Overhauser Dynamic Nuclear Polarization with Selectively Deuterated BDPA Radicals
The Overhauser effect (OE), commonly observed in NMR spectra of liquids and conducting solids, was recently discovered in insulating solids doped with the radical 1,3-bisdiphenylene-2-phenylallyl (BDPA). However, the mechanism of polarization transfer in OE-DNP in insulators is yet to be established...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
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American Chemical Society (ACS)
2022
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| Online Access: | https://hdl.handle.net/1721.1/141332 |
| _version_ | 1826194279240826880 |
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| author | Delage-Laurin, Léo Palani, Ravi Shankar Golota, Natalie Mardini, Michael Ouyang, Yifu Tan, Kong Ooi Swager, Timothy M Griffin, Robert G |
| author_facet | Delage-Laurin, Léo Palani, Ravi Shankar Golota, Natalie Mardini, Michael Ouyang, Yifu Tan, Kong Ooi Swager, Timothy M Griffin, Robert G |
| author_sort | Delage-Laurin, Léo |
| collection | MIT |
| description | The Overhauser effect (OE), commonly observed in NMR spectra of liquids and conducting solids, was recently discovered in insulating solids doped with the radical 1,3-bisdiphenylene-2-phenylallyl (BDPA). However, the mechanism of polarization transfer in OE-DNP in insulators is yet to be established, but hyperfine coupling of the radical to protons in BDPA has been proposed. In this paper we present a study that addresses the role of hyperfine couplings via the EPR and DNP measurements on some selectively deuterated BDPA radicals synthesized for this purpose. Newly developed synthetic routes enable selective deuteration at orthogonal positions or perdeuteration of the fluorene moieties with 2H incorporation of >93%. The fluorene moieties were subsequently used to synthesize two octadeuterated BDPA radicals, 1,3-[α,γ-d8]-BDPA and 1,3-[β,δ-d8]-BDPA, and a BDPA radical with perdeuterated fluorene moieties, 1,3-[α,β,γ,δ-d16]-BDPA. In contrast to the strong positive OE enhancement observed in degassed samples of fully protonated h21-BDPA (ε ∼ +70), perdeuteration of the fluorenes results in a negative enhancement (ε ∼ -13), while selective deuteration of α- and γ-positions (aiso ∼ 5.4 MHz) in BDPA results in a weak negative OE enhancement (ε ∼ -1). Furthermore, deuteration of β- and δ-positions (aiso ∼ 1.2 MHz) results in a positive OE enhancement (ε ∼ +36), albeit with a reduced magnitude relative to that observed in fully protonated BDPA. Our results clearly show the role of the hyperfine coupled α and γ 1H spins in the BDPA radical in determining the dominance of the zero and double-quantum cross-relaxation pathways and the polarization-transfer mechanism to the bulk matrix. |
| first_indexed | 2024-09-23T09:53:37Z |
| format | Article |
| id | mit-1721.1/141332 |
| institution | Massachusetts Institute of Technology |
| language | English |
| last_indexed | 2024-09-23T09:53:37Z |
| publishDate | 2022 |
| publisher | American Chemical Society (ACS) |
| record_format | dspace |
| spelling | mit-1721.1/1413322022-03-22T03:34:06Z Overhauser Dynamic Nuclear Polarization with Selectively Deuterated BDPA Radicals Delage-Laurin, Léo Palani, Ravi Shankar Golota, Natalie Mardini, Michael Ouyang, Yifu Tan, Kong Ooi Swager, Timothy M Griffin, Robert G The Overhauser effect (OE), commonly observed in NMR spectra of liquids and conducting solids, was recently discovered in insulating solids doped with the radical 1,3-bisdiphenylene-2-phenylallyl (BDPA). However, the mechanism of polarization transfer in OE-DNP in insulators is yet to be established, but hyperfine coupling of the radical to protons in BDPA has been proposed. In this paper we present a study that addresses the role of hyperfine couplings via the EPR and DNP measurements on some selectively deuterated BDPA radicals synthesized for this purpose. Newly developed synthetic routes enable selective deuteration at orthogonal positions or perdeuteration of the fluorene moieties with 2H incorporation of >93%. The fluorene moieties were subsequently used to synthesize two octadeuterated BDPA radicals, 1,3-[α,γ-d8]-BDPA and 1,3-[β,δ-d8]-BDPA, and a BDPA radical with perdeuterated fluorene moieties, 1,3-[α,β,γ,δ-d16]-BDPA. In contrast to the strong positive OE enhancement observed in degassed samples of fully protonated h21-BDPA (ε ∼ +70), perdeuteration of the fluorenes results in a negative enhancement (ε ∼ -13), while selective deuteration of α- and γ-positions (aiso ∼ 5.4 MHz) in BDPA results in a weak negative OE enhancement (ε ∼ -1). Furthermore, deuteration of β- and δ-positions (aiso ∼ 1.2 MHz) results in a positive OE enhancement (ε ∼ +36), albeit with a reduced magnitude relative to that observed in fully protonated BDPA. Our results clearly show the role of the hyperfine coupled α and γ 1H spins in the BDPA radical in determining the dominance of the zero and double-quantum cross-relaxation pathways and the polarization-transfer mechanism to the bulk matrix. 2022-03-21T18:30:39Z 2022-03-21T18:30:39Z 2021-12-08 2022-03-21T18:15:29Z Article http://purl.org/eprint/type/JournalArticle https://hdl.handle.net/1721.1/141332 Delage-Laurin, Léo, Palani, Ravi Shankar, Golota, Natalie, Mardini, Michael, Ouyang, Yifu et al. 2021. "Overhauser Dynamic Nuclear Polarization with Selectively Deuterated BDPA Radicals." Journal of the American Chemical Society, 143 (48). en 10.1021/jacs.1c09406 Journal of the American Chemical Society Creative Commons Attribution-Noncommercial-Share Alike http://creativecommons.org/licenses/by-nc-sa/4.0/ application/pdf American Chemical Society (ACS) PMC |
| spellingShingle | Delage-Laurin, Léo Palani, Ravi Shankar Golota, Natalie Mardini, Michael Ouyang, Yifu Tan, Kong Ooi Swager, Timothy M Griffin, Robert G Overhauser Dynamic Nuclear Polarization with Selectively Deuterated BDPA Radicals |
| title | Overhauser Dynamic Nuclear Polarization with Selectively Deuterated BDPA Radicals |
| title_full | Overhauser Dynamic Nuclear Polarization with Selectively Deuterated BDPA Radicals |
| title_fullStr | Overhauser Dynamic Nuclear Polarization with Selectively Deuterated BDPA Radicals |
| title_full_unstemmed | Overhauser Dynamic Nuclear Polarization with Selectively Deuterated BDPA Radicals |
| title_short | Overhauser Dynamic Nuclear Polarization with Selectively Deuterated BDPA Radicals |
| title_sort | overhauser dynamic nuclear polarization with selectively deuterated bdpa radicals |
| url | https://hdl.handle.net/1721.1/141332 |
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