHM decreases to 16.2 ± 0.8 ppm, which is a superior value achieved in similar reported pulsed magnets.
{"title":"Construction and testing of a high-homogeneity 55 T pulsed magnet for high-field nuclear magnetic resonance measurements","authors":"Wenqi Wei, Luchen Wei, Shunkun Ouyang, Kangjian Luo, Zhuo Wang, Shiyu Liu, Yongkang Luo, Xiaotao Han","doi":"10.1016/j.jmr.2025.107862","DOIUrl":"10.1016/j.jmr.2025.107862","url":null,"abstract":"<div><div>High-field nuclear magnetic resonance (NMR) experiments call for the further development of pulsed magnets with a more practical winding structure and higher magnetic field homogeneity. This study presents the construction method and test results of a high-homogeneity pulsed magnet based on an optimized localized split structure. A winding craft using gap spacers was developed for the precise winding of split-gap transition wires. Magnetic field mapping was achieved in a steady-state low field of 32 mT using a Hall probe, with a measured magnetic field inhomogeneity of 198 ± 19 ppm over 1 cm diameter of spherical volume (DSV). The full-width at half-maximum (FWHM) of NMR spectra was adopted as a means of evaluating the magnetic field homogeneity in the pulsed field. In the optimal position, the measured FWHM is 42.2 ± 2.5 ppm at the low field of 7.7 T over a sample volume of 12.6 mm<sup>3</sup>. At the high field of 50 T, the FWHM decreases to 16.2 ± 0.8 ppm, which is a superior value achieved in similar reported pulsed magnets.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"374 ","pages":"Article 107862"},"PeriodicalIF":2.0,"publicationDate":"2025-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143593396","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}
Pub Date : 2025-03-07DOI: 10.1016/j.jmr.2025.107861
J.W. Zwanziger, A.R. Farrant, U. Werner-Zwanziger
For computing the magnetic shielding in solids, density functional theory as implemented in a plane wave basis has proven to be a reasonably accurate and efficient framework, at least for lighter atoms through the third row of the periodic table. In materials with heavier atoms, terms not usually included in the electronic Hamiltonian can become significant, limiting accuracy. Here we derive and implement the zeroth-order regular approximation (ZORA) relativistic terms in the presence of both external magnetic fields and internal nuclear magnetic dipoles, to derive the ZORA-corrected magnetic shielding in the context of periodic boundary conditions and a plane wave basis. We describe our implementation in an open source code, Abinit, and show how it correctly predicts magnetic shieldings in various scenarios, for example the heavy atom next to light atom cases of the III–V semiconductors such as AlSb.
{"title":"Relativistic effects on the magnetic shielding in solids: First-principles computation in a plane wave code","authors":"J.W. Zwanziger, A.R. Farrant, U. Werner-Zwanziger","doi":"10.1016/j.jmr.2025.107861","DOIUrl":"10.1016/j.jmr.2025.107861","url":null,"abstract":"<div><div>For computing the magnetic shielding in solids, density functional theory as implemented in a plane wave basis has proven to be a reasonably accurate and efficient framework, at least for lighter atoms through the third row of the periodic table. In materials with heavier atoms, terms not usually included in the electronic Hamiltonian can become significant, limiting accuracy. Here we derive and implement the zeroth-order regular approximation (ZORA) relativistic terms in the presence of both external magnetic fields and internal nuclear magnetic dipoles, to derive the ZORA-corrected magnetic shielding in the context of periodic boundary conditions and a plane wave basis. We describe our implementation in an open source code, <span>Abinit</span>, and show how it correctly predicts magnetic shieldings in various scenarios, for example the heavy atom next to light atom cases of the III–V semiconductors such as AlSb.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"374 ","pages":"Article 107861"},"PeriodicalIF":2.0,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143578012","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}
Pub Date : 2025-03-07DOI: 10.1016/j.jmr.2025.107864
Dominique Lagasca , Rupam Ghosh , Yiling Xiao , Kendra K. Frederick
Dynamic nuclear polarization (DNP) solid-state NMR enables detection of proteins inside cells through sensitivity enhancement from nitroxide biradical polarization agents. AsymPolPOK, a novel water-soluble asymmetric nitroxide biradical, offers superior sensitivity and faster build-up times compared to existing agents like AMUPol. Here, we characterize AsymPolPOK's behavior in mammalian HEK293 cells, examining its cellular distribution, reduction kinetics, and DNP performance. We demonstrate that electroporation achieves uniform cellular delivery of AsymPolPOK, including nuclear permeation, with no cytotoxicity at millimolar concentrations. However, the cellular environment rapidly reduces AsymPolPOK to its monoradical form, with one nitroxide center showing greater reduction resistance than the other. While AsymPolPOK maintains high DNP enhancements and short build-up times in lysates, its performance in intact cells depends critically on delivery method and exposure time to cellular constituents. Electroporation yields higher, more uniform enhancements compared to incubation, but prolonged exposure to the cellular environment diminishes DNP performance in both cases. These findings establish AsymPolPOK's potential for in-cell DNP NMR while highlighting the need for developing more bio-resistant polarization agents to further advance cellular structural biology studies.
{"title":"Stability of the polarization agent AsymPolPOK in intact and lysed mammalian cells","authors":"Dominique Lagasca , Rupam Ghosh , Yiling Xiao , Kendra K. Frederick","doi":"10.1016/j.jmr.2025.107864","DOIUrl":"10.1016/j.jmr.2025.107864","url":null,"abstract":"<div><div>Dynamic nuclear polarization (DNP) solid-state NMR enables detection of proteins inside cells through sensitivity enhancement from nitroxide biradical polarization agents. AsymPolPOK, a novel water-soluble asymmetric nitroxide biradical, offers superior sensitivity and faster build-up times compared to existing agents like AMUPol. Here, we characterize AsymPolPOK's behavior in mammalian HEK293 cells, examining its cellular distribution, reduction kinetics, and DNP performance. We demonstrate that electroporation achieves uniform cellular delivery of AsymPolPOK, including nuclear permeation, with no cytotoxicity at millimolar concentrations. However, the cellular environment rapidly reduces AsymPolPOK to its monoradical form, with one nitroxide center showing greater reduction resistance than the other. While AsymPolPOK maintains high DNP enhancements and short build-up times in lysates, its performance in intact cells depends critically on delivery method and exposure time to cellular constituents. Electroporation yields higher, more uniform enhancements compared to incubation, but prolonged exposure to the cellular environment diminishes DNP performance in both cases. These findings establish AsymPolPOK's potential for in-cell DNP NMR while highlighting the need for developing more bio-resistant polarization agents to further advance cellular structural biology studies.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"374 ","pages":"Article 107864"},"PeriodicalIF":2.0,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143601469","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}
Pub Date : 2025-03-06DOI: 10.1016/j.jmr.2025.107865
Ajeak Vigneswaran , Tanner A. Buschmann , Michael P. Latham
Side-chain methyl group NMR spectroscopy provides invaluable insights into macromolecular structure, dynamics, and function, particularly for large biomolecular complexes. Accurate assignment of methyl group resonances in two-dimensional spectra is essential for structural and dynamics studies. Traditional methyl group assignment strategies rely on either transferring assignments from backbone resonance data or NOESY data and high-resolution experimental structures; however, these methods are often limited by molecular size or availability of structural information, respectively. Here, we describe the use of AlphaFold2 structural models as a basis for the manual, distance-based assignment of side-chain methyl group resonances in the folded domains of S. cerevisiae Xrs2. While AlphaFold2 models facilitated initial assignments for the methyl resonances, inaccuracies in the side-chain coordinates highlighted the need for improved structural models. By generating >500 ColabFold-derived models and filtering with methyl residual dipolar couplings (RDCs), we identified structural models with superior agreement to experimental data. These refined models enabled additional methyl group assignments while suggesting an iterative approach to simultaneously improve structure prediction and resonance assignment. Our findings outline a workflow that integrates machine learning-based structural predictions with experimental NMR data, offering a pathway for advancing methyl group assignment in systems lacking high-resolution experimental structures.
{"title":"Leveraging AlphaFold2 and residual dipolar couplings for side-chain methyl group assignment: A case study with S. cerevisiae Xrs2","authors":"Ajeak Vigneswaran , Tanner A. Buschmann , Michael P. Latham","doi":"10.1016/j.jmr.2025.107865","DOIUrl":"10.1016/j.jmr.2025.107865","url":null,"abstract":"<div><div>Side-chain methyl group NMR spectroscopy provides invaluable insights into macromolecular structure, dynamics, and function, particularly for large biomolecular complexes. Accurate assignment of methyl group resonances in two-dimensional spectra is essential for structural and dynamics studies. Traditional methyl group assignment strategies rely on either transferring assignments from backbone resonance data or NOESY data and high-resolution experimental structures; however, these methods are often limited by molecular size or availability of structural information, respectively. Here, we describe the use of AlphaFold2 structural models as a basis for the manual, distance-based assignment of side-chain methyl group resonances in the folded domains of <em>S. cerevisiae</em> Xrs2. While AlphaFold2 models facilitated initial assignments for the methyl resonances, inaccuracies in the side-chain coordinates highlighted the need for improved structural models. By generating >500 ColabFold-derived models and filtering with methyl residual dipolar couplings (RDCs), we identified structural models with superior agreement to experimental data. These refined models enabled additional methyl group assignments while suggesting an iterative approach to simultaneously improve structure prediction and resonance assignment. Our findings outline a workflow that integrates machine learning-based structural predictions with experimental NMR data, offering a pathway for advancing methyl group assignment in systems lacking high-resolution experimental structures.</div></div>","PeriodicalId":16267,"journal":{"name":"Journal of magnetic resonance","volume":"374 ","pages":"Article 107865"},"PeriodicalIF":2.0,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143578011","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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