Enhancing the Sensitivity of Solid-State NMR Experiments with Very Low Gyromagnetic Ratio Nuclei with Fast Magic Angle Spinning
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Ames Laboratory Accepted Manuscripts Ames Laboratory 6-4-2018 Enhancing the Sensitivity of Solid-State NMR Experiments with Very Low Gyromagnetic Ratio Nuclei with Fast Magic Angle Spinning and Proton Detection Amrit Venkatesh Iowa State University and Ames Laboratory, [email protected] Matthew .J Ryan Iowa State University, [email protected] Abhranil Biswas Iowa State University, [email protected] Kasuni C. Boteju Iowa State University, [email protected] Aaron D. Sadow Iowa State University and Ames Laboratory, [email protected] See next page for additional authors Follow this and additional works at: https://lib.dr.iastate.edu/ameslab_manuscripts Part of the Physical Chemistry Commons, and the Radiochemistry Commons Recommended Citation Venkatesh, Amrit; Ryan, Matthew J.; Biswas, Abhranil; Boteju, Kasuni C.; Sadow, Aaron D.; and Rossini, Aaron J., "Enhancing the Sensitivity of Solid-State NMR Experiments with Very Low Gyromagnetic Ratio Nuclei with Fast Magic Angle Spinning and Proton Detection" (2018). Ames Laboratory Accepted Manuscripts. 194. https://lib.dr.iastate.edu/ameslab_manuscripts/194 This Article is brought to you for free and open access by the Ames Laboratory at Iowa State University Digital Repository. It has been accepted for inclusion in Ames Laboratory Accepted Manuscripts by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Enhancing the Sensitivity of Solid-State NMR Experiments with Very Low Gyromagnetic Ratio Nuclei with Fast Magic Angle Spinning and Proton Detection Abstract Many transition metals commonly encountered in inorganic materials and organometallic compounds possess NMR-active nuclei with very low gyromagnetic ratios (γ) such as 89Y, 103Rh, 109Ag, and 183W. A low-γ leads to poor NMR sensitivity and other experimental challenges. Consequently, nuclei with low-γ are often impossible to study with conventional solid-state NMR methods. Here, we combine fast magic angle spinning (MAS) and proton detection to enhance the sensitivity of solid-state NMR experiments with very low-γ nuclei by 1–2 orders of magnitude. Coherence transfer between 1H and low-γ nuclei was performed with low-power double quantum (DQ) or zero quantum (ZQ) cross-polarization (CP) or dipolar refocused insensitive nuclei enhanced by polarization transfer (D-RINEPT). Comparison of the absolute sensitivity of CP NMR experiments performed with proton detection with 1.3 mm rotors and direct detection with 4 mm rotors shows that proton detection with a 1.3 mm rotor provides a significant boost in absolute sensitivity, while requiring approximately 1/40th of the material required to fill a 4 mm rotor. Fast MAS and proton detection were applied to obtain 89Y and 103Rh solid-state NMR spectra of organometallic complexes. These results demonstrate that proton detection and fast MAS represents a general approach to enable and accelerate solid-state NMR experiments with very low-γ nuclei. Disciplines Chemistry | Physical Chemistry | Radiochemistry Authors Amrit Venkatesh, Matthew J. Ryan, Abhranil Biswas, Kasuni C. Boteju, Aaron D. Sadow, and Aaron J. Rossini This article is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/ameslab_manuscripts/194 Subscriber access provided by Iowa State University | Library A: Spectroscopy, Molecular Structure, and Quantum Chemistry Enhancing the Sensitivity of Solid-State NMR Experiments with Very Low-Gyromagnetic Ratio Nuclei with Fast MAS and Proton Detection Amrit Venkatesh, Matthew J. Ryan, Abhranil Biswas, Kasuni C. Boteju, Aaron D. Sadow, and Aaron J Rossini J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b05107 • Publication Date (Web): 04 Jun 2018 Downloaded from http://pubs.acs.org on June 5, 2018 Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. 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ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts. is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties. Page 1 of 27 The Journal of Physical Chemistry 1 2 3 4 5 6 7 Enhancing the Sensitivity of Solid-State NMR 8 9 10 11 Experiments with Very Low-Gyromagnetic Ratio 12 13 14 15 16 Nuclei with Fast MAS and Proton Detection 17 18 19 20 Amrit Venkatesh,1,2 Matthew J. Ryan,1 Abhranil Biswas,1 Kasuni C. Boteju,1 Aaron D. Sadow,1,2 Aaron J. 21 22 Rossini1,2* 23 24 25 1 26 Iowa State University, Department of Chemistry, Ames, IA, USA, 50011 27 28 2US DOE Ames Laboratory, Ames, Iowa, USA, 50011 29 30 31 32 33 34 35 36 37 38 39 AUTHOR INFORMATION 40 41 Corresponding Author 42 43 44 *e-mail: [email protected], phone: 515-294-8952. 45 46 47 48 49 50 51 52 53 54 55 56 57 58 1 59 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 2 of 27 1 2 3 4 Abstract 5 6 7 8 Many transition metals commonly encountered in inorganic materials and organometallic 9 10 compounds possess NMR-active nuclei with very low gyromagnetic ratios (γ) such as 89Y, 103Rh, 11 12 109Ag and 183W. A low-γ leads to poor NMR sensitivity and other experimental challenges. 13 14 15 Consequently, nuclei with low-γ are often impossible to study with conventional solid-state 16 17 NMR methods. Here, we combine fast magic angle spinning (MAS) and proton detection to 18 19 20 enhance the sensitivity of solid-state NMR experiments with very low-γ nuclei by one to two 21 1 22 orders of magnitude. Coherence transfer between H and low-γ nuclei was performed with low- 23 24 power double quantum (DQ) or zero quantum (ZQ) cross-polarization (CP) or dipolar refocused 25 26 27 insensitive nuclei enhanced by polarization transfer (D-RINEPT). Comparison of the absolute 28 29 sensitivity of CP NMR experiments performed with proton detection with 1.3 mm rotors and 30 31 direction detection with 4 mm rotors shows that proton detection with a 1.3 mm rotor provides a 32 33 significant boost in absolute sensitivity, while requiring approximately 1/40th of the material 34 35 89 36 required to fill a 4 mm rotor. Fast MAS and proton detection were applied to obtain Y and 37 38 103Rh solid-state NMR spectra of organometallic complexes. These results demonstrate that 39 40 proton detection and fast MAS represents a general approach to enable and accelerate solid-state 41 42 43 NMR experiments with very low-γ nuclei. 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 2 59 60 ACS Paragon Plus Environment Page 3 of 27 The Journal of Physical Chemistry 1 2 3 Introduction 4 5 6 Solid-state NMR spectroscopy is a powerful tool for the study of inorganic materials 7 1-3 8 because it can potentially be applied to nearly all of the elements in the periodic table. 9 10 However, many elements have unfavorable properties for NMR spectroscopy such as low natural 11 12 abundance, large quadrupole moments (for quadrupolar nuclei with spin I > ½) and low 13 14 15 15 gyromagnetic ratios (γ and Larmor frequency below that of N). For example, the transition 16 17 metals silver, tungsten, yttrium and rhodium all possess highly abundant NMR-active isotopes 18 19 4 20 with very low-γ (Table S1). 21 22 Unfortunately, nuclei with a low-γ are often very difficult to observe and manipulate in 23 24 NMR experiments because γ determines the Larmor frequency (ν0 = γB0), the radiofrequency 25 26 27 (RF) field (ν1 = γB1), the equilibrium nuclear magnetization and the magnitude of the induced 28 29 NMR signal (NMR sensitivity ∝ γ3/2).5 Furthermore, NMR experiments with low-γ nuclei are 30 31 32 generally impeded by additional factors such as long longitudinal relaxation times (T1), acoustic 33 34 ringing, poor coherence transfer efficiency, etc. The sensitivity of solid-state NMR experiments 35 36 with low-γ nuclei has been improved by using cross polarization (CP)6 to transfer the 37 38 19 1 39 polarization from high-γ nuclei such as F or H to the low-γ nucleus. For example, Merwin and 40 109 89 183 41 Sebald applied CP to enhance sensitivity and obtain direct detection Ag, Y and W CP 42 43 magic angle spinning (CPMAS) solid-state NMR spectra.7-9 However, CP experiments with low- 44 45 γ nuclei often require extremely long contact times in excess of 30 ms that lead to very high 46 47 9 48 probe duty cycles.