{"title":"Heteronuclear Polarization Transfer under Steady-State Conditions: The INEPT-SSFP Experiment","authors":"Rihards Aleksis, Elton T. Montrazi, Lucio Frydman","doi":"10.1021/acs.jpclett.4c02016","DOIUrl":null,"url":null,"abstract":"NMR finds a wide range of applications, ranging from fundamental chemistry to medical imaging. The technique, however, has an inherently low signal-to-noise ratio (SNR)─particularly when dealing with nuclei having low natural abundances and/or low γs. In these cases, sensitivity is often enhanced by methods that, similar to INEPT, transfer polarization from neighboring <sup>1</sup>Hs via <i>J</i>-couplings. In 1958, Carr proposed an alternative approach to increase NMR sensitivity, which involves generating and continuously detecting a steady-state transverse magnetization, by applying a train of pulses on an ensemble of noninteracting spins. This study broadens Carr’s steady-state free precession (SSFP) framework to encompass the possibility of adding onto it coherent polarization transfers, allowing one to combine the SNR-enhancing benefits of both INEPT and SSFP into a single experiment. Herein, the derivation of the ensuing INEPT-SSFP (ISSFP) sequences is reported. Their use in <sup>13</sup>C NMR and MRI experiments leads to ca. 300% improvements in SNR/ <i></i><span style=\"color: inherit;\"></span><span data-mathml='<math xmlns=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\" overflow=\"scroll\"><msqrt><mrow><mi mathvariant=\"normal\">unit time</mi></mrow></msqrt></math>' role=\"presentation\" style=\"position: relative;\" tabindex=\"0\"><nobr aria-hidden=\"true\"><span overflow=\"scroll\" style=\"width: 5.003em; display: inline-block;\"><span style=\"display: inline-block; position: relative; width: 4.548em; height: 0px; font-size: 110%;\"><span style=\"position: absolute; clip: rect(1.026em, 1004.55em, 2.616em, -999.997em); top: -2.156em; left: 0em;\"><span><span><span style=\"display: inline-block; position: relative; width: 4.548em; height: 0px;\"><span style=\"position: absolute; clip: rect(3.128em, 1003.58em, 4.151em, -999.997em); top: -3.974em; left: 0.912em;\"><span><span><span style=\"font-family: STIXMathJax_Main;\">unit time</span></span></span><span style=\"display: inline-block; 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width: 0px; height: 3.98em;\"></span></span></span></span></span><span style=\"display: inline-block; width: 0px; height: 2.162em;\"></span></span></span><span style=\"display: inline-block; overflow: hidden; vertical-align: -0.372em; border-left: 0px solid; width: 0px; height: 1.503em;\"></span></span></nobr><span role=\"presentation\"><math display=\"inline\" overflow=\"scroll\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><msqrt><mrow><mi mathvariant=\"normal\">unit time</mi></mrow></msqrt></math></span></span><script type=\"math/mml\"><math display=\"inline\" overflow=\"scroll\"><msqrt><mrow><mi mathvariant=\"normal\">unit time</mi></mrow></msqrt></math></script> over conventional <i>J</i>-driven polarization transfer experiments, and sensitivity gains of over 50% over <sup>13</sup>C SSFP performed in combination with <sup>1</sup>H decoupling and NOE. These enhancements match well with numerical simulations and analytical evaluations. The conditions needed to optimize these new methods in both spectroscopic and imaging studies are discussed; we also examine their limitations, and the valuable vistas that, in both analytical and molecular imaging NMR, could be opened by this development.","PeriodicalId":62,"journal":{"name":"The Journal of Physical Chemistry Letters","volume":null,"pages":null},"PeriodicalIF":4.8000,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"The Journal of Physical Chemistry Letters","FirstCategoryId":"1","ListUrlMain":"https://doi.org/10.1021/acs.jpclett.4c02016","RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
引用次数: 0
Abstract
NMR finds a wide range of applications, ranging from fundamental chemistry to medical imaging. The technique, however, has an inherently low signal-to-noise ratio (SNR)─particularly when dealing with nuclei having low natural abundances and/or low γs. In these cases, sensitivity is often enhanced by methods that, similar to INEPT, transfer polarization from neighboring 1Hs via J-couplings. In 1958, Carr proposed an alternative approach to increase NMR sensitivity, which involves generating and continuously detecting a steady-state transverse magnetization, by applying a train of pulses on an ensemble of noninteracting spins. This study broadens Carr’s steady-state free precession (SSFP) framework to encompass the possibility of adding onto it coherent polarization transfers, allowing one to combine the SNR-enhancing benefits of both INEPT and SSFP into a single experiment. Herein, the derivation of the ensuing INEPT-SSFP (ISSFP) sequences is reported. Their use in 13C NMR and MRI experiments leads to ca. 300% improvements in SNR/ unit time⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯√ over conventional J-driven polarization transfer experiments, and sensitivity gains of over 50% over 13C SSFP performed in combination with 1H decoupling and NOE. These enhancements match well with numerical simulations and analytical evaluations. The conditions needed to optimize these new methods in both spectroscopic and imaging studies are discussed; we also examine their limitations, and the valuable vistas that, in both analytical and molecular imaging NMR, could be opened by this development.
期刊介绍:
The Journal of Physical Chemistry (JPC) Letters is devoted to reporting new and original experimental and theoretical basic research of interest to physical chemists, biophysical chemists, chemical physicists, physicists, material scientists, and engineers. An important criterion for acceptance is that the paper reports a significant scientific advance and/or physical insight such that rapid publication is essential. Two issues of JPC Letters are published each month.